Diurnal Cycle of Precipitation and Cloud Clusters in the MJO and ITCZ Over the Indian Ocean

Abstract

Satellite observations of the diurnal cycle of precipitation and cloud clusters show a dominant nighttime maximum over the tropical Indian Ocean, similar to other basins. The nighttime maximum is associated with the relatively long lifetime of large convective systems that initiated during the afternoon when the sea surface temperature (SST) reached its diurnal maximum as first showed in Chen and Houze (1997, https://doi.org/10.1002/qj.49712353806). Shipborne and island-based radar data from Dynamics of the Madden-Julian Oscillation show distinct characteristics of the diurnal cycle in the equatorial region and Intertropical Convergence Zone (ITCZ). A secondary afternoon precipitation maximum occurs under light surface winds (<5 m/s) when the diurnal cycle of SST is large (0.5–1.7 °C) in the equatorial region during the suppressed phase of the Madden-Julian Oscillation (MJO). The afternoon maximum was from short-lived convective systems with rain rates >10 mm/hr. In contrast, during the active MJO and in the ITCZ, the secondary afternoon maximum is mostly absent as the surface winds were generally >5 m/s and reduced afternoon SST warming to less than 0.5 °C. The Tropical Rainfall Measurement Mission Multiplatform Precipitation Analysis does not resolve the secondary afternoon maximum in heavier rain rates from short-lived small systems, but it suggests a more pronounced night-morning maximum in the ITCZ than in the MJO. Infrared 208-K cloud cluster analysis show that this difference in the morning maximum was due to the greater number of long-lasting, large convective systems (>~200 km in diameter) persisting into the morning in the ITCZ.