The Diurnal Cycle of Tropical Cloudiness and Rainfall Associated with the Madden–Julian Oscillation

Abstract

AbstractThis study examines the diurnal cycle of rainfall and cloudiness associated with the Madden?Julian oscillation (MJO) using TRMM rainfall rate and ISCCP multilevel cloud fraction data. There are statistically significant differences in diurnal cycle amplitude and phase between suppressed and enhanced envelopes of MJO convection. The amplitude of the diurnal rainfall rate and middle?deep cloudiness increases within enhanced MJO convection, especially over the ocean. However, the differences in diurnal cycle amplitude between enhanced and suppressed MJO are generally smaller than the differences in daily mean values, so that its relative contribution to total rainfall or cloudiness variance within enhanced MJO convection becomes smaller. Near the coastlines of islands within the Maritime Continent, the diurnal cycle amplitude tends to increase 5?10 days prior to the arrival of the peak enhanced MJO convection, but this relationship is weaker over the interior areas of larger islands where the climatological diurnal amplitude is already large. Within enhanced MJO convection, the diurnal rainfall peak is frequently delayed by about 3 h and cloud height decays at slower rate compared to suppressed conditions. More stratiform rainfall occurs following the peak convective rainfall within enhanced MJO convection, delaying the total rainfall peak by a few hours as a result of its greater horizontal extent. The results of this study suggest that the MJO modulates both the amplitude and phase of the diurnal cycle of tropical rainfall and cloudiness by influencing cloud type population distribution and associated rainfall rates.