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Winter precipitation (P) in East Asia (EA) is characterized by a wetter south and a drier north. Most of the existing research has concentrated on elucidating the mechanisms of winter P in southern EA, with relatively less attention given to northern East Asia (NEA). Our analysis showed that the correlation coefficient (c.c.) of average winter precipitation anomaly percentage (PAP) between southern EA and NEA is 0.24 for the period 1950–2023, indicating substantial regional difference. An empirical orthogonal function (EOF) analysis was conducted on the winter PAP in NEA. The first and second mode (EOF1 and EOF2) account for 45.5% and 17.9% of the total variance, respectively. EOF1 is characterized by a region-wide uniform spatial pattern whereas EOF2 exhibits a north–south dipole pattern. Further analysis indicated that the two EOF modes are related to distinct atmospheric circulation and external forcings. Specifically, EOF1 is linked to a wave train from Central Siberia toward Japan, while EOF2 is connected with an anomaly similar to the Western Pacific pattern. Variations in mid–high latitude sea surface temperatures, sea ice, and snow are potential factors influencing EOF1. EOF2 exhibits a close relationship with tropical SST anomalies. [ABSTRACT FROM AUTHOR]

The winter precipitation in southern China (SC) typically displays a negative anomaly during La Niña events. However, the precipitation anomaly in SC showed inverse distribution in the winter of 2020/21 and 2021/22 when La Niña conditions prevailed. Negative precipitation anomaly was observed during the winter of 2020/21, whereas a distinct pattern of positive precipitation anomalies appeared during the winter of 2021/22. This abnormal phenomenon prompts us to explore why there were positive precipitation anomalies in SC under the background of La Niña. The results show that the sea surface temperature (SST) in South China Sea (SCS) can modulate winter precipitation in SC, excluding the influence of La Niña. To clarify the physical processes, by utilizing the three-pattern decomposition of global atmospheric circulation (3P-DGAC), the three-dimensional atmospheric circulation bridge was established between the SST in SCS and winter precipitation in SC effectively. The positive SST anomalies in SCS trigger local anomalous anticyclone, transporting massive water vapor to SC. Meanwhile, the local meridional and zonal circulations related to SST warming in SCS favor abnormal updraft flow over SC, which are conducive to the strengthening of convective potential. Overall, the three-dimensional atmospheric circulation induced by the SST warming in SCS contributes significantly to the increment of winter precipitation in SC. Besides, the predicted results of BCC_CSM1.1 (m) model emphasized the important role of the SST in SCS on the winter precipitation in SC. Our findings suggest that the SST in SCS might provide a viable source for advancing the regional seasonal climate prediction. [ABSTRACT FROM AUTHOR]

Abstract: A central goal at the interface of ecology and conservation is understanding how the relationship between biodiversity and ecosystem function (B–EF) will shift with changing climate. Despite recent theoretical advances, studies which examine temporal variation in the functional traits and mechanisms (mass ratio effects and niche complementarity effects) that underpin the B–EF relationship are lacking. Here, we use 13 years of data on plant species composition, plant traits, local‐scale abiotic variables, above‐ground net primary productivity (ANPP), and climate from the alpine tundra of Colorado (USA) to investigate temporal dynamics in the B–EF relationship. To assess how changing climatic conditions may alter the B–EF relationship, we built structural equation models (SEMs) for 11 traits across 13 years and evaluated the power of different trait SEMs to predict ANPP, as well as the relative contributions of mass ratio effects (community‐weighted mean trait values; CWM), niche complementarity effects (functional dispersion; FDis) and local abiotic variables. Additionally, we coupled linear mixed effects models with Multimodel inference methods to assess how inclusion of trait–climate interactions might improve our ability to predict ANPP through time. In every year, at least one SEM exhibited good fit, explaining between 19.6% and 57.2% of the variation in ANPP. However, the identity of the trait which best explained ANPP changed depending on winter precipitation, with leaf area, plant height and foliar nitrogen isotope content (δ15N) SEMs performing best in high, middle and low precipitation years, respectively. Regardless of trait identity, CWMs exerted a stronger influence on ANPP than FDis and total biotic effects were always greater than total abiotic effects. Multimodel inference reinforced the results of SEM analysis, with the inclusion of climate–trait interactions marginally improving our ability to predict ANPP through time. Synthesis. Our results suggest that temporal variation in climatic conditions influences which traits, mechanisms and abiotic variables were most responsible for driving the B–EF relationship. Importantly, our findings suggest that future research should consider temporal variability in the B–EF relationship, particularly how the predictive power of individual functional traits and abiotic variables may fluctuate as conditions shift due to climate change.

• Wetter winters as a result of climate change increase N and S topsoil availability in forests. • Surprisingly high leaching rates of additionally available nutrients. • No short-term effects of wetter winters on decomposition and tree growth. • Groundwater N and S pollution likely increases with winter climate change. Climate models project moderate to large increases in air temperature for most temperate ecosystems with an overall increase in winter precipitation and a shift from snow towards rain. We investigated the effects of increased winter rainfall on the ecosystem functioning of European beech forests at their north-eastern distribution range. In a large-scale field experiment we manipulated winter climate at nine forest sites by increasing the amount of rainfall and excluding snow. Nutrient availability in the topsoil and leaching in 50 cm depth as well as litter decomposition and radial growth of mature European beech trees were analysed. It was hypothesized that (1) wetter winters lead to increased nutrient deposition as well as leaching, with an overall increase in net nutrient availability, (2) decomposition decreases in response to water addition containing also additional nutrients and (3) primary production during the subsequent growing season increases as presumably not all additionally available nutrients would be leached. We found an increase in topsoil nitrate and sulfate availability during winter in response to rain addition, likely as a consequence of collecting more atmospheric deposition, and surprisingly high leaching rates of the additionally available nutrients. During the subsequent early growing season, no difference in nutrient availability could be observed anymore. Enhanced nutrient availability in the topsoil and leaching do not seem to have a strong short-term influence on forest ecosystem processes in ecosystems which are close to their critical load of N deposition. Decomposition rates during winter and early growing season as well as stem diameter growth during the following growing season were not influenced. This indicates that additional nutrients in the topsoil in response to wetter winters are not available for plant growth but pollute ground- and surface waters. [ABSTRACT FROM AUTHOR]

Western Himalayas (WH) receives precipitation through eastward propagating synoptic weather systems, Western Disturbances (WDs), embedded in large scale subtropical westerly jet (SWJ) during Northern Hemispheric boreal winter (December, January and February; DJF). In the recent decade, WDs have undergone certain changes in their characteristic's viz., decreased associated precipitation, no significant changes in the WDs frequency and intensity, etc. However, Non-WDs days and associated precipitation gained its importance as it contributes ~ 20% of winter precipitation over WH. In this study, structure, dynamics and moisture availability associated with changing WDs and Non-WDs precipitating days are analyzed. Robust statistical methods and Theil-Sen slope on ERA5 data during 1987–2020 is considered to comprehend why active WDs' (Non-WDs) precipitation frequency is declining (notably increasing). Interestingly, it is as well found that all the WDs do not precipitate and there are Non-WDs days when precipitation occur. It shows declining trend in WD precipitation and the increasing importance of Non-WDs. The findings show formation of 'Ω shape' flow - where high pressure is locked between two low pressure systems - over Indian subcontinent during Non-WDs days. Such dynamical wind col formation ('Ω shape') from lower (850Hpa) to upper (200 hPa) troposphere provides conducive situation for enhanced moisture incursion from Bay of Bengal (BoB) towards and over the WH during Non-WDs days leading to precipitation. This new finding needs to be looked from sustaining and replenishment of glaciers; agriculture; socioeconomic benefits during winters and needs to be addressed. [ABSTRACT FROM AUTHOR]

Winter precipitation anomalies in South China (SC) frequently result in severe disasters. However, the evaluation of prediction performance and distinctions between positive precipitation anomaly events (PPA, wet condition) and negative precipitation anomaly events (NPA, dry condition) in current operational models remains incomplete. This study employed the Climate Forecast System version 2 (CFSv2) to assess winter precipitation prediction accuracy in SC from 1983 to 2021. Differences in predicting PPA and NPA events and the underlying physical mechanisms were explored. The results indicate that CFSv2 can effectively predict interannual variations in winter precipitation in SC, as there is a significant time correlation coefficient of 0.68 (0.62) between observations and predictions, with a lead time of 0 (3) months. The model revealed an intriguing asymmetry in prediction skills: PPA outperformed NPA in both deterministic and probabilistic prediction. The higher predictability of PPA, as indicated by the perfect model correlation and signal-to-noise ratio, contributed to its superior prediction performance when compared to NPA. Physically, tropical signals from the ENSO and extratropical signals from the Arctic sea ice anomaly, were found to play pivotal roles in this asymmetric feature. ENSO significantly impacts PPA events, whereas NPA events are influenced by a complex interplay of factors involving ENSO and Arctic sea ice, leading to low NPA predictability. The capability of the model to replicate Arctic sea ice signals is limited, but it successfully predicts ENSO signals and reproduces their related circulation responses. This study highlights the asymmetrical features of precipitation prediction, aiding in prediction models improvement. [ABSTRACT FROM AUTHOR]

The influence of winter circumglobal teleconnection （CGT） on the interannual variability of winter precipitation in the Southeast Asian low-latitude highlands were statistically analyzed using ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts （ECMWF）， monthly mean precipitation data from the Climate Hazards Group Infrared Precipitation with Station data （CHIRPS） developed by the United States Geological Survey and the University of California and the monthly mean precipitation data of the Global Precipitation Climatology Project （GPCP） provided by the Global Precipitation Climatology Center.Results of correlation analysis show that the CGT presents two main patterns with approximately the same variance contribution rate.On the vertical direction， the CGT shows an equivalent barotropic structure with four anomalous centers.During the CGT positive phase， the negative anomalous centers are located near the Mediterranean Sea and the Indian Peninsula， and the positive anomalous centers near the Arabian Peninsula and Southeast Asian low-latitude highlands.The first mode of CGT （CGT1） significantly correlates with winter precipitation over the Southeast Asian low-latitude highlands on the interannual time scale.When the CGT1 is in the positive phase in winter， the anomalous "anticyclone， cyclone， anticyclone， cyclone" control the Western Europe， the northwestern Arabian Peninsula， the Arabian Sea and Southeast Asian low-latitude highlands， respectively.The anomalous southwesterly wind on the east side of the anomalous cyclone will increase the water vapor from the Bay of Bengal and the South China Sea to the Southeast Asian low-latitude highlands.The more water vapor converged and condensed in Southeast Asian low-latitude highlands finally results in heavier winter precipitation over the Southeast Asian low-latitude highlands.On the contrary， when the CGT1 is in the negative phase in winter， the Western Europe， the northwestern Arabian Peninsula， the Arabian Sea and the Southeast Asian low-latitude highlands are controlled by the anomalous "cyclone， anticyclone， cyclone， anticyclone".The anomalous northeast wind on the east flank of the anomalous anticyclone will reduce the water vapor from the Bay of Bengal and the South China Sea to the Southeast Asian low-latitude highlands.The anomalous divergence and descending motion further lead to less precipitation in winter over the Southeast Asian low-latitude highlands.The significant positive correlation between CGT and precipitation over the Southeast Asian low-latitude highlands， sharing almost the same key physical process as winter， can be observed in December， January and February.Results of typical case further confirm the key physical process through which the CGT modulates the interannual variability of winter precipitation over the Southeast Asian low-latitude highlands.

The North China Plain, a crucial region for winter wheat cultivation, exhibits yield deeply affected by the variability of winter precipitation. This study examines the interdecadal variation in the relationship between the North Pacific Oscillation (NPO) and winter precipitation in the North China Plain (WPNC). Utilizing the East Asian winter monsoon (EAWM) as an intermediary, we have observed an interdecadal variation in the relationship between WPNC and NPO after the late‐1990s. Before 1994, the relationship between NPO and EAWM/WPNC both exhibited a significant positive correlation, while after 1998, their correlation decreased and became insignificant. This interdecadal variation can be attributed to the eastward shift of the winter NPO's location after the late‐1990s. Our investigation found that the eastward shift of the NPO's location is closely linked to the phase transition of the Atlantic Multidecadal Oscillation (AMO) phase after the late‐1990s. The warm sea surface temperatures (SST) over the North Atlantic cause ascending motion, and the outflows induce a compensatory anticyclonic circulation over the North Pacific. The easterlies anomaly on the south side of the anticyclone weakens climatological westerlies, increasing SST and upper‐level air temperatures in the North Pacific through the wind–evaporation–SST–longwave radiation effect. The resulting warmer air strengthens the atmospheric temperature gradient, enhancing the vertical integration of baroclinic energy conversion and shifting the NPO eastward, reducing its correlation with WPNC. [ABSTRACT FROM AUTHOR]

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The amount of winter precipitation in Japan is increasing only in the Kanto-Koshin region, which includes the Tokyo metropolitan area located on the Pacific Ocean side of Japan. This study investigated long-term historical changes in winter precipitation in Japan using a large ensemble of regional climate simulations that capture the observed increases in precipitation in the Kanto-Koshin region. In addition, self-organizing maps (SOMs) were applied to the atmospheric pressure to explore historical changes in weather pattern (WP) leading to precipitation. The results suggest that long-term changes in precipitation/snowfall could be due to differences in the WP frequency of southern-coastal cyclones and WP-related precipitation due to altered background states during the winter. The former and latter can be interpreted as dynamic and thermodynamic impacts of historical climate change. As for the Kanto-Koshin region, atmospheric circulation analogs revealed that thermodynamic and dynamic effects account for ~ 2/3 and ~ 1/3 of the precipitation changes, respectively, while dynamic effects (increases in south coast cyclone occurrence) dominantly account for snowfall changes. These changes could be attributed to the large-scale historical increases in air temperature and water vapor content. [ABSTRACT FROM AUTHOR]

For the regions with a long-term snow cover, the amount of solid precipitation is one of the driving factors in the formation of floods. The article considers the possibility of using the orographic correction to the velocity of vertical movements of air masses due to the relief in estimating winter precipitation and forecasting maximum snowmelt-induced stages. The significant influence of autumn freezing on the floodplain inundation and, accordingly, maximum water levels of the Ob River near the city of Barnaul is shown. [ABSTRACT FROM AUTHOR]

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Based on the 103 stations precipitation over Songhua River Basin （SRB）， the reanalysis data of NCEP/NCAR， the sea surface temperature （SST） from NOAA， the interannual variation in snowfall over SRB and its relationship with west north Pacific SST anomalies （SSTA） during boreal winter for 1979 -2019 are investigated by using statistical analysis methods.The results show that the snowfall over SRB during winter is mainly characterized by its interannual variation （explains 83.3% of total variation）， and the first leading EOF mode of interannual snowfall anomalies of SRB during winter is dominated by a homogeneous structure （explains 55.3% of total variance） indicating significant covariability over the SRB.The atmospheric circulation associated with the interannual SRB winter snowfall suggests that the above-normal （below-normal） snowfall is induced by positive （negative） geopotential height anomalies over the region from Okhotsk to Aleutian island and negative （positive） geopotential height anomalies over the mid-low latitude to the south of Okhotsk Sea.Further analyses indicate that the dipole structure of SSTA over WNP during winter has a profound impact on the simultaneous interannual snowfall over SRB.The positive WNP SSTA dipole （positive and negative SSTA over Japanese Sea and east to the Philippines Islands， respectively） can induce positive geopotential height anomalies in the upper troposphere and anomalous anticyclone in the lower troposphere in the mid-high latitudes over WNP， as well as the negative geopotential height anomalies in the upper troposphere and anomalous cyclone in the lower troposphere in the mid-low latitudes.The region from north Pacific to the SRB is covered by anomalous southeasterly winds during winter under the influence of these anomalous atmospheric circulation.As a result， the moisture from the sea to the south of Aleutian and the sea to the east of China are transported to the SRB accompanied by anomalous convergent flow in situ， which are favorable for the increasing snowfall over SRB； and vice versa.

Mid‐latitude storms act as crucial atmospheric bridges between global teleconnection patterns and regional precipitation distribution during boreal winter over South Asia. In this work, we study the spatio‐temporal variability of seasonal precipitation over South Asia over the last four decades, which reveals distinct regional precipitation patterns across seasons. For the winter region of South Asia (WRSA), the second Empirical orthogonal function (EOF2) of 500 hPa geopotential heights shows a significant positive correlation with precipitation. Furthermore, using regression analysis, we estimate that the first six EOFs explain most of the interannual variability in winter precipitation during the positive phase of AMO. The results show that six standard climate indices influence winter precipitation over WRSA. We observed a decadal variability in the relationship between ENSO and winter precipitation over WRSA that is modulated by Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). The positive phase of AMO strengthens the positive relationship between ENSO and winter precipitation over WRSA. The model results also show that two other oscialltions, DMI and AAO, significantly explain the variability of winter precipitation over WRSA. The atmospheric patterns extracted in this study significantly improve winter precipitation forecasting skill of linear regression models compared to those based on standard climate indices, especially during positive AMO winters. The results from this study can be used to improve seasonal predictability of winter precipitation over WRSA. [ABSTRACT FROM AUTHOR]

Winter (December to March) precipitation is the major source of rainfed agriculture, storage, and perennial water flow in the western river system of Pakistan. Hence, this study uses precipitation data and variables of land–ocean and atmosphere from the Pakistan Meteorological Department and European Centre for Medium-Range Weather Forecasts (ECMWF) and fifth-generation reanalysis data (ERA5), respectively, to investigate the changes in winter precipitation and its sensitivity to different land–ocean and atmosphere variables, which are rarely investigated in Pakistan. Non-parametric techniques, such as the modified Mann–Kendal, Sen slope, kernel density-based probability function (PDF), empirical orthogonal function (EOF), and correlation analysis, were used to assess the changes and modes of variability in winter precipitation. The overall seasonal precipitation showed a significant decreasing trend with a (−0.1 mm d−1 yr−1) in the seasonal mean and monthly precipitation, except in February which showed a significant increase (>0.11 mm d−1 yr−1). The highest decrease in daily precipitation (<−0.1 mm d−1 yr−1) was in the north, with a moderate decrease in the southeast. The extreme precipitation indices exhibited an erratic decreasing tendency, but the maximum daily precipitation index increased; post-2000 precipitation extremes displayed an increase, and the seasonal and monthly precipitation exhibited the highest deviations during the drought period (1995–2000). The leading precipitation mode (EOF1) is sensitive to the local land surface processes and significantly correlated (>0.60) with the central Pacific and Indian Ocean's basin-wide sea surface temperature, corroborating the influence of ENSO-induced meridional/zonal deviation of Hadley–Walker circulations. The Hadley and Walker cells affect the south-westerlies' jet stream strength, impacting the water vapor transport and precipitation over Pakistan. These changes in the precipitation magnitude will affect rain-fed agriculture, especially the Rabi cropping pattern and perennial river flow. [ABSTRACT FROM AUTHOR]

Link for citation: Samoilova S.Yu., Lovtskaya O.V., Kudishin A.V., Arnaut D.V. Analysis of factors for formation of the Chumysh river maximum runoff (Western Siberia). Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 5, рр.116-128. In Rus. The relevance of the study stems from the necessity to refine the methods of medium-term flood forecasts when sufficient hydrometeorological data are not available. The purpose of the work is to assess probable application of spatially distributed precipitation models to forecast runoff volume of flood, to develop stochastic models for predicting flood volume and its maximum discharge using hydrometeorological observation data, distributed precipitation datasets from reanalysis and remote sensing data of high spatial and temporal resolution. Methods include geoinformation, complex geographical and hydrometeorological analysis, statistical methods (correlation and regression analysis). Results. The Chumysh basin moistening was estimated due to the data from spatially distributed precipitation models and hydrometeorological observation data; the relationship of total precipitation with runoff volume and maximum flood discharge was analyzed. A comparative evaluation of the obtained dependencies made it possible to identify key predictors for deriving the multiple linear regression equation. The statistical model was developed for predicting volumes and maximum discharges of Chumysh flood at Talmenka settlement using hydrometeorological observation data and reanalysis ones of high spatial and temporal resolution.

Climate change has a greater impact on high-altitude and mountain regions than on lowlands. The first priority should be to detect these changes in high mountainous regions, as they will directly affect water resources in the main stems. The present study examines the effect of climate change on snow-rain phase separation in the future in the Behesht Abad and Koohrang zones of Iran's central Zagros mountains, one of the country's highest mountain ranges. The study region's 1985–2019 precipitation, temperature, and precipitation type data were used for this purpose. Future climate change was predicted using the National Center for Environmental Protection's (NCEP) atmospheric reanalysis data and the CanESM2 model for the three scenarios RCP 2.6, RCP 4.5, and RCP 8.5. Furthermore, the SDSM 5.3 model was used to perform the downscaling. The original and modified Mann-Kendall tests were used to detect data trends. Different methods were investigated, and observational reports were compared to separate the precipitation phase during the basic period, and in conclusion, the methods Kienzle and USCE yielded good results. According to the findings of this study, climate change will cause significant changes in the temperature distribution of precipitation in the studied mountain region in the future. The probability of extreme precipitation will increase along with a decrease in precipitation rate variability relative to the historical period during the fall-winter season. Additionally, the changes will increase precipitation during warmer temperatures and decrease it during periods of cooler temperatures and change in snow and rain rates in the future, relative to the historical period. [ABSTRACT FROM AUTHOR]

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Abstract The India–Burma troughs (IBTs) with different shapes (i.e., narrow and wide IBT-like circulations) can significantly affect winter precipitation over different regions in southern China through modulating the paths of water vapor transportation ahead of the IBTs. The effect of the wide/narrow IBT- (WIBT/NIBT-) like circulation cannot be depicted by traditional IBT indices that mainly focus on the IBT’s intensity. This study defines the WIBT and NIBT indices, which can effectively distinguish different water vapor transportation in front of the WIBT and NIBT and relevant water vapor convergence and therefore successfully reflect different distributions of winter precipitation anomalies over southern China. Further exploration reveals that a Rossby wave from the Mediterranean Sea to the Bay of Bengal (BoB) contributes to the variability of the NIBT, while the El Niño–Southern Oscillation (ENSO) can modulate the variability of the WIBT by stimulating the Matsuno–Gill response. The WIBT and NIBT indices should be considered as important supplements to the traditional IBT indices, which are favorable to more detailed diagnosis and prediction of winter climate over southern China.

The study topicality relates to the analysis of available methods for assessing snow reserves in river basins and forecasting floods. To predict runoff volume and maximum flood levels, statistical models resting on the correlation dependence of runoff parameters on snow reserves or multiple linear regression equations are usually used in the absence of sufficient hydrometeorological information. An important point is that there are no justified comparisons of traditional forecasting methods based on calculations of winter precipitation amount (snow reserves) and statistical models of multiple regression. The aim of the study is to carry out the comparative analysis of methods for calculating winter precipitation amounts in the basin by means of traditionally applied altitude dependencies and the author's estimation method using orographic correction to the velocity of vertical movements of air masses; to carry out the comparative analysis of traditional statistical forecasting methods and models of multiple linear regression by the example of the Amyl River basin. Methods: comprehensive geographical and hydrometeorological analysis; dependence establishment based on long-term hydrometeorological observations using methods of mathematical statistics (correlation and regression analysis); snow reserves simulation with the use of orographic correction to the velocity of vertical movements. Results. By altitude dependencies and the author’s assessment considering orographic correction to the velocity of vertical movements of air masses, two different approaches to estimate of winter precipitation amounts suggest similar statistical dependences with close values of determination coefficients. Models for predicting runoff volumes and maximum flood stages based on pair correlation and multiple regression analysis were developed. The comparative analysis of traditional methods for forecasting runoff layers based on calculations of winter precipitation amount (snow reserves) and statistical models of multiple regression also showed similar results. The applied one-factor dependencies turned out to be the best in forecasting snowmelt-induced maximum levels.

Observations indicate that the winter precipitation over Southeast Asia (SEAP) shows significantly increased trends from 1979 to 2014, which can be partly reproduced under the historical all-forcing simulations from the 12 Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. By analyzing separate external forcings run with the Detection and Attribution experiments, we find that the effects of anthropogenic forcing rather than natural variation play a primary role in driving the increasing of SEAP trends simulated in the historical all-forcing experiments. Further analysis indicate that the observed increasing trend is closely associated with the decadal shift of the Southeast Asian precipitation after the mid-1990s, which could be also driven by anthropogenic forcing to some extent. Anthropogenic forcing can favor a La Niña-like pattern of sea surface temperature (SST) warming in the tropical Pacific and result in the decadal increase of SEAP via the enhanced zonal SST gradient and the Pacific Walker circulation. This study thus provides some evidence of the impacts of anthropogenic forcing to drive recent changes in the winter SEAP.

The change of average winter precipitation in the South China Sea (SCS) since 1999 was investigated by analyzing the average precipitation between 1999 and 2014 and 1980–1993. The spatial distribution of the winter precipitation difference between the two periods showed that the negative anomalies were distributed from the equatorial eastern Pacific to the equatorial central Pacific, and the positive anomalies were distributed in the subtropical western Pacific, the Maritime Continent, and northern part of Australia, which is a typical spatial distribution of precipitation anomalies during La Niña events. In the tropical Pacific, the Walker circulation is intensified, in which air rises from the Maritime Continent and air in the tropical western Pacific descends at the equatorial central Pacific. Therefore, the change in sea surface temperature showed a typical La Niña pattern. In the East Asian regions, the local Hadley circulation in which air rises above the SCS and descends in the mid-latitudes of East Asia is intensified. This circulation is related to the anomalous pressure distribution of the west-high and east-low pattern in East Asia and the strengthening of the East Asian winter monsoon. In addition, this result is in-line with increased snow depth in mid-latitude East Asia in recent years. [ABSTRACT FROM AUTHOR]

The study topicality relates to the effect of climate changes and increased recurrence of dangerous hydrological events on rivers of southern Siberia. The observed and predicted changes in flood regimes are caused by a variety of factors and require different approaches in order to characterize the types of these changes. The aim of the study is stochastic modeling of solid precipitation total in the Abakan river basin, establishing relationship between precipitation and maximum water levels in the Abakan river during the flood period under spatial and temporal variability of hydrometeorological factors. Methods: comprehensive geographical and hydrometeorological analysis, dependence establishment based on long-term hydrometeorological observations using mathematical statistics methods, methods (developed by V.P. Galakhov) for estimating precipitation total in the basin with regard for orographic correction to the velocity of vertical movements in the frontal zone. Results. The crucial factor in the formation of maximum flood levels is winter precipitation amount. Heavy rainfalls during flood recession may significantly influence the maximum water levels. However, climate changes of recent decades in river mountain basins of southwestern and eastern Siberia are evidence of dependences between autumn soil freezing and formation of snowmelt-induced maximum stages. In some years during the flood period, decreased maximum water levels are probable in basins with prevailing foothill plains, unlike those with overwhelmingly mountainous landscapes. We have developed a method for calculating winter annual precipitation total in the Abakan basin taking into account physical features of precipitation formation in the mountains, in particular the orographic correction to the velocity of vertical movements. The independent data suggest that algorithms for calculating snowmelt-induced maximum stages based on regression dependencies do not always give adequate results, therefore updating with regard for freezing processes in the foothill plain is required. Besides, extra observation data are called for obtaining the general statistical dependence.

The accurate identification of precipitation type at ground level is one of the greatest difficulties for forecasters during winter. Special types of precipitation can be a threat to public safety and human health and can disrupt transportation and commerce, causing seriously loss of the economy. Winter precipitation may also cause serious disasters to aircraft navigation. In those situations, the consequences can be catastrophic, with heavy and prolonged freezing precipitation, collapsed power lines causing prolonged power outages, transportation networks of many types completely paralyzed, and even major long-term damage to infrastructure and vegetation in the most severe cases. Therefore, the accuracy of precipitation type is crucial for winter precipitation forecast. Accurate predictions from weather forecast models of timing (onset and duration), intensity, spatial extent, and phase (i.e., precipitation type) are crucial for decision-making and can help minimize the potential impacts. The research progress of precipitation type forecast in recent decades is investigated. The methods and techniques for predicting precipitation phases are reviewed systematically, which can be roughly divided into three categories. The index criterion methods are based on observations, numerical weather prediction weather predictions on thickness, area of warm atmosphere, significance level temperature, regression equation for vertical temperature profile, and model diagnosis. Some of those methods are highly dependent on the accuracy of the numerical model. The second type of methods are based on the microphysical processing scheme of numerical weather prediction model and ensemble prediction system. It includes microphysical scheme method and ensemble prediction method. The last type is the artificial intelligence prediction method including decision tree, artificial neural network, and deep learning etc. In recent years, sophisticated microphysical parameterizations schemes are widely used in high resolution regional forecast models, which help with precipitation-type prediction. The forecast accuracy of precipitation type model has been improved, which has become an important product support in precipitation type forecast. For instance, the precipitation type prediction product of ECMWF and the probabilistic prediction of precipitation type by ECMWF ensemble prediction. The probabilistic prediction has further improved the prediction skills compared with the deterministic model. However, even with such complex algorithms of NWP, correctly predicting what phase of precipitation ends up at the ground remains a challenging task. Besides this, many researches on the formation mechanism of microphysical processes are difficult to be applied to the precipitation type prediction, so it still needs continuous efforts to apply these achievements to improve the precipitation type prediction skill of numerical prediction model and increase the accuracy of precipitation type prediction by artificial intelligence and other technologies.

Previous studies have reported that enhanced eddy moisture convergence causes future increase of winter precipitation in the eastern North America in a warmer climate. This study investigates the mechanisms of the change in moisture convergence. Using ensemble simulations from climate models and composite analysis of moisture budget, we show that in the southeast United States, two thirds of the enhanced moisture convergence is caused by local thermodynamics due to increase of moisture, while one third is caused by stronger eddy wind convergence. In the north, it is primarily caused by the increase of moisture gradient associated with the spatial distribution of both the climatological temperature and the large amplitudes of the eddy temperature in the region of the storm tracks. Results help to better understand the physical mechanism of more winter precipitation in the eastern North America in a warmer climate. Plain Language Summary: It has been reported that winter precipitation will increase in the eastern North America under global warming, which is caused by the enhanced eddy moisture convergence. We perform composite analysis of moisture budget using large ensemble simulations of climate models, and find out that the enhanced eddy moisture convergence in the southeast United States can be explained by the combination of climatological eddy wind convergence and increase of moisture content. The intensity of eddy wind convergence will enhance and contribute about one third of the eddy moisture convergence increase in the southeast United States. In the north of eastern North America, the climatological eddy wind brings more moisture into the region due to enhanced moisture gradient. The contrast of different mechanisms in the south and north can be explained by the climatology and future change of the spatial pattern of water vapor and temperature. These results help us to better understand the physical mechanisms that are responsible for the future precipitation increase during winter in the eastern North America under global warming. Key Points: Winter precipitation increases with warming due to enhanced eddy moisture convergence in the eastern North AmericaLocal thermodynamics associated with increased moisture and stronger eddies induce more moisture convergence in the southeast United StatesEnhanced moisture gradient in regions of large eddy magnitudes causes more moisture convergence in the north of eastern North America [ABSTRACT FROM AUTHOR]

Background and Objectives: When it comes to climate change, the first emphasis should be detecting these changes in high mountainous regions, since they will have a direct impact on water supplies in the major stems. In the Behesht Abad and Koohrang zones of Iran's central Zagros mountains, one of the country's highest mountain ranges, the influence of climate change on snow-rain phase separation in the future is investigated. Because of the Karun River's varied exploitation, understanding how it will evolve in the future and under the effect of climate change is critical. The aim of the research is to determine the consequences of climate change on precipitation in the region, particularly in terms of future changes in snow and rain phases. Materials and methods: For this, the research region's precipitation, temperature, and precipitation type data from 1985 to 2018 were used. For the three scenarios RCP2.6, RCP4.5, and RCP8.5, the National Center for Environmental Protection's (NCEP) atmospheric reanalysis data and the CanESM2 model were used to forecast future climate change. Furthermore, the downscaling was done using the SDSM5.3 model. To find data patterns, the classic and modified Mann-Kendall tests were performed. Fixed temperature approaches, the UBC watershed model, the USCE model, and Kienzel's suggested method were utilized to separate the precipitation phase. Results: To separate the precipitation phase throughout the fundamental period, observational reports were examined, and the approaches Kienzle and USCE gave satisfactory results. Climate change will also produce major changes in the precipitation temperature distribution in the examined mountain region in the future, according to the findings of this study. Also, a significant portion of the influence of climate change on the snow and rain phases. The modifications are done in such a way that rainfall will rise at higher temperatures and decrease at lower temperatures in the prediction period (2026-2060) compared to the observation period (1985-2018). The greatest total rainfall recorded at Shahrekord station during the observation period was 5.7 °C, which has fallen to 0 °C in the projected period. The temperature range of precipitation at this station was -10 to +18 degrees Celsius during the observation period, and will climb to an average of -10 to +24 degrees Celsius for all three scenarios over the forecast period. The range of precipitation in the future and measurements at Koohrang station is essentially the same, but climate change has produced a rapid shift in the amount of precipitation in this temperature range. Over example, during the 34-year observation period, the greatest rainfall that occurred at a temperature of 1.6 °C was a total of 5700 mm, which was reduced to -1.6 °C and a value of 3700 mm owing to climate change for the next 34 years. The highest limit of the precipitation range at Boroojen station has increased from +18 °C in the historical era to +24 °C in the anticipated period as a result of the modifications. Conclusion: The results of the trend test on the predicted data demonstrate that it is present in the monthly rainfall in the study stations in a substantial way. The temperature distribution of precipitation varies as a result of these changes, which are caused by the impacts of climate change on the study region. [ABSTRACT FROM AUTHOR]

This study presents results from regular observation of permanent and summer-persisting firn-ice bodies in the highest parts of the Dinaric Alps. The sizes of six small glaciers and two snow patches on the Prokletije Massif (in Albania) and the Durmitor Massif (in Montenegro) were measured from 2011 to 2018. In recent years, specific cycles of interannual behavior have been observed: a year of considerable snow accumulation (a »recharge« phase), followed by two to four years of gradual decrease (a »wastage« phase). At present, the small glaciers studied exist in unbalanced conditions, which in the long term may lead to their degradation. Progressive warming makes short-term cycle minimums increasingly severe. Their retreat after the summer of 2017 was probably the most pronounced since the Little Ice Age, and small glaciers are on the verge of extinction.

According to the forecast of IPCC (Intergovernmental Panel of the Climate Change), an increase in precipitation is expected in this century in the Arctic. The main reason is intensification of evaporation from waters of the Arctic Ocean opening due to the intensive melting of sea ice. It is supposed that these changes will be most severe in winters in the Arctic regions, which are subject to significant anthropogenic load. In this respect, the intensively developed Nadym Lowland may be considered as a promising area for researches. The results of our study showed that the circulation conditions (primarily cyclones coming from the North Atlantic under the Eastern (E) circulation form of the G.Ya. Vangenheim–A.A. Girs classification) significantly influence on the isotopic composition of precipitation in this region. Thus, in the cold period of 2016–2017, the isotopic composition of precipitation changed for δ18О by 21 ‰, and for δD by 167 ‰ (weighted average values δ18О = −22.3 ‰, δD = −172.6 ‰, and dexc = 5.6 ‰). The use of the dew point temperature at the moment of precipitation in the calculations of the isotopic-temperature dependences allows obtaining the following coupling equation: δ18О = 0.67Tdp − 15.2 (R2 = 0.67). On the basis of the joint analysis of synoptic, trajectory and isotopic data, the main regions-sources of atmospheric moisture, precipitated in the Nadym Lowland during the cold period of 2016–2017, were determined. The major contributions were made by the Atlantic Ocean (35.7%), the North Atlantic Ocean and the Arctic Ocean (30.4%), and the Black Sea-Caspian region (20%). The last one is characterized by the most weighted isotopic composition. Inland source regions have contributed the least to precipitation (slightly larger 10%), and their lightweight isotopic composition is related to cryogenic fractionation.

The India–Burma troughs (IBTs) with different shapes (i.e., narrow and wide IBT-like circulations) can significantly affect winter precipitation over different regions in southern China through modulating the paths of water vapor transportation ahead of the IBTs. The effect of the wide/narrow IBT- (WIBT/NIBT-) like circulation cannot be depicted by traditional IBT indices that mainly focus on the IBT's intensity. This study defines the WIBT and NIBT indices, which can effectively distinguish different water vapor transportation in front of the WIBT and NIBT and relevant water vapor convergence and therefore successfully reflect different distributions of winter precipitation anomalies over southern China. Further exploration reveals that a Rossby wave from the Mediterranean Sea to the Bay of Bengal (BoB) contributes to the variability of the NIBT, while the El Niño–Southern Oscillation (ENSO) can modulate the variability of the WIBT by stimulating the Matsuno–Gill response. The WIBT and NIBT indices should be considered as important supplements to the traditional IBT indices, which are favorable to more detailed diagnosis and prediction of winter climate over southern China. [ABSTRACT FROM AUTHOR]

Gasterophilus spp. have been found to be widespread in reintroduced Przewalski's horses in the Kalamaili Nature Reserve (Northwest China). However, data on the annual variation in Gasterophilus infections are lacking. To analyze the epidemiological features and determine the cause of the annual variation in Gasterophilus infections, we treated 110 Przewalski's horses with ivermectin and collected Gasterophilus larvae from fecal samples each winter from 2007 to 2019. All 110 Przewalski's horses studied were found to be infected by Gasterophilus spp., and a total of 141 379 larvae were collected. Six species of Gasterophilus were identified with the following prevalence: G. pecorum (100%), G. nasalis (96.36%), G. nigricornis (94.55%), G. haemorrhoidalis (56.36%), G. intestinalis (59.09%), and G. inermis (3.64%). The mean infection intensity of Gasterophilus spp. larvae in Przewalski's horses was 1285 ± 653. G. pecorum (92.96% ± 6.71%) was the most abundant species. The intensity of Gasterophilus spp. (r = –0.561, P < 0.046) was significantly correlated with winter precipitation. Our findings confirmed that, in the Kalamaili Nature Reserve, gasterophilosis is a severe parasitic disease in Przewalski's horses. Winter precipitation at the beginning of the year can indirectly affect the intensity and composition of Gasterophilus spp. in Przewalski's horses at the end of the year. Therefore, the water‐related ecological regulation should be carried out to help reduce the parasite infection of Przewalski's horses. [ABSTRACT FROM AUTHOR]

In this study, the interdecadal increase in winter precipitation in northwest China (NWC) since the late 1980s and the associated moisture flux transport are investigated. The results show that an interdecadal change in moisture flux transport also occurred in the late 1980s, resulting in anomalous moisture transport convergence over NWC. The examination of boundary moisture transport shows enhanced incoming net moisture flux transport over NWC after the late 1980s. The zonal and meridional components both play a key role in the net moisture flux transport, with increased incoming transport from the western boundary dominated and followed by increased incoming transport from the southern boundary. The circulation responsible for the moisture flux transport anomalies is a Eurasian (EU)‐like teleconnection over mid‐to‐high latitudes of the Eurasian continent. The EU teleconnection pattern transformed from a positive phase to a negative phase in the late 1980s. The related anomalous cyclone over central Asia and the anomalous anticyclone over Japan result in westerly anomalies to the west of NWC and southeasterly anomalies to the east, respectively. Together, these anomalies enable an enhanced net gain of moisture transport and the anomalous moisture transport convergence over NWC. The enhanced moisture supply, strengthened upward movement and anomalous convergence result in an interdecadal increase in winter precipitation in NWC. In addition, the transition of the EU teleconnection is likely attributed to changes in the zonal mean wind. Sea surface temperature warming in the North Atlantic and northwestern Pacific regions also play a role in the change in the EU teleconnection pattern. [ABSTRACT FROM AUTHOR]

This study reveals an intensified impact of winter (November–February mean) Arctic Oscillation (AO) on simultaneous precipitation over the mid–high latitudes of Asia (MHA) since the early 2000s. The unstable relationship may be related to the changes in the tropospheric AO mode and the subtropical jet. Further analyses suggest that their changes may be attributable to the interdecadal changes in the stratospheric polar vortex. During 2002–2017, the anomalously weak stratospheric polar vortex is accompanied by intensified upward-propagating tropospheric planetary-scale waves anomalies. Subsequently, the stratospheric geopotential height anomalies over the North Atlantic high-latitudes propagate downward strongly, causing the changes in the tropospheric AO mode, that is, the positive height anomalies over the North Atlantic high-latitudes are stronger and extend southward, corresponding to the stronger and eastward extension of negative height anomalies over the North Atlantic mid-latitudes. Thus, the Rossby wave source anomalies over Baffin Bay and the Black Sea are strong, and correspondingly so too are their subsequently excited the Rossby waves anomalies. Meanwhile, the planetary-scale waves anomalies propagate weakly along the low-latitude waveguide, causing the intensified and southward shift of the subtropical jet. Therefore, the strong Rossby waves anomalies propagate eastward to the MHA. By contrast, during 1979–1999, the strong stratospheric polar vortex anomaly is accompanied by weak upward-propagating planetary-scale waves anomalies, resulting in weaker height anomalies over the North Atlantic mid–high latitudes. Consequently, the anomalous Rossby waves are weak. In addition, the subtropical jet weakens and shifts northward, which causes the Rossby waves anomalies to dominate over the North Atlantic, and thereby the impact of winter AO on simultaneous precipitation over the MHA is weak.

Despite the implications of winter precipitation for socioeconomic activities and transportation services, the influence of cities on winter precipitation is less studied compared to that on summer precipitation. Here we investigated the statistical relations between precipitation, temperature, and impervious surface fraction in 12 major cities across the contiguous United States. The results showed negative correlations between snowfall intensity and impervious surface fraction. The correlations depend on latitude and the distance to complex terrain features (water bodies or topography), with stronger correlations for inland cities than coastal/lakeside cities. We further selected Kansas City for modeling analyses based on the Weather Research and Forecasting model. Simulation results indicated that the heating effect of urban land occurs in the near-surface atmosphere during the precipitation period, leading to changes of different hydrometers and an overall tendency of reducing snowfall but increasing rainfall. • Statistical analyses quantifying the influence of urbanization on winter precipitation across 12 U.S. cities over 10 years. • Modeling simulation elucidating the physical processes through which urban land influences winter precipitation. • Snow only, rain only and mixed precipitation eventsand a season-long simulation conducted over Kansas City. • The urban-induced temperature results in reduced snowfall and increased rainfall especially during mixed-precipitation event. [ABSTRACT FROM AUTHOR]

Low-elevation mountains represent unique model systems to study species endangered by climate warming, such as subalpine and alpine species of butterflies. We aimed to test the effect of climate variables experienced by Erebia butterflies during their development on adult abundances and phenology, targeting the key climate factors determining the population dynamics of mountain insects. We analysed data from a long-term monitoring of adults of two subalpine and alpine butterfly species, Erebia epiphron and E. sudetica (Nymphalidae: Satyrinae) in the Jeseník Mts and Krkonoše Mts (Czech Republic). Our data revealed consistent patterns in their responses to climatic conditions. Lower precipitation (i.e., less snow cover) experienced by overwintering larvae decreases subsequent adult abundances. Conversely, warmer autumns and warmer and drier springs during the active larval phase increase adult abundances and lead to earlier onset and extended duration of the flight season. The population trends of these mountain butterflies are stable or even increasing. On the background of generally increasing temperatures within the mountain ranges, population stability indicates dynamic equilibrium of positive and detrimental consequences of climate warming among different life history stages. These contradictory effects warn against simplistic predictions of climate change consequences on mountain species based only on predicted increases in average temperature. Microclimate variability may facilitate the survival of mountain insect populations, however the availability of suitable habitats will strongly depend on the management of mountain grasslands. [ABSTRACT FROM AUTHOR]

This study investigates the interannual variability of winter precipitation over the Three River Source (TRS) region in China based on precipitation observations collected at stations in the TRS region and reanalysis datasets for the period of 1980–2015. The results suggest that the TRS winter precipitation has distinct interannual variability with discordant trends in different months, that is, an increasing trend is found in November and February, a decreasing trend is found in other winter months, and interannual variations in precipitation are different in different months. The mechanisms for the interannual variation in monthly precipitation over the TRS region are significantly different in different winter months. The interannual variability of TRS precipitation in November is modulated by an anomalous westerly water vapour transport (WVT) branch. This anomalous WVT branch is related to a North Atlantic‐Europe‐Tibetan Plateau (NA‐E‐TP) wave‐train that originates in the North Atlantic due to the ocean–atmosphere interaction. In December, a circum‐global teleconnection (CGT) wave‐train can induce anomalous westerly WVT in the TRS region, resulting in increased precipitation there. This CGT wave‐train is triggered by warm SST anomalies in the central‐eastern tropical Pacific associated with the El Niño‐Southern Oscillation (ENSO). The interannual variability of TRS precipitation in January and February is affected by southwesterly WVT anomalies over the TRS region, which are associated with a southeastward propagating wave‐train over Eurasia caused by the North Atlantic Oscillation (NAO). In March, the interannual variability of TRS precipitation is modulated by the leading mode of the Eurasian circulation that resembles the Scandinavian (EU1) pattern, which can cause anomalous southwesterly WVT in the TRS region. In winter, the characteristics of sea surface temperature anomalies, weather systems, and atmospheric circulations associated with interannual variations of monthly precipitation in the TRS region are different for individual winter months. [ABSTRACT FROM AUTHOR]

We employed the modern analog technique to quantitatively reconstruct temperature and precipitation over the past 2500 yr based on fossil pollen records from six high-elevation lakes in northern Colorado. Reconstructed annual temperatures for the study area did not deviate significantly from modern over the past 2500 yr despite hemispheric expressions of Medieval Climate Anomaly warmth and Little Ice Age cooling. Annual precipitation, however, shifted from lower than modern rates from 2500 to 1000 cal yr BP to higher than modern rates after 1000 cal yr BP, a greater than 100 mm increase in precipitation. Winter precipitation accounts for the majority of the change in annual precipitation, while summer precipitation rates did not change significantly over the past 2500 yr. The large change in winter precipitation rates from the first to second millennium of the Common Era is inferred from a shift in fossil pollen assemblages dominated by subalpine conifers, which have southern sites as modern analogs, to assemblages representing open subalpine vegetation with abundant Artemisia spp. (sagebrush), which have more northern modern analogs. The change helps to explain regional increases in lake levels and shifts in some isotopic and tree-ring data sets, highlighting the risk of large reductions in snowpack and water supplies in the Intermountain West. [ABSTRACT FROM AUTHOR]

Prediction of winter precipitation is challenging because besides its amount also its variable phase might have a strong impact on people, transportation, and infrastructure in general. We combine a bulk microphysics numerical weather prediction with a 1D spectral bin microphysical model, which explicitely treats the processes of melting, ice nucleation and refreezing as a first step towards a potential nowcasting application. Polarimetric weather radar observations from the German national meteorological service (DWD) are used to evaluate the approach. The potential of the strategy is demonstrated by its application to the black ice event occurring in Berlin, Germany, on 20 January 2014. The methodology is able to clearly identify the classical mechanism leading to freezing rain at the surface, which might be exploited in future nowcasting algorithms.

Over the past three decades, several general circulation models of the atmosphere and ocean (atmospheric and oceanic general circulation models – GCMs) have been improved by modeling the hydrological cycle with the use of isotopologues (isotopes of water) HDO and H2 18O. Input parameters for the GCM models taking into account changes in the isotope composition of atmospheric precipitation were, above all, the results obtained by the network GNIP – Global Network of Isotopes in Precipitation. At different times, on the vast territory of Russia there were only about 40 simultaneously functioning stations where the sampling of atmospheric precipitation was performed. In this study we present the results of the isotope composition of samples taken on the foothills of the Altai during two winter seasons of 2014/15 and 2015/16. Values of the isotope composition of precipitation changed in a wide range and their maximum fluctuations were 25, 202 and 18‰ for δ18О, dexc and δD, respectively. The weighted-mean values of δ18О and δD of the precipitation analyzed for the above two seasons were close to each other (−21.1 and −158.1‰ for the first season and −21.1 and −161.9‰ for the second one), while dexc values differed significantly. The comparison of the results of isotope analysis of the snow cover integral samples with the corresponding in the time interval the weighted-mean values of precipitation showed high consistency. However, despite the similarity of values of δ18О and δD, calculated for precipitation and snow cover, and the results, interpolated in IsoMAP (from data of the GNIP stations for 1960–2010), the dexc values were close to mean annual values of IsoMAP for only the second winter season. According to the trajectory analysis (the HYSPLIT model), the revealed differences between both, the seasons, and the long-term average values of IsoMAP, were associated with a change of main regions where the air masses carrying precipitation were formed, namely, the North Atlantic (the winter season of 2014/15) and the inland areas with open ice-free water bodies (the season of 2015/16). Thus, with the correct interpretation of the results, the data on the snow cover isotope composition on the Altai foothills can be used as an alternative data sources instead of the GNIP data.

Urban modification of precipitation regimes is well documented in the urban climate literature. Studies investigating urbanization and non-convective precipitation, specifically winter precipitation, are limited. The theoretical framework here argues that the collective influence of urbanization extends beyond traditional city limits and the surrounding rural areas and can impact regional climate in non-adjacent cities. This paper utilizes the weather research and forecasting model (WRF-ARW) to simulate a cold-season synoptic system over the Northeastern United States over a variety of urban land surface scenarios. This case study centers on the potential boundary layer urban heat island effect on the lower troposphere and its ability to impact winter precipitation type at the local to regional scales. Results show a significant reduction in temperatures near the modified surface and subtle reductions over adjacent urban areas. When surface wind speeds are less than 5 ms−1, the boundary layer heat island increases air temperatures on the order of 3–4 °C at altitudes up to 925 mb. When combined with encroaching warm air near 850 mb during transitional precipitation events, the boundary layer heat island increases the thickness of the melting layer and consequently exposes falling hydrometeors to longer melting duration and phase change. Model simulations also show regional connections through remote temperature and relative humidity changes in urban areas removed from reforested areas.

This study contributes to an improved understanding of Central Southwest Asia (CSWA) wintertime (November–April) precipitation by analyzing the dominant spatial–temporal modes of the regional winter precipitation and examining their relationship with global sea surface temperature (SST) and large-scale atmospheric circulation fields, for 1950/51–2014/15. Empirical orthogonal function (EOF) analysis results show that the first mode (EOF-1) of winter precipitation is characterized by a mono-sign pattern, with significant links to El Niño-Southern Oscillation (ENSO). EOF-2 displays a north–south dipole related to the latitudinal shift in the jet stream position, while the west–east dipole in EOF-3 appears to be influenced by the thermal contrast between the equatorial regions and higher latitudes. Further, we focus on the interdecadal change of connection between wintertime ENSO and EOF-1 observed around the early 1980s. The relationship is weak during 1950/51–1983/84 (P1), but strong and statistically significant in 1984/85–2014/15 (P2). In P1, without the ENSO signal, EOF-1 related atmospheric circulation anomalies are confined mainly over the mid- to high-latitudes of the Northern Hemisphere, associated with the extratropical East Atlantic–Western Russia (EA–WR) teleconnection. In P2, however, a close connection to the tropical Pacific is observed that includes a pronounced SST expression similar to that of ENSO. As a result of the increased relationship between ENSO and EOF-1 in P2, the regional impact of EA–WR observed over CSWA in P1 is linearly superimposed by the anomalous hemispheric–wide atmospheric response forced by the ENSO conditions in the Pacific. [ABSTRACT FROM AUTHOR]

In this study, we examined the relationship between the mid-latitude circulation and the extended winter (November–February) precipitation over the Arabian Peninsula by using observational and NCEP/NCAR reanalysis data (1948–2012). Special emphasis is given to a mid-latitude circumglobal wave train (CGT) that is known to influence the precipitation in the northern hemisphere during both winter and summer seasons. We found a linkage between mid-latitude CGT and winter precipitation over the Arabian Peninsula. The CGT wavelike pattern is associated with anomalous trough above western parts and high pressure over eastern parts of Arabian Peninsula. At lower levels, the CGT is associated with anomalous low over northwestern and high over southeastern parts of the Arabian Peninsula and adjacent parts of the Arabian Sea. The anomalous circulation is further associated with a precipitation pattern over the Arabian Peninsula entailing significantly enhanced precipitation over the central and northwestern parts and reduced precipitation over southeastern parts of the Arabian Peninsula. We further examined the global teleconnection pattern using a precipitation index summarizing winter precipitation over the Arabian Peninsula. The upper-level signature associated with the precipitation index resembles the CGT-like wave pattern with anomalous low over northwestern parts and high over southeastern parts of the Arabian Peninsula. The imprint of the CGT on winter precipitation over the Arabian Peninsula is distinct from that of the North Atlantic Oscillation (NAO), despite the two modes of variability bear some similarities in their upper-level atmospheric pattern above the Arabian Peninsula. [ABSTRACT FROM AUTHOR]

The external source/sink of potential vorticity (PV) is the original driving force for the atmospheric circulation. The relationship between surface PV generation and surface PV density forcing is discussed in detail in this paper. Moreover, a case study of the extreme winter freezing rain/snow storm over South China in January 2008 is performed, and the surface PV density forcing over the eastern flank of the Tibetan Plateau (TP) has been found to significantly affect the precipitation over South China in this case. The TP generated PV propagated eastward in the middle troposphere. The associated zonal advection of positive absolute vorticity resulted in the increasing of cyclonic relative vorticity in the downstream region of the TP. Ascending air and convergence in the lower troposphere developed, which gave rise to the development of the southerly wind. This favored the increasing of negative meridional absolute vorticity advection in the lower troposphere, which provided a large-scale circulation background conducive to ascending motion such that the absolute vorticity advection increased with height. Consequently, the ascending air further strengthened the southerly wind and the vertical gradient of absolute vorticity advection between the lower and middle troposphere in turn. Under such a situation, the enhanced ascending, together with the moist air transported by the southerly wind, formed the extreme winter precipitation in January 2008 over South China. [ABSTRACT FROM AUTHOR]