Long-term trends in visibility and atmospheric extinction coefficient over Yunnan-Guizhou Plateau in southwest China for 1961-2006
In this study on the regional climatic variability of visual range, atmospheric extinction coefficient (AEO) and haze episodes, we applied the data of visibility, precipitation, relative humidity, wind speed and weather phenomenon observed at 203 stations across the Yunnan-Guizhou Plateau (YGP) in Southwest China from 1961 to 2006. Long-term trends of the annual mean visibility and AEO were calculated as a linear tendency by using a linear regression model for each station. An analysis of the annual frequency of visibility >19 km, AEO and the annual days of haze was also performed with the Mann-Kendall test for detecting a significant trend with an abrupt change over the 46 years. It was found that the visibility of 84.2% stations decreased on the YGP with the negative trends from -11 to -1 km per 10 years, while the visibility at 15.8% stations increased mostly on the high level and sparsely-populated areas. An overall decline in the annual mean visibility from 34km in 1960s to about 27 km in the 21st century across the YGP was with the negative trends of -0.96 km/10yrs and -1.6 km/10yrs respectively during 1961-1979 and 1980-2006. The annual frequency of visibility>19 km lessened at 71% stations over YGP with an averaged trend of -2% per year. The annual mean haze episodes rose on the east and central region of YGP. Using the Mann-Kendall test, the interannual changes in frequency of visibility>19 km, haze episodes and AEO were characterized with the abrupt changes. The abrupt changes occurred during the 1970s and the1990s, respectively. The negative trend in visibility and the positive trend in AEO could result from the enhanced aerosol concentrations and atmospheric pollution over the YGP.
国家科技期刊平台
NSTL
万方数据
维普
