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The Tibetan Plateau (TP), also called the Third Pole, is considered to be "the world water tower". The northwestern TP (NWTP), which has an average elevation higher than 4800 m, is an arid region where the summer precipitation is largely overestimated by the ERA5 global reanalysis product. We hypothesize that this wet bias is mainly caused by unrealistic lower-level winds that trigger strong convection over the region; it can be reduced by using a high-resolution regional climate model with a large domain that allows realistically representing interactions between the Westerlies and Asian summer monsoons. Here, downscaling using the Weather Research and Forecasting (WRF) model driven by ERA5 was conducted with a large domain (8°‒50° N, 65°‒125° E) at 9 km for the period 1979‒2019 (WRF9km). Precipitation values from WRF9km and ERA5 were evaluated against satellite observations; compared with ERA5, WRF9km captured the climatological summer precipitation over the NWTP with a much-reduced wet bias. The ERA5 overestimation is mainly caused by excessive convective precipitation, likely linked to strong vertical motions over the NWTP induced by an overestimated lower-level southerly wind. [ABSTRACT FROM AUTHOR]

South Asian monsoon crosses the Himalayan Mountains (HMs) and brings moisture for precipitations in the South Tibetan Plateau. A distinct dry‐belt was found in the north of the central HM region, where there are the highest and steepest mountains in the world. Through in situ and remote‐sensing observations and convection‐permitting numerical experiments, the current study demonstrates that the formation of the dry‐belt is mainly due to the depletion of water vapor when the monsoonal flow climbs the steep south slope of the HMs. The foehn phenomenon is notable over the north slope of the HMs, but the hot and dry downslope flow does not significantly reduce the amount of the precipitation; instead, it can delay the peak of the diurnal precipitation in the north side of the HMs. Plain Language Summary: The central Himalaya Mountains (HMs) possess the highest and steepest mountains. Recent in situ and remote‐sensing observations show a dry‐belt in the north side of the central HMs. Although it is plausible to speculate that the dry‐belt results from the foehn wind on the leeside of the HMs, this study shows that the formation of the dry‐belt is mainly caused by the drastic depletion of water vapor along the south slope of central HMs. The foehn wind mainly delays the diurnal peak of precipitation but hardly reduces the amount of precipitation. Key Points: A distinct dry‐belt was found in the north of the central Himalaya MountainsThe dry‐belt is mainly due to the depletion of water vapor over the south slope of the Himalaya MountainsThe foehn wind can postpone the diurnal cycle of the precipitation in the north side of the Himalaya Mountains [ABSTRACT FROM AUTHOR]

Solar radiation changes (dimming/brightening) have recently received growing attention within the research community, although there is currently no generally accepted explanation. This article aims to provide a new perspective for identifying the reasons behind solar dimming/brightening by using long‐term measurements of direct and diffuse solar radiation, unlike previous studies which have focused on global solar radiation. We postulate that extinction processes can be more readily revealed by direct and diffuse radiation measurements with the help of a modelling tool that treats the two components separately. An example is presented for Golmud and Lhasa in the northern and southern Tibetan Plateau (TP) respectively, over the period 1957–2013. The following is found: (a) ground‐based observed cloud cover alone hardly explains the observed solar dimming at the two sites; (b) both the cloud‐free direct radiation transmittivity (τdir) and diffuse radiation proportion (pdif) declined; (c) variations in pdif are overwhelmingly dominated by variations in aerosols, while those in τdir are related to variations in both aerosol and water vapour; (d) on top of the suggested reduced aerosol concentrations, decreased snow cover can partly explain declined diffuse radiation via lowered surface albedo; (e) the decline in τdir can be partly attributed to the wetting atmosphere via strengthened absorption; and (f) the impact of volcanic eruptions was also identified from such radiative parameters, lasting into the following summer and especially strong in the southern TP. Location, surrounding topography, and upward‐looking hemispherical view shed (generated by Solar Analyst with dark grey as view‐blocked) of the two sites (Golmud and Lhasa). [ABSTRACT FROM AUTHOR]

The southern Tibetan Plateau (STP) is the region in which water vapor passes from South Asia into the Tibetan Plateau (TP). The accuracy of precipitable water vapor (PWV) modeling for this region depends strongly on the quality of the available estimates of water vapor advection and the parameterization of land evaporation models. While climate simulation is frequently improved by assimilating relevant satellite and reanalysis products, this requires an understanding of the accuracy of these products. In this study, PWV data from MODIS infrared and near-infrared measurements, AIRS Level-2 and Level-3, MERRA, ERA-Interim, JRA-55, and NCEP final reanalysis (NCEP-Final) are evaluated against ground-based GPS measurements at nine stations over the STP, which covers the summer monsoon season from 2007 to 2013. The MODIS infrared product is shown to underestimate water vapor levels by more than 20% (1.84 mm), while the MODIS near-infrared product overestimates them by over 40% (3.52 mm). The AIRS PWV product appears to be most useful for constructing high-resolution and high-quality PWV datasets over the TP; particularly the AIRS Level-2 product has a relatively low bias (0.48 mm) and RMSE (1.83 mm) and correlates strongly with the GPS measurements ( R = 0.90). The four reanalysis datasets exhibit similar performance in terms of their correlation coefficients ( R = 0.87-0.90), bias (0.72-1.49 mm), and RMSE (2.19-2.35 mm). The key finding is that all the reanalyses have positive biases along the PWV seasonal cycle, which is linked to the well-known wet bias over the TP of current climate models. [ABSTRACT FROM AUTHOR]

Multisphere interactions over the Tibetan Plateau directly impact its surrounding climate and environment at a variety of spatiotemporal scales. Remote sensing and modeling are expected to provide hydrometeorological data needed for these process studies, but in situ observations are required to support their calibration and validation. For this purpose, we have established a dense monitoring network on the central Tibetan Plateau to measure two state variables (soil moisture and temperature) at three spatial scales (1.0°, 0.3°, and 0.1°) and four soil depths (0-5, 10, 20, and 40 cm). The experimental area is characterized by low biomass, high soil moisture dynamic range, and typical freeze-thaw cycle. The network consists of 56 stations with their elevation varying over 4470-4950 m. As auxiliary parameters of this network, soil texture and soil organic carbon content are measured at each station to support further studies. To guarantee continuous and high-quality data, tremendous efforts have been made to protect the data-logger from soil water intrusion, to calibrate soil moisture sensors, and to upscale the point measurements. As the highest soil moisture network above sea level in the world, our network meets the requirement for evaluating a variety of soil moisture products and for soil moisture scaling analyses. It also directly contributes to the soil-water-ice-air-ecosystem interaction studies on the third pole. The data will be publicized via the International Soil Moisture Network and the recent 2-yr data will become accessible soon. [ABSTRACT FROM AUTHOR]

Abstract: The Tibetan Plateau (TP) exerts strong thermal forcing on the atmosphere over Asian monsoon region and supplies water resources to adjacent river basins. Recently, the Plateau experienced evident climate changes, which have changed atmospheric and hydrological cycles and thus reshaped the local environment. This study reviewed recent research progress in the climate changes and explored their impacts on the Plateau energy and water cycle, based on which a conceptual model to synthesize these changes was proposed and urgent issues to be explored were summarized. The TP has experienced an overall surface air warming and moistening, solar dimming, and wind stilling since the beginning of the 1980s. The surface warming depends on elevation and its horizontal pattern is consistent with the one of the glacier change. Accompanying the warming was air moistening, and both facilitated the trigger of more deep-clouds, which resulted in solar dimming. Surface wind speed declined from the 1970s, as a result of atmospheric circulation adjustment caused by the differential surface warming between the Asian high-latitude and low-latitude. The climate changes had weakened the thermal forcing over the TP. The warming and wind stilling lowered the Bowen ratio and led to less surface sensible heating. Atmospheric radiative cooling was enhanced, mainly by outgoing longwave emission from the warming planetary system and slightly by solar radiation reflection. Both processes contributed to the thermal forcing weakening over the Plateau. The water cycle was also altered by the climate changes. The wind stilling may have weakened water vapor exchange between the Asia monsoon region and the Plateau and thus led to less precipitation in the monsoon-impacted southern and eastern Plateau, but the warming enhanced land evaporation. Their overlap resulted in runoff reduction in the southern and eastern Plateau regions. By contrast, more convective precipitation over the central TP was triggered under the warmer and moister condition and yielded more runoff; meanwhile, the solar dimming weakened lake evaporation. The two together with enhanced glacier melts contributed to the lake expansion in the central TP. [Copyright &y& Elsevier]

Summary: A mesoscale Tibetan Plateau Soil Moisture/Temperature Monitoring Network (SMTMN) has been established to study large-scale soil–vegetation–atmosphere interactions and to validate satellite soil moisture products. Soil moisture at four layers (0–5cm, 10cm, 20cm, and 40cm) of 30 sites was monitored since July, 2010. This paper firstly introduces the network and then presents preliminary spatiotemporal analyses based on the in situ soil moisture measurements in SMTMN. Three temporal scales (half-hourly, daily, and 10-days) and three time periods corresponding to typical soil wetness conditions, including frozen soil in winter times, are discussed. Primary findings are: (a) generally 13 randomly distributed sites in the study domain are required (i.e. number of required sites) to estimate areal mean soil moisture with correlation coefficient ⩾0.99 and root mean square difference ⩽0.02m3 m−3. This provides guidance for future soil moisture network establishment in similar regions; (b) both number of required sites and the most representative site are insensitive to temporal scales while conversely sensitive to soil wetness conditions; (c) the combination of a few optimally-selected sites can give more robust estimate of areal mean soil moisture than a single site does because the former contains more information on spatial heterogeneity. These findings can provide not only a practical compromise between maintenance cost and risk on reliability for an existing soil moisture network, but also insights for soil moisture upscaling studies and satellite soil moisture products validations. [ABSTRACT FROM AUTHOR]