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The increasing concentration of atmospheric CO2 since the Industrial Revolution has affected surface air temperature. However, the impact of the spatial distribution of atmospheric CO2 concentration on surface air temperature biases remains highly unclear. By incorporating the spatial distribution of satellite-derived atmospheric CO2 concentration in the Beijing Normal University Earth System Model, this study investigated the increase in surface air temperature since the Industrial Revolution in the Northern Hemisphere (NH) under historical conditions from 1976–2005. In comparison with the increase in surface temperature simulated using a uniform distribution of CO2, simulation with a nonuniform distribution of CO2 produced better agreement with the Climatic Research Unit (CRU) data in the NH under the historical condition relative to the baseline over the period 1901–30. Hemispheric June–July–August (JJA) surface air temperature increased by 1.28°C ± 0.29°C in simulations with a uniform distribution of CO2, by 1.00°C ± 0.24°C in simulations with a non-uniform distribution of CO2, and by 0.24°C in the CRU data. The decrease in downward shortwave radiation in the non-uniform CO2 simulation was primarily attributable to reduced warming in Eurasia, combined with feedbacks resulting from increased leaf area index (LAI) and latent heat fluxes. These effects were more pronounced in the non-uniform CO2 simulation compared to the uniform CO2 simulation. Results indicate that consideration of the spatial distribution of CO2 concentration can reduce the overestimated increase in surface air temperature simulated by Earth system models. [ABSTRACT FROM AUTHOR]

The impact of Northern Hemisphere stratospheric final warming (SFW) events on surface air temperature (SAT) in April and May is examined based on the fifth-generation reanalysis data from the European Centre for Medium-Range Weather Forecasts (ERA5) and historical simulations from the Coupled Model Intercomparison Project Phases 6 (CMIP6). In ERA5, early SFWs occur in mid-March and lead to colder SAT in the Arctic, North Atlantic, and the Eurasian hinterland and warmer SAT in the Black Sea–eastern Europe region in April–May, while the anomalous SAT related to late SFWs that occur in early May is nearly the opposite. In addition, the effect of SFWs on SAT over the North Atlantic and Eurasia is more significant in April (May) in early (late) SFW years. The main pathway that SFW affects SAT over North Atlantic and Eurasia is through a tropospheric quasi-barotropic wave train, successively exhibiting anomalous high (low) centers above warmer (colder) SAT. This wave train seems associated with the Northern Annular Mode at 200 hPa in April, indicating its crucial role in linking SFWs and anomalous SAT. Generally, CMIP6 models can well reproduce the onset process of early and late SFWs but fail to capture its impact on spring SAT because of the underrepresentation of the associated Eurasian wave train due to ensemble means. The intercomparison among the models reveals that, models with realistic anomalous tropospheric wave train over Eurasia also simulate better surface impact of SFWs. [ABSTRACT FROM AUTHOR]

The relative importance of oceanic modes to global surface air temperature (SAT) and terrestrial precipitation during 1934–2020 was investigated using a variety of statistical and dynamical system methods. Through singular spectrum analysis, we present the distribution of decadal (10–20‐year), multidecadal (20–50‐year), and secular (>50‐year) variabilities of global SAT and terrestrial precipitation anomalies. Three sea surface temperature modes were identified by singular value decomposition that affect the low‐frequency variabilities of global SAT and terrestrial precipitation anomalies—namely, global warming (GW), the Interdecadal Pacific Oscillation (IPO), and the Atlantic Multidecadal Oscillation (AMO). The relative importance GW, the IPO, and the AMO in SAT and terrestrial precipitation was obtained through a normalized multivariate information flow analysis. Besides a high information flow percentage (60%) from GW to global SAT, especially over the northern Indian Ocean and tropical West Pacific, information flow from the AMO to the northwestern Pacific was also found. In terms of terrestrial precipitation, a large area with a wet trend was found over Eurasia at mid‐to‐high latitudes, and this trend was especially remarkable in the boreal winter half‐year (November–April), as compared with that in the boreal summer half‐year (May–October). By employing artificial neutral networks with a self‐organized map to cluster the key patterns of vertically integrated water vapour flux, we found that the synoptic circulation related to the wet trend is characterized by westerly flow that transports water vapour from the northeastern Atlantic to Eurasia, which is favourable for precipitation there both in the boreal winter and summer half‐year. [ABSTRACT FROM AUTHOR]

As one of the most significant circulation systems over the Northern Hemisphere in the cold season, the East Asian winter monsoon (EAWM) has been broadly investigated from the seasonal-mean perspective, while subseasonal variations in the EAWM still remain ambiguous. Based on Season-reliant Empirical Orthogonal Function (S-EOF) analysis, this study shows that the subseasonal strength reversal of the EAWM (SR-EAWM), featuring a weaker (or stronger) EAWM in early winter (December) and a stronger (or weaker) EAWM in late winter (January–February), is a distinct leading mode of the month-to-month variation of the EAWM. The weak-to-strong SR-EAWM is characterized by an anomalous low over Eurasia and a weakened East Asian major trough (EAT) in early winter, with an intensified Siberian High and a deepened EAT in late winter. The SR-EAWM is preceded by surface air temperature anomalies over Davis Strait (DST) and those over central-eastern North America (CENAT) in September–October. The DST mainly influences the SR-EAWM in early winter through a "sea ice bridge" of the November Baffin Bay sea ice concentration anomaly (BBSIC). The BBSIC could intensify the DST in December by altering surface heat flux, thus exciting a downstream atmospheric response and modulating the strength of the EAT in early winter. The CENAT affects the SR-EAWM in late winter by inducing an "ocean bridge" of the western North Atlantic sea surface temperature anomaly (WNASST). The WNASST can persist into late winter and then significantly affects the SR-EAWM by regulating Eurasian circulation anomalies and the downstream EAT. The bridge roles of the BBSIC and WNASST can be further verified by a linear baroclinic model. Finally, two physical-empirical models are established using the DST/BBSIC and the CENAT indices, respectively. Both exhibit promising prediction skills. The results highlight that the DST, BBSIC, and CENAT are crucial predictability sources for the SR-EAWM. [ABSTRACT FROM AUTHOR]

Based on modern observations, historical proxy data, and climate model simulations, this paper provides a comprehensive overview of the past, present and future evolution characteristics of the Atlantic Meridional Overturning Circulation (AMOC), as well as its impact on the surface air temperature (SAT) at regional and hemispherical scales. The reconstruction results based on the proxy data indicate that the AMOC has weakened since the late 19th century and experienced overall weakening throughout the 20th century with low confidence. Direct observations show that the AMOC weakened during 2004–2016, but it is not possible to distinguish between its decadal variability and long-term trend. Climate models predict that if greenhouse gas emissions continue to increase, AMOC will weaken in the future, but there will not be a sudden collapse before 2100. For the thermodynamic effects of AMOC, the increased surface heat flux release and meridional heat transport (MHT) over the North Atlantic associated with the strong AMOC cause an increase in the hemispherical SAT. At the millennial scale, climate cooling (warming) periods correspond to a weakened (strengthened) AMOC. The enhanced MHT of a strong AMOC can affect Arctic warming and thus influence regional SAT anomalies and SAT extremes through mutual feedback between Arctic sea ice and AMOC. In terms of dynamic effects, a strong AMOC modulates the Rossby wave trains originating from the North Atlantic and spreading across mid-to-high latitudes in the Northern Hemisphere and causes an increase in the variabilities in the circulation anomalies over the Ural and Siberian regions. Ultimately, a strong AMOC significantly affects the frequencies of extreme cold and warm events in the mid-to-high latitude regions over Eurasia. In addition, AMOC can also influence regional and global SAT anomalies through its dynamic adjustment of planetary-scale circulation. Decadal variation in AMOC is closely related to the Atlantic Multidecadal Oscillation (AMO). During positive phases of AMO and AMOC, enhanced surface heat fluxes over the North Atlantic lead to abnormal warming in the Northern Hemisphere, while during negative phases, the reverse case occurs. Under high emission scenarios in the future, the possibility of AMOC collapse increases due to freshwater forcing. However, most advanced climate models underestimate the strength of the AMOC and its impact on the AMO and relevant climate change, which presents a major challenge for future understanding and prediction of the AMOC and its climate effects. [ABSTRACT FROM AUTHOR]

This study investigates the association of spring (April–May) Arctic sea ice melt with simultaneous surface air temperature (SAT) over mid-high latitudes of Eurasia from 1979 to 2019 by using observational datasets and simulation experiments. The results show that spring SAT anomalies associated with Arctic sea ice melt display a dipole pattern over Eurasia. A high Arctic sea ice melt corresponds to positive SAT anomalies over northern Eurasia and negative SAT anomalies over most of Asia. The 500 hPa geopotential height anomalies exhibit a wave train structure, and a dominant positive center is located over the Ural Mountains with two negative centers over East Asia and western Europe. This atmospheric circulation anomaly differs from the traditional Eurasian pattern and the North Atlantic-Eurasian teleconnection pattern due to their different spatial modes. Simulation experiments forced by Arctic sea ice anomalies reproduce the major characteristics of observational associations. Observations and numerical simulations indicate that high Arctic sea ice melt years are often associated with heavy sea ice in winter-spring, which is favorable for the occurrence of Arctic anticyclonic circulation anomaly and lead to a positive SAT anomaly in the Arctic. The Arctic warming not only strengthens polar zonal westerly winds by increasing local baroclinicity, but also weakens zonal winds in mid-latitude through a reduction meridional temperature gradient. It may contribute to the Arctic anticyclonic anomalies enhancement, and then induces a wave train southeastward propagating into the mid-low latitudes. This configuration of atmospheric circulation anomalies provides favorable conditions for the SAT variations over Eurasia. [ABSTRACT FROM AUTHOR]

This study investigates the interdecadal variation of the intensity of the interannual variability (IIV) of surface air temperature (SAT) over mid‐ and high‐latitude Asia (MHLA) in winter months (December–February) during 1980–2015 and the role of the Arctic sea‐ice. Results show only the IIV of February SAT is significantly enhanced around the late‐1990s, which partly results from enhanced IIV of the frequency of extreme warm and cold events (FEWE and FECE). The influence of the sea‐ice in the Barents Sea from December to February on the February SAT, FEWE and FECE over MHLA is remarkably enhanced around the late‐1990s. During 1998–2015, the sea‐ice anomalies contribute to the enhanced IIV of February SAT over MHLA by modulating the monthly and synoptic tripole patterns over northern Eurasia, the positive phase of which exhibits an anomalous low over Eurasia north of 60°N and anomalous highs over southern Europe and MHLA. On the monthly average, the increased sea‐ice induces Rossby waves and then a positive phase of the monthly tripole pattern, inducing weakened East Asian trough and Siberian high, enhanced westerlies over 50°–70°N, and resultant decreased blocking high frequency over Eurasia north of 60°N. These anomalies favor increased February SAT over MHLA. On synoptic timescales, the increased blocking over the north side of the Ural Mountains favors more (fewer) extreme positive (negative) phases of the synoptic tripole pattern and hence increased FEWE (decreased FECE) over MHLA, further strengthening the increased SAT. Numerical experiments basically confirm the mechanisms above. Key Points: Intensity of interannual variability of February surface air temperature over mid‐ and high‐latitude Asia reinforces after 1998Intensity of interannual variability of frequency of February extreme warm and cold events over the region is enhanced after 1998Sea‐ice anomalies in the Barents Sea play an important role via modulating monthly and synoptic circulation over northern Eurasia [ABSTRACT FROM AUTHOR]

Quantitative estimates of the relationship of the snow cover and sea ice extent in the Northern Hemisphere with surface air temperature in the annual cycle and interannual variability are obtained from modern satellite data and reanalysis data over the 1979–2020 period. The results indicate a general significant coherence and negative correlation between surface air temperature and the snow cover and sea ice extent not only in the annual cycle, but also for most months in the interannual variability. At the same time, specific features appear in the fall months, associated with regional features of the variability of temperature and the snow cover during the season of its formation in Eurasia and North America. For the winter months, an increase in the absolute value of parameters of the sensitivity of the snow cover and sea ice extent to temperature variations in recent decades and of the coefficients of their correlation is noted, while for the warm months, the opposite changes are observed. Along with a statistically significant negative correlation of the total snow cover and sea ice extent with variations in the hemispheric surface air temperature in the annual cycle, cross-wavelet analysis revealed a statistically significant negative correlation for the longest-term interdecadal variations with a manifestation in recent years of significant anticorrelation for interannual variations, in particular for variations with periods typical for El Niño events. [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]

Large‐scale cold and warm spells successively attacked North Asia (NA) and resulted in a subseasonal alternation of extreme surface air temperature (SAT) before and after 15 January 2021. Our results show the synergistic effect of annual cycle and intraseasonal oscillation component (AC and ISO) of SAT and circulation anomalies caused temperature extremes. Before 15 January 2021, an eastward‐propagating Rossby wave train strengthened the cold circulation regime with an enhanced Ural blocking high (UBH) and surface Siberian high (SH). Circulation anomalies of the negative ISO were superimposed on the counterpart of AC, which easily resulted in cold extremes via nonlinear interaction of meridional temperature gradient. After mid‐January 2021, however, weakened UBH and SH caused warm advection and spells over NA. This synergistic effect of AC and ISO anomalies in SAT accounted for most historical temperature extremes, implying that AC anomalies have important indications for subseasonal alternation of temperature extremes. Plain Language Summary: Large‐scale cold and warm spells successively occurred in North Asia (NA) and resulted in the intraseasonal oscillation (ISO) of surface air temperature (SAT) extremes during 2020/21 winter. Here, we find the annual cycle (AC) of SAT and circulation anomalies provided a favorable background in regulating the subseasonal alternation of cold and warm extremes. The negative (positive) anomalies of AC (denoted PACN (PACP)) are characterized by enhanced (weakened) Ural blocking high (UBH) and Siberian high (SH), corresponding to cold (warm) NA circulation regimes before (after) 15 January 2021. During PACN (negative anomalies of ISO, PISON), a quasi‐barotropic Rossby wave train in the midlatitudes of Eurasia enhanced AC (ISO) of the UBH and SH, causing cold extremes in NA. While during the PACP and positive anomalies of ISO (PISOP), circulation anomalies like negative Arctic oscillation (AO) weakened UBH and SH, jointly resulting in warm extremes in NA. The subseasonal temperature change process in NA was mainly attributed to the conveyance of AC anomalies of meridional temperature gradient by subseasonal winds. Historical temperature extremes were almost attributed to the synergistic effect of AC and ISO of SAT anomalies, implying that the AC anomalies have important indications for subseasonal alternation of cold and warm extremes. Key Points: The successive cold and warm spells caused a subseasonal alternation of extreme surface air temperature (SAT) in North Asia during the 2020/21 winterThe annual cycle (AC) of meridional temperature gradient dominated by the nonlinear interaction of subseasonal advection in this winterCold and warm extremes in historical winters were verified by the synergistic effect of AC and intraseasonal oscillation in SAT anomalies [ABSTRACT FROM AUTHOR]

This study investigates the relationship between the central tropical Pacific (CTP) sea surface temperature (SST) and the surface air temperature (SAT) variability unrelated to canonical El Niño–Southern Oscillation (ENSO) over mid–high-latitude Eurasia during boreal summers over the past half-century. The results show that their relationship experienced a decadal shift around the early 1980s. Before the early 1980s, the Eurasian SAT–CTP SST connection was weak; after that time, the relationship became stronger, and the SAT anomalies exhibited a significant wavelike pattern over Eurasia. Such a decadal change in the Eurasian SAT–CTP SST relationship could be attributed to decadal changes in the mean state and variability of CTP SST. The warmer mean state and enhanced SST variability after the early 1980s reinforced the convective activities over the tropical Pacific, leading to significantly anomalous divergence/convergence and Rossby wave sources over the North Pacific. This outcome further excited the wave train propagating along the Northern Hemisphere zonal jet stream to northern Eurasia and then affected the surface heat fluxes and atmospheric circulations over the region, resulting in wavelike SATs over Eurasia. However, during the period before the early 1980s, the CTP SST had a weak impact on the North Pacific atmospheric circulation and was consequently not able to excite the wave train pattern to impact the Eurasian atmospheric circulation and SATs. The physical processes linking the CTP SST and Eurasian SAT are further confirmed by numerical simulations. The results of this study are valuable to understanding the variability of summer Eurasian SATs. [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]

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]

This study analyzes the dominant modes of interannual variability of surface air temperature (SAT) during boreal autumn over the mid-high latitudes of Eurasia and investigates their associations with snow cover, atmospheric circulation and sea surface temperature (SST). The first, second and third empirical orthogonal function (EOF) mode of autumn SAT anomalies displays same-sign distribution, an east–west dipole pattern and a south–north dipole pattern, respectively. Analysis of surface heat fluxes indicates that snow changes explain only small patches of SAT anomalies related to the first two EOFs via altering surface shortwave radiation. Atmospheric circulation anomalies have important contributions to the formation of SAT anomalies. Southerly (northerly) wind anomalies generally favor positive (negative) SAT anomalies via bringing warmer (colder) air from lower (higher) latitudes. The atmospheric circulation anomalies related to the first EOF mode are attributed to a combination of the Arctic Oscillation (AO) and the Scandinavia pattern and those related to the second EOF mode have a close relation with the East Atlantic/West Russian (EAWR) and circumglobal teleconnection (CGT) patterns. Formation of the atmospheric circulation anomalies related to the third EOF mode is partly related to the Arctic sea ice change around the Barents–Kara Seas. SST anomalies have little contribution to the atmospheric circulation anomalies associated with the first three EOF modes of Eurasian autumn SAT interannual variations. Hindcast skill of the SAT anomalies related to the first (second) EOF mode is improved when taking both the AO and Scandinavia (EAWR and CGT) patterns into account. [ABSTRACT FROM AUTHOR]

The interannual variability of March snow water equivalent (SWE) in Northern Eurasia and its influencing factors are studied. The surface air temperature (SAT) and precipitation are the dominant factors for the snow accumulation in northern Europe and the remaining region, respectively. The strongest contribution of SAT to snow accumulation is mainly found in those months with moderate mean SAT. The strongest contribution of precipitation is not collocated with the climatological maxima in precipitation. The leading mode of March SWE variability is obtained and characterized by a spatial dipole. Anomalies in atmospheric water vapor divergence, storm activity and the associated atmospheric circulation can explain many of the associated precipitation and SAT features. Anomalies in autumn Arctic sea ice concentration (SIC) over the Barents Sea and Kara Sea (B/K Sea) and a dipole pattern of November snow cover (SC) in Eurasia are also observed. The atmospheric circulation anomalies that resemble a negative phase of North Atlantic Oscillation (NAO)/Arctic Oscillation (AO) are strongly projected onto the wintertime atmospheric circulation. Both observations and model experiment support that the autumn B/K Sea SIC has some impacts on the autumn and AO/NAO-like wintertime atmospheric circulation patterns. The dipole pattern of November Eurasian SC seems to be strongly forced by the autumn B/K Sea SIC and its feedback to the atmospheric circulation is important. Therefore, the impacts of autumn B/K Sea SIC on the autumn/wintertime atmospheric circulation and thus the March SWE variability may be modulated by both constructive and destructive interference of autumn Eurasian SC. [ABSTRACT FROM AUTHOR]

This study reveals a close relation between autumn Arctic sea ice change (SIC) in the Laptev Sea-eastern Siberian Sea-Beaufort Sea and subsequent spring Eurasian surface air temperature (SAT) variation. Specifically, more (less) SIC over the above regions in early autumn generally correspond to SAT warming (cooling) over the mid-high latitudes of Eurasia during subsequent spring. Early autumn Arctic SIC affects spring Eurasian SAT via modulating spring Arctic Oscillation (AO) associated atmospheric changes. The meridional temperature gradient over the mid-high latitudes decreases following the Arctic sea ice loss. This results in deceleration of prevailing westerly winds over the mid-latitudes of the troposphere, which leads to increase in the upward propagation of planetary waves and associated Eliassen-Palm flux convergence in the stratosphere over the mid-high latitudes. Thereby, westerly winds in the stratosphere are reduced and the polar vortex is weakened. Through the wave-mean flow interaction and downward propagation of zonal wind anomalies, a negative spring AO pattern is formed in the troposphere, which favors SAT cooling over Eurasia. The observed autumn Arctic SIC-spring Eurasian SAT connection is reproduced in the historical simulation (1850-2005) of the flexible global ocean-atmosphere-land system model, spectral version 2 (FGOALS-s2). The FGOALS-s2 also simulates the close connection between autumn SIC and subsequent spring AO. Further analysis suggests that the prediction skill of the spring Eurasian SAT was enhanced when taking the autumn Arctic SIC signal into account. [ABSTRACT FROM AUTHOR]

This study analyzes the variability of northern Eurasian snow cover (SC) in autumn and the impacts of atmospheric circulation changes. The region of large SC variability displays a southward shift from September to November, following the seasonal progression of the transition zones of surface air temperature (SAT). The dominant pattern of SC variability in September and October features a zonal distribution, and that in November displays an obvious west-east contrast. Surface air cooling and snowfall increase are two factors for larger SC. The relative contribution of SAT and snowfall changes to SC, however, varies with the region and depends upon the season. The downward longwave radiation and atmospheric heat advection play important roles in SAT changes. Anomalous convergence of water vapor flux contributes to enhanced snowfall. The changes in downward longwave radiation are associated with those in atmospheric water content and column thickness. Changes in snowfall and the transport of atmospheric moisture determine the atmospheric moisture content in September and October, and the snowfall appears to be a main factor for atmospheric moisture change in November. These results indicate that atmospheric circulation changes play an important role in snow variability over northern Eurasia in autumn. Overall, the coupling between autumn Eurasian snow and atmospheric circulation may not be driven by external forcing. [ABSTRACT FROM AUTHOR]

The asymmetry in the teleconnection of the central Eurasian winter surface air temperature (SAT) with the Atlantic multidecadal oscillation (AMO) is discussed using observations and model simulations. Observations indicate that the winter SAT over central Eurasia (30°-70°E, 30°-50°N) shows significant positive anomalies during the warm AMO period but weak and insignificant anomalies in the cold AMO period. In general, the warm winters in central Eurasia are associated with large-scale negative sea level pressure anomalies in Europe, anomalous southwesterly winds at 850 hPa over Europe, the '+ − +' geopotential height anomalies at 500 hPa in the south of Greenland, northern Europe, western Asia, and the slant north-south '+ −' pattern jet stream anomalies at 200 hPa in the north and south of the Caspian Sea. Reverse patterns occur during cold winters. These statistically significant features are observed in the warm phase of AMO. Reversed circulation anomalies are observed during the cold phase of AMO; however, these anomalies are weak and not statistically significant. Furthermore, the asymmetry in the atmospheric response to AMO is well supported by simulations with a suite of GFDL atmospheric model idealized experiments and four CMIP5 models historical experiments. Both observations and simulations indicate that Rossby waves propagating from the North Atlantic eastward to Eurasia emerge in the warm AMO and disappear in the cold AMO. Thus, the different propagations of Rossby waves, induced by the different surface thermal conditions of the warm and cold AMO, are the potential connection between the North Atlantic Ocean and central Eurasian climate, and may explain the asymmetry. [ABSTRACT FROM AUTHOR]

Present study investigates local relationship between surface air temperature and snow water equivalent (SWE) change over mid- and high-latitudes of Eurasia during boreal spring. Positive correlation is generally observed around the periphery of snow covered region, indicative of an effect of snow on surface temperature change. In contrast, negative correlation is usually found over large snow amount area, implying a response of snow change to wind-induced surface temperature anomalies. With the seasonal retreat of snow covered region, region of positive correlation between SWE and surface air temperature shifts northeastward from March to May. A diagnosis of surface heat flux anomalies in April suggests that the snow impact on surface air temperature is dominant in east Europe and west Siberia through modulating surface shortwave radiation. In contrast, atmospheric effect on SWE is important in Siberia and Russia Far East through wind-induced surface sensible heat flux change. Further analysis reveals that atmospheric circulation anomalies in association with snowmelt over east Siberia may be partly attributed to sea surface temperature anomalies in the North Atlantic and the atmospheric circulation anomaly pattern associated with snowmelt over Russia Far East has a close association with the Arctic Oscillation. [ABSTRACT FROM AUTHOR]

A previous study indicated that the Arctic Oscillation (AO) and Siberian High (SH) are two important drivers for the interannual variation of winter surface air temperature (SAT) over southeast Asia. This study reveals that the impact of the winter SH on the southeast Asian SAT was stable. By contrast, the connection between the winter AO and southeast Asian SAT displays a pronounced interdecadal change around the late-1990s. Significant impact of the winter AO on the southeast Asian SAT can only be detected after the late-1990s. The result shows that change in the impact of the winter AO on southeast Asian SAT was mainly attributed to change in the spatial structure of the AO. Before the late-1990s, significant atmospheric signals related to the winter AO were confined to the North Atlantic region and the atmospheric anomalies over Eurasia were weak. As such, impact of the winter AO on the southeast Asian SAT was weak. By contrast, after the late-1990s, winter AO displays a more zonally symmetric structure, with significant negative sea level pressure (SLP) anomalies over the Arctic, and positive anomalies over mid-latitudes. Specifically, the positive SLP anomalies over East China induce clear northerly wind anomalies over southeast Asia, which lead to negative SAT anomalies there via wind-induced temperature advection. Hence, the winter AO has a significant impact on the southeast Asian SAT after the late-1990s. Further analysis shows that after the late-1990s, hindcast skill of the winter southeast Asian SAT anomalies was enhanced when taking both the winter AO and SH into account. [ABSTRACT FROM AUTHOR]

In the present paper, the linkage between the predominant modes of boreal winter surface air temperature (SAT) anomalies over Eurasia and the preceding autumnal Eurasian snow cover is investigated for the period of 1979–2014. The first leading winter Eurasian SAT mode exhibits a strong signal over the region northward from 40°N; in association with this SAT mode, a significant zonal dipole pattern in snow cover can be observed in the midlatitude Eurasia during November. Such anomalous November snow cover strengthens the wave activity flux upward propagating over the middle latitudes, which can change the stratospheric polar vortex thereafter. In the following winter, the anomalous polar vortex signal propagates downward to the surface and gives rise to the negative Arctic Oscillation‐like structure. Consequently, this leads to the winter SAT anomalies occupying the area north of 40°N. The second leading winter Eurasian SAT mode shows negative values northward from 60°N as well as positive over the middle latitudes of Eurasia; in association with the second SAT mode, the significant anomalous snow cover appears to the east of the Ural Mountains during October. Such an anomalous snow signal can persist from October until the subsequent winter and produce a wave‐like structure with a southeastward propagation from the Ural Mountains to the midlatitude Eurasia in the midtroposphere and upper troposphere, which results in the dipole anomalous temperatures lying in the middle to high latitudes of Eurasia. The preceding autumn snow cover signal is valuable for the prediction of the winter SAT over the Eurasian continent. Key Points: The midlatitude Eurasian zonal dipole pattern of November snow cover can exert an influence on the first mode of winter Eurasian surface air temperatureThe second mode of winter Eurasian surface air temperature has a close relationship with the October snow cover to the east of the Ural MountainsSnow cover‐related wave activity plays a crucial role in the connection between the autumn snow cover and winter surface air temperature over the Eurasian Continent [ABSTRACT FROM AUTHOR]