The role of synoptic and intraseasonal anomalies on the life cycle of rainfall extremes over South America: non-summer conditions
The role of synoptic and intraseasonal anomalies on the life cycle of rainfall extremes over South America: non-summer conditions
复制标题
天气和季节内异常对南美洲极端降雨生命周期的作用：非夏季条件
作者：
Fernando E. Hirata;A. Grimm
以往的研究表明，天气扰动与季内异常的相互作用对南大西洋辐合带和拉普拉塔盆地南半球夏季强降水具有重要作用。在这里，我们进行了类似的分析，以研究南半球春季(SON)、秋季(MAM)和冬季(JJA)的极端降水演变。南美洲东南部的一个相对均匀的地区，其界限随季节变化不大，受到极端降水事件的严重影响，日降雨量的第95个百分位数的值表明，春季较高(16.94百万毫米/天−1)，冬季较低(13.79亿毫米/天−1)。从1979年到2013年，极端降雨事件在春季较频繁(131次)，而在秋季较少(112次)。与夏季极端事件类似，天气尺度的波浪仍然是该区域极端降水的主要驱动因素。这些波动与南美洲东南部极端降水发展过程中的季节内异常之间的相互作用被观测到，特别是在中性ENSO和拉尼娜条件下。厄尔尼诺期间的极端事件与天气波有关，与季内异常没有显著的相互作用。
Previous study showed that the interaction of synoptic disturbances with intraseasonal anomalies is important for heavy rainfall in the South Atlantic Convergence Zone and the La Plata basin during the austral summer. Here, we conduct similar analysis to study the evolution of rainfall extremes during austral spring (SON), fall (MAM) and winter (JJA). A relatively homogeneous region over southeastern South America, whose limits change little from season to season, is heavily affected by extreme precipitation events, as indicated by the value of the 95th percentile of daily rainfall, higher during the spring season (16.94 mm day−1) and lower in winter (13.79 mm day−1). From 1979 to 2013, extreme rainfall events are more frequent in spring (131 events) and less frequent in fall (112 events). Similar to summertime extreme events, synoptic-scale waves continue to be the main drivers of extreme precipitation over the region. The interaction between these waves and intraseasonal anomalies during the development of rainfall extremes over southeastern South America is observed especially during neutral ENSO and La Niña conditions. Warm ENSO phases tend to favor more frequent extremes in all three seasons and extreme events during El Niños are associated with synoptic waves, with no significant interaction with intraseasonal anomalies.