Chaco low-level jet events characterization during the austral summer season
Chaco low-level jet events characterization during the austral summer season
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南半球夏季查科低空急流事件特征
DOI：
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发表时间：
2002
期刊：
影响因子：
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通讯作者：
A. Saulo
中科院分区：
文献类型：
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作者：
P. Salio;M. Nicolini;A. Saulo
[1] 之前的研究表明，南美洲东南部对流最大值与水汽通量汇聚之间存在关系。 Nicolini 和 Saulo [2000] 探讨了查科喷射事件期间这种相互依赖性加剧的假设。他们将这些事件定义为安第斯山脉以东的低空急流在 1997 年至 1998 年南方暖季期间使用 ETA 操作产品穿透最南端至 25°S 的极端情况。本文的兴趣集中在查科急流事件（CJE）的气候特征以及利用欧洲中期天气预报中心（ERA）研究这一假设的可能性，该研究涵盖了 15 年期间（1979-1993 年）。 CJE 代表安第斯山脉以东低空急流事件的子群，这些事件在 ERA 数据集中并不常见。它们的持续时间从 1 到 10 天不等，更常见的是从 1 到 5 天。代表该集合的环流和热力场的突出特征是南纬39°附近气团的最大对比度，从太平洋穿透的斜压波列中存在以西经70°为中心的槽，以及阿根廷北部和巴拉圭上空的最大热量和湿度。在 CJE 期间，低层和中层会出现重要的湿气通量和辐合，其强度比夏季平均值强约 10 倍。水蒸气通量异常的强度增强了研究这些事件的重要性，以确定南美洲东南部的水平衡。认为 CJE 代表南美洲东南部气候的一个重要特征的说法是基于这样的事实：虽然 CJE 只占南半球夏季的 17%，但它们占阿根廷东北部降水的很大一部分（最多 55%）。然而，必须将这些结果与未来的现场实验进行对比，以检验本文提出的假设。
[1] Previous studies showed a relationship between convection maxima and the convergence of vapor flux over southeastern South America. Nicolini and Saulo [2000] explored the hypothesis of an intensification of this mutual dependency during the Chaco Jet events. They defined these events as extreme cases of low-level jets east of the Andes that penetrate southernmost to 25°S using ETA operative products during the 1997–1998 austral warm season. The interest of the present paper centers on the climatic characterization of the Chaco Jet events (CJEs) and the possibility of researching this hypothesis using the European Centre for Medium-Range Weather Forecasts reanalyses (ERA), which cover a 15-year period (1979–1993). The CJEs represent a subensemble of low-level jet events east of the Andes that are infrequent in the ERA data set. Their duration varies from 1 to 10 days, more frequently extending from 1 to 5 days. The outstanding features of the circulation and the thermodynamic field that represent this ensemble are a maximum contrast of air masses in a latitude close to 39°S, the presence of a trough centered on 70°W within a baroclinic wave train penetrating from the Pacific Ocean, and a maximum of heat and moisture over northen Argentina and Paraguay. During the CJEs, there is an important flux of moisture and convergence at low and mid levels that is about 10 times more intense than the summer mean. The intensity found in the water vapor flux anomaly reinforces the importance of studying these episodes for the purpose of determining the water balance over southeastern South America. The statement that the CJEs represent an important characteristic of the southeastern South American climate is founded on the fact that, although the CJEs only represent 17% of the austral summer days, they account for a significant fraction of the precipitation (a maximun of 55%) over northeastern Argentina. However, it is indispensable to contrast these results with future field experiments to test the hypothesis addressed in this paper.