Spatio-temporal variability of vertical gradients of major meteorological observations around the Tibetan Plateau

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ABSTRACT:The Tibetan Plateau (TP) affects its surroundings significantly through thermal and dynamic processes. Reductions in near-surface wind speed (W s ) have been observed from ground measurements but how the trends of W s vary with the elevation is less clear. Trends of W s with respect to elevation were investigated using long-term daily records taken from 1970 to 2012 of W s and maximum (T max ), minimum (T min ), and mean (T mean ) air temperatures from 139 stations over and around the TP. The major findings are as follows. (1) Pronounced reductions in W s can be observed in all seasons and annually across the TP. Spring demonstrates the most prominent weakening. The rate of reductions in W s was amplified with elevation, and higher-elevation environments experienced greater changes in W s than lower-elevation areas. Elevation-dependent reductions in W s have intensified from 1970 to 2012. (2) Statistically significant negative correlations between W s and corresponding near-surface temperatures were detected. We suggested that the elevation-dependent warming and thereby the increased surface roughness at higher-elevation environments may contribute to the elevation-dependent reductions in W s over and around the TP. More detailed mechanisms causing this pattern are to be further explored.

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

normalY = a normalX prefix+ b

where Y represents temperatures; X is the elevation of each station; and a and b are the estimated NLRs and regression intercepts.…”

Section: Methodsmentioning

confidence: 99%

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Elevation‐dependent reductions in wind speed over and around the Tibetan Plateau

Guo

Wang

Tian

et al. 2016

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“…The TP has been experiencing an overall rapid wetting and warming in recent years (Liu and Chen, ; Niu et al ., ; Yang et al ., , ; Chen et al ., ) and an interesting EDW phenomenon (Qin et al ., ; Pepin et al ., ). These phenomena are assumed to influence the hydrologic cycle and its elements, especially against the elevation due to a larger span of elevation over and around the TP (Guo et al ., , ). The topography over and around the TP was described in Figure (a) using the digital elevation model from the shuttle radar topography mission (http://srtm.usgs.gov), which generally decreases from northwest to southeast.…”

Section: Methodsmentioning

confidence: 99%

Does summer precipitation trend over and around the Tibetan Plateau depend on elevation?

Wang

Guo

et al. 2017

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The Tibetan Plateau (TP) experienced a rapid warming and wetting in recent decades. The elevation dependence of warming rate has been established, while the question of trend in precipitation against the elevation gradient remains open. By using the in situ observation of precipitation, air temperature, and surface specific humidity from 91 stations over and around the TP, this study investigated how the trends in summer precipitation varied along the elevation gradient over and around the TP during the period 1970–2014. The major findings are as follows: (1) the trends in summer precipitation from 1970 to 2014 displayed an increasing tendency at a rate of 0.83% decade−1 km−1 with the increased elevation, and the rate for 1991–2014 (2.23% decade−1 km−1) is even greater and (2) the temporal trends in surface air temperature, surface specific humidity (surface water vapour) from in situ observations and total column of water vapour from Japanese 55‐year reanalysis (JRA‐55) data over most stations consistently display similar elevation dependence, which provides a plausible explanation for the elevation dependence of the summer precipitation trends based on the Clausius–Clapeyron relationship. The large‐scale atmospheric circulations are other possible factors influencing the elevation dependence of summer precipitation trends, which needs further investigations.

“…Changes in surface variables are usually affected by changes in atmospheric fields such as wind speed, air temperature, geopotential height, relative, and specific humidity (Guo et al, 2016b;Li et al, 2018). There do exist positive and negative feedbacks between these atmospheric and surface meteorological fields, both in time and space.…”

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confidence: 99%

Observed changes in temperature extremes over China–Pakistan Economic Corridor during 1980–2016

Ullah

You

Ullah

et al. 2018

This study uses the daily maximum and minimum temperature data sets of 48 meteorological stations to assess the observed changes in temperature extremes over China–Pakistan Economic Corridor (CPEC) during 1980–2016. The nonparametric Mann–Kendall, Sen's slope estimator, least squares method, and two‐tailed simple t‐test methods were used to assess the trend in nine temperature extreme indices. The results of the study indicated that the trends in annual mean anomalies of cold nights, cold days, and frost days significantly decreased at the rates of −1.09, −1.58, and −1.05 day/decade, respectively. The number of warm nights, warm days, and summer days exhibited significant positive trends at the rates of 1.49, 1.04, and 4.32 day/decade, respectively. In addition, the trends of the warmest day and coldest day also increased significantly at the rates of 0.45 and 0.51 °C/decade, respectively. The trend of diurnal temperature range decreased significantly with −0.35 °C/decade. The spatial distribution of temperature extreme indices indicated that the number of cold nights, cold days, and diurnal temperature range have been decreased, while the trends of warm nights, warm days, summer days, warmest day, and coldest day have been increased over the whole country. Large‐scale atmospheric circulation changes derived from ERA‐Interim reanalysis show that a weak (strong) wind pressure, increasing (decreasing) geopotential height, and rapid warming (cooling) over the northern (southern) region have contributed to the changes in temperature extremes in Pakistan to some extent. With respect to elevation‐dependent warming (EDW), the trends of cold nights, warm days, summer days, warmest day, and diurnal temperature range showed significant positive correlations with increasing elevation. However, the trends of cold days, warm nights, frost days, and coldest day showed significant negative relationships with increasing elevation. The findings of this study will be helpful in the adaptation of climate change and mitigation of climatological disasters in the region. The study recommends that future studies should investigate the natural and anthropogenic drivers of temperature extremes and the possible mechanism of EDW in the CPEC region.