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Duo C.,Lhasa Campus of Institute of Plateau Meteorology | Duo C.,Tibet Institute of Plateau Atmospheric and Environmental science | Xie H.,University of Texas at San Antonio | Wang P.,Tibet Meteorological Bureau | And 4 more authors.
Journal of Applied Remote Sensing | Year: 2014

A temporal variation and spatial distribution of the snow-covered area (SCA) over the Tibetan Plateau (TP) are analyzed using moderate-resolution imaging spectrometer (MODIS)/Terra 8-day snow cover products (MOD10A2) from 2001 to 2013 and the SCA is compared with in situ snow cover days (SCD) from the meteorological network in the TP. Results show that at monthly levels the minimum SCA occurs in July, followed by August, and the SCA increases rapidly from September, reaching the maximum in March; on average, 2002, 2005, and 2008 are snowy years, whereas 2001, 2003, 2007, and 2010 are less-snow years. Apart from strong seasonal variations, the general trend of interannual snow cover variations from 2001 to 2013 is not obvious, remaining at a relatively stable status. The snow cover over the TP is characterized by uneven geographic distribution. In general, snow is abundant with a long duration in the high mountains while it is less abundant and with a short duration in the vast interior of the TP. The interannual variations of snow cover over the TP from ground-based meteorological stations using SCD are very consistent with MODIS SCA, with a correlation coefficient of 0.80 (P < 0.01), indicating that MOD10A2 data have high accuracy to capture and monitor spatiotemporal variations of snow cover over the TP. © 2014 The Authors.

Lin W.L.,Chinese Academy of Meteorological Sciences | Lin W.L.,Tibet Institute of Plateau Atmospheric and Environmental science | Xu X.B.,Chinese Academy of Meteorological Sciences | Sun J.Y.,Chinese Academy of Meteorological Sciences | And 2 more authors.
Science China Earth Sciences | Year: 2011

Lorentz curve fittings are applied to frequency distributions of the concentrations of O3, CO, NOx and SO2 recorded at the Jinsha regional atmospheric background station (JSH) from June 2006 to July 2007, and the peak concentrations of these species for the different seasons are obtained. The peak concentrations are considered to be representative of different background levels for certain processes. The peak concentrations are compared with the corresponding mean (median) concentrations, and the suitability and limitations of the mean (median) values as the background levels are discussed. The mean (median) values might represent the background concentrations in the region under some circumstances, but in other cases these values often underestimate or overestimate the true background concentrations owing to the transport of pollutants and other factors. The effects of air masses transported from different regions on the pollutant background concentrations are obtained by analyzing the 72-hour backward trajectories of air masses 100 m above the ground at JSH. These trajectories are estimated using the HYSPLIT model and then clustered for the measurement period. The spatial distribution and seasonal variations of trajectories and the corresponding mean concentrations of O3, SO2, NOx and CO for different clusters are analyzed. After filtering the seasonal changes in pollutant concentrations, the relative influences of air masses from different regions are obtained. The results show that JSH can be used to obtain the atmospheric background information of different air masses originating from or passing over the Yangtze River Delta, Central South China and the Jianghan Plain. Air masses from Central China, South China, and the western Yangtze River Delta contribute significantly to O3 at JSH. Air masses from the north and northeast of JSH (i. e., the Jianghan Plain, Huang-Huai Plain and North China Plain) and the south (Central South China) contribute significantly to SO2, CO and NOx concentrations. Air masses originating from the ocean often bring clean air. Air masses originating from high altitudes over northwestern regions often have lower CO and NOx concentrations, lower relative humidity, and higher concentrations of O3 and SO2. © 2011 Science China Press and Springer-Verlag Berlin Heidelberg.

Chu D.,Institute of Plateau Meteorology | Chu D.,Tibet Institute of Plateau Atmospheric and Environmental science | Pubu T.,Tibet Weather Observatory | Norbu G.,Tibet Weather Observatory | And 3 more authors.
Acta Meteorologica Sinica | Year: 2011

Measuring rainfall from space appears to be the only cost effective and viable means in estimating regional precipitation over the Tibet, and the satellite rainfall products are essential to hydrological and agricultural modeling. A long-standing problem in the meteorological and hydrological studies is that there is only a sparse raingauge network representing the spatial distribution of precipitation and its quantity on small scales over the Tibet. Therefore, satellite derived quantitative precipitation estimates are extremely useful for obtaining rainfall patterns that can be used by hydrological models to produce forecasts of river discharge and to delineate the flood hazard area. In this paper, validation of the US National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC) RFE (rainfall estimate) 2.0 data was made by using daily rainfall observations at 11 weather stations over different climate zones from southeast to northwest of the Tibet during the rainy season from 1 June to 30 September 2005 and 2006. Analysis on the time series of daily rainfall of RFE-CPC and observed data in different climate zones reveals that the mean correlation coefficients between satellite estimated and observed rainfall is 0.74. Only at Pali and Nielamu stations located in the southern brink of the Tibet along the Himalayan Mountains, are the correlation coefficients less than 0.62. In addition, continuous validations show that the RFE performed well in different climate zones, with considerably low mean error (ME) and root mean square error (RMSE) scores except at Nielamu station along the Himalayan range. Likewise, for the dichotomous validation, at most stations over the Tibet, the probability of detection (POD) values is above 73% while the false alarm rate (FAR) is between 1% and 12%. Overall, NOAA CPC RFE 2.0 products performed well in the estimation and monitoring of rainfall over the Tibet and can be used to analyze the precipitation pattern, produce discharge forecast, and delineate the flood hazard area. © The Chinese Meteorological Society and Springer-Verlag Berlin Heidelberg 2011.

Ran L.,CAS Institute of Atmospheric Physics | Lin W.L.,Chinese Academy of Meteorological Sciences | Lin W.L.,Meteorological Observation Center | Deji Y.Z.,Tibet Institute of Plateau Atmospheric and Environmental science | And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2014

Through several years of development, the city of Lhasa has become one of the most populated and urbanized areas on the highest plateau in the world. In the process of urbanization, current and potential air quality issues have been gradually concerned. To investigate the current status of air pollution in Lhasa, various gas pollutants including NOx, CO, SO2, and O3, were continuously measured from June 2012 to May 2013 at an urban site (29.40° N, 91.08° E, 3650 m a.s.l.). The seasonal variations of primary gas pollutants exhibited a peak from November to January with a large variability. High mixing ratios of primary trace gases almost exclusively occurred under low wind speed and showed no distinct dependence on wind direction, implying local urban emissions to be predominant. A comparison of NO2, CO, and SO2 mixing ratios in summer between 1998 and 2012 indicated a significant increase in emissions of these gas pollutants and a change in their intercorrelations, as a result of a substantial growth in the demand of energy consumption using fossil fuels instead of previously widely used biomass. The pronounced diurnal double peaks of primary trace gases in all seasons suggested automobile exhaust to be a major emission source in Lhasa. The secondary gas pollutant O3 displayed an average diurnal cycle of a shallow flat peak for about 4-5 h in the afternoon and a minimum in the early morning. Nighttime O3 was sometimes completely consumed by the high level of NOx. Seasonally, the variations of O3 mixing ratios displayed a low valley in winter and a peak in spring. In autumn and winter, transport largely contributed to the observed O3 mixing ratios, given its dependence on wind speed and wind direction, while in spring and summer photochemistry played an important role. A more efficient buildup of O3 mixing ratios in the morning and a higher peak in the afternoon was found in summer 2012 than in 1998. An enhancement in O3 mixing ratios would be expected in the future and more attention should be given to O3 photochemistry in response to increasing precursor emissions in this area. © 2014 Author(s).

Chu D.,Tibet Institute of Plateau Atmospheric and Environmental science | Chu D.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Zhang Y.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research | Bianba C.,Tibet Institute of Plateau Atmospheric and Environmental science | Liu L.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research
Journal of Geographical Sciences | Year: 2010

Land use change is the result of the interplay between socioeconomic, institutional and environmental factors, and has important impacts on the functioning of socioeconomic and environmental systems with important tradeoffs for sustainability, food security, biodiversity and the vulnerability of people and ecosystems to global change impacts. Based on the results of the First Land Use Survey in Tibet Autonomous Region carried out in the late 1980s, land use map of Lhasa area in 1990 was compiled for the main agricultural area in Lhasa valley using aerial photos obtained in April, May and October 1991 and Landsat imagery in the late 1980s and 1991 as remotely sensed data sources. Using these remotely sensed data, the land use status of Lhasa area in 1991, 1992, 1993, 1995, 1999 and 2000 were mapped through updating annual changes of cultivated land, artificial forest, grass planting, grassland restoration, and residential area and so on. Land use map for Lhasa area in 2007 was made using ALOS AVNIR-2 composite images acquired on October 24 and December 26, 2007 through updating changes of main land use types. According to land use status of Lhasa area in 1990, 1995, 2000 and 2007, the spatial and temporal land use dynamics in Lhasa area from 1990 to 2007 are further analyzed using GIS spatial models in this paper. © 2010 Science in China Press and Springer-Verlag Berlin Heidelberg.

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