热带对流季内振荡强度异常特征及其与海表温度的关系

Characteristics of Tropical Convection Intraseasonal Oscillation Anomaly and Their Relationship with Sea Surface Temperature

利用外逸长波辐射(outgoing longwave radiation,OLR)资料分析了热带对流季内振荡(ISO)强度的季节变化及年际异常特征,重点研究其与海表温度的关系。结果表明:最强的OLR季内振荡主要位于高海表温度(SST)区,即热带印度洋和热带西太平洋区域,终年存在,冬、春季最强,振荡中心偏于夏半球。OLR季内振荡强度年际异常显著区域是热带中东太平洋区域、西北太平洋区域和西南太平洋区域,它与SST年际异常存在局地正相关关系,伴随环流的辐合辐散,并与ENSO事件关系密切。另外,El Ni^no事件发生之前,热带印度洋和热带西太平区域OLR季内振荡增强,其中心随事件的发展逐渐东移,事件发生后这两个区域ISO减弱,这与OLR季内振荡强度年际异常显著的区域具有内在连贯性。海表温度是决定OLR季内振荡强度季节变化、年际异常的一个关键因子。

The seasonal and interannual variability of intraseasonal oscillation（ISO） intensity of tropical convection is investigated by using NCAR/NOAA outgoing longwave radiation（OLR） data, along with the relationship with sea surface temperature（SST）. It shows that there are two strongest ISO areas, namely, tropical Indian Ocean and tropical western Pacific Ocean, companied with large SST zonal deviation in climatological fields for any seasons. There are three noticeable areas of interannual anomaly of OLR ISO intensity, i.e., tropical middle and eastern Pacific（TMEP）, tropical northwest Pacific（TNP） and tropical southwest Pacific（TSP）. In these areas, there are noticeably positive correlation relationships between anomalies of OLR ISO intensity and SST interannually, along with the circulation anomaly convergence （divergence）in the low （high） level at the same time, which is also closely related to El Nino（La Nina）events according to the time coefficient series. In addition, the ISO enhances and moves eastward gradually before El Nino event takes place, and weakens later in the tropical Indian Ocean and tropical west Pacific, which links up with the areas of OLR ISO interannual anomaly intrinsically, because OLR ISO weakens in TNP and TSP and enhances in TMEP after the El Nino event occurs. In the climatological fields, OLR ISO is weak in TMEP, TNP and TSP, whereas the SST interannual anomaly is notable in these areas. It shows that SST interannual anomaly is very important for that of OLR intensity and an even crucial factor. It is well known that ENSO is the strongest interannul signal of SST, which is most notable in the winter and spring, so it is easy to understand that there is a close relationship between the above local relations of ISO intensity and SST interannual anomaly with ENSO. SST interannual anomaly is too weak to produce the marked ISO anomaly in the western Pacific, so there is weak relation between ISO intensity and SST interannual anomaly. Comparing the seasonal with interannual variation of OLR intensity, it is found that SST is a key factor to determine the seasonal and interannual variations of OLR intraseasonal oscillation intensity.