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

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 Niño (La Nina) events according to the time coefficient series. In addition, the ISO enhances and moves eastward gradually before El Niño 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 Niño 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.