Investigation of Characteristics of Warm Clouds in Thailand under Different Climate Patterns with Contoured Frequency by Optical Depth Diagrams and Ground-Based Meteorological Data

Abstract

 The study investigates the relationship between climate pattern, rainfall, and internal warm cloud structure in Thailand using ground-based meteorological and satellite data. Situated in the tropical climate zone, Thailand faces drought conditions exacerbated by changes in warm cloud patterns due to climate change. Results indicate a negative correlation between rainfall and Oceanic Nino Index (ONI) and Pacific Decadal Oscillation (PDO), with rainfall decreasing as ONI and PDO values increase, especially in April and October. In contrast, Indian Ocean Dipole (IOD) shows a weaker correlation with the rainfall during the period from 1991 to 2022.

 During the period from 2006 to 2014, the internal warm cloud structure over Thailand was analyzed using Contoured Frequency by Optical Depth Diagrams (CFODDs) derived from CloudSat Cloud Profiling Radar (CPR) and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS). The results show the warm cloud process, indicated by the transfer of cloud droplets to drizzle and rain as cloud particle size increases near the cloud top. The cloud droplet mode occurs from 4 to 15 μm, drizzle mode occurs from 15 to 21 μm and dominance of rain mode occurs above 21 μm.

 Differences in cloud structures are observed under seasonal and El Niño–Southern Oscillation (ENSO) phases, with the warm clouds contain larger cloud droplet effective radius (R_e) during the wet season compared to the dry season. Meanwhile, in cloud structure exhibit thicker cloud and faster transfer drizzle mode to rain mode with R_e increasing during La Niña phase compared to El Niño phase. These differences in cloud structures are attributed to variations in aerosols, differences in humidity, and temperature influenced by geographical characteristics.