2003年天气气候异常灾害机理的定量分析Ⅱ——黄淮秋汛

QUANTITATIVE ANALYSES OF MECHANISMS OF ANOMALOUS WEATHER/CLIMATE DISASTERS IN 2003 Ⅱ ——Autumn Floods in the Basins of Yellow and Huaihe Rivers

关键词:  黄淮流域  秋汛  局地经向环流  上升运动  诊断分析

Key words:  Yellow and Huaihe Rivers Basins  autumn floods  local meridional circulation  rising motions  diagnostic analysis

摘要:

利用NCEP/NCAR再分析资料和局地经向环流线性诊断模式,定量分析导致2003年黄淮秋汛的主要物理过程,并结合天气形势来确立(1～3天)短期预报的着眼点。数值诊断结果表明:(1)预报降水的开始和发展趋势可参考贝加尔湖-新疆低槽及其分裂西风小槽的槽前暖平流与长江流域副热带高压脊西北侧的西南风暖平流的叠加过程。这两股暖平流在黄淮流域所驱动的经向环流上升支占总体上升运动的23.1%,且主要出现在强降水前3天内,强度达到-0.015Pa/s。(2)预报降水的强度和持续时间可参考高空西风急流在黄河流域北侧的建立和维持。与该急流有关的平均西风动量平流在黄淮流域所驱动的上升支占总体上升运动的28.8%,且主要出现在强降水后4天内,强度达到-0.02Pa/s。此外,与强降水同步发生且起正反馈作用的潜热加热所驱动的上升支占总体上升运动的44.2%,在强降水期间达到-0.03Pa/s。(3)预报秋汛结束可参考对流层中上层冷平流侵入黄淮流域以及高空西风急流南压到长江流域北侧,迫使南亚高压脊和副热带高压脊撤出长江流域的一系列过程。与该过程有关的平均温度平流、平均西风动量平流及平均热量垂直输送所驱动的下沉支控制黄淮流域,会导致黄淮秋汛结束。

Abstract:

Based on NCEP/NCAR reanalysis data,the mechanisms of autumn floods in 2003 in the Yellow and Huaihe Rivers Basins(YHRB) were analyzed quantitatively using a linear diagnostic numerical model for 100～125°E averaged meridional circulation.The results show the following:(1) Favorable weather patterns for flood initiation were characterized by the merging of warm advection due to the southwesterly in front of the southeastward-propagating baroclinic troughs and that at the northwestern flank of subtropical high.These warm advections contributed to total rising motions by 23.1% in YHRB,which enhanced up to -0.015Pa/s within three days before the onset of heavy rain.(2) The favorable weather patterns for flood intensification and maintenance were characterized by the development of upper tropospheric jet to the north of YHRB.The jet-related horizontal transports of momentum made 28.8% contribution to total rising motions,which increased to -0.02Pa/s within four days after the onset of heavy rain.Moreover,the latent heating made 44.2%(with -0.03Pa/s during flood period) contribution to the total rising motions,showing the active interaction between latent heat release and strong upward motions.(3) Favorable patterns for flood ending were featured by a series of changes: invasion of cold advection to YHRB,retreat of upper tropospheric jet to the north of Yangtze River Basin(YRB) and withdrawal of subtropical highs from YRB.The associated physical processes caused obvious sinking motions in YHRB,leading to the end of YHRB autumn floods in 2003.