西南地区东部夏季典型旱涝年的OLR特征

Characteristics of Outgoing Longwave Radiation Related to Typical Flood and Drought Years over the East of Southwest China in Summer

利用1959—2006年西南地区东部20个测站的逐日降水量资料和1979—2006年全球OLR（Outgoing Longwave Radiation）逐日格点资料,分析了西南地区东部夏季典型旱涝年OLR的异常特征。结果表明：按照区域降水指数可确定3个典型干旱年（2006,1994和1997年）和3个典型洪涝年（1998,1980和1993年）,而1998年和2006年分别是1959年以来西南地区东部降水偏多和偏少最明显的年份。西南地区东部典型旱涝年夏季OLR分布有明显的差异,洪涝（干旱）年,从青藏高原东部一直到江淮地区OLR值偏低（高）,同时孟加拉湾南部及赤道东印度洋地区OLR值也偏低（高）,而菲律宾及其附近地区OLR值偏高（低）。从3个关键区平均的逐日变化来看,赤道东印度洋地区对流活动典型涝年强于典型旱年,菲律宾及其附近地区对流活动则是旱年强于涝年,青藏高原东部至江淮流域地区（包括西南地区东部）极端涝年盛行上升运动。涝年热带地区的ITCZ以向西移动的特征为主,而旱年热带地区的ITCZ夏季前期则以向东移动的特征为主。典型涝年孟加拉湾南部及赤道东印度洋地区的对流北传的特征较明显,6月中旬以后大部分时间可以传到30°N以北，典型旱年孟加拉湾南部及赤道东印度洋地区的对流主要呈现南北振荡、偶有中断的活动特征，很少时间能达到30°N。低纬热带地区关键区域OLR5～9月一般都具有准40天左右的显著低频变化周期，而准12～15天的准双周变化周期在部分时段也显著。典型涝年夏季OLR40天左右低频对流经向和纬向传播在西南地区东部区域得到加强，低频对流偏强，引起降水偏多，而典型早年夏季则相反，OLR40天左右低频对流经向和纬向传播在该区域得到削弱，低频对流偏弱，引起降水偏少。

The abnormal OLR features of the typical flood and drought years in summer are analyzed based on the global daily and monthly OLR grid data from 1979 to 2006 and the daily precipitation data at 20 stations in the east of Southwest China from 1959 to 2006. The rainfall indexes show that the summer precipitation in 2006（1998） was the least（most） one since 1959. The OLR distributions represent obvious difference between the extreme drought years and flood ones. The OLR values were lower（higher） than normal over the area from the eastern Tibetan Plateau to Changjiang-Huaihe valleys, and also so over the south of Bengal bay and the east Indian ocean near equator areas, but higher （lower） over the Philippines and its surrounding region in flood（drought） years. The convection activities over the east Indian ocean near equator areas in extremely severe flood years were stronger than those of drought ones, but opposite over the Philippines and its surrounding region. The area from the eastern Tibetan Plateau to Changjiang-Huaihe valleys including the east of Southwest China prevail ascending flow in summer of flood years. The main movement features of tropical ITCZ in flood years were westward whereas eastward in the early summer of drought years. The northward features were obvious of convection over the south of Bengal bay and the east Indian ocean near equator areas in flood years and it arrived to the north of 30°N after the middle dekad of June. In the area the convection presented south-north oscillation and break sporadically and it arrived to 30°N rarely. The key area OLR represents low frequency period about 40 d and quasi-bi-weekly period about 12～15 d during some days. The OLR 40 d low frequency convection made stronger（weaker） and resulted in more（less） rainfall in summer of flood（drought） years through meridional and zonal propagation.