Search

This paper details the creation of a tropical cyclone (TC) size dataset using the NCEP/NCAR Reanalysis I dataset for landfalling TCs along the United States coastline from 1948 to 2022. The radius of the outermost closed isobar (ROCI) is used as the size parameter. The dataset comprises landfall ROCI for 220 TCs. Storms are split into three zones (Texas–Alabama, Florida and Georgia–Maine) to determine if TC size varies geographically. Results showed a significant difference in landfall size, with Florida storms larger on average than the Texas–Alabama storms. Additionally, TC size increased with increasing intensity from tropical storm to Category 3, and storms tended to be larger later in the hurricane season, but there was no significant trend in landfall size over the 75‐year period. ROCI exhibited statistically significant positive correlations with longitude and wind speed and a negative correlation with the outermost closed isobar's pressure. The dataset's creation is an example of how reanalysis datasets can be used to develop a TC size climatology. [ABSTRACT FROM AUTHOR]

The observation facts of trend and variability are estimated for a century‐long timescale, as well as some possible attributions affecting temperature extremes over Beijing‐Tianjin‐Hebei region. In this paper, the new constructed daily maximum and minimum temperature series during the last 100 years in situ stations of Beijing, Tianjin and Baoding city are used, and two 30‐year baseline climatology of 1961–1990 and 1980–2010 are both used in calculating extreme temperature events. The results indicate that there are long‐lasting, frequent and serious extreme warming over Beijing‐Tianjin‐Hebei region, especially for extreme low temperature, with larger declining trends (at 5% significance) from 1981 to 2010 baseline than those from 1961 to 1990 baseline. And from a statistical perspective, El Niño decay years and surface sea temperature (SST) anomalies at some typical ocean regions of the Arabian Sea and the Bengal Bay on the northern Indian Ocean, the Western Pacific and the Mid Atlantic, Southern Indian Ocean and around 45°–85°E, 68°–82°N on the southwest Arctic Ocean can be used as the warning signals denoting extreme warming over Beijing‐Tianjin‐Hebei region. Additionally, urbanization has a significant (at 5% significance) effect on extreme warming over Beijing‐Tianjin‐Hebei region since 1979, with 24.3% warming contribution for annual minimum temperature. [ABSTRACT FROM AUTHOR]

Climate is a powerful driver of agricultural and natural systems, and spatial climate datasets are currently in great demand. This is especially true in the Arequipa Department of Peru, a region with low seasonal precipitation, remarkable topographic variability, and significant water demand in a highly managed water system. This paper presents the Arequipa Climate Maps (ACM) datasets, a high resolution (1 km) spatial 30‐year (1988–2017) climate dataset for the Arequipa Region, in Peru. Four interpolation methods, and combinations of those methods, were tested to produce 30 years of daily precipitation, maximum and minimum air temperature: Ordinary Kriging (OK), Thin Plate Splines (TPS), Regression Kriging (RK), and Regression Thin Plate Splines (RTPS). The mixed method RTPS‐TPS and RTPS using locally fitted polynomial and potential regressions were found to best represent the spatial variability of precipitation and daily extreme temperatures, respectively, and helped compensate the bias resulting from the lack of weather stations at higher elevations. These methods were then selected to create the ACM dataset, which contains climate maps of 30‐year annual and monthly climate normals (ACM–Normals) and 30 years of annual, monthly, and daily climate maps (ACM–YMD). In addition, insights on weather station gap filling in mountainous areas and bias corrections for avoidance of anomalous precipitation and to assure consistency between annual, monthly and daily data are presented, together with discussion about the quality and limitations of the dataset, and its comparison with other datasets. [ABSTRACT FROM AUTHOR]

The rise in the Earth's global average surface temperature and the increase of extreme weather events have been the focus of scientific discussion in the last decades. Extreme heat combined with other environmental extremes, like high concentrations of air pollution, may induce health problems—especially in socioeconomically vulnerable populations. Spring in South America requires particular attention due to its association with hot, dry weather and air pollution in most parts of the continent. This paper intends to better comprehend the behaviour of heatwaves during the austral winter–spring transition. We propose identifying the spatial coverage, frequency and intensity of heatwaves in homogeneous areas of maximum air temperature near the surface (Tmax). We employed cluster analyses during the period between July and October for 41 years (1979–2019) through the ERA5 reanalysis. Homogeneous Tmax areas in South America were defined by cluster analyses that indicated three homogeneous Tmax regions, as follows: a larger area of the continent including the tropical region (Area 1), eastern and southeastern South America (Area 2) and southernmost and steep areas in the Andes (Area 3). The heatwave events identified via ERA5 reanalysis were classified according to their intensity (intense, moderate and weak events). Spatial frequency and trend analyses were also performed regarding the intensity and persistence of heatwave episodes. These methods allowed the identification of the behavioural aspect of heatwaves spanning the last four decades. The Mann–Kendall statistical test (MK) was applied in order to analyse the heatwave trend with a statistical significance level of 5%. A total of 191 heatwave episodes were identified. Of this total, 47.12, 35.60 and 17.28% of episodes occurred in Areas 2, 3 and 1, respectively. The hotter area extending from northeast to southwest in central South America stood out by its largest frequencies of intense heatwave episodes. Across the continent there was a significant increase in the intensity and persistence of heatwaves over the period of 1979 through to 2019. [ABSTRACT FROM AUTHOR]

This sequence of papers examines spatio‐temporal variations of precipitation over the Tibetan Plateau (TP) based on satellite observations. Here in Part 2, spatial patterns of seasonal and diurnal variations of precipitation have been examined based on the Global Precipitation Measurement Mission (GPM) and three additional satellite products. The results show a spatial dipole pattern of two distinct seasonalities: The central TP is marked by strong July peaks and exhibits rainfall contributions of the monsoon season (May–September) of more than 70%, whereas northwestern and southern regions of the plateau exhibit significantly smaller amplitudes in the annual cycle. In some southern regions which are characterized by very high summer mean precipitation and more extreme rain rates, winter months (October–April) contribute significantly to the total annual mean precipitation. In addition, there are larger differences in seasonal curves along a west‐to‐east axis, than along a north‐to‐south axis. The spatial patterns of diurnal precipitation over the TP are more complex compared to seasonality and point to multiple components, which construct the regional differences. These show also a seasonal dependence and are characterized by a stronger afternoon to early evening peak (17:00 LST time, 11:00 UTC) and weaker nighttime peak (23:00 LST, 17:00 UTC) during the monsoon season and over the plateau compared to its surroundings. Furthermore, it was shown that convective precipitation during the monsoon season contribute only up to 30% to the total precipitation, whereas more than 70% is produced by the 90th percentile of daily rain rates. An important characteristic of summer precipitation is hence that a significant part of the extreme precipitation is non‐convective. This paper reveals new features of spatial patterns in seasonal and diurnal precipitation and highlights the importance of non‐monsoonal components for seasonal precipitation variations. [ABSTRACT FROM AUTHOR]

This paper examines the oceanic mean states associated with the Pacific decadal oscillation (PDO) and the Atlantic multidecadal oscillation (AMO) and their relations to the El Niño (EN). The mean states refer to the simultaneous occurrences of warm (W) and cold (C) phases of these oscillations: WAMO/CPDO, CAMO/WPDO and CAMO/CPDO. In general, the sea surface temperature (SST) anomaly patterns of the mean states show a combination of the PDO and AMO related anomaly patterns in the Pacific Ocean, and the strongest AMO‐related anomaly signals in the Atlantic Ocean with almost antisymmetric SST anomaly patterns in the northern and southern extratropical sectors of this Ocean. One of the most important results of this paper concerns the contrasting features between the CAMO/WPDO and the WAMO/CPDO mean states, which are noticeable for the SST, zonal circulation cell and precipitation during the austral autumn. Besides the opposite inter‐basin equatorial Atlantic/eastern equatorial Pacific cells, the CAMO/WPDO and WAMO/CPDO mean states also feature, respectively, a weakened and strengthened Walker cell in the tropical Pacific during the austral autumn. The results here indicate that the inter‐basin east–west cell between the equatorial Atlantic and eastern Pacific contributes to strengthen (weaken) the Walker cell during the austral autumn of the WAMO/CPDO (CAMO/WPDO) mean state. We also found that the mean states alter the EN features. The EN‐related largest positive SST anomalies occur in the central tropical Pacific during the WAMO/CPDO, and in the eastern tropical Pacific during the CAMO/WPDO. The Atlantic and Pacific oceanic mean states play an important role in modulating the EN features and their effects on the South American rainfall. The results presented in this paper might be relevant for climate monitoring and modelling studies. [ABSTRACT FROM AUTHOR]

In this paper we present daily mean wind speed as a new variable in the publicly accessible E‐OBS gridded datasets. Each of the variables in the E‐OBS dataset is provided at a spatial resolution of 0.1° × 0.1° and 0.25° × 0.25°. The variable "daily mean wind speed" starts from 1980 and is updated every month. The main method that we apply is the use of adaptive covariate selection to model the monthly mean wind speed as a function of covariates, like altitude, distance to coast and surface roughness. Then, we use Gaussian process regression to interpolate the daily anomalies from the station locations to the grid locations. In addition, we develop ensemble dispersion improvement auto‐tune (EDIT) to improve the reliability of the local ensemble spread. In order to communicate the methodological uncertainty in the resulting dataset, the E‐OBS wind speed grid is provided as a 20‐member ensemble of random realizations. As part of a preliminary analysis, we investigate the hypothesized wind speed stilling effect in recent decades. Indeed, we do find a small yet significant wind speed stilling effect in the E‐OBS dataset. [ABSTRACT FROM AUTHOR]

VALUE is a network that developed a framework to evaluate statistical downscaling methods including model output statistics such as simple bias correction and quantile mapping; perfect prognosis methods such as regression models and analog methods; and weather generators. The first experiment addresses the downscaling performance in present climate with perfect predictors. This paper presents a synthesis of the VALUE special issue, with a focus on the results of this first experiment. This paper presents a synthesis of the results. Model output statistics performs mostly well, but requires predictors at a resolution close to the target one. Perfect prog performance depends crucially on model structure and predictor choice. Weather generators perform in principle well for all aspects that can be expressed by the available model structure. Inter‐annual variability is underrepresented by both perfect prog and weather generator approaches. Spatial variability is poorly represented by almost all participating methods (inherited by model output statistics from the driving model, not represented by the perfect prog and weather generator methods). Further studies are required to systematically assess (a) the role of predictor choice for perfect prog; (b) the performance of spatial weather generators, to study the performance based on GCM predictors; (c) downscaling skill in simulated future climates; and (d) the credibility of simulated predictors in a future climate. [ABSTRACT FROM AUTHOR]

This paper compares multiple gridded data sets of daily UK precipitation to evaluate structural uncertainty in our reconstructions of historical rainfall. The data sets compared reflect two different sampling strategies and three different grid interpolation methods. In order to separate the influence of sampling and interpolation uncertainties, one of the data sets (produced by the Met Office) has been recreated using the sampling strategy of stations used in the European (E‐OBS) data set. The results confirm and build upon previous studies showing that relying on a relatively sparse but homogeneous network of stations limits the ability of the resulting data set to reliably estimate extreme rainfall at the daily timescale. It is shown that gridding methods that additionally make use of reference climatological data can avoid systematic bias in both the average and extreme events even when using a relatively sparse network of observations. This is an encouraging result in terms of our potential to reliably extend such data sets further back in time where the availability of digitized data is substantially lower than the more modern era. This paper compares multiple gridded rainfall data sets for the UK to analyse structural uncertainty in historical reconstructions of rainfall. In particular, as well as highlighting the shortcomings of using a sparse network of long‐running rainfall stations (as per E‐OBS), this paper shows that gridding methods that make use of reference climatological data help avoid systematic bias. This is a promising and valuable result for purposes of extending rainfall series back in time. [ABSTRACT FROM AUTHOR]

The Mediterranean is characterized with a large number of local winds. One region in the Mediterranean—the Balkan Peninsula or simply the Balkans—is particularly rich with local winds of different types including downslope and upslope winds, gap flows, and thermally induced breezes from land to sea and vice versa. This study presents the first comprehensive review of all currently known local winds in the Balkans, with coastal winds reviewed separately from inland winds. Besides providing the main climatological and dynamics characteristics of these winds, this paper also hints on the existence of various connections between several local winds that have not been reported previously. In total, this article lists 27 different local winds above the Balkans with 17 and 10 being coastal and inland winds, respectively. By far, the most researched local wind in the Balkans has been the Adriatic bora that blows along the Croatian coast. Interestingly, there are more papers investigating bora than the number of studies on all other winds in the Balkans. Local winds over the Adriatic have been explored more than the winds above the Aegean, and these, in turn, were investigated more often than the winds that blow over the Ionian and Black Seas. The most researched inland wind is the koshava wind that blows over the northern and central Serbia. Typical synoptic situations for most local winds are also provided with the note that the synoptic precursors of few local winds have not previously been documented. Lastly, this article discusses the prospects for further research in this field with the emphasis on the investigation of potential relationships between different local winds in this region. The first review of all local winds above the Balkans (27 in total). Besides providing the main climatological and dynamics characteristics of local winds in the Balkans, this article also finds potential relationships between several local winds. Prospects for further research in this field critically discussed. [ABSTRACT FROM AUTHOR]

In recent years, numerous studies have investigated the relationship of extreme precipitation intensities with temperature derived from a binning method using present‐day weather data. The aim of this approach is that these dependencies, or so‐called apparent scaling rates, provide insights on how precipitation extremes could evolve in the future climate. In a recent paper, Bao et al. showed that there is a large discrepancy between the present‐day apparent scaling rates—showing a negative dependency of daily rainfall extremes on temperature for Darwin—and the climate change response showing a substantial increase in daily rainfall extremes. Their results provide compelling evidence that it may not be straightforward to predict the climate change response from the temperature scaling. We agree with this statement, but disagree with the physical explanation put forward in that study and think that moisture limitations are the most likely cause. Therefore, we advocate the use of dew point temperatures in scaling studies as a much more direct proxy of the absolute humidity of the air in which precipitation extremes develop, which we think is physically more consistent with the underlying mechanism causing the increase in precipitation extremes with global warming. [ABSTRACT FROM AUTHOR]

Extra‐tropical cyclones are a relevant feature in the climate at middle and high latitudes. Despite their importance, most studies typically focus only on cyclones identified at a single atmospheric level and on events close to the surface. This paper provides a new perspective on the Southern Hemisphere (SH) cyclone events based on the multilevel cyclone tracking algorithm STACKER. The algorithm, using relative vorticity, detects the raw tracks at single levels and objectively combines them to provide the 3D events and their evolutionary timeline. As a result, a 3D cyclone climatology, based on ECMWF Reanalysis ERA‐I data from 12 pressure levels in the troposphere and lowermost stratosphere is presented. To the best of our knowledge, this is the first analysis carried out throughout the troposphere and the lowermost extratropical/subpolar stratosphere in order to give a comprehensive picture of the cyclone events as physical entities throughout their lifetime. Cyclone properties analysed are track densities, translational velocity, vorticity and lifetimes. For the subtropical and extra‐tropical SH, results support many previous ideas about cyclone characteristics, but new insights are also obtained. A total of 58,231 multilevel cyclone events lasting at least 2 days were detected, with vertical structures spanning two or more levels. This means an average of 303 cyclone events of all types per month, between 2001 and 2017, disregarding seasonality. Results show that cyclones are most frequently detected at the lowest levels of 925 and 700 hPa. By considering that cyclonic systems can be grouped into families according to their vertical extent, results per month on average show that shallow systems are the most frequent events with approximately 248 systems detected, followed by 43 intermediary and 11 deep events. Shallow and deep systems have a large percentage of events with genesis at 925 and 700 hPa. Density statistics show that shallow events are present at all latitude ranges mostly poleward of 30°S with high‐ and medium‐intensities, while intermediate ones are mostly restricted to mid‐latitudes and deep events are mostly confined to sub‐polar and polar latitudes. Cyclones over Antarctica seem to be mostly intermediary and deep cyclones, with longer lifetimes and lower velocities. [ABSTRACT FROM AUTHOR]

The characterization of the alpine extreme precipitation is the basis to study the projected changes in frequency and intensity of heavy rainfall and is needed to improve the resilience of communities to high‐impact weather. Climatological features of extreme daily and sub‐daily precipitation are documented here for the Swiss Alps and surrounding regions at a high spatial resolution (1 km2). The basis is 12 years of data from rain gauges and CombiPrecip, a rainfall field produced by locally adjusting the radar precipitation map to the values measured by rain gauges. The agreement between rain gauges and CombiPrecip concerning both the timing and the magnitude of the extreme events is quantified by cross‐validation; overall, it increases with diminishing the severity of the extremes and increasing accumulation time. If the extremes represent on average the 10 most intense rainfall accumulations per year, in general 50–65% of rain gauges extremes are extremes also for CombiPrecip, 40–50% of CombiPrecip extremes are not extremes according to rain gauges, and CombiPrecip extremes are till 7% lower than rain gauges extremes. The maps presented in this paper show that both daily and sub‐daily extremes are more intense along the alpine slopes compared to the crest of the Alps in all seasons, with the Lago Maggiore region showing the largest values. The fraction of yearly rainfall due to extremes is generally smaller in the Alps than in flat terrain. Extreme 1‐hr precipitation is more clustered in time in the inner Alps, but is less frequent, and exhibits a strong diurnal cycle in summer. The paper also shows that sub‐daily and daily extremes occur essentially over the same 24‐hr period. [ABSTRACT FROM AUTHOR]

This paper quantifies the potential benefit of limiting the global warming to 1.5°C above the preindustrial level on the high‐latitude climate of the Southern Hemisphere compared to 2.0°C and above. A set of Coupled Model Intercomparison Project Phase 5 global climate model experiments is used in order to determine the mean projected changes in surface air temperature, sea level pressure, surface winds and sea ice distribution over and around Antarctica. Alongside, changes in selected variables related to extremes (such as the annual number of extremely cold mornings and extremely cold days) are also quantified as a function of the Representative Concentration Pathway (RCP) considered reaching the given warming threshold. Physical mechanisms for the projected variations in sea ice are proposed, including surface air temperature, changes in low‐level air temperature advection and meridional winds. Results show that there would be significant differences in the atmospheric and sea ice variable changes depending on the warming threshold and RCP considered, and that indeed keeping the global warming under 1.5°C could have a noticeable impact particularly on the distribution of sea ice over the Southern Ocean. [ABSTRACT FROM AUTHOR]

Two skilful 2‐month‐leading hybrid downscaling prediction schemes in October for winter surface air temperature (SAT) over China are proposed in this paper. The schemes are based on the year‐to‐year increment approach and the coupled climate patterns between the winter SAT over China and its predictors. Observed North Pacific sea surface temperature (SST) from the preceding July to September, Arctic sea ice concentration (SIC) in the preceding August and winter sea level pressure (SLP) over pan Eurasia from version 2 of the Climate Forecast System (CFSv2) are selected as the predictors based on the fundamental physics. Individual‐predictor schemes (IP‐schemes), that is, SLP‐scheme, SST‐scheme, SIC‐scheme, indicate that these predictors exhibit prediction skills in different regions. Multi‐predictor scheme I (MP‐schemeI) is developed by combining three predictors. However, MP‐schemeI shows limited skill in predicting SAT over Northeast China (NECTA), due to the limited skill of CFSv2 over the extratropics. Thus, MP‐schemeII is established, in which a hybrid downscaling model for NECTA is constructed. These two MP‐schemes have comparable prediction skill over China, but MP‐schemeII outperforms MP‐schemeI over NEC. The temporal (spatial) anomaly correlation coefficient (ACC) increases from 0.23 (0.15) in MP‐schemeI to 0.36 (0.21) in MP‐schemeII, and the ratio of the same sign of anomalous years (Anomalous‐RSS) improves from 39.1% to 56.5% over NEC. For the winter SAT over China, the MP‐schemes greatly enhance the prediction compared with CFSv2 outputs and the IP‐schemes. The temporal (spatial) ACC increases from 0.29 (0.05) in CFSv2 to 0.52 (0.29) in the MP‐schemes, and the station‐average root‐mean‐square error decreases by about 48.0% compared with CFSv2. Moreover, the RSS (Anomalous‐RSS) of the winter SAT over China is 55.9% (47.4%) in CFSv2 and 64.7% (63.2%) in the MP‐schemes. This indicates that the MP‐schemes perform better in predicting anomalous winters. [ABSTRACT FROM AUTHOR]

From the perspectives of remote sensing and climatic factors like surface meteorological parameters, large‐scale atmospheric circulations, and external forcing factors (EFFs), the authors synthesize and review spatiotemporal variations of PM2.5 over North China and how climate anomalies affect autumn and winter haze variability in North China according to recent studies. This review focuses on both interannual and interdecadal timescales. It is shown that circulations play an important role in influencing haze variability. Atmospheric circulations, which would be modulated by EFFs like sea surface temperature, sea ice, and snowpack, can affect the climate variability in haze over North China via modulation of surface‐layer parameters that are closely connected with the haze phenomenon. Therefore, EFFs are deemed significant factors impacting the climate variability of haze over North China, serving as paramount precursory signals for haze prediction. Furthermore, this paper suggests potential future research directions for haze variability studies in North China on the basis of summarizing and concluding the associated processes/mechanisms on how climatic factors affect haze variability, which could provide reference for treating and forecasting in situ hazy conditions. [ABSTRACT FROM AUTHOR]

In Assam, local severe convective storms (LSCS) are recognized as exceptionally powerful and destructive meteorological events resulting in both death and loss of property, as well as livelihood. A valuable aid to assessing and managing LSCS lies in a reliable database of historical severe storms. In this paper, we investigate the temporal and spatial characteristics of LSCS in the state of Assam lying in the North Eastern Province of India and provide a climatology of LSCS for the state, with respect to: distribution, storm types, frequency, seasonality, and time of occurrence. This was accomplished by developing a LSCS database through a systematic scanning of newspapers and other available sources. This historical database on LSC S dating from 1962 to 2016 was used to identify the areas where the threat and risks from these storms is maximum. Our findings show that LSCS occur throughout the state of Assam, but there are unique geographical areas where the propensity for the occurrence severe to intense local convective storm is much higher. From the monthly distribution of LSCS events, as have been found by previous researchers, the most active month is April. The monthly distributions of hail follow similar pattern as the total number of LSCS events, however, seasonality of lightning differ from other LSCS categories. The probability of LSCS is not uniform throughout the day and tend to reach their most vigorous development during the latter part of the evening and night hours. The observed seasonal pattern of LSCS day's distribution corresponds with the time of the year when convective heating of the lower atmosphere is at its highest in the region, thereby increasing instability of the atmosphere. In addition, climatological mean wind at upper level (200 hPa) show influence of subtropical westerlies and at 925 hPa indicate possible low‐level moisture transport for the peak LSCS months. Therefore, high storm frequencies are to be anticipated. Although November, December and January show the lowest frequency during the entire year, it is still surprisingly high considering that convectional heating and instability of the atmosphere has decreased substantially by then. The results from this study could be applied to produce a hazard map of LSCS for the state of Assam. Such a hazard map will benefit numerous stakeholders, in particular, to direct disaster management authority in terms of interventions for LSCS risk in the state of Assam. [ABSTRACT FROM AUTHOR]

Information on the variability of precipitation in time and space is critical for many water resource projects. However, precipitation records at the location of interest are often either limited or unavailable due to an inadequate network of rainfall measurements. To address this need, regionalization methods have been employed to characterize spatial patterns of precipitation and to transfer precipitation information from one location to another where records are scarce. Hence, the overall objective of the present paper is to propose a stochastic weather model for generating daily precipitation at ungauged locations. The proposed approach consists of two components: (a) a regionalization approach for identifying homogeneous groups of observed daily precipitation series, and (b) a stochastic model for constructing daily precipitation events at ungauged locations within homogeneous groups. This statistical approach identifies groups of precipitation stations with similar statistical characteristics based on the combination of two multivariate statistical techniques: principal component analysis (PCA) and ordinal factor analysis (OFA). While the application of PCA in climatological regionalization studies based on precipitation amount is common, the application of OFA to include precipitation occurrence in the identification of regions is unusual. The feasibility of the approach is assessed using daily precipitation data from a network of precipitation stations in the Catskill Mountain region of New York State, United States. [ABSTRACT FROM AUTHOR]

This paper analyzes climate trends in satellite‐blended model reanalyses for the east Antilles islands of Guadeloupe, Dominica and Martinique (14–17°N, 62.5–60.5°W). Trends are studied for the dry winter (JFM) and wet summer (JAS) seasons, for parameters including: aerosol profile, tropospheric NO2 concentration, rainfall and hydrology, outgoing longwave radiation, potential evaporation, sea level, air and sea temperature and salinity in the upper ocean. Climate change emerges in the form of 2–4 and 6–8‐year surges in near‐surface temperature and mid‐tropospheric subsidence. While near‐surface specific humidity exhibits a rising trend especially in summer, the mid‐troposphere is drying. Coastal zones show little trend in rainfall, but cloud forests on the volcanic slopes are getting wetter. Faster rising trends are noted for sea surface height, and for sea temperatures in low salinity zones that affect tropical cyclone intensification. This work quantifies the spatial and temporal nature of climate variability in the east Antilles islands of Guadeloupe, Dominica and Martinique and advocates for increasing integration of mesoscale analysis into studies on local socio‐economic vulnerability. [ABSTRACT FROM AUTHOR]

This paper highlights detailed projected changes in rainfall over Thailand for the early (2011–2040), middle (2041–2070) and late (2071–2099) periods of the 21st century under the representative concentration pathways (RCP) 4.5 and RCP 8.5 using the high‐resolution multi‐model simulations of the Coordinated Regional Climate Downscaling Experiment (CORDEX) Southeast Asia. The ensemble mean is calculated based on seven members consisting of six general circulation models (GCMs) and three regional climate models (RCMs). Generally, the ensemble mean precipitation agrees reasonably well with observations, best represented by the Global Precipitation Climatology Center (GPCC) data, over Thailand during the historical period (1976–2005). However, inter‐model variations can be large among ensemble members especially during dry months (December to March) for northern‐central‐eastern parts, and throughout the year for the southern parts of Thailand. Similarly for future projection periods, inter‐model variations in the sign and magnitude of changes exist. The ensemble means of projected changes in rainfall for both RCPs during dry months show distinct contrast between the northern‐central‐eastern parts and the southern parts of Thailand with generally wetter and drier conditions, respectively. The magnitude of change can be as high as 15% of the historical period, which varies depending on the sub‐region, season, projection period, and RCP scenario. In contrast, generally drier conditions are projected during the wet season (June to September) throughout the country for both RCPs where the rainfall reduction can be as high as 10% in some areas. However, the magnitude of projected rainfall changes of some individual models can be much larger than the ensemble means, exceeding 40% in some cases. These projected changes are related to the changes in regional circulations associated with the winter and summer monsoons, which are projected to weaken. The drier (wetter) condition is associated with the enhanced subsidence (rising motion). [ABSTRACT FROM AUTHOR]

This sequence of papers, consisting of two parts, examines temporal and spatial variations of convection and precipitation over the Tibetan Plateau (TP) based on recent satellite observations. Here in Part 1, seasonal and diurnal variations of cloud vertical structure and cloud properties have been derived from four combined CloudSat and Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation satellite data sets and compared between three subregions in the TP which are marked by different dominating large‐scale atmospheric circulations and moisture sources. The results show that the plateau is generally dominated by low‐level single‐layer clouds and stratiform cloud types. Cloud occurrence frequencies peak during the summer monsoon season between May and September and are generally higher during daytime compared with nighttime in all the three subregions. The fraction of detected ice cloud layers in the TP domain exceeds 50% during all months and 80% between January and April. While ice cloud layers occur as altostratus clouds in the westerly dominated north and transition zone, high‐level cirrus cloud occurs frequently accompanied by lower level cumulus clouds in the monsoon‐dominated south, especially during nighttime. This study complements previous satellite observations of clouds over the TP and reveals firstly the high contribution of stratiform ice cloud layers in the westerly dominated north, secondly the importance of the monsoon season which outweighs day‐night differences and affects the examined cloud parameters in all regions and finally the significant regional differences of cloud characteristics within the plateau. It is therefore suggested to focus on the relative importance of stratification, mesoscale convective systems and advection in future studies on hydro‐climatic changes in the TP region. [ABSTRACT FROM AUTHOR]

This paper has examined the relative significance of uncertainty in future climate projections from a subset of the coupled model intercomparison project phase 5 (CMIP5) global climate models for the Prairie Provinces of western Canada. This was undertaken by determining: (a) the contribution of model and scenario uncertainty and natural variability to the total variance of these future projections, and (b) the timing of climate signal emergence from the background noise of natural climate variability. We examined future projections of mean temperature, precipitation and summer climate moisture index (CMI). In this region, natural climate variability plays an important role in future uncertainty until the end of this century, particularly for precipitation and to a lesser extent, summer CMI. Model uncertainty also contributes to total uncertainty for these variables throughout this century, while scenario uncertainty becomes more important towards the end of the century. For the region as a whole, significant climate change (i.e., signal/noise >2) occurs earliest for summer mean temperature, with median time of emergence around 2035 for the RCP8.5 radiative forcing scenario. Although the median precipitation signal emerges from the noise (i.e., signal/noise >1) around the 2070s in winter and the 2080s in spring, significant values do not occur in any season for this variable before 2100. For summer CMI, the median time of emergence for significant change is around 2085. At the grid scale, signal‐to‐noise ratios are significant for all seasons for mean surface air temperature, with earliest times of emergence occurring in summer. In contrast, the summer precipitation signal is not significant this century; for summer CMI, significant values are obtained in the eastern half of the region, occurring from about 2065 onwards. Median times of emergence are towards the end of the century for summer CMI in western Saskatchewan and in Alberta, although some areas of Alberta do not exhibit significant signals this century. [ABSTRACT FROM AUTHOR]

Long‐term trends in equatorial African rainfall have proven difficult to determine because of a dearth in ground‐measured rainfall data. Multiple, satellite‐based products now provide daily rainfall estimates from 1983 to the present at relatively fine spatial resolutions, but in order to assess trends in rainfall, they must be validated alongside ground‐based measurements. The purpose of this paper is twofold: (a) to assess the accuracy of four rainfall products covering the past several decades in western Uganda; and (b) to ascertain recent, multi‐decadal trends in annual rainfall for the region. The four products are African Rainfall Climatology Version 2 (ARC2), Climate Hazards Group InfraRed Precipitation with Stations (CHIRPS), Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks–Climate Data Record (PERSIANN‐CDR), and TAMSAT African Rainfall Climatology And Timeseries (TARCAT). The bias and accuracy of 10‐day, monthly, and seasonal rainfall totals of the four products were assessed using approximately 10 years of data from 10 rain gauges. The homogeneity of the products over multiple time periods was assessed using change‐point analysis. The accuracy of the four products increased with an increase in temporal scale, and CHIRPS was the only product that could be considered sufficiently accurate at estimating seasonal rainfall totals throughout most of the region. TARCAT tended to underestimate totals, and ARC2 and PERSIANN were in general the least accurate products. Only annual rainfall estimates from CHIRPS and TARCAT were significantly correlated with ground‐measured rainfall totals. TARCAT was the most homogeneous product, while ARC2, CHIRPS, and PERSIANN had significant negative change points that caused a drying bias over the 1983–2016 period. After adjusting the satellite‐based rainfall estimates based on the timing and magnitude of the change points, annual rainfall totals derived from all four products indicated that western Uganda experienced significantly increasing rainfall from 1983 to 2016. [ABSTRACT FROM AUTHOR]

There were a large number of active meteorological stations in Rwanda prior to the mid‐1990s and since around 2010. However, from around the time of the Rwandan genocide in 1994 throughout the late 2000s, the number of active stations was greatly reduced. To address temporal and spatial gaps in meteorological observation in several African nations (including Rwanda), the ENACTS (Enhancing National Climate Services) initiative reconstructs rainfall and temperature data by combining station data with satellite rainfall estimates, and with reanalysis products for temperature. Bias correction factors are applied to the satellite and reanalysis data and the merged final product is spatiotemporally complete from the early 1980s to the present at a high spatial resolution (4–5 km). This paper offers the first analysis of Rwanda's climatology using this new ENACTS data set for 1981–2016. The temperature and rainfall climatology of Rwanda are analysed at both annual and seasonal timescales as are the climatological influences of topography and regional winds. Climatology maps of mean rainfall intensity, rainy day, 5‐day dry spell and extreme rain day (20+mm) frequency are shown, and spatial pattern correlations are analysed. The rainfall climatology of Rwanda exhibits a clear seasonal bimodality typical of the East Africa region. Topography has a significant effect with the more mountainous, higher‐elevation western part of the country being consistently cooler and wetter than the lower, flatter eastern region. Southeasterly winds tend to prevail over Rwanda, but in some seasons, the climatological winds weaken and shift direction. While spatial patterns of rainy day and dry spell frequency are consistent with the spatial patterns of the seasonal rainfall total, climatologically drier regions have a higher mean rainfall intensity on rainy days. This analysis demonstrates the value of the ENACTS product and illustrates climatological patterns in Rwanda over the last 30 years. [ABSTRACT FROM AUTHOR]

This paper revisits teleconnections for three major rainy seasons at the Greater Horn of Africa for the period 1901–2013. Sea surface temperature‐based climate indices known to influence Short, Kiremt, and Long Rains are used in a comprehensive statistical analysis to detect non‐stationary behaviour in teleconnections and to split them into interannual and decadal time scales. Physical mechanisms are proposed for identified significant non‐stationary teleconnections. Interannual variability in the October–December Short Rains is predominantly influenced by the Indian Ocean Dipole (IOD) with a percent variance explained (PVE) of up to 80% in recent years. However, abrupt shifts in this teleconnection occurred around 1918, 1951, 1987, and recently. The Short Rains also correlate strongly with El Niño‐Southern Oscillation (ENSO). However, ENSO influence on Short Rains is mediated by in‐phase occurrence of IOD. Decadal variations in Short Rains are more directly explained by low‐frequency variability in the Pacific Ocean (PO). A hitherto undocumented non‐stationary relation was found between Atlantic Niño 3 and June–September Kiremt Rains. The non‐stationarity seems to be related to a decadal regime shift in the West African monsoon system in the late 1960s. The variability of Kiremt Rains is also strongly associated with ENSO, although the recent increased correlation is not non‐stationary. Consistent with recent studies, the post‐1998 March–May Long Rains decline is strongly associated with decadal variability in the PO. The PVEs in the stable correlations using Pacific Decadal Oscillation and Interdecadal Pacific Oscillation indices range from 25 to 64%, mostly due to low‐frequency variability (>8 years). The results have ramifications for seasonal‐to‐decadal forecasting and can be taken to design modelling studies to gain insights into the physical mechanisms. Annual mean precipitation from 1981 to 2013 in millimeter, derived from climate Hazard infrared precipitation with station version 2.0 (CHIRPS2.0). The boxes represent the regions for which seasonal SPIs are created: MAM precipitation over GHA (red), OND precipitation over equatorial East Africa (blue), and JJAS precipitation over the Ethiopian Highlands. The interannual and decadal relationships between these rainfall indices and SST‐based remote indices of climate variability are examined. The strength, non‐stationarity, and unknown physical explanations are also explored. [ABSTRACT FROM AUTHOR]

The 1981–2010 monthly precipitation climatologies for Norway at 1 km resolution are presented. They are computed by an interpolation procedure (HCLIM+RK) combining the output from a numerical model with the in situ observations. Specifically, the regional climate model data set HCLIM‐AROME, based on the dynamical downscaling of the global ERA‐Interim reanalysis onto 2.5 km resolution, is considered together with 2009 rain‐gauges located within the model domain. The precipitation climatologies are defined by superimposing the grid of 1981–2010 monthly normals from the numerical model and the kriging interpolation of station residuals. The combined approach aims at improving the quality of gridded climatologies and at providing reliable precipitation gradients also over those remote Norwegian regions not covered by observations, especially over the northernmost mountainous areas. The integration of rain‐gauge data greatly reduces the original HCLIM‐AROME biases. The HCLIM+RK errors obtained from the leave‐one‐out station validation turn out to be lower than those provided by two considered interpolation schemes based on observations only: a multi‐linear local regression kriging (MLRK) and a local weighted linear regression (LWLR). As average over all months, the mean absolute (percentage) error is 10.0 mm (11%) for HCLIM+RK, and 11.4 (12%) and 11.6 mm (12%) for MLRK and LWLR, respectively. In addition, by comparing the results at both station and grid cell level, the accuracy of MLRK and LWLR is more sensitive to the spatial variability of station distribution over the domain and their interpolated fields are more affected by discontinuities and outliers, especially over those areas not covered by the rain‐gauge network. The obtained HCLIM+RK climatologies clearly depict the main west‐to‐east gradient occurring from the orographic precipitation regime of the coast to the more continental climate of the inland and it allows to point out the features of the climatic subzones of Norway. The paper presents the 1981–2010 monthly precipitation climatologies over Norway at 1‐km grid spacing. The climatologies are computed by an interpolation scheme (HCLIM+RK) combining the in situ observations with the regional climate model data set HCLIM‐AROME, based on the dynamical downscaling of the global ERA‐Interim reanalysis. The comparison with methods using observations only proved that HCLIM+RK improves the accuracy of Norwegian climatologies and provides reliable precipitation patterns also over the remote areas not covered by rain‐gauges. [ABSTRACT FROM AUTHOR]

This paper compares extreme value statistics of daily maximum 10 m wind speed in winter simulated by the regional climate model COSMO‐CLM at a horizontal resolution of 15 km (C15) with the reanalyses ERA‐Interim and Arctic System reanalysis (ASR version 1 and 2) and with a satellite data set (CCMPv2). Our C15 simulation (1979/1980–2015/2016, November–April) is thereby the longest high‐resolution simulation available for the Arctic. The results show that the extreme wind speeds tend to increase over the ocean with increasing the horizontal model resolution. A horizontal resolution of ≤15 km is required to sufficiently capture all extreme wind characteristics, in particular for the tip jets and barrier winds over the Irminger Sea and in the Denmark Strait, and for the low‐level jets in the Nares Strait. Of almost equal importance are physical parameterizations of surface fluxes and of turbulence. Capturing extreme wind characteristics has a direct effect on climate relevant air–ice–ocean interactions, such as triggering open‐ocean deep convection, polynya dynamics, or on the sea ice and freshwater balance of the Arctic. State‐of‐the‐art global climate models and reanalyses (e.g., ERA‐Interim) underestimate the extreme near‐surface wind speeds in the Arctic and around Greenland. Regional climate models, for example, ASR/WRF or COSMO‐CLM, resolve the mesoscale wind systems that frequently produce extreme winds, which we estimated i.a. as 10‐year return levels (see the figure). Capturing extreme wind characteristics has a direct effect on climate relevant air–ice–ocean interactions, such as triggering open‐ocean deep convection, polynya dynamics, or on the sea ice and freshwater balance of the Arctic. [ABSTRACT FROM AUTHOR]

In this paper we analyse the relationship between the mean and extreme precipitation for five stations in Hungary and the circulation types at the 500 hPa level, for a 52‐year period, 1958–2010. We used daily rainfall data for each station and a calendar of the daily circulation types at the 500 hPa geopotential height for Hungary based on an automatic classification scheme. A trend analysis showed that, in general, the mean and extreme precipitation rarely exhibit significant trends, similarly to previous studies. The only exception was found for the number of annual and summer rainy days in Budapest with significant negative trends (p = .05), as well as the number of days with rainfall amounts greater than the 95% probability level for Debrecen with a significant positive trend. It was found that the circulation types that are mainly responsible for the largest precipitation amounts overall show (in some cases significant) negative trends, as well as the precipitation amounts that are associated with them (Cwsw, Cse, Cwnw). In most cases, the circulation types that are prevailing during the extreme precipitation events are associated with western or almost‐western atmospheric circulations (Cwsw, Ase) and Mediterranean‐ or Atlantic‐origin depressions. [ABSTRACT FROM AUTHOR]

The characteristics of the northern and southern modes of the East Asian winter monsoon (EAWM) and their relationships with El Niño‐Southern Oscillation (ENSO) are further investigated in this paper using reanalysis data. The results demonstrate that the northern mode shows strong inter‐decadal variations, whereas the southern mode is marked by noticeable inter‐annual variations. The west–east pressure gradient plays a leading role in influencing northern mode, and both the west–east and north–south pressure gradients have significant impacts on the southern mode. The two modes are closely related, but their relationship shows inter‐decadal variations. The relationship between the southern mode and ENSO is significant and stable, but the relationship between the northern mode and ENSO is unstable and shows obvious inter‐decadal variations. The relationship between the northern mode and ENSO is significant before the late 1960s and after late 1990s, but it is not significant during the period between the late 1960s and late 1990s. ENSO influences the activity of northern mode mainly by changing the west–east pressure gradient. During the periods of a weak relationship between northern mode and ENSO, the variations in west–east pressure gradient may be dominated by the climate systems at mid–high latitudes, and the effects of ENSO are confined or offset. The inter‐decadal variations in the relationship between northern mode and ENSO may be modulated by the Pacific Decadal Oscillation (PDO) and Atlantic Multi‐decadal Oscillation (AMO), but their roles and importance have varied over time. The relationship between EAWM and ENSO and its inter‐decadal variations vary with the EAWM index, which is induced by the differences between the northern and southern modes. When the EAWM index is more closely correlated with the southern (northern) mode, its relationship with ENSO is (not) significant and stable (unstable). [ABSTRACT FROM AUTHOR]

Long‐term decreasing trends of near‐surface wind speed (SWS) have been well demonstrated in China, and at the same time the factors causing the slowdown in SWS have also been explored. However, changes in wind speed and pressure gradient force (PGF) at higher elevations have received little attention. In this paper, the spatio‐temporal changes of wind speed and PGF at different heights were explored in eastern China during the period 1980–2011, and the potential causes inducing the changes of wind speed were analysed. The results included that the reduction in wind speed emerged from the near surface to 300 hPa, while the PGF also exhibited a synchronous reduction. The influence of PGF on the decrease of wind speed was relative smaller at near surface than that at higher levels (850–300 hPa). At the near surface, 71.8% of changes in annual mean SWS could be attributed to the changes of PGF, in which the seasonal difference of the influence of PGF on wind speed was less than 7.0%. At the higher levels, most of the changes in wind speed (>90%) was induced by PGF, in which the seasonal difference of the influence of PGF was less than 1.0%. Furthermore, the changes of PGF in eastern China could be mainly influenced by both the Northern Hemisphere annular mode (NAM) and the Pacific Decadal Oscillation (PDO). The NAM could affect the inter‐annual and inter‐decadal changes of PGF, and the effects of NAM played more significant role on the inter‐annual scale than that on the inter‐decadal scale. At the same time, the correlation between NAM and PGF increased with height. Otherwise, the PDO mainly affected the inter‐decadal changes of PGF, and their correlation decreased with height. [ABSTRACT FROM AUTHOR]

Previous studies have reported that much of the surface wind speed (SWS) over the mid‐latitudes of the northern hemisphere has declined. However, very few studies have investigated the relatively recent phenomenon of wind recovery. Based on 68 wind data series, this paper examines changes in wind speed in northwest China between 1969 and 2015. In 1992, following a decade of sharply decreasing at a rate of 0.036 m s−1 a−1 (p < .05), the SWS began to significant increase at a rate of 0.004 m s−1 a−1. The specific reasons for this increase are as follows: (a) The decrease in SWS during the pre‐1992 slowdown period is the result of declining wind speeds in spring and summer, whereas increases in wind speed during the post‐1992 recovery period are caused by increased wind in winter. (b) The number of days featuring strongly varying wind speeds has changed. Specifically, the number of days above 2 m s−1 all show a significant decreasing trend from 1969 to 1992, whereas the number of days of 1–3 m s−1 shows a significant upward trend from 1993 to 2015. (c) Stations located between 1,000 and 1,500 m.a.s.l. (meter above sea level) are more sensitive to climate change than those at other altitudes, which shows the biggest decline (increase) trend during wind speed slowdown (recovery) period. These stations could potentially act as climatic indicators to predict future wind speed changes. SWS in northwest China have been affected by changes both in large‐scale atmospheric circulation and in regional warming. Surface pressure gradient variations between high‐ and low‐latitude regions may be important contributors to wind speed changes under asymmetric warming. However, urbanization is only moderately responsible for trend changes in SWS. [ABSTRACT FROM AUTHOR]

Over the last decades, general circulation model (GCM) simulations have been regularly evaluated in terms of their ability to reproduce the historical frequency of significantly recurrent weather patterns (WP) observed at the regional scale. Thus, a good simulation of the frequency of these particular WP by the GCM is generally conditioning the good representation of the regional statistics of surface variables such as temperature and precipitation. In this paper, the seasonal frequency of eight particular WP have been calculated using the daily geopotential height fields simulated by an ensemble of 26 Coupled Model Intercomparison Project Phase 5 (CMIP5) GCM. These WP are known as significantly influencing the French regional hydro‐climatology in terms of both frequency of low‐flows and high‐precipitation events. Four different bias correction methods have been applied on the simulated geopotential height fields before the calculation of the seasonal WP frequencies. The GCM ensemble showed overall good performances in terms of the simulation of WP seasonal frequencies. The application of a spatially and temporally non‐homogenous correction of simulated geopotential height fields improved significantly the simulation of WP frequencies for the four seasons. Finally, the evolution of the WP frequencies over the next century has been quantified. Three WP (WP2, WP4 and WP8) have pronounced seasonal changes, with WP2 and WP4 being less frequent in summer and autumn seasons, respectively, while WP8 being more frequent over spring, summer and autumn seasons. The strong simulated frequency evolution of WP2 and WP8 is an interesting result, which predicts the climate to be drier with time for France. Thus, WP2 (western oceanic circulation), grouping rainy days over the northern France region, is simulated as less frequent in future summers, while WP8 (anticyclonic situations), which groups non‐rainy days over France, is simulated as more frequent in future summers. [ABSTRACT FROM AUTHOR]

The leewards shores of the Laurentian Great Lakes are highly susceptible to lake‐induced snowfall. During the late autumn and winter season, cold air advection over relatively warm lakes can induce instability in the lower planetary boundary layer (PBL), facilitating the exchange of moisture and energy fluxes and fuelling the development of snowfall. Snowfall in this region can have disastrous impacts on local communities such as the November 2014 Buffalo storm that caused 13 fatalities. This paper discusses historical snowfall trends along the Canadian leewards shores of Lakes Superior and Huron‐Georgian Bay and explores several lake‐induced predictor variables that may influence the snowfall trends. Spatio‐temporal snowfall and total precipitation trends were computed for the 1980–2015 period over the Great Lakes Basin (GLB) using the Daymet (version 3) gridded estimated data set. Results show a significant decrease in snowfall, at a rate of 40 cm/36 years, and a significant decrease in total precipitation of 20 mm/36 years, along the Ontario snowbelts of Lake Superior and partially along that of Lake Huron‐Georgian Bay at the 95% confidence level during the cold season. Attributions to these negative spatio‐temporal trends are explored using data from the North American Regional Reanalysis (NARR) and the Canadian Ice Service (CIS) data sets. Predictor variables show significant warming in lake surface temperature (LST) at a rate of over 6 K/36 years for Lake Superior, significant decrease in ice cover fraction for both lakes, and an increase in the vertical temperature gradient (VTG) between the LST and the 850 mb level. While the behavioural trends of these variables are believed to enhance snowfall through increased evaporation, there are other complex processes involved, such as inefficient moisture recycling and increased moisture storage in warmer air masses that may inhibit the development of snowfall along the immediate leewards shores of Lake Superior. [ABSTRACT FROM AUTHOR]

The Sahel region is known for the multi‐decadal occurrence of severe drought that commenced in the late 1960s. A still open question is whether or not the region's rainfall has returned to “normal.” This paper provides a compelling answer to that question by examining the longest and most comprehensive gauge series for the region ever published. It extends from 1854 to 2014 and is based on 602 gauge records. A comparative series for the Guinea Coast region to the south is also presented, as the two regions collectively provide insight into the long‐term variability of the West African monsoon. In contrast to many previous studies, here the question of recovery and regime change is not restricted to the core of the Sahelian rainy season (July–September), but is separately discussed also for the coastal phase (April–May), transition phase (June), Sahelian phase (July–September) and the second transition phase (October–November) of the West African monsoon. These analyses suggest that full recovery from the droughts of the 1970s and 1980s has not occurred that a major change in the rainfall regime occurred around 1968 and that since that time large‐scale teleconnections have also changed markedly. The shift post‐1968 is evident in all phases of the monsoon except the coastal phase, in which a change to drier conditions occurred a decade later. Overall, recovery has been greater in the east than in the west, creating a change in the climatological east–west rainfall gradient. The drier post‐1968 conditions appear to be associated with a general weakening of the intensity of the West African monsoon and only a small southwards displacement of the rainfall maximum. These changes have strong implications for the future of this region and for seasonal prediction. [ABSTRACT FROM AUTHOR]

ABSTRACT: Homogeneous meteorological data are a prerequisite for reliable climatological studies. This paper investigates the homogeneity of wind data from 213 m high Cabauw tower located in The Netherlands. The wind measurements are conducted at 10, 20, 40, 80, 140 and 200 m above ground. The analysed data cover the period from February 1986 to January 1997 and from April 2000 to December 2015. This study presents the first homogeneity analysis of wind data from a tall meteorological mast. Homogeneities of wind speed and wind direction series were investigated independently using the ReDistribution Method. Overall, the wind measurements at Cabauw tower are very homogeneous. The only wind speed inhomogeneity was detected at 200 m above ground and it seems to be, at least to a certain extent, caused by the rapid expansion of the town of Lopik in the 1990s. Lopik's growth to the west, however, only influenced the east winds on the Cabauw tower. Small inhomogeneities in wind direction data were detected at 20, 40 and 80 m levels, whereas a fairly large inhomogeneity was observed at 10 m above ground. Several potential causes of inhomogeneities in wind direction data are discussed, but the major contributor could not be determined with certainty. In addition, the homogeneity of real measurements from Cabauw tower is compared against the synthetically created wind data for Cabauw tower using the Monte‐Carlo method of random sampling. The results show that the detected anomalies are not due to the random noise in the time series. [ABSTRACT FROM AUTHOR]

ABSTRACT Water scarcity is a critical issue in Iberia but few studies have investigated future drought over the region. The few that do are continental or global studies and do not report the range of possible future projections. In this paper, historical drought and future projections of drought were examined, using observed and downscaled rainfall data from climate models, for the main Iberian international basins (Douro, Tagus and Guadiana). Two drought indices were used, the standardized precipitation index ( SPI) and the drought severity index ( DSI). However, problems were found in the distribution fitting required for the calculation of SPI which render this index inadequate for assessing droughts in Iberia. The skill of CMIP5 climate models in representing historical drought for the Douro, Tagus and Guadiana is very variable with some not showing enough persistence of dry conditions, and others simulating droughts that are too long and too severe. Nevertheless, the observed range of drought conditions for these basins was encompassed by the ensemble members. Furthermore, we found no relationship between performance in simulating mean large-scale circulation and model ability to reproduce the historical drought characteristics for the region. All models project an intensification of drought conditions for the three basins. However, some only project small increases, while most project extreme multi-year droughts by the end of the century. We found that climate model future projections are neither related to their performance in simulating historical drought nor to their large-scale circulation patterns. This result emphasises the need for climate change impact studies to take into account the whole range of climate model projections in order to provide the best information for robust adaptation. Choosing one or a subset of climate models based on historical performance would not lead to a credible and justified reduction in uncertainty. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper presents a regional and seasonal study of extreme point rainfall scaling from 10 min to 2 years. To do this, the highest point-based rainfall list based on these temporal periods was calculated from the Spanish Meteorological Service ( AEMET) precipitation databases with more than 11 000 rain-gauge stations, with the longest series ranging from 1805 to 2014 (209 years). This list constitutes the register of single station largest amounts of precipitation in Spain ever recorded for selected periods, including for example the values for 2 h (193 mm), 24 h (817 mm) or 1 year (5503 mm). Rainfall extremes for 10 min periods are evenly distributed in coastal and inland areas. Daily precipitation extremes are mostly concentrated over the Mediterranean coast while from durations from one month to two years, extremes are located in southern and northwest Spain. Extreme data obtained were compared with existing worldwide rainfall records for equivalent periods. Results indicate that Spanish extreme rainfall scaling relating R depth (in mm) against D duration (in minutes) may be expressed as a potential law R = 21.8 D0.422 ( R = 43.6 D0.507 for worldwide data). We propose the upper envelope line (greater or equal to extreme rainfall values) parallel to the potential fit law as a simple method to estimate possible extreme records for different time scales. Using this method, worldwide envelope may be expressed as R = 60.5 D0.507 and the Spanish envelope as R = 39.3 D0.422. Further analysis stratifying results by season and region show that seasonal scaling has more variability than regional scaling. The methodology described can be readily applied to other regions for which detailed rainfall databases exist. Applications of the results include using the scaling found as a reference for classification of heavy precipitation events for temporal scales. [ABSTRACT FROM AUTHOR]

ABSTRACT The feedbacks of vegetation growth to climate are very important and exhibit large differences, depending on seasons and characteristics of plants and climate. Through two simulations, this work investigated these differences among the influences of the seasonal growth of different vegetation on surface energy budgets over the latitudinal range of 30-90°N and detected associated causes. The seasonal growth of vegetation is expressed as an increase in leaf area index ( LAI) during the growing season (April-October) compared to boreal winter (December-January-February). The results showed that notable effects occurred in latent heat flux, downward solar radiation and reflected solar radiation for dominant plant functional types ( PFTs). With a seasonal increase in LAI, the latent heat flux of 'needleleaf evergreen boreal tree' ( NEB) decreased, while it increased for the other dominant PFTs. Such unexpected behaviours of NEB were mainly contributed by the weak changes in its transpiration, which was associated to land-atmosphere feedbacks (the decreased downward solar radiation) and competitions among PFTs (the intensified transpirations of the deciduous vegetation PFTs). Surface downward solar radiation decreased for all dominant vegetation PFTs because of more low clouds. The reflected solar radiation of 'broadleaf deciduous temperate tree' increased along with increased LAI because its leaf albedo is higher than that of the background soil, and the reflected solar radiation of 'broadleaf deciduous boreal shrub' drastically decreased during April and May, which resulted from its interactions with accumulated snow. This paper sufficiently proves that the feedbacks of different vegetation to surface energy balance could vary widely, not only in magnitudes but also in directions. Therefore, it is very important to accurately parameterize vegetation phenology and optical properties for a better representation of vegetation-climate interactions. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates winter (DJF) precipitation variability over East Anglia at the daily and 2 d timescales using rain gauge data from 134 sites. The first three principal components (PCs) explain 80.2% (82.0%) of the variance in daily (2 d totals). Precipitation displays higher spatial coherence in winter, with the first three PCs of summer daily totals (Neal and Phillips, 2009, International Journal of Climatology 29: 1661-1679) explaining only 72.3% of the variance. The winter PCs for both 24- and 48-h timescales display precipitation maxima in South Essex (PC 1), NE Norfolk (PC 2), and NW Cambridgeshire (PC 3). The rainfall maximum over South Essex is more important in winter than in summer. Lamb Weather Types and synoptic charts are used to explain the causes of the PCs. A precipitation regionalization is also produced. Discharge for 11 rivers is then modelled as a linear function of the rainfall patterns (as represented by the PC scores). With the exception of the River Babingley, whose discharge is not significantly related to the PCs, these models explain on average 26.5% of the variance. For most rivers, there are significant relationships between discharge and precipitation that fell up to 4 d ago on average. In general, East Anglian river flows show persistence over 6-8 d. [ABSTRACT FROM AUTHOR]

The paper traces the origins of the terms climate and climatology in the English language. The term climate has a 600-year history, but only came into widespread scientific use about 150 years ago. Climatology began to find wide usage in the mid-late 19th century. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Hong Kong is a high-density sub-tropical city with 7 million people living in an urban area of just over 260 km2. Tall and closely packed buildings are the common urban morphology. How the urban geometry influences the microclimate in summer daytime is a primary planning concern. The sky view factor (SVF) has been commonly used to indicate the impact of urban geometry on air temperature differences in cities. However, only limited discussions in this aspect have been addressed for daytime course in high-rise and high-density urban environment such as Hong Kong. This paper firstly provides a comprehensive review of SVF analysis in urban climatology studies and then presents a simulation approach to investigate the role of SVF in determining summer daytime intra-urban air temperature differences in urban Hong Kong. An ArcGIS-embedded computer program is developed for calculating continuous SVF values for an entire urban environment and an SVF map is generated. The result is evaluated against meteorological data observed in field measurements. The regression analysis shows that the spatial average of SVF values has a close negative relationship with daytime intra-urban temperature differences. The study indicates that SVF is a significant factor for understanding the microthermal climate in Hong Kong's street canyons. The paper further raises discussions on the application of SVF analysis to urban planning. The study demonstrates that the SVF analysis is a useful and effective tool for planners and urban climatologists conducting studies on high-rise and high-density sub-tropical cities. The understanding can provide support for the development of planning standards and good practice. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

This paper presents a simple methodology to identify sea breeze frontal passage in the city of São Paulo, Brazil, based in hourly wind direction data. Fifty-year time series of annual frequency of sea breeze frontal passage and of its time of arrival in São Paulo are generated and related to global climate indicators and local variables. The frequency of occurrence and time of arrival of sea breeze shows long-term oscillations in the interannual and decadal time scales. Multiple regression is used to identify the variables that explain the observed variance of both frequency of occurrence and timing of the sea breeze in São Paulo. Local variables such as air temperature in São Paulo and sea surface temperature (SST) in the vicinity of the coast explain more than 95% of the total R2 (R2 = 51%) in a multiple regression model of the frequency of sea breeze frontal passage. Global climate indices such as the Atlantic Multidecadal Oscillation, the Southern Oscillation Index (SOI) and the Pacific Decadal Oscillation explain about 85% of the total R2 (R2 = 52%) in a multiple regression model of the time of arrival of the sea breeze in São Paulo. The sea breeze circulation is shown to impact the rainfall in São Paulo and vicinity and to be associated with extreme rainfall events. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue including the issues that are associated with aspects of global change and the role of cities and the status of modeling at the meso-scale.

ABSTRACT This paper studies how the anthropogenic-induced global warming affects the East Asian winter monsoon ( EAWM) by using 26 Coupled Model Intercomparison Project phase 5 ( CMIP5) models. The simulated present-day EAWM is evaluated and future projections under RCP4.5 and RCP8.5 scenarios are presented in terms of the climatology and interannual variability. All 26 models can well reproduce the spatial pattern of EAWM climatology and 16 out of the 26 models can reasonably capture major features of interannual variability. The projection made by 26-model ensemble mean indicate that winter surface air temperature averaged over 20°-60°N, 100°-140°E will increase by 3 °C in RCP4.5 and 5.5 °C in RCP8.5 towards the end of the 21st century. The corresponding regional mean precipitation will increase by 12.3% in RCP4.5 and 21.8% in RCP8.5. The strong warming over high-latitude North Pacific due to melting sea ice in the Bering Sea and Okhotsk Sea leads to significant intensification and a northward shift of the Aleutian Low, resulting in prominent increase in the low-level northerly along the coastal regions of northeastern Asia. At 500 hPa the characteristic East Asian Trough is projected to weaken slightly and tilt more eastward with latitude. The selected 16-model ensemble mean projects future enhanced interannual variability of surface air temperature and sea-level pressure over mid-latitude North Pacific and high-latitude East Asia ( EA) and reduced variability over eastern China, suggesting that the EAWM will be more variable in the high-latitude EA and mid-latitude North Pacific but less variable in East China. Accordingly, the year-to-year precipitation variability will be significantly enhanced over high-latitude EA. Majority of the 26 models project that the leading mode of EAWM interannual variation (the 'northern mode') will become more dominant in the warmer climate. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper investigates the interannual variability of precipitation over the South Asian monsoonal region in May, during which the South Asian summer monsoon is generally established. The South Asian monsoonal region in this study is referred to as a broad area that includes the Arabian Sea, the Indian peninsula, the Bay of Bengal, and the Indochina peninsula. The precipitation exhibits a significant enhancement in May, compared to that in the previous month. The present results indicate that the interannual variability of May precipitation in this region is significantly regulated by two independent factors: The Europe-West Asia ( EWA) teleconnection and El Niño Southern Oscillation. The EWA teleconnection pattern is characterized by the see-saw pattern of upper-tropospheric geopotential height anomalies between the Europe and the Iranian plateau. Both the factors modulate the meridional gradient of tropospheric temperature and lower-tropospheric zonal winds, and thus affect the rainfall in the monsoonal region. Therefore, both the extratropical circulation teleconnection and tropical forcing are crucial for inducing rainfall variability in May over the monsoonal region. [ABSTRACT FROM AUTHOR]

ABSTRACT In this paper, we analyse observed changes in characteristics of sub-daily heavy summer precipitation and erosive precipitation events for the Czech Republic, taking into consideration 51 years of data (1961-2011) for 17 stations. The sub-daily data were checked for consistency with the daily control records, and unreliable data were removed from the data set. Subsequently, four statistical tests were applied to assess the homogeneity of the data set. The trend magnitude was estimated using the Theil-Sen slope estimator, and two tests were applied to evaluate its significance. For most of the indices, the tests did not indicate inhomogeneity, with the exception of characteristics related to rainfall intensity. The trends are positive for most of the stations and most precipitation characteristics, and significant positive trends are much more frequent than negative trends. The analysis revealed a significant increase in the contribution of heavy precipitation to the precipitation total in half of the stations at short aggregation levels. [ABSTRACT FROM AUTHOR]

This paper presents to date the most complete global climatology of the size of tropical cyclones (TCs) between 1999 and 2009 using the QuikSCAT satellite data. Here, TC size is defined as the azimuthal mean radius of 17ms-1 surface winds from the TC centre. While the TC size climatology for the Western North Pacific (WNP) and North Atlantic (NA) has been documented in previous studies, those for the Eastern North Pacific (ENP), South Indian Ocean (SI) and South Pacific (SP) have yet to be examined in detail, which is the objective of this study. Among all the basins, TCs over the WNP are the largest and have the largest variance, while those over the ENP are the smallest. In addition, TCs in the Northern Hemisphere (WNP, NA and ENP) have two seasonal size peaks, but those in the Southern Hemisphere (SI and SP) have only one. An important finding is that for all basins, the size of a TC does not necessarily increase with latitude monotonically, but reaches the maximum at some latitudinal region. Such a result agrees well with a recent theoretical study in terms of a balance between the inertial stability associated with the TC circulation and the import of angular momentum into the TC. [ABSTRACT FROM AUTHOR]

Seventeen years of 3‐hr, 0.25° resolution, precipitation data from the Tropical Rainfall Measurement Mission (TRMM) multi‐satellite precipitation analysis (TMPA) product are used to develop a global climatology of precipitation in tropical cyclones (TCs). Due to very large SDs for rainfall in each stratification by intensity class or cyclone basin, our methodology concentrates on frequency distributions and percentage representation in different rainfall rate categories. The stratifications reveal that the TC rainfall climatologies are dependent on three inter‐related factors: TC intensity, TC size and TC basin. The interdependence of the three is examined. The distributions of TC intensity classes in the different basins are not a significant contributor to the fact that certain basins (Northwest Pacific, North Atlantic) have higher TC rainfall rates than other basins (Northeast Pacific, South Indian). In contrast to this, the distributions of TC size classes between basins are a significant contributor to why some basins are wetter than others. A climatology is also presented of lifetime accumulated rainfall (LAR) in TCs. The record LAR belongs to hurricane Ivan in 2004, with 300 km3 of rain over the 0–350 km radius, and 432 km3 over 0–500 km. The largest LAR values occur almost exclusively in two cyclone basins: The Northwest Pacific and the North Atlantic. Not unexpectedly, LAR is determined primarily by TC duration, which accounts for around 70% of the variance. Examination of the full 17‐year dataset reveals a decreasing trend in both median and extreme TC rainfall rates in all basins except the Northeast Pacific. However, mechanisms responsible for this decrease are yet to be identified and may be primarily due to the sample size or data inhomogeneities. The difference between the trends and those expected from physical principles is a concern which we hope will be taken up by other investigators. [ABSTRACT FROM AUTHOR]

ABSTRACT The aim of this paper is to study the model's simulated frequency, track, intensity and location of cyclonic storms (CSs) and severe cyclonic storms (SCSs) in the Bay of Bengal (BoB), India. For the purpose, the PRECIS (Providing REgional Climates for Impacts Studies) a regional climate modelling system, of UK Met Office, is used. This model is integrated for the period 1961-1990 (baseline) and the future time period 2071-2100 (High emission scenario, A2). To run the model, the initial and lateral boundary conditions are supplied by UK Met Office. The analysis of frequency, track, intensity and location are carried out for May, June, September and October for the period 1961-1990 and 2071-2100. To evaluate the model's performance in simulating storms frequency during 1961-1990, chi square test is carried out with observed storms for the same period. The model's simulated frequency of storms is an overestimation of observations although the frequency of model's simulated storms during 2071-2100 is less than that of during 1961-1990. In general, model's simulated storms are found moving in the northwest direction from their initial location in all months during 1961-1990 and 2071-2100. In model's simulations, the drop in central pressure is relatively more in the months of May, June, September and October during 2071-2100 compared with that during 1961-1990. During 2071-2100, more intense storms may be possible in the months of May and June compared with that of September and October. It is observed that the model is able to simulate the initial locations of storms during 1961-1990 and 2071-2100 close to observations for the months of June and September, especially. [ABSTRACT FROM AUTHOR]

ABSTRACT The stability and moisture content of the different atmospheric levels are commonly used to assess the risk index in the propagation and evolution of a hypothetical forest fire. The Haines Index (HI) combines these terms to determine the environmental potential for wildfire growth. In this paper the environmental stability and humidity associated with the lower atmospheric layers in the Western Mediterranean Basin are investigated by analysing HI calculations over a 29-year period. The HI climatology can be applied to the study of plume-dominated forest fires. These fires tend to present very erratic propagation behaviour and create highly dangerous situations for fire brigades. Thus the knowledge of the typical index values and the meteorological situations that generate them could be extremely useful for minimizing the fire risk and planning specific fire-fighting activities. In this study we carry out a spatial and temporal analysis of the Index and its terms in the Valencia region on the basis of NCEP/ NCAR reanalysis data from 1980 to 2008, obtaining a detailed climatological analysis of the HI in the Valencia region for each variant of elevation, which can be used as a reference tool. Moreover, using NCEP reanalysis maps at 500 and 850 hPa, we also perform a daily synoptic analysis for the studied period which is finally associated to the different values that the Index can show in this area. As a result three dominant synoptic weather situations have been defined in this region: continental, maritime and convective. A direct proportionality has been found between increases in the HI and convective situations. [ABSTRACT FROM AUTHOR]