The Diurnal Cycle of Rainfall and Cloudiness Associated with ENSO

The diurnal cycle is one of the fundamental modes of atmospheric variability, which explains a large portion of total tropical rainfall and cloudiness variability. However, current models still do not represent the diurnal cycle of rainfall accurately and its dynamics and variability over the open ocean are not fully understood. To shed light on how such a fundamental mode of variability interacts with large-scale variability, this study examines the variability of the regional and global diurnal cycle of tropical rainfall and cloudiness associated with El Nino Southern Oscillation. Using Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) rainfall, and GridSat brightness temperature data, we examine the variability of the amplitude and phase of the diurnal cycle of rainfall and cloud-top temperature. During El Nino, the amplitude of diurnal cycle of rainfall tends to be enhanced over the tropical Pacific Ocean while the opposite is true during La Nina. The phase of the diurnal cycle also tends to be delayed during El Nino, associated with enhanced development of stratiform rain following convective rain. Such a relationship suggests that the interaction between mesoscale and planetary scale is critical for understanding the fundamental variability of the atmosphere such as the diurnal cycle.