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Using ERA5 reanalysis data, we conducted an EOF analysis of summer precipitation in the eastern part of southwestern China (ESWC) over the past 60 years. Our study aimed to investigate the spatial distribution characteristics and interannual variability of summer precipitation in the ESWC, as well as to reveal the possible physical mechanisms influencing its interannual variability. The results indicate that, at the interannual scale, the first two modes of summer precipitation in the ESWC exhibit a uniform pattern and a north–south dipole pattern, respectively. The maximum and minimum time coefficients of the first mode correspond to the severe flood and drought events in 1998 and 2006, respectively, indicating that their time coefficients reflect the typical events well. The tri-pole sea surface temperature anomaly in the North Atlantic, along with the sea ice anomaly near the Barents Sea, induces a quasi-zonal wave train in the upper troposphere. This wave train propagates from the tropical and mid-latitude Atlantic, traverses the mid-high latitudes of Eurasia, and reaches the eastern part of China. The wave train induces cyclonic (anticyclonic) anomalies in the north (south) of the ESWC, facilitating the convergence of high-latitude dry and cold air with warm and moist southwesterly winds from the tropical ocean. This convergence promotes increased summer precipitation in the ESWC. We provided valuable insights into the interannual variability of summer precipitation in the ESWC, shedding light on the physical mechanisms responsible for these variations. [ABSTRACT FROM AUTHOR]

In winter 2020/2021, several episodes of cold air outbreaks have wreaked havoc across much of China, resulting in exceptionally low temperatures over northern‐to‐southeastern China. Our analysis shows that the anomalous circulation leading to the cold wave in China was characterized as: (a) a strengthening of the Siberian high, (b) a deepening of the East Asian trough, and (c) a weakening of the stratospheric polar vortex. Prior to the winter, in summer and autumn, the largest sea ice loss along the Siberian coast was observed. We therefore address the question whether the substantial sea ice loss has contributed to the cold wave. First, applying singular value decomposition (SVD) analysis, we find strong coherence between the autumn Arctic sea ice coverage and temperatures over the central‐to‐east Asian region with the sea ice component (SVD1_SIC) reaching a record high in 2020 and displaying a decadal shift around 2005. Associated with both the interannual and decadal variations of the SVD1_SIC, there are similar circulation anomalies as described in (a), (b) and (c) above. Second, applying self‐organizing maps, wintertime daily air temperatures are clustered into nine nodes with Node‐1 mostly resembling "warm Arctic, cold Eurasia" pattern. The frequency of Node‐1 shows a similar decadal shift as observed in SVD_SIC1 above, with a correlation of about 0.56. Associated with Node‐1, the circulation anomalies are consistent with features highlighted in (a), (b) and (c) above. Thus, taking all the evidence into account, we conclude that the substantial sea ice loss along the Siberian coast contributed significantly to the 2020/2021 winter cold wave in China. The mechanism behind the contribution in this study highlights that the Arctic sea ice loss is favourable for certain circulation patterns on climate timescale, reinforcing disruptive chain of reactions on weather timescale, and leading to severe cold events. [ABSTRACT FROM AUTHOR]

Based on rainfall data for the period of 1960–2018 from 382 stations in southwest China and multiple reanalysis datasets, interannual variation of rainfall in late spring over Southwest China and associated sea surface temperature and atmospheric circulation anomalies are examined. The first leading mode of late-spring rainfall anomalies displays a uniform-distribution pattern. The second leading mode shows a zonal dipole pattern. The leading mode is related to an atmospheric wave train over mid-high latitudes of Eurasia, with a center of action of atmospheric anomaly over Southwest China. The atmospheric anomalies over Southwest China modulate late-spring rainfall there via modulating vertical motion and water vapor transport. In addition, the leading mode of late-spring rainfall anomalies has a close relation with sea surface temperature anomalies (SSTA) in the central and eastern equatorial Pacific. SSTA in the central and eastern equatorial Pacific impacts late-spring rainfall anomalies over Southwest China via modulation of the tropical Walker and Hadley circulation. The second leading mode of late-spring rainfall variation over Southwest China is closely associated with SSTA in the tropical western Pacific and a mid-high latitude wave train. SSTA in the tropical western Pacific and the mid-high latitudes wave train together leads to out-of-phase variation of meridional wind anomalies between western and eastern parts of Southwest China, which further results in a zonal dipole rainfall anomaly over Southwest China. [ABSTRACT FROM AUTHOR]

The impact of soil freezing‐thawing processes on August rainfall in Southern China (SC) during 1979–2008 and related physical mechanisms are investigated using the coupled land‐atmosphere model Grid‐Point Atmospheric Model version 2.0—Community Land Model version 2.0 (GAMIL2.0‐CLM2.0). The moisture‐budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long‐term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40°N, which is not only weakened the meridional thermal contrast but also induced an anomaly "north high–south low" circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the "southern flooding" during 1979–2008 from the point of frozen soil changing. Key Points: The coupled land‐atmosphere model (Grid‐Point Atmospheric Model version 2.0‐Community Land Model version 2.0) with the consideration of supercooled water reproduces the trend of the August rainfall in Southern ChinaThe dynamic processes of the vertical moisture advection play a vital role in the long‐term trend of the August rainfallThe decreasing soil ice content has contributed to the wetter of Southern China in August over 1979–2008 [ABSTRACT FROM AUTHOR]

An unprecedented cold event occurred in Central and eastern Eurasia during the 2020/21 winter, including five episodes of consecutive cold spells (EP1–5). Through analysis of both observational and simulations, we show that the concurrent Arctic sea-ice loss and extratropical Pacific decadal oscillation (EPDO) warming are potential drivers for the cold event. Their relative contributions to the intraseasonal evolutions of atmospheric circulation and concomitant cold surges are thoroughly investigated. The circulation anomalies highlight the gradual development of the negative Arctic oscillation, accompanied by strengthened Siberian high and deepened Aleutian low. Stratospheric pathways were integrally involved in the dynamical response and the timing of episodes. Our results suggest that the sea-ice, irrespective of seasonality, and autumn EPDO experiments can generally capture the spatial patterns of atmospheric circulation and temperature in observation, albeit weaker in magnitude. Autumn (winter) sea-ice loss led to the EP1–3 (EP2–3) cold spells, and autumn EPDO led to the EP1–3 cold surges; whereas the EP4–5 cold spells induced by autumn SIC and PDO were not statistically robust. The Eurasian cooling response to winter PDO is weak due to the extensive warming over southern China and Eurasian highlatitudes that offsets the midlatitude cooling. The largest coolings were found in SIC and EPDO combined experiments, suggesting their synergic importance in driving such cold events. Our results have implications for the potential predictability of winter extreme events over Eurasia in the context of ongoing sea-ice decline and a recent shift to the positive PDO phase. [ABSTRACT FROM AUTHOR]

Weather and climate extremes often cause devastating disasters and motivate research to improve their understanding. Here, the spatiotemporal variations in the frequency of winter extreme cold days (WECDS) in northern China (NC) were investigated. The results show that the first EOF mode reflects the spatially consistent anomalies and explains 39% of the total variance. The second EOF mode represents the east-west contrasted anomalies and explains 17% of the total variance. In the winter, when the negative Arctic Oscillation (AO) co-occurs with the stronger Siberian high (SH), cold air from the polar region is more easily advected southward, causing the increased number of WECDS in all of NC. The co-occurrence of negative AO and stronger SH may be related to excessive snow in the preceding autumn over northeastern Eurasia through the local positive feedback between the snow and surface air temperatures and the tropospheric-stratospheric interaction. On the other hand, in the winter when the negative AO co-occurs with the weaker SH, eastern NC is still under the influence of cold-air intrusion from the polar region relevant to the negative AO, whereas western NC is impacted by the anomalous warm-air advection related to the weaker SH. The weakening of the SH may be caused by the El Niño teleconnection. The reproducibility of the observed variations and possible causalities of WECDS in NC by 10 coupled models participating in CMIP5 has been assessed. All the models can reproduce the observed dominant EOF modes. The relevant large-scale circulation anomalies and possible causalities can also be well simulated by the multimodel ensemble. [ABSTRACT FROM AUTHOR]

Since the late 1990s, the global warming has ground to a halt, which has sparked a rising interest among the climate scientists. The hiatus is not only observed in the globally averaged surface air temperature (SAT), but also in the China winter temperature trend, which turns from warming during 1979–1997 to cooling during 1998–2013. However, the reasons and the relevant mechanisms of the warming hiatus are far from being understood. Arctic sea ice (ASI), one of the tipping points of the Earth system change, has contributed to the dramatic climate change. It is found that the ASI over the Barents–Kara Seas in the warming hiatus period (1998–2013) has declined about three times faster than that in the previous continuing warming period (1979–1997). The observational analysis and the wave ray trajectories suggest that, for the hiatus period, the ASI over the Barents-Kara Seas explains 61.4% of the decreasing SAT trend and 14.4% of the interannual SAT variation in China. The possible dynamical process is as follows: the anomalous ASI loss associated with the significant warming in Barents-Kara Seas can excite a downstream teleconnection wave train pattern over the Eurasia continent. The significant easterly winds in the subpolar region slacken the polar-front jet, while the anomalous westerly winds over the Tibetan Plateau reinforce the East Asian subtropical jet. As a result, the concurrent out-of-phase variations in the intensity of the jets lead to the cold flow moving southward from the Arctic and converging in China. The northwest–southeast tilted dipole pattern of the height centers over Eurasia, accompanied with the weakened polar-front jet, usually favors the persistence of Ural blocking (UB). Furthermore, in the lower level, the anomalous high pressure belt over the northern Eurasian continent can help cold northeasterly winds blow from the Russian Far East to China and bring about the cold winters. Thus, the accelerated melting of ASI can exert a profound influence on China warming hiatus in recent two decades. [ABSTRACT FROM AUTHOR]

• Circulation over mid-high-latitude Eurasia shows significantly 10 − 30-day ISO during boreal winter. • Both the phase and amplitude of this ISO evidently modulates surface air temperature anomaly in China. • Extremely high-temperature events tend to appear in Phase 3–5, and extremely cold events tend to occur in Phase 6–1. Using reanalysis and gauge data, the modulation of the intraseasonal oscillation (ISO) both in terms of its phase and amplitude originating from mid-to-high latitude Eurasia on surface air temperature (SAT) over China in boreal winter is investigated. The dominante period of the ISO at mid-to-high latitudes is 10–30 days during boreal winter. Based on an empirical orthogonal function analysis, ISO phase and amplitude over mid-to-high latitude Eurasia are defined. The phase is defined based on the ratio of the first two principal components, and the amplitude is defined as the square root of the sum of the squares of the first two principal components. During Phase 2–5 (6‒1), China is mainly controlled by intraseasonal warm (cold) anomaly air, as the quasi-barotropic ISO anticyclone (cyclone) over mid-to-high latitude gradually propagates southeastward to East Asia. In Phase 2 (Phase 6), the strongest positive (negative) anomaly appears over northern China, while in Phase 3–4 (Phase 7–8) it is over northeastern China, and Phase 5 (Phase 1) in southern China. When the ISO amplitude exceeds one standard deviation, the SAT anomaly over China is enhanced. When the amplitude is under negative one standard deviation, the anomaly over China is evidently weakened and the area passing the statistical significance test is obviously reduced. Modulated by ISO, the extremely high-temperature events over China in boreal winter tend to appear in Phase 3–5, especially in Phase 4, whilst the extremely cold events are likely to occur in Phase 6–1. [ABSTRACT FROM AUTHOR]

This paper addresses the interannual variation of winter air temperature over Northeast China and its connection to preceding Eurasian snow cover. The results show that there is a significant negative correlation between October Eurasian snow cover and following-winter air temperature over Northeast China. The snow cover located in eastern Siberia and to the northeast of Lake Baikal plays an important role in the winter air temperature anomaly. More (less) eastern Siberia snow in October can cause an atmospheric circulation anomaly pattern in which the atmospheric pressure is higher (lower) than normal in the polar region and lower (higher) in the northern mid-high latitudes. Due to the persistence of the eastern Siberia snow from October to the following winter, the winter atmospheric anomaly is favorable (unfavorable) to the widespread movement of cold air masses from the polar region toward the northern mid-high latitudes and, hence, lower (higher) temperature over Northeast China. Simultaneously, when the October snow cover is more (less), the SST in the northwestern Pacific is continuously lower (higher) as a whole; then, the Aleutian low and the East Asia trough are reinforced (weakened), favoring the lower (higher) temperature over Northeast China. [ABSTRACT FROM AUTHOR]

New characteristics of surface wind speed variations in Northwest China and the possible explanations for them have remained undetermined over the recent decades. This study presents the characteristics and possible mechanisms of surface wind speed variations in Northwest China from 1979 to 2019. The results show that the surface wind speed in Northwest China underwent a two-stage change rather than a persistent decline from 1979 to 2019; specifically, it declined significantly before the early 2000s and then increased gradually thereafter. The meridional pressure gradient decrease caused by the meridional temperature gradient reduction corresponded to a decrease in the winter surface wind speed in Northwest China during 1979–2002. The meridional pressure gradient increase caused by the meridional temperature gradient increase was consistent with an increase in the winter surface wind speed in Northwest China during 2003–2019. This suggests that the spatially inhomogeneous variations in surface air temperature in Eurasia's mid-high latitudes may be the main reason for the surface wind speed variations in Northwest China. Furthermore, the decadal strengthening of the East Asian winter monsoon (EAWM) may have resulted in an upward trend of the surface wind speed in Northwest China after the early 2000s by strengthening the Siberian High (SH). Although the variations in the surface wind speed in Northwest China are inconsistent with those in the winter Arctic Oscillation (AO) index, there is a significant negative correlation between them on the interannual timescale. With a negative (positive) AO phase, the surface wind speed in Northwest China increases (decreases) in winter. • Surface wind speed in Northwest China has shifted from decrease to increase since 2003. • Regional warming/cooling may be the main reason for the variations in surface wind speed. • Decadal strengthening of EAWM may intensify wind speed after the early 2000s. • AO can explain the surface wind speed variations at the interannual timescale. [ABSTRACT FROM AUTHOR]

This study investigates and compares the reasons for high-frequency heavy and light snowfall in winter on interannual timescales over northeast China (NEC) during 1961–2017. Results indicate that the frequency and its variability are strong over southeastern NEC for heavy snowfall but over northern NEC for light snowfall. Analysis of the annual cycle shows that the maximum frequency of heavy snowfall occurs in November and March due to more warm–wet air masses and increased atmospheric instability, and that of light snowfall occurs in December–January due to drier conditions and increased atmospheric stability. The frequency of heavy snowfall exhibits an increasing trend which partly results from the warming trend in NEC, while that of light snowfall shows a decreasing trend. High-frequency heavy snowfall is associated with a positive North Atlantic Oscillation (NAO), warmer regional air temperatures, an increased water vapor budget associated with an anomalous anticyclone occupying the Kuril Islands, and relatively unstable atmospheric layers. High-frequency light snowfall is associated with a strengthened East Asian winter monsoon, colder regional air temperatures, a decreased water vapor budget, and relatively stable atmospheric layers. High-frequency heavy and light snowfall are both related to eastward-propagating quasi-stationary waves over Eurasia, but with different features. The waves of the former are located in midlatitude Eurasia and related to the positive phase of the NAO. The waves of the latter exhibit two pathways, located in midlatitude and northern Eurasia, respectively. The northern one can be partially attributed to a weak polar vortex. In addition, higher sea surface temperatures of the Kuroshio Extension may contribute to high-frequency heavy snowfall. [ABSTRACT FROM AUTHOR]