西南区域持续性干旱事件的行星尺度和天气尺度扰动信号

以2009-2010年发生在中国西南地区的持续性干旱事件为例,通过干旱和大气变量的物理分解得到了一些干旱事件发生的新认识.气象干旱多为年循环的气候干季与干旱扰动的叠加所致.一次干旱扰动大约为30-50天,而一次持续性干旱事件是由几次干旱扰动组成的.大气高度场和风场中存在三种时间尺度的扰动.一种是年际行星尺度的大气扰动,与ENSO冷暖事件有关,起源于赤道并传播到中高纬度地区需要2-4年.另一种是季节内行星尺度的大气扰动,与来自赤道地区的30-50天振荡有关.此外,大气中还存在天气尺度的扰动.利用行星尺度大气扰动向赤道外传播与天气尺度扰动的叠加,区域持续性干旱事件能够找到前期预报信号.

Planetary-scale and regional-scale anomaly signals for persistent drought events over Southwest China

New knowledge on persistent droughts was obtained by the physical decomposition of dryness index and atmospheric variables from the recent severe event occurred in 2009—2010 over Southwest China.Meteorological drought can be decomposed into two parts of climate dry season and various dry anomalies.A period of dry anomaly is about 30—50 days and a persistent drought event consists of several times of dry anomalies.Atmospheric variable anomalies with three different time-space scales exist in geopotential height and winds.One of planetary-scale zonal-mean atmospheric anomalies associated with El Nio-Southern Oscillation cycle originates from the equatorial zone and propagates to mid-high latitudes in about 2—4 years.Another planetary-scale atmospheric anomaly which also originates from the equatorial zone is associated with 30—50-day oscillation.The third is the regional-scale atmospheric anomalies.The propagation of these planetary-scale atmospheric anomalies from the equatorial zone to extra-tropical latitudes and adding regional-scale atmospheric anomaly can be used as precursors to predict regional persistent droughts.