Wintertime precipitation episodes in central Chile: Associated meteorological conditions and orographic influences
Wintertime precipitation episodes in central Chile: Associated meteorological conditions and orographic influences
复制标题
DOI：
10.1175/jhm562.1
复制
发表时间：
2007-04-01
影响因子：
3.8
通讯作者：
Garreaud, Rene
中科院分区：
文献类型：
--
作者：
Falvey, Mark;Garreaud, Rene
智利中部（南纬32度-35度）是南美太平洋海岸和安第斯山脉主分水岭之间的一片山区、人口稠密的地带，海拔5000米。在这项研究中，利用降水计、河流流量、无线电探空仪和特殊传感器微波成像仪（SSM/I）被动微波辐射计在 10 年期间（1993-2002 年）的观测来表征智利中部的冬季降水事件。降水事件通常发生在冷锋暴雨从西向东移动到该地区时，其中跨山气流在较低层被阻挡。安第斯山脉对气候降水模式的影响延伸至海岸上游数百公里。在大陆上空，冬季降水与雨量计站点周围的平均地形高度密切相关，而不是与仪器的实际海拔高度相关，尽管现有的降雨观测没有很好地对较高海拔地点进行了采样。安第斯山脉海岸和山麓之间，尽管海岸地形复杂，但降水格局相对均匀。在安第斯山脉的西面，推断出1到3之间的气候增强因子。对沿海站点的无线电探空仪数据的回归分析表明，降水与纬向（跨山）水分通量密切相关。当湿气通量乘以相对湿度时，发现最强的关系。该变量解释了智利中部地区日平均降水量 50% 的差异以及各个站点记录的日降水量高达 60% 的差异。研究了导致安第斯山脉强降水增强事件的因素。安第斯山脉的强但孤立的降水事件往往发生在即将到来的风暴的温暖前额区域，并与山脉顶部附近和上方异常高的水分通量有关。以整个智利中部大范围降雨为特征的强烈锋面事件导致安第斯山脉的增强程度有所不同，但平均而言相当弱。
Central Chile (32 degrees-35 degrees S) is a mountainous and densely populated strip of land between the South American Pacific coast and the main divide of the Andes, 5000 m in height. In this study, wintertime precipitation episodes in central Chile are characterized using precipitation gauge, river discharge, radiosonde, and Special Sensor Microwave Imager (SSM/I) passive microwave radiometer observations over a 10-yr period (1993-2002). Precipitation episodes that typically occur as cold frontal rainstorms move over the region from west to east, within which the cross-mountain flow is blocked at lower levels. The influence of the Andes on the climatological precipitation pattern extends several hundred kilometers upstream of the coast. Over the mainland, the wintertime precipitation is most strongly related to the height of the mean topography surrounding the rain gauge sites, rather than the actual altitudes of the instruments, although higher-elevation locations are not well sampled by available rainfall observations. Between the coast and foothills of the Andes, the precipitation pattern is relatively uniform despite the complex coastal topography. On the western face of the Andes climatological enhancement factors of between 1 and 3 are inferred.Regression analysis against radiosonde data at a coastal site reveals that the precipitation is strongly related to the zonal (cross mountain) moisture flux. The strongest relationship is found when the moisture flux is multiplied by the relative humidity. This variable explains 50% of the variance in daily area average precipitation in central Chile and up to 60% of the variance in the daily precipitation recorded at individual stations. The factors contributing to events of heavy precipitation enhancement in the Andes were examined. Events of heavy, but isolated, precipitation in the Andes tend to occur in the warmer, prefrontal sector of approaching storms and are associated with unusually high moisture fluxes near to and above the crest of the mountain range. Strongly frontal episodes, characterized by widespread rainfall throughout central Chile, lead to variable, but on average rather weak, enhancement in the Andes.