A Case Study of a Chaco Low-Level Jet Event
A Case Study of a Chaco Low-Level Jet Event
复制标题
查科低空喷射事件案例研究
DOI：
10.1175/mwr2815.1
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发表时间：
2004
影响因子：
3.2
通讯作者：
M. Nicolini
中科院分区：
文献类型：
--
作者：
A. Saulo;M. Seluchi;M. Nicolini
本文对夏季查科急流事件中低空急流的生命周期进行了分析。这是通过使用Eta/Centro de Previsao del Tempo e Estudos Climaticos （CPTEC）区域模式来实现的，以便获得主要过程的高时空细节。分析了不同纬度的低层环流和位势高度演变，更详细地描述了地形和差变暖对该流演变的影响。该研究表明，在组织良好的北流扫过的不同纬度上，所分析的特定事件的生命周期并不相同，在连续两天内从158 s扩展到328S。所有研究纬度的一个共同特征是存在与局部效应相关的日循环，这在模拟的头一天半中更为明显。这种循环不仅可以通过夜间风的最大值来确定，而且可以通过靠近地表的地转风的振荡来确定，这是对倾斜地形上不同变暖的响应。然而，在第二天，日振荡被天气尺度强迫所取代。这个偏北气流的经向增长基本上是对阿根廷西北低压的深化作出反应，从而成为对天气扰动的地转响应。然而，在这次事件的最后阶段，位于洋流南端的一个偏北风区发展起来，这明显增加了北风向高纬度地区的渗透。最后一种扩展主要是由于地转成因的组成部分。本文提供的证据支持了这种二次发展是LLJ和出口区降水之间的反馈的假设。
This paper concentrates on the analysis of the life cycle of the low-level jet (LLJ) during a summer Chaco jet event. This is accomplished through the use of the Eta/Centro de Previsao del Tempo e Estudos Climaticos (CPTEC) regional model, in order to obtain high temporal and spatial detail of the main processes taking place. Both the low-level circulation and the geopotential height evolution at different latitudes are analyzed to provide a more detailed description of the effects of topography and differential warming on the evolution of this current. This study shows that the life cycle of the particular event analyzed is not the same at the different latitudes swept by this well-organized northerly current, expanding from 158 to 328S during two consecutive days. A common feature to all the examined latitudes is the presence of a diurnal cycle linked to local effects, which is more evident during the first day and a half of the simulation. This cycle was identified not only by a nocturnal maximum of the wind, but also by the oscillations of the geostrophic wind close to the surface in response to differential warming over sloping terrain. However, during the second day, the diurnal oscillation is superseded by synoptic-scale forcing. The meridional growth of this northerly current reacts basically to a deepening of the northwestern Argentinean low, consequently becoming a geostrophic response to a synoptic perturbance. How- ever, during the final stages of this event, a northerly wind area located over the southern tip of the current, which notably increases the northerlies' penetration toward higher latitudes, develops. This last extension is mainly due to a component of ageostrophic origin. Evidence is provided in support of the hypothesis that this secondary development is a feedback between the LLJ and the precipitation at the exit region.