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We present new temperature and precipitation reconstructions for the past 25 000 cal. years BP from across eastern Beringia based on a network of pollen diagrams, an updated modern pollen calibration database, and an improved methodology using the modern analogue technique (MAT). Time series show July temperatures were around 4 °C lower during full glacial and January temperatures were about 2 °C lower than present. Annual temperatures rose beginning around 16 000 cal. years BP, reaching a maximum around 12 000 cal. year BP. The warming was more rapid in southern Beringia. Annual precipitation varied by 250 mm during the past 25 000 cal. years BP. Maps of reconstructed precipitation patterns show increasingly drier conditions since 12 000 cal. years BP. that vary regionally, suggesting Holocene atmospheric circulation changes at multiple time and space scales. Orbitally forced seasonality changes during the late glacial and early Holocene resulted in reversed seasonal temperature reconstructions due to methodological constraints using the MAT and (or) non-analogue conditions. The magnitude of millennial-scale climate variability in this region was greater during the last glacial and late glacial periods than during the past 8000 years.

The occurrence of African dust outbreaks over different areas of the western Mediterranean Basin were identified on an 11-year period (2001–2011). The main atmospheric circulation patterns causing the transport of African air masses were characterized by means of an objective classification methodology of atmospheric variable fields. Next, the potential source areas of mineral dust, associated to each circulation pattern were identified by trajectory statistical methods. Finally, an impact index was calculated to estimate the incidence of the African dust outbreaks produced during each circulation pattern, in the areas of study. This work was funded by the Spanish Ministry of the Environment and Rural and Marine Affairs under the project “Estudio y evaluacion de la contaminacion atmosferica por material particulado y metales en España” (UCA 2009020083) and by research projects GRACCIE-CSD2007-00067, MICROSOL (CGL2011-27020) and VAMOS (CGL2010-19464/CLI).

The record-breaking mei-yu in the Yangtze-Huaihe River valley (YHRV) in 2020 was characterized by an early onset, a delayed retreat, a long duration, a wide meridional rainbelt, abundant precipitation, and frequent heavy rainstorm processes. It is noted that the East Asian monsoon circulation system presented a significant quasi-biweekly oscillation (QBWO) during the mei-yu season of 2020 that was associated with the onset and retreat of mei-yu, a northward shift and stagnation of the rainbelt, and the occurrence and persistence of heavy rainstorm processes. Correspondingly, during the mei-yu season, the monsoon circulation subsystems, including the western Pacific subtropical high (WPSH), the upper-level East Asian westerly jet, and the low-level southwesterly jet, experienced periodic oscillations linked with the QBWO. Most notably, the repeated establishment of a large southerly center, with relatively stable latitude, led to moisture convergence and ascent which was observed to develop repeatedly. This was accompanied by a long-term duration of the mei-yu rainfall in the YHRV and frequent occurrences of rainstorm processes. Moreover, two blocking highs were present in the middle to high latitudes over Eurasia, and a trough along the East Asian coast was also active, which allowed cold air intrusions to move southward through the northwestern and/or northeastern paths. The cold air frequently merged with the warm and moist air from the low latitudes resulting in low-level convergence over the YHRV. The persistent warming in the tropical Indian Ocean is found to be an important external contributor to an EAP/PJ-like teleconnection pattern over East Asia along with an intensified and southerly displaced WPSH, which was observed to be favorable for excessive rainfall over YHRV.2020年江淮流域梅雨开始早, 结束晚, 持续时间长, 雨带南北跨度大, 降水量大, 暴雨过程多, 是一次破纪录的梅雨事件. 分析发现, 东亚季风环流系统表现出明显的准双周振荡 (QBWO), 它与梅雨的开始和结束、 雨带的北移和停滞、 强降水过程的发生和维持有很好的对应关系. 梅雨期包括西太平洋副热带高压、 高层东亚西风急流和低空西南风急流在内的多个季风环流子系统均经历了与 QBWO 相关的周期性振荡, 尤其是低空西南急流的不断加强, 南风大值中心反复建立和位置的相对稳定, 使得源自热带的水汽输送一次次加强, 水汽辐合与上升运动反复发展, 从而导致梅雨在江淮流域长时间持续, 暴雨过程频频发生. 另一方面, 梅雨期欧亚中高纬度地区环流呈现出 “两脊一槽” 型, 阻塞高压活动频繁, 东亚沿岸低槽活跃, 经西北和/或东北路径的冷空气不断南侵我国, 与低层一次次加强的西南暖湿水汽在江淮区域频繁交汇, 这是造成今年梅雨异常偏强的另一重要因素. 作为一个重要的外强迫因子, 热带印度洋的持续增暖使得东亚地区环流呈现出 EAP/PJ 型遥相关型, 对应西太副高偏强偏南, 从而有利于长江中下游地区降水明显偏多.

Southern Africa produces almost a third of the Earth's biomass burning (BB) aerosol particles, yet the fate of these particles and their influence on regional and global climate is poorly understood. ORACLES (ObseRvations of Aerosols above CLouds and their intEractionS) is a 5-year NASA EVS-2 (Earth Venture Suborbital-2) investigation with three intensive observation periods designed to study key atmospheric processes that determine the climate impacts of these aerosols. During the Southern Hemisphere winter and spring (June–October), aerosol particles reaching 3–5 km in altitude are transported westward over the southeast Atlantic, where they interact with one of the largest subtropical stratocumulus (Sc) cloud decks in the world. The representation of these interactions in climate models remains highly uncertain in part due to a scarcity of observational constraints on aerosol and cloud properties, as well as due to the parameterized treatment of physical processes. Three ORACLES deployments by the NASA P-3 aircraft in September 2016, August 2017, and October 2018 (totaling ∼350 science flight hours), augmented by the deployment of the NASA ER-2 aircraft for remote sensing in September 2016 (totaling ∼100 science flight hours), were intended to help fill this observational gap. ORACLES focuses on three fundamental science themes centered on the climate effects of African BB aerosols: (a) direct aerosol radiative effects, (b) effects of aerosol absorption on atmospheric circulation and clouds, and (c) aerosol–cloud microphysical interactions. This paper summarizes the ORACLES science objectives, describes the project implementation, provides an overview of the flights and measurements in each deployment, and highlights the integrative modeling efforts from cloud to global scales to address science objectives. Significant new findings on the vertical structure of BB aerosol physical and chemical properties, chemical aging, cloud condensation nuclei, rain and precipitation statistics, and aerosol indirect effects are emphasized, but their detailed descriptions are the subject of separate publications. The main purpose of this paper is to familiarize the broader scientific community with the ORACLES project and the dataset it produced.

This paper makes a case for why Hawaii is the rainbow capital of the world. It begins by briefly touching on the cultural and historical significance of rainbows in Hawaii. Next it provides an overview of the science behind the rainbow phenomenon, which provides context for exploring the meteorology that helps explain the prevalence of Hawaiian rainbows. Last, the paper discusses the art and science of chasing rainbows.

17 pags., 4 figs., 2 tabs., Sea ice plays a pivotal role in Earth's climate and its past reconstruction is crucial to investigate the connections and feedbacks with the other components of the climate system. Among the available archives that store information of past sea ice are marine and ice cores. Recent studies on the IP biomarker extracted from marine sediments has shown great skill to infer past changes of Arctic sea ice. In ice matrixes, sodium, bromine and iodine have shown potential to store the fingerprint of sea ice presence. The development of an unambiguous sea ice proxy from ice cores, however, has proven to be a challenging task especially in the Arctic realm. In this work we analyze the sodium, bromine and iodine records in the RECAP ice core, coastal eastern Greenland, to investigate the sea ice variability in the northern North Atlantic Ocean through the last 11,000 years of the current interglacial, i.e. the Holocene. We compare the RECAP records with marine sea ice proxy records available from the northern North Atlantic. We suggest that RECAP sodium concentrations can be associated with variability of sea ice extent, while the bromine-to-sodium ratios and iodine are associated respectively with seasonal sea ice and bioproductivity from open ocean and fresh sea ice surfaces. According to our interpretation, we find that sea ice was at its lowest extent and seasonal in nature during the early Holocene in all regions of the North Atlantic. Increasing sea ice signals are seen from ca. 8–9 ka b2k, in line with long-term Holocene cooling. The increasing sea ice trend appears uninterrupted in the Fram Strait and North Iceland while reaching a maximum ca. 5 ka b2k in the East Greenland region. Sea ice modifications during the last 5000 years display great variability in East Greenland with intermediate conditions between the early and mid Holocene, possibly associated with local fjord dynamics. The last sea ice maximum was reached across all regions 1000 years b2k., The RECAP ice coring effort was financed by the Danish Research Council through a Sapere Aude grant, the NSF through the Division of Polar Programs, the Alfred Wegener Institute, and the European Research Council under the European Community's Seventh Framework Programme (FP7/2007e2013)/ERC grant agreement The RECAP ice coring effort was financed by the Danish Research Council through a Sapere Aude grant, the NSF through the Division of Polar Programs, the Alfred Wegener Institute, and the European Research Council under the European Community's Seventh Framework Programme (FP7/2007e2013)/ERC grant agreement 610055 through the Ice2Ice project. Additional funding support for the paper has been provided by the Centre for Climate Dynamics at the Bjerknes Centre. through the Ice2Ice project. Additional funding support for the paper has been provided by the Centre for Climate Dynamics at the Bjerknes Centre.

The primary objective of the paper was the determination of the atmospheric circulation favouring the occurrence of strong and very strong stress of the human organism due to heat stress in Poland. The paper was prepared based on data obtained from the Institute of Meteorology and Water Management – National Research Institute and the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR). The criterion of extreme stress of the human organism adopted in the paper covered conditions in which the Universal Thermal Climate Index (UTCI) value was higher than 32 °C. The research showed a statistically significant increase in half of the analysed stations and an increasing tendency or no changes in the remaining stations. Moreover, after 1990, conditions particularly strenuous for the organism were recorded (UTCI > 40 °C) over a major part of the territory of Poland. The occurrence of days with strong and very strong heat stress in Poland was related to the presence of high-pressure systems blocking zonal circulation. The research permitted the designation of three types in which the pressure field showed common features, but differed in the location of anticyclonic systems.

Large scale anomalous circulation is one of the main causes of extreme climate in East Asia. Data mining and statistical analysis of climate reanalysis data are important research methods to understand the characteristics of atmospheric circulation and the occurrence of extreme climate. In this paper, we first use SOM to distinguish the anomalous general circulation models in East Asia from 1979 to 2020. According to the results, we establish the response relationship and monitoring system between various models and climatic factors, and analyze the trend and dynamic mechanism of temperature anomalies in China. Secondly, the atmospheric circulation anomaly model is related to the extreme temperature and precipitation events in East Asia, and studies the climate anomaly characteristics under the complex effects of atmospheric circulation anomaly and monsoon system. The following analysis follows all the basic characteristics of land logistics of marine logistics, but due to the high risk of transportation, transportation time is long, so freight management is different. The existing marine logistics transportation management system has many deficiencies in information exchange, cargo management and transportation. The proposal and application of blockchain technology can effectively supplement it. The consensus mechanism is the core of blockchain technology. The decentralized credit structure and the nonoperability of the consensus mechanism of blockchain can effectively overcome the risk of freedom of contract, optimize the maritime logistics and transportation management model, improve the rationality of the sense of responsibility, ensure the transaction efficiency and transportation safety, and comply with the flexible trend of modern maritime trade. This paper introduces the monitoring system and applies it to the management of climate abnormal circulation and marine logistics transportation, which can effectively improve the management of climate abnormal circulation and marine logistics transportation.

Polar Regions are characterized by extreme weather and climate. The polar meteorology plays a significant role in global climate system. Further, the global warming has generated renewed interest in the study of Polar Regions as the changes in polar and sea-ice extent have widespread implication on atmospheric circulation. India initiated first multi-disciplinary scientific expedition to Antarctica in 1981. The meteorological data are being collected from the very first Indian expedition to Antarctica. The present paper reviews the progress of India's scientific research in polar meteorology. The analysis of 25 years meteorological data collected at Maitri station for the period 1991–2015 is presented in the paper. The observed trend in the temperature data of 19 Antarctic stations obtained from READER project for the period 1991–2015 has also been examined. The 25 years long term temperature record shows cooling over Maitri station. The Maitri station showed cooling of 0.054 °C per year between 1991 and 2015, with similar pronounced seasonal trends. The nearby Russian station Novolazarevskaya also showed a cooling trend of 0.032 °C per year. The trend analysis of other meteorological parameters for the period 1991–2015 is also presented. The Antarctic Peninsula and almost all of West Antarctica showed warming during 1991–2015. The majority of stations in East Antarctica close to the coast show cooling or no significant trend. The analysis also found slight decreasing trend in the pressure over the 1991–2015 time period which is not statistically significant. The wind speed, however, does show a significant declining trend of 0.14 knots/year over the same period.

This paper introduces three quantitative indicators to conduct research for characterizing Northeast China cold vortex persistence activity: cold vortex persistence, generalized “cold vortex,” and cold vortex precipitation. As discussed in the first part of paper, a hindcast is performed by multiple regressions using Northeast China precipitation from 2012 to 2014 combination with the previous winter 144 air-sea system factors. The results show that the mentioned three cold vortex index series can reflect the spatial and temporal distributions of observational precipitation in 2012–2014 and obtain results. The cold vortex factors are then added to the Forecast System on Dynamical and Analogy Skills (FODAS) to carry out dynamic statistical hindcast of precipitation in Northeast China from 2003 to 2012. Based on the characteristics and significance of each index, precipitation hindcast is carried out for Northeast China in May, June, July, August, May–June, and July–August. It turns out that the Northeast Cold Vortex Index Series, as defined in this paper, can make positive corrections to the FODAS forecast system, and most of the index correction results are higher than the system’s own correction value. This study provides quantitative index products and supplies a solid technical foundation and support for monthly precipitation forecast in Northeast China.

In air quality forecasting systems, failure to consider the considerably large anthropogenic heat emissions generated daily in the Beijing megacity by intensive human activities is one of the major causes of model failure. In this paper, we employ the nested air quality prediction model system coupled with the weather research and forecasting model and an urban canopy model to integrate anthropogenic heat emissions over Beijing into the modeling system and exhaustively evaluate their potential effects on air quality forecast by analyzing the wind field, boundary layer structure (height and atmospheric circulation), and surface and vertical distribution of pollutants. Consequently, the effects of anthropogenic heat on the boundary layer structure, greatly pronounced in urban areas, exhibited substantial variability at different levels depending on the time. The effects were evident during both daytime and night, but played a more prominent singular role in the night in the absence of solar short-wave radiation. Basically, anthropogenic heat acts not only by directly inducing the ascent of a warm air mass from the low parts of the atmosphere over urban areas to the top of the boundary layer, but also by indirectly driving wind convergence and inducing the descent of a cooled air mass from a high altitude to the boundary layer through a complex atmospheric circulation process. Incorporating anthropogenic heat emissions into the modeling system was effective in improving predictions by reducing the normalized mean bias by 20%–30% (for wind speed) and root mean square error by 361–558 m (for boundary layer height) and by 10–23 µg m–3 (for surface PM10), with a significant reduction in the underestimation of ozone concentration by approximately 20 ppb at urban sites. This paper is expected to provide new insights into the improvement of model accuracy for air quality forecasts over megacities.

In this paper, climatic analysis of non-precipitation periods (NPP) in Lithuania was performed, assessing their recurrence and trends from 1991 to 2020 using two criteria – when precipitation was

Variabilities and changes due to natural and anthropogenic causes in the water cycle always presented a challenge for water management planning. Practitioners traditionally coped with variabilities in the hydrological processes by assuming stationarity in the probability distributions and attempted to address non-stationarity by revising this probabilistic properties via continued hydro-climatological observations. Recently, this practice was questioned and more reliance on Global Circulation Models was put forward as an alternative for water management plannig. This paper takes a brief assessment of the state of Global Circulation Models (GCM) and their applications by presenting case studies over Global, European and African domains accompanied by literature examples. Our paper demonstrates core deficiencies in GCM based water resources assessments and articulates the need for improved Earth system monitoring that is essential not only for water managers, but to aid the improvements of GCMs in the future.

The article describes the most important results from selected papers concerning the climate of Poznan. The structure of the paper is twofold. The first part presents articles and topics which are based on the data recoded in the Poznan-Ławica airport meteorological station. The second part presents papers where, in addition to data from the airport station, data from the network measurements of municipal stations are also included. This section contains issues concerning the urban heat island, the surface urban heat island, relations between the urban heat island and atmospheric circulation, the characteristics of air temperature and surface temperature according to the Corine Land Cover classification types, as well as information on the creation of a statistical model of air temperature in town according to satellite and in situ data derived from municipal station.

Newtonian relaxation allowing RCM to follow GCM is a widely used technique for climate downscaling and regional weather forecasting. A thorough assessment on effects of the relaxation procedure in an idealized framework is presented in this paper for both synoptic variability and long-term mean climate. LMDz is a global atmospheric general circulation model that can be configured as a regional model if the outside domain of the focused region is applied with a relaxation. It thus plays the role of both GCM and RCM in this paper. Same physical parameterization and identical dynamical configuration are kept to ensure a rigorous comparison between the two models. The experimental set-up that can be referred to as “Master (GCM) versus Slave (RCM)” considers the GCM as the reference to assess the behavior of RCM. A further simulation with RCM in a higher resolution configuration allows isolating the effect of relaxation procedure from that of mesh refinement. In terms of mean climate in GCM and RCM, there are noticeable differences, not only in the border areas, but also within the domain. In terms of synoptic variability, there is a general spatial resemblance and temporal concomitance between the two models. But there is a dependence on variables, seasons, spatiotemporal scales and spatial mode of atmospheric circulation. Winter/Summer has the most/least resemblance between the RCM and the GCM. A better similarity is noticed when atmospheric circulations manifested on large scales. No-correlation cases can be remarked when the dominant circulation of the region is at a small scale.

Potential vorticity (PV) streamers and cutoffs are indicators of Rossby wave breaking (RWB) near the extratropical tropopause. The Rossby wave breaking forms an elongated high-PV stratospheric air tongue that extends to the equator and a tropospheric low PV air tongue that extends to the pole. There are two types of RWB: equatorward and poleward ones. Frequently, PV tongues stretch into narrow filaments, so-called PV streamers that split into PV cutoff vortices. Here the terms stratospheric PV streamer and cutoff refer to stratospheric features of isentropic surfaces (PV > 2 PVU; where 1 PVU = 10−6 K_kg−1 m2_s−1). In this paper, we study a configuration of the potential vortex field using model data. The main areas of RWB in winter and summer are shown. Atmospheric blocking events represent some of the most high-impact weather patterns in the mid-latitudes, but they have often been the cause of unsuccessful future climate projections. In this paper, we have examined the seasonal frequency of global blocking events in relation to a change in the mean EOF index based on some modeling results obtained by using a climate system model, PlaSim-ICMMG-1.0.

The paper presents the effect of North Atlantic Oscillation of macroscale atmospheric circulation (NAO) on the hydrological conditions of Lake Morskie Oko located at an altitude of 1392.8 m a.s.l. in the highest range of the Carpathians. The paper applied detailed hydrometric information from the years 1971-2010 concerning water level fluctuations, water temperature, terms of the commencement and end of ice phenomena and ice cover, as well as meteorological data concerning air temperature and atmospheric precipitation, and monthly and seasonal NAO indices. The performed analysis suggests that the majority of analysed hydrological characteristics of Lake Morskie Oko was not prone to variability of NAO intensity in its various phases. The situation results from the local conditions, particularly responsible for the course of processes and phenomena in Lake Morskie Oko, simultaneously obscuring the effect of macroscale factors.

Based on the new "etheric" concept that "every planet, object or particle carries an etheric layer that moves with itself, and this etheric layer forms a local absolute reference frame" and the modified Newton's first law that "an object will remain stationary in the etheric absolute reference frame or move at a constant speed along the shortest optical path on a plane with equal etheric density without external force", this paper explores the causes of atmospheric circulation and ocean current, and obtains that the overall motion direction of atm ospheric circulation and ocean current is opposite to the rotation direction of the earth, and the overall motion speed increases with the increase of distance from the center of the earth. It is also pointed out that the atmospheric circulation and ocean current are caused by the influence of the earth's etheric wind on the atmosphere and sea water. Atmospheric circulation and ocean currents are driven by the earth's rotation. According to the characteristics of the global circulation around the earth, this paper puts forward the conjecture that the virus may spread along the latitude line through the atmospheric circulation.

In this paper, we consider the use of structure learning methods for probabilistic graphical models to identify statistical dependencies in high-dimensional physical processes. Such processes are often synthetically characterized using PDEs (partial differential equations) and are observed in a variety of natural phenomena, including geoscience data capturing atmospheric and hydrological phenomena. Classical structure learning approaches such as the PC algorithm and variants are challenging to apply due to their high computational and sample requirements. Modern approaches, often based on sparse regression and variants, do come with finite sample guarantees, but are usually highly sensitive to the choice of hyper-parameters, e.g., parameter $\lambda$ for sparsity inducing constraint or regularization. In this paper, we present ACLIME-ADMM, an efficient two-step algorithm for adaptive structure learning, which estimates an edge specific parameter $\lambda_{ij}$ in the first step, and uses these parameters to learn the structure in the second step. Both steps of our algorithm use (inexact) ADMM to solve suitable linear programs, and all iterations can be done in closed form in an efficient block parallel manner. We compare ACLIME-ADMM with baselines on both synthetic data simulated by partial differential equations (PDEs) that model advection-diffusion processes, and real data (50 years) of daily global geopotential heights to study information flow in the atmosphere. ACLIME-ADMM is shown to be efficient, stable, and competitive, usually better than the baselines especially on difficult problems. On real data, ACLIME-ADMM recovers the underlying structure of global atmospheric circulation, including switches in wind directions at the equator and tropics entirely from the data., Comment: 21 pages, 8 figures, International Conference on Data Mining 2017

The paper demonstrates that quasi-biennial oscillation (QBO)-like oscillations can be simulated in an ensemble of dry GCM dynamical cores that are driven by a simple Held–Suarez temperature relaxation and low-level Rayleigh friction. The tropical stratospheric circulations of four dynamical cores, which are options in NCAR’s Community Atmosphere Model, version 5 (CAM5), are intercompared. These are the semi-Lagrangian (SLD) and Eulerian (EUL) spectral transform, finite-volume (FV), and spectral element (SE) dynamical cores. The paper investigates how the model design choices impact the wave generation, propagation, and dissipation mechanisms in the equatorial region. SLD, EUL, and SE develop spontaneous QBO-like oscillations in the upper equatorial stratosphere, whereas FV does not sustain the oscillation. Transformed Eulerian-mean (TEM) analyses reveal that resolved waves are the dominant drivers of the QBOs. However, the Eliassen–Palm flux divergence is strongly counteracted by the TEM momentum budget residual, which represents the forcing by diffusion and thermal damping. Interestingly, a reversed Brewer–Dobson circulation accelerates the downward propagation of the SLD’s QBO, whereas the EUL’s and SE’s QBOs are slowed by a mean ascent. Waves are abundant in the SLD’s, EUL’s, and SE’s tropical atmosphere despite the absence of moist convection as a typical wave trigger. Dynamic instabilities are suggested as a wave-triggering mechanism in the troposphere and wave-dissipation process in the stratosphere. In particular, there are indications that the increased occurrences of strongly negative instability indicators in SLD, EUL, and SE are related to more vigorous wave activities and higher magnitudes of the resolved wave forcing in comparison to FV.

The weather natural disaster prevention for quantitative daily rainfall forecasting derived from the SACZ-ULCV weather pattern is proposed in this paper by using intertwined statistical downscaling (SD) and soft computing (SC) approaches. The fuzzy statistical downscaling (FSD) is first introduced and, then, employed for dealing with the SACZ-ULCV atmospheric circulation-type specific weather pattern for supporting daily precipitation (rainfall) forecasting. This paper also addresses the performance comparison of the FSD and the neural statistical downscaling (NSD) approaches when taking into account 12 major urban centers all over the state of Sao Paulo, Brazil, for the summer period. The SACZ-ULCV summer pattern is identified in meteorological satellite images when the cloudiness of the Brazilian Northeast upper level cyclonic vortices (ULCV) meets the South Atlantic convergence zone (SACZ). Increasing the convection and the cloudiness over the Southeast region of Brazil, the SACZ-ULCV causes severe rainfalls and thunderstorms with impact on the population. Finding a manner to anticipate these extreme rainfall events is of vital importance for minimizing or avoiding disasters, and saving lives. Daily rainfall forecasting had their performance improved either by using the proposed FSD or NSD in comparison to the Multilinear Regression ETA model. Results demonstrate the FSD and the NSD become feasible alternatives for achieving a correspondence from meteorological and thermo-dynamical variables to the daily rainfall variable.

This paper presents an analysis of the homogenised mean maximum (T max) and minimum (T min) temperatures. The data used in the analysis were collected at eight stations in the Autonomous Province of Vojvodina (Serbia) during the 1949–2008 period. The trends obtained from the slopes of the regression lines using the least square method show 0.9 °C/60 years for T max and 1.1 °C/60 years for T min; the non-parametric Mann–Kendall test was used to determine the statistically significant increasing trends of these two extreme parameters. In this paper, we analyse the influence of the Vangengeim–Girs classification of atmospheric circulation on the T max and T min trends in the Autonomous Province of Vojvodina (Serbia) using linear and quadratic models based on the least square method. Linear stepwise regression and the forward method reveal the highest dependence of T max and T min when the W or E circulation types are included in the model. Non-linear models show a greater contribution of T max and T min at W, E and C circulation types, respectively. The correction of the variance contribution of quadratic models ranges from approximately 16 to 44 % for T max and 32 to 38 % for T min.

This paper uses a method of atmospheric flow analogues to reconstruct an ensemble of atmospheric variables (namely sea-level pressure, surface temperature and wind speed) between 1781 and 1785. The properties of this ensemble are investigated and tested against observations of temperature. The goal of the paper is to assess whether the atmospheric circulation during the Laki volcanic eruption (in 1783) and the subsequent winter were similar to the conditions that prevailed in the winter 2009/2010 and during spring 2010. We find that the three months following the Laki eruption in June 1783 barely have analogues in 2010. The cold winter of 1783/1784 yields circulation analogues in 2009/2010. Our analysis suggests that it is unlikely that the Laki eruption was responsible for the cold winter of 1783/1784, of the relatively short memory of the atmospheric circulation.

Abrupt drought–flood change events caused by atmospheric circulation anomalies have occurred frequently and widely in recent years, which has caused great losses and casualties in China. In this paper, we focus on investigating whether there will be a rainfall occurrence with higher intensity after a drought period in the Huang–Huai–Hai River basin. Combined with the Chinese climate divisions and the basin's DEM (digital elevation model), the basin is divided into seven sub-regions by means of cluster analysis of the basin meteorological stations using the self-organizing map (SOM) neural network method. Based on the daily precipitation data of 171 stations for the years 1961–2011, the changes of drought times with different magnitudes are analyzed, and the number of consecutive days without precipitation is used to identify the drought magnitudes. The first precipitation intensity after a drought period is analyzed with the Pearson-III frequency curve, then the relationship between rainfall intensity and different drought magnitudes is observed, as are the changes of drought times for different years. The results of the study indicated that the occurrence times of different drought levels show an overall increasing trend; there is no clear interdecadal change shown, but the spatial difference is significant. (2) As the drought level increases, the probability of extraordinary rainstorm becomes lower, and the frequency of occurrence of spatial changes in different precipitation intensities vary. In the areas I and II, as the drought level increases, the occurrence frequency of different precipitation intensities first shows a decreasing trend, which becomes an increasing trend when extraordinary drought occurs. In the area III, IV and V, the probability of the different precipitation intensities shows an overall decreasing trend. The areas VI and VII are located at the mountains with high altitudes where the variation of different precipitation intensities with the increase in drought level is relatively complex. (3) As the drought times increase, areas I, II and V, which are located on the coastal and in the valley or basin, are vulnerable to extreme precipitation processes; areas III, IV, VI and VII are located in the inland area, where heavier precipitation is not likely to occur. (4) The local rainfall affected by multiple factors is closely related with drought occurrence. The characteristics between the first rainfall intensity after a drought period and different drought magnitudes (or drought occurrence times) are preliminarily examined in this paper, but its formation mechanism still requires further research.

This paper focuses on the development of simplified mathematical models of the cryosphere which may be useful in further understanding possible global climate change impacts and in further assessing future impacts captured by global circulation models (GCMs). The mathematical models developed by leveraging the dominating effects of freezing and thawing within the cryosphere to simplify the relevant heat transport equations are tractable to direct solution or numerical modeling. In this paper, the heat forcing function is assumed to be a linear transformation of temperature (assumed to be represented by proxy realizations). The output from the governing mathematical model is total ice volume of the cryosphere. The basic mathematical model provides information as a systems modeling approach that includes sufficient detail to explain ice volume given the estimation of the heat forcing function. A comparison between modeling results in the estimation of ice volume versus ice volume estimates developed...

Large-scale planetary waves are diagnosed from an analysis of profiles retrieved from the Thermal Emission Spectrometer aboard the Mars Global Surveyor spacecraft during its scientific mapping phase. The analysis is conducted by assimilating thermal profiles and total dust opacity retrievals into a Mars global circulation model. Transient waves are largest throughout the northern hemisphere autumn, winter and spring period and almost absent during the summer. The southern hemisphere exhibits generally weaker transient wave behaviour. A striking feature of the low-altitude transient waves in the analysis is that they show a broad subsidiary minimum in amplitude centred on the winter solstice, a period when the thermal contrast between the summer hemisphere and the winter pole is strongest and baroclinic wave activity might be expected to be strong. This behaviour, here called the ‘solsticial pause,’ is present in every year of the analysis. This strong pause is under-represented in many independent model experiments, which tend to produce relatively uniform baroclinic wave activity throughout the winter. This paper documents and diagnoses the transient wave solsticial pause found in the analysis; a companion paper investigates the origin of the phenomenon in a series of model experiments.

A major question for climate studies is to quantify the role of turbulent eddy fluxes in maintaining the observed ocean‐atmosphere state. It has been argued that eddy fluxes keep the midlatitude atmosphere in a state that is marginally critical to baroclinic instability, which provides a powerful constraint on the response of the atmosphere to changes in external forcing. No comparable criterion appears to exist for the ocean. This is particularly surprising for the Southern Ocean, a region whose dynamics are very similar to the midlatitude atmosphere, but observations and numerical models suggest that the currents are supercritical. This paper aims to resolve this apparent contradiction using a combination of theoretical considerations and eddy-resolving numerical simulations. It is shown that both marginally critical and supercritical mean states can be obtained in an idealized diabatically forced (and thus atmosphere-like) Boussinesq system, if the thermal expansion coefficient is varied from large atmosphere-like values to small oceanlike values. The argument is made that the difference in the thermal expansion coefficient dominantly controls the difference in the deformation scale between the two fluids and ultimately renders eddies ineffective in maintaining a marginally critical state in the limit of small thermal expansion coefficients. The responseofthe atmosphere andoceancirculations to changes in the external forcing is a crucial question for studies of climate and climate change. A major difficulty in answering this question is that the response of the mean circulation is strongly affected by changes in the macroturbulence in the two fluids. Heuristic arguments havebeenputforwardtopredicttheturbulentadjustment to changes in the external forcing, both for the atmosphere and the ocean. Surprisingly the arguments put forward for the two fluids are remarkably different, despite the dynamical similarities between the two fluids. The goal of this paper is to revisit the heuristic arguments developed for the atmosphere and explore in which pa

From the 344 state climate divisions in the conterminous United States, nine distinct regions of warm-season drought variability are identified using principal component analysis. The drought metric used is the Palmer hydrological drought index for the period 1895–2008. The focus of this paper is multidecadal drought variability in the Southeast (SEUS) and eastern Gulf South (EGS) regions of the United States, areas in which the low-frequency forcing mechanisms of warm-season drought are still poorly understood. Low-frequency drought variability in the SEUS and EGS is associated with smoothed indexed time series of major ocean–atmosphere circulation features, including two indices of spatiotemporal variability in the North Atlantic subtropical anticyclone (Bermuda high). Long-term warm-season drought conditions are significantly out of phase between the two regions. Multidecadal regimes of above- and below-average moisture in the SEUS and EGS are closely associated with slow variability in sea surface temperatures in the North Atlantic Ocean and with the summer mean position and mean strength of the Bermuda high. Multivariate linear regression indicates that 82%–92% of the low-frequency variability in warm-season moisture is explained by two of the three leading principal components of low-frequency variability in the climate indices. The findings are important for water resource managers and water-intensive industries in the SEUS and EGS. The associations identified in the paper are valuable for enhanced drought preparedness and forecasting in the study area and potentially for global models of coupled ocean–atmosphere variability.

The paper presents parameters of the diurnal rainfall cycle for rainfall equal or exceeding 2.5 mm h −1 during both the summer and winter halves of the year. It then discusses the impact of various circulation systems on the distribution of the frequency of rainfall occurrence during a 24-h day in the summer half of the year. The results of these investigations contribute to a greater understanding of the atmospheric processes associated with heavy precipitation and may be used to improve the forecasting of the temporal distribution of short-duration convective precipitation. A pattern with a single heavy rainfall maximum was identified. A variety of diurnal patterns of amplitude and time of maximum rainfall emerged depending on the atmospheric circulation determining the thermal and humidity properties of air masses. The paper was based on hourly rainfall records in Krakow and on a daily catalogue of atmospheric circulation types in southern Poland spanning the period 1886–2007.

43 páginas, 1 tabla, 9 figuras, This paper analyses the influence of different atmospheric circulation indices on the multi-scalar drought variability across Europe by using the Standardized Precipitation Evapotranspiration Index (SPEI). The monthly circulation indices used in this study include the North Atlantic oscillation (NAO), the East Atlantic (EA), the Scandinavian (SCAN) and the East Atlantic–Western Russia (EA–WR) patterns, as well as the recently published Westerly Index (WI), defined as the persistence of westerly winds over the eastern north Atlantic region. The results indicate that European drought variability is better explained by the station-based NAO index and the WI than by any other combination of circulation indices. In northern and central Europe the variability of drought severity for different seasons and time-scales is strongly associated with the WI. On the contrary, the influence of the NAO on southern Europe droughts is stronger than that exerted by the WI. The correlation patterns of the NAO and WI with the SPEI show a spatial complementarity in shaping drought variability across Europe. Lagged correlations of the NAO and WI with the SPEI also indicate enough skill of both indices to anticipate drought severity several months in advance. As long as instrumental series of the NAO and WI are available, their combined use would allow inferring European drought variability for the last two centuries and improve the calibration and interpretation of paleoclimatic proxies associated with drought., The authors wish to acknowledge Ricardo Trigo and one anonymous reviewer for their detailed and helpful comments to the original manuscript. The data for this paper are available at Spanish National Research Council repository (http://​sac.​csic.​es/​spei/​database.​html), at Climate Research Unit (http://​www.​cru.​uea.​ac.​uk/​cru/​data/​nao/​) and the Climate Prediction centre of the NOAA (http://​www.​cpc.​ncep.​noaa.​gov/​data/​teledoc/​telecontents.​shtml). This work was supported by the research project CGL2014-52135-C3-1-R and Red de variabilidad y cambio climático RECLIM (CGL2014-517221-REDT) financed by the Spanish Commission of Science and Technology and FEDER, Ephyslab (UVIGO-CSIC Associated Unit) and “LIFE12 ENV/ES/000536-Demonstration and validation of innovative methodology for regional climate change adaptation in the Mediterranean area (LIFE MEDACC)” financed by the LIFE programme. C. A-M received a postdoctoral fellowship #JCI-2011-10263. Iberdrola Renovable provided partial support from contracts.

Rainfall is a fundamental process within the Earth's hydrological cycle because it represents a principal forcing term in surface water budgets, while its energetics corollary, latent heating, is the principal source of atmospheric diabatic heating well into the middle latitudes. Latent heat production itself is a consequence of phase changes between the vapor, liquid, and frozen states of water. The properties of the vertical distribution of latent heat release modulate large-scale meridional and zonal circulations within the Tropics, as well as modify the energetic efficiencies of midlatitude weather systems. This paper highlights the retrieval of latent heating from satellite measurements generated by the Tropical Rainfall Measuring Mission (TRMM) satellite observatory, which was launched in November 1997 as a joint American–Japanese space endeavor. Since then, TRMM measurements have been providing credible four-dimensional accounts of rainfall over the global Tropics and subtropics, information that can be used to estimate the space–time structure of latent heating across the Earth's low latitudes. A set of algorithm methodologies for estimating latent heating based on precipitation-rate profile retrievals obtained from TRMM measurements has been under continuous development since the advent of the mission s research program. These algorithms are briefly described, followed by a discussion of the latent heating products that they generate. The paper then provides an overview of how TRMM-derived latent heating information is currently being used in conjunction with global weather and climate models, concluding with remarks intended to stimulate further research on latent heating retrieval from satellites.

Barry Saltzman was a giant in the fields of meteorology and climate science. A leading figure in the study of weather and climate for over 40 yr, he has frequently been referred to as the “father of modern climate theory.” Ahead of his time in many ways, Saltzman made significant contributions to our understanding of the general circulation and spectral energetics budget of the atmosphere, as well as climate change across a wide spectrum of time scales. In his endeavor to develop a unified theory of how the climate system works, he played a role in the development of energy balance models, statistical dynamical models, and paleoclimate dynamical models. He was a pioneer in developing meteorologically motivated dynamical systems, including the progenitor of Lorenz’s famous chaos model. In applying his own dynamical-systems approach to long-term climate change, he recognized the potential for using atmospheric general circulation models in a complimentary way. In 1998, he was awarded the Carl-Gustaf Rossby medal, the highest honor of the American Meteorological Society “for his life-long contributions to the study of the global circulation and the evolution of the earth’s climate.” In this paper, the authors summarize and place into perspective some of the most significant contributions that Barry Saltzman made during his long and distinguished career. This short review also serves as an introduction to the papers in this special issue of the Journal of Climate dedicated to Barry’s memory.

The variability of occurrence of snow cover and the impact of atmospheric circulation on the snow cover occurrence in the period 1966/1967–2019/2020 in Poznań (Poland) have been examined. The implementation of the primary study objective covers the comprehensive analysis of the winter snow and thermal conditions using various indicators. This paper is based on daily data from the years 1966–2020 concerning the winter period. Winters in Poznań are highly variable and differentiated, considering the duration of particular seasons, number of days with snow cover, mean snow cover thickness, winter snowiness coefficient, or winter severity index. Negative trends concerning days with snow cover total snow cover depth winter snowiness coefficient and winter severity index in Poznań prove statistically significant. A higher probability of occurrence of snow cover was determined during cyclonic than anticyclonic circulation. The westerly and northerly types especially favoured the occurrence of days with snow cover. The increase of snow cover was associated with the northerly inflow mainly. Westerly types of circulation caused the decrease of snow cover predominantly.

In this paper an application of clustering algorithms for statistical downscaling in short-range weather forecasts is presented. The advantages of this technique compared with standard nearest-neighbors analog methods are described both in terms of computational efficiency and forecast skill. Some validation results of daily precipitation and maximum wind speed operative downscaling (lead time 1‐5 days) on a network of 100 stations in the Iberian Peninsula are reported for the period 1998‐99. These results indicate that the weighting clustering method introduced in this paper clearly outperforms standard analog techniques for infrequent, or extreme, events (precipitation . 20 mm; wind . 80 km h21). Outputs of an operative circulation model on different local-area or large-scale grids are considered to characterize the atmospheric circulation patterns, and the skill of both alternatives is compared.

Several papers have described a significant trend toward the positive phase of the Southern Hemisphere annular mode (SAM) in recent decades. The SAM is the dominant mode of atmospheric variability in the Southern Hemisphere (SH) so such a change implies a major shift in the broadscale climate of this hemisphere. However, the majority of these studies have used NCEP‐NCAR reanalysis (NNR) data, which are known to have spurious negative trends in SH high-latitude pressure. Thus, given that the SAM describes the relative atmospheric anomalies at mid- and high southern latitudes, these errors in the NNR data have the potential to invalidate the published findings on changes in the SAM. Therefore, it is important that a ‘‘true’’ benchmark of trends in the SAM is available against which future climate scenarios as revealed through climate models can be examined. In this paper this issue is addressed by employing an empirical definition of the SAM so that station data can be utilized to evaluate true temporal changes: six stations are used to calculate a proxy zonal mean sea level pressure (MSLP) at both 408 and 658S during 1958‐2000. The observed increase in the difference in zonal MSLP between 408 (increasing) and 658S (decreasing) is shown to be statistically significant, with the trend being most pronounced since the mid-1970s. However, it is demonstrated that calculated trends in the MSLP difference between 408 and 658S and the SAM itself are exaggerated by a factor of 3 and 2, respectively, in the NNR. The SH high-latitude errors in the early part of this reanalysis are greatest in winter as are subsequent improvements. As a result, the NNR shows the greatest seasonal trend in the SAM to be in the austral winter, in marked contrast to observational data, which reveal the largest real increase to be in summer. Equivalent data from two ECMWF reanalyses, including part of the new ERA-40 reanalysis, are also examined. It is demonstrated that ERA-40 provides an improved representation of SH high-latitude atmospheric circulation variability that can be used with high confidence at least as far back as 1973—and is therefore ideal for examining the recent trend in the SAM—and with more confidence than the NNR right back to 1958.

This paper examines the mean annual cycle of rainfall and general circulation features over West Africa and central Africa for 1958–97. Rainfall is examined using a 1400-station archive compiled by the first author. Other circulation features are examined using the NCEP–NCAR reanalysis dataset. Important features of the reanalysis zonal wind field are shown to compare well with the seasonal evolution described by the radiosonde observations. In addition to the well-known African easterly jet (AEJ) of the Northern Hemisphere, the seasonal evolution of its Southern Hemisphere counterpart is also described. Thermal wind calculations show that although the southern jet is weaker, its existence is also due to a local reversal of the surface temperature gradient. In the upper troposphere, a strong semiannual cycle is shown in the 200-mb easterlies and a feature like the tropical easterly jet (TEJ) is evident south of the equator in January and February. The paper describes the movement of the rainbelt ...

The paper assesses the present-day state and long-term forecast of intrasecular oscillations of water level in large Eurasian lakes. The analysis of the North Atlantic climate change influence on the catchments hydrological regime of the Caspian Sea and Ladoga and Onega lakes was made on the basis of the reanalysis data and numerical simulation results. The connection between some indexes of atmospheric and oceanic circulation describing climatic variability of the North Atlantic and Europe and hydrological regime of Volga and Neva rivers basins was estimated. The paper investigates the causal effects between climatic characteristics and catchments hydrological regime and the lakes water level. Several years’ time lag of hydrological regime (rivers runoff, the Caspian Sea level) response to changes in atmospheric circulation was shown. The dynamics of precipitation in the Caspian catchment correspond to changes in circulation indexes. Moisture transport from the Atlantic to the European part of Russia in the 21st century was estimated using the combined scenario of climate changes based on the hybrid of greenhouse and cyclic effects. The simulation results reveal possible decrease of moisture transport and atmospheric precipitation over the European part of Russia for the next 15-20 years resulting (with several years’ time lag) in the ongoing water level decrease in the Caspian Sea and Lake Ladoga. Moisture transport increase is expected from around 2035 to 2070, which will presumably lead to precipitation increase and water level rise in these water bodies.

Tucson, Arizona, is an example of the many cities in the southwestern United States experiencing rapid growth and urban sprawl over the last several decades. The accompanying extensive modification of land use and land cover leads to many environmental impacts, including urban heat islands. The primary aim of this paper is to expand knowledge of the phenomenon for Tucson, by quantifying the amount of urban warming, and by mapping temperature patterns over the city and examining related aspects of the local-scale atmospheric circulation. The secondary aim is to document how an applied empirical research project was integrated into an introductory undergraduate climatology class via active learning. The paper begins and concludes with general and practical comments on combining the research and educational aspects of the project. An analysis of 30-yr temporal trends in urban and nonurban minimum temperatures across the region shows the rate of urban warming to be about three-quarters of the general regional...

This paper intends to explore rice yield fluctuations to large-scale atmospheric circulation indices (LACIs) in Bangladesh. The annual dataset of climate-derived yield index (CDYI), estimated using principal component analysis of Aus rice yield data of 23 districts, and five LACIs for the period 1980–2017 were used for this purpose. The key outcomes of the study were as follows: three sub-regions of Bangladesh, northern, northwestern, and northeastern, showed different kinds of CDYI anomalies. The CDYI time series in north and northeastern regions exhibited a substantial 6-year fluctuation, whereas a 2.75- to 3-year fluctuation predominated the northwestern region. Rice yield showed the highest sensitivity of LACIs in the northern region. Indian Ocean dipole (IOD) and East Central Tropical Pacific SST (Nino 3.4) in July and IOD index in March provide the best yield prediction signals for northern, northwestern, and northeastern regions. Wavelet coherence study demonstrated significant in-phase and out-phases coherences between vital climatic variables (KCVs) and CDYI anomalies at various time-frequencies in three sub-regions. The random forest (RF) model revealed the IOD as the crucial contributing factor of rice yield fluctuations in the country. The multifactorial model with different LACIs and year as predictors can predict rice yield, with the mean relative error (MRE) in the range of 4.82 to 5.78% only. The generated knowledge can be used to early assess rice yield and recommend policy directives to ensure food security.

This paper focuses on the effect of sea ice melting under the effect of the mechanism of decreasing albedo of dry and wet ice and snow on the structure of atmospheric circulation. In particular, the Impact on storm tracks in the Pacific and Atlantic Oceans is analyzed. Extreme weather events are usually associated with atmospheric blocking conditions. Blocking is such meteorological conditions in which a large anticyclonic atmospheric vortex is observed over an area for several days. The Molteni-Tibaldi blocking criterion and the magnitude of the local anticyclonic wave activity (LAWA) are used to estimate the number of blockings. Extreme values of LAWA may indicate the presence of atmospheric blockings. As a result, there is a weakening and eastward shift of Atlantic storm trajectories. There is almost no influence on the Pacific storm tracks.

We present in Table 1 of this paper a series of free tropospheric radon profiles, obtained in the summer of 1994 on flights originating from Moffett Field, California (37.4°N, 122.0°W). These data were collected with the intent of acquiring a high-quality, statistically significant set of observations, in one season and at one location, suitable for use in the development and validation of three-dimensional global circulation and chemical transport models, as demonstrated in the companion paper [Stockwell, et al., this issue]. The profiles, which extend from the surface to 11.5 kilometers, were obtained on 11 flights flown in the period June 3 to August 16. A series of high-pressure whole-air samples (typically 11 or 12 per profile) were collected as the plane ascended to altitude, and analyzed immediately after each flight in a ground-based laboratory. A thorough discussion of sampling, analysis, calibration, and quality control procedures is provided.

The paper concentrates on the response of the atmospheric circulation non-tropical regions of the Northern Hemisphere to considerable sea surface temperature anomalies regularly occurring in the equatorial Pacific Ocean, related to the El Nino event. It has been established that during El Nino, zonal western circulation and meridional southern circulation tend to decay (being −2.6% and −5.4% respectively), while meridional northern circulation intensifies (+8.0%). The paper examines regional peculiarities of the non-tropical atmospheric response to the processes taking in the tropics. It is shown that atmospheric circulation reconstruction is most essential in the Siberian (10.4%) and Pacific (10.2%) sections and is minimal (4.3%) in the Atlantic region. These peculiarities of the regional atmospheric circulation reconstruction may be taken into account to predict short-term climatic variations in the Northern Hemisphere.

This paper discusses a simulation obtained with the Geophysical Fluid Dynamics Laboratory ‘‘SKYHI’’ troposphere‐stratosphere‐mesosphere general circulation model run at very high horizontal resolution (;60-km grid spacing) and without any parameterization of subgrid-scale gravity wave drag. The results are for a period around the austral winter solstice, and the emphasis is on the simulated Southern Hemisphere (SH) winter circulation. Comparisons are made with results obtained from lower horizontal resolution versions of the same model. The focus in this paper is on two particularly striking features of the high-resolution simulation: the extratropical surface winds and the winter polar middle atmospheric vortex. In the extratropical SH, the simulated surface westerlies and meridional surface pressure gradients in the high-resolution model are considerably stronger than observed and are stronger than those simulated at lower horizontal resolution. In the middle atmosphere, the high-resolution model produces a simulation of the zonal mean winter polar vortex that is considerably improved over that found with lower resolution models (although it is still significantly affected by the usual cold pole bias). Neither the improvement of the middle atmospheric polar vortex simulation nor the deterioration of the simulation of surface winds with increased model resolution shows a clear convergence, even at the ;60-km grid spacing employed here.

This is the second in a pair of papers in which the possible impacts of tropical deforestation are examined using a version of the NCAR CCM1. The emphasis in this paper is on the influence of tropical deforestation on the large-scale climate system. This influence is explored through the examination of the regional moisture budget and through an analysis of the Hadley and Walker circulations. Modification of the model surface parameters to simulate tropical deforestation produces significant modifications of both Hadley and Walker circulations, which result in changes distant from the, region of deforestation. A mechanism for propagation to middle and high latitudes of disturbances arising from tropical deforestation is proposed based on Rossby wave propagation mechanisms. These mechanisms, which have also been associated with the extratropical influences of ENSO events, provide a pathway for the dispersion of the tropical disturbances to high latitudes.

The Southern Carpathians (Romania) are one of the highest, steepest and most massive sectors of the Carpathian Mountains, with a strong imprint of the Pleistocene glaciation, which are widely affected by a broad spectrum of natural hazards (avalanches, rock wall weathering and landslides, flash floods). This paper focuses on the detection of recent changes in annual temperature and precipitation extremes over the 1961–2018 period based on observational data, discussing their spatial distribution and dependencies (on altitude, latitude and longitude). Trend analysis was applied on a set of 16 indices selected from the core indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI). The results show a significant warming trend, well reflected by the strong decline of frost days and icing days and a significant increase in absolute maximum temperatures, summer days and warm spell duration. Trends in precipitation extremes are more various, suggesting a climate drying trend, apparently stronger in the areas with a fast rise of maximum temperatures (evidence of coupled warming-drying climate change signal) and an increasing frequency of heavy precipitation events and resulted water amounts, in the areas affected by summer convection intensification. Except TNn with trends slopes revealing a winter nighttime amplification with elevation, high elevations (at above 2000 m) show only slight changes in temperature and precipitation extremes compared to the lower areas, explaining the general lack of elevation dependency of trends. Longitude explains 48 to 54% of trends in heavy precipitation indices. Changes in the large-scale atmospheric circulation (e.g. intensification of westerly circulation, increasing frequency of blocking conditions), cloudiness and summer convection have been identified among the main factors influencing trend behaviour and their spatial distribution.

[1] The aim of this paper is to define a method for determining reasonable estimates of rainfall modeled by global circulation models (GCMs) coupled with regional climate models (RCMs). The paper describes and uses two new procedures designed to give confidence in the interpretation of such rainfall estimates. The first of these procedures is the use of circulation patterns (CPs) to define quantile-quantile (Q-Q) transforms between observed and RCM-estimated rainfall (the CPs were derived from sea level pressure (SLP) fields obtained from reanalysis of historical daily weather in a previous study). The Q-Q transforms are derived using two downscaling techniques during a 20 year calibration period and were validated during a 10 year period of observations. The second novel procedure is the use of a double Q-Q transform to estimate the rainfall patterns and amounts from GCM-RCM predictions of SLP and rainfall fields during a future period. This procedure is essential because we find that the CP-dependent rainfall frequency distributions on each block are unexpectedly different from the corresponding historical distributions. The daily rainfall fields compared are recorded on a 25 km grid over the Rhine basin in Germany; the observed daily data are averaged over the grid blocks, and the RCM values have been estimated over the same grid. Annual extremes, recorded on each block during the validation period, of (1) maximum daily rainfall and (2) the lowest 5% of filtered rainfall were calculated to determine the ability of RCMs to capture rainfall characteristics which are important for hydrological applications. The conclusions are that (1) RCM outputs used here are good at capturing the patterns and rankings of CP-dependent rainfall; (2) CP-dependent downscaling, coupled with the double Q-Q transform, gives good estimates of the rainfall during the validation period; (3) because the RCMs offer future CP-dependent rainfall distributions that are different from the observed distributions, it is judged that these predictions, once modified by the double Q-Q transforms, are hydrologically reasonable; and (4) the climate in the Rhine basin in the future, as modeled by the RCMs, is likely to be wetter than in the past. The results suggest that such future projections may be used with cautious confidence.

As the most populated region of the world, Asia is a major source of aerosols with potential large impact over vast downstream areas, Papers published in this special section describe the variety of aerosols observed in China and their effects and interactions with the regional climate as part of the East Asian Study of Tropospheric Aerosols and their Impact on Regional Climate (EAST-AIRC), The majority of the papers are based on analyses of observations made under three field projects, namely, the Atmospheric Radiation Measurements (ARM) Mobile Facility mission in China (AMF-China), the East Asian Study of Tropospheric Aerosols: An International Regional Experiment (EAST-AIRE), and the Atmospheric Aerosols of China and their Climate Effects (AACCE), The former two are U,S,-China collaborative projects, and the latter is a part of the China's National Basic Research program (or often referred to as "973 project"), Routine meteorological data of China are also employed in some studies, The wealth of general and speCIalized measurements lead to extensive and close-up investigations of the optical, physical, and chemical properties of anthropogenic, natural, and mixed aerosols; their sources, formation, and transport mechanisms; horizontal, vertical, and temporal variations; direct and indirect effects; and interactions with the East Asian monsoon system, Particular efforts are made to advance our understanding of the mixing and interaction between dust and anthropogenic pollutants during transport. Several modeling studies were carried out to simulate aerosol impact on radiation budget, temperature, precipitation, wind and atmospheric circulation, fog, etc, In addition, impacts of the Asian monsoon system on aerosol loading are also simulated.

This paper reports an original economic valuation of the impact of climate change on the provision of forest regulating services in Europe. To the authors’ knowledge the current paper represents the first systematic attempt to estimate human well-being losses with respect to changes in biodiversity and forest regulating services that are directly driven by climate change. First, selected 34 European countries are grouped by their latitude intervals to capture the differentiated regional effects of forests in response to climate change. Moreover, the future trends of forest areas and stocked carbon in 2050 are projected through the construction and simulation of global circulation models such as HADMC3 following four different future developing paths described by the four IPCC scenarios. Finally, the valuation exercise is anchored in an ecosystem service based approach, involving the use of general circulation models and integrated assessment models. Our findings address two dimensions in the evaluation of climate impacts on European forests: Firstly, future projections yield different states of the world depending upon the IPCC scenario adopted. Secondly, spatial issues matter in an assessment of the distributional impacts of climate change, as these impacts are not distributed in a uniform way across the European countries under consideration.

In the period following a geomagnetic storm the high-latitude, magnetospheric-driven convection pattern is normally weak. However, the neutral circulation, set up by ion-neutral momentum coupling during the main phase of the storm, may continue for several hours after the storm has ended. This persistent neutral circulation has the potential to drive Hall currents for some hours. In this paper we investi- gate these "flywheel" currents by simulating a storm which occurred on the 23 rd of November 1982 using the National Center for Atmospheric Research Thermosphere Ionosphere General Circulation Model (NCAR-TIGCM). The resulting high-latitude, height-integrated Hal/currents are dominated by the neutral-wind-driven component for several hours after the end of main phase of the storm. The direction of these currents is reversed from normal. Analysis of the neutral and ion components of this current system indicates that the neutral component may drive as much as 80% of the high-latitude current system immediately after the storm has ended, and may continue to dominate this system for 4 to 5 hours. stant in the E-region for the transfer of momentum from the plasma to the neutral gas implies that the neutral winds that were forced by the ions during the main phase of the geomag- netic storm can persist for a long time after the cessation of magnetospheric-driven forcing, and may drive significant ionospheric and magnetospheric field-aligned currents over the polar cap in a way that is similar to that of the dynamo in low and middle latitudes. Lyons et al. (1985) studied these winds and they showed that, in practice, the neutral circulation in the high-latitude E region can drive a significant Hall current system for up to six hours after the cessation of strong magne- tospheric convection - the so-called neutral "flywheel" effect. Some experimental support for this concept exists in the results published by several authors (e.g. Maezawa, 1976; Zanetti, 1984), who showed that ionospheric currents can reverse direction when B z is northward. In this paper we extend the Lyons et a1.(1985) study to investigate the link between the neutral circulation and these reversed currents during the period following a geomagnetic storm.

In 2018, large parts of northern Europe were affected by an extreme drought. A better understanding of the characteristics and the large-scale atmospheric circulation driving such events is of high importance to enhance drought forecasting and mitigation. This paper examines the historical extremeness of the May–August 2018 meteorological situation and the accompanying meteorological and hydrological (streamflow and groundwater) drought. Further, it investigates the relationship between the large-scale atmospheric circulation and summer streamflow in the Nordic region. In May and July 2018, record-breaking temperatures were observed in large parts of northern Europe associated with blocking systems centred over Fennoscandia and sea surface temperature anomalies of more than 3 °C in the Baltic Sea (May, July) and the Barents Sea (July). Extreme meteorological drought, as indicated by the three-month standard precipitation index (SPI3) and precipitation-evapotranspiration index (SPEI3), was observed in May, and covered large parts of northern Europe by July. Streamflow drought in the Nordic region started to develop in June, and in July 68 % of the stations had record-low or near-record-low streamflow. Extreme streamflow conditions persisted in the southeastern part of the region throughout 2018. Many groundwater wells had record-low or near-record-low levels in July and August. However, extremeness in groundwater levels and (to a lesser degree) streamflow show a diverse spatial pattern. This points to the role of local terrestrial processes in controlling the hydrological response to meteorological conditions, including aquifer properties. Composite analysis of low summer streamflow and 500 mb geopotential height anomalies revealed a distinction between summer streamflow variability in western/northern Norway and the rest of the region. Low summer streamflow in western/northern Norway is related to high-pressure systems centred over the Norwegian Sea. In the rest of the Nordic region, low summer streamflow is associated with a high-pressure system over the North Sea and a low-pressure system over Greenland and Russia at similar latitudes, resembling the pattern of 2018. This study provides new insight into different hydro-meteorological aspects of the 2018 northern European drought, as well as identification of large-scale atmospheric circulation patterns associated with summer streamflow drought in the Nordic region.