[ACG37-P01] Abrupt climate shift in the mature rainy season of the Philippines in the mid-1990s
キーワード：climate shift, interdecadal change, Philippines, tropical cyclones, intraseasonal oscillations
A robust climate shift around 1993/1994 from early August to early September, specifically August 9 to September 7, is detected in stations located over the western coast of the Philippines. For the epoch, 1979-1993, this period is characterized by enhanced convection and corresponds to the peak of the summer rainy season of the Philippines. However, for the epoch 1994-2008, this period features a persistent decrease in rainfall, which is accompanied by upper-level convergence, lower-level divergence, and decrease in relative humidity that expands from the South China Sea to the Philippine Sea. The persistent increase in the sea surface temperature over the equatorial Indian Ocean has been favorable for convection development, which can potentially induce these changes in the large-scale conditions. Additionally, these changes in the large-scale conditions suppress the development of synoptic-scale disturbances including tropical cyclones in the vicinity of the Philippines. Another potential influencing factor is the arrival of a positive 30-60-day filtered outgoing longwave radiation anomalies over the Philippines in the recent epoch, which can also inhibit the development of synoptic-scale disturbances. This study highlights the changes in the rainfall of the summer monsoon of the Philippines and the importance of sub-seasonal analysis in decadal to interdecadal climate change studies.