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This study investigates the influences of initial soil moisture over the Tibetan Plateau (TP) on precipitation simulation, and the respective effects of boundary layer vertical diffusion for heat (Kh) and vapor (Kq). Results indicate that the responses of boundary layer vertical diffusion to soil moisture are obvious mainly in the daytime. Wetter land surface corresponds to weaker vertical diffusion, which could strengthen thermal forcing and dynamic lifting in the lower atmosphere, and encourage water vapor saturation near the top of boundary layer to prevent the environmental dry air entrainment/invasion, which would be beneficial to more convection and precipitation. Wetter land surface over the TP could enhance the contrast between the cold in the northwestern TP and the warm in the southeastern TP, which would be conducive to the southeastward propagation of precipitation. The simulation of heat and moisture in the boundary layer could be improved by perturbing the relative intensity of Kh and Kq. From the perspective of heat and moisture, Kh affects atmospheric stability, while Kq affects moisture and its vertical transport in the boundary layer. The Kh and Kq have competitive effects on precipitation intensity by influencing the relative importance of moisture and atmospheric stability conditions in the boundary layer. Adjusting the relative intensity of Kh and Kq would deactivate the competitive effects. Stronger Kh but weaker Kq would alleviate the overestimated precipitation by inhibiting vertical transport of moisture to the top of boundary layer and attenuating convective instability in the boundary layer. Significance Statement: The purpose of this study is to better understand the effects of boundary layer vertical heat and moisture diffusion in the response of precipitation to soil moisture. This is important because boundary layer vertical diffusion is a crucial factor influencing the relation between soil moisture and precipitation. Our results reveal the competitive effects of boundary layer vertical diffusion for heat and vapor on the simulation of precipitation. These results point a potential way toward better understanding the response of precipitation to soil moisture. [ABSTRACT FROM AUTHOR]

Snow cover over the Tibetan Plateau (TP)–the Third Pole of the earth has been recognized as a reliable signal of summer floods or droughts in East Asia (EA). The distribution of snow cover can be influenced by vegetation, however, the impacts of changes in cover of non-growing season vegetation–withered grass stem over TP on the climatic effects of snow cover remains poorly understood. Here, we showed that the relationship between TP winter snow cover (TPWSC) and EA summer precipitation (EASP) strengthened starting in the early 1990s but weakened after the early 2000s. The weakening of the TPWSC–EASP relationship was linked to the effects of vegetation cover increment (VCI) on winter and spring snow cover over the TP. A possible mechanism behind this linkage is that VCI leads to a shortened persistence of TPWSC anomalies and weakened surface diabatic heating anomalies in spring. Consequently, the influences of TP thermal forcing on the downstream atmospheric circulation in summer were altered, resulting in a different pattern of EASP anomalies. These findings highlight the importance of snow—vegetation feedback and its potential to alter the effectiveness of snow cover in seasonal climate prediction. [ABSTRACT FROM AUTHOR]

This study investigated the north–south thermodynamic flux exchanges in the westerly and easterly forced by the change of the location of the South Asia High (SAH) at intra-seasonal timescales in summer. The results show that there were differences in heat and momentum exchanges between the westerly and easterly and the location change of the SAH at both 100 and 200 hPa. The circulation pattern and the strength of the westerly around the SAH eddy changes relate to thermal and dynamic flux exchanges in the SAH eddy location. When the SAH is located over the Tibetan Plateau (the eastern pattern, EP), poleward eddy heat and momentum fluxes are on the western side, and equatorward eddy heat and momentum fluxes are on the eastern side of the SAH, thus are benefit to induce a westward movement. When the SAH reaches the Iranian Plateau (the western pattern, WP), the heat and momentum fluxes turn from poleward to equatorward, which is favourable for the SAH to move eastward. On average, the WP or EP of the SAH is maintained for approximately 4 days, then the westerly jet begins to decrease, and the SAH begins to move eastward and return to the Tibetan Plateau. The heat and momentum fluxes forced by the SAH also change the strength and location of the westerly and easterly jets on both sides of the SAH, which induces propagating downstream waves in the subtropical westerly jet. [ABSTRACT FROM AUTHOR]

Frozen soil distributed over alpine cold regions causes obvious changes in the soil hydrothermal regime and influences the water–heat exchanges between land and atmosphere. In this study, by comparing the effects of snow cover anomalies and frozen soil thawing anomalies on the soil hydrothermal regime, the impact of the frozen soil thawing anomalies in spring on precipitation in early summer over the Tibetan Plateau (TP) was investigated via diagnostic analysis and model simulations. The results show that a delay (advance) in the anomalies of frozen soil thawing in spring can induce distinct cold (warm) anomalies in the soil temperature in the eastern TP. These soil temperature cold (warm) anomalies further weaken (enhance) the surface diabatic heating over the mideastern TP; meanwhile, the anomalies in the western TP are inconspicuous. Compared to the albedo effect of snow cover anomalies, impacts of frozen soil thawing anomalies on soil hydrothermal regime and surface diabatic heating can persist longer from April to June. Corresponding to the anomalous delay (advance) of frozen soil thawing, the monsoon cell is weakened (enhanced) over the southern and northern TP, resulting in less (more) water vapor advection over the eastern TP and more (less) water vapor advection over the southwestern TP. This difference in water vapor advection induces a west–east reversed pattern of precipitation anomalies in June over the TP. The results have potential for improving our understanding of the interactions between the cryosphere and climate in cold regions. Significance Statement: Frozen soil and snow are widely distributed over alpine and high-latitude cold regions, and their feedbacks to climate have attracted much attention. The purpose of this study is to investigate the role of frozen soil in effects of snow cover anomalies on surface diabatic heating and its feedback to subsequent precipitation over the Tibetan Plateau. The results highlight that frozen soil modulates the effect of snow cover anomalies on the soil hydrothermal regime from April to June and interseasonal variations of frozen soil thawing anomaly zones result in a thermal contrast between the western and eastern Tibetan Plateau, which further lead to a reversed pattern of early summer precipitation anomalies over the Tibetan Plateau. These findings emphasize the role of frozen soil in land–atmosphere interactions. [ABSTRACT FROM AUTHOR]

Soil moisture can be an important preceding signal in seasonal precipitation prediction because of its persistence and influence on the energy and water balance between land and atmosphere. The thawing process of frozen ground on the Tibetan Plateau (TP) during spring makes it difficult to accurately simulate soil variables (e.g., soil moisture and temperature) due to defective parameterizations in numerical models during spring. In this study, we investigate the effectiveness of soil moisture correction using an indirect nudging scheme to simulate the coupling between spring soil moisture and the subsequent precipitation with an advanced research version of the weather research and forecasting (WRF) model. The results without assimilation show that extreme cold and dry land surface states during spring cause a large bias in the spatial pattern of summer precipitation over almost the entire TP. However, the experiments with indirect assimilation in spring show that the spatial pattern of summer precipitation improved significantly. This comparison emphasizes the importance of correcting the spring soil moisture during the freeze–thaw period to significantly adjust the heat and water vapour exchange between the land and atmosphere. Additionally, changes in the circulation of the subtropical–tropical jet, vertical ascent, and region‐related moisture recycling can support an active convection environment over the eastern TP, thereby increasing summer precipitation. Furthermore, the pattern shift in water vapour convergence in summer highlights the regional horizontal transportation of water vapour. The differences between experiments with and without deep‐soil temperature nudging illustrate the significance of soil temperature in soil moisture simulation in the freeze–thaw process. More so, the deep‐soil temperature nudging scheme requires in‐depth studies to correct its variation and quantify its degree of impact on soil moisture. [ABSTRACT FROM AUTHOR]

Tibetan Plateau (TP) snow cover undergoes significant temporal and spatial variations during the winter and spring months. This study investigates the relationship between the spatiotemporal distribution of winter-spring snow cover (SC) over the TP and summer precipitation in eastern China (EC) using the singular value decomposition (SVD) method. Four simulation experiments are designed to validate the results of SVD analysis. Both observations and simulations show that heavier snow cover in the southern TP leads to more rainfall in the Yangtze River basin and northeastern China, and less precipitation in southern China, whereas heavier snow cover in the northern TP results in enhanced rainfall in southeastern and northern China and weakened precipitation in the Yangtze River basin. The linkage is attributed to anomalous westerly winds in the upper troposphere at around 200 hPa and to changes of the southern branch of westerlies at 500 hPa on the south side of the TP, which are caused by lasting diabatic heat anomalies over the TP. The shifts in position of the westerly jet at the exit region and negative anomalies of geopotential height at 500 hPa further result in anomalous anticyclone over the East China Sea and the corresponding 850-hPa water vapor convergence and influence the anomalous summer precipitation belt in EC. [ABSTRACT FROM AUTHOR]

The characteristics of seasonal precipitation over the Tibetan Plateau (TP) were investigated using TRMM (Tropical Rainfall Measuring Mission) precipitation data (3B43). Sensitive regions of summer precipitation interannual variation anomalies were investigated using EOF (empirical orthogonal function) analysis. Furthermore, the profiles of cloud water content (CWC) and precipitable water in different regions and seasons were analyzed using TRMM-3A12 data observed by the TRMM Microwave Imager. Good agreement was found between hydrometeors and precipitation over the eastern and southeastern TP, where water vapor is adequate, while the water vapor amount is not significant over the western and northern TP. Further analysis showed meridional and zonal anomalies of CWC centers in the ascending branch of the Hadley and Walker Circulation, especially over the south and east of the TP. The interannual variation of hydrometeors over the past decade showed a decrease over the southeastern and northwestern TP, along with a corresponding increase over other regions. [ABSTRACT FROM AUTHOR]

Summary This study calculated the annual and inter-annual variations in the precipitation recycling ratio (PRR) on the Qinghai–Xizang Plateau (QXP); and by using water mass balance equation; we evaluated the estimated evaporation in the area. The results indicate that the estimated evaporation relate strongly to surface air temperature, relative humidity and wind speed. As temperatures on the QXP increase, the changes of PRR vary by regions within the plateau. Between 1979 and 2008, the PRR decreased in the western QXP, which is an arid area, but it increased in the other areas. The strongest increasing PRR trend is 3.1%/10 a in the northeastern QXP, but a decreasing trend, ranging downward to −2.5%/10 a, was observed in the western QXP. There is a significant seasonal change in precipitation recycling (PR) over QXP. The PR peak values occurred in July in all regions, and PR was very low (approaching 0.0) in winter half-year period. The monthly maximum PRR reached 0.62, which occurred in July over the southeastern QXP, where is a rich center of precipitation. These results imply that there is remarkable change of moisture resource of precipitation in last decades. On the QXP, large-scale moisture advances decrease with increased temperature, and the local moisture cycle is reinforced in wet regions. [ABSTRACT FROM AUTHOR]

In this article, the trends and variability of precipitation and precipitable water (PW) over the Qinghai-Xizang (Tibet) Plateau (QXP) (1970-2009) were analysed by using ERA-40 (The European Center for Medium-Range Weather Forecasts (ECMWF) 40 years Re-analysis) and NCEP (The National Centers for Environmental Prediction)/NCAR reanalyses data and the ground observed precipitation data from 60 sites. The results showed that the precipitation over the QXP had an overall increasing trend; however, a slight decreasing trend was observed over the southeast. This decreasing precipitation trend might be related to the South Asia monsoon degradation. Since 1970, a decreasing PW trend has occurred over the QXP in which the southeast is the most significant region. Because of the rising temperatures in the QXP, a remarkable PW conversion rate (PWCR) increase of 0.87% per decade has occurred over the past 40 years. Because of its steep terrain, the PWCR in the middle eastern region of the QXP increased faster than that of the other regions. The mean PWCR in the wet southern region of the QXP was higher than that of the dry northern region, which was higher in the winter than that in the summer. Although much precipitation occurred in the summer, in the wet regions, the PWCR was higher in the winter than in the summer. The PWCR peak in the wet and dry regions occurred during the precipitation-short and precipitation-sufficient seasons, respectively. Copyright © 2011 John Wiley & Sons, Ltd. [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]

Abstract: The sensible and latent heat fluxes during the transition season over the western Tibetan Plateau from the NCEP-1 (NCEP/NCAR Reanalysis 1), AR-II (NCEP-DOE Reanalysis 2) and ERA40 reanalysis datasets were compared and analyzed. The results show that the phase change in soil moisture has a significant effect on the sensible and latent heat fluxes over the western Tibetan Plateau (TP) due to the freezing–thawing processes during the transition from the dry to the wet period. The uncertainties in the sensible and latent heat fluxes over the western TP are quite high in the reanalysis data, and depend largely on the success of the soil moisture simulations in the models. Improving the hydrological process simulations in the land-surface models in seasonally frozen ground and in the active frozen soil layer may be an effective way of enhancing the reliability of the surface heat fluxes from the reanalysis data over the Tibetan Plateau. [Copyright &y& Elsevier]

A short‐lived (less than 2 days) inner Tibetan Plateau vortex (TPV) with heavy precipitation was simulated using the Weather Research and Forecasting model, and the sensitivity experiments with and without surface diabatic heating and atmospheric latent heating released by precipitation were conducted to investigate the roles of surface and atmospheric diabatic heating on the genesis and development of TPV. Results show that before the genesis of the TPV, there is an anomalous increase of surface heating flux; while a disturbance of potential vorticity (PV) at 500 hPa moves over this region, the PV is enhanced and induces the generation of TPV. The precipitation in turn reduces the surface heating flux. The release of condensation latent heating by precipitation during the development of TPV does not further contribute to its reinforcement. Instead, it is more likely a result of precipitation, tending to stabilize the atmosphere and conducive to the decay of TPV. The PV diagnoses further reveal that in the early phase, the strong diabatic heating in the lower levels associated with the increasing surface heating flux has a significantly positive contribution to the generation of the TPV. The precipitation results in the decrease of positive diabatic heating contribution at low levels. Inversely, the diabatic heating in the middle levels associated with the released latent heating of precipitation condensation tends to have the negative contribution to TPV, resulting in the decay of TPV. The study of this case can deepen our understanding on the mechanism of TPV and its precipitation. Key Points: The surface diabatic heating prior to the precipitation is crucial to the formation of TPVThe condensation latent heating caused by precipitation only seems to be a result of precipitation [ABSTRACT FROM AUTHOR]

• The increase in withered grass stems (WGS) area over the Tibetan Plateau reduces the winter snow depth and snow cover fraction by up to 6 mm and 3 %, respectively. • The increase in WGS area results in a reduction in surface albedo, causing an increase in net radiation absorption by up to 1.6 W/m2 and a rise in ground temperature by up to 0.1 °C. • Ground temperature rise caused by the increment of WGS area promotes snow decline, such negative impacts seem more obvious with heavier snow cover. Along with climate change, the coverage of short vegetation, such as alpine grass over the Tibetan Plateau (TP), has significantly increased in the past decades. However, the changes in non-growing season alpine grass—withered grass stems (WGS), as well as their impact on snow cover and surface energy budget, still remain unclear. In this study, we derived vegetation stem area index (L s) data by using GLASS's leaf area index (LAI) as a way to analyze the impacts of WGS on snow depth, snow cover fraction, surface temperature and surface albedo in winter (December-January-February) over the TP during the period 1982–2018, and numerical experiments were conducted by the Community Land Model version 5.0 (CLM5.0) to investigate physical mechanism behind impacts of WGS. The results reveal that an increment in WGS coverage significantly increases net radiation at the surface, as well as the net radiation arrived at the ground due to the enhancing downward longwave radiation to the ground from the WGS, raising the ground temperature by up to 0.1 °C in winter. On average, ground warming reduces snow depth (up to about 6 mm) and snow cover fraction (up to about 3 %). This negative impact of WGS on snow cover seems more obvious in areas with heavier snow cover. Overall, this study highlights the feedback of changes in non-growing season vegetation cover to climate change in cold regions. [ABSTRACT FROM AUTHOR]