East Atlantic/Western Russia Research Articles

The Influence of North Atlantic Sea Surface Temperature and Sea Ice in the Barents Sea on Spring Mongolian Cyclone Activity

Abstract The Mongolian cyclone, a type of extratropical cyclone, significantly impact regional weather. This study objectively identifies and tracks the Mongolian cyclone during spring (March to May) from 1950 to 2022, analyzing the relationships between its interannual variability, atmospheric circulations, sea surface temperature (SST), and Arctic sea ice concentration (SIC). The results show that the negative height anomaly over Lake Baikal is a key circulation system for the abnormal increase in spring Mongolian cyclones. Anomalous decreases in North Atlantic SST during spring leads to a negative East Atlantic/Western Russia (EA/WR) pattern, resulting in a negative height anomaly over Lake Baikal. Additionally, the reduction in Barents Sea SIC weakens the polar vortex circulation, contributing to the negative anomaly over Lake Baikal and promoting Mongolian cyclone development. Numerical simulations confirm these observations, indicating that both the negative anomalies in North Atlantic SST and Barents Sea SIC independently affect the interannual variation in spring Mongolian cyclone frequency. Furthermore, the combined effect of SST and SIC anomalies has a more pronounced influence on spring Mongolian cyclone activity compared to their individual effects.

Влияние колебаний циркуляции атмосферы на уровень Каспийского моря

Changes in the Caspian Sea level from 1950 to 2023 are considered. The focus is on the intense sea level drop from 2005 to 2023. During this period, as a result of global warming, the number of cases of westerlies blocking in the summer atmosphere increased, which led to an air temperature rise in the Caspian Sea region. The influence on these processes of the negative phases of the EA/WR (East Atlantic-Western Russia) and NAO (North Atlantic Oscillation) atmospheric circulation patterns that set in after 2000 is confirmed. It is assumed that the air temperature rise contributed to intense evaporation from the surface of the Caspian Sea and the drop of its level.

Analysing the Effects of Atmospheric Teleconnections on Streamflow Regime in the Eastern Black Sea Basin in Türkiye

Analysing the variations in hydrological cycle components is essential for water resources planning and management. In this study, the relationship between the streamflow data belonging to five discharge gauging stations in the Eastern Black Sea Basin in Türkiye and the Arctic Oscillation (AO), East Atlantic-Western Russia (EAWR), North Atlantic Oscillation (NAO) and North Sea Caspian Pattern (NCP) was investigated. For this purpose, Spearman’s correlation test, ensemble empirical mode decomposition (EEMD) and relative importance analysis were used. Accordingly, Spearman’s correlation coefficients were calculated between raw streamflow data, decomposed streamflow data via EEMD and atmospheric teleconnections. Then, the relative importance analysis was applied to determine the atmospheric teleconnections’ influences on streamflow data. The findings showed that the relationship between raw streamflow data and atmospheric teleconnections is generally more significant and negative in the winter and spring. Furthermore, it was observed that the linkage between the decomposed streamflow data and atmospheric teleconnections could differentiate. Although no significant correlation between atmospheric teleconnections and raw streamflow data was detected in some months, significant correlations were detected between atmospheric teleconnections and decomposed streamflow data. This reveals the importance of examining the relationship between atmospheric teleconnections and streamflow data for different periods. The relative importance analysis revealed that the influence of atmospheric teleconnections on streamflow data could change from station to station and from component to component. This study showed that investigating the effects of atmospheric teleconnections on streamflow data for different components and periods is important.

Seasonal and interannual variability of Mediterranean Sea overturning circulation

The overturning streamfunction is a widely used metric to monitor ocean circulation changes in the North Atlantic Ocean. Analogously, it is known that an overturning circulation develops in the Mediterranean Sea, although substantially weaker and smaller than in the Atlantic. In this work we use monthly mean fields from a high-resolution ocean reanalysis (1/16°×1/16°) to explore seasonal and interannual variability of Mediterranean Sea overturning circulation in depth and water mass parameter spaces (potential density, potential temperature, salinity) from 1987 to 2018 (both included). Results show a clear single zonal clockwise transport cell in all three spaces that extends from the Strait of Gibraltar to the Levantine Basin, in which water masses tend to densify as they move eastward. This densification is mainly controlled by salinity in the Eastern Mediterranean basin (EMED), while in the Western Mediterranean (WMED) both salinity and potential temperature variations should be taken into account. In contrast, the meridional overturning transport, much more complex, is able to better capture smaller-scale variations since it responds faster to perturbations in the circulation.Seasonal variations in overturning transport are reflected in the size and strength of overturning cells in all spaces, being cells remarkably narrower in winter than in summer. Regarding interannual changes, we show that the meridional overturning transport in density space is significantly correlated with the North Atlantic Oscillation, the Mediterranean Oscillation Index and the Scandinavian pattern during wintertime in the WMED, and with the Eastern Atlantic and the East Atlantic–Western Russian in the EMED. The overturning metric in density space captures well the Eastern Mediterranean Transient, that occurred during years 1992–1996. Finally, we explore the usefulness of overturning metric to detect and track water mass changes associated to shorter scale events, using as example the strong deep convection events of years 2004–2006 in the Gulf of Lion, which marked the beginning of the Western Mediterranean Transition.

The merit of the North Sea‐Caspian pattern in explaining climate variability in the Euro‐Mediterranean region

AbstractTeleconnection patterns are one of the key features to understanding high‐frequency natural climate variability. The North Sea‐Caspian Pattern (NCP) was identified as a middle tropospheric dipole and its hydroclimatological implications have been substantially restricted to the Eastern Mediterranean region. Thus, the hydroclimatological influences of the NCP in the Euro‐Mediterranean region were investigated via a comparative approach with dominant tropospheric teleconnections in the Eurasian region and synoptic features such as ridge‐trough positioning and strength. By using high‐resolution ERA5 reanalysis data, cross‐correlations between indexes, anticorrelations at 500 hPa and composite anomaly maps for seasonally representative months were produced to understand the working mechanism of the NCP. Comparisons included the East Atlantic/Western Russian (EAWR) pattern, a rotated principal component analysis (RPCA) variant of NCP which utilizes pole‐based representation. Analysis revealed that the NCP was correlated well with the Mediterranean trough displacement and with the strength of the East Asian trough. Climate anomalies indicated by the NCP were greater and more spatially consistent compared to other teleconnections. The NCP also showed higher contrasts of temperature and precipitation than the EAWR based on the composite anomaly maps. In conclusion, the NCP explained climate variability in all seasons linking remote centres of action within Eurasia's east and west extremes.

Revealing the Formation of the Dipole Mode of Eurasian Snow Cover Variability During Late Autumn

AbstractA zonal dipole pattern of the interannual variability of Eurasian snow cover during late autumn has attracted growing interest due to its extensive influences on large‐scale atmospheric circulations and climate anomalies, but it remains unknown what influences the formation of this pattern. This study revealed the potential drivers and the related physical processes of the dipole mode of the snow cover variability during 1979–2018. Results showed that the atmospheric circulation anomalies play a crucial role in forming the dipole mode, which could be further attributed to the influences of the atmospheric teleconnection patterns and the variations of sea surface temperature (SST) and sea ice concentration. Specifically, the anomalous circulations related to the teleconnections of the Eastern Atlantic pattern, East Atlantic–Western Russia pattern, and Scandinavian pattern could lead to the anomalies of air temperature and snowfall that directly shape the variability of snow cover. In addition, a dipole structure of the SST anomalies over the North Atlantic exerts an important effect on the snow cover variability through exciting an eastward propagating Rossby wave train prevailing over Eurasia. Moreover, the snow cover variability is closely linked to the sea ice variations over the Barents Sea that can regulate the anomalous circulations over Eurasia by altering the atmospheric dynamic and thermodynamic conditions. These influencing factors jointly account for about 66% of variances in the dipole mode of snow cover variability, suggesting that our findings can substantially improve the understanding of the Eurasian snow cover variations.

Causes for an extreme cold condition over Northeast Asia during April 2020

Although 2020 was the fourth warmest year on record in northern Asia, the cold condition in April 2020 caused severe damage to the agricultural and marine ecosystems in northeastern Asia. Previous studies have indicated that the dipole atmospheric circulation over Siberia and the East Sea (Japan Sea) produced this cold environment with strong northwesterly wind. However, the potential causes of the dipole circulation over northeastern Asia remain unclear. In this study, we found that the East Atlantic/Western Russia (EAWR) pattern and blocking combined to produce the atmospheric structure. The wave train originated from the vorticity forcing of northwestern/central Russia and propagated from Western Europe to the East Sea via the background westerly and northerly winds. In addition, the Siberian blocking days increased eleven times in April 2020 relative to the climatological average, and an easterly (westerly) anomaly was observed over Mongolia–northeastern China (northern Russia). The strong blocking and EAWR pattern led to the robust atmospheric dipole structure with a prevailing northerly flow in April 2020, thereby causing the extreme cold condition over northeastern Asia. Our results provide novel insights into the cause of extreme cold condition in April over northeastern Asia.

Enhancing Forecast Skill of Winter Temperature of East Asia Using Teleconnection Patterns Simulated by GloSea5 Seasonal Forecast Model

GloSea5, a seasonal forecast system of the UK Met Office, shows reasonable skill among state-of-the-art operational seasonal forecast systems. However, the average surface temperature (T2m) in winter (December–February) of GloSea5 is particularly low in East Asia. To improve the seasonal forecast skill over East Asia, we focused on the high skill score of global teleconnection patterns simulated by GloSea5. Among the well-predicted teleconnection patterns, we selected those highly correlated with the East Asian T2m: East Atlantic (EA), Polar/Eurasia (PE), East Atlantic/Western Russia (EAWR), and West Pacific (WP) patterns. A multiple linear regression model was constructed using the selected teleconnection indices as predictors. These results are promising. The statistical skill-score evaluation of the constructed linear regression model using the anomaly correlation coefficient (ACC), root mean squared error (RMSE), and mean-squared skill score (MSSS) showed an improvement in the predicted T2m of East Asia, where the values of ACC and MSSS increased by 0.25 and 0.37, respectively, and the RMSE decreased by 0.63 compared to the dynamic forecast model results. These results suggest that a well-designed combined statistical and dynamical approach for seasonal prediction can be beneficial for some regions where the predictability of the dynamic model exhibits a low value.

КРУПНОМАСШТАБНЫЕ ЛЕТНИЕ ВОЛНЫ ТЕПЛА НА ЮГЕ ЕВРОПЕЙСКОЙ РОССИИ

For large-scale heat waves that occur in the south of the European part of Russia (EPR), the frequency variability since the beginning of the 20th century is considered, including variations on decadal scales and a trend during the global warming period, accompanying variations in the aridity index SPI, and the structure of the longest waves. The geographic distribution of air temperature anomalies on the territory of the Russian Federation, large-scale circulation conditions, the North Atlantic sea surface temperature (SST) anomalies, which accompanied heat waves in the south of the EPR, are analyzed using the composite analysis. In particular, the wave structure was revealed of the composite field of the air temperature anomaly for days with heat waves and the related 500 hPa geopotential height (H500) fields over Russia. The H500 field structure generally corresponds to the negative phase of the East Atlantic-Western Russia (EAWR) circulation pattern. Similar structures of the geopotential field are observed during heat waves in the northern half of the EPR. However, in this case, there are specific features that contribute to the inflow of cold air from the north to the southern regions. It is shown that the values of the EAWR index are significantly shifted towards negative values in the months when long heat waves occur over the southern EPR. The waves are accompanied by positive anomalies of the North Atlantic SST and the strongly increased blocking anticyclone activity. The downward trend in the EAWR index observed in recent decades and the SST rise expected with the global warming increase a risk of droughts in the main grain-producing region of the country.

The Dominant Modes of Spring Land Surface Temperature Over Western Eurasia and Their Possible Linkages With Large‐Scale Atmospheric Teleconnection Patterns

AbstractPrevious studies suggest that the spring land surface temperature (LST) anomaly over Western Eurasia (WEA; 20°N–70°N, 0–70°E) is a potential driver for Asian even global climate. However, the interannual variability of LST over WEA together with its causes has not received enough attention. Based on multi‐source observations and reanalysis data, three dominant modes of spring LST over WEA were identified, and the roles of atmospheric teleconnection patterns in LST anomalies via altering cloud and water vapor were investigated from the perspective of surface energy budget. The first empirical orthogonal function (EOF1) mode exhibits a homogeneous warming pattern that is closely related to a negatively in‐phase combination of the Scandinavian and East Atlantic/Western Russia (EA/WR) patterns. Under the control of a predominant anomalous anticyclone, the warming is the result of enhanced downward longwave radiation due to more water vapor in a warmer atmosphere associated with anomalous southerly and more incident solar radiation due to reduced cloud cover. The EOF2 mode, which displays a meridional dipole structure, is dominated by the North Atlantic Oscillation. Coupled with an anomalous cyclone and anticyclone over western Europe and around the Caspian Sea, respectively, the former LST anomalies are primarily caused by cloud‐shortwave radiation processes, whereas the latter are dominated by downward longwave radiation due to water vapor. The EOF3 mode, characterized by a zonal dipole pattern, is dominated by the water vapor greenhouse effect related to the Eurasian pattern. The results of the study may provide a valuable signal for climate prediction.

How Do Multiscale Interactions Affect Extreme Precipitation in Eastern Central Asia?

AbstractThe variability of extreme precipitation in eastern central Asia (ECA) during summer (June–August) and its corresponding mechanisms were investigated from a multiscale synergy perspective. Extreme precipitation in ECA displayed a quasi-monopole increasing pattern with abrupt change since 2000/01, which was likely dominated by increased high-latitude North Atlantic SST anomalies as shown by diagnosed and numerical experiment results. Increased SST via adjusting the quasi-stationary wave train that related to the negative North Atlantic Oscillation (NAO) and the east Atlantic/western Russia (EA/WR) pattern guided the cyclonic anomaly in central Asia, deepened the Lake Balkhash trough, and enhanced the moisture convergence in ECA. These anomalies also exhibited interdecadal enhancement after 2000. On the synoptic scale, two synoptic transient wave trains correlated with extreme precipitation in ECA by amplifying the amplitude of the quasi-stationary waves and guiding transient eddies in ECA. The induced transient eddies and deepened Lake Balkhash trough strengthened positive meridional vorticity advection and local positive vorticity, which promoted ascending motions, and guided the southerly warm moisture in ECA especially after 2000. Meanwhile, additional mesoscale vortices were stimulated and strengthened near the Tianshan Mountain in front of the wave trough, which, together with the enhanced meridional circulation, further increased extreme precipitation in ECA.

Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years

Abstract. High-resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lion was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mbar in the Northern Hemisphere (20–90∘ N and 100∘ W–80∘ E). Correlations revealed a pattern similar to the East Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 years of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone sea surface temperature (SST) reconstructions that documented an increase in the west–east basin gradients during EMT-type events.

Spatiotemporal distributions of pan evaporation and the influencing factors in China from 1961 to 2017

Pan evaporation (EVP) is an important element of the hydrological cycle and exhibits a close relationship with climate change. In this study, the generalized regression neural network (GRNN) model and extreme gradient boosting (Xgboost) model were applied to estimate the monthly EVP. The spatiotemporal distributions of EVP and influencing factors in China and eight subregions from 1961 to 2017 were analyzed. The root mean square error (RMSE) of all GRNN models was approximately 10%, and the Nash-Sutcliffe efficiency (NSE) coefficient was larger than 0.94 in different subregions. The annual mean EVP in all subregions and throughout China showed decreasing trends before 1993, while EVP increasing trends occurred in East China (EC), South China (SC), Southwest China (SWC), west of Northwest China (WNC), and throughout China after 1994. Subsequently, the variable importance in projection (VIP) between EVP and climatic factors obtained by partial least squares (PLS) regression and the relative contribution calculated by Xgboost stepwise regression analysis (SRA) were used to investigate the climatic parameter sensitivity to EVP. The results indicated that the combined effects of the vapor pressure deficit (VPD), sunshine duration (SSD), and wind speed (WIN) were the main reasons for the variations in EVP across China. At the seasonal scale, SSD, WIN, relative humidity (RHU), and VPD were the most sensitive climatic factors to EVP in different seasons. In addition, the Pacific decadal oscillation (PDO) index showed a significant negative correlation with EVP, and the El Niño 3.4 (N3.4) and East Atlantic/Western Russia (EA/WR) indices revealed positive correlations in most regions from 1961 to 1993, while the North Atlantic oscillation (NAO) was negatively correlated with EVP. Moreover, N3.4 and Atlantic multidecadal oscillation (AMO) were positively correlated with EVP from 1994 to 2017. Finally, the yearly number of heatwave events (HWN) was highly correlated with EVP because of the high VPD and SSD levels during the heatwave event periods.

The impact of teleconnections on the temporal dynamics in aboveground net primary productivity of the Mongolian Plateau grasslands

AbstractTemporal dynamics in aboveground net primary productivity (ANPP) are significant for environmental protection and economic development in the Mongolian Plateau grasslands (MPGs). Climate control of ANPP's temporal variations has intensified in response to local meteorological conditions, while the contributions of large‐scale atmospheric circulations to ANPP variations are poorly understood in the MPGs. First, we explored the temporal dynamics in annual ANPP, and then, we analyzed correlations among annual ANPP, local meteorological variables, and three different teleconnections during 1982–2015 in this study. Our analytical results indicated that (a) ANPP exhibited an increasing trend during the entire study period. However, the increasing trend did not persist, and two reversals occurred in 1998 and 2007. (b) ANPP variations were primarily influenced by summer precipitation in most regions and by summer precipitation and temperature together in other regions of the MPGs. (c) The Atlantic Multidecadal Oscillation (AMO) in winter negatively dominated annual ANPP variations by influencing summer precipitation and summer temperature in central Mongolia. The North Atlantic Oscillation (NAO) in winter exerted strong positive impacts on ANPP variations by influencing summer precipitation in Inner Mongolia, China. The East Atlantic Western Russia (EAWR) in spring controlled annual ANPP variations by influencing summer precipitation in western and eastern Mongolia. (d) The winter AMO, winter NAO and spring EAWR significantly dominated the annual ANPP variations in 49.78% of the MPGs, with values of 18.90, 9.81 and 21.07%, respectively. (e) Reversals of the winter AMO, winter NAO and spring EAWR between negative and positive phases resulted in two reversals of ANPP trends. This study will improve our understanding of the role of large‐scale atmospheric circulations in regulating ANPP variations and will be valuable in guiding the development of grazing land management in Mongolia and Inner Mongolia, China.

Influence of Wave Climate on Intra and Inter-Annual Nearshore Bar Dynamics for a Sandy Beach

The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at the Bulgarian Black Sea due to wave climate. On seasonal to short-term (1–2 years) time scale, monthly field measurements of the outer bar profiles were related to respective modeled nearshore wave data. Hereby, seaward-shoreward bar migration was examined depending on the wave forcing, wave non-linearity, wave transformation scenarios, storms and direction of wave incidence. Analysis revealed that intra-annually highly non-linear waves were responsible for outer bar displacement, while the direction of migration depended on wave period, duration of conditions with wave steepness >0.04, angle of approach and total duration of storms. Short-term bar evolution was mainly governed by wave height and storms’ parameters as the angle of approach and duration. The correlation between the outer bar location and wave height annual variations initiated the first for the explored Black Sea region examination of possible connection between wave height’s temporal fluctuations and the variability of climatic indices the North Atlantic Oscillation (NAO), the Atlantic Multi-decadal Oscillation (AMO), the East Atlantic Oscillation (EA), the Arctic Oscillation (AO), the East Atlantic-Western Russia (EA/WR) and the Scandinavian (SCAND) patterns. According to the results the inter-annual outer bar location may vary depending on periods of maximum annual wave fluctuations, which in turn predominantly depend on indices the EA (4–5, 10–11, 20–30 years), the EA/WR (2–4, 9–13 years) and the NAO (15 years).

Surface temperature‐related variations in the East Asian summer monsoon during three warming stages

AbstractThe global mean surface temperature has experienced different warming stages, but there is less work on discussion of the regional climate changes under the background of different global warming rates. This study investigated the surface temperature (ST)‐related trends in the East Asian summer monsoon (EASM) and underlying mechanisms during three warming stages, with a view to develop a new understanding of the responses of the EASM to global warming. Based on the statistical method of piecewise linear regression (PLR) to ST anomaly time series, the ST variation process from 1958 to 2014 has been divided into three stages with different linear trends: 1958–1975 (hiatus), 1976–1997 (acceleration) and 1998–2014 (slowdown). During the first stage, accompanied by two anomalous lower‐level cyclones, a weakening trend of the southerly winds over eastern China is observed. The enhanced cyclone over the Yellow Sea, with local ST cooling, is associated with the CGT‐like (circumglobal teleconnection) pattern, while the other one over the Philippines can be attributed to the local sea surface temperature (SST) warming. The ST‐related anomalous EASM circulation exhibits an enhanced lower‐level anticyclone over the northern Philippine Sea during the second stage. The warming around Lake Baikal and the phase change of the East Atlantic/Western Russia (EAWR) pattern can weaken upper‐level East Asian jet stream (EAJS) and then provide a favourable condition for the descent related to the lower‐level anticyclonic anomaly. As for the third stage, the anomalous ST and related EASM circulation both display a dipole pattern. Through influencing the meridional thermal contrast and distribution of convergence over East Asia (EA), the interaction between anomalous ST and EASM circulation may be the major mechanism that results in the increased (decreased) ST and enhanced barotropic anticyclone (cyclone) over southern (northern) EA.

Variation in Seasonal Precipitation over Gaza (Palestine) and Its Sensitivity to Teleconnection Patterns

The seasonal precipitation (SP) trend and its sensitivity to teleconnection patterns over the East Mediterranean (EM) region remain inconsistent. Based on rainfall records during 1974–2016 at seven meteorological stations in the Gaza region, this study aims to (1) analyze the observed SP trend over the Gaza region, and (2) examine the SP sensitivity to climate indices. Pearson and Spearman correlations between climate indices and SP in the current and following years were calculated, and the seasonal period (particular month) with the highest correlation was identified. Results show that the climate indices, with greater impact on SP over the Gaza region in the autumn and spring, were in the order; El Niño-Southern Oscillation (ENSO) > East Atlantic/Western Russia (EAWR) > North Atlantic Oscillation (NAO) > Arctic Oscillation (AO). The indices’ impact was minimal in the winter precipitation. ENSO types’ correlations (Southern Oscillation Index-SOI and Niño 3.4) were moderate and significant at α = 0.05. Rainfall at most stations positively correlates with AO and EAWR in spring and autumn. During the study period, warm phases of ENSO (i.e., El Niño) intensified autumn precipitation. Simultaneously with warm phases of EAWR or AO, more influence on autumn precipitation is exerted. Cold phases of ENSO (i.e., La Niña) have an adverse impact compared to El Niño. EAWR co-variation was evident only with the ENSO. Regarding AO, a non-meaningful action was noticed during the neutral phases of ENSO and EAWR. The findings of this study help understand and predict the seasonal trend of precipitation over the Gaza region. This is essential to set up climate change mitigation and adaptation strategies in the EM region.

Drivers of Eurasian Spring Snow-Cover Variability

AbstractThe variability of spring snow cover over Eurasia can have notable impacts on the current and following season climate, but the causes of it are poorly understood. This study investigates the potential drivers and the associated physical processes for the first two empirical orthogonal function (EOF) modes of the Eurasian spring snow-cover variability during 1967–2018, which are characterized by a continent-wide coherent pattern and a west–east dipole structure, respectively. Analyses show that the spring surface air temperature and snowfall are the direct factors influencing the two modes. We further examined the contributions to the snow-cover variability of atmospheric teleconnection patterns, sea surface temperature (SST) anomalies, and variations of Arctic sea ice during spring. The results indicate that circulation anomalies associated with the Arctic Oscillation, Polar–Eurasian pattern, and West Pacific pattern can partly explain the formation of the EOF1 mode, while the EOF2 mode has a close relationship with the East Atlantic–Western Russia pattern. In addition, a horseshoe-like monopole structure of SST anomalies over the North Atlantic plays an important role in regulating the EOF2 mode by inducing a wave train circulation. Moreover, the EOF2 mode is also affected by anomalous circulations induced by the sea ice anomalies in the Barents–Kara Seas. An empirical model using these drivers satisfactorily reproduced the temporal variations of the two EOF modes, implying that our results can substantially improve comprehension of the variability of Eurasian spring snow cover.

Moisture transport to a typical transitional climate zone in North China forced by atmospheric and oceanic internal variability under the background of global warming

AbstractNorth Central China (NCC) (34°–42°N, 95°–107°E), a typical transitional climate zone between westerlies and monsoon, shows multiple time‐scale variations in precipitation under the background of global warming. Thus, NCC moisture transport (NMT) was analysed based on reanalysis data from 1979–2015. By using the spatially unbounded dynamic recycling model, main NMT pathways and moisture sources were identified for the summer rainfall of NCC. The trend pattern of NMT manifests as a seesaw pattern with a weakening northwesterly transport but an enhancing southwesterly transport, suggesting an interaction between the mid‐latitude westerlies and the Indian monsoon. The temporal evolution of the NMT trend pattern exhibits interannual and multidecadal variability superimposed on long‐term trends, which correspond to the atmospheric and oceanic physical processes, respectively. The partial least squares regression analysis demonstrated that the temporal evolution of NMT trend patterns can be well explained by atmospheric and oceanic internal climate variability (ICV). At interannual time scales, the atmospheric ICV, composed of the circumglobal teleconnection (CGT) and East Atlantic (EA) and East Atlantic/Western Russia (EAWR) teleconnections, forms a Eurasian wave train that weakens westerly transport via the Europe blocking flow and enhances southwesterly transport via local circulation anomalies with a zonal dipole structure. However, oceanic ICV, composed of the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), exerts influence on a multidecadal time scale to decelerate the mid‐latitude westerly jet over the North Atlantic, providing favourable upstream background conditions for the formation of the Europe blocking and further maintaining the atmospheric ICV‐induced Eurasian wave train. Thus, the internal oceanic and atmospheric processes at different time scales couple to contribute to long‐term changes in precipitation over NCC under the background of global warming.

Extreme waves and climatic patterns of variability in the eastern North Atlantic and Mediterranean basins

Abstract. The spatial and temporal variability of extreme wave climate in the North Atlantic Ocean and the Mediterranean Sea is assessed using a 31-year wave model hindcast. Seasonality accounts for 50 % of the extreme wave height variability in the North Atlantic Ocean and up to 70 % in some areas of the Mediterranean Sea. Once seasonality is filtered out, the North Atlantic Oscillation and the Scandinavian index are the dominant large-scale atmospheric patterns that control the interannual variability of extreme waves during winters in the North Atlantic Ocean; to a lesser extent, the East Atlantic Oscillation also modulates extreme waves in the central part of the basin. In the Mediterranean Sea, the dominant modes are the East Atlantic and East Atlantic–Western Russia modes, which act strongly during their negative phases. A new methodology for analyzing the atmospheric signature associated with extreme waves is proposed. The method obtains the composites of significant wave height (SWH), mean sea level pressure (MSLP), and 10 m height wind velocity (U10) using the instant when specific climatic indices have a stronger correlation with extreme waves.