MS Atmospheric Science Thesis Defense of JC Albert Peralta: Intraseasonal Dynamics of the Region of Influence of the Asian Summer Monsoon over the Philippines

The Department of Physics of the School of Science and Engineering of Ateneo de Manila University cordially invites you to an MS Atmosopheric Science Thesis Defense by JC Albert Peralta on April 16, 2019, 10:00 a.m. to 12:00 p.m., at Heyden Hall, Manila Observatory. His thesis is entitled, “Intraseasonal dynamics of the region of influence of the Asian Summer Monsoon over the Philippines,” under the supervision of Dr. Gemma Teresa T. Narisma. His thesis panelists are Ms. Genevieve Lorenzo, Dr. Julie Dado, and and Dr. James Simpas. 

Abstract. The Asian Summer Monsoon (ASM) manifests in the Philippines during June to September as a southwesterly wind flow and rainfall predominantly affecting the western side of the country. This study focused on the intraseasonal dynamics of ASM by assessing the area where its climatologically-persistent high rainfall is observed, i.e., its Region of Influence (ROI), over the Philippines. Validation procedures with respect to 49 observation stations reveal that the TRMM 3B42v7 rainfall dataset is best to use among 4 datasets. The ROI is defined as the contour where 3.0mm/p is measured for at least 75% of all pentads. The resulting area is robust in both time coverage, interannual variability and high correlation with surface winds. Orographically-enhanced ascent of moist southwesterly flow over windward areas is seen as general mechanism that produce favorable rainfall conditions over the ROI. The spatial pattern of the ROI inner band revealed 3 distinct curves labeled as the Luzon, Visayas and Mindanao subregions of the ROI, each with their own unique properties. The Habagat Rainfall Index (HRI) was utilized to detect mosoon rainfall exteremes per subregion. Seasonal wet (dry) monsoons seasons develop over the Luzon and Visayas subregions if faster (slower) low-level southwesterly winds due to favorable (suppressing) shear conditions enhances (diminishes) the observed convective cell over the ROI. On the other hand, extremes on Mindanao subregion form when the seasonal low-level westerly winds are slower. Its seasonal wet monsoon seasons also have a similar convection cell enhancement due to westerly flows but coupled with external moisture by less-frequent intraseasonal easterly flow, while suppression of the convection cell mechanism due to less organized upper level features give rise to its dry monsoon seasons.