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Abstract: ; hereafter LHA) (Levin, Z., Halfon, N., Alpert, P., 2010. Reassessment of rain experiments and operations in Israel including synoptic considerations. Atmos. Res. 97, 513–525. DOI:10.1016/j.atmosres.2010.06.011.), reanalyzed the results of the operational seeding in northern Israel between 1975 and 2007 and the preceding Israel 2 cloud seeding experiment (1969–1975) and concluded that there is no net increase in precipitation over the target areas. Our analysis revealed that a synoptic bias during Israel 2 is one of the reasons for the apparent positive effect of seeding in the northern target area and the negative effect in the southern area both of which disappeared in the following experiment in the south (Israel 3; 1975–1995) and the operational seeding in the north. ;hereafter BRG) criticized our paper primarily on the ground that we did not consider the positive results of Israel 1 experiment (1960–1967). It should be noted that in Israel 1 different seeding lines were used from those in both Israel 2 and the operational period. In addition, its raw data is not accessible anymore for reanalysis. Furthermore, Israel 2 had been designed as a confirmatory cross-over experiment to Israel 1 and failed to reproduce its promising results with double ratio (DR) of ~1.00, namely, zero rainfall enhancements. The same DR values were also found in Israel 3 and in the operational seeding. Therefore, because of the differences in the two experiments, the lack of access to the raw data and the disappointing results of the confirmatory experiment, we decided to concentrate our analysis on the more recent seeding activities. The attempt by BRG to explain the reduction of the DR to ~1.00 in the operational seeding period by the suppression due to pollution have been disproved by and also fail to explain the sharp decline of the target/control ratio right at the beginning of the operational seeding period when the lucky draw in this area came to its end (see LHA). [Copyright &y& Elsevier]

Attenuation correction of measured reflectivity (Z H) and differential reflectivity (Z DR) is critical in short-wavelength radar applications, especially during extreme precipitation events such as heavy rain. This paper develops an improved self-consistent approach (improved ZPHI method) for attenuation correction in practical environment. In particular, a non-negative constraint is imposed on the specific attenuation, which is inferred from the monotonic increasing characteristic of differential propagation phase (Φ DP). The copolar correlation coefficient (ρ HV) is used to partition the Φ DP profiles into independent range segments, which are featured by different hydrometeor phases such as liquid rain or mixed-phase precipitation. Additional minimization constraint is imposed on the cost function of the difference between preprocessed Φ DP and reconstructed Φ DP to ensure its appropriate convergence. In addition, an exponential Z DR − Z H relation derived from local raindrop size distribution (DSD) data is applied in the procedure of Z DR correction. Polarimetric measurements from a C-band radar (CPOL) in Hangzhou of China during two extreme precipitation events are used to demonstrate the improved attenuation correction method. DSD observations from disdrometers and radar data from a nearby system operating at non-attenuated frequency (i.e., S-band) at Huangshan Mountain are used to evaluate the attenuation correction performance. This paper also studies the impact of attenuation correction on the radar-derived quantitative precipitation estimation (QPE) product, through cross-comparison with rain gauge observations. Results show that the polarimetric observations from CPOL radar are effectively enhanced and more consistent with collocated S-band measurements and the simulated radar moments based on DSD data. Hourly rainfall products derived from R (Z H) and R (Z H , Z DR) are significantly improved, which are comparable to R (K DP) after attenuation correction. • An improved attenuation correction method is proposed for C-band polarimetric radar applications. • The routinely operating C-band radar in Hangzhou, China is used to demonstrate the proposed attenuation correction scheme. • Cross-comparison with disdrometer data and collocated S-band observations shows great performance of this correction method. • The QPE products derived from R (Z H) and R (Z H , Z DR) are significantly improved after attenuation correction. [ABSTRACT FROM AUTHOR]

Severe droughts are increasingly frequent around the world, in particular in the desert area. There is a shortage of water that can be partly avoided by the implementation of precipitation enhancement projects. The concept implies cloud seeding with appropriate artificially produced aerosols. The main lack of that methodology is a scientific basis of the evaluation of seeding effects. The twofold contributions of this paper are the following: (1) introducing a new one-dimensional (1D) numerical model for cloud seeding experiments (1D MCSE) and (2) testing the performances of a novel aerosol at enhancing surface precipitation using the 1D MCSE. The novel aerosol is core/shell sodium chloride (NaCl)/titanium dioxide (TiO 2 ) nanostructure, also known as the shell structured TiO 2 /NaCl. The introduced numerical model is a coupled dynamics and microphysics scheme. Two principally different approaches of numerically simulating the performances of the shell structured TiO 2 /NaCl are utilized in this paper. In the first approach the cloud droplet nucleation on the novel aerosols is evaluated via the lookup tables which were constructed by using the parcel model. The activation characteristics were modelled as function of ambient temperature, vertical velocity, relative humidity, the number of aerosols, and their chemical characteristics expressed by kappa parameter. In the second approach, the activation features of shell structured TiO 2 /NaCl are explicitly resolved in the MCSE 1D model using the diffusion equation constructed from the laboratory experiments in cloud chambers with this novel aerosol. The performances of the novel aerosols were compared against the pure NaCl that has traditionally been used for precipitation enhancement, as well as against the base case without any seeding (i.e., cloud droplet nucleation only on the natural aerosols). In all analyzed cases, the novel aerosol shows profoundly better performances as precipitation enhancer than the pure NaCl. The superiority of this novel seeding material to pure NaCl is particularly noticeable in the unsaturated environments with the relative humidity below 75%. Analysis of spatiotemporal windows for these two artificial aerosols shows that the resulting precipitation enhancement from the shell structured TiO 2 /NaCl is >15% larger than using the pure NaCl and about 30% larger than in natural case. In addition, this paper demonstrates a large flexibility of the 1D MCSE to produce a variety of different outputs which are of great importance in the cloud seeding experiments. [ABSTRACT FROM AUTHOR]

In this paper we study the sensitivity of the quantitative precipitation forecast (QPF) to different physical parameterization schemes and configuration settings of WRF (Weather Research and Forecasting) model for a catastrophic event occurred in Calabria, Southern Italy. The event lasted four days, from 30 October 2015 to 2 November 2015, and affected mostly the eastern side of the peninsula. Several raingauges measured >500 mm for the whole event, with the maximum recorded in Chiaravalle (739 mm for the whole event, which is about half of the yearly rainfall). Damages to railway, roads and properties were extensive. To show the sensitivity of the QPF to the model settings and physical parameterization schemes, twelve configurations of WRF are considered, in addition to the control run ( CC ), which is the configuration used for the operational forecast at ISAC-CNR in Lamezia Terme. In particular, we tested the sensitivity of the QPF to four different microphysical schemes, three Planetary Boundary Layer (PBL) schemes (non-local and local), two cumulus parameterization schemes, two different horizontal resolutions (1 km vs 3 km), and different initial and boundary conditions. The QPF is verified both by quantitative measures and qualitative scores, using the observations of 156 raingauges quite uniformly distributed over Calabria. The analysis refers to 12 h and 24 h rainfall, but some details are given also for shorter time scales. Results show that most of the WRF configurations are able to predict most of the features of the precipitation field. However, there are differences at the local scale (few tens of kilometers) that are important for several purposes, including civil protection. In particular, using a non-local PBL closure scheme was fundamental to correctly simulate the heavy precipitation close to the sea for this case, while other configurations predicted the rainfall more anchored to mountain peaks. The good performance of non-local PBL scheme confirms the findings of a previous study over Calabria. The results of this paper show the sensitivity of the QPF at the local scale for different WRF configurations and an ensemble approach is envisaged to improve the prediction of such catastrophic events. [ABSTRACT FROM AUTHOR]

The Mediterranean region is a unique area characterized by a large spectrum of atmospheric phenomena, some of which have a high impact on many aspects of human activities, safety and wellbeing. The area is long considered as a hot spot of such atmospheric phenomena deserving multidisciplinary scientific attention. The scientific research that has been carried out on these high impact atmospheric processes that occur in the Mediterranean area is indeed widespread and the available international literature is very extensive. The paper touches initially the temperature and precipitation regimes, followed by a discussion of floods and droughts. The exciting cyclogenetic patterns of explosive cyclones and medicanes are presented in separate sections. The lightning activity and the presence of dust and other pollutants are also presented herein. The atmospheric chemistry of the region which is increasingly becoming of utmost importance for the area under study is distinctly discussed. Attempts to modify the weather (the precipitation, in particular) are outlined too. The effects of climatic change on various atmospheric processes are considered throughout this paper, in addition to a dedicated section on temperature and precipitation. [ABSTRACT FROM AUTHOR]

In the present paper, we made an investigation of extreme rainfall events for 1860―1909 in the Korean Peninsula, and the possible atmospheric circulation state by comparing recent rainfall variability with atmospheric circulation indices. In the present study, very significant historical rainfall records and flood damage records since the mid-19th century, modern rainfall records and global climate reanalysis data were applied. Results show: (1) Pentad extreme rainfall events had undergone a clear decrease, with an abrupt falling after shifting point of 1879―1880. (2) The monthly frequencies of extreme rainfall events revealed remarkable descent trends for June–October, which changed from 29 time/pentad to 7.3 time/pentad on average, especially for July–September. (3) Almost all climate zones except for northern land displayed significant decreasing trends, nevertheless no clear incidence of extreme rainfall event was found over the typical pluvial regions. (4) Through an analogue method by comparing the extreme precipitation weather and the atmospheric mechanism for recent decades (1961―2016), we suggested that West Pacific Subtropical High had experienced a strengthen change for the past period and the typhoon-related torrential rain processes had been suppressed for the study area, and the upper air jet stream might have been displaced poleward during 1860―1909. This study made a first investigation of the extreme rainfall events since the mid-19th century applying both instrumental and documental records in the study area, and some significant findings were obtained, which will help in understanding extreme climate variability and its mechanism of late 19th century and early 20th century in the Korean Peninsula. • Several main climate variables which are related to SR-NPKP were investigated. • 13 indices having a close connection with the variability of SR-NPKP were obtained. • Neural network model was proposed for 1-yr lag prediction of SR-NPKP. [ABSTRACT FROM AUTHOR]

This paper introduces the use of Bayesian full Procrustes shape analysis in object-oriented meteorological applications. In particular, the Procrustes methodology is used to generate mean forecast precipitation fields from a set of ensemble forecasts. This approach has advantages over other ensemble averaging techniques in that it can produce a forecast that retains the morphological features of the precipitation structures and present the range of forecast outcomes represented by the ensemble. The production of the ensemble mean avoids the problems of smoothing that result from simple pixel or cell averaging, while producing credible sets that retain information on ensemble spread. Also in this paper, the full Bayesian Procrustes scheme is used as an object verification tool for precipitation forecasts. This is an extension of a previously presented Procrustes shape analysis based verification approach into a full Bayesian format designed to handle the verification of precipitation forecasts that match objects from an ensemble of forecast fields to a single truth image. The methodology is tested on radar reflectivity nowcasts produced in the Warning Decision Support System — Integrated Information (WDSS-II) by varying parameters in the K-means cluster tracking scheme. [ABSTRACT FROM AUTHOR]

An intercomparison of eight different microphysics parameterization schemes available in the Weather Research and Forecasting (WRF) model and an analysis of the sensitivity of predicted precipitation to horizontal resolution are presented in this paper. Three different case studies, corresponding to severe rainfall events occurred over the Liguria region (Italy) between October 2010 and November 2011, have been considered. In all the selected cases, the formation of a quasi-stationary mesoscale convective system over the Ligurian Sea interacting with local dynamical effects (orographically-induced low-level wind and temperature gradients) played a crucial role in the generation of severe precipitations. The data set used to evaluate model performances has been extracted from the official regional network, composed of about 150 professional WMO-compliant stations. Two different strategies have been exploited to assess the model skill in forecasting precipitation: a traditional approach, where forecasts and observations are matched on a point-by-point basis, and an object-based method where model success is based on the correct localization and intensity of precipitation patterns. This last method overcomes the known fictitious models performance degradation for increasing spatial resolution. As remarkable results of this analysis, a clear role of horizontal resolution on the model performances accompanied by the identification of a set of best-performing parameterization schemes emerge. The outcomes presented here offer important suggestions for operational weather prediction systems under potentially dangerous heavy precipitations triggered by the mechanisms discussed throughout the paper. [ABSTRACT FROM AUTHOR]

In this paper, 34 western track typhoons making landfall over China during the period of 2006–2016 from Jun. to Oct. are taken as research objects. They are divided into strong and weak monsoon influenced categories according to the East Asian summer monsoon index. Using precipitation product that was derived from hourly precipitation observed at automatic weather stations (AWS) in China and retrievals from CMORPH [CPC (Climate Prediction Center) morphing technique] satellite data, Japanese 55-year Reanalysis products (JRA-55) and Blackbody brightness temperature (TBB) data from FengYun 2E (FY-2E) satellite, precipitation intensity and distribution characteristics of strong monsoon influenced typhoons. In addition, the weak monsoon influenced typhoons was compared through composite analysis. Furthermore, to explore the water vapor conditions, dynamic factors, thermal structure, development conditions of mesoscale convective systems, and long-term typhoon maintenance mechanisms of typhoons under both conditions. This research is attempted to obtain the regularity of influences exerted on typhoon precipitation intensity and distribution by summer monsoon, and the possible influencing mechanisms of summer monsoon on typhoon precipitation. Results show that the stronger (weaker) the monsoon flow is, the stronger (weaker) the precipitation intensity of post-landfall western typhoon. Monsoon provides a sufficient amount of water vapor through direct moisture channel. The stronger monsoon flow is, the more obvious the coupling of low-level convergence and upper-level divergence, and thus provides a stronger lifting for typhoon precipitation. A strong monsoon condition is more conducive to the genesis and development of mesoscale convection system. A strong monsoon condition is also favorable for the maintenance of post-landfall typhoon's warm core structure, thereby prolonging the precipitation through delaying the decay of typhoons. All these factors lead up to the influences on precipitation of typhoons by summer monsoon directly or indirectly. • Strong monsoon flow does lead to a significant increase and asymmetry in precipitation. • Stronger monsoon flow provides stronger lifting for typhoon precipitation through more obvious coupling of low-level convergence and upper-level divergence. • A strong monsoon condition is more conducive to the genesis and development of mesoscale convection system. • A strong monsoon condition can prolong the precipitation through delaying the decay of landfall typhoons by the maintenance of warm core structure. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a study on the Support Vector Machine (SVM) performance in a problem of daily precipitation prediction. Several novelties are included in the proposed analysis: first, a large set of novel predictive variables is considered, including upper air sounding data, variables derived from a numerical weather prediction model as well as the synoptic pattern of the atmosphere (by means of the Hess–Brezowsky classification). The importance of several of these predictive variables in the SVM performance is analyzed in the paper. In addition, two types of observational rain data are used in the experiments: first data from rain gauges (pluviometers) are considered, in order to establish the precipitation prediction, and then observational data from airports (METAR and SPECI reports) are used to carry out a similar study. The excellent performance of the SVM approach is shown by comparison with several alternative neural computation-based approaches (multi-layer perceptron, Extreme Learning Machine) and with classical algorithms such as decision trees and K-nearest neighbor classifier. Finally, the results of the persistence model are used as reference to certify the good performance of the proposed technique. [Copyright &y& Elsevier]

Abstract: This paper examines the commonly-held hypothesis that cloud seeding reduces precipitation in regions adjacent to seeding target areas, sometimes referred to as “downwind” but more correctly referred to as “extra area” effects (“the robbing Peter to pay Paul” hypothesis). The overall concept in the potential creation of extra area effects from seeding is illustrated with respect to the hydrologic cycle, which includes both dynamical and microphysical processes. For the first time, results were synthesized from five operational and research weather modification experiments, including winter orographic snowpack enhancement and summer experiments to enhance rainfall. One of the most surprising aspects of these results is that extra area seeding effects on precipitation appear to be uniformly positive (5–15% increases, perhaps greater for some convective systems) for both winter and summer seeding projects examined in this paper. The spatial extent of the positive extra area seeding effects may extend to a couple hundred kilometers for winter orographic seeding projects and summer convective seeding projects (such as North Dakota, Texas, Thailand). Both microphysical and dynamical effects of seeding appear to be contributors to these extra area effects. Future work needs to incorporate larger data sets from some of the larger more sustained projects with advanced cloud models and tracer experiments. [Copyright &y& Elsevier]

Abstract: This paper presents an extensive revision of Magono and Lee's (1966) classification of natural snow crystals, which has been widely used in snow and ice studies to describe snow crystal shapes. The new classification catalogs snow crystals and other solid precipitation particles into 121 categories, in contrast to Magono and Lee's 80 categories. Of these, 28 categories were created to classify new types of snow crystals that have been discovered in polar regions since 1968, seven were created after reconsidering the original categories, and six categories were created to classify solid precipitation particles such as frozen cloud particles and small raindrops. Because our observational area extended from middle latitudes (Japan) to polar regions, we refer to our new classification scheme as ‘global-scale classification’ or ‘global classification’. The global classification consists of three levels – general, intermediate, and elementary – which are composed of 8, 39, and 121 categories, respectively. This paper describes the characteristics of each type of snow crystal, ice crystal, and solid precipitation particle. [Copyright &y& Elsevier]

A new formulation of aerosol scavenging by convective precipitations, consistent with the Emanuel convective mass-flux scheme, is implemented into the Laboratoire de Météorologie Dynamique general circulation model, LMDz. The aerosols 210Pb and 7Be are used as inert tracers to evaluate LMDz performance in terms of atmospheric transport in the tropics. Wind fields are calculated over 2007 in a regular grid with a resolution of 1.875° in longitude, 1.24° in latitude and 40 vertical levels. The first part of the paper addresses the sensitivity of LMDz simulations to convective schemes and to scavenging parameterizations. Results are analyzed at two tropical stations and one mid-latitude station by comparing simulated aerosol concentrations with available data, collected at surface stations. On a daily scale, the observed variations of concentrations are poorly reproduced by any considered model at both tropical stations. Nevertheless, fluctuations at timescales longer than a few days may be captured over periods of a few weeks to a few months by the new formulation. The second part of this paper focuses on the new implemented parameterization of convective scavenging. The objective is to interpret mismatches of simulated concentrations with observed data and to determine which transport mechanisms are responsible for peaks of 7Be concentrations recorded at tropical stations. Typical meteorological situations in Polynesia are analyzed in view of convective transport and scavenging of 7Be. In particular, the sensitivity to the location of the South Pacific Convergence Zone is examined on concentrations in Polynesia. Results demonstrate that 7Be plumes are brought downward in the middle atmosphere by large-scale subsidence associated to the subtropical jet, in a 35°–25°S band. At surface, 7Be plumes are associated either to shallow convection or to deep convection with moderate precipitations. Within moderate convective events, surface concentrations are enhanced by surface release due to re-evaporation of precipitations. Most 7Be surface plumes reaching the Polynesian stations are produced locally in the neighborhood of stations and advected over one or two days by surface large-scale winds. The largest mismatches may be attributed to uncertainties in the simulation of precipitations within deep convective cloud systems that develop along troughs. [ABSTRACT FROM AUTHOR]

Abstract: Twenty-nine sprites were observed during four years from 2007 to 2010 with one most sprite-productive storm on 1–2 August 2007 which produced 16 sprites. In this paper, the most sprite-productive storm is analyzed by using data from lightning detection network, Doppler radar, MTSAT (Multi-Function Transport Satellite) satellite, TRMM (Tropical Rainfall Measuring Mission), NCEP. The results show that most sprites appeared in groups and in shape of carrot. Most sprites occurred frequently when the cloud top brightness temperature is getting warm and radar reflectivity is becoming weak with characteristics of sharp decrease of negative CGs and slight increase of positive CGs. The parent cloud-to-ground lightning flashes (CGs) were positive and located in region with cloud top brightness temperature of −40 to −60°C and radar reflectivity of 15–35dBZ. The sprite-producing storm was fortunately scanned by TRMM during sprite time period. One orbit data could be used for PR (Precipitation Radar, 2A25) and two orbit data for TMI (TRMM Microwave Imager, 2A12 and 1B11). Results based on TRMM indicated that storm reflectivity with 30dBZ was at about 12km in the convective region and 4km in stratiform region. The precipitation ice mostly located in 6–8km with the largest value of 2.1g/m3, but most cloud ice located between 10 and 14km with no cloud ice below 6km and very few at 6.0–8.0km. The cloud water content located mostly between 4 and 6km. Characteristics of vertical cross sections of radar reflectivity, precipitation ice and cloud ice agree well. Vertical cross sections along convective and stratiform regions show that contents of precipitation ice and cloud ice in convective region were larger than that in stratiform region. But cloud water in stratiform region was larger than that in convective region. The storm evolution could be seen clearly from characteristics of precipitation ice, cloud ice, cloud water and polarization corrected temperature at two different times. The CG distribution agrees well with low values of polarization corrected temperature region, indicating that lightning flashes have close relationship with ice particles. Although this paper is a case study of sprite-producing thunderstorm based on TRMM data, the results provided detailed information of microphysical structure of this sprite-producing storm. [Copyright &y& Elsevier]

Abstract: This paper explores the many aspects of precipitation measurement that are relevant to providing an accurate global assessment of this important environmental parameter. Methods discussed include ground data, satellite estimates and numerical models. First, the methods for measuring, estimating, and modeling precipitation are discussed. Then, the most relevant datasets gathering precipitation information from those three sources are presented. The third part of the paper illustrates a number of the many applications of those measurements and databases, namely hydropower, data assimilation and validation of Regional Climate Models (RCM). The aim of the paper is to organize the many links and feedbacks between precipitation measurement, estimation and modeling, indicating the uncertainties and limitations of each technique in order to identify areas requiring further attention, and to show the limits within which datasets can be used. Special emphasis is put on the central role of the upcoming Global Precipitation Measurement (GPM) mission in precipitation science. [Copyright &y& Elsevier]

Abstract: Cities are becoming increasingly vulnerable to flooding because of rapid urbanization, installation of complex infrastructure, and changes in the precipitation patterns caused by anthropogenic climate change. The present paper provides a critical review of the current state-of-the-art methods for assessing the impacts of climate change on precipitation at the urban catchment scale. Downscaling of results from global circulation models or regional climate models to urban catchment scales are needed because these models are not able to describe accurately the rainfall process at suitable high temporal and spatial resolution for urban drainage studies. The downscaled rainfall results are however highly uncertain, depending on the models and downscaling methods considered. This uncertainty becomes more challenging for rainfall extremes since the properties of these extremes do not automatically reflect those of average precipitation. In this paper, following an overview of some recent advances in the development of innovative methods for assessing the impacts of climate change on urban rainfall extremes as well as on urban hydrology and hydraulics, several existing difficulties and remaining challenges in dealing with this assessment are discussed and further research needs are described. [Copyright &y& Elsevier]

Abstract Precipitation complexity measurement is often overlooked in precipitation time series research. Entropy, as a measure of system complexity, can be used to diagnose the complexity of precipitation. However, it is difficult to judge the applicability of different theoretical entropy models for solving precipitation uncertainty problems. This paper introduces the distinction degree theory and the serial number sum theory to screen the optimal entropy model for precipitation complexity measurement. The optimal entropy model was used to analyze the spatiotemporal differences of monthly precipitation complexity in Heilongjiang Province, China. Possible influencing factors of precipitation complexity were also examined. The results indicated that in the complexity measurement of precipitation based on entropy theory, the stability and reliability of sample entropy was higher than those of fuzzy entropy, wavelet entropy and permutation entropy. The complexity of monthly precipitation in the selected study area significantly increased with time. The average complexity of monthly maximum precipitation, monthly average precipitation and monthly minimum precipitation were 0.665, 0.622 and 0.545, respectively, and their tendency change rates were 0.070/decade, 0.055/decade and 0.038/decade, respectively. The areas with high monthly precipitation complexity were concentrated in the central, eastern and northwest parts of the study area, and the precipitation was less predictable. Monthly precipitation in the southwest was less complex and more predictable. The highest monthly precipitation complexity was 1.012, at Hulin station, and the lowest was 0.510, at Mingshui station. The increasing complexity of monthly precipitation in the province was strongly related to local industrial and agricultural production. The superposition effects of altitude, topographic relief, change in grassland area and agricultural production formed the basic pattern of spatial differences in monthly precipitation complexity. The results may provide a scientific guidance for regional precipitation predictability measurement, effective assessment of droughts and floods, and water resources management. Highlights • The optimal entropy model was selected to diagnose complexity in precipitation time series. • Complex monthly precipitation was concentrated in the central eastern and northwest parts of the study area. • Monthly precipitation complexity had a strong relationship with local industrial and agricultural production. • This study may provide a scientific guidance for regional water resources management. [ABSTRACT FROM AUTHOR]

Abstract Attica, which is the region with the largest population in Greece, suffers from numerous high rainfall intensity events inducing flash floods and, consequently, significant damages in the urbanized areas. High rainfall intensities are frequently connected with convection, a quiet often phenomenon during either the transitional seasons or the late summer thunderstorms. The objective of this paper is to implement and evaluate a stratiform-convective classification technique for the rainfall events occurred in Attica during the period 2005–2016. As this methodology requires only the precipitation records, the satisfactory evaluation of this classification approach allows further applications, such as, a climatological analysis regarding convective and stratiform trends in the study area and generally in Greece. Particularly, the rain gauge stations' records used correspond to 10-minute time series from 32 rainfall stations for the same period, and these data are analyzed and processed in order to fit a suitable exponential curve describing the stratiform component. A critical annual threshold of rainfall intensity in mm/6h is then calculated, separating the prevailing convective and stratiform regime above and below this value, respectively. The analysis is performed in three individual subareas of Attica region demarcated initially according to their morphological characteristics and subsequently by checking the cross-correlation for each pair of stations. This critical intensity threshold is determined for each year separately, in order to illustrate the uncertainty and the difficulty in identifying a standard threshold, as it is related to the annual behavior of precipitation. Using this threshold, a total of about 180 six-hour case events is detected as purely convective cases, however this number ranges for each subarea. For these cases, a further analysis is performed with the aim of verifying their convective character. Verification includes time-accurate lightning data, surface synoptic observations from the Hellenic National Meteorological Service and six-hour surface analysis charts from UK MetOffice. Findings, which are presented via indicative verification indices, show in general encouraging performance, considering the highly variable nature of convective precipitation which poses considerable problems in its identification with quite simple techniques. Highlights • Implementation and evaluation of a precipitation classification technique • Determination of critical rain rate for convective or stratiform prevailing regime • Annual percentage of convective and stratiform precipitation amounts for Attica • Evaluation for the overall analysis and for different classes of rain rate [ABSTRACT FROM AUTHOR]

Abstract The accurate measurement of rainfall intensity is always challenging due to high spatial and temporal variation of the precipitation, particularly on arid and semiarid regions. The United Arab Emirates (UAE) lies in an arid region with a high shortage of rainfall events. Thus, accurate and continuous monitoring for efficient management of water resources is of particular importance. There are many techniques and instruments that were developed for collecting and/or estimating precipitation. Recently, multi-satellite sensors were globally utilized over the past three decades to measure the precipitation. The Global Precipitation Measurement (GPM) satellite has a capability to detect and measure all types of precipitation using advanced instruments. This article validates the accuracy of the GPM IMERG (Integrated Multi-satellitE Retrievals from Global Precipitation Measurement) early, late and final rainfall products over the UAE using multiple spatial and temporal assessments over the period from Jan 2015 to Dec 2017. The IMERG early-run-product showed a good detection accuracy and low estimation error over the UAE except for the eastern part, while the late-run-product showed a slight improvement. The final-run-product showed the highest detection and low estimation error compared to other products. The correlation between rain-gauge and satellite data demonstrated a contradiction, which reveals that the early-run-product had the highest correlation. Nevertheless, the correlation with the final-run-product was quite lower than the early-run-product. Based on these results, the GPM IMERG final-run-product provides not only a better understanding of the rainfall variability and pattern over the UAE, but also could serve as a reliable product to complementing and/or substituting ground precipitation measurements for ungauged or poorly gauged regions. This paper presents results of one of the earliest assessments of the GPM IMERG products in the Middle East. The outcomes could pave the road for further improvement of the IMERG algorithms in the future. Highlights • GPM precipitation products were evaluated spatially and temporally over the UAE. • The IMERG near-real time products showed high correlation with ground observations. • The IMERG final-run-product showed high detection and low estimation error. • The influence of elevation and coastal proximity on results was analyzed. [ABSTRACT FROM AUTHOR]

Abstract Global Satellite Mapping of Precipitation (GSMaP) product is an important satellite precipitation product of Global Precipitation Measurement (GPM) mission, which provides an alternative means to ground-based rainfall estimates, in which case a rigorous product assessment was required before implementation. The objective of this paper is to evaluate and calibrate the errors of GSMaP_Gauge (GG) products, then SWAT model is chosen to evaluate its performance in hydrological simulation. It was found that the GG has a superior ability in detecting moderate rainfall events of 10–20 mm/d, while other magnitude accuracy needs to be strengthened. The Nash-Sutcliffe coefficient of efficiency (NS), coefficient of determination (R2) and the percent bias (PBIAS) were used to evaluate hydrological model performance in the daily scale, supporting the view that GG still allow considerable room for improvement. SWAT model driving by GG performed relatively poorly which is 0.77 ≤ R2 ≤ 0.84, 0.53 ≤ NS ≤ 0.64 and |PBIAS| < 9%, while the performance of corrected GG is relatively better that is 0.85 ≤ R2 ≤ 0.87, 0.70 ≤ NS ≤ 0.75 and |PBIAS| < 15%. Through the error's correction of GG, it brings a better performance of runoff simulation under SWAT modeling, leading to 11.94% and 6.1% maximum increase in NS and R2 respectively. Certain shortcomings are also noted that improvements to the relative runoff depth errors are limited or worse. But in general, GSMaP product has the potential to be an alternative data source for the research on hydrological simulation and water resources management in data-poor or ungauged basins. Highlights • GSMaP_Gauge has a superior ability in detecting moderate rainfall events of 10–20 mm/d. • GSMaP_Gauge-based model has the potential to describe well the runoff. Through correction of its errors, it brings the improvement of runoff simulation. • Certain shortcomings are that there are still large relative runoff depth errors, mainly reflected in the base flow. • The results can provide a deep insight to the GSMaP estimates'error features correction and potential utilization in water resources management. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we analyzed the effect of SST on the precipitation of coastal areas of the eastern China. The relationship between the precipitation and SST of different seasons based on CMDC's monthly precipitation data and NOAA's SST data from 1979 to 2016 was calculated. Analysis on the links between precipitation and SST has shown a significant correlation in winter and spring, with three positive strong oceanic signals and two negatively correlated sea areas. Meanwhile, the precipitation and SST of highly correlated regions have increased during the past 38 years. Considering the seasonal variation, precipitation presents upward trend in summer and winter with appreciable seasonal variations. For one of the highly related areas, such as the East China Sea (ECS) and the north of Philippine Sea (PS), the SST there has been increased in all four seasons. Spectral analysis also shows that the precipitation and the MEI have the same cycles about 3–5 years. Moreover, lead-lag analysis between precipitation time-series and three climate indexes (Niño 1 + 2 SST index, Niño 3 SST index and SIOD SST index) were applied. The results show that when the SSTs lead 2 to 4 months, they are highly related to the precipitation in the coastal areas of the eastern China. Highlights • Precipitation and SST concentrations in the study area show a significant correlation in winter and spring; • Precipitation and SST experienced different rises from 1979–2016. Precipitation presents an upward trend in summer and winter; • In SST correlated areas, they all had been increasing during the period of 1979–2016 about 1.1 °C on average; • Precipitation and three index (Niño 1 + 2 SST index, Niño 3 SST index, and SIOD SST index) indicated lead-lag relationship; • When Niño 1 + 2 SST index leads precipitation by three months, the two variables are significant positive correlated. [ABSTRACT FROM AUTHOR]

Surface-based microwave radiometer is used to measure the tropospheric parameter profiles continuously for 24 h. The measurement technology and retrieval methods are described clearly in this study. This paper focuses on the BP network and elaborates on it from a new perspective based on the Jacobian matrices between layers. Gradient descent is achieved by Jacobian matrices to train the network. A layered method is proposed to improve the efficiency and accuracy in training networks to obtain tropospheric water vapor and temperature profiles. Differently from the traditional method, the layered method divides the troposphere of 0–10 km into three layers based on the physical principles of cloud generation. Three networks, named as the bottom, the middle, and the upper network, are developed for the three layers. Therefore, three networks can be trained at the same time,using the same input and different output samples. According to the theories and the radiosonde data of 2012–2015 of Harbin China (45.46°N 126.40°E), a numerical experiment is designed to examine the layered method. The downwelling monochromatic radiative transfer model (MonoRTM) is used to calculate the atmospheric radiation brightness temperatures (BTs) with the radiosonde data. The experimental results show that the RMSEs of temperature and water vapor profiles of the layered method are reduced by 25.6% and 26.2%, respectively, at the altitude above 6 km, respectively, and the efficiency is improved by 20 times compared with the traditional method. [ABSTRACT FROM AUTHOR]

This paper investigates the annual and seasonal precipitation variability at 20 stations over upper Indus River basin (UIRB) by using an innovative trend analysis (ITA) method, Mann-Kendall (MK) and Sen's slope estimator tests. Moreover, the annual precipitation time series is investigated for five precipitation intensities i.e. light, low, moderate, high and heavy; and on a seasonal scale for extreme values i.e. light and heavy precipitation intensities. Annual precipitation showed an increasing trend at four stations in the northeast region and a decreasing trend at two stations in the southeast region of UIRB. On a seasonal scale, the results showed that Garidopatta, Peshawar, Astore and Gupis stations are more sensitive to seasonal precipitation variabilities. Changes in heavy precipitation (> 90th percentile) are found more severe in winter and summer seasons in the northern regions suggesting a probable flooding aggravation. However, a reduction in flooding event observed during the spring season in the southern regions of the UIRB indicating a shift in the precipitation regime from south to north. The results of light precipitation (< 10th percentile) intensity showed that winter and spring seasons are more vulnerable to the occurrence of prolonged drought events. Moreover, ITA method has the advantage of detecting the sub-trends in the precipitation series because of its ability to present the results in graphical format. The results of this study could help to understand seasonal and annual precipitation variability over UIRB and will have imperative insinuations for further studies. [ABSTRACT FROM AUTHOR]

Accurate predictions of drought events to plan and manage the adverse effects of drought on agriculture and the environment requires tools that precisely predict standardized drought metrics. Improving on the World Meteorological Organization approved Standardized Precipitation Index (SPI), the multi-scalar Standardized Precipitation and Evapotranspiration Index ( SPE I), a variant of the SPI, is a relatively recent drought index, which takes into account the impacts of temperature change on overall dryness, along with precipitation and evapotranspiration effects. In this paper, an extreme learning machine (ELM) model was applied to predict SPE I in a drought-prone region in eastern Australia, and the quality of the model's performance was compared to that of a multiple linear regression (MLR), an artificial neural network (ANN), and a least support vector regression (LSSVR) model. The SPE I data were derived from climatic variables recorded at six weather stations between January 1915 and December 2012. Model performance was evaluated by means of the normalized root mean square error (NRMSE), normalized mean absolute error (NMAE), coefficients of determination (r 2 ), and the Nash-Sutcliffe efficiency coefficient (NASH) in the testing period. Results showed that the ELM and ANN models outperformed the MLR and LSSVR models, and all four models revealed a greater predictive accuracy for the 12-month compared to the 3-month SPE I predictions. For the 12-month SPE I predictions, optimal models had r 2 that ranged from 0.668 for the LSSVR model (Station 6) to 0.894 for the ANN model (Station 4). The good agreement between observed and predicted SPE I at different locations within the study region indicated the potential of the developed models to contribute to a more thorough understanding of potential future drought-risks in eastern Australia, and their applicability to drought assessments over multiple timescales. The models and findings have useful implications for water resources assessment in drought-prone regions. [ABSTRACT FROM AUTHOR]

The paper is motivated by the enormous variability of short-term rainfall time structures which need to be discretized into several typical variants and explained from the viewpoint of rainfall types producing them. We present six variants of the time structure of 6-h rainfalls in Czechia, distinguished by a novel methodology for designing synthetic hyetographs. Reference 6-h rainfall episodes were extracted from radar-derived precipitation time series with a time resolution of 10 min, adjusted by daily data from rain gauges. The variants were distinguished by three indexes that quantify the precipitation concentration within time steps from one to six hours. The episodes with steady precipitation intensity during the entire episode are mainly stratiform or possibly mixed and frequently take much longer than six hours because of circulation patterns producing them; central and northeastern cyclonic types are most represented. All other variants of episodes frequently occur when a trough is situated above Central Europe. Episodes with steady intensity lasting about three hours are still mainly stratiform or mixed while two variants represented by “two-humped” hyetographs are usually mixed or convective. Two variants of most concentrated episodes are mainly convective or possibly mixed; they are characterized by enhanced frequency of southwestern and eastern cyclonic types. Future research on cluster frequencies among maximum precipitation episodes in various regions will enable the improvement of design hydrographs of small streams where runoff is basically influenced by the rainfall time structure. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP), being an average of surpassing 4000 m above sea level and around 2.5 × 10 6  km 2 , is the highest and largest plateau in the world and also called as the “Third Pole”. Due to its elevated land surface and complex terrain, the TP is subjected to combined regulations of multiple climate systems and associated large-scale atmospheric circulations. In this paper, we comprehensively review the recent studies of atmospheric moisture transport versus precipitation across the TP, with the attempt to link the two, which did not receive much attention previously. This review focuses on the atmospheric moisture transport and associated circulation patterns in this region, widely adopted approaches to identify the atmospheric moisture transport, qualitative and quantitative analyses for the role of water vapor transport on the precipitation, as well as the internal physical mechanism between atmospheric moisture transport and precipitation over the TP. Moreover, directions of future research are discussed based on the following aspects, which include 1) proposing an integrated statistical-physical framework for demonstrating the influence of atmospheric moisture transport and associated circulation patterns on the precipitation, especially the extremes, in the high-cold mountainous region; 2) quantifying the contribution of atmospheric water vapor from the surrounding sources as well as the local moisture recycling on the TP's precipitation; 3) providing higher quality data for atmospheric water vapor and precipitation; 4) emphasizing on the physical mechanism sustaining the atmospheric moisture transport as well as its potential influence on the extreme precipitation, including amount, frequency, intensity and duration. It is expected that this review will be beneficial for exploring the linkage between atmospheric moisture transport versus precipitation across the TP. [ABSTRACT FROM AUTHOR]

To improve the accuracy of radar rainfall estimates, this study examines rainfall relationships derived from polarimetric variables calculated from Drop Size Distributions (DSDs) measured by POSS (Precipitation Occurrence Sensor System) and PARSIVEL (PARticle Size and VELocity) disdrometers for eight different rainfall events in Korea associated with the Changma front, low pressure systems, typhoons, or the indirect effects of typhoons. Analysis of the correlation coefficients between polarimetric variables as independent parameters shows that multicollinearity is expected for Z–K DP , Z–A H , and K DP –A H . Of these, R(Z, K DP ) is the only relationship that had too low an accuracy for application to radar rainfall estimation. R(Z, Z DR , K DP ) and R(Z, K DP , A H ) were also omitted from this analysis because their intercept coefficients were too large. Analysis of the sensitivity of radar rainfall estimation to DSDs variation shows that the latest observed DSDs perform well, as much as 2.4 mm h −1 for RMSE (Root Mean Square Error) and 0.23 for NE (Normalized Error) in maximum. The statistical scores of each radar rainfall estimator vary between different rainfall events. This paper examines a new approach to radar rainfall estimation that is similar to the ensemble technique widely used in numerical prediction models. The ensemble members were chosen based on the average and standard deviation of their RMSE and NE for eight rainfall events. Two different weighting schemes were applied to each ensemble and the members were weighted equally or, alternatively, weighted based on their statistical scores. The performance of eight ensemble sets was examined using four independent rainfall events. There is little difference in the accuracy of each ensemble with respect to the weighting scheme applied. An ensemble composed of R(Z,Z DR ), R(Z), and R(K DP ), all given an equal weighting, was the most accurate. [ABSTRACT FROM AUTHOR]

Concern about climate change has amplified the need for accurate information about variations in statistical characteristics of extreme rainfall events in both smaller temporal and spatial scale. For this reason, in this paper the hourly precipitation measurements obtained at the Department of Meteorology and Climatology of the Aristotle University of Thessaloniki meteorological station, during the period 1947–2003, are used. A new threshold determining method is proposed, in order to define the extreme rainfall event in Thessaloniki, based upon the polynomial trends of the cumulative distribution functions, retrieved from hourly precipitation measurements. Through this approach, three statistical goodness-of-fit tests were carried out, in order to come up with the best fitting probability distributions, for annual and seasonal extreme precipitation conditions. Based upon this fitting distribution procedure, return periods for different precipitation extreme values were calculated. Results indicate that the value of 6.5 mm/h is the hourly threshold of extreme precipitation in Thessaloniki over the studied period. Furthermore, the Generalized Pareto, and the Johnson SB, the log-Gamma and the Lognormal are the best fitted probability models for the description of annual and seasonal extreme rainfall events, respectively. Last but not least, the contribution of hourly data in the accuracy of the results is discussed. [ABSTRACT FROM AUTHOR]

Abstract: A Local Area Weather Radar (LAWR) is an X-band weather radar developed to meet the needs of high resolution rainfall data for hydrological applications. The LAWR system and data processing methods are reviewed in the first part of this paper, while the second part of the paper focuses on calibration. The data processing for handling the partial beam filling issue was found to be essential to the calibration. LAWR uses a different calibration process compared to conventional weather radars, which use a power-law relationship between reflectivity and rainfall rate. Instead LAWR uses a linear relationship of reflectivity and rainfall rate as result of the log transformation carried out by the logarithmic receiver as opposed to the linear receiver of conventional weather radars. Based on rain gauge data for a five month period from a dense network of nine gauges within a 500×500m area and data from a nearby LAWR, the existing calibration method was tested and two new methods were developed. The three calibration methods were verified with three external gauges placed in different locations. It can be concluded that the LAWR calibration uncertainties can be reduced by 50% in two out of three cases when the calibration is based on a factorized 3 parameter linear model instead of a single parameter linear model. [Copyright &y& Elsevier]

Abstract: This paper presents first exploratory results and analyses performed on a 30-year (1978–2007) homogeneous precipitation database that has been created for the Calabria peninsula, southern Italy. The database consists of complete time series of daily values of precipitation from 88 stations distributed over the region. The database temporal resolution is one day while its spatial resolution is about 10 km. Calabria offers an interesting scenario for mesoclimatic studies in spatial and temporal rainfall variability. The region is located in the Central Mediterranean Basin, which has a strong seasonal variability that mirrors in large precipitation differences among seasons. The complex orography of the region leads to different exposures of the territory to the rain-bearing air masses and large differences in rainfall can occur in few tens of kilometers. Different kinds of Mediterranean storms are important for Calabria: a) storms originating in the lee of the Alps; b) storms that enter the Basin or develop in the western Mediterranean (Gulf of Lyon, Rhone valley, Iberia, Gibraltar); c) storms from northern Africa; d) storms moving over the central Mediterranean from Balkans and eastern Europe. Again, their interaction with local orography determines complex rainfall patterns and variability. In this paper, the maps of average values of precipitation, rain frequency, rain rate, persistence of rainfall and length of dry periods are presented. Precipitation spatial structure shows that the orography and the sea have a major role, while the seasonal dependence of rainfall unequivocally reveals the influence of the synoptic scale conditions. A large number of cast-studies of heavy precipitation events have been investigated in the past and several of them refer to the east side of Calabria. The results shown here confirm this issue in a climatological sense: despite the fact that yearly precipitation is larger on the west side of the peninsula, most intense rainstorms affect mainly the east side, which is favorably exposed to these storms. The current database represents a foundation for further investigations. [Copyright &y& Elsevier]

Abstract: The WMO Field Intercomparison of Rainfall Intensity (RI) Gauges started on October, 1st 2007 at Vigna di Valle (Italy) and was concluded in May 2009. Those catching type instruments, out of the selected rain gauges based on various measuring principles, and the four rain gauges selected as reference instruments to be installed in a pit, were preliminarily calibrated in the laboratory before their final installation at the Field Intercomparison site. The recognized WMO laboratory at the University of Genoa was involved in this task, using the same standard tests adopted for the previously held WMO Laboratory Intercomparison of RI gauges. Further tests were performed to investigate the one-minute performance of the involved instruments. The present paper deals with basically Tipping-Bucket Rain gauges (TBRs) and Weighing Gauges (WGs), using results from tests performed under constant flow rates in laboratory conditions. The objective of this initial phase of the Intercomparison was to single out the counting errors associated with each instrument, so as to help the understanding of the measured differences between instruments in the field during the second phase. Results and comments on the preliminary laboratory calibration exercise are reported in this paper together with their implications for the analysis of the outcome of the Intercomparison in the Field. [Copyright &y& Elsevier]

Abstract: In 1986, the Tornado and Storm Research Organisation (TORRO) developed and published an eleven point Hailstorm Intensity Scale and this has been used to characterise more than 2500 hailstorms known to have occurred in Britain and Ireland since the first documented hailstorm event of 1141 AD; this scale has recently (2005) been revised with additional parameters. Most analyses relate to Great Britain, but reference is made to the more extreme recorded events in Ireland. The most intense hailstorm in these Islands reached intensity H8 on the TORRO international scale which extends from intensities H0 to H10. For the 75 years 1930 to 2004 this paper examines significant, damaging (H2 or more intensity) storms in respect of seasonal frequency and geographical distribution. This paper also discusses the climatology (including diurnal incidence) of the less common, but potentially devastating storms of H5 intensity or more, using the much longer period 1800 to 2004 and with particular attention to hail swath lengths and widths. The synoptic origins for these major events, where known, are discussed, with particular reference to Lamb''s classification of weather types across the British Isles from 1861 onwards. More than 2500 British and Irish hailstorms are recorded in TORRO''s database of which over 1300 are of hailstorm intensity H2 or more, including 156 British storms since 1800 that reached intensity H4–5 or more on the TORRO H scale. The geographical distribution of hailstorms in the British Isles shows that the highest frequency of significant, damaging storms (H2 or more intensity with hailstones usually over 15 mm diameter) is in central and eastern England, with the East Midlands, East Anglia and the lower Thames Valley most conspicuous when the incidences are mapped. Since 1870 the severest (H5 intensity or greater) events have been predominantly associated with cyclonic, southerly or south-easterly weather types; however a significant minority (19%) occurred with an anticyclonic element in the classification. For storms of this severity (e.g. with potential for severe structural damage, pitting of aircraft bodywork and even the risk of serious injuries), reporting will have been more consistent over a longer period. These destructive storms, (the most recent “cluster” of which was between 1992 and 1997) have typically followed a track from the S, SSW or SW to the N, NNE or NE with a swath length often 25 km or more (reaching 335 km in one case) and a swath width sometimes in excess of 10 km. Analysis of the database since 1800 indicates a very conspicuous July maximum for these more extreme (H5 intensity plus) events. [Copyright &y& Elsevier]

Abstract: There is growing interest in the impact of climate change on urban hydrological processes. Such assessment may be based on the precipitation output from climate models. To date, the model resolution in both time and space has been too low for proper assessment, but at least in time the resolution of available model output is approaching urban scales. In this paper, 30-min precipitation from a model grid box covering Kalmar City, Sweden, is compared with high-resolution (tipping-bucket) observations from a gauge in Kalmar. The model is found to overestimate the frequency of low rainfall intensities, and therefore the total volume, but reasonably well reproduce the highest intensities. Adapting climate model data to urban drainage applications can be done in several ways but a popular way is the so-called Delta Change (DC) method. In this method, relative changes in rainfall characteristics estimated from climate model output are transferred to an observed rainfall time series, generally by multiplicative factors. In this paper, a version of the method is proposed in which these DC factors (DCFs) are related to the rainfall intensity level. This is achieved by calculating changes in the probability distribution of rainfall intensities and modelling the DCFs as a function of percentile. Applying this method in Kalmar indicated that in summer and autumn, high intensities will increase by 20–60% by year 2100, whereas low intensities remain stable or decrease. In winter and spring, generally all intensity levels increase similarly. The results were transferred to the observed time series by varying the volume of the tipping bucket to reflect the estimated intensity changes on a 30-min time scale. In an evaluation of the transformed data at a higher 5-min resolution, effects on the intensity distribution as well as single precipitation events were demonstrated. In particular, qualitatively different changes in peak intensity and total volume are attainable, which is required in light of expected future changes of the precipitation process and a step forward as compared with simpler DC approaches. Using the DC transformed data as input in urban drainage simulations for a catchment in Kalmar indicated an increase of the number of surface floods by 20–45% during this century. [Copyright &y& Elsevier]

Abstract: The hydro-meteorological evaluation of a flood event in July 1997 (the Odra flood in Central Europe) demonstrated that new procedures to estimate design floods for the reservoir outflow structures in the Czech Republic (CR) were needed. Therefore, the techniques of the estimation of Probable Maximum Precipitation (PMP) were developed in a national research project (1998–2000), and the activity focused on the improvement of the area related PMP estimates was going on within a present national project. In the frame of the evaluation of the next extreme precipitation event in August 2002 (the Labe flood in the CR and Germany), we compared the catchments related precipitation with the PMP estimates. In this paper, an outline of the PMP estimation techniques is given and the use of data from the Czech gauges is described, the aim being the statistical derivation of the point and area PMP estimates for precipitation duration of 1 to 5 days. The use of radar data in assessing the maximized area reduction factor is discussed and the relationship resulting from the radar measurements over the CR territory is presented. An evaluation of the radar-based area rainfall enabled us to transform the point PMP to the area PMP estimate designed for the river basins in CR. In the last part of the paper, the results obtained by comparing the rainfalls in 1997 and 2002 flood events with the PMP estimates are presented. The comparison showed that the maximum area rainfalls over small Czech catchments (the 3rd order river basins) did not exceed 63% of the corresponding PMP values. [Copyright &y& Elsevier]

Summer weather can cause severe situations in the Carpathian basin. Convective events such as thunderstorms (sometimes tornado-producing supercells) and squall lines occur frequently during the summer. In the first part of this paper, some typical convective storm events and their atmospheric conditions are presented. Most of the convective storms are associated with cold fronts but the most dangerous phenomena can be connected to waves on frontal systems or cutoff cyclones. To solve the problem of very short range forecasts of these phenomena, the Hungarian Meteorological Service (HMS) runs a project to develop a nowcasting system (the MEANDER system), which is described in the second part of the paper. This system supports a framework for several nowcasting procedures and produces complex objective analyses and forecasts as long as 3 h. The MEANDER system has two main segments: an analysis segment and a forecasting segment. Input and processed parameters are divided into basic parameters (such as pressure, temperature, geopotential, etc.) and derived parameters (such as visibility, present weather) which are calculated from the basic parameters. In the objective analysis, radar and satellite data are also involved. In the forecasting procedure, the objective analysis at the beginning time, and the (practically at 3 h forecast) fields of the background dynamical model at the final time are considered as nowcasted fields. Between these two times, basic parameters follow the tendency of the numerical model, but gradually approach the forecasted values of the background numerical model. To forecast radar parameters (precipitating systems), so-called replacement vectors are applied. These are calculated from the nowcasted basic parameters. The MEANDER system has both a special update segment to catch rapidly growing cloud systems and a warning segment to issue automated weather warnings as well. [Copyright &y& Elsevier]

The physical properties of hailstones registered by a hailpad network (size distribution, mass, kinetic energy) are essential data for the establishment of a regional hail climatology. Nevertheless, when comparing these data to the same properties of hailstones inside the cloud, the melting process must be taken into account. This paper presents a brief theoretical study of the changes effected on hailstone size distribution due to the melting process. The paper is based on previous studies dealing with the melting of hailstones before they reach the ground. The aim is to analyze the influence of this melting process on hailstone size distribution. An initial melting simulation was carried out in order to achieve this aim. Despite the common assumption that hailstone size distribution on the ground is exponential, it was found that when the in-cloud size distribution is exponential, on the ground, there are fewer small hailstones than what would be expected in an exponential distribution.The data registered by the hailpad network in Leo´n (Spain) for 1 year were used to estimate the size of every hailstone before the melting process. The results show that the hailstone size distribution simulated inside the cloud resembles more closely an exponential distribution than the hailstones on the ground.The type of hailstone size distribution inside the cloud will be the starting point for calculating the hailstone size distribution on the ground. Several equations describing the melting processes are used to calculate a new probability density function that initially corresponds to an exponential distribution that undergoes a partial melting process. The result is a function that is not monotonously decreasing like the exponential function, but rather a function that has a peak for a given size. This new function fits better the data found than the exponential function and actually resembles the gamma function. [Copyright &y& Elsevier]

In this paper we present an approach for the profiling of aerosol microphysical and optical properties combining ceilometer and sun/sky photometer measurements in the GRASP code (General Retrieval of Aerosol and Surface Properties). For this objective, GRASP is used with sun/sky photometer measurements of aerosol optical depth (AOD) and sky radiances, both at four wavelengths and obtained from AErosol RObotic NETwork (AERONET), and ceilometer measurements of range corrected signal (RCS) at 1064 nm. A sensitivity study with synthetic data evidences the capability of the method to retrieve aerosol properties such as size distribution and profiles of volume concentration (VC), especially for coarse particles. Aerosol properties obtained by the mentioned method are compared with airborne in-situ measurements acquired during two flights over Granada (Spain) within the framework of ChArMEx/ADRIMED (Chemistry-Aerosol Mediterranean Experiment/Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) 2013 campaign. The retrieved aerosol VC profiles agree well with the airborne measurements, showing a mean bias error (MBE) and a mean absolute bias error (MABE) of 0.3 μm 3 /cm 3 (12%) and 5.8 μm 3 /cm 3 (25%), respectively. The differences between retrieved VC and airborne in-situ measurements are within the uncertainty of GRASP retrievals. In addition, the retrieved VC at 2500 m a.s.l. is shown and compared with in-situ measurements obtained during summer 2016 at a high-atitude mountain station in the framework of the SLOPE I campaign (Sierra Nevada Lidar AerOsol Profiling Experiment). VC from GRASP presents high correlation ( r  = 0.91) with the in-situ measurements, but overestimates them, MBE and MABE being equal to 23% and 43%. [ABSTRACT FROM AUTHOR]

The territory of Southern Russia presents a great diversity of climates and complex orography that lead to a very different precipitation distribution. Annual precipitation amounts differ between 222 mm in the coast of the Caspian Sea and > 2000 mm in the highest parts of the Caucasus Mountains. In order to investigate the statistical structure of daily precipitation across the study region the daily precipitation Concentration Index (CI) was used. In present paper, the CI was calculated for 42 meteorological stations during the 1970–2010 period. The analysis of precipitation concentration identified that the distribution of daily precipitation is more regular over the west, north and south regions compared to the east (the Caspian Sea coast and the Caspian Depression). The Crimean peninsula is characterized by low CI values in the north and high values in the eastern part. [ABSTRACT FROM AUTHOR]

Gust fronts are thunderstorm-related phenomena usually associated with severe winds which are of great importance in theoretical meteorology, weather forecasting, cloud dynamics and precipitation, and wind engineering. An important feature of gust fronts demonstrated through both theoretical and observational studies is the periodic collapse and rebuild of the gust front head. This cyclic behavior of gust fronts results in periodic forcing of vertical velocity ahead of the parent thunderstorm, which consequently influences the storm dynamics and microphysics. This paper introduces the first gust front pulsation parameterization scheme in the WRF-ARW model (Weather Research and Forecasting-Advanced Research WRF). The influence of this new scheme on model performances is tested through investigation of the characteristics of an idealized supercell cumulonimbus cloud, as well as studying a real case of thunderstorms above the United Arab Emirates. In the ideal case, WRF with the gust front scheme produced more precipitation and showed different time evolution of mixing ratios of cloud water and rain, whereas the mixing ratios of ice and graupel are almost unchanged when compared to the default WRF run without the parameterization of gust front pulsation. The included parameterization did not disturb the general characteristics of thunderstorm cloud, such as the location of updraft and downdrafts, and the overall shape of the cloud. New cloud cells in front of the parent thunderstorm are also evident in both ideal and real cases due to the included forcing of vertical velocity caused by the periodic collapse of the gust front head. Despite some differences between the two WRF simulations and satellite observations, the inclusion of the gust front parameterization scheme produced more cumuliform clouds and seem to match better with real observations. Both WRF simulations gave poor results when it comes to matching the maximum composite radar reflectivity from radar measurement. Similar to the ideal case, WRF model with the gust front scheme gave more precipitation than the default WRF run. In particular, the gust front scheme increased the area characterized with light precipitation and diminished the development of very localized and intense precipitation. [ABSTRACT FROM AUTHOR]

Quantitative precipitation estimation (QPE) is one of the important applications of weather radars. However, in complex terrain such as Tibetan Plateau, it is a challenging task to obtain an optimal Z – R relation due to the complex spatial and temporal variability in precipitation microphysics. This paper develops two radar QPE schemes respectively based on Reflectivity Threshold (RT) and Storm Cell Identification and Tracking (SCIT) algorithms using observations from 11 Doppler weather radars and 3264 rain gauges over the Eastern Tibetan Plateau (ETP). These two QPE methodologies are evaluated extensively using four precipitation events that are characterized by different meteorological features. Precipitation characteristics of independent storm cells associated with these four events, as well as the storm-scale differences, are investigated using short-term vertical profile of reflectivity (VPR) clusters. Evaluation results show that the SCIT-based rainfall approach performs better than the simple RT-based method for all precipitation events in terms of score comparison using validation gauge measurements as references. It is also found that the SCIT-based approach can effectively mitigate the local error of radar QPE and represent the precipitation spatiotemporal variability better than the RT-based scheme. [ABSTRACT FROM AUTHOR]

Regional precipitation patterns may change in a warmer climate, thereby increasing flood and drought risks. In this paper, annual, annual maximum, intense, heavy, moderate, light, and trace precipitation are employed as indicators to assess changes in precipitation patterns under two scenarios in which the global mean temperature increases by 1.5 °C and 2.0 °C relative to pre-industrial levels using the regional climate model COSMO-CLM (CCLM). The results show that annual precipitation in China will be approximately 2.5% higher under 1.5 °C warming relative to the present-day baseline (1980–2009), although it will decrease by approximately 4.0% under an additional 0.5 °C increase in global mean temperature. This trend is spatially consistent for regions with annual precipitation of 400–800 mm, which has experienced a drying trend during the past half century; thus, limiting global warming to 1.5 °C may mitigate these drying conditions. The annual maximum precipitation continues to increase from present day levels to the 2.0 °C warming scenario. Relative to the baseline period, the frequency of trace and light precipitation days exhibits a negative trend, while that of moderate, heavy, and intense precipitation days has a positive trend under the 1.5 °C warming scenario. For the 2.0 °C warming world, the frequency of days is projected to decrease for all precipitation categories, although the intensity of intense precipitation increases. Spatially, a decrease in the number of precipitation days is expected to continue in central and northern China, where a drying trend has persisted over the past half century. Southeastern China, which already suffers greatly from flooding, is expected to face more heavy and intense precipitation with an additional 0.5 °C increase in global mean temperature. Meanwhile, the intensity of intense precipitation is expected to increase in northern China, and the contribution of light and moderate precipitation to the annual precipitation is expected to decrease in southeastern China. Therefore, flood risk in northern China and drought risk in southern China should draw more attention for a global air temperature increase from 1.5 °C to 2.0 °C. [ABSTRACT FROM AUTHOR]

This paper analyses the observed spatiotemporal characteristics of drought phenomenon in Syria using the Standardised Precipitation Index (SPI) and the Standardised Precipitation Evapotranspiration Index ( SPE I). Temporal variability of drought is calculated for various time scales (3, 6, 9, 12, and 24 months) for 20 weather stations over the 1961–2012 period. The spatial patterns of drought were identified by applying a Principal Component Analysis (PCA) to the SPI and SPE I values at different time scales. The results revealed three heterogeneous and spatially well-defined regions with different temporal evolution of droughts: 1) Northeastern (inland desert); 2) Southern (mountainous landscape); 3) Northwestern (Mediterranean coast). The evolutionary characteristics of drought during 1961–2012 were analysed including spatial and temporal variability of SPI and SPE I, the frequency distribution, and the drought duration. The results of the non-parametric Mann–Kendall test applied to the SPI and SPE I series indicate prevailing significant negative trends (drought) at all stations. Both drought indices have been correlated both on spatial and temporal scales and they are highly comparable, especially, over a 12 and 24 month accumulation period. We concluded that the temporal and spatial characteristics of the SPI and SPE I can be used for developing a drought intensity - areal extent - and frequency curve that assesses the variability of regional droughts in Syria. The analysis of both indices suggests that all three regions had a severe drought in the 1990s, which had never been observed before in the country. Furthermore, the 2007–2010 drought was the driest period in the instrumental record, happening just before the onset of the recent conflict in Syria. [ABSTRACT FROM AUTHOR]

In this paper, the statistical properties of summer and winter precipitation over the northern China plain are investigated by using a two-dimensional video disdrometer (2DVD) and a micro-rain radar (MRR). The properties of summer precipitation presented herein are bulk properties (radar reflectivity, reflectivity-weighted fall velocity, liquid water content, and rainfall rate), raindrop fall velocity, axis ratio, and particle size distribution. Well correlations can be found among the diurnal cycles of radar reflectivity, liquid water content, and rainfall rate, whereas reflectivity-weighted fall velocity is poorly related to other bulk properties. The vertical profiles exhibit that radar reflectivity for stratiform rain is increasing with the altitude decreasing, in contrast, liquid water content and rainfall rate are reducing during the falling. These facts are useful for the radar-based rainfall rate retrieval algorithm. Axis ratio measurements are, for the first time, obtained and analyzed in northern China, which are particularly important for improving microphysical scheme in the climate models. In the constraint gamma model, the μ − Λ relation is adapted to the particle size distribution of stratiform rain, while the normalized gamma distributions for convective rain are separated to maritime-like and continental categories following the orientations and mechanisms of the storms. A new bulk-property-based algorithm is developed for the classification of convective and stratiform precipitation. For winter precipitation, radar reflectivity and snowfall rate for aggregates are calculated from the disdrometer data. The relationship of radar reflectivity and snowfall rate is obtained and validated with MRR data. The characteristics of summer and winter precipitation will be used to improve the microphysical scheme and evaluate the representation of precipitation in the climate models. [ABSTRACT FROM AUTHOR]

The aim of this study is to test how effective and physically correct are the mathematical approaches of operational indices used by relevant National Agencies across the globe. To do so, the following indices were analysed Standardized Precipitation Index (SPI) -1, 3, 6, 12 and 24, Standardized Precipitation – Evapotranspiration Index (SPEI) – 1, 3, 6, 12 and 24, Effective Drought Index (EDI) and Index of Drying Efficiency of Air (IDEA). To make regions more comparable to each other and follow the spatial development of drought SPI index was advised by World Meteorological Organisation to be used widely by official meteorological services. The SPI and SPEI are used for Drought Early Warning in the USA, National Drought Mitigation Center and NASA, and in the EU by the European Drought Centre (EDC) and in the Balkan Region by National Meteorological Agencies. The EDI Index has wide application in Asia. In this paper four different issues were investigated: 1) how the mathematical method used in a drought indicator's computation influence drought indices' (DI) comparative analyses; 2) the sensitivity of the DIs on any change of the length of observational period; 3) similarities between the DIs time series; 4) and how accurate DIs are when compared to historical drought records. Results suggest that it is necessary to apply a few crucial changes in the Drought Monitoring and Early Warning Systems: 1) reconsider use of SPI and SPEI family indices as a measure of quality of other indices; and for Drought Early Recognition Programs 2) switch to DIs with a solid physical background, such as EDI; 3) Adopt solid physics for modelling drought processes and define the physical measure of drought, e.g. EDI and IDEA indices; 4) investigate further the IDEA index, which, supported by our study as well, is valuable for simulation of a drought process. [ABSTRACT FROM AUTHOR]

In the first part of this paper, monthly precipitation data from Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks–Climate Data Record (PERSIANN-CDR) and Tropical Rainfall Measuring Mission 3B42 algorithm Version 7 (TRMM-3B42V7) are evaluated over Iran using the Generalized Three-Cornered Hat (GTCH) method which is self-sufficient of reference data as input. Climate Data Unit (CRU) is added to the GTCH evaluations as an independent gauge-based dataset thus, the minimum requirement of three datasets for the model is satisfied. To ensure consistency of all datasets, the two satellite products were aggregated to 0.5° spatial resolution, which is the minimum resolution of CRU. The results show that the PERSIANN-CDR has higher Signal to Noise Ratio (SNR) than TRMM-3B42V7 for the monthly rainfall estimation, especially in the northern half of the country. All datasets showed low SNR in the mountainous area of southwestern Iran, as well as the arid parts in the southeast region of the country. Additionally, in order to evaluate the efficacy of PERSIANN-CDR and TRMM-3B42V7 in capturing extreme daily-precipitation amounts, an in-situ rain-gauge dataset collected by the Islamic Republic of the Iran Meteorological Organization (IRIMO) was employed. Given the sparsity of the rain gauges, only 0.25° pixels containing three or more gauges were used for this evaluation. There were 228 such pixels where daily and extreme rainfall from PERSIANN-CDR and TRMM-3B42V7 could be compared. However, TRMM-3B42V7 overestimates most of the intensity indices (correlation coefficients; R between 0.7648–0.8311, Root Mean Square Error; RMSE between 3.29mm/day-21.2mm/5day); PERSIANN-CDR underestimates these extremes (R between 0.6349–0.7791 and RMSE between 3.59mm/day-30.56mm/5day). Both satellite products show higher correlation coefficients and lower RMSEs for the annual mean of consecutive dry spells than wet spells. The results show that TRMM-3B42V7 can capture the annual mean of the absolute indices (the number of wet days in which daily precipitation > 10 mm, 20 mm) better than PERSIANN-CDR. The results of daily evaluations show that the similarity of Empirical Cumulative Density Function (ECDF) of satellite products and IRIMO gauges daily precipitation, as well as dry spells with different thresholds in some selected pixels (include at least five gauges), are significant. The results also indicate that ECDFs become more significant when threshold increases. In terms of regional analyses, the higher SNR of the products on monthly (based on the GTCH method) and daily evaluations (significant ECDFs) is mostly consistent. [ABSTRACT FROM AUTHOR]

This paper investigates the use of standardised precipitation index (SPI) and the enhanced vegetation index (EVI) as indicators of soil moisture. On the other hand, we attempted to produce a drought sensitivity map (DSM) for vegetation cover using two one-class support vector machine (OC-SVM) algorithms. In order to achieve promising results a combination of both 30 years statistical data (1978 to 2008) of synoptic stations and 10 years MODIS imagery archive (2001 to 2010) are used within the boundary of Kermanshah province, Iran. The synoptic data and MODIS imagery were used for extraction of SPI and EVI, respectively. The objective is, therefore, to explore meaningful changes of vegetation in response to drought anomalies, in the first step, and further extraction of reliable spatio-temporal patterns of drought sensitivity using efficient classification technique and spatial criteria, in the next step. To this end, four main criteria including elevation, slope, aspect and geomorphic classes are considered for DSM using two OC-SVM algorithms. Results of the analysis showed distinct spatio-temporal patterns of drought impacts on vegetation cover. The receiver operating characteristics (ROC) curves for the proposed DSM was used along with the simple overlay technique for accuracy assessment phase and the area under curve (AUC = 0.80) value was calculated. [ABSTRACT FROM AUTHOR]

Improvement of precipitation prediction requires an understanding of the organization mechanism, such as the initiation and evolution of organized convective systems. This paper is a follow-up of a previous study on cloud propagation over the Indonesian Maritime Continent (IMC). Here, the infrared blackbody brightness temperature data is analyzed. A comprehensive cloud statistics model, including span, speed, duration, all possible directions, and size was estimated by applying the modified tracking reflectivity echoes by correlation (TREC) method to time-latitude-longitude space. Comparisons were made to cloud statistics during the first and second campaigns of Coupling Processes in the Equatorial Atmosphere, hereinafter called CPEA-I and CPEA-II. Although the two campaigns were conducted in different monsoon seasons, the cloud propagation directions during each campaign were similar. The cloud systems moved in most directions, except north and east, and preferred southwestward, westward and northwestward movements. Thus, westward-moving clouds were more dominant than eastward-moving clouds, in agreement with previous studies. This feature is consistent with the prevailing easterly wind in the middle and upper troposphere despite the difference in low-level wind during each campaign. The two campaign periods were different due to the phase of the Madden-Julian Oscillation (MJO). CPEA-I took place over the active MJO phase, with larger-sized clouds than CPEA-II. Thus, the MJO had an enormous impact on cloud size, but such an impact was not significantly observed in the speed, lifetime, span and direction of propagation. In the two campaigns, clouds moved with a speed of 3–30 m s −1 and in duration from a few hours to longer than one day. Clouds with long spans and high speeds were generally observed during the strong vertical shear of horizontal winds. In contrast, clouds with short spans and low speeds were found in the more varied environment of the IMC, but were dominant over land, which may have been associated with the diurnal heating cycle. Finally, the present results showed more complex behavior than a previous study in the Bay of Bengal, indicating precipitation mechanisms over the IMC including interactions between large-scale atmospheric phenomena (e.g., monsoon and MJO) with the diurnal precipitation cycles. [ABSTRACT FROM AUTHOR]

Most of the adverse weather phenomena in Catalonia (northeast Iberian Peninsula) are caused by convective events, which can produce heavy rains, large hailstones, strong winds, lightning and/or tornadoes. These thunderstorms usually have marked paths. However, their trajectories can vary sharply at any given time, completely changing direction from the path they have previously followed. Furthermore, some thunderstorms split or merge with each other, creating new formations with different behaviour. In order to identify the potentially anomalous movements that some thunderstorms make, this paper presents a two-step methodology using a database with 8 years of daily rainfall fields data for the Catalonia region (2008–2015). First, it classifies daily rainfall fields between days with “no rain”, “non-potentially convective rain” and “potentially convective rain”, based on daily accumulated precipitation and extension thresholds. Second, it categorises convective structures within rainfall fields and briefly identifies their main features, distinguishing whether there were any anomalous thunderstorm movements in each case. This methodology has been applied to the 2008–2015 period, and the main climatic features of convective and non-convective days were obtained. The methodology can be exported to other regions that do not have the necessary radar-based algorithms to detect convective cells, but where there is a good rain gauge network in place. [ABSTRACT FROM AUTHOR]

Although many theoretical and observational studies have investigated the mechanism of conditional symmetric instability (CSI) release and associated it with mesoscale atmospheric phenomena such as frontal precipitation bands, cloud heads in rapidly developing extratropical cyclones and sting jets, its climatology and contribution to precipitation have not been extensively documented. The aim of this paper is to quantify the contribution of CSI release, yielding slantwise convection, to climatological precipitation accumulations for the North Atlantic and western Europe. Case studies reveal that CSI release could be common along cold fronts of mature extratropical cyclones and the North Atlantic storm track is found to be a region with large CSI according to two independent CSI metrics. Correlations of CSI with accumulated precipitation are also large in this region and CSI release is inferred to be occurring about 20% of the total time over depths of over 1 km. We conclude that the inability of current global weather forecast and climate prediction models to represent CSI release (due to insufficient resolution yet lack of subgrid parametrization schemes) may lead to errors in precipitation distributions, particularly in the region of the North Atlantic storm track. [ABSTRACT FROM AUTHOR]

The Madden-Julian Oscillation (MJO) is the dominant mode of sub-seasonal climate variability in the global tropics. As such it represents an opportunity for intra-seasonal rainfall prediction and, perhaps, for explaining dynamics that underlie longer term variability and trends. This opportunity is of substantial interest for tropical Africa, where rainfall variability has significant impacts on agriculture, energy, and natural ecosystems. The objective of this review paper is to inventory and assess the state of knowledge of MJO influence on African rainfall. A number of studies have identified statistical links between MJO and sub-seasonal rainfall variability in West, East, and Southern Africa. The proposed mechanisms to explain this influence differ by region and by season, and they often involve multiscale interactions between local precipitation processes and MJO-associated atmospheric dynamics. Dynamically-based forecast systems have some skill in predicting MJO evolution to time horizons of 3–4 weeks, and some can capture teleconnections to Africa. On longer time scales, there is evidence that MJO activity both modulates and is modulated by the El Niño Southern Oscillation and the Indian Ocean Dipole. The implications of these interactions for MJO connections to Africa require further research, as does the potential for trends in MJO behavior and impacts on Africa under global climate change. [ABSTRACT FROM AUTHOR]