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首页> 外文期刊>Monthly Weather Review >Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil
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Dynamical and Synoptic Characteristics of Heavy Rainfall Episodes in Southern Brazil

机译：巴西南部暴雨过程的动力学和天气特征

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摘要

The dynamical and synoptic characteristics that distinguish heavy rainfall episodes from nonheavy rainfall episodes in southern Brazil are discussed. A heavy rainfall episode is defined here as one in which the 50 mm day~(-1) isohyet encloses an area of not less than 10 000 km~2 in the domain of southern Brazil. One hundred and seventy such events are identified in the 11-yr period of 1991-2001. The mean flow patterns in the period of 1-3 days preceding the episodes show some striking synoptic-scale features that may be considered forerunners of these episodes: (ⅰ) a deepening midtropospheric trough in the eastern South Pacific approaches the continent 3 days before, (ⅱ) a surface low pressure center forms in northern Argentina 1 day before, (ⅲ) a northerly low-level jet develops over Paraguay 2 days before, and (ⅳ) a strong moisture flux convergence over southern Brazil becomes prominent 1 day before the episode. A parameter called rainfall quantity, defined as the product of the area enclosed by the 50 mm day~(-1) isohyet and the average rainfall intensity, is correlated with fields of atmospheric variables such as 500-hPa geopotential and 850-hPa meridional winds. Significant lag correlations show that the anomalies of some atmospheric variables could be viewed as precursors of heavy rainfall in southern Brazil that can be explored for use in improving the forecasts.
机译：讨论了区分巴西南部暴雨和非暴雨的动力学和天气特征。这里定义为强降雨事件，其中50 mm day〜（-1）的isohyet包围了巴西南部区域不少于10000 km〜2的区域。在1991-2001年的11年中，发现了170起此类事件。事件发生前1-3天的平均流量模式显示出一些惊人的天气尺度特征，可以认为是这些事件的先兆：（ⅰ）南太平洋东部的对流层中层低谷在3天前接近该大陆， （ⅱ）1天前在阿根廷北部形成地面低压中心，（ⅲ）2天前在巴拉圭上空形成北低空急流，（ⅳ）巴西南部1天前强烈的水汽通量汇聚变得显着。插曲。称为降雨量的参数，定义为50 mm day〜（-1）等值杂波所包围的面积与平均降雨强度的乘积，与大气变量（例如500-hPa地势和850-hPa经向风）相关。显着的滞后相关性表明，某些大气变量的异常可被视为巴西南部暴雨的前兆，可对其进行勘探以改善预报。

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