Date of Award

2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Dr. Ademe Mekonnen

Abstract

Given the Maritime Continent’s (MC’s) critical role in the global climate, examining variations in diurnal cycle and its interaction with the Madden–Julian Oscillation (MJO), Kelvin and Equatorial Rossby waves may lead to improved sub-seasonal forecasts. This study used satellite data of TRMM, TRMM Precipitation Features (PFs), and convective classifications from ISCCP. The convection becomes more organized through the afternoon and evening, leading to peak rainfall over the islands around 1800–2100 local standard time (LST). Over the next few hours, some of that rainfall transitions to stratiform rain over land. The convection then propagates offshore overnight with rainfall peaking along the coast around 0300–0600 LST and over oceans around 0600–0900 LST. The coastal and oceanic diurnal ranges also seem to be larger in stratiform rainfall, in contrast to the land where convective precipitation dominates. The diurnal cycle of rainfall and convection may influence by the presence of the MJO, Kelvin waves, and Equatorial Rossby (ER) waves. The presence of MJO phases does not modulate the morning rainfall over land rather it moderately modulates afternoon rainfall. The MJO exerted a more significant impact on rainfall over the coast and ocean compared to land. Well-organized convection is marginally higher in the afternoon than in the morning over the MC. However, non-organized scattered convection peak over the coast and sea. The MJO impacts the variability of both well-organized and scattered convection more than it does to rainfall. We classified wave phases into four types: wet, dry, increasing, and decreasing wave phases. The wet wave phase is associated with active convection and high rain rate while the dry wave phase is characterized by suppressed convection and less rainfall. Decreasing and increasing phases serve as a transition between wet and dry phases. Rainfall over the MC peaks 2 during MJO wet phases and is minimum during dry phases. But Kelvin and ER wave phase effects on rainfall is weaker than the MJO. Kelvin wave dry and decreasing phases increase the organized deep convection over land but not much over the coast and sea. However, when an ER wave is in the wet and increasing phase, it shows a strong influence over all regions. There are shallow convection peaks when MJO and Kelvin wave phases are wet and decreasing while it is minimum during the dry wave phase. It peaks over land and coast when the ER wave phase is dry and increasing, respectively.

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