Semi-diurnal variation of rainfall simulated by cloud-system-resolving model

Description

We studied the characteristics of rainfall over the tropics in the cloud-system-resolving model (Non-hydrostatic ICosahedral Atmospheric Model; NICAM). Semi-diurnal variation of surface rainfall was found over continental area such as Africa, India, and the Amazon. No semi-diurnal variation of rainfall is represented over the ocean such as the Pacific and Indian Oceans, while diurnal variation of rainfall is significant over the ocean area. Slight signal of semi-diurnal variation is seen near larger island over maritime continent. This semi-diurnal variation of rainfall over the continental area, with primary peak in the afternoon and secondary peak at early in the morning, is confirmed in TRMM/PR and TMI observation. The timing of the primary peak is almost same between TRMM observations and NICAM simulation, while the secondary peak in TRMM/PR and TMI observation is earlier than NICAM.

Detailed analysis of semi-diurnal variation of rainfall over Africa by the METEOSAT infrared observations revealed that the afternoon peak is associated with the large number of small-size deep convection. This is consistent with the percentage of convective rainfall observed by TRMM/PR and TMI. Early morning peak of rainfall is rather corresponding to the smaller percentage of convective rain by TRMM/PR and TMI.