资源环境科技发展态势分析平台

Intraseasonal precipitation, wind, and vertically integrated moisture flux variability were assessed from June to August between 1998 and 2009. To that end, we used daily precipitation data from the Tropical Rainfall Measuring Mission (TRMM) and ERA-Interim reanalysis. The composites of precipitation anomalies showed that during the intraseasonal enhancement of convective activity over the area assessed, increased precipitation occurs over the northern coast of South America; the opposite is true during the decrease in intraseasonal convective activity. The convective activity over the region of maximum precipitation variance is intraseasonally enhanced during 210 days, whereas the decrease occurs during 194 days. During the days on which the convective activity over the region of maximum precipitation variance was enhanced (decreased) by the Madden-Julian oscillation, the frequency of African easterly waves (AEWs) cases was greater (lower). The most significant average characteristics observed during this period were the displacement of positive precipitation anomalies toward the north and the intensification of the flux toward the tropical North Atlantic Ocean. This pattern disfavours precipitation over the northern coast of South America. On the other hand, during the dry period of Madden-Julian oscillation, there was a decrease in AEWs cases which, although there was negative precipitation anomalies over the northern coast of South America, there were positive anomalies over northwest South America. Therefore, the increase (decrease) in convective activity over the region of maximum precipitation variance favours (disfavours) the frequency of AEWs over this region and, consequently, the precipitation over the northern coast of South America decreases (increases) during the dry season (June to August).