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This paper utilizes reanalysis data and statistical methods to elucidate the physical mechanisms of intraseasonal variations of precipitation over southern China during the boreal winter, as well as the two primary factors influencing these variations. Anomalous southerly (northerly) wind over southern China will result in the strong moisture convergence (divergence) in enhanced (suppressed) scenarios, and the stronger positive (negative) horizontal advection of absolute vorticity at upper troposphere induces the anomalous ascending (descending) motion in enhanced (suppressed) scenarios. The Madden–Julian oscillation (MJO) in the tropics and a wave train over the North Atlantic and Eurasia with four activity centres in the mid–high latitudes (referred as NAE‐wave train) are the two primary factors that modulate the intraseasoanl precipitation over southern China. The intraseasonal circulation induced by MJO and NAE‐wave train exhibits distinct features, resulting in different physical mechanisms of their influences. The moisture flux divergence anomalies over southern China associated with MJO mainly stem from the meridional moisture convergence, whereas the meridional moisture advection is the first contributor in the influence of NAE‐wave train. The anomalous vorticity advection at upper troposphere associated with MJO is primarily influenced by the meridional advection, but that associated with NAE‐wave train is dominated by the zonal advection. Anomalous precipitation induced by MJO is concentrated mainly over South China, while that caused by NAE‐wave train is primarily located in the mid–lower Yangtze River basin. Therefore, different phases locking of MJO and NAE‐wave train could lead to various precipitation anomalies over southern China. [ABSTRACT FROM AUTHOR]

This paper uses monthly surface air temperature (SAT) data from the Climatic Research Unit dataset and the Coupled Model Intercomparison Project phase 6 multimodel ensemble simulations to investigate the variations in the annual‐mean and four seasons SAT across the Eurasian and North Africa landmasses and the possible causes. The SAT over multiple timescales has significant seasonal and regional differences. The trend, variance of decadal variation (DV), and variance of interannual variability (IV) show that the differences between Siberia and mid‐low latitudes are much larger in winter and spring than in summer and autumn. The SAT exhibits a robust warming trend over Siberia in winter (0.21–0.42°C·decade−1) than over mid–low latitudes in summer (<0.07°C·decade−1). The cause is the combined diversity effects of greenhouse gases (GHG) and anthropogenic aerosols (AA) in four seasons over different regions. The warming trend of Siberia in winter is affected by the combination of strong warming effect by GHG and the weak cooling effect by AA, and the trend of mid–low latitudes in summer is opposite. The leading modes of the DV show a consistent spatial pattern over the whole Eurasia in four seasons while the IV show a meridional dipole pattern across 40°N except in summer. The internal climate variability is the main driver of the SAT IV and DV, but the effect of anthropogenic activity and natural forcing may reinforce the IV and DV in some regions. The combined role of GHG and AA forcings can significantly enlarge the DV in many parts of Eurasia, and the AA and natural forcing have significant effect on the IV in the high latitudes. [ABSTRACT FROM AUTHOR]

Spring Arctic Oscillation (AO) has been revealed to exert a great impact on the Northern Hemispheric climate; however, its seasonal prediction skill has been limited so far. In this paper, we find that the dominant mode of the winter 500‐hPa geopotential height anomalies over the mid‐latitude Eurasia has a close connection with the succeeding spring AO. The analysis on the physical processes indicates that the troposphere–stratosphere interaction plays an important role in the connection between the two. This predominant atmospheric mode in the mid‐latitude Eurasia during winter can change the vertical wave activity and lead to an anomalous stratospheric polar vortex. Thereafter, the signal of the anomalous stratospheric polar vortex propagates downward to troposphere in the subsequent spring, consequently inducing the anomalous AO pattern in the troposphere. The results in this study imply that this previous winter leading atmospheric mode over the mid‐latitude Eurasia may supply a potential source for a spring AO's prediction. [ABSTRACT FROM AUTHOR]

The regional amplitude and phase characteristics of surface (2 m) air temperature (SAT) annual cycle (AC) over the Northern Hemisphere land area are analysed by the clustering method for the period 1953–2018. The five clusters are found in the nonlinear changes of AC amplitude and the six clusters are found in the AC phase. The spatial distributions of clusters are not the same for amplitude and phase, but the similarity is that both the amplitude and phase have remarkably different trends in the mainland of Eurasia and North America, even though these two regions locate over the similar latitudinal zone. Descending trends of AC amplitude are found for the whole period 1953–2018 in most areas, except in and around Greenland. However, when checking the nonlinear variation and making a piece‐wise linear fit, the abnormal increasing trend (stronger seasonality) appears in the major part of Eurasia after the year 1990. The comparisons of surface radiation fluxes in Eurasia and North America indicate that the long‐term reduction of the reflection and absorption of clouds and aerosols with the declined surface albedo after 1980–1985 may lead to the amplitude amplification after 1990 in Eurasia. In contrast, the variation of surface radiation in North America remains unchanged, where the decreasing trend of amplitude may result from other causes. The overall phase trend is increasing (toward earlier season), but in North America after 1990, the phase shift becomes delayed. The phase variations are correlated to North Atlantic Oscillation (NAO) cold season index over almost all regions, especially in Europe. [ABSTRACT FROM AUTHOR]

The two dominant patterns of the winter (December–February) intraseasonal surface air temperature (SAT) over central Asia is derived by empirical orthogonal function analysis, with the first (mode 1) featuring a regional monopole and the second (mode 2) featuring a northwest–southeast‐orientated dipole. Mode 1 is characterized with warmer (colder) Arctic and colder (warmer) Eurasia along with an anomalous high (low) over the Ural Mountains, while mode 2 is characterized with northwest–southeast dipole over Eurasia along with wave train‐like atmospheric circulation anomalies from the western Atlantic to Asia. Whether the two intraseasonal modes are modulated by lower‐boundary forcing is then investigated, and the results suggest that mode 1 is significantly modulated by sea ice concentration over the Greenland Sea, but by central‐Pacific ENSO for mode 2. Finally, the underlying mechanisms are diagnosed, and the results suggest that the diabatic heating related with decreased sea ice in Greenland Sea induce a positive height anomaly over Urals which favours the formation of Ural blocking and therefore tends to intensify the occurrence of mode 1. Also, central‐Pacific El Niño excites the Pacific–North American teleconnection, which alters North Atlantic subtropical jet extension, favours intensified energy conversion to intraseasonal wave train and subsequently intensifies the occurrence of mode 2. This study highlights the joint role of Arctic sea ice and the SST in the tropical central Pacific. [ABSTRACT FROM AUTHOR]

Previous studies indicated that El Niño–Southern Oscillation (ENSO) significantly impacts the zonal shift of the South Asian High (SAH) in boreal summer. This analysis reveals that the influence of ENSO on the zonal shift of the SAH has experienced a significant interdecadal weakening around the early 1980s. Specifically, ENSO has a significant relation with the SAH's zonal shift before the early 1980s. However, after the early 1980s, the impact of the ENSO on the SAH is weak. We further examined the physical processes for the interdecadal change of the ENSO–SAH relation. It is indicated that interdecadal change of relationship between ENSO and SAH zonal shift is attributable to change in the connection between ENSO and Indian summer monsoon (ISM). Before the early 1980s, ENSO could exert significant impacts on the ISM and lead to significant condensational latent heating anomalies around the northern Indian Peninsula. The atmospheric heating anomalies around the northern Indian Peninsula trigger an atmospheric wave train extending eastward from North Africa toward the Iranian Plateau (IP), which further leads to changes in the zonal location of the SAH. Hence, the ENSO exerts significant impacts on the summer SAH zonal shift. By contrast, after the early 1980s, ENSO had a weak impact on the ISM and could not lead to apparent atmospheric heating anomalies over IP. As such, ENSO has a weak effect on the SAH zonal shift. Further analysis indicates that interannual variation of the SAH zonal shift is related to an atmospheric wave train over mid–high latitudes of Eurasia after the early 1980s. [ABSTRACT FROM AUTHOR]

There is a lack of studies elucidating the characteristics of interannual variability in different models, especially for northern Eurasia. Therefore, spatial patterns of interannual variability in summer precipitation over northern Eurasia across 15 models of Coupled Model Intercomparison Project Phase 5 (CMIP5) were investigated using empirical orthogonal function (EOF) analysis and cluster analysis. The spatial patterns of EOF1‐3 obtained from the models exhibited similar features across the models. The spatial pattern characteristics of the interannual variability of models were similar to those of the actual observations. However, their contribution rates and the order of magnitude of the EOFs in each model differ among models and from observations. Despite the similarity between the patterns of the EOF in the models and the observations, the atmospheric circulations causing the pattern differed in the models and actual observations, resulting in uncertainty in the models. This indicates that in the analysis of extreme events and their impact, the reproducibility and uncertainty of climate models with regard to interannual variability need to be adequately evaluated. In addition, similar to many climate models, the spatial pattern of interannual variability, which is different from any of EOF1‐3 for the observations, has been more strongly represented than the actual observations. Clarification of the factors governing the common but unsuitable variability across models may be expected to decrease the uncertainty of the models in terms of interannual variability. [ABSTRACT FROM AUTHOR]

The relationship between the spring precipitation in the middle and lower reaches of the Yangtze River valley and the North Atlantic Oscillation in the preceding winter is investigated based on data diagnosis. Through affecting the dynamics and thermodynamics in near‐surface atmosphere over Eurasia, the North Atlantic Oscillation in January can exert significant influence on the Eurasian snow cover to form a dipole pattern of snow anomalies. The dipole pattern of snow anomalies stimulates the Rossby wave train in the middle and high latitudes of the Northern Hemisphere in the following spring. Two activity centres associated with the wave train, one in the middle latitudes of Northwest Pacific with an anomalous anticyclone circulation and another in Mongolia with an anomalous cyclone circulation, bring the water vapour from the south and converge over the middle and lower reaches of the Yangtze River, resulting in the excessive precipitation over there. The results indicate that the North Atlantic Oscillation in January can act as a precursor signal for predicting the spring rainfall anomalies in the middle and lower reaches of the Yangtze River. [ABSTRACT FROM AUTHOR]

Temporal evolution of relationships between surface temperature and modes of low‐frequency circulation variability is compared between five reanalyses (20CRv3, 20CRv2c, ERA‐20C, JRA‐55, and NCEP‐1) in winter from 1958 to 2010 over the northern Extratropics. The relationships are evaluated using 15‐year running correlations between temperature anomalies (from the CRU TS v. 4.03 data set) and the intensity of circulation modes (detected in 500 hPa heights by rotated principal component analysis). The analysis, utilizing mean absolute differences between time series of running correlations, points to the large agreement between ERA‐20C, JRA‐55, and NCEP‐1. Circulation modes in those reanalyses are highly similar, which in turn lead to the agreement in temporal development of correlations. In contrast, relationships of some circulation modes with temperature in 20CRv3 and 20CRv2c differ due to differences in the position, strength, and shape of the action centres. This concerns circulation modes located over Eurasia and the Atlantic, mainly North Atlantic Oscillation and Eurasian mode type 1 (EU1). Composite maps, calculated for all running periods, indicate dissimilar temporal evolution of action centres in both 20CR reanalyses. Increased differences in correlations occur mainly during periods when the position and strength of action centres diverge the most. Relationships of circulation modes located over North America and the Pacific with temperature share large resemblance between all reanalyses, including those from the 20CR family. Differences appear to be smaller in 20CRv3 compared to the preceding version, 20CRv2(c), suggesting that the development of the 20CR reanalysis has succeeded in correcting and diminishing biases. [ABSTRACT FROM AUTHOR]

The observed spatial–temporal variations in daily snowfall over the Eurasian continent from 1980 to 2019 are explored in this study. The results show that the snowfall amount and its number of days are mainly centred in the high latitudes and high terrain regions of the Eurasian continent (such as North Asia), while they are relatively small in Southern Europe, Central Asia and East Asia. During the past decades, a decreasing trend can be observed for snowfall amounts and the numbers of days over most regions of Eurasia, while increases are clear in terms of the mean intensity. In response to climate warming in recent decades, the first date of snowfall occurrence postponed and the ending date advanced across the Eurasian continent. Furthermore, the change characteristics of the different grades of snowfall are also investigated across this region, including light snowfall, moderate snowfall, heavy snowfall and snowstorm. The light snowfall and number of days show a decreasing tendency, which mainly results in a decrease in the total snowfall amount and number of days. However, the amounts of heavy snowfall and snowstorms and their numbers of days are significantly increased, implying that the Eurasian continent has experienced increased severe snowfall events during recent decades. [ABSTRACT FROM AUTHOR]

Many studies based on observed data indicate the inverse relationship between the Eurasian snow cover/depth and the Indian summer monsoon rainfall (ISMR). The purpose of this study is to confirm the inverse snow-ISMR relationship by using the observed snow depth data as boundary conditions in the spectral general circulation model (GCM) of Indian Institute of Technology, Delhi (IITD), and to examine the influence of Eurasian snow depth on the monsoon circulation. The original model belonging to the European Centre for Medium range Weather Forecasts (ECMWF) at resolution T21 has been modified extensively to a higher resolution of T80L18 at IITD. A two-dimensional Lanczos digital filter has been used to represent the orography realistically. The Historical Soviet Daily Snow Depth (HSDSD) version II data set has been used for conducting sensitivity experiments using the above model. Two sensitivity experiments have been designed, corresponding to two contrasting cases: one with high Eurasian snow depth in spring followed by deficient ISMR and the second with low snow depth followed by excess ISMR. The difference fields of mean monsoon circulation simulated in the above two experiments are examined in detail in order to confirm the influence of Eurasian snow depth on ISMR and to examine the Asian summer monsoon circulation and rainfall. Copyright © 2006 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The middle and lower reaches of Yangtze River (MLYR) experienced a historically high number of persistent cloudy and rainy days throughout winter 2018/2019. The persistent cold and rainy weather caused severe social impacts and economic losses. Climatic monitoring shows that a weak central Pacific (CP) El Niño event initiated in November 2018 with an increase in the sea surface temperature (SST) in the central and eastern tropical Pacific. During the mature phase of the CP El Niño, the western North Pacific Subtropical High (WNPSH) was stronger than normal and the western boundary moved westward. However, the weak CP El Niño event alone is not enough to explain the abnormally strong and northward displacement of WNPSH and associated heavy rainfall in winter of 2018/2019. This study highlights the eastward propagating Rossby wave train in the middle‐upper troposphere along with the Asian westerly jet‐induced anomalous high pressure and anticyclonic circulation over East Asia, which contributed to the intensification and northward displacement of WNPSH. The synergic influence of both the CP El Niño and Rossby wave train over Eurasia resulted in an intensified and northward shifted WNPSH, which, together with the intensification of the India Burma trough, strengthened the transport of water vapour into the MLYR basin. Accompanied by frequent outbreaks of cold air and confluence of cold and warm air over the MLYR basin, cold and rainy weather persisted in winter 2018/2019 in this region. [ABSTRACT FROM AUTHOR]

The sea surface temperature anomalies (SSTAs) in the tropical Pacific (TP) and North Atlantic (NA) are both important factors regulating the winter rainfall over southern China (SC). Our results show the combined impact of SSTAs exhibits an offset effect before 1985, after a decadal transition period, the two SSTAs patterns form an additive effect on the interannual timescale after 1995. These distinct impacts of the TP and NA result in the southward shift of the winter rainfall variability, which is associated with the decadal change of the TP and NA. Both the background modes in TP and NA show a phase transition during the period 1985–1995, accompanied by the interannual variations of the SSTAs in two ocean basins before 1985 and after 1995. Before 1985, the canonical El Niño‐related southerly winds of the anticyclone over the western North Pacific transport sufficient water vapour and enhance rainfall in SC. While the concurrent dipole NA SSTA‐related wave train propagates to Eurasia, causing a cyclone and divergence of water vapour fluxes suppressing the local rainfall. After 1995, the El Niño‐related warm SSTAs move westward and strengthen the rainfall anomalies in the Yangtze River basin. Meanwhile, a tripole mode of SSTAs replaces the dipole counterpart in NA, resulting in the anomalous cyclonic circulation over South Asia with more rainfall in the south edge of SC. The decadal changes of the TP and NA mode combination could affect the seasonal distribution and prediction of China winter rainfall. [ABSTRACT FROM AUTHOR]

In this study, we investigated the interdecadal variability (IDV) of winter precipitation in the Greater Mekong Subregion (GMS) between 1892 and 2016. The results showed that the precipitation IDV was characterized mainly by opposite variations between the southern and northern parts of GMS. This IDV pattern was closely linked to the Atlantic multidecadal oscillation (AMO). Rossby waves excited by the AMO modulated the atmospheric circulation across Eurasia, inducing an EU‐like teleconnection with alternating cyclonic and anticyclonic anomalies across Eurasia. The GMS was directly affected by the anticyclonic anomaly over East Asia. This anticyclonic anomaly had dual effects on the GMS precipitation. Firstly, it caused a descending anomaly over the northern GMS and generated easterly anomalies that impeded the moisture transport from the northern BOB. Secondly, it strengthened the East Asian winter monsoon (EAWM) that weakened the western North Pacific anticyclone (WNPAC) to facilitate moisture transport from South China Sea to the southern GMS. Consequently, the precipitation varied inversely between the southern and northern parts of GMS. Numerical experiments confirmed the causal link between the AMO and IDV of winter precipitation in the GMS. [ABSTRACT FROM AUTHOR]

This study investigates the variability of summer surface air temperature (SAT) over northern Eurasia and its precursory signals in the tropical Atlantic and northern Asian land. The leading mode of summer SAT variations features a northern Eurasian SAT tripole (NEST) pattern, with two same‐sign SAT anomaly regions over eastern Europe–western Siberia and the Far East region and an opposite‐sign SAT anomaly region around the Baikal Lake. It is found that sea surface temperature (SST) or SAT anomalies in the tropical Atlantic and rainfall‐soil moisture anomalies around the Baikal Lake during May can modulate the NEST pattern. The SST anomalies in the tropical Atlantic persist from May to summer and induce a downstream zonal wave train across northern Eurasia, consequently causing the variation in the summer NEST pattern. May rainfall anomalies around the Baikal Lake affect the overlying atmospheric circulation during summer through the 'memory' effect of soil moisture and the soil moisture‐rainfall interaction, correspondingly modulating the downstream wave train and the associated NEST pattern. Based on the above results, a statistical prediction model is established using the two precursory signals, that is, SAT in the tropical Atlantic and rainfall around the Baikal Lake during May. The leave‐three‐out cross‐validation shows that the model has a high skill in predicting the summer NEST pattern, with a correlation coefficient of 0.51 (significant at the 99.8% confidence level) between observation and prediction during the period 1980–2016. [ABSTRACT FROM AUTHOR]

The western Pacific pattern (WP), characterized by a meridional dipole structure in geopotential height anomalies centred at approximately 50°N over the North Pacific, is one of the most prominent teleconnection patterns over the Northern Hemisphere (NH) in boreal winter. Several methods to identify the WP exist in the literature. Based on eight WP indices defined by different methods, this study analyses their dominant frequencies, spatial structures, climatic impacts, and relations to the Arctic Oscillation (AO) and El Niño‐Southern Oscillation (ENSO). The correlation coefficients of the eight WP indices show a considerable spread, but most of them are statistically significant. Most of the WPIs capture a pronounced power peak at approximately 5 years. The meridional dipole structure of the WP can be captured by all the WPIs, but it shows a large spread in the location of the centre. Several WPIs are significantly correlated with the winter AO, with marked signals of atmospheric anomalies over the Arctic region. The connections of the WP with the simultaneous winter ENSO depend largely on their definitions. The impacts of the WP on the surface air temperature over many parts of Eurasia and North America are also sensitive to its definition. Differences in surface air temperature anomalies are related to differences in the spatial structure of the WP as captured by the range of WPIs. [ABSTRACT FROM AUTHOR]

In the context of global warming, determining to what extent natural variability and external forcing have an impact on climate change is crucial for formulating mitigation policies and adaptation plans. We quantifiably and effectively separate unnatural trends from the global land surface air temperature (SAT) changes during 1951–2015 by calculating the long‐term correlation exponent through detrended fluctuation analysis and applying mainly probability statistics methods. We provide effective discriminated evidence for whether the observed SAT change exceeds its natural internal variability. Furthermore, we search the range of SAT changes caused by unnatural trends, and identify their corresponding minimum contributions to warming relative trends in different regions. The unnatural warming of the mid‐ to high latitude inland areas of Eurasia and North America is basically high, and the warming responses to unnatural forcing are most intense in these areas. Compared to earlier detection, we find the minimum unnatural trend contributes more than 80% to the observed SAT change in North America, northern Greenland, eastern Africa, and the mid‐ to high latitudes of Eurasia. In addition, the temporal evolutions of unnatural trends in key areas are determined. In North Africa, Western Australia, the United States and Mexico, the unnatural impact became significant at the earliest. Meanwhile, the overall unnatural trend in North Africa is the most significant, followed by western Brazil, and grows most rapidly over time in the two key areas. [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]

The prolonged droughts that frequently occur in northern China are related to persistent anomalies of circulation and the low‐frequency waves. To explore the formation of the low‐frequency waves and the related internal variability and external forcing, the intra‐seasonal kinetic energy (KE) and the corresponding energy transfer terms are investigated algorithmically with multiscale energy and vorticity analysis. The results show two major energy sources located over the central North Atlantic (NA) and Europe, with increasing baroclinicity and energy conversion. The major energy conversion is from basic flow to intra‐seasonal KE, which corresponds to a southeastern extension of NA jet stream (JS) exit and the northward shift in the entrance of Afro Asian JS. JS shifts are helpful to the conjunction of both JS, and thereby enhance JS waveguide and wave energy dispersion. In addition, with increasing surface temperature and diabatic heating over Europe and the Mediterranean Sea, there are increase baroclinicity that facilitates the buoyancy energy conversion, ascending KE flux and positive pressure flux in the lower troposphere, those result in higher mid‐upper‐troposphere KE. The divergent energy contributes to the development and enhancement of the low‐frequency waves, favouring the extratropical eddy, wave structure, and quasi‐stationary waves amplitude, which is thereby conducive to magnified wave amplitude and extreme droughts in northern China. The results emphasize the internal dynamics and local forcing and provide prediction reference for extratropical extremes. [ABSTRACT FROM AUTHOR]

Previous studies suggested that autumn Arctic sea ice concentration (SIC) change around the Kara–Laptev seas has a marked impact on the following winter Siberian High (SH). This analysis reveals that the autumn Arctic SIC‐winter SH connection experienced a marked interdecadal weakening around the late‐1990s according to observational and reanalysis data. Before the late‐1990s, autumn Arctic SIC loss induces pronounced Arctic warming via modulating surface heat fluxes and reduces poleward meridional temperature gradient, which leads to weakening of westerly winds over mid‐latitude Eurasia and contributes to formation of a high‐pressure ridge around Ural mountain. The Ural high‐pressure ridge provides a favourable dynamical condition for the amplification of SH. Consequently, the autumn Arctic SIC‐winter SH connection is strong. In addition, the North Atlantic is dominated by a marked triple sea surface temperature anomaly pattern from autumn to winter, which also partly contributes to a strengthened SH via modulating the Ural high‐pressure ridge. After the late‐1990s, Arctic warming and atmospheric anomalies over Eurasia related to the autumn Arctic SIC loss are much weaker. Accordingly, the autumn Arctic SIC‐winter SH connection is very weak. Changes in the autumn Arctic SIC‐related Arctic warming and atmospheric anomalies are suggested to be related to differences in the autumn Arctic SIC anomalies, with a much weaker amplitude and northward retreat after than before the late‐1990s. Further analysis indicates that the weaker autumn Arctic SIC anomalies over Kara–Laptev seas after the late‐1990s is related to the northward retreat of the mean Arctic SIC. [ABSTRACT FROM AUTHOR]

This study reveals an obvious interdecadal change in the summer water vapour budget over Northeast Asia around the late‐1990s accompanied with the abrupt rainfall decrease. After the late‐1990s, water vapour transported into Northeast Asia is apparently reduced under control of a local anomalous anti‐cyclone. The water vapour transport is further explored by decomposing the water vapour flux into stationary and transient components, which are associated with the mean flow and transient eddy, respectively. The results indicate that the stationary component accounts for nearly 84% of the total water vapour budget change, much larger than the contribution from the transient component (16%). The correlation coefficient between the interdecadal variation of net and stationary (transient) water vapour budget is 0.95 (0.14). Hence, the stationary term plays a dominant role in contributing to interdecadal change in the total water vapour transport. In addition, change in the water vapour budget over Northeast Asia around the late‐1990s is primarily attributed to the wind field change at the lower troposphere. A further comparison of the water vapour budgets in four boundaries of Northeast Asia shows that the water vapour budgets via the southern and northern boundaries display remarkable changes around the late‐1990s, exerting significant influences on the total moisture budget change. The anomalous atmospheric water vapour transport circulations in association with the southern and northern boundaries both present a wave‐like teleconnection pattern over the Eurasia, whose formation may be partly due to the combined impacts from the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation. [ABSTRACT FROM AUTHOR]

The eastern Pacific (EP) El Niño‐Southern Oscillation (ENSO) is an important impact factor for the East Asian trough (EAT) variability during boreal winter. However, not all ENSO events can result in anomalous EAT events, which indicates that there could be some other factors modulating the relationship between ENSO and the EAT. The analysis of atmospheric circulations indicates that the intensity of the Asian Polar vortex (PV) plays an important role in the El Niño‐EAT connection. The strengthened Asian PV favours the wave‐train triggered by El Niño events propagates eastward from the North Pacific to East Asia and finally weakens the EAT. In contrast, during El Niño years with the weakened Asian PV, El Niño's influences are confined over western Siberia and the wave activity flux over Eurasia is weak, which consequently leads to a weak response of the EAT. For the La Niña‐EAT connection, the North Pacific Oscillation (NPO) is a potential modulating factor. The La Niña and negative‐phase NPO have a strengthened effect on the EAT, resulting in a strong response of the EAT to La Niña events. In contrast, the effects of La Niña and positive‐phase NPO on the EAT are offset, leading to a weak response of the EAT to La Niña events. The above results are further confirmed by a numerical simulation of the pre‐industrial Control experiment. Therefore, the simultaneous occurrence of the Asian PV and NPO should be a great concern when understanding and predicting the EAT based on ENSO information. [ABSTRACT FROM AUTHOR]

This study examines projected changes in surface air temperature (SAT) and precipitation over mid–high latitudes of Eurasia during boreal spring in a 1.5/2°C warmer world (relative to pre‐industrial level) using historical, RCP4.5 and RCP8.5 simulations from 16 climate models of the Coupled Model Intercomparison Project Phase 5. Results show that spatial patterns of spring SAT and precipitation changes over Eurasia in the 1.5/2°C warmer world relative to the current climate (1979–2005) are similar between the two RCPs, but with a slightly larger amplitude in the RCP8.5. Spring SAT warmings over Eurasia are faster than the global annual mean. Amplitudes of the spring Eurasian SAT warmings are larger over higher latitudes. An additional 0.5°C global warming leads to extra spring Eurasian SAT warmings, with the magnitude larger than 0.5°C. Changes in the spring maximum temperature are comparable to the mean temperature changes both in the 1.5 and 2°C warming targets. Significant increases in the mean and extreme precipitation are only seen over parts of Eurasia. An additional 0.5°C global warming does not lead to obvious changes in the mean and extreme spring precipitation. Further analyses show that there are large uncertainties in the projected changes in the inter‐annual variability of the Eurasian spring SAT and precipitation. [ABSTRACT FROM AUTHOR]

In statistical modelling of extreme precipitation, most of previous studies were proposed for some certain regions, the effects of diverse extreme distribution and threshold remain unclear on a global scale. In this study, we evaluated the performance of different extreme distribution and threshold across the global land areas, and proposed the optimal criteria in distribution and threshold determination for monthly extreme precipitation modelling. The performance of the generalized extreme value (GEV) distribution and generalized Pareto distribution (GPD) models were compared and the applicability of GPD models with thresholds determined by different percentiles in each grid was analysed. The results show that the GPD model is more suitable than the GEV model for monthly extreme precipitation, and the threshold over global land areas is likely to be associated with the spatial distribution of annual precipitation magnitude. The 97–99th percentile is most applicable to arid regions (e.g., the northern edge of North America, central Asia, North Africa, southwest Asia, central South America). The 93–96th percentile is most applicable to semi‐arid and semi‐humid regions (e.g., eastern North America, a strip region in northern Eurasia, and inland semi‐arid areas in Asia). The 90–92 percentile is most applicable to humid regions (e.g., central and southern North America, most areas in South America, Eurasia [except central Eurasia], southern and central Africa). [ABSTRACT FROM AUTHOR]

The combined impact of Greenland sea ice, Eurasian snow, and the El Niño–Southern Oscillation (ENSO) on the out‐of‐phase relationship between the Indian summer monsoon (ISM) and Korean summer monsoon (KSM) were investigated through numerical experiments. The results revealed that Indian and Korean summer rainfalls showed nonlinear responses to ENSO and Greenland sea ice forcing when the events co‐occurred. Above‐normal Greenland sea ice and a concurrent La Niña showed a distinct in‐phase relationship with ISM and out‐of‐phase relationship with KSM. Below‐normal and above‐normal Greenland sea ice during boreal autumn surrounded the Greenland region with anomalous low pressure and high pressure, respectively. These were associated with a barotropic +west/−east or –west/+east dipole pattern, respectively, over Eurasia during the subsequent winter and spring seasons. Furthermore, these patterns led to positive and negative snow depth anomalies, respectively, over western Eurasia and the opposite snow tendency over eastern Eurasia during the subsequent spring. This variability in Eurasian snow patterns may play a crucial role in ISM and KSM. The co‐occurrence of ENSO variability also generates high‐ and low‐pressure anomaly patterns over the Indian Ocean that may be related to unfavourable or favourable ISM, respectively, while influencing the negative or positive phases of a Pacific Japan (PJ)‐like teleconnection pattern that may be related to unfavourable or favourable KSM, respectively. Therefore, coexisting ENSO forcing may play a dominant role in ISM and KSM, but Greenland sea ice forcing and Eurasian snow variation intensify the out‐of‐phase relationship between ISM and KSM. [ABSTRACT FROM AUTHOR]

Global temperature change is strongly affected by internal climate variability (ICV). The temporal change of the ICV on the decadal to multi‐decadal scales is referred as the decadal modulated oscillation (DMO) that plays a dominated role in the occurrence of enhanced warming and warming hiatus. However, investigation on the DMO in modern historical period has received limited attention. In this study, the ensemble empirical mode decomposition (EEMD) method was applied to the surface air temperature (SAT) during the boreal cold season to extract the DMO signal in the past century. Two most sensitive areas of DMO trend over northern Eurasia and northwestern North America were identified and used to build a time series of regionally enhanced DMO. It showed an obvious decadal periodic oscillation at 11–23 years and exhibited increasing amplitude. In addition, regression analysis using Niño3.4, Pacific Decadal Oscillation (PDO), Atlantic Multi‐decadal Oscillation (AMO), and Arctic Oscillation (AO) revealed a major role of the AO in DMO over the mid‐to‐high latitudes in the Northern Hemisphere (NH). However, such strong oscillation signal has not been detected in most of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models, and the extracted regionally enhanced DMO are capable of improving the predictability of SAT over the mid‐to‐high latitudes in the NH. [ABSTRACT FROM AUTHOR]

This study evaluates the possible influence of the winter surface conditions in Eurasia on the summer circulation over the Asian continent and Indo‐Pacific region. We have analysed multi‐seasonal ensemble reforecasts for 30 years (1979–2008) using the National Centers for Environmental Prediction Climate Forecast System version 2 initialized at the beginning of each month from January to May. It is found that the reforecasts initialized in winter (e.g., February) overestimate the snow cover fraction, depth and water equivalent, as well as surface albedo in the excessively snow‐covered portion of Eurasia from March to June. These biases are generated and perpetuated by a snow‐albedo feedback, leading to excessive upwards shortwave radiation reflected from the overly snow‐covered surface and an intense cold bias from the surface to mid‐troposphere. Originating over land, the cold bias is extended eastwards over the northwestern North Pacific by the advection of prevailing westerly winds. The cold air temperature in the broad mid‐latitude Asian‐Pacific region causes significantly lower geopotential heights at pressure levels in the middle and upper troposphere and thus increases the upper‐level westerly winds on its southern flank over the Asian continent and Indo‐Pacific. A slower than observed snow melting rate helps the winter cold bias persists well into the summer season in these runs. As a result, compared with the reforecasts initialized in spring (e.g., May), winter‐initialized reforecasts feature lower geopotential heights in the upper troposphere over Eurasia and a stronger subtropical jet over the Asian continent and the North Pacific from May to September, especially in early summer. The CFSv2 reforecasts in both sets of cases have too little total cloud fraction over Eurasia during June–August, leading to enhanced downwards shortwave radiation. [ABSTRACT FROM AUTHOR]

A 60 year minimum temperature record of 11 stations in inner Eurasia enabled the characterization of the Siberian High (SH) intensity. The decline in the SH intensity is observed in tandem with the positive mode of the Arctic Oscillation (AO), both increasing in recent years. The coldest 1968-1969 winter in the 60 year period corresponds with the lowest AO annual index value. Spatial correlation analyses indicate that enhanced cyclogenetic conditions over the eastern flank of the Icelandic Low (IL) are associated with a milder SH. Seasonal composite analyses of the circulation pattern during the coldest 1968-1969 winter are characterized by a retreat of the IL, allowing a westward expansion of the SH cold core. A robust methodology, assuring an adequate representation of extremely cold spells in both their extent and duration, was developed. This methodology yielded three exceptional events, the most severe one lasting 10 days and affecting all stations in the SH domain. Analysing this event on a fine temporal resolution enabled the detection of short-term synoptic scale processes, such as the polar air mass penetration, resulting in a mean minimum temperature of − 40 °C over the whole domain. This short-term polar air incursion and its termination featuring this spell, as modulated by the location of the IL, point at its important role in modifying the SH. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The relationship between decadal variability in springtime (March-May) snow water equivalent (SWE) over Eurasia and springtime rainfall over China is investigated for 1979-2004 using satellite-observed SWE, rainfall observations from 595 stations, and NCEP/NCAR reanalysis data. Decreasing springtime SWE in Eurasia corresponded to reduced springtime rainfall over southeastern and northeast China, and more rainfall over southwestern and northwestern China. This relationship was supported by the feedback effect of snow in high-latitude areas to changes in background atmospheric circulation. A decadal shift in springtime Eurasian SWE occurred in the late 1980s, marked by a change from persistent positive phases in 1979-1987 to frequent negative phases. The reduction in Eurasian SWE resulted in reduced upward surface heat flux to the atmosphere and, thereby, higher boundary layer height due to increased downward heat flux into subsurface soil. These changes resulted in reduced upward and poleward wave flux activity, which corresponded to anomalous negative heights/pressures in the Arctic and anomalous positive heights/pressures in mid-latitude regions from the upper-level troposphere to the surface. There was an anomalous anti-cyclonic circulation over Siberia and the western Pacific subtropical high was weakened, accompanied by an anomalous northerly in eastern China and westerly in northwestern China. The anomalous northerly resulted in reduced water vapour convergence in southeastern and northeast China, and reduced water vapour export for southwestern and northwestern China. Thus, negative rainfall anomalies developed over southeastern and northeast China, and positive rainfall anomalies appeared over southwestern and northwestern China. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

In contrast to the weakened relationship between the Indian summer monsoon and El Niño-Southern Oscillation (ENSO) since 1970s, the East Asian summer monsoon (EASM) has exhibited a strengthened relationship with ENSO. In this study, observational and numerical evidences manifest that spring NAO may exert notable impacts on the enhancement of the EASM-ENSO relationship. Anomalous spring NAO induces a tripole sea surface temperature anomaly (SSTA) pattern in North Atlantic which persists into ensuring summer. The tripole SSTA excites downstream tele-connections of a distinct Rossby wave train prevailing over the northern Eurasia and a simple Gill-Matsuno-type quadrupole response over western Pacific. The former modulates the blocking highs over the Ural Mountain and the Okhotsk Sea. The latter enhances the linkage between the western Pacific subtropical high and ENSO. The co-effects of the two tele-connection patterns help to strengthen (or weaken) the subtropical Meiyu-Baiu-Changma front, the primary rain-bearing system of the EASM. As such, spring NAO is tied to the strengthened connection between ENSO and the EASM. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

This study identifies intraseasonal oscillations in summer precipitation over northern Eurasia using multi-channel singular spectrum analysis (MSSA) and a gridded daily precipitation data set for northern Eurasia. The analysis period is June-August of 1979-2002. Empirical orthogonal function analysis was first performed on 8-day low-pass-filtered precipitation anomalies at 2.5° grid resolution for northern Eurasia; MSSA was then carried out on the ten leading principal components (PCs). Three quasi-periodic oscillations with timescales of 45, 15, and 9 days were identified. The spatiotemporal structures of precipitation oscillations were defined by composite analysis based on the reconstructed time series of the spatiotemporal PCs obtained from the MSSA. The composite life cycle of each mode was classified into eight phase categories. The 45-day oscillation is characterised by a slow eastward progression of a broad east/west contrastive pattern which is associated with a replacement of elongated dry and wet zones across northern Eurasia. The 15-day oscillation shows a regular eastward phase propagation of precipitation anomalies with a tripole structure across the domain. The eastward displacement of dry and wet zones occurs in association with this oscillation. Spatiotemporal behaviours of the precipitation anomalies associated with the 9-day oscillation are similar to those of the 15-day oscillation, but the spatial scale of this oscillation is somewhat smaller. To explore the connections between the oscillations of precipitation and large-scale atmospheric circulation patterns, a similar composite method was applied to 300-hPa geopotential height anomalies over the Northern Hemisphere. The circulation patterns responsible for the 45-day oscillation are characterised by a wave train extending across the northeastern Atlantic/northern Eurasian sector. The wave train, with zonal wavenumbers of 3-4, indicates slow eastward moving and quasi-stationary features. The circulation patterns linked to the 15-day oscillation exhibit an eastward propagating wave train extending from northeastern Europe into the North Pacific/North American sector. In spatial scale, this wave train has zonal wavenumbers of 5-6. The wave trains associated with the 9- and 15-day oscillations have similar behaviour patterns over northern Eurasian. However, the 9-day wave train has a comparatively smaller spatial scale with zonal wavenumbers of 6-7. Therefore, the intraseasonal oscillations of precipitation are connected to the well-organised wave trains that extend from the Euro-Atlantic region to northern Eurasia, suggesting that the oscillation on each intraseasonal time scale must be produced by propagation of the corresponding wave train. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The Baiu frontal activity (BFA) clearly shows spatiotemporal differences in its interannual variability. This work examines the physical mechanisms behind these differences. On interannual time scales, the Baiu front can be divided into three subregions: (1) the western Baiu (WB), (2) the central Baiu (CB), and (3) the eastern Baiu (EB). Time series analysis revealed that the dominant periods in these three subregions are long eastward periods of approximately 2 years in the WB, 4 years in the CB, and 6 years in the EB. The biennial oscillation of the Asian monsoon controls the interannual variation in the WB through specific meridional circulation in the western North Pacific, whereas the El Niño/Southern Oscillation forces the interannual variation in the CB through the Pacific-East Asian teleconnection. The interannual variation in the EB is controlled by mid-latitude atmospheric circulations, not by effects from the Tropics. The summertime North Atlantic Oscillation (SNAO) with a 6-year period excites the stationary Rossby waves, the energies of which reach Japan through the strong upper tropospheric westerlies over Eurasia. Geopotential height anomalies then appear around Japan with an equivalent barotropic structure that modifies the precipitation in the EB. Copyright © 2009 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article presents a study concerning the winter snow accumulation over northern Eurasia which involves the use of 283 February mean snow depth time series (1936-2001), interpolated into 5 x 5° grid points, from the former Soviet Union, Finland and Norway through empirical orthogonal function (EOF) analysis. After the EOF analysis and the reciprocal relation of significantly rotated five personal computers (PCs) with Northern Hemisphere teleconnection patterns for the 700 hPa height, it is determined that the atmospheric circulation influences the spatial variability of snow accumulation over northern Eurasia.