Winter Surface Air Temperature Research Articles

Emergent constraints on the future East Asian winter surface air temperature changes

Abstract In East Asia, the climate variability in boreal winter is dominated by the East Asian winter monsoon, one of the most energetic monsoon systems that can lead to disasters. The key variable, the East Asian winter surface air temperature (SAT), has significantly changed over the past century and has substantially impacted agriculture, ecosystems, economics, and public health. However, its projections are limited by considerable uncertainties. Here, we identify the first leading mode that explains almost 32.1% of the inter-model spread in future SAT change. Our research delves into the evolution of present-day biases under future scenarios and their consequential impact on the SAT. Models with stronger western currents in the North Pacific exhibit a warmer North Pacific at mid-latitudes during historical periods. Additionally, these models consistently demonstrate stronger western currents in the future, contributing to the amplified warming of the western North Pacific, thereby warming Eurasia via the weakened trough and subtropical jet through barotropic responses to the warm North Pacific. Incorporating observational sea surface temperature (SST) constraints reduces uncertainties by 15.6%, revealing a more reliable SAT change pattern by the end of the 21st century.

The out‐of‐phase variation of surface air temperature anomalies over northern Central Asia between January and February: The role of intraseasonal variations in tropical convection

AbstractThe out‐of‐phase mode of winter surface air temperature anomalies (SATAs) over northern Central Asia (NCA; 45°–65°N, 40°–100°E) between January and February is investigated in this study. This mode corresponds to warm (cold) SATAs in January (February) over NCA and is mainly modulated by the enhanced tropical convection anomalies over the Maritime Continent in previous late December, associated with MJO phase 4. These tropical convection anomalies can induce anomalous tropospheric Rossby‐wave sources over the North Pacific in late December. The eastward‐propagating Rossby‐wave train, triggered by these anomalous Rossby‐wave sources, can cause negative and positive tropospheric geopotential height anomalies over the Greenland–Scandinavia region and NCA in the following early–mid‐January, subsequently leading to warm SATAs over NCA in January. The negative geopotential height anomalies over the Greenland–Scandinavia region in early–mid‐January can trigger upward‐propagating wave activity fluxes (WAFs) into the stratosphere, resulting in negative stratospheric geopotential height anomalies in late January–early February. These stratospheric anomalies, by triggering downward‐propagating WAFs, can in turn lead to positive tropospheric geopotential height anomalies over the Greenland–Scandinavia region in early February. These anomalies over the Greenland–Scandinavia region can maintain themselves in the following mid‐ and late February by feedback of anomalous storm tracks, and cause negative geopotential height anomalies and subsequently cold SATAs over NCA in February by triggered southeastward‐propagating Rossby‐wave train.

Distinguishing Impacts on Winter Temperatures in Northern Mid-to-High Latitude Continents during Multi-year and Single-year La Niña Events: A Modeling Study

Abstract Utilizing a 2200-year CESM1 pre-industrial simulation, this study examines the influence of property distinctions between single-year (SY) and multi-year (MY) La Niñas on their respective impacts on winter surface air temperatures across mid-to-high latitude continents in the model, focusing on specific teleconnection mechanisms. Distinct impacts were identified in four continent sectors: North America, Europe, Western Siberia (W-Siberia), and Eastern Siberia (E-Siberia). The typical impacts of simulated SY La Niña events are featured with anomalous warming over Europe and W&E-Siberia and anomalous cooling over North America. Simulated MY La Niña events reduce the typical anomalous cooling over North America and the typical anomalous warming over W&E-Siberia but intensify the typical anomalous warming over Europe. The distinct impacts of simulated MY La Niñas are more prominent during their first winter than during the second winter, except over W-Siberia, where the distinct impact is more pronounced during the second winter. These overall distinct impacts in the CESM1 simulation can be attributed to the varying sensitivities of these continent sectors to the differences between MY and SY La Niñas in their intensity, location, and induced sea surface temperature anomalies in the Atlantic Ocean. These property differences were linked to the distinct climate impacts through the Pacific North America, North Atlantic Oscillation, Indian Ocean-induced wave train, and Tropical North Atlantic-induced wave train mechanisms. The modeling results are then validated against observations from 1900 to 2022 to identify disparities in the CESM1 simulation.

Impact of the Eurasian Zonal Circulation on the Interannual Variability of Winter Surface Air Temperature and Subseasonal Temperature Reversal in North China

AbstractThis study focuses on the interannual variability of winter mean surface air temperature (SAT) and subseasonal SAT reversal in North China, which have profound impacts on national life and economic activities. The analysis explores the temporal and spatial distribution characteristics of these variations and their relationship with the Eurasian Zonal Circulation (EZ). The findings reveal distinct interdecadal changes in North China’s winter mean SAT, along with a general subseasonal reversal of cold and warm conditions. In comparison to the North Atlantic oscillation/Arctic Oscillation, the EZ has a more significant influence on the interannual variability of winter and subseasonal reversals. Strong EZ years are associated with the weakening of the Siberian High and the Ural Blocking High, causing the East Asian Trough to move eastward, which leads to the retention of cold air from the north and increased SAT in North China. Conversely, weak EZ years exhibit opposite circulation patterns. The winter mean EZ is influenced by preceding autumn Arctic sea ice concentrations (SIC). Reduced autumn SIC results in decreased heat flux and reduced eddy energy, leading to substantial attenuation of the winter storm track across Scandinavia and Western Asia. This attenuation, mediated through the interaction between eddies and mean flow, triggers a slowdown of Eurasian zonal circulation and intensification of the Siberian High. These conditions favor a positive phase of the winter Scandinavia pattern, facilitating the transport of cold Arctic air into North China. Likewise, subseasonal reversals in SIC influence corresponding alterations in the EZ.

Observed winter Barents Kara Sea ice variations induce prominent sub-decadal variability and a multi-decadal trend in the Warm Arctic Cold Eurasia pattern

The observed winter Barents-Kara Sea (BKS) sea ice concentration (SIC) has shown a close association with the second empirical orthogonal function (EOF) mode of Eurasian winter surface air temperature (SAT) variability, known as Warm Arctic Cold Eurasia (WACE) pattern. However, the potential role of BKS SIC on this WACE pattern of variability and on its long-term trend remains elusive. Here, we show that from 1979 to 2022, the winter BKS SIC and WACE association is most prominent and statistically significant for the variability at the sub-decadal time scale for 5–6 years. We also show the critical role of the multi-decadal trend in the principal component of the WACE mode of variability for explaining the overall Eurasian winter temperature trend over the same period. Furthermore, a large multi-model ensemble of atmosphere-only experiments from 1979 to 2014, with and without the observed Arctic SIC forcing, suggests that the BKS SIC variations induce this observed sub-decadal variability and the multi-decadal trend in the WACE. Additionally, we analyse the model simulated first or the leading EOF mode of Eurasian winter SAT variability, which in observations, closely relates to the Arctic Oscillation (AO). We find a weaker association of this mode to AO and a statistically significant positive trend in our ensemble simulation, opposite to that found in observation. This contrasting nature reflects excessive hemispheric warming in the models, partly contributed by the modelled Arctic Sea ice loss.

Subtropical SST improved the understanding of the subseasonal reversal of surface air temperature in winter over the mid-high latitudes of Asia

The mid-high latitudes of Asia are cold air gathering places and dust source areas, whose subseasonal reversal of surface air temperature (SAT) between early winter (December 1 to January 14) and late winter (January 15 to February 28) could trigger extreme temperature at mid-low latitudes. Based on the observed interannual variation of SAT over mid-high latitudes of Asia (SATMH-A) in early and late winter after detrending from 1979 to 2021, the across-latitude linkage between the SATMH-A subseasonal reversal and subtropical sea surface temperature (SST) was revealed. The southern Indian Ocean SST anomalies caused the Ural high weakened through meridional circulations and led to a warm SATMH-A in early winter, but had little effect on SATMH-A in later winter. Whereas the North Atlantic SST anomalies enhanced the cold air intrusion in late winter by exciting Rossby wave to strengthen the Ural blocking, while the SATMH-A in early winter was largely unresponsive. The SST factors in Indian Ocean and North Atlantic primarily impacted the SATMH-A in early and late winter respectively. Their synergies effectively modulated the subseasonal reversal, which was conducive to improving the explanation and prediction for the SATMH-A subseasonal reversal. Especially in the winter of 2020/21 and 2021/22, the mean prediction bias was only 0.03 °C and 0.20 °C in early and late winter contributed by the two SST factors. Moreover, the improved prediction ability on the subseasonal scale was also helpful for the accurate predictions of SATMH-A on winter-mean scale. Findings of this study also have the potential to be applied to more accurately predict temperature extremes in mid-low latitudes.

The impact of ENSO and NAO initial conditions and anomalies on the modeled response to Pinatubo-sized volcanic forcing

Abstract. Strong, strato-volcanic eruptions are a substantial, intermittent source of natural climate variability. Initial atmospheric and oceanic conditions, such as El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), also naturally impact climate on interannual timescales. We examine how initial conditions of ENSO and NAO contribute to the evolution of climate in the period following a Pinatubo-type eruption using a large (81-member) ensemble of model simulations in GISS model E2.1-G. Simulations are initialized from sampled conditions of ENSO and NAO using the protocol of the coordinated CMIP6 Volcanic Model Intercomparison Project (VolMIP) – where aerosols are forced with respect to time, latitude, and height. We analyze paired anomalous variations (perturbed – control) to understand changes in global and regional climate responses under positive, negative, and neutral ENSO and NAO conditions. In particular, we find that for paired anomalies there is a high probability of strong (∼1.5 ∘C) warming of northern Eurasia surface air temperature in the first winter after the volcanic eruption for negative NAO ensembles coincident with decreased lower stratospheric temperature at the poles, decreased geopotential height, and strengthening of the stratospheric polar vortex. Climate anomalies (relative to average conditions across the control period), however, show no mean warming and suggest that the strength of this response is impacted by conditions present in the selected period of the control run. Again using paired anomalies, we also observe that under both +ENSO and −ENSO ensembles sea surface temperature decreases in the first post-eruptive boreal winter coinciding with surface cooling from volcanic aerosols. Neutral ENSO ensembles, on the other hand, show variability in their response with no clear trend in post-eruptive warming or cooling. In general, paired anomalies from unperturbed simulations give insight into the evolution of the climate response to volcanic forcing; however, when compared with anomalies from climatological conditions, it is clear that paired anomalies are significantly affected by sampled initial conditions occurring at the time of the volcanic eruption.

Impact of stratospheric variability on subseasonal temperature reversals during late winter over the mid-high latitudes of East Asia

Significant phase shifts in winter surface air temperature (SAT) anomalies have successively occurred in East Asia (EA) during recent years, leading to detrimental effects on socio-economic activities. In this study, we identify the fourth principal mode of month-to-month SAT variations over EA in winter (November–February) using the Season-reliant Empirical Orthogonal Function (S-EOF) analysis. The fourth S-EOF mode (S-EOF4) represents subseasonal SAT reversals over the mid-high latitudes of EA during late winter (January–February), with cold (warm) anomalies over Northeastern Asia in January and widespread warm (cold) anomalies over midlatitude EA in February. Results indicate that the cold-to-warm S-EOF4 is associated with a northward shift of the Siberian High in January and a quasi-barotropic low-pressure system over the Ural region in February. The formation of the S-EOF4 is accompanied by stratospheric temperature anomalies over eastern Siberia–Alaska in January. Stratospheric warming corresponds to cold-to-warm transitions over the mid-high latitudes of EA, and vice versa. Further investigation suggests that stratospheric warming would simultaneously lead to a weakened Arctic stratospheric polar vortex (SPV), which mainly stretches into Northern Eurasia and directly influences cold anomalies over Northeastern Asia in January. The delayed impact of stratospheric variability on the reversal of EA SAT anomalies is accomplished by an “ocean bridge” of the midlatitude North Atlantic sea surface temperature (SST) anomaly. The weakened SPV promotes anomalous westerly winds in the midlatitude North Atlantic and generates a significant SST cooling, which then regulates a cyclonic anomaly over the Ural region and results in warm anomalies over the midlatitude EA in February. The bridge role of the North Atlantic SST anomaly is well supported by a linear baroclinic model. In addition, the deepening of the Aleutian Low in December could significantly enhance the climatological wavenumber 1, serving as the tropospheric precursor of stratospheric warming. These findings contribute to an in-depth comprehension of EA subseasonal temperature variability, offering valuable insights for enhancing seasonal prediction strategies.

Physical Mechanism of Winter Temperature Multidecadal Variations in Arid Central Asia: The Role of the Atlantic Multidecadal Oscillation (AMO)

Abstract This study investigates the influence of the Atlantic multidecadal oscillation (AMO) on the multidecadal variability of winter surface air temperature in arid central Asia (ACASAT). Apart from a long-term warming trend, the observational analysis shows that the winter ACASAT exhibits a significant multidecadal variability, which is characterized by antiphase fluctuations with the AMO. The mechanism for this negative correlation between the AMO and the winter ACASAT is explored from the aspect of wave teleconnection. The AMO provides energy for the Scandinavian teleconnection pattern at middle and low altitudes by regulating the high-altitude wave train over the middle and high latitudes of Eurasia, and thus has an impact on the remote climate in arid central Asia. Results from the linear baroclinic model (LBM) provide evidence for the linkage between the AMO and the Scandinavian teleconnection pattern. When the AMO is in its warm periods, the Scandinavian teleconnection pattern is in a positive phase, which further makes the cold air from the northeast strengthen, leading to the anomalously colder surface air temperature in arid central Asia. Based on the relationship that the North Atlantic Oscillation (NAO) leads the AMO by 15–20 years, it is further found that there is a leading relationship between the NAO and the winter ACASAT via the AMO. On this basis, an empirical model using the NAO as a predictor was established to predict the ACASAT, and the empirical model shows good hindcast performance. Results from the model show that the winter ACASAT will continue to rise in the next 10 years and decline after 2030.

Diurnal Cycle Dependence of ENSO Influence on the Winter Surface Air Temperature in Southeastern China

Abstract It is well known that El Niño–Southern Oscillation (ENSO) can influence the East Asian winter climate by modifying the atmospheric circulation over the western North Pacific (WNP). While the impact on precipitation in southeastern China has been extensively studied, the ENSO signal in surface air temperature (SAT) remains overlooked. In this paper, we identify robust ENSO footprints in the winter daily minimum SAT in southeastern China, with El Niño winters generally accompanied by warmer-than-normal minimum SAT anomalies. In contrast, the responses of maximum SAT are weak and negligible, suggesting a diurnal cycle–dependent ENSO influence. Further analysis indicates that this diurnal cycle dependence stems primarily from the disparate surface radiative heating between day and night induced by ENSO-related local total cloud cover (TCC) change. The warmer minimum SAT occurring in the early morning of El Niño winters is mainly caused by the enhanced surface downward longwave radiative heating as a result of the TCC increase. However, in the afternoon of El Niño winters, although the anomalous horizontal advection of warm air plays a role, there is surface radiative cooling as the weakening of solar radiation due to TCC reflection overwhelms the increase in downward longwave radiation, which leads to a weakened sensible heat flux and thus has a cooling effect on the SAT. Ultimately, these two processes effectively cancel each other out and together produce insignificant maximum SAT responses. Our conclusions carry important implications for the seasonal to interannual winter climate prediction in southeastern China. Significance Statement The purpose of this study is to better understand how ENSO influences winter surface air temperature in southeastern China. Despite insignificant responses of winter daily maximum temperature to ENSO, we find here a robust ENSO influence on the daily minimum temperature, with warm anomalies tending to occur during El Niño events. Further evidence suggests that this diurnal cycle–dependent ENSO influence is mainly caused by ENSO-induced change in local cloudiness, which has a different radiative heating effect between day and night. Our findings are of great importance for improving regional climate prediction, which will benefit social and economic activities.

Intraseasonal variations in winter surface air temperature over China and its prediction skill in ECMWF System5

AbstractBased on the daily average temperature data of 2374 stations in China from 1993 to 2022 and the monthly average temperature data of European Centre for Medium‐Range Weather Forecasts (ECMWF) System5 in winter, this article analyses the intraseasonal variations of winter surface air temperature (SAT) over China by using seasonal empirical orthogonal function decomposition (S‐EOF) and compare the prediction skill differences of the first three dominant modes in ECMWF System5. The first mode (S‐EOF1) is characterized by out‐of‐phase changes in SAT anomalies (SATA) between December and January. Both the Siberian high (SH) and the central Pacific El Niño‐Southern Oscillation (CP ENSO) can impact S‐EOF1. The second mode (S‐EOF2) is characterized by consistency in warm anomalies over the Northeast and Qinghai‐Tibet Plateau's variation, while the other areas are characterized by the out‐of‐phase change in SATA. S‐EOF2 is closely related to Arctic oscillation (AO). The third mode is characterized by alternating changes over 3 months in winter, which is related to the Pacific meridional mode (PMM) and the North Atlantic SST tripole (NAT). Comparing the ECMWF System5 prediction skill for the first three leading modes for the intraseasonal variations in winter SAT, the prediction skill is not high. The model did not predict the extent of warm anomalies and the intraseasonal fluctuation in S‐EOF1, which may be due to the poor prediction skills for the range and intensity of the CP ENSO and the SH. The second mode has the highest prediction skill among the three modes. For the prediction skill of AO is good. The model can capture the intraseasonal reverse SATA between December and January but did not capture the reverse SATAs between January and February. Because the model does not predict obvious PMM and NAT well.

Prediction of Intermonth Modes of Winter Air Temperature over China

Abstract The features and causes of the leading intermonth modes of winter surface air temperature anomalies (SATA) over China are investigated, and associated prediction models are developed. The first three intermonth modes of winter SATA over China are obtained by extended empirical orthogonal function (i.e., EEOF1–3) analysis. The results show that EEOF1 represents consistent variations in the whole winter, with a variance contribution of 32.3%, whereas EEOF2 and EEOF3 show spatiotemporally inconsistent changes, and their variance contributions are 16.9% and 12.5%, respectively. EEOF2 has out-of-phase variations between December and January–February, and EEOF3 exhibits a temporal warm–cold alternating pattern, with spatially reversing changes over northwestern and southern China. However, the Climate Forecast System, version 2 (CFSv2) presents a limited prediction skill for winter SATA over China and their intermonth modes. Further investigations indicate that the September sea ice over the Barents–Laptev Seas, the November snow cover over western Europe and East Asia, and the November northern Atlantic sea surface temperature can be, respectively, adopted to develop prediction schemes for the consistent mode (EEOF1 scheme) and two inconsistent modes (EEOF2 and EEOF3 schemes) based on specific mechanisms. These schemes show effective performances in predicting both individual modes and the reconstruction field of SATA over China. The temporal correlation coefficients (TCCs) between cross-validation results and observations are 0.48, 0.51, and 0.31 for the EEOF1–3 modes, respectively (the 90% confidence level is 0.27). For the reconstruction field, the TCCs are 0.40, 0.27, and 0.45 in December, January, and February, respectively, which are much higher than those of the CFSv2 outputs (0.23, −0.16, and −0.09).

The Leading Intermodel Spread of the Projected Changes in the Eurasian Continent Winter Surface Air Temperature and Large‐Scale Circulations From the CMIP6 Simulations

AbstractThis study investigates the intermodel spread of changes in the Eurasian winter surface air temperature (SAT) based on Coupled Model Intercomparison Project 6 (CMIP6) and explains it from the perspective of circulation under shared socioeconomic pathway 2–4.5. Results show that the leading intermodel spread of Eurasian SAT change, derived from the intermodel empirical orthogonal function analysis (EOF), is characterized by a warming pattern of SAT change. This warming pattern is associated with the changes in the weakened Siberian High and Aleutian Low, the weakened subtropical jet, the poleward polar jet, and the tilting trough. The combination of these circulations has prevented the intrusion of the cold air to the south and therefore results in the warming SAT change pattern. Their relative contribution weights of the weakened Siberian High and Aleutian Low, the tilting East Asian trough, the weakened subtropical jet, and the poleward polar jet are 12.73%, 20.43%, 30.24%, 20.96%, and 15.64%, respectively. All these changes may be traced to the warm sea surface temperature (SST) changes in the western North Pacific and tropical Atlantic Ocean, via the meridional temperature gradient and wave trains, respectively. These warmings would be the potential metrics for reducing the intermodel uncertainties of the winter SAT projection at the end of the 21st century over the Eurasian continent.

An abrupt change of winter surface air temperature over the northern part of Korean Peninsula in the late 1980s and related atmospheric circulation variability

The aim of this study is to detect the variation of winter surface air temperature (SAT) over the northern part of Korean Peninsula (NPKP) for the period of 1949–2020 under global warming, as well as to investigate its possible mechanisms. All temperature data used for the study were obtained from representative 37 weather stations over NPKP. Results are as follows. 1) Winter temperature anomaly series manifested a clear shifting point in the late 1980s, with upward rate of about 0.19 °C per decade for the period of 1949–2020, and those were generally smaller than normal year prior to the shifting point, but were greater after 1988. 2) Spatial patterns of first mode of empirical orthogonal function before or after the shifting point in the Northern Hemisphere had reversely alternated, as an evidence describing the possible linkage between negative (positive) phase of Arctic oscilliation and cold (warm) winter over the study area. 3) A schematic diagram shows the connections of atmospheric circulation indices with the winter temperature over the study area: the East Asian trough had the best relationship with winter SAT over the study area among the East Asian winter monsoon components affecting East Asia. However, the possible causes of the winter temperature variation in the study area need to be further investigated.

Interannual Variability of the Wintertime Asian–Bering–North American Teleconnection Linked to Eurasian Snow Cover and Maritime Continent Sea Surface Temperature

Abstract Recent studies propose that the Asian–Bering–North American (ABNA) teleconnection is a distinct atmospheric pattern that is related to Eurasian and North American winter climate besides the Pacific–North America (PNA) pattern, while its origin remains elusive. This study investigates the interannual variability of the ABNA during the past 42 winters (1979–2020) and the associated prior surface boundary forcings. The ABNA explains coherent surface air temperature changes in northern Asia, eastern Siberia–Alaska, and eastern North America, even after removing the impacts of the PNA, the Arctic Oscillation, the North Atlantic Oscillation, and the North Pacific Oscillation. Surface boundary conditions linked to the ABNA could be traced back to a Eurasian snow cover dipole pattern (ESCDP) and a Maritime Continent sea surface temperature anomaly (MCSST) in November. The ESCDP leads to a displacement of the Arctic stratospheric polar vortex via troposphere–stratosphere coupling. The anomalous polar vortex propagates downward in the following winter and generates the tropospheric ABNA pattern. The MCSST induces a diabatic heating anomaly, which is associated with a tropical western Pacific precipitation anomaly (TWPP) in winter. The TWPP excites a poleward Rossby wave train that propagates across the North Pacific and directly strengthens the ABNA. The above physical processes can be well reproduced by a linear baroclinic model (LBM). Based on the ESCDP and MCSST predictors, an empirical model is established and shows a promising prediction skill of the ABNA during the hindcast period. This can provide a useful strategy for seasonal prediction of winter climate in the Northern Hemisphere extratropics. Significance Statement Extreme cold events have influenced both Asian and North American continents during the past decades, causing huge socioeconomic impacts. The Asian–Bering–North American teleconnection is found to be responsible for coherent changes of winter climate in these two continents besides the Pacific–North America pattern. Our results indicate that Eurasian snow cover and the Maritime Continent sea surface temperature are important sources of predictability for the Asian–Bering–North American teleconnection, and can be used to predict coherent and cross-continent variations of winter surface air temperature. We propose that the Asian–Bering–North American teleconnection and these two predictors should be included in operational monitoring and prediction systems, helping to improve the prediction skill of winter climate in the Northern Hemisphere continents.

State of China's climate in 2022

China experienced a warm and dry climate in 2022. The average annual surface air temperature (SAT) was 10.51°C, which was the second highest since 1961. The annual average rainfall was 606.1 mm, which was the lowest since 2012. The seasonal SAT broke the record in spring, summer, and autumn, while the SAT in winter was slightly cooler. More rainfall was observed in winter and spring, but less in summer and autumn. During the flood season from May to September, rainfall was 11.9% less than normal, which was the third lowest since 1961. The spatial distribution of rainfall anomalies exhibited a wet/dry pattern in the north/south of central and eastern China. The onset of the rainy season was generally earlier but with significant differences in rainfall. More rainfall was observed in the pre-flood season in South China and the rainy season in North China and Northeast China. In contrast, less rainfall occurred in the Mei-yu season in the middle and lower reaches of the Yangtze and Huaihe River valleys, the southwestern rainy season, and the autumn rainy season in West China. In 2022, China's drought and flood disasters were stark, and heat waves were strong. Severe droughts occurred along the Yangtze River valley during summer and autumn, while heavy rainfall and flooding struck South China in the pre-flood season and Northeast China in June–July. A historically strongest summer heat wave occurred in central and eastern China, while drastic cooling prevailed in most of China at the end of November. Landfalling typhoons were extremely less frequent.摘要2022 年我国气候暖干特征明显, 年平均气温偏高 0.62℃, 位居1961年以来历史第二高; 年降水量偏少5%, 为2012 年以来最少, 冬春季降水偏多, 夏秋季降水偏少. 汛期(5–9 月)降水量偏少11.9%, 位居1961年以来第3少, 中东部降水距平呈“北多南少”分布. 雨季进程偏早, 雨量空间差异大, 华南前汛期, 华北雨季, 东北雨季降水量偏多, 而长江中下游和江淮梅雨降水偏少. 华南, 东北洪涝灾害重, 南方夏秋连旱严重, 中东部遭遇最强高温过程, 登录台风异常偏少.

Subseasonal reversals of winter surface air temperature in mid-latitude Asia and the roles of westward-shift NAO

Reversals of surface air temperature anomalies over mid-latitude Asia (SATMA) have become more frequent. Six winters have been reversed over the last decade, which had serious negative consequences for agricultural production, ecological systems, and human health. This subseasonal reversal can be observed in the second mode of season-reliant empirical orthogonal function analysis, showing a persistent opposite anomaly between early and late winter. The difference in SATMA between early and late winter exceeds 3 °C when the reversal occurs. At the time of the reversal, the North Atlantic jet stream extends eastward in early winter and recedes westward in late winter. The main influencing system changes from the Scandinavia teleconnection to the Ural blocking high, accompanied by a change from strong southerly to northerly winds. These factors jointly lead to the reversal of SATMA between early and late winter. More importantly, the North Atlantic Oscillation (NAO) has been shown to affect SATMA variability in a variety of different ways. Changes in SATMA are influenced not only by the intensity of the NAO, but also by its spatial distribution. When the southern center of the NAO shifts westward and is located over the North Atlantic, atmospheric circulation and SATMA in early and late winter show similar changes to those seen in SATMA reversal winters. In contrast, when the NAO southern center shifts eastward and is located over Western Europe, persistent anomalies are observed in atmospheric circulation and SATMA throughout the winter. Therefore, when studying the relationship between SATMA and the NAO, attention should be paid to the different responses of SATMA to the spatial distribution of the NAO at subseasonal timescales.

WINTER ATMOSPHERIC BLOCKINGS IN THE NORTHERN HEMISPHERE UNDER CLIMATE CHANGES IN RECENT DECADES (1980–2018)

The analysis of winter atmospheric blockings in the Northern Hemisphere (NH) under climate changes in 1980–2018 was carried out. The results of the analysis indicate a significant increase in the total duration of winter atmospheric blockings τ in the NH in recent decades. The noted trend was revealed against the background of a rapid increase in the NH surface air temperature T in winter seasons. The parameter of sensitivity of the atmospheric blockings duration to changes in the NH surface air temperature in winter seasons for the period 1980–2018 was estimated. The statistically significant estimate obtained means an increase in τ by more than one and a half times with an increase in the mean winter surface air temperature of the NH by 1K. A more significant relationship with T was obtained for values of τ above the average value of τc for the period 1980–2018, while at τ τc, the relationship was found to be statistically insignificant. The noted features are associated with differences in different phases of the key modes of climatic variability. In particular, the mean value of the surface air temperature of the NH in winter in the positive phase of the Atlantic Multidecadal Oscillation (AMO) within the analyzed period of 1980–2018 significantly exceeded the corresponding mean value of T in the negative phase of AMO. At the same time, it was found that the mean value of the winter blockings duration in the NH in the positive AMO phase is one and a half times longer than in the negative AMO phase. For winter seasons, the estimates of the relationship between τ and the intensity of the Arctic anticyclonic center of action depending on the AMO phase were obtained.

Winter surface air temperature variation over Pakistan during 1970–2014 and its principal drivers in the tropical ocean

This study examined the leading modes of Dec–Feb (DJF) month's surface temperature (DJFTs) and associated mechanisms of the most significant drivers affecting temperature variability during the season from 1970 to 2014. EOF1 of DJF temperature reveals uniform spatial patterns over most of Pakistan, except extreme north, accounting for 84.38% of the total variance. The typical warm (cold) years were 1970, 1981, 1988, 1990, 1993, 2004, 2006, 2009, 2010 (1972, 1974, 1975, 1984, 2008, 2012). Favorable atmospheric conditions for warm temperature events (DJFTs) in Pakistan is an anomalous anticyclone spread over northeast Pakistan to Tibet at low to upper levels. This condition is controlled by the south and western part, of which there are significant southerly and convergent flows at low level with ascending motion over the study area. Further, examination revealed a close relationship of warm DJFTs with Western Indian Ocean warming and Eastern Indian Ocean indices but insignificant relation with the Nino3.4 index. Ocean warming related to Dipole Mode Index over eastern Indian Ocean (DMIE) is more influential (r = 0.51) than over the western Indian Ocean (DMIW) index (r = 0.37). The Ocean warming related to DMIE (EIOW), especially in Nov-Dec-Jan (NDJ) season, forced a significant ascending motion locally and then induced warm DJFTs-associated circulation pattern, propagating northward to Europe. By the dynamic diagnosis, the adiabatic and diabatic heating for the warm DJFTs is not remarkable. However, the horizontal temperature advection is positive and significant over most parts of Pakistan, both in the DJF and NDJ season, from the surface to the top of the troposphere. It suggests that the warm temperature advection is the possible prominent way of the EIOW on the warm DJFTs.

Inter‐Model Spread of the Simulated Winter Surface Air Temperature Over the Eurasian Continent and the Physical Linkage to the Jet Streams From the CMIP6 Models

AbstractThe model uncertainty, one of the major sources of projection uncertainty, is still a challenge in the climate simulation. In this study, we investigated the inter‐model spread of the simulated winter surface air temperature (SAT) over the Eurasian continent and the physical link to the upper‐level jet streams from the Coupled Model Inter‐comparison Project Phase 6 models. Extracted by the inter‐model empirical orthogonal function analysis, the leading inter‐model spread of SAT over the Eurasian continent is characterized by a cold pattern, particularly over high latitudes, which is closely associated with the out‐of‐phase variation in the intensity of the East Asian polar front jet (EAPJ) and East Asian subtropical jet (EASJ). The weakened‐EAPJ‐enhanced‐EASJ pattern is linked to the intensified Siberian high, the strengthened Aleutian low, and the deepened East Asian trough. All the variations would benefit the cold air invasion, resulting in the leading inter‐model spread of the SAT. The possible mechanism for the inter‐model uncertainty in the out‐of‐phase variation in the intensity of the two jets would be traced to the cooling over the Northwest Pacific oceans, which has reduced (enhanced) the meridional temperature gradient over high (low) latitudes and thereby contributed to the out of phase variation in the two jets. Our findings would help provide a potential metric for understanding the winter SAT change over the Eurasian continent.