Changes in Wind Speed and Extremes in Beijing during 1960--2008 Based on Homogenized Observations |
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| Authors: | LI Zhen YAN Zhongwei TU Kai LIU Weidong and WANG Yingchun |
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| Institution: | Key Laboratory of Regional Climate--Environment in Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, Graduate University of the Chinese Academy of Sciences, Beijing 100049,Key Laboratory of Regional Climate--Environment in Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, Graduate University of the Chinese Academy of Sciences, Beijing 100049,Key Laboratory of Regional Climate--Environment in Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029,Institute of Urban Meteorology, China Meteorological Administration, Beijing 100089,Beijing Meteorological Bureau, Beijing 100089 |
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| Abstract: | Daily observations of wind speed at 12 stations in the Greater Beijing Area
during 1960--2008 were homogenized using the Multiple Analysis of Series for
Homogenization method. The linear trends in the regional mean annual and
seasonal (winter, spring, summer and autumn) wind speed series were -0.26,
-0.39, -0.30, -0.12 and -0.22 m s-1 (10 yr)-1, respectively.
Winter showed the greatest magnitude in declining wind speed, followed by
spring, autumn and summer. The annual and seasonal frequencies of wind speed
extremes (days) also decreased, more prominently for winter than for the
other seasons. The declining trends in wind speed and extremes were formed
mainly by some rapid declines during the 1970s and 1980s. The maximum
declining trend in wind speed occurred at Chaoyang (CY), a station within
the central business district (CBD) of Beijing with the highest level of
urbanization. The declining trends were in general smaller in magnitude away
from the city center, except for the winter case in which the maximum
declining trend shifted northeastward to rural Miyun (MY). The influence of
urbanization on the annual wind speed was estimated to be about -0.05 m
s-1 (10 yr)-1 during 1960--2008, accounting for around one fifth
of the regional mean declining trend. The annual and seasonal geostrophic
wind speeds around Beijing, based on daily mean sea level pressure (MSLP)
from the ERA-40 reanalysis dataset, also exhibited decreasing trends,
coincident with the results from site observations. A comparative analysis
of the MSLP fields between 1966--1975 and 1992--2001 suggested that the
influences of both the winter and summer monsoons on Beijing were weaker in
the more recent of the two decades. It is suggested that the bulk of wind in
Beijing is influenced considerably by urbanization, while changes in strong
winds or wind speed extremes are prone to large-scale climate change in the
region. |
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| Keywords: | homogenization daily mean wind speed urbanization mean sea level pressure geostrophic wind East Asian monsoon |
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