斜压基本气流对东亚夏季风区气旋扰动低频发展影响的数值模拟研究

本文将夏季气候平均的基本气流分解为正压和斜压分量,使用一个线性斜压模式,研究了不同斜压基本气流对热带西北太平洋地区初始气旋性环流扰动低频发展演变的重要作用.其中,控制试验较好地模拟出初始气旋扰动向西北方向传播、在西北太平洋季风槽附近停滞增强、在东亚地区出现经向波列和在南海到海洋大陆地区形成西北—东南向波列等特征.改变斜压分量的敏感性试验结果表明,正压基流不能为西传的初始扰动供给足够的能量;海陆热力差异引起东亚地区的纬向温度梯度和北风垂直切变,是东亚太平洋型经向波列形成和维持的重要因素;当基本气流中的斜压纬向偏差部分线性增大时,扰动的能量会呈e指数迅速增强,提示在气候变化的背景下,基本气流微小的改变可能带来天气或季节内扰动强度的剧烈响应.

Numerical simulation of the influence of baroclinic basic flow on cyclone perturbation low-frequency development in East Asia summer monsoon areas

Using a linear baroclinic model (LBM), the summer climatology basic flow is decomposed into barotropic and baroclinic components and reconstructed to study the role of different components of baroclinic basic flow in the low-frequency development and evolution of initial cyclone perturbation. The control run simulates several evolution characters similar to observations successfully, such as the north-westward propagation, the stall and enhancement in WNP (western-North Pacific) monsoon trough, and the formation of meridional wave train in East Asia and the northwest-southeast wave train form the South China Sea to the maritime continent. When the baroclinic component of basic flow is changed, the sensitive experiment shows that the barotropic flow cannot provide enough energy for the west-propagation of initial perturbation. The zonal temperature gradient and north wind vertical shear in East Asia due to ocean-land thermal contrast are the critical factor for the perturbation developing into EAP (East Asia Pacific) type merdional wave train and sustaining. When the zonal anomaly part of baroclinic flow increases linearly, the perturbation energy will intensify in the speed exponentially, which suggests in the climate change background, the tiny change of basic state may produce huge responses of weather or intraseasonal perturbation intensity.