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Keywords:

  • wind speed decline;
  • pressure-gradient force;
  • urban effects;
  • monsoon;
  • climate change;
  • China

Abstract

This study extends upon previous analyses and details near-surface wind speed change in China and its monsoon regions from 1969 to 2005, using a new dataset consisting of 652 stations. Moreover, causes of wind speed changes are examined. Major results show that most stations in China have experienced significant weakening in annual and seasonal mean wind during the study period. The averaged rate of decrease in annual mean wind speed over China is − 0.018 ms−1a−1. Decrease in seasonal mean wind differs. The largest rate of decline is in spring at − 0.021 ms−1a−1 and the least is in summer at − 0.015 ms−1a−1. Spatially, large declines are found in northern China, the Tibetan Plateau and the coastal areas in east and southeast China, while central and south–central China have the least change in their wind speed. Significant weakening of wind speed has occurred primarily in strong wind categories. Decreases in light wind categories are trivial, and light wind has even increased slightly in parts of central China. These changes indicate reduced fluctuations in wind and wind storms in recent decades, contributing to decreased frequency and magnitude of dust storms. The trivial changes in summer winds in east and southeast China suggest fairly steady monsoon winds over the decades.

A main cause of the weakening wind is shown to be the weakening in the lower-tropospheric pressure-gradient force, a result pointing to climate variation as the primary source of the wind speed change. Superimposed on the climate effect is the urban effect. While analysis of winds between urban and rural stations reinstate the urban frictional effect, a peculiar stronger increase in wind at urban stations than at rural stations after the abrupt urbanization since 1990 indicates a new aspect of the urban effect on wind speed. Copyright © 2010 Royal Meteorological Society