Tibetan Plateau Snow Cover Research Articles

Uncovering the interannual predictability of the 2003 European summer heatwave linked to the Tibetan Plateau

Known as the Third Pole, the Tibetan Plateau (TP) significantly influences global weather and climate, but its potential for improving subseasonal-to-interannual predictions remains underexplored. Through coupled climate simulations and hindcast experiments, we uncovered interannual predictability of the 2003 European summer heatwave that persisted from June to August with devastating impacts. Hindcasts initialized from the atmosphere, land, and ocean states of a coupled simulation that assimilates soil moisture and soil temperature data over the TP show substantial skill in predicting this heatwave two years in advance. Hindcast sensitivity experiments isolated the indispensable role of the spring TP snow cover anomalies and their impact on the Atlantic and Pacific Oceans in exciting the Rossby waves that contributed to the anomalous European summer temperature. These findings highlight the dominant and remote influence of the TP and motivate research on its role in enhancing the predictability of extreme events worldwide.

Combined Impacts of Autumn Snow Cover on the Tibetan Plateau and Northeast Asia on the Winter Eurasian Temperature

ABSTRACTThis study explores the combined effects of autumn snow cover anomalies on the Tibetan Plateau (TP) and Northeast Asia (NEA) on winter Eurasian temperature using observational data for the period 1972–2021 and a linear baroclinic model (LBM). Distinctive wintertime temperature patterns are found across the Eurasian continent corresponding to increased autumn snow cover in NEA when TP experiences normal, above‐normal, or below‐normal snow cover condition. In the scenario with an anomalous increase in autumn snow cover in NEA in combination with normal snow cover condition in TP, the overall winter temperature anomalies tend to be generally weak across the Eurasian continent. In years when autumn TP snow cover is above normal, the spatial distribution of winter temperature anomalies over the Eurasian continent associated with more NEA snow cover exhibits a ‘cold Arctic‐warm Eurasia’ (CAWE) pattern. The emergence of this CAWE pattern can be attributed to the low‐pressure system induced by the intensified NEA snow cover, which is further reinforced by the atmospheric wave train generated by negative North Atlantic sea surface temperature anomalies (SSTAs) in winter. This low‐pressure system amplifies the polar vortex and causes cooling in polar regions. Simultaneously, southeasterly winds along the southwestern flank of the North Pacific high‐pressure system contribute to warming in the mid‐latitude regions of Eurasia. While in years when autumn snow cover in TP is less than normal, more snow cover over NEA is accompanied by a ‘warm Arctic‐cold Eurasia’ (WACE) temperature anomaly pattern prevalent during the winter season. The decrease in autumn Barents‐Kara Sea ice is accompanied by a circulation pattern akin to the negative phase of the Arctic Oscillation during winter, favouring the southward intrusion of cold air, thus contributing to this WACE temperature anomaly pattern. Further analysis reveals that the impact of snow cover on the WACE temperature pattern is, for the most part, independent of the Arctic sea ice.

The Subseasonal Feedback of Extreme Anomalous Tibetan Plateau Snow Cover Events on the Atmosphere

Abstract The Tibetan Plateau snow cover exhibits notable subseasonal variability and plays a crucial role in influencing the atmosphere. This study employs numerical experiments to investigate the atmospheric feedback resulting from extreme anomalous snow cover events on the Tibetan Plateau, with a focus on both local and nonlocal atmospheric temperatures. The findings reveal that diabatic heating, directly induced by these events, leads to a local surface energy cooling response over the Tibetan Plateau, contributing to a reduction in local temperatures. This cooling effect amplifies local atmospheric temperature anomalies associated with extreme anomalous Tibetan Plateau snow cover events, constituting approximately 50% of the total final local surface air temperature anomalies. Furthermore, the Tibetan Plateau snow cover, through adiabatic processes, exerts a nonlocal influence on atmospheric temperature and circulation. The atmospheric temperature responses downstream of the Tibetan Plateau vary at different heights and regions, featuring both cold and warm anomaly responses. These variations depend on the relative contributions of horizontal advection and vertical advection in adiabatic heating. Significance Statement Snow cover is influenced by the atmosphere, and in turn, it affects the atmosphere. This study examines the feedback of extreme anomalous Tibetan Plateau snow cover events on the atmosphere at the subseasonal time scale, with a focus on atmospheric temperature. Our findings indicate that Tibetan Plateau snow cover has both local and nonlocal feedback effects on the atmosphere. In particular, extreme anomalous Tibetan Plateau snow cover amplifies local surface air temperature anomalies. The feedback contributes to approximately 50% of the total final local surface air temperature anomalies.

Intensified Impact of Spring Tibetan Plateau Snow Cover on Summer Compound Heat Waves in Western Europe after 1998

Abstract This study revealed a significant interdecadal change in the impact of spring western Tibetan Plateau (TP) snow cover (TPSC) on subsequent summer compound heat waves (CHWs) in western Europe (WE) after 1998. This interdecadal change is attributed to a change in a western Europe high–western TP low (WEH–TPL) atmospheric circulation pattern. This pattern arises due to both the inherent variability of TPSC and the phase transition of the Atlantic multidecadal oscillation (AMO) after 1998. The increased magnitude and persistence of western TPSC from spring to summer after 1998 enhanced the snow–atmosphere coupling effect, intensifying ascent and decent motion over the TP and WE, respectively, and strengthening the WEH–TPL pattern. In addition, the post-1998 positive AMO phase favors continuous and stable downstream Rossby wave propagation, enhancing the WEH–TPL pattern and the TPSC–CHWs relationship. Further analyses reveal that the interdecadal changes in the TPSC and the AMO around 1998 contribute to the presence of “double jets” over the North Atlantic–central Eurasian sectors. The TPSC–related anomalous atmospheric circulation and AMO phase shift contribute to the southern and northern branches of the intensified westerly jet, respectively. These conditions create a favorable environment for the formation and persistence of summer CHWs in WE. Numerical modeling experiments with a linear baroclinic model confirm these findings. Our findings suggest that in the context of a changing climate, TPSC plays a pivotal role in the genesis of summer CHWs in WE and may serve as a valuable predictor for CHWs. Significance Statement This study discovered that starting from 1998 there was a significant change in how spring snow cover on the western Tibetan Plateau affects summer compound heat waves in western Europe. After 1998, the snow cover on the western Tibetan Plateau increased in size and lasted longer from spring to summer, intensifying the interaction between the snow and the atmosphere. This led to more rising and sinking air over the Tibetan Plateau and western Europe, respectively. Also, after 1998 a positive phase of the Atlantic multidecadal oscillation (AMO) was favorable for the circulation connection between western Europe and the Tibetan Plateau. Further analysis showed that these changes in snow cover and the AMO after 1998 caused “double jets” in the North Atlantic and central Eurasia that created better conditions for summer heat waves in western Europe. Numerical models are used to confirm these findings. Our research indicates that, in a changing climate, the snow cover on the western Tibetan Plateau plays a crucial role in the development of summer heat waves in western Europe and can be a useful predictor for these heat waves.

Combined Effects of Multiple Forcing Factors on Extreme Summer Multivariate Compound Heatwaves Over Western Europe

AbstractThe 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.

Impact of summer Tibetan Plateau snow cover on the variability of concurrent compound heatwaves in the Northern Hemisphere

Concurrent compound heatwaves (CCHWs) occurring simultaneously in multiple regions in the Northern Hemisphere (NH) pose high-end risks to human health and global supply chains. Over the past decade, CCHWs related to human health have substantially increased in occurrence. However, the mechanisms of the CCHWs remain uncertain. This work has revealed a significant relationship between the variability of summer CCHWs in the NH and changes in quasi-stationary waves during 1979–2021, which can be attributed to the variation of summer snow cover over the western Tibetan Plateau (SC_WTP). Excessive SC_WTP causes diabatic cooling by modulating the surface energy budget and stimulating a tripolar Rossby wave source. The atmospheric response to the SC_WTP-driven disturbance manifests as a circumglobal circulation pattern, weakening the meridional temperature gradients and causing a ‘double jet stream’ in the NH. These changes modulate the phase, amplitude and proportion of quasi-stationary waves with wavenumbers 4–6, leading to an increase in CCHWs in the NH. In addition, population exposure to CCHWs reaches 4.91 billion person-day when the SC_WTP increases by one standard deviation. Our study highlights the significance of early warning and forecasting implications related to SC_WTP for CCHWs that impact human health within the context of climate change.

A dynamic link between spring Arctic sea ice and the Tibetan Plateau snow increment indicator

Tibetan Plateau snow has long been recognized as a sensitive indicator of climate variability. However, the commonly used snow indicator cannot fully represent the interannual variability in late autumn Tibetan Plateau snow. Here, we establish a snow indicator for Tibetan Plateau snow variability: the snow cover extent increment within late autumn. This snow increment indicator improves the standard deviation by 72.6% and diabatic cooling by 89.7% over the entire Tibetan Plateau, which shows a robust link to the subsequent spring Arctic sea-ice concentration. Faster Tibetan Plateau snow cover extent increment leads to stronger Tibetan Plateau cooling and disturbance along the subtropical westerly jet, thereby inducing a Tibetan Plateau-Arctic wave train and a spring Arctic cyclonic anomaly. This cyclonic system favors the reduction in spring Arctic sea-ice by equatorward sea ice drift, implying a link between spring Arctic sea-ice and the Tibetan Plateau snow increment indicator through the wave train and sea-ice dynamic processes.

Impact of spring Tibetan Plateau snow cover on extreme precipitation in Pakistan in July and August 2022

Record-breaking extreme precipitation occurred in July and August 2022 in Pakistan, causing flooding and landslides. In this study, the characteristics and mechanisms of these extreme precipitation events are investigated. The consecutive extreme precipitation events emerged in July and mid to late August. Precipitation above 500 mm occurred in the northern and southern regions of Pakistan, and the maximum precipitation was concentrated in the same regions. The diagnosis indicated that the precipitation extremes were closely tied to anomalous late spring snow cover in the western Tibetan Plateau. In July, owing to the reduction of late spring snow cover, the strengthened diabatic heating promoted the South Asian High (SAH) and its pumping effect, which contributed to abundant water vapor and strong southeasterly jet along the southwest Tibetan Plateau. Cooperating with the cyclone over Arabian Sea, extreme precipitation with a return period of 50 years occurred in Pakistan. In August, the SAH was an anomalously strong and eastward extension at 200 hPa. In the middle troposphere, the blocking high-pressure over western Russia was extremely active, and the West Pacific Subtropical High shifted anomalously westward, extending to the Tibetan Plateau. Cyclone anomalies occurred over the Arabian Sea and Bay of Bengal. With the atmospheric circulation anomaly, the southeasterly jet shifted southward, and water vapor was transported from the Arabian Sea and Bay of Bengal to south Pakistan, causing extreme precipitation with a return period of 30 years in August.

Impact of Tibetan Plateau Spring Snow on the Summer Heat Wave Frequency Over the Indochina Peninsula

AbstractIn 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.

The Role of Coupled North Pacific Atmosphere–Ocean Interactions in Impacts of Tibetan Plateau Snow Anomalies on the Northern Hemisphere Winter Atmospheric Circulation

Abstract Previous studies indicate observed influences of autumn and winter Tibetan Plateau (TP) snow-cover anomalies on the winter Pacific–North American (PNA) teleconnection. This study simulates atmospheric and oceanic responses to persistent autumn–winter TP snow forcing using an atmospheric general circulation model (AGCM) and a coupled atmospheric-oceanic general circulation model (AOGCM), and quantifies the role of atmosphere–ocean interactions over North Pacific in TP snow effects. The AOGCM experiment induces a stronger and more realistic remote PNA response to heavy TP snow anomalies, and also a significant winter horseshoe-like North Pacific sea surface temperature (SST) pattern resulting from an anomalous equivalent barotropic cyclone, or a strengthened Aleutian low, with associated cyclonic wind stress anomalies. The horseshoe-like SST anomaly pattern is used as boundary forcing (without prescribed heavy TP snow) in another AOGCM experiment, which simulates an enhanced winter Aleutian low and a PNA-like response similar to the original AOGCM responses, indicating that that the direct Pacific–North American atmospheric response to persistent TP snow forcing in the AGCM is amplified in the AOGCM by the North Pacific midlatitude atmosphere–ocean interactions. This suggests that the mechanisms of the winter PNA responses to TP snow forcing involve dynamical atmospheric processes such as horizontal propagation of Rossby wave energy and transient eddy feedbacks, and also North Pacific atmosphere–ocean interactions, which provide a positive feedback on the development of the remote PNA teleconnection. Significance Statement The Tibetan Plateau has a 2.5 million km2 area and a 4000 m average elevation, and is often called “the third pole” because of its polar-like climate in midlatitude Eurasia. A heavy Tibetan Plateau snow cover increases the albedo effect and causes tropospheric cold temperature and low height changes that can be carried or advected to the North Pacific by the prevailing westerlies. The purpose of this study is to better understand how Tibetan Plateau snow anomalies influence the North Pacific and the remote atmospheric circulation through numerical simulations. Our results find that those North Pacific responses amply the direct atmospheric response to Tibetan Plateau snow-cover anomalies. This greatly improves our understanding of physical mechanisms of Tibetan Plateau snow impacts.

Teleconnections among tipping elements in the Earth system

Tipping elements are components of the Earth system that may shift abruptly and irreversibly from one state to another at specific thresholds. It is not well understood to what degree tipping of one system can influence other regions or tipping elements. Here, we propose a climate network approach to analyse the global impacts of a prominent tipping element, the Amazon Rainforest Area (ARA). We find that the ARA exhibits strong correlations with regions such as the Tibetan Plateau (TP) and West Antarctic ice sheet. Models show that the identified teleconnection propagation path between the ARA and the TP is robust under climate change. In addition, we detect that TP snow cover extent has been losing stability since 2008. We further uncover that various climate extremes between the ARA and the TP are synchronized under climate change. Our framework highlights that tipping elements can be linked and also the potential predictability of cascading tipping dynamics.

Contribution of the Tibetan Plateau Snow Cover to the Record-breaking Rainfall Over the Yangtze River Valley in June 2020

ABSTRACT In June 2020, the Yangtze River Valley (YRV) experienced the most severe and long-persisting rainfall in past decades, causing hundreds of people’s death and huge property loss. Based on the high-resolution MODIS/Terra snow cover data for the 2000–2021 period and the linear baroclinic model (LBM), this study investigates the dynamic influence and the potentially predictable source from the Tibetan Plateau (TP) snow cover (TPSC) on this record-breaking YRV rainfall. The TPSC anomalies in the critical area (76°−83°E, 28°−35°N) can persist for more than six months and induce a Rossby wave train propagating northeastward. For the excessive TPSC, barotropic negative geopotential height anomalies prevail over northern East Asia and positive geopotential height anomalies over the northwestern Pacific. Such a circulation configuration favours a deepened cold vortex over Northeast China and the westward-developing western Pacific subtropical high, which leads to an intensified Meiyu-Baiu-Changma front and rich Meiyu rainfall. The LBM sensitive experiments can reproduce the above physical processes associated with the TPSC anomalies, realistically. Moreover, the quantitative contributions of the indices representing the TPSC and the three oceans (Pacific, Indian Ocean, and Atlantic) to the record-breaking Meiyu rainfall are examined, and the TPSC index explains most of the total variance of the rainfall anomaly among the indices, reaching 42.75%. This highlights the importance of the TP thermal forcing to the extreme climate conditions in June 2020.

Connection between the North Atlantic sea surface temperature and the late autumn snow cover anomalies over the central Tibetan Plateau

Many studies have investigated the effects of the snow anomalies over the Tibetan Plateau (TP), yet the original causes of these anomalies are not fully understood. In this study, we explore the possible connection between the late autumn (November) central TP snow cover anomalies and the monthly sea surface temperature (SST) over the North Atlantic (NA) in autumn and find significant correlations over the mid-latitude NA during October and November. By analyzing the air-sea interaction over the NA, we show that a well-organized horseshoe-like SST anomaly pattern coupled with a surface anomalous anticyclone centered over the mid-latitude NA in October and its persistence in November may play a key role in the November central TP snow cover anomalies. Such an October surface anomalous anticyclone could effectively result in the surface turbulent heat flux anomalies via the surface wind-induced horizontal temperature advection, which is conducive to the formation of the horseshoe-like SST anomalies over the mid-latitude NA. The resultant anomalous SST pattern could further contribute to a North Atlantic Oscillation (NAO)-like pattern in November and stimulate the wave trains eastward to the TP. The anomalous anticyclone (cyclone) associated with the wave trains to the southwest (north) of the TP suppresses the precipitation over the central TP and thus reduces the local snow cover. The atmospheric circulation responses to the persistent NA-SST anomalies are well validated by the numerical experiments. The above result might help to predict the condition of the central TP snow cover anomalies in November, one month ahead.

Accounting for Topographic Effects on Snow Cover Fraction and Surface Albedo Simulations Over the Tibetan Plateau in Winter

AbstractThe Tibetan Plateau (TP) is the highest land in the world and has a very complex topography. However, the influence of topography on TP snow cover simulations has not been adequately addressed in most land surface models. The analysis of satellite observations indicates that snow cover fraction (SCF) simulation biases increase with the topography complexity, and this increasing trend slows down when the standard deviation of topography is greater than 200 m. The result also shows that using the SCF schemes without consideration of topography leads to a consistent overestimation in winter. To account for the topographic effects, we introduce a modified topographic factor to the SCF schemes. Then we conduct regional simulations using the Simplified Simple Biosphere Model version 3 (SSiB3) and evaluate the results at the location of observation sites to reduce the uncertainty induced by forcing data. Compared with the default SCF scheme, the mean winter SCF bias is reduced from 3.83% to −0.10%. The optimization of SCF simulations further improves the winter surface albedo and land surface temperature (LST) simulations. The winter surface albedo bias over the TP is reduced from 0.020 to 0.007, with a maximum reduction by −0.133. The winter LST bias is reduced from −3.33 to −3.04 K, with a maximum reduction by 3.60 K. This study highlights the importance of topographic effects in simulating snow cover distribution and land surface energy budget for reducing the “cold bias” in winter climate simulations over the TP.

Impacts of Autumn‐Winter Tibetan Plateau Snow Anomalies on North Atlantic‐Europe and Arctic Climate

AbstractPrevious empirical studies have indicated strong influences of autumn and winter Tibetan Plateau (TP) snow cover extent (SCE) anomalies on the winter Pacific‐North American (PNA) and also East Atlantic teleconnection patterns over the North Atlantic and Europe. Our early numerical experiments reproduced an observed wintertime PNA response to an extensive heavy TP snow anomaly. This study further investigates impacts of autumn‐winter TP snow anomalies on North Atlantic‐Europe and Arctic climate. Expressing snow conditions as snow water equivalent (SWE), observational analysis shows that the principal component time series associated with the leading empirical orthogonal function (EOF1) pattern of autumn TP SWE anomalies is significantly correlated to a remote equivalent barotropic tripole structure in winter, which resembles the negative phases of two teleconnections, North Atlantic Oscillation (NAO) at the surface and West Atlantic (WA) in the mid‐troposphere. This indicates that the hydrological effect of TP SWE differs from the albedo effect of TP SCE in snow‐atmosphere teleconnections. Numerical experiments using autumn TP SWE EOF1 and its persistent changes in winter as idealized snow forcing in a coupled atmosphere‐ocean general circulation model simulate a winter negative NAO/WA response over the North Atlantic‐Europe sector and a negative Arctic Oscillation over the Northern Hemisphere similar to observations. The NAO/WA responses result from mechanisms of horizontal propagation of stationary Rossby wave energy and a transient eddy feedback. Results also indicate that heavy TP SWE induces significant Eurasia cooling, and a consistent pattern of Arctic sea ice anomalies, demonstrating widespread Northern Hemispheric impacts of TP snow anomalies.

The Seasonal Evolution of the Tibetan Plateau Snow Cover Related Moisture During Spring‐to‐Summer

AbstractThe 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.

Modulation of the Tibetan Plateau snow cover on the interannual variations of the MJO-Related winter surface air temperature anomalies over East Asia

Modulation of the Tibetan Plateau snow cover on the interannual variations of the MJO-Related winter surface air temperature anomalies over East Asia

Contribution of the Tibetan Plateau Winter Snow Cover to Seasonal Prediction of the East Asian Summer Monsoon

ABSTRACT How to improve the prediction skill of the East Asian summer monsoon (EASM) is a challenging but essential issue. This study examines the impact of the winter Tibetan Plateau (TP) snow cover (TPSC) on the subsequent EASM during the past two decades. Based on the high-resolution MODIS/Terra snow cover data, a new snow cover critical area (76°−83°E, 28°−35°N) is identified in the southwestern TP for the EASM seasonal prediction. Results show that the increase of the TPSC within this critical area during prior winter significantly increases summer precipitation over the Yangtze River Basin (YRB). The TPSC anomaly induces anomalous cooling in the overlying atmospheric column, leading to an anomalous cyclonic circulation in the upper troposphere. Such anomalous cyclonic circulation may further contribute to the local snow cover increase, and through such a snow-albedo feedback process, the excessive TPSC anomaly is strengthened and persists through the following summer. Coexisting with the positive anomalous TPSC, the South Asian High, the western Pacific Subtropical High, and the Subtropical Westerly Jet shift southward. A deep cyclonic circulation is induced in northeastern China by the excessive TPSC anomaly, which is reproduced in the linear baroclinic model simulation. Northerly flow is crucial for accumulating water vapour and favours more rainfall over the YRB. A physical empirical prediction model is established to quantify the TPSC contribution to the seasonal prediction of the EASM. Empirical hindcast output shows the prediction skill of the EASM is significantly improved with the additional predictor of the winter TPSC. In particular, the TPSC has greatly improved the prediction of the extreme EASM in 2020. The above results indicate that the prior winter TPSC anomaly in this critical area can provide another predictability source for the EASM, besides El Niño-Southern Oscillation and the North Atlantic Oscillation.

An Interdecadal Change in the Influence of ENSO on the Spring Tibetan Plateau Snow-Cover Variability in the Early 2000s

AbstractEl Niño–Southern Oscillation (ENSO) and the Tibetan Plateau snow cover are important factors in interannual climate variability. The relationship between ENSO and the Tibetan Plateau snow variation is still undetermined. While some studies suggested that ENSO is a key factor of changes in snow cover over the Tibetan Plateau, other studies noted independence between the two. The present study revealed a prominent interdecadal change in the relationship between ENSO and the spring Tibetan Plateau snow-cover variation in the early 2000s. There is a significant positive correlation between ENSO and the spring Tibetan Plateau snow-cover variation in the period 1988–2003, but an obvious negative relationship is detected in the period 2004–19. The interdecadal change in the ENSO–snow relationship is related to the distinct pathway of ENSO influence on the spring Tibetan Plateau snow-cover variation during the two periods. In the period 1988–2003, ENSO induces anomalous convection over the tropical western North Pacific that in turn causes atmospheric circulation and moisture anomalies over the Tibetan Plateau. The resultant winter snow anomalies over the central-eastern Tibetan Plateau persist to the following spring. In the period 2004–19, ENSO induces North Atlantic sea surface temperature (SST) anomalies in winter that are maintained to the following spring. The North Atlantic SST anomalies then stimulate the atmospheric circulation anomalies extending to the Tibetan Plateau that induce snow-cover anomalies there in spring. The different processes of ENSO influence lead to opposite anomalies of spring snow cover over the Tibetan Plateau in the two periods.

Decreasing Influence of Summer Snow Cover Over the Western Tibetan Plateau on East Asian Precipitation Under Global Warming

In recent years, some studies emphasized the influence of western Tibetan Plateau summer snow on the East Asian summer precipitation. With the temperature rise in the past decades, the snow cover over the western Tibetan Plateau in summer has significantly decreased. This raises the question whether the impact of the Tibetan Plateau snow has changed. The present study identifies a prominent change in the influence of the western Tibetan Plateau snow cover on the East Asian summer precipitation. Before the early 2000’s, positive precipitation anomalies extend from the southeastern Tibetan Plateau through the Yangtze River to Japan and Korea and negative anomalies cover southeast China corresponding to more Tibetan Plateau snow cover. After the early 2000’s, with the reduction of snow cover variability, below-normal and above-normal summer precipitation occurs over northern China-Mongolia and northeast Asia, respectively, corresponding to more Tibetan Plateau snow cover. The change in the influence of the Tibetan Plateau snow on the East Asian summer precipitation is associated with an obvious change in the atmospheric circulation anomaly pattern. Before the early 2000’s, the wind anomalies display a south-north contrast pattern with anomalous convergence along the Yangtze River. After the early 2000’s, an anomalous cyclone occupies Northeast China with anomalous southerlies and northerlies over northeast Asia and northern China, respectively. The Tibetan Plateau snow cover variation after the early 2000’s is associated with the northeast Indian summer precipitation. The model experiments confirm that the weakened influence of summer western Tibetan Plateau snow cover on the East Asian atmospheric circulation and precipitation with the reduced snow cover anomalies.