Modeled Chaco low-level jets and related precipitation patterns during the 1997–1998 warm season

Modeled Chaco low-level jets and related precipitation patterns during the 1997–1998 warm season
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模拟 1997-1998 年暖季查科低空急流和相关降水模式

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发表时间：
2006
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通讯作者：
A. Saulo
A. Saulo
中科院分区：
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文献类型：
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作者：
M. Nicolini;A. Saulo

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摘要查科急流事件（CJE）是安第斯山脉以东的南美低空急流事件的一个子集，其特点是向极地渗透增强并对南美洲东南部降水产生强烈影响。本研究使用巴西天气预报和气候研究中心 (Centro de Previsão de Tempo e Estudos Climáticos, CPTEC) 运行的 Eta 模型短期天气预报来描述 1997-1998 年暖季期间的 CJE 和相关降水。 Eta/CPTEC 模型输出，优先考虑巴西南部、乌拉圭和阿根廷北部中部地区的夜间最大值，以及高地势附近的白天最大值（阿根廷西北部、巴西高原）。对 CJE 期间出现的热力学和动力强迫的分析有助于解释模拟的降水循环：夜间最大值主要是通过夜间低层辐合增强来解释的，而白天最大值主要是对辐射变暖的响应。 CJE 环境中存在的边界层收敛和对流不稳定性共同作用，提供对流的动态强迫和潜力。模拟降水周期辅以“当前天气”的地面观测，证实了模拟降水中发现的主要振荡。
SummaryChaco jet events (CJEs) are a subset of South American low-level jet events to the east of the Andes, characterized by enhanced poleward penetration and by a strong impact on precipitation over southeastern South America. The present study uses the Eta model short range weather forecasts produced operationally in the Brazilian Center for Weather Forecasts and Climate Studies (Centro de Previsão de Tempo e Estudos Climáticos, CPTEC) to characterize the CJEs and the related precipitation during the 1997–1998 warm season.An enhanced diurnal cycle in precipitation with respect to that found during the warm season mean can be recognized during CJEs in Eta/CPTEC model output, with preference for a nocturnal maximum over southern Brazil, Uruguay, and the central part of northern Argentina, and a daytime maximum near high topography (northwestern Argentina, the Brazilian Planalto). The analysis of thermodynamic and dynamic forcing appearing during CJEs, helps to explain the modeled precipitation cycle: the nocturnal maximum is mostly explained by enhanced low-level convergence at night, while the diurnal one is mainly a response to radiative warming. Boundary-layer convergence, and convective instability, present within the CJEs environment, work together to provide both dynamic forcing and potential for convection. The simulated precipitation cycle is complemented with surface observations of “current weather” that corroborate the main oscillations found in simulated precipitation.