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Based on the detection data obtained by the LMI (Lightning Mapping Imager)—China's first satellite-based lightning observation payload—from 2018–2022, combined with the ERA5 (ECMWF Reanalysis v5) reanalysis data of the same period, the temporal and spatial characteristics of lightning activities over the Tibetan Plateau and its response to the atmospheric circulation background are studied in detail in this paper. Based on the LMI data, we obtained consistent and continuous long-time-series lightning observation data for the whole region of the plateau for the first time, and the results show that the lightning density in the Tibetan Plateau is much smaller than that in the central and eastern land regions of China (CELR) at the same latitude. Lightning activity was unevenly distributed over the plateau and had obvious seasonal variation characteristics. The monthly amount of lightning and its ratio in the total amount of lightning for the whole year show the characteristics of "increasing first and then decreasing". Most lightning occurs in June and July, which is about a month earlier than that in the CELR. The amount of lightning fluctuated in May and decreased rapidly after August, which is consistent with the local convective thunderstorm season. The hourly lightning frequency at different altitudes over the Tibetan Plateau is consistent with local convections and unique topography, and it is closely related to the features of the local night rain. The results also reveal comparative features between lightning and the atmospheric circulation background on the plateau, such as the wind field, CAPE (convective available potential energy), temperature, and humidity at 500 hPa. In the context of global warming, the average temperature in the central and western regions of the plateau increased in the past five years. This shows that the Tibetan Plateau, as a summer heat source, has a gradual warming trend, and the corresponding convections and lightning activities are also increasing gradually. Lightning activities can be used as an indicator of DCSs (deep convective systems). This paper gives a more comprehensive understanding of the characteristics of lightning activities all over the Tibetan Plateau, especially in the western part of the plateau, which lacked ground-based lightning observation data before. In addition, it reveals the comparative features between the lightning activities and the circulation background over the plateau in the past five years, which is helpful for further understanding the contribution of lightning activities to the plateau's climate change. It can provide some reference for monitoring and researching the severe convective weather over the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) plays a key role in the water cycle of High Asia and its downstream regions. The respective influence of the Indian and East Asian summer monsoon on TP precipitation and the regional water resources, together with the detection of moisture transport pathways and source regions are subject of recent research. In this study we present a twelve-year high-resolution climatology of the atmospheric water transport (AWT) on and towards the TP, using a new dataset, the High Asia Reanalysis (HAR), which better represents the complex topography of the TP and surrounding high mountain ranges than coarse resolution datasets. We focus on spatio temporal patterns, vertical distribution and transport through the TP boundaries. The results show that the mid-latitude westerlies have a higher share in summertime AWT on the TP than assumed so far. Water vapour (WV) transport constitute the main part, whereby transports of water as cloud particles (CP) play also a role in winter in the Karakoram and western Himalayan regions. High mountain valleys in the Himalayas facilitate AWT from the south whereas the high mountain regions inhibit the AWT to a large extend and limit the influence of the Indian summer monsoon. No transport from the East Asian monsoon to the TP could be detected. Our results show that 40% of the atmospheric moisture needed for precipitation comes from outside the TP, while the remaining 60% are provided by local moisture recycling. How far precipitation variability can be explained by variable moisture supply has to be studied in future research by analysing the atmospheric dynamic and moisture recycling more in detail. [ABSTRACT FROM AUTHOR]

Mêdog and Nagqu are two typical climate regions of the Tibetan Plateau, with different atmospheric conditions and local orography. This may lead to different diurnal variation patterns of clouds and precipitation. This paper investigates the diurnal variations of clouds and precipitation in Mêdog and Nagqu, using ground-based measurements from Ka-band cloud radar and a Particle Size and Velocity (PARSIVEL) disdrometer. High frequencies of cloud cover and precipitation occur from 23:00 local solar time (LST) to 05:00 LST in Mêdog, while low frequencies appear from 11:00 LST to 17:00 LST. The occurrence frequencies in Nagqu maintain high values from 13:00 LST to 21:00 LST. In terms of mean rain rate, heavier rainfall appears in the evening and at night in Mêdog, with peaks at 00:00 LST and 18:00 LST, respectively. In Nagqu, the heaviest rainfall occurs at 12:00 LST. In addition, the afternoon convective rainfall in Nagqu is characterized by a much higher concentration of large drops, which can be classified as continental-like. The morning rainfall has the lowest concentration of large drops and can be classified as maritime-like. Finally, the mechanisms of diurnal variations in the two regions are discussed. The diurnal cycle of clouds and precipitation in Mêdog may be associated with the nocturnal convergence of moisture flux and mountain–valley wind circulation. Diurnal variations in Nagqu have a high correlation with the diurnal cycle of solar radiation. The high nocturnal frequency of clouds and precipitation in the two regions at night is closely related to the convergence of moisture flux. [ABSTRACT FROM AUTHOR]

Recent climate and environment over the Tibetan Plateau (TP) have undergone significant changes, dominated by variations in the Westerlies and the Indian summer monsoon. However, long‐term shifts in atmospheric circulation during the transitional seasons are still lacking. Here we investigate the modern distribution of Tsuga pollen over the central‐western TP and confirm it as an indicator of variable atmospheric circulation in spring. By combining our Tsuga record from Taro Co with existing records in the Tsuga pollen source area, we suggest that a potential particle transport pathway from the southern slope of the Himalayas to the interior of the plateau appeared in the spring of the late Holocene. Our results show that the springtime atmospheric circulation over the southwestern TP during the early and late Holocene is closely related to the substantial remnants of ice sheets at northern high latitudes and the frequency of El Niño events, respectively. Plain Language Summary: The spring climate over the Tibetan Plateau (TP) is undergoing significant changes that yield profound impacts on environmental changes such as variations in vegetation phenology and alpine treeline. Knowledge of long‐term variations in atmospheric circulation during spring can improve the understanding of current climatic and environmental change and the projection of future variability. In this paper, we use an exotic pollen grain, which can be transported long distances in the air, as an indicator to trace the variability of spring atmospheric circulation over the TP. The results indicate that the spring meridional atmospheric circulation from the southern slope of the TP to its interior has been enhanced in the last four thousand years, which is mainly influenced by the frequency of El Niño events. Key Points: Spring atmospheric circulation change over the southwestern Tibetan Plateau (TP) during Holocene is reconstructedMeridional atmospheric circulation in spring over the southwestern TP is strengthened in the late HoloceneHigh‐(low‐) latitude forcing mainly influence the variations in spring atmospheric circulation during the early (late) Holocene [ABSTRACT FROM AUTHOR]

The westerly jet (WJ) is an important component of atmospheric circulation, which is characterized by prominent seasonal variations in intensity and position. However, the response of the WJ over Asia during the Last Glacial Maximum (LGM) is still not clear. Using general circulation model experiments, the seasonal behaviors of the WJ over central Asia and Japan are analyzed in this paper. The results show that, compared to the present day (PD), the WJ presents a complicated response during the LGM, both in intensity and position. Over central Asia, it becomes weaker in both summer and winter. But over Japan, it is enhanced in summer but becomes diminished in winter. In terms of position, the WJ over central Asia shifts southward in both summer and winter, whereas the WJ over Japan moves southward in summer but does not change obviously relative to PD in winter. Such WJ changes are well explained by meridional temperature gradients in high troposphere, which is closely linked to seasonal thermal anomalies over the Tibetan Plateau (TP). Despite cooler LGM conditions, the anomalous warming center over the TP becomes stronger in summer. Derived from the heat budget equation, the stronger heating center is mainly caused by the weaker adiabatic cooling generated from ascending motion over the area south of the TP. In winter, the cooling over the TP is also strengthened, mostly owing to the subsidence-induced weaker adiabatic heating. Due to the importance of the WJ, the potential role of TP thermal effects should be a focus when explaining the East Asian climate change during the LGM. [ABSTRACT FROM AUTHOR]

Extreme glacier melt has important implications for climate change studies and glacier‐related hazards. Few attempts have been made to study the characteristics and mechanisms of extreme melt on the Tibetan Plateau (TP) and surroundings, one of the largest concentrations of glaciers beyond the polar regions. To address this gap, we investigated the magnitude and possible drivers of anomalous early spring glacier melt in 2022 on the central TP using multi‐source observations (October 2020–July 2022) of Kuoqionggangri and Sangqu glaciers and an energy and mass balance model. Our results show that anomalous melt of both glaciers occurred in early spring (18 March–10 April 2022), when glaciers are traditionally expected to be frozen. There were 89 cumulative hours with air temperatures above 0°C, with a positive cumulative air temperature of 121.80°C hour at 5,700 m on Kuoqionggangri Glacier. The glacier‐wide cumulative melts on Kuoqionggangri and Sangqu glaciers from 18 March to 10 April 2022 were 22 ± 14.2 and 48 ± 37.5 mm w.e., respectively. Such anomalous glacier melt was driven by high incoming shortwave radiation and sensible heat flux, which were influenced by low cloud fraction and precipitation, and high air temperature during early spring. The weakening and northward‐shift of the westerlies, coupled with descending air motions over the central TP, reduced cloud fraction and hindered the transport of cold, moist air to the central TP. These changes occurred both in the central TP and the Himalaya, indicating the influence of macroscale atmospheric circulation patterns on this extreme glacier melt. Plain Language Summary: The Tibetan Plateau (TP) and surroundings have the largest amount of ice outside of the Arctic and Antarctic. Extreme glacier melt not only accelerates glacier mass loss, but is also important for changing climates and triggering glacier‐related disasters. Here, results show that extreme weather conditions and anomalous glacier melt occurred in early spring 2022 on the central TP. High air temperature, low cloud fraction and precipitation were the main characteristics of extreme weather events. Accompanying this extreme event, anomalously high incoming shortwave radiation and sensible heat flux control extreme glacier melt. We found that extreme weather conditions occurred in both the central TP and the northern foothills of the Himalaya. Our results indicate that extreme weather events and glacier melt were linked to large‐scale atmospheric circulation and regional climate conditions. This study contributes to a deeper insight into the characteristics and processes of glacier melt. In the future, more efforts are needed to monitor glacier melt and identify the causes of extreme glacier melt on the TP, which holds significant scientific and practical importance. Key Points: Extreme weather conditions and glacier melt occurred in the early spring of 2022 on central Tibetan PlateauExtreme glacier melt was driven by anomalously high incoming shortwave radiation and sensible heat fluxA strong northward shift of westerly winds in early spring 2022 led to extreme weather conditions and glacier melt [ABSTRACT FROM AUTHOR]

The South Asian summer monsoon (SASM) is a significant monsoon system that exerts a profound impact on climate and human livelihoods. According to 38 models from the Coupled Model Intercomparison Project Phase 6, the SASM circulation is projected to weaken significantly under global warming as seen in the weakened low-level westerly wind over the northern tropical Indian Ocean; however, the associated climate dynamics is still under debate. Here, we identify that the weakened low-level westerly wind is closely related to the enhanced latent heating over the Tibetan Plateau (TP), which corresponds with increased summer precipitation in the future. The intensified TP latent heating triggers an anomalous meridional circulation with ascending motions over the plateau and descending motions to the south, leading to an anomalous low-level anticyclone over the northern tropical Indian Ocean. This anticyclone greatly weakens the prevailing low-level westerlies of the SASM through easterly anomalies at the anticyclone's southern flank. Moisture budget analysis further reveals that increased atmospheric water vapor, rather than the vertical dynamic component, makes the largest contribution to the increased precipitation over the TP. This result confirms that the enhanced TP latent heating is a driver of atmospheric circulation change and contributes to weakening the SASM circulation. [ABSTRACT FROM AUTHOR]

Based on the observational and reanalysis datasets, a dipole pattern of the early summer (June) precipitation over the eastern Tibetan Plateau (TP) is identified through empirical orthogonal function. In contrast to previous researches, this paper introduces the May North Atlantic Oscillation (NAO) as a preceding signal and investigates its connection with subsequent early summer precipitation over the eastern TP during 1980–2019, focusing on predictive aspects. Results reveal that the correlation between NAO and primary eastern TP precipitation pattern (Precip_EOF1) has weakened since 2000. During 1980–2000, an equivalent barotropic Silk Road Pattern (SRP) observed across Eurasia triggers southerly wind anomalies over the TP. This, in turn, leads to the northward shift of the water vapor, which favors the ascending motion over the northern TP (NTP) due to water vapor convergence. Additionally, the SRP-related sensible heating also plays a critical role in vertical motion over the eastern TP by enhancing the TP thermal effect. Consequently, these factors contribute to shaping the dipole pattern of eastern TP precipitation. However, the weakened relationship between NAO and Precip_EOF1 during 2001–2019 is attributed to the absence of NAO-related atmospheric circulation over Eurasia. Further analysis suggests that these circulation anomalies arise from the interdecadal variability of the NAO and its phase shift. Moreover, when the influence of sea surface temperature anomalies over the northern North Atlantic is removed, the correlation of Precip_EOF1 with NAO and Atlantic Multidecadal Oscillation (AMO) both become insignificant. This suggests that the NAO-related dipole pattern of eastern TP precipitation is modulated by preceding northern North Atlantic sea surface temperature rather than AMO on the interdecadal timescale. • The relationship between North Atlantic Oscillation (NAO) and Tibetan Plateau (TP) precipitation has weakened since 2000. • The change in NAO-related Silk Road Pattern (SRP) is the dominant reason for the unstable correlation. • The interdecadal variability in TP precipitation is attributed to the NAO phase shift. • This relationship is modulated by northern North Atlantic sea surface temperature on the interdecadal scale. [ABSTRACT FROM AUTHOR]

Cumulus (Cu) from shallow convection is one of the dominant cloud types over the Tibetan Plateau (TP) in the summer according to CloudSat- CALIPSO observations. Its thermodynamic effects on the atmospheric environment and impacts on the large-scale atmospheric circulation are studied in this paper using the Community Atmospheric Model, version 5.3 (CAM5.3). It is found that the model can reasonably simulate the unique distribution of diabatic heating and Cu over the TP. Shallow convection provides the dominant diabatic heating and drying to the lower and middle atmosphere over the TP. A sensitivity experiment indicates that without Cu over the TP, large-scale condensation and stratiform clouds would increase dramatically, which induces enhanced low-level wind and moisture convergence toward the TP, resulting in significantly enhanced monsoon circulation with remote impact on the areas far beyond the TP. Cu therefore acts as a safety valve to modulate the atmospheric environment that prevents the formation of superclusters of stratiform clouds and precipitation over the TP. [ABSTRACT FROM AUTHOR]

Tibetan Plateau (TP) snow cover is featured by sub‐seasonal changes, affecting weather and climate in surrounding and downstream areas. Previous studies emphasize the effect of background atmospheric circulation on rapid changes of TP snow cover as a whole. However, spatial discrepant changes of snow cover over the TP with complex topography and uneven snowfall remain unaddressed. Our research indicates that snow cover fraction dominates the rapid changes of surface albedo across the TP, and snow depth also significantly influences surface albedo changes through modulating snow albedo in central and eastern TP with shallow snow. However, the excessive snow amount and empirical snow cover fraction schemes introduce spatially divergent biases of surface albedo changes in simulations. Our research highlights the instant response of TP surface albedo to both snow coverage and depth in snow season, and provides a promising perspective for improving TP snow and surface albedo simulations. Plain Language Summary: Tibetan Plateau (TP) snow cover is characterized not only by obvious seasonal changes, but also by rapid sub‐seasonal changes, which has a significant impact on the weather and climate of the downstream areas by affecting the surface albedo over the TP. Previous studies have generally concluded that the background atmospheric circulation dominates rapid changes of overall TP snow cover. However, rapid changes of snow cover exhibit spatial discrepancies over the TP with complex topography and uneven snowfall. Our study finds that snow coverage and depth both contribute to rapid changes of surface albedo and energy budget over the TP, which further lead to rapid changes of snow cover. However, current numerical models tend to overestimate the snow and fail to simulate spatial different changes of snow coverage and depth, leading to spatially divergent simulation biases in surface albedo, surface energy balance and local atmospheric circulation over the TP. Therefore, there is an urgent need to improve the snow parameterization in models to enhance the intra‐seasonal simulation of snow cover and surface albedo over the TP. Key Points: Observed surface albedo over the Tibetan Plateau (TP) has significant weekly scale fluctuations during winterSnow cover fraction and snow depth jointly dominate observed rapid changes of surface albedo over the TPExcessive snow amount and empirical snow cover fraction schemes lead to spatially divergent bias of surface albedo change [ABSTRACT FROM AUTHOR]

This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. In response to soil moisture increase, the local air temperature significantly decreases, and precipitation increases in summer. The wetter ANWC results in a warmer and rainless climate over the Central part of North China Plain (CNCP). While the influence of increasing soil moisture on the Tibetan Plateau (TP) precipitation is negligible due to the high altitude. A cooler climate over ANWC leads to an abnormal descending motion occurring. Meanwhile, an anomalous high pressure and an abnormal anticyclonic circulation occurs in 500 hPa over the west of ANWC. Correspondingly, a huge anomalous cyclone circulation occurs over the northeastern part of China and Mongolia, which can hinder the northward movement of the East Asian summer Monsoon (EASM) and reduce the water vapor transport into Central China Plain. As a result, the weakened EASM thus leads to rainless over CNCP. As soil moisture increases over ANWC is stronger, the magnitudes of the influence on the atmospheric field become larger. This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. • This paper examines the local and non-local climatic effects of wetter arid areas of Northwestern China (ANWC) in summer using a fully coupled climate model. • It finds that the wetter ANWC can result in a warmer and rainless climate over the Central part of North China Plain (CNCP) through a complex atmospheric circulation response. • A cooler climate leads to an abnormal descending motion occurring over ANWC. • A huge anomalous cyclone circulation over the northeastern part of China and Mongolia can block the East Asian summer Monsoon northward and decrease the water vapor transport into Central China Plain. • This study highlights the wetter ANWC effect on local climate and provides more information about the mechanism of wetter ANWC remote effect on non-local climate. [ABSTRACT FROM AUTHOR]

The relationship between Tibetan Plateau (TP) snow cover and the East Asian summer monsoon (EASM) has long been discussed, but the underlying mechanism remains controversial. In this paper, the snow-albedo and snow-hydrology feedbacks over the TP are investigated based on multiple sources of snow data for the period 1979-2011. The results indicate that winter snow cover plays an important role in cooling local air temperature through the snow-albedo effect; the TP surface net solar radiation in years with above-normal snow cover is approximately 18 W m−2 less than that in below-normal snow cover years. However, data analysis demonstrates that persistent effects of winter snow cover are limited to the period from winter to spring over most parts of the central and eastern TP. Therefore, the preceding snow cover over the central and eastern TP exerts little influence over either the in situ summer atmospheric heat source or the EASM, because of its limited persistence. In contrast, the effects of winter or spring snow cover anomalies over the western TP and the Himalayas can last until summer, and these anomalies further influence the EASM by modulating moisture transport to eastern China and favoring eastward-propagating synoptic disturbances that are generated over the TP. Generally, above-normal snow cover over the western TP and the Himalayas facilitates abundant summer precipitation between the Yangtze and Yellow River basins, which is confirmed by results from a regional Weather Research and Forecasting model simulation. [ABSTRACT FROM AUTHOR]

This study investigates the interdecadal change in the covariability between the Tibetan Plateau (TP) east–west dipole precipitation and Indian precipitation during summer and primarily explores the modulation of atmospheric circulation anomalies on the covariability. The results reveal that the western TP precipitation (WTPP), eastern TP precipitation (ETPP), and northwestern Indian precipitation (NWIP) have covariability, with an in-phase variation between the WTPP and NWIP and an out-of-phase variation between the WTPP and ETPP. Moreover, this covariability was unclear during 1981–2004 and became significant during 2005–2019, showing a clear interdecadal change. During 2005–2019, a thick geopotential height anomaly, which tilted slightly northward, governed the TP, forming upper- and lower-level coupled circulation anomalies (i.e., anomalous upper-level westerlies over the TP and lower-level southeasterlies and northeasterlies around the southern flank of the TP). As such, the upper- and lower-tropospheric circulation anomalies synergistically modulate the summer WTPP, ETPP, and NWIP, causing the covariability of summer precipitation over the TP and India during 2005–2019. The upper- or lower-level circulation anomalies cannot independently result in significant precipitation covariability. During 1981–2004, the upper- and lower-level circulation anomalies were not strongly coupled, which caused precipitation non-covariability. The sea surface temperature anomalies (SSTAs) in the western North Pacific (WNP) and tropical Atlantic (TA) may synergistically modulate the upper- and lower-level coupled circulation anomalies, contributing to the covariability of the WTPP, ETPP, and NWIP during 2005–2019. The modulation of the WNP and TA SSTs on the coupled circulation anomalies was weaker during 1981–2004, which was therefore not conducive to this precipitation covariability. This study may provide valuable insights into the characteristics and mechanisms of spatiotemporal variation in summer precipitation over the TP and its adjacent regions, thus offering scientific support for local water resource management, ecological environment protection, and social and economic development. [ABSTRACT FROM AUTHOR]

Based on 360 event-based precipitation samples collected at six stations on the North Tibetan Plateau (NTP) in 2019–2020, we analyzed the influence of meteorological parameters, sub-cloud evaporation, moisture sources, and moisture transmission pathways on precipitation and its seasonal variations. The results show that precipitation δ18O, δ2H, and d-excess values show obvious seasonal variations, being depleted in winter and enriched in summer. Although temperature is an important variable that affects the change in δ18O values of precipitation, the results of the sub-cloud evaporation effect and moisture tracing show that differences in moisture sources caused by seasonal changes in large-scale water moisture transport are an important cause of seasonal changes in δ18O and d-excess of precipitation at NTP. Depleted δ18O and enriched d-excess in winter represent the source of moisture transported by the westerlies from the Mediterranean area and Central Asia. Enriched δ18O and d-excess values in summer precipitation are related to the temperature effect. In addition, the meridional motion of the atmospheric flow has an effect on the precipitation isotope values in the NTP. When the meridional circulation is enhanced, the water vapour from low latitudes is easily transported northwards, enriching the summer precipitation isotope values in the central and eastern parts of the plateau. This provides a new insight into the explanation of stable oxygen isotopes in climate proxies across the westerlies-dominated Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Overestimation of precipitation over steep mountains is always a common bias of atmospheric general circulation models (AGCMs). One basic reason is the imperfection of parameterization schemes. Sub-grid topography has a non-negligible role in the dynamics of the actual atmosphere, and therefore the sub-grid topographic parameterization schemes have been the focus of model development. This study proposes a sub-grid parameterization scheme for topographic vertical motion in CAM5-SE (Community Atmospheric Model version 5 with spectral element dynamical core) to revise the original vertical velocity by adding the topographic vertical motion, resulting in a significant improvement in simulations in precipitation over steep mountains. The results show a better improvement in precipitation simulation in steep mountains, such as the steep edge of the Tibetan Plateau and the Andes. The positive deviations of the precipitation on the mountain tops and the negative deviations in the windward slope are revised. The improved scheme of topographic vertical motion reduces the model biases of summer mean precipitation simulations by up to 48 % (6.23 mm d -1) on the mountain tops. The improvement in convective precipitation (4.83 mm d -1) contributes the most to the improvement in the total precipitation simulation. In addition, we extend the dynamic lifting effect of topography from the lowest layer (Single experiment) to multiple layers, approaching the bottom model layers (Multi experiment). Moreover, the water vapor transport in low-altitude regions in front of the windward slope is also considerably improved, leading to simulations of much more realistic circulation patterns in the multi-layer scheme. Since the sub-grid parameterization scheme addresses the more detailed problem caused by topography, the water vapor is transported further to the northwest in the multi-layer scheme. The topographic vertical motion schemes in both the Single and Multi experiments can improve the model performance in simulating precipitation in all regions with complex terrain. [ABSTRACT FROM AUTHOR]

This paper investigates the dynamical processes through which the Tibetan Plateau (TP) influences the East Asian summer monsoon (EASM) within the framework of the moist static energy (MSE) budget, using both observations and atmospheric general circulation model (AGCM) simulations. The focus is on the most prominent feature of the EASM, the so-called meiyu-baiu (MB), which is characterized by a well-defined, southwest-northeast elongated quasi-stationary rainfall band, spanning from eastern China to Japan and into the northwestern Pacific Ocean between mid-June and mid-July. Observational analyses of the MSE budget of the MB front indicate that horizontal advection of moist enthalpy, and primarily of dry enthalpy, sustains the front in a region of otherwise negative net energy input into the atmospheric column. A decomposition of the horizontal dry enthalpy advection into mean, transient, and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection. Numerical simulations in which the TP is either retained or removed show that the TP influences the stationary enthalpy flux, and hence the MB front, primarily by changing the meridional stationary eddy velocity, with reinforced southerly wind over the MB region and northerly wind to its north. Changes in the longitudinal thermal gradient are mainly confined to the near downstream of the TP, with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended MB region. [ABSTRACT FROM AUTHOR]

In this paper, the possible reason of Tibetan Plateau (TP) temperature increasing was investigated. An increase in T (minimum temperature) plays a robust role in increased TP temperature, which is strongly related to SST over the warm pool of the western Pacific Ocean, the subtropical westerly jet stream (SWJ), and the tropical easterly upper jet stream (TEJ), and the 200-hPa zonal wind in East Asia. Composite analysis of the effects of SST, SWJ, and TEJ on pre- and post-abrupt changes in T (annual temperature) and T over the TP shows remarkable differences in SST, SWJ, and TEJ. A lag correlation between T/ T, SST, and SWJ/TEJ shows that changes in SST occur ahead of changes in T /T by approximately one to three seasons. Partial correlations between T/ T, SST, and SWJ/TEJ show that the effect of SWJ on T/ T is more significant than the effect of SST. Furthermore, simulations with a community atmospheric model (CAM3.0) were performed, showing a remarkable increase in T over the TP when the SST increased by 0.5°C. The main increase in T and T in the TP can be attributed to changes in SWJ. A possible mechanism is that changes in SST force the TEJ to weaken, move south, and lead to increased SWJ and movement of SWJ northward. Finally, changes in the intensity and location of the SWJ cause an increase in T/ T. It appears that TP warming is governed primarily by coherent TEJ and SWJ variations that act as the atmospheric bridges to remote SSTs in warm-pool forcing. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP), being an average of surpassing 4000 m above sea level and around 2.5 × 10 6  km 2 , is the highest and largest plateau in the world and also called as the “Third Pole”. Due to its elevated land surface and complex terrain, the TP is subjected to combined regulations of multiple climate systems and associated large-scale atmospheric circulations. In this paper, we comprehensively review the recent studies of atmospheric moisture transport versus precipitation across the TP, with the attempt to link the two, which did not receive much attention previously. This review focuses on the atmospheric moisture transport and associated circulation patterns in this region, widely adopted approaches to identify the atmospheric moisture transport, qualitative and quantitative analyses for the role of water vapor transport on the precipitation, as well as the internal physical mechanism between atmospheric moisture transport and precipitation over the TP. Moreover, directions of future research are discussed based on the following aspects, which include 1) proposing an integrated statistical-physical framework for demonstrating the influence of atmospheric moisture transport and associated circulation patterns on the precipitation, especially the extremes, in the high-cold mountainous region; 2) quantifying the contribution of atmospheric water vapor from the surrounding sources as well as the local moisture recycling on the TP's precipitation; 3) providing higher quality data for atmospheric water vapor and precipitation; 4) emphasizing on the physical mechanism sustaining the atmospheric moisture transport as well as its potential influence on the extreme precipitation, including amount, frequency, intensity and duration. It is expected that this review will be beneficial for exploring the linkage between atmospheric moisture transport versus precipitation across the TP. [ABSTRACT FROM AUTHOR]

Based on the definition of potential vorticity substance (W) and its equation, an index "iPV" representing the leading mode of the surface potential vorticity circulation (PVC) over the Tibetan Plateau is defined to characterize the orographic potential vorticity (PV) forcing on the atmospheric general circulation. The relationships between the iPV index and the East Asian monsoon in July, as well as the Silk Road pattern in Eurasia, are investigated on an interannual time scale. Results show that the iPV in July is closely related to the interannual variability of the East Asian monsoon. Corresponding to the positive phase of iPV with negative (positive) PVC over the north (south) of the plateau, strong positive PV anomalies and westerly flows develop in the troposphere over the plateau. Consequently, in the downstream region, the zonal PV advection increases with height just above the Jianghuai Meiyu front, which is conducive to the generation of upward movement. Over the East Asian area, the upper troposphere is controlled by the eastward shifted South Asian High. In the lower troposphere, the southwesterly flow anomaly on the northwestern side of the strengthened western Pacific subtropical high transports abundant water vapor to the north, forming a convergence in the Jianghuai area, leading to the formation of large-scale precipitation along the Meiyu front. Results from partial correlation analysis also demonstrate that the link between the variability of the East Asian monsoon in July and the plateau PV forcing is affected very little by the Silk Road pattern, whereas the plateau PV forcing plays a key "bridging" role in the influence of the Silk Road pattern on the East Asian monsoon. [ABSTRACT FROM AUTHOR]

Extreme precipitation events frequently occur at the southeastern edge of the Tibetan Plateau (SETP), causing severe disasters. In this study, we selected the top 100 regional extreme precipitation events over the SETP region during the period of 2001–2020, and analyzed their evolutionary characteristics of large-scale thermodynamic anomalies prior to the extreme precipitation events occurring, with the aim of exploring their precursor signals. The results show that, accompanying the wave train propagating across the Eurasian continent and reaching East Asia, the extreme events over SETP during the summer season are dominated by the background large-scale atmospheric circulations characterized by the strengthened Southern Asia high (SAH), the westward-extended Western Pacific subtropical high (WPSH), and an intensified eastern Asia trough. Additionally, an analogue of low-level vortex embedded in the background large-scale circulations is developed at least 4 days prior to the occurrence of extreme events. Under the combined effects of these anomalies, the warm and cold air converge in the SETP area. Further analysis also suggests that the upper-troposphere divergence aloft combined with lower pressures at surface level lead to the upward vertical motion of circulations, along with the enhanced water-vapor transport conveyed both by the East Asian summer monsoon and the Indian summer monsoon. All anomalies mentioned above provide the favorable environment for the occurrence of precipitation extremes in the SETP region. [ABSTRACT FROM AUTHOR]

The wave activity flux representing the energy propagation direction of planetary Rossby wave generally originates from a large wave source area. This study investigates the interdecadal variability and formation mechanism of Rossby wave source over the Tibetan Plateau (TP-RWS) and its impact on the atmospheric circulation and precipitation pattern in East Asia based on the ERA-20C reanalysis dataset in summer (June–July–August) during 1900 to 2010. Results show that the region with the maximum variabilities of Rossby wave source (RWS) in the past 110 years appears over the Tibetan Plateau (TP) during boreal summer, and the TP-RWS shows prominent characteristics of interdecadal oscillation. Secondly, the TP-RWS is mainly composed of the vortex stretching term (RWS-S1) and the absolute vorticity advection term (RWS-S2). The interdecadal TP-RWS is a synergistic result of the snow cover over northwestern TP associated with the RWS-S1, and the deep convection over southeastern TP associated with the RWS-S2. Furthermore, the interdecadal TP-RWS can lead to an alternatively positive and negative pattern of geopotential height anomalies from the northwestern TP to the North Pacific, which has a great climate effect on the precipitation in Huang-huai River Basin, South Korea and Japan Island. Under the guidance of the anomalous cyclonic circulation in East Asia, the prevailing southerly and easterly winds occur over the West Pacific and the Huang-huai River Basin, which lead to the water vapor convergence and upward movement at middle and lower troposphere. [ABSTRACT FROM AUTHOR]

Snow on the Tibetan Plateau (TP) is an important signal for the prediction of East Asian climate. In this study, the relationship between the TP spring snowmelt and spring and summer precipitation in Northwest China (NWC) was investigated, along with the possible mechanisms linked to the impacts of snowmelt on precipitation. The results showed that the TP spring snowmelt had significant impacts on spring and summer precipitation in NWC. For example, when there was a large spring snowmelt in the central- eastern TP, the spring and summer precipitation in the Hexi Corridor and southeast NWC was excessive, especially in summer; when there was a large spring snowmelt in the northern TP, the spring and summer precipitation was deficient across the whole of NWC, while a large spring snowmelt in the western TP led to deficient spring and summer precipitation in eastern NWC but excessive precipitation in western NWC. The possible mechanisms for this included the fact that more spring snowmelt over the TP led to higher soil moisture contents, which further resulted in weakened subtropical westerly and enhanced ridge over Xinjiang. By changing the TP thermal forcing, these anomalous atmospheric circulation conditions transported water vapor into NWC, thus creating excessive summer precipitation in that region. [ABSTRACT FROM AUTHOR]

Despite knowledge of the presence of the Tibetan Plateau (TP) in reorganizing large-scale atmospheric circulation, it remains unclear how surface albedo darkening over TP will impact local glaciers and remote Asian monsoon systems. Here, we use a coupled land-atmosphere global climate model and a glacier model to address these questions. Under a high-emission scenario, TP surface albedo darkening will increase local temperature by 0.24 K by the end of this century. This warming will strengthen the elevated heat pump of TP, increasing South Asian monsoon precipitation while exacerbating the current "South Flood-North Drought" pattern over East Asia. The albedo darkening-induced climate change also leads to an accompanying TP glacier volume loss of 6.9%, which further increases to 25.2% at the equilibrium, with a notable loss in western TP. Our findings emphasize the importance of land-surface change responses in projecting future water resource availability, with important implications for water management policies. Impacts of Tibetan Plateau darkening remain unclear. Here authors show that darkening under the RCP8.5 scenario will increase South Asian monsoon precipitation and the "South Flood-North Drought" pattern over East Asia, while lead to local glacier loss. [ABSTRACT FROM AUTHOR]

The influence of the Madden–Julian oscillation (MJO) on precipitation over the Tibetan Plateau (TP) during boreal summer is investigated using observational and reanalysis data during 1980–2020. The results show that summer precipitation over most areas of the eastern TP increases (decreases) in MJO Phases 1–2 (5–6), especially when the eastward-propagating MJO active convection is located over the Indian Ocean (Western Pacific) in Phase 2 (6). The most significant negative precipitation anomalies in Phase 4 (8) are located over the southern (northeastern) TP. Moreover, MJO has a relatively weakened effect on the TP summer precipitation in Phases 3 and 7 when its convection migrates to the eastern Indian Ocean and the western–central Pacific, respectively. The MJO-phase dependence of the TP summer precipitation anomalies is closely associated with the anomalous atmospheric circulation and evolution of the horizontal moisture flux convergence directly induced by MJO. When the MJO convection centers are located over the western Indian Ocean and the Pacific, high-level anticyclonic and low-level cyclonic anomalous circulations over the TP are excited. In contrast, when MJO locates over the Indian Ocean and the Maritime Continent, its diabatic heating can inspire high-level cyclonic and low-level anticyclonic circulation anomalies over the TP. The vertical motions and moisture transport from the Bay of Bengal caused by the MJO-excited large-scale circulation can modulate the TP summer precipitation. This study advances the understanding of the TP intraseasonal variability. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) plays a vital role in Asian and even global atmospheric circulation, through the interactions between land and atmosphere. It has experienced significant climate warming and spatially and temporally variant wetting over the past half century. Because of the importance of land surface status to the interactions, determining the wetting and drying of the TP from individual changes in precipitation (Prep) or temperature is difficult. Soil moisture (SM) is the water synthesis of the surface status. The persistent deficit of SM (SM drought) is more sensitive to climate change than normal SM. This study first explored the climate wetting and drying of the TP from variations in historical SM droughts over 1961–2014, with a focus on spatiotemporal patterns, long-term variations, and climate causes of summer (May–September) SM droughts based on multiple observation and reanalysis data. The results showed comparatively frequent and severe droughts in the central and southern area, particularly in the semiarid and subhumid regions. SM drought exhibited an abrupt and significant (p < 0.05) alleviation in the interior and central-west TP in the middle to late 1990s. The prominent drought alleviation indicated a hydroclimate shift to a wetter plateau, not merely steady trends as given in the literature. We demonstrated that the wetting shift was dominated by Prep over potential evapotranspiration (PET). By contrast, the in-phase trends were combined forces of Prep and PET, with increased forces of PET after the wetting shift. Furthermore, the Prep dominance was largely attributed to a phase transition of the Atlantic multi-decadal oscillation from cold to warm since the mid-1990s. The PET impacts on the wetting trends were likely dominated by solar radiation, wind speed, and vapor pressure deficit. Regionally, the wetting shift was distinct from the arid to semiarid and semiarid to subhumid climate. Such spatiotemporal changes may affect the TP's atmospheric circulation and, subsequently, the Asian monsoon and global circulation, in addition to the fragile ecosystem in the TP. [ABSTRACT FROM AUTHOR]

Thundersnow is a special kind of thunderstorm that combines snowfall and lightning. A 10‐year thundersnow climatology over China was obtained based on observations during 2008–2017. Our results show that thundersnows are widely distributed in China, and most of the high‐frequency areas are located in the Tibetan Plateau and northeastern China. The average frequency of thundersnow decreases with decreasing altitude, and thundersnow usually occurs at low‐altitude stations once every 10 years. Thundersnow, which likely induces great total snowfall depths, appears mostly in spring, autumn and late winter and can occur in high‐altitude areas in summer. The blizzard probability on a thundersnow day is 12.7%. The percentage of positive cloud‐to‐ground lightning of winter thundersnow is approximately 20.7%, which is lower than those in other seasons. The negative phase of the Arctic Oscillation and anomalous western North Pacific anticyclone are favorable background conditions for thundersnow events. Plain Language Summary: Though the snowfall process is different from common rainfall processes that are accompanied by lightning, it can also occasionally produce lightning. This special type of thunderstorm is called thundersnow. It can induce heavy snowfall, which results in partial paralysis of modern cities. Electrified winter clouds may pose an aviation hazard. Although the frequency of thundersnow is low, it is widely distributed in China. Thundersnow can occur throughout the year, mainly in February‐May and October‐November. Thundersnow events increase the probability of blizzards, especially in the Shandong Peninsula in spring, North China and the Changbai Mountain in autumn, and the middle and lower reaches of the Yangtze River basin and Bohai Rim in winter. The variations of the thundersnow number are closely associated with extratropical atmospheric circulation anomalies. The climatological and atmospheric conditions of thundersnow in China that are revealed by this study help establish an important basis for thundersnow forecasting. Key Points: A 10‐year climatology of thundersnow in China was revealed for the first timeThe high‐frequency areas of thundersnow are mainly located in the Tibetan Plateau and northeastern ChinaThundersnow is significantly influenced by the Arctic Oscillation and associated with the anomalous western North Pacific anticyclone [ABSTRACT FROM AUTHOR]

Spring gale is a dynamic power for DSs (DSs), which presents a close connection with the DSs of northern China. Both display declining trends during the past 68 years (1954–2021). In this study, the influencing factors of spring gales and DSs around northern China and possible adjustment functions of the East Atlantic (EA) teleconnection pattern have been investigated. It was found that the major systems controlling spring gales include the North Polar vortex (NPV), mid–high‐latitude blocking highs (BHs), air pressure status of the Tibetan Plateau (TP) over the Eurasian continent, India–Burma trough (IBT) and western Pacific subtropical high (WPSH). Under synthetic atmospheric circulation conditions of an enlarged NPV, lower air pressure over the TP, a strong IBT, and a southeastward‐retreated WPSH, spring gales increase, and the frequency of DS occurrence is increased, and vice versa. Additionally, spring gales are also negatively affected by BHs. The most important is the Baikal BH, which has influence not only in previous seasons but also in the contemporary spring. Furthermore, the NPV and IBT have close negative correlation with the EA pattern, whereas the TP and WPSH have positive correlation with the EA pattern both in previous seasons and in the contemporary spring. A high‐pitched EA pattern results in a strong western current north of Lake Baikal, which may prohibit the expansion of the NPV in the sector of northern China. A shrunk NPV means infrequent cold air attacks and decreased gales and DSs. [ABSTRACT FROM AUTHOR]

During the boreal spring (March–May), the precipitation that occurs from March over the southeastern Tibetan Plateau (TP) can account for 20–40% of the total annual amount. The origin of this phenomenon has not been clearly understood from a climatological perspective. In this study, the role of topographical and thermal forcing on the precipitation over the southeastern TP in early spring (March) was investigated through sensitivity numerical simulations based on general circulation model. The simulated results show the favorable circulation and static stability to early spring precipitation over the southeastern TP when the model is simultaneously forced by realistic topography, zonal symmetric radiative equilibrium temperature, and diabatic heating over the TP and its surrounding areas. The quasi-stationary wave pattern over the Eurasian continent forced by realistic and TP topographical forcing leads to prolonged low pressure and intensified zonal winds over the southeastern TP due to quasi-steady wave activities. Thermal forcing experiments reveals that sensible heating over the southeastern TP not only strengthens the cyclonic circulation, ascending motion and statically unstable over the southeastern TP through thermal adaptation and the Sverdrup balance, but also triggers an anticyclone at upper tropospheric level extending from north of the Bay of Bengal to the eastern TP, which further favors precipitation over the southeastern TP. This work will provide useful background information for spring climate prediction over the TP. [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) is a complex phenomenon, influenced by both tropical and mid-latitude dynamics and by the presence of the Tibetan Plateau. The EASM front (EASMF) separates tropical and extratropical air masses as the monsoon marches northwards. Although the different factors behind EASM progression are illustrated in a number of studies, their interactions, in particular between tropical and extratropical air masses, still need to be clarified. In this study we apply Eulerian and Lagrangian methods to the ERA5 reanalysis dataset to provide a comprehensive study of the seasonal progression of and interannual variability in the EASM, and we highlight the dynamics of the air masses converging at its front. A frontal detection algorithm is used to perform a front-centred analysis of EASM progression. The analysis highlights the primary role of the subtropical westerly jet (STWJ) and of the western North Pacific subtropical high (WNPSH) in controlling the strength and the poleward progression of the EASMF, in particular during Mei Yu, the primary stage of EASM progression. These forcings act to steer the southerly advection of low-level moist tropical air, modulated by the seasonal cycle of the Asian monsoon. The Mei Yu stage is distinguished by an especially clear interaction between tropical and extratropical air masses converging at the EASMF. The analysis of composites based on the latitude of the EASMF during Mei Yu reveals the influence exerted by the STWJ on the cool extratropical flow impacting on the northern side of the EASMF, whose progression is also dependent on the location of the WNPSH. In turn, this affects the extent of the warm moist advection on its southern side and the distribution and intensity of resultant rainfall over China. This study shows the validity of an analysis of EASM progression focused on its front and on the related low- and mid-level airstreams, at least in the Mei Yu stage. The framework highlighted shows how the regional flow over East Asia drives the low-level airstreams that converge at the EASMF, thus controlling the shape of EASM progression. This framework provides a basis for studies of climate variability and extreme events and for model evaluation. [ABSTRACT FROM AUTHOR]

Abstract: A Mt. Geladaindong (GL) ice core was recovered from the central Tibetan Plateau (TP) spanning the period 1940–2005 AD. High-resolution major ion (Na+, K+, Ca2+, Mg2+, Cl−, SO4 2−, NO3 −) time-series are used to investigate variations in atmospheric dust loading through time. The crustal source ions vary seasonally with peaks in dust concentrations occurring during the winter and spring which are consistent with atmospheric dust observations at local meteorological stations. However, both similarities and dissimilarities are displayed between the decadal variation of atmospheric dust in the GL core and dust observation records from meteorological stations, which can be attributed to local environmental effects at the stations. This paper compares the 1980s and 1970s as case periods for low and high atmospheric dust loading, respectively, two periods reflecting shifts in spring atmospheric circulation (a weakening of zonal and meridional winds) from the 1970s (a period of enhanced dust aerosol transportation to central TP) to the 1980s (a period of diminished dust aerosol transportation to central TP), especially a significant decrease of meridional wind speeds in the 1980s. GL ice core dust proxies (Ca2+ and K+) are correlated with Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) data in spring over the TP and in the northwestern China (especially for K+). Thus variability of crustal ions in central TP ice core provides a proxy for reconstructing a history of atmospheric dust loading not only on the TP, but also in northwestern China. [Copyright &y& Elsevier]

Understanding the Tibetan Plateau (TP) thermal processes is of utmost significance in changing climate. This study investigates the effect of soil moisture in changing the TP thermal profile and consequently summer precipitation in South Asia (SA). Soil moisture from Special Sensor Microwave Imager (SSM/I) developed from the F-08, F-11, and F-13 fundamental climate data record and atmospheric reanalysis from ERA-Interim, MERRA-2, and NCEP/CFSR during 1988–2008 are used. A generalized linear method that assesses the reciprocal forcing between two connected fields, named the coupled manifold technique (CMT), is applied to TP soil moisture and SA summer precipitation. It is revealed that interannual variations of SA precipitation are significantly (confidence level = 99%) impacted by TP soil moisture and the explained ratio of variance in SA is 0.3–0.4. Composite analysis indicates that SA summer precipitation has positive anomalies in response to dry TP soil moisture in the previous spring and vice versa. For understanding the possible mechanism, thermal processes, relative humidity, wind components, and moisture flux anomalies were calculated for dry and wet TP soil moisture and summer precipitation. The results suggested that TP soil moisture is likely to regulate near-surface energy balance and diabatic heating profile over TP. As a result, the surrounding lower-level westerlies (easterlies) (at 850 hPa) converge (diverge), associated with divergence (convergence) at the upper troposphere (200 hPa). The westerlies (easterlies) are usually moisture-rich (moisture-deficient) and thus cause more (less) precipitation in western (eastern) SA. It is thus suggested that the spring soil moisture may affect the thermal profile of TP, affecting the summer precipitation in SA as a consequence. [ABSTRACT FROM AUTHOR]

Recent studies have demonstrated that mechanical effects have a greater contribution to the East Asian summer monsoon (EASM) than thermodynamical effects. However, a theoretical basis for the underlying dynamical mechanism has not been elucidated. The present study shows that topographically forced barotropic Rossby wave theory well explains the seasonal evolution of the monsoonal precipitation and its amplitude and peak location. The subtropical zonal wind impinging on the Tibetan Plateau is a key factor, and the resulting downstream cyclonic and anticyclonic circulation anomalies form a peak zonal geopotential height gradient in between, leading to the development of the meridional wind and the accompanying moisture transport to the EASM region. As the season approaches the summer monsoon period, the peak geopotential height gradient—thus the monsoonal rainband—shifts to the west from the western North Pacific to East Asia. The findings in this study can be applied to subtropical monsoons worldwide. Plain Language Summary: Recent observational and modeling studies have demonstrated that the Northern Hemispheric sole subtropical‐midlatitude monsoon occurring downstream of the Tibetan Plateau is controlled by both thermodynamical and dynamical factors. The former involves the land‐sea temperature contrast and Tibetan Plateau‐related elevated heating, whereas the latter includes the dynamical effects due to the squeezing of the air crossing the Tibetan Plateau, which provides a greater contribution to the East Asian summer monsoon (EASM) than the former effect. However, a theoretical basis for the underlying physical mechanism responsible for the EASM precipitation has not been elucidated. The topographically forced barotropic stationary Rossby wave theory, which corresponds to traditional midlatitude atmospheric wave dynamics with topographical forcing, well explains the seasonal evolution of the downstream East Asian precipitation. The subtropical westerly wind impinging on the Tibetan Plateau and the vertical squeezing of the air result in the downstream cyclonic and anticyclonic circulation flow fields, which leads to the development of the southerly wind in between these anomalies and produces moisture transport to the EASM region. Key Points: Topographically forced stationary Rossby wave theory well explains the seasonal evolution of the downstream East Asian precipitationAs the season approaches the summer monsoon period, the monsoonal rainband shifts to the west from the western North Pacific to East AsiaThe subtropical zonal wind impinging on the Tibetan Plateau is a primary factor for the enhancement of meridional wind in the EASM region [ABSTRACT FROM AUTHOR]

By using multisourced data and two sets of sensitivity runs from the coupled general circulation model CESM1.2.0, we investigated the effects of the spring [March, April, and May (MAM)] surface sensible heating over the Tibetan Plateau (SHTP) on the interannual variability of the North Pacific Ocean sea surface temperature (SST) and mixed layer. The results indicated that an above-normal MAM SHTP can generate a Rossby wave downstream and form an anomalous equivalent barotropic anticyclone over the North Pacific, inducing anticyclonic wind stress anomalies. As a result of Ekman transport and Ekman pumping, sea currents converge near 40°N, accompanied by weak downwelling motion. The mixed layer heat budget diagnosis indicates that the net heat fluxes, together with meridional advection anomalies, contributed significantly to changes in the mixed layer temperature (MLT). As a result, the SST anomalies (SSTAs) and MLT anomalies both present a horseshoelike pattern. In addition, the significant warm SSTAs show a maximum in the late spring, but the significant warm MLT anomalies centered under the sea surface (25-m depth) could be sustained until summer, acting like a signal storage for the anomalous spring SHTP. Moreover, the midlatitude ocean–atmosphere interaction provides a positive feedback on the development of the anomalous anticyclone over the North Pacific, since the SSTA pattern could strengthen the oceanic front and induce more active transient eddy activities. The eddy vorticity forcing that is dominant among the total atmospheric forcings tends to produce an equivalent barotropic atmospheric high pressure, which in turn intensifies the initial anomalous anticyclone. [ABSTRACT FROM AUTHOR]

The changing characteristics of lake ice phenology over the Tibetan Plateau (TP) are investigated using historical satellite retrieved datasets during 2002–15 in this study. The results indicate that the freezing process mainly starts in December, and the ice melting process generally occurs in April for most lakes. However, the changes in lake ice phenology have varied depending on the location in recent years, with delayed break-up dates and prolonged ice durations in the southern TP, but no consistent changes have occurred in the lakes in the northern TP. Further analysis presents a close connection between the variation in the lake ice break-up date/ice duration over the southern TP and the winter North Atlantic Oscillation (NAO). The positive NAO generally excites an anomalous wave activity that propagates southward from the North Atlantic to North Africa and, in turn, strengthens the African–Asian jet stream at its entrance. Because of the blocking effect of the TP, the enhanced westerly jet can be divided into two branches and the south branch flow can deepen the India–Myanmar trough, which further strengthens the anomalous cyclonic circulation and water vapor transport. Therefore, the increased water vapor transport from the northern Indian Ocean to the southern region of the TP can increase the snowfall over this region. The increased snow cover over the lake acts as an insulating layer and lowers the lake surface temperature in the following spring by means of snow–ice feedback activity, resulting in a delayed ice break-up date and the increased ice duration of the lakes over the southern TP in recent years. [ABSTRACT FROM AUTHOR]

The modulation of the intensity of nascent Tibetan Plateau vortices (ITPV) by atmospheric quasi-biweekly oscillation (QBWO) is investigated based on final operational global analysis data from the National Centers for Environmental Prediction. The spatial and temporal distributions of the ITPV show distinct features of 10-20-day QBWO. The average ITPV is much higher in the positive phases than in the negative phases, and the number of strong TPVs is much larger in the former, with a peak that appears in phase 3. In addition, the maximum centers of the ITPV stretch eastward in the positive phases, indicating periodic variations in the locations where strong TPVs are generated. The large-scale circulations and related thermodynamic fields are discussed to investigate the mechanism by which the 10-20-day QBWO modulates the ITPV. The atmospheric circulations and heating fields of the 10-20-day QBWO have a major impact on the ITPV. In the positive QBWO phases, the anomalous convergence at 500 hPa and divergence at 200 hPa are conducive to ascending motion. In addition, the convergence centers of the water vapor and the atmospheric unstable stratification are found in the positive QBWO phases and move eastward. Correspondingly, condensational latent heat is released and shifts eastward with the heating centers located at 400 hPa, which favors a higher ITPV by depressing the isobaric surface at 500 hPa. All of the dynamic and thermodynamic conditions in the positive QBWO phases are conducive to the generation of stronger TPVs and their eastward expansion. [ABSTRACT FROM AUTHOR]

This study demonstrates the two different Rossby wave train (RWT) patterns related to the developing/decaying upper atmospheric heat source over the Tibetan Plateau (TPUHS) in boreal summer. The results show that the summer TPUHS is dominated by quasi-biweekly variability, particularly from late July to mid-August when the subtropical jet steadily stays to the north of the TP. During the developing period of TPUHS events, the intensifying TPUHS corresponds to an anomalous upper-tropospheric high over the TP, which acts as the main source of a RWT that extends northeastward, via North China, the central Pacific and Alaska, to the northeastern Pacific region. This RWT breaks up while the anomalous high is temporarily replaced by an anomalous low due to the further deepened convective heating around the TPUHS peak. However, this anomalous low, though existing for only three to four days due to the counteracting dynamical effects of the persisting upper/lower divergence/convergence over the TP, acts as a new wave source to connect to an anomalous dynamical high over the Baikal region. Whilst the anomalous low is diminishing rapidly, this Baikal high becomes the main source of a new RWT, which develops eastward over the North Pacific region till around eight days after the TPUHS peak. Nevertheless, the anomaly centers along this decaying-TPUHS-related RWT mostly appear much weaker than those along the previous RWT. Therefore, their impacts on circulation and weather differ considerably from the developing to the decaying period of TPUHS events. [ABSTRACT FROM AUTHOR]

Based on high-quality data from eddy covariance measurements at the Qomolangma Monitoring and Research Station for Atmosphere and Environment (QOMS) and the Southeast Tibet Monitoring and Research Station for Environment (SETS), near-ground free convection conditions (FCCs) and their characteristics are investigated. At QOMS, strong thermal effects accompanied by lower wind speeds can easily trigger the occurrence of FCCs. The change of circulation from prevailing katabatic glacier winds to prevailing upslope winds and the oscillation of upslope winds due to cloud cover are the two main causes of decreases in wind speed at QOMS. The analysis of results from SETS shows that the most important trigger mechanism of FCCs is strong solar heating. Turbulence structural analysis using wavelet transform indicates that lower-frequency turbulence near the ground emerges from the detected FCCs both at QOMS and at SETS. It should be noted that the heterogeneous underlying surface at SETS creates large-scale turbulence during periods without the occurrence of FCCs. Regarding datasets of all seasons, the distribution of FCCs presents different characteristics during monsoonal and non-monsoonal periods. [ABSTRACT FROM AUTHOR]

Variations of surface air temperature (SAT) are key in affecting the hydrological cycle, ecosystems and agriculture in western China in summer. This study assesses the seasonal forecast skill and reliability of SAT in western China, using the GloSea5 operational forecast system from the UK Met Office. Useful predictions are demonstrated, with considerable skill over most regions of western China. The temporal correlation coefficients of SAT between model predictions and observations are larger than 0.6, in both northwestern China and the Tibetan Plateau. There are two important sources of skill for these predictions in western China: interannual variation of SST in the western Pacific and the SST trend in the tropical Pacific. The tropical SST change in the recent two decades, with a warming in the western Pacific and cooling in the eastern Pacific, which is reproduced well by the forecast system, provides a large contribution to the skill of SAT in northwestern China. Additionally, the interannual variation of SST in the western Pacific gives rise to the reliable prediction of SAT around the Tibetan Plateau. It modulates convection around the Maritime Continent and further modulates the variation of SAT on the Tibetan Plateau via the surrounding circulation. This process is evident irrespective of detrending both in observations and the model predictions, and acts as a source of skill in predictions for the Tibetan Plateau. The predictability and reliability demonstrated in this study is potentially useful for climate services providing early warning of extreme climate events and could imply useful economic benefits. [ABSTRACT FROM AUTHOR]

The thermal forcing of the Tibetan Plateau (TP) during boreal spring, which involves surface sensible heating, latent heating released by convection and radiation flux heat, is critical for the seasonal and subseasonal variation of the East Asian summer monsoon. Distinct from the situation in March and April when the TP thermal forcing is modulated by the sea surface temperature anomaly (SSTA) in the North Atlantic, the present study shows that it is altered mainly by the SSTA in the Indian Ocean Basin Mode (IOBM) in May, according to in-situ observations over the TP and MERRA reanalysis data. In the positive phase of the IOBM, a local Hadley circulation is enhanced, with its ascending branch over the southwestern Indian Ocean and a descending one over the southeastern TP, leading to suppressed precipitation and weaker latent heat over the eastern TP. Meanwhile, stronger westerly flow and surface sensible heating emerges over much of the TP, along with slight variations in local net radiation flux due to cancellation between its components. The opposite trends occur in the negative phase of the IOBM. Moreover, the main associated physical processes can be validated by a series of sensitivity experiments based on an atmospheric general circulation model, FAMIL. Therefore, rather than influenced by the remote SSTAs of the northern Atlantic in the early spring, the thermal forcing of the TP is altered by the Indian Ocean SSTA in the late spring on an interannual timescale. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) has long been regarded as a key driver for the formation and variations of the Indian summer monsoon (ISM). Recent studies, however, have indicated that the ISM also exerts a considerable impact on rainfall variations in the TP, suggesting that the ISM and the TP should be considered as an interactive system. From this perspective, the covariability of the July-August mean rainfall across the Indian subcontinent (IS) and the TP is investigated. It is found that the interannual variation of IS and TP rainfall exhibits a dipole pattern in which rainfall in the central and northern IS tends to be out of phase with that in the southeastern TP. This dipole pattern is associated with significant anomalies in rainfall, atmospheric circulation, and water vapor transport over the Asian continent and nearby oceans. Rainfall anomalies and the associated latent heating in the central and northern IS tend to induce changes in regional circulation that suppress rainfall in the southeastern TP and vice versa. Furthermore, the sea surface temperature anomalies in the tropical southeastern Indian Ocean can trigger the dipole rainfall pattern by suppressing convection over the central IS and the northern Bay of Bengal, which further induces anomalous anticyclonic circulation to the south of TP that favors more rainfall in the southeastern TP by transporting more water vapor to the region. The dipole pattern is also linked to the Silk Road wave train via its link to rainfall over the northwestern IS. [ABSTRACT FROM AUTHOR]

Although precipitation extremes exert a major influence on populations and the environment, trend analysis for the entire Qinghai-Tibetan plateau (QTP) has not previously been undertaken. In this study, meteorological data from 83 weather stations was used to analyze the temporal trends and spatial distribution of 10 extreme precipitation indices over the QTP during 1975-2014. The Mann Kendall test and Sen's slope estimator were used to determine significances and magnitudes of station trends. Spatially, stations recording increasing trends were mainly distributed in the southwestern, central and northern regions. Stations with decreasing trends were centered on the eastern and southeastern areas. Temporally, all indices had an increasing trend except for consecutive dry days (CDD) and consecutive wet days (CWD) during the study period. The contribution of extreme precipitation to total precipitation showed a significant increasing trend. These findings may be due to the complex interaction between the large-scale circulation and topography. In general, the changes of extreme precipitation indicated an enhanced tendency, with the frequency, intensity and amount of heavy precipitation increasing over time. Furthermore, altitude dependency of extreme precipitation does not exist in QTP, with topography effects on changes in precipitation extremes being more obvious in the higher elevation, flat, and hill stations. [ABSTRACT FROM AUTHOR]

The variation of precipitation plays an important role in the eco-hydrological processes and water resources regimes on the Tibetan Plateau (TP). Based on the monthly mean precipitation data of 65 meteorological stations over the TP and surrounding areas from 1961 to 2015, variations, trends and temporal--spatial distribution of precipitation have been studied; furthermore, the possible reasons were also discussed preliminarily. The results show that the annual mean precipitation on the TP was 465.5 mm during 1961-2015. The precipitation in summer (June-August (JJA)) accounted for 60.1% of the whole year's precipitation, the precipitation in summer half-year (May-October) accounted for 91.0%, while the precipitation in winter half-year (November-April) only accounted for 9.0% of the whole year's precipitation. During 1961--2015, the annual precipitation trend was 3.8 mm/10a and the seasonal precipitation trends were 3.0 mm/10a, 0.0 mm/10a, --0.1 mm/10a and 0.4 mm/10a in spring, summer, autumn and winter on the TP, respectively. The precipitation has decreased from the southeastern to northwestern TP; the trend of precipitation has decreased with the increase of altitude, but the correlation was not significant. The rising of air temperature and land cover changes may cause the precipitation by changing the hydrological cycle and energy budget. Furthermore, different patterns of atmospheric circulation can also influence precipitation variation in different regions. [ABSTRACT FROM AUTHOR]

Based on a comprehensive collection of hail observations and the NCEP-NCAR reanalyses from 1960 to 2012, the long-term trends of hail day frequency in mainland China and the associated changes in atmospheric circulation patterns were analyzed. There was no detectable trend in hail frequency from 1960 to the early 1980s, but a significant decreasing trend was apparent in later periods throughout most of China and in particular over the Tibetan Plateau from the early 1980s and over northern and northwestern China from the early 1990s. Hail frequency in southern China did not decrease as significantly as in other regions over the last couple of decades. An objective classification method, the obliquely rotated T-mode principal component technique, was used to investigate atmospheric circulation patterns. It was found that 51.85% of the hail days occurred during two major circulation types, both of which were associated with cold frontal systems in northern China. More specifically, the synoptic trough in East Asia, signified by the meridional circulation at 850 hPa, became considerably weaker after 1990. This change in the synoptic pattern is consistent with a weakening trend in the East Asian summer monsoon, the primary dynamic forcing of moisture transport that contributes to the generation of severe convection in northern China. The long-term variability of hail day frequency over the Tibetan Plateau was more strongly correlated with the change in mean freezing-level height (FLH) than the strength of the East Asian monsoon. [ABSTRACT FROM AUTHOR]

Unrealistic topographic effects are generally incorporated in global climate simulations and may contribute significantly to model biases in the Asian monsoon region. By artificially implementing the Arakan Yoma and Annamese Cordillera-two south-north-oriented high mountain ranges on the coasts of the Indochina Peninsula-in a 1° global climate model, it is demonstrated that the proper representation of mesoscale topography over the Indochina Peninsula is crucial for realistically simulating the seasonality of the East Asian-western North Pacific (EAWNP) summer monsoon. Presence of the Arakan Yoma and Annamese Cordillera helps simulate the vertical coupling of atmospheric circulation over the mountain regions. In late May, the existence of the Arakan Yoma enhances the vertically deep southwesterly flow originating from the trough over the Bay of Bengal. The ascending southwesterly flow converges with the midlatitude jet stream downstream in the southeast of the Tibetan Plateau and transports moisture across the Indochina Peninsula to East Asia. The existence of the Annamese Cordillera helps the northward lower-tropospheric moisture transport over the South China Sea into the mei-yu-baiu system, and the leeside troughing effect of the mountains likely contributes to the enhancement of the subtropical high to the east. Moreover, the eastward propagation of wave energy from central Asia to the EAWNP suggests a dynamical connection between the midlatitude westerly perturbation and mei-yu-baiu. Including the Annamese Cordillera also strengthens a Pacific-Japan (PJ) pattern-like perturbation in late July by enhancing the cyclonic circulation (i.e., monsoon trough) in the lower-tropospheric western North Pacific. This suggests the contribution of the mountain effects to the intrinsic variability of the summer monsoon in the EAWNP. [ABSTRACT FROM AUTHOR]

Palaeoelevation reconstructions of mountain belts have become a focus of modern science since surface elevation provides crucial information for understanding both geodynamic mechanisms of Earth's interior and the influence of mountain growth on climate. Stable oxygen isotopes palaeoaltimetry is one of the most popular techniques nowadays, and relies on the difference between δ18O of palaeoprecipitation reconstructed using the natural archives, and modern measured values for the point of interest. Our goal is to understand where and how complex climatic changes linked with the growth of mountains affect δ18O in precipitation. For this purpose, we develop a theoretical expression for the precipitation composition based on the Rayleigh distillation and the isotope-equipped atmospheric general circulation model LMDZ-iso outputs. Experiments with reduced height over the Tibetan Plateau and the Himalayas have been designed. Our results show that the isotopic composition of precipitation is very sensitive to climate changes related to the growth of the Himalayas and Tibetan Plateau. Specifically our simulations suggest that only 40% of sampled sites for palaeoaltimetry depict a full topographic signal, and that uplift-related changes in relative humidity (northern region) and precipitation amount (southern region) could explain absolute deviations of up to 2.5%of the isotopic signal, thereby creating biases in palaeoelevation reconstructions. [ABSTRACT FROM AUTHOR]

Rapid increases in pollutant emissions in conjunction with stagnant meteorological conditions result in haze pollution in China. Recent frequent haze in China has attracted worldwide attention. Here we show a relationship between the haze events and Tibetan Plateau (TP)'s environment and climate changes. Based on observational data taken over recent decades, we identify central-eastern China (CEC) as a climatological large-scale "susceptible region" of frequent haze, which is harbored by the TP with its impact on midlatitude westerly winds. The observational and modeling studies demonstrate that the interannual variations in the thermal forcing of TP are positively correlated with the incidences of wintertime haze over CEC. Further analysis indicates that the climate warming of the TP induced changes in atmospheric circulation, driving frequent haze events in CEC. The frequent haze occurrences in CEC are consistent with decreasing winter monsoon winds, intensifying downward air flows and increasing atmospheric stability in the lower troposphere over the CEC in association with upstream plateau's thermal anomalies. Therefore, variations of haze in China are related to mechanical and thermal forcing by the TP. Our results also suggest that implications of the large TP topography for environment and climate changes should be taken into account for air pollution mitigation policies in China. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau (TP) is representative of typical clean atmospheric conditions. Aerosol optical depth (AOD) retrieved by the Multi-angle Imaging SpectroRadiometer (MISR) is higher over Qaidam Basin than the rest of the TP throughout the year. Different monthly variation patterns of AOD are observed over the southern and northern TP, whereby the aerosol load is usually higher in the northern TP than in the southern part. The aerosol load over the northern part increases from April to June, peaking in May. The maximum concentration of aerosols over the southern TP occurs in July. Aerosols appear to be more easily transported to the main body of the TP across the northern edge rather than the southern edge. This is maybe partly because the altitude is lower at the northern edge than that of the Himalayas located along the southern edge of the TP. Three-dimensional distributions of dust, polluted dust, polluted continental aerosol and smoke are also investigated, based on Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) data. Dust is found to be the most prominent aerosol type on the TP, and other types of aerosols affect the atmospheric environment slightly. A dividing line of higher dust occurrence in the northern TP and lower dust occurrence in the southern TP can be observed clearly at an altitude of 6-8 km above sea level, especially in spring and summer. This demarcation appears around 33- 35 N in the middle of the plateau, and it is possibly associated with the high-altitude terrain in the same geographic location Comparisons of CALIPSO and MISR data show that the vertical dust occurrences are consistent with the spatial patterns of AOD. The different seasonal variation patterns between the northern and southern TP are primarily driven by atmospheric circulation, and are also related to the emission characteristics over the surrounding regions. [ABSTRACT FROM AUTHOR]

The southwesterly low-level jet (LLJ) located to the east of the Tibetan Plateau in southern China plays an important role in summertime convective initiation over north China. This study adopts a novel perspective and uses hindcast experiments in order to investigate the role of moisture in LLJ and associated heavy rainfall formation, employing a global atmospheric general circulation model (AGCM). In the sensitivity experiments, an increase of humidity in the inflow region leads to a weaker LLJ but stronger diurnal wind oscillations. The weaker LLJ is due to a decreased lower-tropospheric east-west pressure gradient resulting from a low pressure anomaly over southeastern China induced by deep convection and related condensational heating. On the other hand, the stronger diurnal variation of the LLJ originates from stronger day-and-night thermal differences over the sloping terrain, which is related to drier conditions over the mountain range. Moreover, the increased humidity and decreased LLJ counteract one another to impact precipitation in the outflow region. The change of precipitation is mainly determined by the altered moisture flux divergence. If the increase in humidity dominates, then the moisture flux convergence is enhanced and favors more precipitation over north China. Otherwise, if the decreased LLJ dominates, then the moisture flux convergence is reduced, which constrains precipitation. It is highlighted that the moist diabatic and dynamic processes are intimately coupled, and that a correct simulation of moisture flux convergence is vital for AGCMs to reproduce the LLJ-related precipitation, particularly the nocturnal precipitation peak, which is a deficiency in many current models. [ABSTRACT FROM AUTHOR]

Spring persistent rainfall (SPR) over southern China has great impact on its society and economics. A remarkable feature of the SPR is high frequency. However, SPR frequency obviously decreases over the period of 1997-2011. In this study, the possible causes have been investigated from the perspective of the individual and concurrent effects of the East Asian subtropical jet (EASJ) and East Asian polar front jet (EAPJ). A close relationship is detected between SPR frequency and EASJ intensity (but not EAPJ intensity). Associated with strong EASJ, abundant water vapor is transported to southern China by the southwesterly flow, which may trigger the SPR. Additionally, frequencies of both strong EASJ and weak EAPJ events are positively correlated with SPR frequency. Further investigation of the concurrent effect indicates a significant positive correlation between the frequencies of SPR and the strong EASJ-weak EAPJ configuration. Associated with this configuration, southwesterly flow strengthens in the lower troposphere, while northerly wind weakens in the upper troposphere. This provides a dynamic and moist condition, as enhanced ascending motion and intensified convergence of abundant water vapor over southern China, which favors the SPR. All analyses suggest that the EASJ may play a dominant role in the SPR occurrence and that the EAPJ may play a modulation role. Finally, a possible mechanism maintaining the strong EASJ-weak EAPJ configuration is proposed. Significant cooling over the northeastern Tibetan Plateau may induce a cyclone anomaly in the upper troposphere, which could result in an accelerating EASJ and a decelerating EAPJ. [ABSTRACT FROM AUTHOR]

The Tarim basin (TB) in northwestern China is one of the most arid regions in the middle latitudes, where water is scarce year-round. This study investigates the variations of summer precipitation in the TB and their association with water vapor fluxes and atmospheric circulation. The results suggest that the variations of summer precipitation in the TB are dominated by the water vapor fluxes from the south and east, although the long-term mean water vapor mostly comes from the west. The anomalous water vapor fluxes are closely associated with the meridional teleconnection pattern around 50°-80°E and the zonal teleconnection pattern along the Asian westerly jet in summer. The meridional teleconnection connects central Asia and the tropical Indian Ocean; the zonal teleconnection resembles the 'Silk Road pattern.' The two teleconnections lead to negative height anomalies in central Asia and positive height anomalies in the Arabian Sea and India and in northern central China. The anomalous pressure gradient force, caused by these height anomalies, leads to anomalous ascending motion in the TB and brings low-level moisture along the eastern periphery of the Tibetan Plateau and water vapor from the Arabian Sea passing over the Tibetan Plateau to influence precipitation development in the study region. [ABSTRACT FROM AUTHOR]