Daily SSWV in the studied area was shown to be highly fluctuating, and a seasonal change of wind speed is shown as seven-days running means (Fig. 5d). Relatively high wind speed was observed during June to July 2009 as a result of Asian summer monsoon, followed by an extremely weak atmospheric dynamic period in August 2009. Subse- quently, SSWV increased steadily after September 2009, and was continuously at a relatively high level, although fluctuating strongly, during October 2009 to January 2010. At the end of January 2010, SSWV decreased abruptly, and remained low after that.