Observed and Modeled Aspects of Central-South American Low Level Jets

发生在中南美洲安第斯山脉以东的低空急流(LLJ)在从亚马逊到拉普拉塔河流域的水汽跨流域输送中发挥着重要作用，目前还没有得到很好的了解或预测。这在一定程度上是由于当地观测覆盖面较差，那里无线电探空站的空间分布稀少，其中一些探空站每天只发射一次。这一研究项目试图填补这一观察空白，并寻求对这些LLJ的更好的理解和预测。研究工作分为三个部分。第一个是利用全球伸缩模式研究低空夹层的不同特征及其与厄尔尼诺和拉尼娜夏季大范围异常的相互作用，该模式允许局部高分辨率。第二个组成部分是在2002-2003年南半球夏季在玻利维亚的两个地点和巴拉圭的一个地点发射无线电探空仪，为期三个月，以获得关于低收入国家日和空间结构的信息。第三部分将进行短期数值模拟，以对照夏季实地观测对模型和再分析进行校准和验证。对这些特征的理解可能会改进区域和全球模型的预测。美国和南美国家的科学家之间的合作具有极大的潜力，可以提升那里的研究活动，并改善当地的长期观测努力。这最后一个目标如果实现，将给气象研究和业务界带来不可估量的好处。

The low level jets (LLJs) that occur east of Andes Mountains in Central-South America and play a major role in the inter-basin transport of water vapor from the Amazon to the La Plata river basin are not well understood or predicted. This is, in part, due to poor observational coverage locally where spatial distribution of radiosonde sites is sparse and some of them have only one launch per day. This research project attempts to fill this observational gap and seek improved understanding and prediction of these LLJs. The research work is divided into three components. The first one is to study different features of the LLJs and their interactions with large-scale anomalies during the El Nino and La Nina summers using a global telescoping model that allows local high resolution. The second component is to launch radiosondes at two sites in Bolivia and one in Paraguay for three months in the Southern Hemisphere summer of 2002-2003 to obtain information on the diurnal and spatial structure of the LLJs. The third component will be to carry out short-term numerical simulations to calibrate and validate both the model and the reanalysis against the summer field observations. Understanding of these features may improve prediction with regional and global models. Collaborations between scientists in the U. S. and South American countries have great potential to elevate the research activities there and improve the long- term observational efforts locally. This last goal, if achieved, will have immeasurable benefits to the meteorological research and operational community.