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There is an urgent need to understand and predict how extreme precipitation events (EPEs) will change at high latitudes, both for local climate change adaptation plans and risk mitigation and as a potential proxy "anticipating" the impact of climate change elsewhere in the world. This paper illustrates that a combination of non‐stationary modelling approaches can be adopted to evaluate trends in EPEs under uncertainty. A large database of daily rainfall events from 281 sparsely distributed weather stations in Finland between 1961 and 2016 was analysed. Among the tested methods, Poisson distributions provided a powerful method to evaluate the impacts of multiple physical covariates, including temperature and atmospheric circulation patterns (ACPs), on the resulting trends. The analysis demonstrates that non‐stationarity is statistically valid for the majority of observations, independently of their location in the country and the season of the year. However, subsampling can severely hinder the statistical validity of the trends, which can be easily confused with random noise and therefore complicate the decision‐making processes regarding long‐term planning. Scaling effects have a strong impact on the estimates of non‐stationary parameters, as homogenizing the data in space and time reduces the statistical validity of the trends. Trends in EPE statistics (mean, 90 and 99% percentiles) and best‐fitted Generalized Pareto parameters in the tails of the distributions appear to be stronger when approaching the Polar region (Lapland) than away from it, consistent with the Arctic amplification of climate change. ACPs are key covariates in physically explaining these trends. In particular, the Arctic Oscillation (AO) and North Atlantic Oscillation (NAO) can explain statistically significant increases in extreme precipitation in Lapland, Bothnian and South regions of Finland, particularly during summer and fall seasons. Non‐stationarity is statistically valid in the majority of observations but masked by subsampling and spatio‐temporal heterogeneity. Trends on extremes and non‐stationary generalized Pareto parameters stronger when approaching the Polar region (Lapland). Artic Oscillation (AO) and North Atlantic Oscillation (NAO) can explain statistically significant trends. [ABSTRACT FROM AUTHOR]

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

There are two aims of this paper: First, the relationship between daily and hourly precipitation extremes and air temperature is investigated for the validity of Clausius–Clapeyron (C–C) scaling; second, the impact of the atmospheric circulation and transport of humidity on the extreme precipitation events occurrence in Poland is analysed based on data obtained from 26 stations across Poland in the period 1951–2015. It was shown that daily‐scale extreme rainfall is less sensitive to changes in local atmospheric temperature but the hourly intensities reveal a similar behaviour at all stations showing a robust signal over the entire country. Regarding the impact of the large‐scale atmospheric circulation, three types were distinguished in cool part of the year: one connected with the positive phase of the North Atlantic Oscillation (NAO), second with a low‐pressure zone in the north and high‐pressure in the south of Europe and the northern Atlantic and third with a low over central Europe. Each time high precipitation in Poland was connected with the advection of humid air from the western sectors (SW, W or NW). In the warm part of the year three types were distinguished too, Poland was always in the scope of low‐pressure systems with the advection of warm air from the southern sectors or when the warm air from the south meets the colder air from the north. Similar localizations of low centres have been found in the case of local‐scale atmospheric circulation types during events with extreme precipitation. Both in cool and warm part of the year such events are connected with the increase of water vapour in the air. In cool season the wet and warm air masses inflow to Poland the most often from Atlantic, in the warm season—from Mediterranean and/or Black Seas. [ABSTRACT FROM AUTHOR]

The precipitation over arid regions may be low, but its environmental impacts can be very dramatic. The decadal variability in precipitation can also effectively disturb climatic environmental regimes. To advance the understanding of precipitation variability over arid regions, this paper focuses on decadal variability in summer precipitation over arid northwest China and its associated atmospheric circulations, using observation‐based data and atmospheric reanalysis during the period 1961–2016. The results show that climatologically, precipitation over this region has a strong seasonality and that 60.2% falls in summer. The summer precipitation increased 15.5 mm, accounting for 52.4% of the total annual increase in this part of China from 1961 to 2016. Decadal changes in summer precipitation occurred in approximately 1991 with a north–south difference structure modulated by large‐scale circulation anomalies over the Indian Ocean and central Asia as well as a shift in water vapour transport. In a positive phase, anticyclonic circulation anomalies occupy the Indian Ocean with cyclonic anomalies over central Asia, favouring stronger northwards moisture transport towards northwest China, and vice versa. Moreover, the significantly enhanced northwards water vapour transport from low‐latitude seas is also critical to the decadal changes approximately in 1991 summer precipitation in arid northwest China. These findings contribute to the understanding of decadal precipitation variability over arid regions, especially the increasing influence of low‐latitude circulations and moisture transport processes. [ABSTRACT FROM AUTHOR]

This paper continues Part I (Wilks DS. Use of stochastic weather generators for precipitation downscaling. WIRES Clim Change 2010, 1(6):898-907) of a two-part review on statistical downscaling of climate changes using parametric 'weather generators', which treated only precipitation downscaling at individual locations. Here the review is extended to include also downscaling of nonprecipitation variables at individual locations, and spatially coherent precipitation and nonprecipitation downscaling. Parametric weather generators are explicitly stochastic models that usually operate on the daily timescale. The use of stochastic methods for climate downscaling is natural and logically consistent because of the inherent indeterminacy of the problem: any number of small-scale weather sequences may be associated with a given set of larger-scale values. Downscaled climate changes are simulated by adjusting or varying the parameters of the weather generators, in a manner consistent with dynamically simulated or otherwise assumed larger-scale climate changes. Two main approaches for such parametric adjustments have been developed, namely changes in the daily weather generator parameters based on imposed or assumed changes in the corresponding monthly statistics, and day-by-day changes to the generator parameters that are controlled by daily variations in simulated atmospheric circulation. These methods are reviewed here, and perspectives on their relative merits are offered. WIREs Clim Change 2012 DOI: 10.1002/wcc.167 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

When a correlation-based circulation pattern classification was applied to daily 700 hPa heights for 25 summer seasons, and the circulation types were related to surface temperature and precipitation for the Lake Superior basin, within-type variability was found to be high. Regarding temperature, the difference between warm and cold days of a type is a positive height anomaly centred to the east of the lake, which is very similar to the height anomaly for winter temperatures identified in an earlier study. The difference between wet and dry days of a type is a pattern quite unlike that for temperature. It is a dipole pattern consisting of a negative anomaly to the northwest of the lake and a positive anomaly to the east and southeast. These small-scale circulation components were missed by the correlation-based classification because they are much smaller than the differences in height between circulation types. Regression models, relating monthly mean temperature anomalies to circulation type frequencies, produced results comparable to those obtained for winter temperature. For precipitation, the variance explained by the regression models is only half that obtained for temperature. Two approaches were used to reduce within-type variability and to improve the regression results: the division of the first few circulation types into warm/cold and wet/dry subtypes on the basis of differences in 700 hPa vorticity (an approach introduced in the earlier paper), and a modified correlation-based circulation pattern classification. The modification consisted of raising the correlation threshold for a few selected grid-points to capture the small-scale circulation component and also, of lowering the threshold for the comparison between maps and map sectors in order to minimize the number of unclassified days. Of the two approaches used to reduce within-type variability, the modified classification scheme produced superior results. In particular, the variance in precipitation explained by the regression models is about 30% higher than that achieved using vorticity to create subtypes. Copyright © 2000 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

This study analyzes the synoptic‐scale circulation patterns favorable for regional extreme precipitation events over southwest China (SWC) from 1979 to 2018 occurring during the rainy seasons. The whole SWC is regionalized into two subregions, western SWC and eastern SWC, according to the spatial distribution of two extreme precipitation indices. Furthermore, the atmospheric patterns associated with the independent regional extreme precipitation events (REPEs) that occurred over the two subregions are categorized into two types using k‐means clustering. For type 1, a Rossby wave train originating from the Northeast Atlantic almost a week before REPEs leads to an anomalous low over the eastern Tibetan Plateau (TP), inducing upper‐troposphere divergence and ascending motion over SWC. Moreover, anomalous convective activities over India and the Bay of Bengal (the enhanced and westward‐extended western Pacific subtropical high) are critical precursors of REPEs over western (eastern) SWC. For type 2, an anomalous high is developed over the Ural Mountains at least a week prior to REPEs. The subsequent anomalous low over Lake Baikal and eastward‐shifted South Asian high are conducive to forming updrafts over SWC. An anomalous anticyclone at the middle‐to‐lower troposphere south of the TP is the main moisture contributor. Discrepancies in the zonal location of the Lake Baikal low and the strength of the Ural Mountain high, as well as the intensity of atmospheric circulation anomalies at low latitudes, are the major differences between the type 2 events occurring in western and eastern SWC. Key Points: Two types of atmospheric circulation anomalies are favorable for extreme precipitation events over southwest China during rainy seasonsRossby wave trains from the Northeast Atlantic and the Ural Mountains are critical precursors of the extreme precipitation eventsThe low‐latitude atmospheric circulation anomalies mainly determine the spatial differences and the extremeness of the events [ABSTRACT FROM AUTHOR]

Surface albedo over the ice‐covered polar ocean is decreased in a highly idealized numerical experiment, which leads to stronger (weaker) warming at high (low) latitudes, and forms Arctic amplification. With stronger warming at both high and low latitudes, the meridional temperature gradient decreases (increases) at midlatitudes (subtropical regions). A cyclonic wind anomaly appears and results in a weak Kuroshio current and warm interdecadal Pacific Oscillation phase. In response to Arctic‐amplified‐warming, the subtropical high weakens, leading to summer monsoon anomaly on its southside and increased westward transport of water vapor, resulting in a seesaw pattern: dry (wet) conditions in summer in North China (southwest United States, SWUS). In winter, the East Asian trough (North American high) decreases and induces decreased (increased) cold air transport to North China (SWUS) in response to Arctic‐amplified‐warming, which makes rain unlikely (likely) and exhibits a seesaw pattern. Moisture convergence always appears in a warmer SWUS winter, and increases precipitation there, which strengthens (counteracts) the precipitation anomaly led by the North American high in a warm (cold) interdecadal Pacific Oscillation phase. It may even shut down the seesaw pattern in winter in the cold interdecadal Pacific Oscillation phase. Plain Language Summary: Polar warming led by smaller surface albedo decreases oceanic circulation and oceanic heat transport while enhancing atmospheric circulation and atmospheric heat transport, resulting in global warming, which could also be achieved by increased carbon dioxide (CO2) forcing. However, there are many differences between the midlow latitude climate response to polar albedo forcing and that to increased CO2 forcing. (1) In polar albedo forcing‐induced global warming, North China becomes drier, and the southwest United States becomes wetter, which is opposite to the results in the increased CO2‐induced global warming. Both results suggest a seesaw pattern of precipitation variability between North China and the southwest United States under climate change. (2) The seesaw pattern also appears in different seasons. In summer, the seesaw pattern is maintained by subtropical high. The summer monsoon determines the water vapor distribution. In winter, the seesaw pattern is maintained by wave‐flow interaction, which maintains synchronous variations between the East Asian trough and North American high. (3) Moisture convergence in winter southwest United States (under global warming) enhances local precipitation. As a result, it strengthens the seesaw pattern in this study, while it may shut down the seesaw pattern in increased CO2‐induced global warming. Key Points: Decrease the surface albedo over the polar ocean could achieve global warming and Arctic amplification without increasing the CO2 concentrationIn response to polar warming, a seesaw of precipitation variability between North China (dry) and the southwest United States (wet) appearsMonsoon and quasi‐stationary planetary wave are the key factors in maintaining the seesaw pattern in summer and winter, respectively [ABSTRACT FROM AUTHOR]

Cenozoic atmospheric circulation, climatic changes, sedimentation and weathering over the Indian sub‐continent were mainly influenced by the northward drift of the Indian Plate, the shrinking Paratethys, India‐Asia collision and the rise of the Himalayas. This study is aimed at exploring the fluvial sedimentary record of the north‐west part of the Himalayan Foreland Basin to interpret weathering and pedogenesis during early Oligocene to Mid‐Miocene time. Palaeopedological investigation of a 3.1 km thick succession from Kangra sub‐basin of the Himalayan Foreland Basin shows that the lower 2 km part of the succession is characterized by the red (10R hue) and the upper 1.1 km part of the succession by the yellow (2.5Y hue) palaeosols with varying intensity of weathering and pedogenesis. The association of sedimentary rocks and pedogenic expression in palaeosols indicate four (Type‐A to Type‐D) pedofacies in the entire Oligocene–Miocene succession. The pedofacies are defined by a decrease in the intensity of palaeopedogenic development from strongly‐developed palaeopedofeatures in Type‐A, moderately‐developed palaeopedofeatures in Type‐B, weakly‐developed palaeopedofeatures in Type‐C and to the only incipient stage of palaeopedogenesis in Type‐D pedofacies. The palaeolatitudinal shift during the convergence of the Indian Plate played a major role in weathering and palaeopedogenesis with the inception of seasonality during the early Oligocene, which is demonstrated by the formation of the red palaeosols with pedogenic CaCO3 and vertic features in tropical conditions. The transition to yellow palaeosols at about 20 Ma is marked by increased humidity, rapid aggradation, pronounced uplift and enhanced erosion of the hinterland. These yellow palaeosols are characterized by the abundance of weakly‐developed Bw and Bss horizons, pure clay pedofeatures and absence of any pedogenic CaCO3 during short pedogenic intervals in subtropical conditions. [ABSTRACT FROM AUTHOR]

Antarctic snowfall consists of frequent clear‐sky precipitation and heavier falls from intrusions of maritime airmasses associated with amplified planetary waves. We investigate the importance of different precipitation events using the output of the RACMO2 model. Extreme precipitation events consisting of the largest 10% of daily totals are shown to contribute more than 40% of the total annual precipitation across much of the continent, with some areas receiving in excess of 60% of the total from these events. The greatest contribution of extreme precipitation events to the annual total is in the coastal areas and especially on the ice shelves, with the Amery Ice Shelf receiving 50% of its annual precipitation in less than the 10 days of heaviest precipitation. For the continent as a whole, 70% of the variance of the annual precipitation is explained by variability in precipitation from extreme precipitation events, with this figure rising to over 90% in some areas. Plain Language Summary: The Antarctic ice sheet is extremely important because of its possible contribution to sea level rise and through the climate records than can be reconstructed using chemical signals locked in the ice. The mass of the ice sheet is constantly changing because of the ice gained by snowfall and the loss of ice at the margins via iceberg calving and melt through contact with relatively warm water masses. The amount of snow falling on the Antarctic is highly variable and dependent on the meteorological conditions over the Southern Ocean and the penetration of marine air into the interior. We show that extreme snowfall events, defined at the heaviest 10% of daily precipitation amounts, contribute a high percentage of the annual snowfall and are the main factor controlling the year‐to‐year variability of snowfall across the continent. This has implications for the reconstruction of past climate records using data from ice cores and the selection of future ice core drilling sites. Key Points: Extreme precipitation events explain 70% of the interannual variance of Antarctic snowfallExtreme precipitation events are particularly important over western West Antarctica and on the Ross and Amery Ice ShelvesTropical climate variability is important in modulating the frequency of extreme precipitation events in the West Antarctic sector [ABSTRACT FROM AUTHOR]

Regional precipitation responses to land warming are separated from other aspects of CO2 forcing using idealized atmosphere‐only climate model experiments. Land warming is crucial in determining the regional responses to direct CO2 forcing and the plant physiological effect and partially mitigates the response to sea surface temperature (SST) warming. The plant physiological effect causes large reductions in transpiration over forest regions but also produces significant land warming which increases moisture convergence in tropical forest regions, opposing transpiration‐related reductions in precipitation. The balance between these two large terms differs by region and explains why some regions actually experience increased precipitation in response to reduced transpiration. Regional circulation changes driven by increased CO2 atmospheric radiative heating appear to be mainly related to land‐sea differences in water cycle adjustments rather than spatial variations in radiative heating. This drives increased rainfall in several monsoon regions, particularly over West Africa. SST warming generally leads to reduced precipitation over land and increases over the oceans, while the associated land warming enhances moisture convergence and precipitation over land. However, the combination of SST and land warming effects is highly nonlinear in the tropics, which is likely to be because of strong coupling between precipitation change and land warming. Plain Language Summary: Land is warming faster than the oceans in response to climate change. A new set of climate model experiments have been used to determine how this enhanced land warming could affect wind and rainfall patterns. In general, land warming drives winds that blow from ocean on to land, similar to a very large‐scale sea breeze. On its own, this would tend to increase rainfall over land. The expected overall rainfall change varies across different regions and depends on the balance between the effect of land warming and other aspects of climate change such as warming of the atmosphere and oceans and changes to water loss from plants. In several monsoon regions, the impact of direct heating of the atmosphere from increased carbon dioxide plays a very important role in rainfall change. In tropical forest regions, reduction in transpiration from plants in response to increased carbon dioxide has a large effect on the whole regional water cycle. Key Points: A new set of AGCM experiments are used to isolate the effect of land warming from other aspects of CO2 forcing and warmingLand warming is crucial in determining the precipitation pattern responses to direct CO2 forcing and plant physiological forcingThe combination of SST and land warming is strongly nonlinear in the tropics, though less so in the extratropics [ABSTRACT FROM AUTHOR]

Changes in the relationship between interannual variation of spring (March–April–May) surface air temperature (SAT) over eastern Eurasia (SAT_EA) and Eurasian snow during 1972–2009 are investigated. The results show that the interannual variation in SAT_EA is significantly correlated with Eurasian snow cover anomalies (SCA) over two key regions, which include the western (SCAW) and eastern (SCAE) parts of the Eurasian continent. A pronounced climate shift of SAT_EA is observed around the late 1980s, and therefore, the data are divided into two subperiods, that is, 1972–1987 (P1) and 1988–2009 (P2). Examinations show that the relationship between SAT_EA and SCAW is impacted by the Arctic Oscillation. In contrast, the relationship between SCAE and the SAT_EA is Arctic Oscillation independent and is significantly increased from P1 to P2. Further analysis shows that the increased correlation between SAT_EA and SCAE from P1 to P2 cannot be well explained by the snow‐related surface heat flux. A wave train‐like anomalous circulation plays an important role in enhancing their relationship through intensified wind‐induced heat advection in P2, which causes reduced snow and increased SAT_EA. A lead‐lag regression analysis of the SCAE and the circulation anomalies indicates that the changes of the SCAE and SAT_EA are mainly responses to atmospheric circulation anomalies that occur 2 months before spring. Numerical experiments that use a linear baroclinic model indicate that the snow anomalies around Lake Baikal may impact the variation of SAT_EA through modulating atmospheric circulation over the East Asia‐North Pacific area. Key Points: The relationship between interannual variation of spring SAT and snow over eastern Eurasia is significantly strengthened after 1987Atmospheric circulation anomalies play an important role in enhancing the SAT‐snow relationshipThe eastern Eurasian snow and SAT anomalies are mainly the response of the circulation anomalies, but positive feedback from snow may also exist [ABSTRACT FROM AUTHOR]

To diagnose the influence of sea surface temperature (SST) biases on temperature and precipitation patterns in the western United States, we analysed atmospheric and coupled global climate model (GCM) simulated output from the Coupled and Atmospheric Model Intercomparison Project versions 3 and 5 (CMIP3, AMIP3, CMIP5, and AMIP5). We further analyse the impact of SST biases in regional climate modelling simulations. CMIP3 and CMIP5 multi‐model ensembles show systematic warm SST biases offshore of California and the Baja California Peninsula (Baja) region, with ensemble mean SST biases of the order of ~3–5 °C. Throughout the western United States, 75% of all models in CMIP3 and CMIP5 exhibit wet precipitation biases and corresponding cold biases in surface temperature. The CMIP5 ensemble shows on average a stronger and more consistent relationship between Baja SST biases and precipitation over the west compared to the CMIP3 ensemble. We attempted to isolate the atmospheric response to regional SST biases using a regional climate model (RCM) based on the Weather Research and Forecasting model with a 36 km grid size. The RCM was driven with the CMIP3‐CCSM3 as boundary conditions with and without corrections of simulated SSTs. Results from RCM simulations further confirm that SST biases impact climate regionally and propagate over the western United States and can explain up to 80% of wet precipitation biases. Our regional GCM comparison and RCM experiment assess the robustness of model estimates of climate mean states and constitute an often neglected prerequisite for characterizing how errors transfer from GCM to regional downscaling modelling frameworks and how they could potentially affect downscaling application and impact studies. This study shows how the coupled global climate models SST biases impact climate regionally and propagate over the western United States and can explain up to 80% of wet precipitation biases. We performed a regional GCM comparison and RCM experiment that assess how errors transfer from GCM to regional downscaling modelling, potentially affecting downscaling application and impact studies. Figure shows RCM wet precipitation differences over SW United States resulting from isolating the effect of using raw (biased) GCM SST minus bias‐corrected SSTs. [ABSTRACT FROM AUTHOR]

The dominant modes wintertime precipitation in northwest China (NWC) and the possible causes are investigated during the period 1961–2013 in the inter‐annual timescale, as winter climate condition could greatly affect local economic development and people's lives. The analysis of this study is divided into three parts. First, the spatiotemporal variability of dominant modes wintertime precipitation is described by an empirical orthogonal function (EOF) method. The atmospheric circulation anomalies associated with wintertime precipitation variations are then discussed through regression and composite analysis. Third, the relationships between wintertime precipitation and sea surface temperature (SST) anomalies are investigated. The results indicate that the leading mode (EOF1) shows a uniform sign in the entire region, and the second mode (EOF2) exhibits a zonal‐dipole pattern; they account for 25.6 and 15.7% of the total variance, respectively. The atmospheric circulation anomalies EOF1 closely related to is the Eurasian (EU) teleconnection pattern. Years when a negative phase of EU pattern occurs tend to be rainy with anomalous southerly transporting water vapour from low‐latitudes and profound ascending motion anomalies. Atmospheric circulation anomalies associated with the second mode resemble the Arctic Oscillation (AO) pattern. AO pattern influences EOF2 precipitation variations through the anomalous circulations over Mongolia and western Europe. The sea surface temperature (SST) anomalies related to EOF1 show an El Niño‐Southern Oscillation (ENSO) like pattern, which may modulate the wintertime precipitation mode through the western North Pacific anticyclone. The EOF2 mode has a close relationship with a tripole SST anomaly mode in the North Atlantic Ocean. This SST pattern is likely to influence wintertime precipitation by modulating the North Atlantic Oscillation (NAO). The results of this study could be beneficial for wintertime precipitation prediction and the decrease of economic losses in NWC and may also provide useful references for other areas with similar climatic features such as the central Asia. (a, c) EOF1 and (b, d) EOF2 of inter‐annual wintertime precipitation variations for 1961–2013 in NWC. (a, b) Regression maps on the normalized time series (unit: mm); (c, d) normalized time series. [ABSTRACT FROM AUTHOR]

Precipitation falling in the Snowy Mountains region of south‐east Australia is a critical resource—providing water for hydroelectricity, as well as irrigated agriculture and environmental flows throughout the economically important Murray River system. Improved understanding of the drivers of precipitation variability is therefore a key research aim. Focussing on synoptic types responsible for delivering precipitation ≥10 mm per day, an analysis is presented of the large‐scale atmospheric circulation drivers (“teleconnections”) of seasonal synoptic type frequency using cross‐wavelet and boosted regression tree methods. Results demonstrate that relationships are not stationary over the period 1900–2012, and complex interactions between teleconnections and synoptic atmospheric circulation drive precipitation variability. Importantly, we demonstrate that teleconnections do not act in isolation. Relationships with the tropical Pacific Ocean are shown to be key drivers of synoptic types associated not only with the dominant tropical moisture pathways to the Snowy Mountains, but also with extra‐tropical sources. Tropical sea surface temperatures are therefore shown to drive synoptic type frequency and facilitate the dominance of synoptic types with tropical moisture sources, most notability since the 1950s. [ABSTRACT FROM AUTHOR]

ABSTRACT: During the last few decades, weather circulation type classifications (CTCs) have been widely used to gain insight into processes at the synoptic scale, but also for studying the relationship between atmospheric circulation and surface climate variability. This study aims to evaluate the best performing CTCs based on COST733 software for the stratification of daily ground‐level precipitation and surface air temperature across Italy by means of four statistical metrics. Six classification methods belonging to the four COST733 groups (threshold‐based, PCA‐based, leader algorithms and optimization algorithms) were investigated on 32 and 26 data time series derived from Italian weather stations for daily mean temperature and daily mean precipitation, respectively. CTCs were computed using gridded mean sea level pressure and geopotential height at 500 hPa derived from the NCEP Reanalysis 2 dataset between 1979 and 2015 and tested on three different numbers of classes (8/9, 11/12 and 18 circulation types). Evaluation metrics showed an evident seasonal variability and high‐spatial heterogeneity reflecting the geographical complexity of the Italian territory. The study points out that the best classification, both for temperature and precipitation, is strongly dependent on the classification variable (mean sea level pressure and geopotential height at 500 hPa) showing relevant differences between surface temperature and precipitation. A low number of circulation types (8/9) resulted as the most appropriate grouping for the Italian domain and the Principal Component Transversal and Simulated Annealing were the best performing classification procedures for ground‐level precipitation and temperature stratification, respectively. [ABSTRACT FROM AUTHOR]

This study presents (1) the temporal variations and trends of monthly and daily temperature and precipitation extremes in Alaska, and (2) the synoptic-scale circulation patterns associated with these extremes. The analysis is based on daily station observations of maximum temperature, minimum temperature and precipitation from 1948-2012 as well as monthly average temperatures and precipitation from 1920-2012 from 13 Alaska climate divisions. The frequencies of daily and monthly temperature extremes show variability and trends over the past 50-90 years consistent with a warming climate in Alaska. This warming is superimposed on low-frequency variability attributed to the Pacific Decadal Oscillation. Unlike the temperature extremes, occurrences of heavy-precipitation extremes do not display a coherent signal through time. The changes do not appear to be linked with an overall increase in the variance of temperature or precipitation. Composite analysis of sea level pressure (SLP) anomalies associated with a representative sample of different daily and monthly temperature extremes across Alaska shows that temperature and moisture advection, subject to topographic and coastal influences, is a key driver of these events. Composite SLP fields for daily and monthly extremes are similar, especially in winter, indicating that monthly extremes represent the recurrence of daily extreme patterns during those extreme months. The SLP anomalies were also often reduced in magnitude in the summer events compared with winter, consistent with the lower variance of temperature and SLP during summer. [ABSTRACT FROM AUTHOR]

In this study, the stochastic deep convection parameterization of Plant and Craig (PC) is implemented in the Community Atmospheric Model version 5 (CAM5) to incorporate the stochastic processes of convection into the Zhang-McFarlane (ZM) deterministic deep convective scheme. Its impacts on deep convection, shallow convection, large-scale precipitation and associated dynamic and thermodynamic fields are investigated. Results show that with the introduction of the PC stochastic parameterization, deep convection is decreased while shallow convection is enhanced. The decrease in deep convection is mainly caused by the stochastic process and the spatial averaging of input quantities for the PC scheme. More detrained liquid water associated with more shallow convection leads to significant increase in liquid water and ice water paths, which increases large-scale precipitation in tropical regions. Specific humidity, relative humidity, zonal wind in the tropics, and precipitable water are all improved. The simulation of shortwave cloud forcing (SWCF) is also improved. The PC stochastic parameterization decreases the global mean SWCF from −52.25 W/m2 in the standard CAM5 to −48.86 W/m2, close to −47.16 W/m2 in observations. The improvement in SWCF over the tropics is due to decreased low cloud fraction simulated by the stochastic scheme. Sensitivity tests of tuning parameters are also performed to investigate the sensitivity of simulated climatology to uncertain parameters in the stochastic deep convection scheme. [ABSTRACT FROM AUTHOR]

ABSTRACT We examine secular changes and multidecadal climate variability on a seasonal scale in northern France over the last 500 years and examine the extent to which they are driven by large-scale atmospheric variability. Multiscale trend analysis and segmentation procedures show statistically significant increases of winter and spring precipitation amounts in Paris since the end of the 19th century. This changes the seasonal precipitation distribution from one with a pronounced summer peak at the end of the Little Ice Age to an almost uniform distribution in the 20th century. This switch is linked to an early warming trend in winter temperature. Changes in spring precipitation are also correlated with winter precipitation for time scales greater than 50 years, which suggests a seasonal persistence. Hydrological modelling results show similar rising trends in river flow for the Seine at Paris. However, such secular trends in the seasonal climatic conditions over northern France are substantially modulated by irregular multidecadal (50-80 years) fluctuations. Furthermore, since the end of the 19th century, we find an increasing variance in multidecadal hydroclimatic winter and spring, and this coincides with an increase in the multidecadal North Atlantic Oscillation ( NAO) variability, suggesting a significant influence of large-scale atmospheric circulation patterns. However, multidecadal NAO variability has decreased in summer. Using Empirical Orthogonal Function analysis, we detect multidecadal North Atlantic sea-level pressure anomalies, which are significantly linked to the NAO during the Modern period. In particular, a south-eastward (south-westward) shift of the Icelandic Low (Azores High) drives substantial multidecadal changes in spring. Wetter springs are likely to be driven by potential changes in moisture advection from the Atlantic, in response to northward shifts of North Atlantic storm tracks over European regions, linked to periods of positive NAO. Similar, but smaller, changes in rainfall are observed in winter. [ABSTRACT FROM AUTHOR]

The relationship between atmospheric blocking and extreme precipitation in summer in Romania during the period 1962-2010 is investigated. Percentile-based indices (R90p) for extreme precipitation events are calculated using data recorded at a large number of meteorological stations (98) covering the entire country. The dominant mode of variability of these indices has a monopolar structure and is related to two distinct atmospheric circulation blocking patterns. High frequency of blocking in the 0°-40°E sector is associated with high frequency of extreme precipitation events over Romania. This is due to enhanced synoptic scale activity associated with advection of relatively high potential vorticity from northeast towards Romanian region, as well as with enhanced synoptic scale activity in the Mediterranean region. Enhanced blocking activity in the 50°-70°E sector favours an eastward extension of Atlantic jet, and the associated instabilities are related to extreme precipitation events over large parts of central and Eastern Europe. We argue that these two distinct blocking patterns explain a substantial part of extreme precipitation variability in Romania during summer. [ABSTRACT FROM AUTHOR]

An annual ( July to June) precipitation reconstruction for the period AD 1760-2010 was developed from a Picea crassifolia regional tree-ring chronology from two sites in the northern mountainous region of the Hexi Corridor, NW China. This reconstruction explains 52.1% of the actual precipitation variance during the period 1951 to 2010. Spatial correlations with gridded land-surface data reveal that our reconstruction contains a strong regional precipitation signal for the Hexi Corridor and for the southern margin of the Badain Jaran Desert. Significant spectral peaks were identified at 31.9, 11.1, 8.0, 7.0, 3.2, 2.6 and 2.2 years. A large-scale comparison indicates that our reconstruction is more consistent with climate records of a Westerly-dominated Central Asia, and that the Westerlies have a greater impact on the precipitation in this region than the Asian summer monsoon. Our reconstructed precipitation series is significantly correlated with sea-surface temperature ( SST) in the tropical Atlantic Ocean (positive), the tropical Indian Ocean (positive), the western tropical Pacific Ocean (positive), and the western North Pacific Ocean (negative). The spatial correlation patterns between our precipitation reconstruction and SSTs of the Atlantic and Pacific Oceans suggest a connection between regional precipitation variations and the high-mid-latitude northern atmospheric circulations ( Westerlies and Asian summer monsoon). [ABSTRACT FROM AUTHOR]

Place-based data is required in wildfire analyses, particularly in regions of diverse terrain that foster not only strong gradients in meteorological variables, but also complex fire behaviour. However, a majority of downscaling methods are inappropriate for wildfire application due to the lack of daily timescales and variables such as humidity and winds that are important for fuel flammability and fire spread. Two statistical downscaling methods, the daily Bias corrected Spatial Downscaling (BCSD) and the Multivariate Adapted Constructed Analogs (MACA) that directly incorporate daily data from global climate models, were validated over the western US using global reanalysis data. While both methods outperformed results obtained from direct interpolation from reanalysis, MACA exhibited additional skill in temperature, humidity, wind, and precipitation due to its ability to jointly downscale temperature and dew point temperature, and its use of analog patterns rather than interpolation. Both downscaling methods exhibited value added information in tracking fire danger indices and periods of extreme fire danger; however, MACA outperformed the daily BCSD due to its ability to more accurately capture relative humidity and winds. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Extratropical and tropical influences on Tibetan Plateau severe and extreme dry and wet summer months are investigated focussing on the large-scale circulation and using results of the coupled climate model ECHAM5/MPI-OM. A pre-industrial control run and scenario runs for the 4th Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) are considered. Tibetan Plateau precipitation in months of wetness and drought is related to atmospheric circulation anomalies in the North-Atlantic/European sector and to sea surface temperature anomalies in the Tropics. Drought on the Tibetan Plateau is associated with a pronounced wave train bridging Eurasia from the North Atlantic to Asia. Increased transient eddy activity in the North Atlantic storm track has a more south-west to north-east orientation. This supports a high pressure anomaly over the eastern North Atlantic and Scandinavia which excites a cross Eurasian wave train reducing the moisture inflow to the Tibetan Plateau from the Arabian Sea. A concurrent warming in the tropical Indian Ocean increases the low level monsoonal westerlies deviating the moisture transport from the Bay of Bengal towards the Indochinese Peninsula and the Philippines. Wetness on the Tibetan Plateau is dominated by a cooling in the tropical oceans, whereas atmospheric flow is predominantly zonal in the extratropics of North America and Europe. Thus, moisture inflow can reach the Tibetan Plateau via the Arabian Sea, the Bay of Bengal and the mid-latitude westerlies. Future scenarios show little change of atmospheric flow composites for wetness and dryness; the Tibetan Plateau droughts increase by 10% for an A1B-scenario, while extreme wet summer months are reduced by approximately 1%. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Extreme events such as heat waves are emerging as a key facet of climate change, but to date, experiments on the impacts on plants are scarce. Experimental simulation of heat waves requires knowledge of regional heat wave characteristics, as plant responses depend heavily on meteorological conditions. We analysed nine Western European meteorological datasets, and found that heat waves occurring during the growing season in this region encompass more sunshine (+ 69%), lower precipitation (−78%) and a larger vapour pressure deficit (VPD) (+ 111%) compared with normal conditions. Possible consequences for plant responses are discussed, with emphasis on the likely seasonal variation of heat wave impacts. We explain why infrared heating (which typically increases VPD) is an appropriate technique for heat wave simulation. Finally, we advocate experiments to take into account the smaller nighttime compared with daytime temperature increases observed during heat waves, and the precipitation deficits before and during heat waves. [ABSTRACT FROM AUTHOR]

The Northern Hemisphere annular mode, also known as the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) is a dominant atmospheric mode in the Northern Hemisphere winter that influences climate fluctuations from the eastern seaboard of the United States to Siberia and from the Arctic to the subtropical Atlantic. After almost a century of scientific investigation, the fundamental mechanisms determining the evolution of the AO/NAO are not yet completely understood. The ocean is favored as the most likely forcing of atmospheric variability, given the time scales of oceanic circulation and its large heat capacity. Our analyses of snow cover, soil temperatures, zonal winds, and geopotential heights identify the effect of land–atmosphere interaction over Eurasia on Northern Hemisphere atmospheric circulation, explaining the predictive signal that links fluctuations of April–October snow cover with the following winter AO/NAO phases. [ABSTRACT FROM AUTHOR]

Extreme climate events in China, including its 10 main river basins, were projected under global warming of 1.5 °C–4 °C using the latest version of a regional climate model (RegCM4) for dynamical downscaling, driven by the outputs of four global climate models. Firstly, evaluation indicated that the simulations satisfactorily reproduced the spatial distribution of temperature extremes and, although with lower performance, the spatial distributions of precipitation extremes were generally captured. Additionally, a better description was achieved over areas with complex terrains by using RegCM4. Next, the model was used to make projections under global warming of 1.5 °C–4 °C. Warm extremes were projected to increase, while cold events were projected to decrease, particularly in northern and western China. In addition, the number of wet days was projected to increase in the northern part of China, and to decrease in the southern part. The maximum consecutive five‐day precipitation and the precipitation intensity were projected to increase significantly throughout China, while the consecutive number of dry days was projected to significantly decrease in northern and western China. The changes of atmospheric moisture content and atmospheric circulation lead to the increase of extreme precipitation. Specifically, the increases in the indices of wetness were closely correlated with the summer precipitation, wind, moisture flux convergence, and surface specific humidity, while the consecutive number of dry days was related to the change in summer moisture flux convergence and precipitation in dry seasons. Notably, the magnitude of the changes in extremes events was projected to increase as the warming target increases. Key Points: A better description was achieved over areas with complex terrains by using RegCM4Model uncertainty in a high‐resolution ensemble of extremes was quantifiedThe magnitude of changes was projected to enhance as the global warming target increases [ABSTRACT FROM AUTHOR]

The mid‐Piacenzian (~3.3–3.0 Ma), which was characterized by high pCO2 (~400 ppm) and global surface air temperatures that were 1.84–3.60 °C above pre‐Industrial levels, provides clues to the likely changes in atmospheric dynamics in a future climate affected by anthropogenic warming, although its suitability as an analogue of the future climate has yet to be assessed. This study investigates the extent to which the dynamics of the East Asian summer monsoon during the mid‐Piacenzian can aid our understanding of East Asian summer monsoon behavior in the Extended Concentration Pathway version 4.5 scenario, using water vapor and moist static energy equations. The temperature‐dependent large‐scale moisture transport explains the similar pattern of precipitation increase in the two climates, whereas regional patterns of vertical motion differ significantly. Two of the main terms of the moist static energy equation control the changes in regional dynamics relative to the pre‐Industrial period. These terms relate to zonal advection of stationary eddy dry enthalpy by the mean zonal wind and meridional stationary eddy velocity over East Asia. Topographic differences between the two cases have a negligible effect on regional precipitation. Plain Language Summary: The mid‐Piacenzian (~3.3–3.0 Ma, mid‐Pliocene warm period) is the most recent warm period in Earth's history, characterized by high pCO2 levels (~400 ppm) and global warming (increase of 1.84–3.60 °C above pre‐Industrial levels). Thus, it is of interest to compare this period with atmospheric dynamics responses to anthropogenic warming in a future climate, especially in terms of the monsoon. This study investigates the extent to which the dynamics of the East Asian summer monsoon during the mid‐Piacenzian aid our understanding of the future behavior of the monsoon according to the Extended Concentration Pathway version 4.5 scenario. The analyses are based on water vapor and moist static energy equations. It is shown that increases in large‐scale moisture transport under thermal control in the two warm climates enhance East Asian summer monsoon precipitation. Regional differences in East Asian summer monsoon precipitation arise from different contributions of dynamic processes, primarily zonal warm advection by zonal wind and meridional stationary eddy velocity. Topographic differences between the two cases have a negligible effect on regional precipitation. Key Points: A comparison of summer monsoon dynamics over East Asia for the mid‐Piacenzian and the ECP4.5 scenario reveals both large‐scale similarities and regional differencesLarge‐scale similarity in moisture transport under thermal control and regional differences in vertical motion regulated by moist static energyNegligible effect of slight topographic difference on regional precipitation [ABSTRACT FROM AUTHOR]