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The Multivariate compound heatwaves (MCHWs) present a significant risk to human health and ecological diversity, which attract widespread attention from researchers and society. The intensity and variability of summer MCHWs over Western Europe (WE) (MCHWs_WE) have substantially increased over the last two decades. The growing chance of such events is likely related to human activity‐induced climate change. However, the possible contributions from multiple atmospheric boundary forcing remain unclear. This study investigates the combined effects of North Atlantic sea surface temperature (SST), Tibetan Plateau (TP) snow cover (SC), and Arctic sea ice (SIC) on the variability of extreme summer MCHWs_WE. Observational analysis shows that an intensified anticyclonic system prevailing over WE, one of the centers of an atmospheric wave train dominating the North Atlantic‐Europe sector and persists from late spring to summer, is the essential system contributing to the extreme MCHWs_WE. Spring North Atlantic SST anomalies in the form of a dipole pattern persist from spring to summer and contribute to the summer extreme MCHWs_WE by exciting a downward propagating Rossby wave train pattern. Additionally, excessive late spring SC over the western TP and SIC over the Arctic, which are stimulated by the North Atlantic anomalous SST‐related wave train, can intensify the MCHWs_WE‐related anticyclonic system through vertical circulation and wave energy transport. The study further quantifies the relative contributions of the aforementioned factors. The findings of this study could potentially offer valuable insights for improving the prediction skill of summer extreme MCHWs_WE. Plain Language Summary: Western Europe (WE) has faced more and more multivariate compound heatwaves (MCHWs) during summer in recent decades, which pose a greater human health risk than univariate heatwaves. In this study, Our study identifies MCHWs in WE as being characterized by high temperatures and humidity, mainly influenced by a strong anticyclonic high pressure system. Furthermore, the strengthening of the MCHWs_WE‐related anticyclone is a consequence of the combined impacts of preceding North Atlantic sea surface temperature (SST), Tibetan Plateau (TP) snow cover (SC), and Arctic sea ice (SIC). Spring positive dipole pattern of North Atlantic SST anomalies, exhibiting persistence from spring to summer, excite downward propagating Rossby waves. There wave trains from the Atlantic to Eurasia serve as a background field that enhances the linkage between SIC, TPSC, and the MCHWs_WE‐related anticyclonic system. These factors ultimately contribute to the strengthening of anticyclones over West Eurasia (WE) through vertical circulation and wave energy transport, which jointly impact MCHWs_WE. Key Points: Multivariate Compound heatwaves in Western Europe (MCHWs_WE) become more frequent in recent decades, which are linked to intensified anticyclonic systemThe development of the anticyclone over WE is associated with the dipole pattern of North Atlantic sea surface temperature, excess Tibetan Plateau snow cover and Arctic sea iceCombined effects of multiple forcing factors can account for approximately 40% of the variability in summer MCHWs_WE [ABSTRACT FROM AUTHOR]

In this work, we investigated the impact of the interannual variation in Tibetan Plateau snow cover (TPSC) on the summer heat wave frequency (HWF) over the Indochina Peninsula (ICP) (HWF_ICP) for 1981–2020. This study shows that the spring TPSC variation over the central Tibetan Plateau (TP) is positively correlated with the summer HWF_ICP and can explain up to 30% of the summer HWF_ICP variance. Analysis of the apparent heat source shows that more‐than‐normal spring snow cover over the central TP has a cooling effect on the above atmosphere, which induces negative geopotential height anomalies in the upper troposphere. The anomalous spring TPSC and its cooling effect can persist until summer. In summer, the TPSC‐associated low anomalies propagate eastward to the East Asia‐Japan Sea area. The anomalous westerly winds along the south flank of these low anomalies strengthen the climatological westerly jet. Changes in the westerlies are accompanied by anomalous ascending and descending air motion north and south of 30°N over the coast of East Asia and the western Pacific. The anomalous descending air motion south of 30°N causes an enhanced subtropical high, less cloud cover, and more downward solar radiation, which are favorable conditions for a greater occurrence of heat waves over the ICP. The results of current study may provide useful information for improving the seasonal forecast skill of the summer HWF_ICP variation. Plain Language Summary: In the context of global warming, extreme heat wave events occur frequently and threaten people's lives and property. The current study revealed that when the spring Tibetan Plateau (TP) snow is more‐than‐normal, the summer heat waves over the Indochina Peninsula (ICP) appear more frequently. The current work investigates the possible reasons for the above link using observational analysis and numerical model experiments. Our results suggest that the TP snow can impact the summer heat waves over the ICP by stimulating an atmospheric wave and modulating the westerly jet over East Asia‐Japan Sea areas. The current work may provide clues to explain the variation of the HWF_ICP. In addition, our work may provide valuable information to improve the forecast skill of extreme heat waves. Key Points: The spring Tibetan Plateau (TP) snow cover was positively correlated with the summer heat wave frequency (HWF) over the Indochina Peninsula (HWF_ICP)The spring TP snow cover impacts the summer HWF_ICP through a propagating atmospheric wave patternTP spring snow cover has the potential to serve as a predictor for seasonal forecasting of the summer HWF_ICP [ABSTRACT FROM AUTHOR]

The current work investigated the seasonal evolution of the Tibetan Plateau (TP) snow cover (TPSC) induced atmospheric moisture anomalies from May to August, by analyzing TP snow‐diabatic and TP snow‐hydrological processes during the 1979–2020 period using both observational data and a baroclinic atmospheric model. The results show that the TPSC and its related atmospheric moisture are featured by a westward retreat from the eastern TP in May to the western TP in August. The TPSC variation related atmospheric apparent heat source shows that excessive TPSC can cause local diabatic cooling to the above atmosphere and can be attributed to a local cyclonic pattern in the upper troposphere. This cyclonic pattern also moves westward along with the seasonal evolution of the TP snow during this period. Anomalous TP snow can impact atmospheric moisture through snow melt and snow evaporating process. Associated with the changes in TP snow, its related anomalous atmospheric moisture and circulations, significant moisture divergence appears over the mid‐eastern Himalaya during May and June (MJ) and the water vapor is mainly transported from the Himalaya to southeastern TP regions including Bhutan, Myanmar, Bengal and eastern India. Differently, during July and August (JA), significant atmospheric moisture divergence is located over the mid‐western Himalaya, and the water vapor is mostly transported from the Himalaya to southwestern TP areas including Nepal and western India. Further analysis shows that the TPSC anomaly induced anomalous atmospheric moisture accounts for 22%–45% of the climatological moisture for the mid‐eastern Himalaya during MJ, whereas it accounts for 65%–78% of the climatological moisture for the mid‐western Himalaya during JA. Key Points: The Tibetan Plateau (TP) snow cover (TPSC) and its related atmospheric moisture are featured by a westward retreat from May to AugustAnomalous TPSC can impact the atmospheric moisture through snow melt and snow evaporating processThe TPSC related water vapor is mainly transported from Himalaya to southeastern TP in May‐June and to southwest TP in July and August [ABSTRACT FROM AUTHOR]

This study evaluates the relationship between El Niño‐Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) in 26 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Of particular concern is the plausible factors for the model's capability of simulating the ENSO‐EAWM relationship. Results show that the model's ability of simulating the ENSO‐EAWM relationship is more dependent upon the longitudinal extension of ENSO‐related equatorial Pacific sea surface temperature (SST) anomalies than the amplitude of the equatorial central‐eastern Pacific SST anomalies. The influence of the amplitude of ENSO on the simulation of the ENSO‐EAWM relationship depends on the westward extension of ENSO‐related equatorial Pacific SST anomalies. Another factor for the model's ability of simulating the ENSO‐EAWM relationship is the SST anomalies in the tropical western North Pacific (WNP). A westward extension of the equatorial Pacific SST anomalies shifts the west branch of anomalous Walker circulation too far westward, which causes westward displaced anomalous ascending (descending) motion around the Philippines through modulating regional meridional vertical circulation in El Niño (La Niña) years. The weak SST anomalies in the tropical WNP lead to the failure of inducing anomalous lower‐level anticyclone (cyclone) over the Philippine Sea through a Rossby wave response in El Niño (La Niña) years. The accompanying weak anomalous lower‐level southwesterly (northeasterly) winds along the west flank of the anomalous anticyclone (cyclone) account for the weak ENSO‐EAWM relationship. Key Points: The El Niño‐Southern Oscillation‐East Asian winter monsoon (ENSO‐EAWM) relationship varies largely among the CMIP6 modelsThe longitudinal location of equatorial Pacific sea surface temperature (SST) anomalies is more critical than the amplitude to simulating the ENSO‐EAWM relationshipThe tropical western North Pacific SST anomalies are another important factor in the simulation of the ENSO‐EAWM relationship [ABSTRACT FROM AUTHOR]

The spring snow cover extent (SCE) over central‐eastern Eurasia (SCE_CEE) shows an obvious decrease around 1988. The period 1979–2019 is thus divided into two subperiods spanning 1967–1988 (P1) and 1989–2019 (P2) to investigate the interdecadal changes in the characteristics of the SCE_CEE and its relationship with surface air temperature (SAT) in the Northern Hemisphere. Positive SCE_CEE anomalies are related to a cooler Eurasia–warmer North America (CEWN) spring SAT pattern, which obviously intensifies from P1 to P2. The possible mechanisms responsible for the interdecadal changes in this snow–SAT relationship are investigated. A local energy budget analysis shows that the impact of the SCE_CEE on the overlying atmosphere is weak and the atmospheric circulation anomalies associated with the SCE_CEE variation are confined mainly to eastern Eurasia and the North Pacific in P1. In contrast, positive SCE_CEE anomalies have a significant cooling effect on the atmospheric column through anomalous heat fluxes and wind‐related cold advection in P2. In P2, more SCE_CEE is associated with an anomalous cyclone in the upper atmosphere, which imposes a significant vorticity perturbation near the East Asian westerly jet core and induces eastward propagation of perturbations. The sea surface temperature anomalies in the North Pacific and the North Atlantic as well as the mean flow over the Eurasian continent help to maintain the zonal propagation of this perturbation, thus forming a hemispheric atmospheric wave pattern that contributes to the enhanced snow–CEWN SAT relationship in P2. Key Points: More spring Eurasian snow is related to a cooler Eurasia–warmer North America surface air temperature (SAT) patternThe relation between spring central‐eastern Eurasian snow and the Northern Hemisphere SAT is enhanced after the late 1980sA snow‐related hemispheric wave pattern is maintained by the North Pacific and Atlantic SST anomalies and mean flow after the late 1980s [ABSTRACT FROM AUTHOR]

By decomposing the variations of daily mean variables into synoptic, intraseasonal, and low‐frequency components, the present study compares seasonal mean latent heat flux (LHF) anomalies related to the three components over the tropical Indo‐Pacific region during El Niño and La Niña years. It is found that the high‐frequency (intraseasonal and synoptic) LHF has an important contribution to total seasonal mean LHF anomalies over the tropical eastern Indo‐western Pacific region. Large seasonal mean LHF anomalies related to high‐frequency wind variations are identified in weak low‐frequency seasonal mean wind regions where high‐frequency LHF may accumulate over a season as it increases in both westerly and easterly phases of high‐frequency wind variations. In those regions, the LHF anomalies related to high‐frequency wind variations cancel part of the low‐frequency LHF anomalies, reducing total seasonal mean LHF anomalies. As El Niño–Southern Oscillation (ENSO)‐induced lower‐level wind anomaly region moves with the stage of ENSO, large seasonal mean LHF anomalies related to high‐frequency wind variations displace with the season. The intensity of high‐frequency wind fluctuations is also a factor influencing the seasonal mean LHF related to high‐frequency wind variations. Thus, the ENSO affects the high‐frequency LHF variations through modulating both the location of weak low‐frequency wind region and intensity of high‐frequency wind fluctuations. Key Points: High‐frequency wind‐related latent heat flux (LHF) has an important contribution to seasonal mean LHF anomalies in ENSO yearsThe region of high‐frequency wind‐related LHF contribution moves with the stage of ENSOThe high‐frequency LHF contribution is associated with weak seasonal mean winds and enhanced high‐frequency wind fluctuations [ABSTRACT FROM AUTHOR]

In this study, the leading empirical orthogonal function mode of the interannual variations of boreal spring (April–May) precipitation over China (SPC) is shown to shift from a mono‐sign distribution during 1964–1985 (P1), with the largest loading over southern China, to a north‐south dipole structure during 1986–2004 (P2), with the northern and southern poles centered over the Yangtze River and the Pearl River Delta, respectively. The results show that the El Niño‐Southern Oscillation(ENSO)‐related negative western tropical Pacific sea surface temperature anomalies persist longer from the previous winter into the following spring in P2 than in P1. The ENSO‐related western tropical Pacific anticyclone in spring is stronger and extends farther northeastward after the mid‐1980s. As a result, in P2, the moisture transport by anomalous southerly winds along the western flank of the western tropical Pacific anticyclone penetrates northward to central China, and moisture convergence and divergence are observed over the Yangtze River and southern China, respectively. The SPC‐related North Atlantic sea surface temperature anomalies (NAST) are stronger after the mid‐1980s than before the mid‐1980s, and the NAST‐related atmospheric wave train over the middle‐latitude Eurasian continent is more pronounced in P2 than in P1. Furthermore, to the east of 90°E, the downstream propagation pathway of the NAST‐related wave train turns southeastward, which may be caused by the weakened intensity of the meridional gradient of the potential vorticity over this region. The pronounced wave train‐related positive height anomalies over the western North Pacific favor a north‐south dipole structure in the SPC variation in P2. Key Points: The leading EOF mode of spring precipitation over China (SPC) changes from a mono‐sign pattern to a north‐south dipole mode in the mid‐1980sThe ENSO‐related western tropical Pacific SST anomalies (SSTAs) contribute to the interdecadal change of the SPCBoth the North Atlantic SSTAs and the mean flow over East Asia favor a north‐south dipole pattern of SPC after the mid‐1980s [ABSTRACT FROM AUTHOR]

This study investigates the changes in the impact of the interannual variation of autumn snow cover over the eastern Tibetan Plateau (TP; ASCETP) on winter surface air temperature (SAT) over North America (NA) in the mid‐1990s using both observational data and a linear baroclinic numerical model. The index of ASCETP shows an abrupt change with a predominant negative phase before and a predominant positive phase after 1994; thus, the analysis is performed for two subperiods: 1979–1994 (P1) and 1995–2014 (P2). An ASCETP‐related energy budget analysis shows that the ASCETP variation has a more pronounced cooling effect on the above atmosphere in P1 than in P2. The snow‐related anomalous negative geopotential height above the TP is more pronounced and extends farther northeastward in P1 than in P2. Further analysis shows that the relationship between the ASCETP and NA winter SAT is not steady. During P1, associated with an anomalous positive ASCETP, negative geopotential height anomalies emerge over the northeastern TP. These negative anomalies impose an anomalous vorticity perturbation near the East Asian westerly jet core that propagates eastward, forming a wave train‐like pattern. It crosses the North Pacific Ocean and reaches the NA region, leading to positive and negative winter SAT anomalies over western and eastern NA, respectively. In contrast, during P2, the impact of anomalous ASCETP on the variation in the winter SAT over NA is weak, probably due to the relatively weak local cooling effect of the ASCETP and the weak ASCETP‐related vorticity forcing around the East Asian westerly jet. Key Points: Anomalous autumn snow cover over the eastern Tibetan Plateau (ASCETP) affects winter surface air temperature (SAT) over North AmericaThe relationship between the ASCETP and North America winter SAT is not steadyAnomalous ASCETP induces a hemispheric‐scale wave train pattern before 1995, which establishes the snow‐SAT relationship [ABSTRACT FROM AUTHOR]

The present study investigates relationship between interannual variations of snow cover and local surface and atmospheric variables, and the formation of interannual snow cover anomalies over the Tibetan Plateau in the cold seasons (autumn, winter, and spring). It is shown that the snow‐related surface heat flux and atmospheric heat source anomalies increase from autumn to spring, whereas precipitation anomalies are most prominent in autumn. This suggests that snow cover anomalies over the central eastern Tibetan Plateau are mainly formed in autumn and their impacts are most prominent in spring. The central eastern Tibetan Plateau snow cover anomalies have high month‐to‐month persistence during October through April, indicative of a large contribution of persistence to snow cover anomalies in winter and spring. The Tibetan Plateau snow cover anomalies in cold seasons are influenced by large‐scale atmospheric circulation anomaly pattern of different paths. In autumn, a wave pattern from the North Pacific to the Tibetan Plateau via the North Atlantic, induced by eastern North Pacific and western North Atlantic sea surface temperature anomalies, plays an important role in the formation of snow cover anomalies. In winter, a North Atlantic Oscillation related wave pattern from the North Atlantic to East Asia may contribute to snow cover anomalies. In spring, a midlatitude wave pattern originating over the western North Atlantic and propagating through the Mediterranean Sea to southern Tibetan Plateau may have a supplementary contribution to snow cover anomalies. Key Points: Cold season snow cover anomalies persist over the central‐eastern Tibetan PlateauCold season snow cover anomalies induce atmospheric column coolingAtmospheric circulation pattern differs for the formation of snow cover anomalies in three cold seasons [ABSTRACT FROM AUTHOR]

This study investigates the interdecadal changes in the relationship between the Eurasian snow cover extent (SCE) and spring precipitation over southern China. The results show that the spring precipitation over southern China has experienced an obvious change from an active to a quiet period since the late 1980s. The entire data set is divided into two subperiods, that is, 1972–1987 (P1) and 1988–2009 (P2). The interannual variation of the spring precipitation of southern China is found to be significantly related to Eurasian SCE anomalies around northwest of Lake Baikal. Less‐than‐normal SCE northwest of Lake Baikal corresponds to more‐than‐normal spring precipitation over southern China. The result of a numerical experiment performed using a baroclinic atmospheric model indicates that the Eurasian snow anomalies around northwest of Lake Baikal can impact the variation of spring precipitation over southern China by modulating the atmospheric circulations over eastern Asia and the western North Pacific region. Further examination shows that the SCE anomalies around Lake Baikal contribute differently to the variation of spring precipitation over southern China before and after the late 1980s. During P1, the SCE anomalies around Lake Baikal contribute to the variation of spring precipitation over China in the form of a mono‐sign pattern, which is similar to the first empirical orthogonal function mode of spring precipitation, while in P2, the SCE anomalies around Lake Baikal favor a north‐south dipole mode of the spring precipitation variation, which bears considerable similarity to the second empirical orthogonal function mode of spring precipitation over China. Key Points: The spring precipitation over southern China shows a pronounced climate change at 1987The spring precipitation over southern China is significantly correlated with spring SCE anomalies northwest of Lake BaikalThe SCE anomalies around Lake Baikal contributed to the spring precipitation in the form of EOF1 and EOF2 mode before and after 1987 [ABSTRACT FROM AUTHOR]