IMPACT OF TROPICAL INTRASEASONAL OSCILLATION ON THE TRACKS OF TROPICAL CYCLONES IN THE WESTERN NORTH PACIFIC

In this work, an index of tropical 20-90 d oscillation (intra-seasonal oscillation; ISO) in the western North Pacific (WNP) was determined via the combined empirical orthogonal function (EOF) method using daily outgoing longwave radiation (OLR) field data from the National Oceanic and Atmospheric Administration (NOAA), daily wind field data (at 850 hPa) from the European Centre for Medium-Range Weather Forecasts (ECMWF) and referencing the Madden-Julian oscillation (MJO) index proposed by Wheeler and Hendon. An in-depth investigation was conducted to examine the impact of the ISO on changes in tropical cyclone (TC) tracks in the WNP during different ISO phases. The research results indicate that during the easterly phase of the ISO, under the impact of the northeastern airflow of anti-cyclonic ISO circulation, the easterly airflow south of the western Pacific subtropical high is relatively weak, and TCs generated in the subtropical high tend to change their tracks east of 140°E; during the westerly phase, there is a relatively high probability that TCs change their tracks west of 140°E. This work also analyzed the ISO flow field situation in cases of typhoons and determined that the track of a tropical cyclone will experience a sudden right turn when the center of the ISO cyclonic (anti-cyclonic) circulation coincides with that of the cyclone.