Interannual Variability of the Baiu Season Estimated from the Equivalent Potential Temperature
Abstract
Baiu is a local name in Japanese, which indicates the rainfall or the rainy season of early boreal summer in the East Asian - western North Pacific (WNP) sector. Although the Japan Meteorological Agency (JMA) estimates the onset and closing dates of Baiu every year, the determination is somewhat complicated, because the estimate is based on many factors such as upper or surface weather charts, precipitation events, weather forecast for a week, and so on. Using equivalent potential temperature and its gradient, this work proposes more simple definition of the onset and closing dates. Then, these interannual variations are examined. The mean onset date is June 1 near Japan, which is comparable to the date of JMA. However, the correlation between these interannual variations is insignificant. The estimated mean closing date is July 20, which is coherent with the date of JMA, and the correlation is significant at the 95% level. The interannual variation of the onset dates is controlled by the meridional shift of monsoon southwesterlies, while that of the closing dates is modified by the anomalous mid-latitude westerlies and the circulation anomalies associated with the WNP summer monsoon in the subtropics. The correlations with the ENSO or the tropospheric biennial oscillation are weak, although the interannual variations of the onset and closing dates show dominant 2-3-year periods.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.A33A0096T
- Keywords:
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- 1616 GLOBAL CHANGE / Climate variability;
- 3305 ATMOSPHERIC PROCESSES / Climate change and variability;
- 3309 ATMOSPHERIC PROCESSES / Climatology;
- 3319 ATMOSPHERIC PROCESSES / General circulation