Comparison of precipitation products to observations in Tibet during the rainy season

Precipitation is an important component of global water and energy transport and a major aspect of climate change. Due to the scarcity of meteorological observations, the precipitation climate over Tibet has been insufficiently documented. In this study, the distribution of precipitation during the rainy season over Tibet from 1980 to 2013 is described on monthly to annual time scales with meteorological observations. Furthermore, four precipitation products are compared to observations over Tibet. These datasets include products derived from the Asian Precipitation-Highly-Resolved Observational Data(APHRO), the Global Precipitation Climatology Centre(GPCC), the University of Delaware(UDel), and the China Meteorological Administration(CMA). The error, relative error, standard deviation, root-mean-square error, correlations and trends between these products for the same period are analyzed with in situ precipitation during the rainy season from May to September. The results indicate that these datasets can broadly capture the temporal and spatial precipitation distribution over Tibet. The precipitation gradually increases from northwest to southeast. The spatial precipitation in GPCC and CMA are similar and positively correlated to observations. Areas with the largest deviations are located in southwestern Tibet along the Himalayas. The APHRO product underestimates, while the UDel, GPCC, and CMA datasets overestimates precipitation on the basis of monthly and inter-annual variation. The biases in GPCC and CMA are smaller than those in APHRO and UDel with a mean relative error lower than 10% during the same periods. The linear trend of precipitation indicates that the increase in precipitation has accelerated extensively during the last 30 years in most regions of Tibet. The CMA generally achieves the best performance of these four precipitation products. Data uncertainty in Tibet might be caused by the low density of stations, complex topography between the grid points and stations, and the interpolation methods, which can also produce an obvious difference between the gridded data and observations.

Regionalization and the Method for Risk Grading for Flash Flood Disaster in Tibet Region

Flash flood is one of the major meteorological disasters on the Tibet Plateau (TP). Flash flood risk regionalization based on the theory of flash flood occurrence risk is the essential basis for relative risk management. The flash flood risk regionalization and the high-resolution grid mountain flood risk level in TP is carried out by using ArcGIS with the indicators of rainfall, days of heavy rain, vegetation cover, slope, relative elevation difference, river network density, population density, average GDP and traffic density. The areas with high mountain flood risk are mainly located in the middle and downstream of Yarlung, the Nujiang River Valley, the Jinsha River and Lancang River Basin. Besides, the results of flash flood disaster risk regionalization were tested by using historical flash flood disaster data and calamity census data. The disasters occurred in high-risk and sub-high-risk regions are accounted for 73%. Flash floods that cause casualties and economic losses of more than 100,000 CNY (Chinese Yuan) occurred in high-risk areas. Flash flood risk assessment may provide reference for the prevention and control of geological disasters in TP, improve disaster prevention and mitigation capabilities, reduce the hazards of flash floods to social development.

Submonthly timescale oscillation characteristics of the East Asian winter monsoon and its effect on the temperature of southwest China in 2010

Using NCEP/NCAR R2 reanalysis daily data and daily meteorologicalobservational data of southwest China in 2010, this paper studied the submonthlytimescale oscillation characteristics of the East Asian winter monsoon (EAWM) and itseffect on the temperature of southwest China in 2010 by bandpass filtering, wavelettransformation, composite analysis and correlation analysis. The main conclusions areas follows: The EAWM in 2010 was dominated by low-frequency oscillations of about 7-,12-, and 30-day periods. There existed obviously negative correlation between theEAWM and the winter temperature in southwest China on submonthly, quasi-weeklyand quasi-biweekly timescales, and negative correlation was more obvious on thequasi-biweekly than the quasi-weekly timescale. There was significant difference in thedistribution of high, middle and low layer of the troposphere when the EAWM was onthe submonthly, quasi-one-week and quasi-two-week timescales in the positive andnegative phase. In the positive EAWM phase, the upper-level subtropical westerly jet isstronger and the East Asia trough is deeper, thus it is favorable for the dominance ofmore powerful north wind and lower temperature in southwest China. On the contrary,in the negative EAWM phase, the upper-level subtropical westerly jet is weaker and theEast Asia trough is shallower, thus unfavorable for the north wind and lowertemperature in southwest China.

Validation of Aura Microwave Limb Sounder water vapor and ozone profiles over the Tibetan Plateau and its adjacent region during boreal summer

We present validation studies of MLS V2.2 and V3.3 water vapor(WV) and ozone profiles over the Tibetan Plateau(Naqu and Lhasa) and its adjacent region(Tengchong) respectively by using the balloon-borne Cryogenic Frost point Hygrometer and Electrochemical Concentration Cell ozonesonde. Coincident in situ measurements were selected to compare the MLS V2.2 and V3.3 WV and ozone profiles for understanding the applicability of the two version MLS products over the region. MLS V2.2 and V3.3 WV profiles respectively show their differences within ?2.2±15.7%(n=74) and 0.3±14.9%(n=75) in the stratosphere at and above 82.5 h Pa. Accordingly, at 100 h Pa, the altitude approaching the tropopuase height, differences are within 9.8± 46.0%(n=18) and 23.0±45.8%(n=17), and they are within 21.5±90.6%(n=104) and 6.0±83.4%(n=99) in upper troposphere. The differences of MLS ozone are within ?11.7±16.3%(n=135, V2.2) and 15.6±24.2%(n=305, V3.3) at and above 82.5 h Pa. At 100 h Pa, they are within ?3.5±54.4%(n=27) and ?8.7±41.6%(n=38), and within 18.0±79.1%(n=47) and 34.2±76.6%(n=160) in the upper troposphere. The relative difference of MLS WV and ozone profile has significant oscillation and scatter at upper troposphere and lower stratosphere partly due to the stronger gradients of WV and ozone concentrations here as well the linear interpolation of sonde data for the intercomparison. At and below 70 h Pa, the relative differences of MLS ozone are significantly larger over Lhasa during the Tibetan Plateau "ozone valley" season, which is also the Asian Summer Monsoon period. The MLS ozone differences over the three sites are similar in their vertical distributions during that period. A simple linear correlation analysis between MLS and sonde profiles indicates that the sensitivity of MLS profile products is related to concentrations at each pressure level. The MLS V3.3 product sensitivity is slightly improved for WV at and above 82.5 h Pa, whereas it is not obvious for ozone. The possible factors contributing to the differences of the MLS profile products of WV and ozone are discussed.

Long-term records of glacier evolution and associated proglacial lakes on the Tibetan Plateau(1976‒2020)

The glaciers on the Tibetan Plateau(TP)constitute critical sources of water for the proglacial lakes and many rivers found downstream.To better understand the evolution of glaciers and the impact of this on proglacial lakes,seven glaciers corresponding to continenṅtal,sub-continental,and marine climate types that are influenced by wester-lies and the Indian summer monsoon were selected for study.The evolution of the edges of these glaciers and their associated progla-cial lakes were identified based on the visual interpretation of Landsat TM/ETM+/OLI images.A dataset covering the period 1976-2020 that included the glacier and proglacial lake edge vectors was then created.The relative errors in the areas of the individual glaciers were less than 3%,and for the proglacial lakes these errors were in the range 0%-7%.The dataset was used to effectively compare the changes in glaciers and proglacial lakes that have occurred over the past four decades.The most striking changes that were found were the retreat of glaciers and the formation of small proglacial lakes.This dataset could also be used as a proxy to support research on changes in mountain glaciers,particularly their response to climate change and water resources.This response is of great scientific significance and is important in many applications,including assessments of the ecological problems caused by melting glaciers.The dataset can be downloaded from http://doi.org/10.57760/sciencedb.j00076.00131.

Concentration and seasonal variation of ^(10)Be in surface aerosols of Lhasa,Tibet

Thirty samples of total suspended particles were collected at a site in western part of Lhasa,Tibet from August 2006 to July 2007.The 10Be concentrations were determined by Accelerator Mass Spectrometer (AMS).Analysis of correlation between 10Be concentrations and meteorological factors revealed that the wet scavenging has little effect on 10Be.10Be can be used as a proxy of transport processes of the upper atmosphere over the Tibetan Plateau.Analysis of correlation between 10Be concentrations and NCEP reanalysis data demonstrated that higher 10Be concentrations in spring were probably caused by the atmosphere exchange from stratosphere to troposphere during February to June.Lower 10Be concentrations during August to September were consistent with the synchronous lower O3 values,suggestive of both 10Be and O3 were probably influenced by the atmosphere exchange from troposphere to stratosphere.

Energetics of Boreal Wintertime Blocking Highs around the Ural Mountains

Based on the daily Japanese 55-yr reanalysis data,this study analyzes the maintenance mechanism for 53 boreal winter blocking highs around the Ural Mountains(UBHs)during 1958-2018 based on the atmospheric energy budget equations.After decomposing the circulation into background flow,low-frequency anomalies,and high-frequency eddies,it was found that the interaction between the background flow and low-frequency anomalies is conducive to the maintenance of the UBHs.Due to the southwestward gradient in the climatological mean air temperature over the Eurasian continent,it is easy for the air temperature anomalies as well as the wind velocity anomalies in the middle and lower troposphere induced by the UBHs to facilitate the positive conversion of baroclinic energy associated with the background flow into the UBHs.Likewise,the conversion of barotropic energy associated with the background flow is also evident in the upper troposphere,in which the climatological mean westerlies have evident southward gradient to the northwest of Lake Baikal and southwestward gradient over Barents Sea.Note that the conversion of baroclinic energy associated with the background flow is dominant throughout the lifecycle of UBHs,acting as the major contributor to the maintenance of the UBHs.Although transient eddies facilitate maintenance of the UBHs via positive conversion of barotropic energy in the middle and upper troposphere,they hinder the maintenance of UBHs via negative conversion of baroclinic energy in the lower troposphere.The diabatic heating anomalies tend to counteract the local air temperature anomalies in the middle and lower troposphere,which damps the available potential energy of UBHs and acts as a negative contributor to the UBHs.