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The Tibetan Plateau (TP) with an average elevation of over 4,000 m asl is the highest and most extensive highland in the world. We used monthly mean sunshine duration from the Chinese Meteorological Administration to examine the spatial and temporal variability of sunshine duration at 71 stations with elevations above 2,000 m asl in the eastern and central TP during the 1961–2005 period. The temporal evolution of the mean annual sunshine duration series shows a significant increase from 1961 to 1982 at a rate of 49.8 h/decade, followed by a decrease from 1983 to 2005 at a rate of −65.1 h/decade, with an overall significant decrease at a rate of −20.6 h/decade during the whole 1961–2005 period, which is mainly due to the summer and spring seasons. This confirms the evidence that sunshine duration in the TP ranges from brightening to dimming in accordance with sunshine duration trends in the rest of China. The surface solar radiation downwards from ERA-40 reanalysis data in the same region confirms the brightening/dimming phenomenon shown by the sunshine duration before/after the 1980s. Otherwise, additional climatic variables such as low cloud amount, total cloud amount, precipitation, relative humidity and water vapor pressure, in most cases, exhibit significant negative correlation with sunshine duration in the TP on an annual and seasonal basis before and after 1982, respectively. The trends of these variables suggest that changes in some of them might be related to the brightening and dimming detected with the use of sunshine duration measurements over the TP. We also hypothesize that the impact of anthropogenic aerosols upon the climatic variables analyzed cannot be rejected, especially in the significant increase in low cloud cover since approximately 1980. [ABSTRACT FROM AUTHOR]

The Tibetan Plateau, with an average elevation of over 4000 m above sea level, is the highest and most extensive highland in the world. Between 1980 and 2005, the annual mean temperature has warmed at the rate of 0.38°C decade-1. However, little attention has been paid to the variation of wind speed, the most important factor controlling evapotranspiration in the Tibetan Plateau. Here we used monthly mean wind speed from the Chinese Meteorological Administration data set to examine the spatial and temporal variability of wind speed at 71 stations (with elevations above 2000 m above sea level) in the eastern and central Tibetan Plateau during 1980-2005, and compared wind speed climatology and their trends with NCEP and ERA-40 reanalyses in the same domain. Compared with surface stations, NCEP overestimates wind speed and ERA-40 underestimates it, with mean annual biases of 0.93 m s-1 for NCEP and -0.75 m s-1 for ERA-40. Both surface stations and NCEP reanalysis show significant decreasing trends, at rates of -0.24 and -0.13 m s-1 decade-1, respectively, mainly evident in spring and summer. ERA-40 fails to capture any decrease. The above results indicate that NCEP captures wind speed better than ERA-40. We speculate that the most likely cause of diminishing wind speed are the asymmetrically decreasing latitudinal surface temperature and pressure gradients over the Tibetan Plateau, which may be part of a large-scale atmospheric circulation shift. [ABSTRACT FROM AUTHOR]

Abstract: Qaidam Basin is a tectonically controlled depression on the northern margin of the Tibetan Plateau. In 2008, a long core was drilled in the Qahansilatu sub-basin in the western Qaidam basin. The sediment layers in the upper 400m alternate between evaporite mineral layers and carbonaceous clay layers. The detailed mineralogical investigation focused on evaporite minerals including halite, gypsum, mirabilite, thenardite, glauberite, eugsterite, and bloedite. Gypsum and halite make up the majority of the evaporate minerals. Environmentally induced variations in the mineralogy and crystal habit of the sulfates have been extensively investigated. Gypsum has prismatic and pyramid habits, such as disc pyramid, stubby prismatic, slender prismatic. Visible isolated gypsum and aggregates (rosette/radial and twins) are mostly scattered in carbonaceous clay layers, suggesting that secondary gypsum is well developed. Gypsum may be a precursor mineral of glauberite, and thenardite is the precursor of bloedite. As a metastable and rare mineral, eugsterite does not appear in other Tibetan areas. It forms at the expense of pre-existing gypsum or thenardite in the core at an experimental temperature of higher than room temperature. The presence of eugsterite indicates a warm and/or hot climate at its deposition time. Mineralogical variations have been explained by the brine evolution of Na–Cl, Na–Ca–SO4, Na–SO4, Na–SO4–Cl, Na–Ca–SO4–Cl, Ca–SO4, and Na–Mg–SO4. For instance, Na–Mg–SO4 corresponds to bloedite, while Na–Ca–SO4–Cl to the assemblage of halite, gypsum and glauberite. The evaporite minerals and carbonaceous clay layers'' alternation indicates the shift between dry and wet climate. According to the thickness, 18 evaporite stages and/or dry climate stages were identified from 0.97Ma to about 0.03Ma. The two early dry climate stages are identified at 0.96–0.97Ma and 0.87Ma. The other 16 evaporite stages occurred from 0.78Ma to about 0.03Ma. The evaporate-rich stages suggested that evaporation was high and groundwater inflow was sufficient at the sub-basin. [Copyright &y& Elsevier]

Abstract: Based on the China Meteorological Administration homogenized dataset, the spatial and temporal variations of monthly mean temperature at 71 stations with elevations above 2000ma.s.l. in the eastern and central Tibetan Plateau (TP) during 1961–2004 are examined. Using principal component analysis (PCA) in S-Mode, four main subregions of temperature variability in the TP are identified. Trend analyses are then carried out on mean series calculated for each subregion and for the eastern and central TP as a whole at annual, seasonal and monthly resolutions. The NE subregion has the most significant warming trends especially in winter and autumn. The PCA method is also applied to sea level pressure (SLP) over the domain of 20°–60°N and 60°–130°E. Different atmospheric circulation patterns are classified in summer and winter. Moreover, temperature series in the TP are often correlated with SLP and associated with different atmospheric circulation patterns. There are more water vapor flux and total cloud cover in the warmer summers and winters. Therefore, we suggest that change in atmospheric circulation is one of the important factors contributing to the recent climate warming of the TP. [Copyright &y& Elsevier]

Abstract: Temperature trend magnitudes at 71 homogenized surface stations with elevations above 2000masl in the eastern and central Tibetan Plateau (TP) and 56 grid points from surface NCEP and ERA-40 reanalyses in the TP''s vicinity are examined. Both the surface meteorological stations and ERA-40 show general warming trends at the majority of locations, especially in winter. NCEP fails to identify this. Compared with the surface stations, both NCEP and ERA-40 reanalysis data underestimate air temperature trends in the TP, but ERA-40 is better than NCEP. There are no simple linear relationships between elevation and temperature trend magnitudes on an annual or seasonal basis in the surface data or ERA-40, and in NCEP this relationship is inconsistent. Instead there are significant correlations between mean annual and seasonal temperatures and temperature trend magnitudes in the surface dataset and NCEP data (but not ERA-40). We suggest this is due to cryospheric feedback since trends are enhanced when mean annual temperatures are near freezing. The absence of any simple elevation dependency in temperature trends suggests that the rapid warming rate derived from high elevation ice-cores in this region should be interpreted with caution. In addition, more attention should be given to the selection of reanalysis to represent surface climate in the TP, since topographical differences between grid points and stations, and other reanalysis model differences such as surface land schemes, cause differences in trend identification and patterns in this critical region. [Copyright &y& Elsevier]