Sensitivity of diurnal cycle of simulated rainfall to cumulus parameterization during Indian summer monsoon seasons

The sensitivity of simulation of the diurnal cycle (DC) to cumulus parameterisation is studied by using nine combinations (3 over Ocean x 3 over land) of cumulus schemes viz. Tiedtke, Emanuel, and Grell schemes for years 2008-2012 in the regional climate model RegCM4.4. The harmonic analysis is used to analyze the DC of rainfall simulated by the nine combinations of CPSs. It is seen that Emanual scheme predicts the spatial distribution of amplitude of the first harmonic and the variance of the diurnal cycle more appropriately compared to other CPSs. However, all schemes advanced the phase of the DC of rainfall by 3-6 h which is the result of the development of early convection in the model. The analysis of the development of rapid convection in the model suggests that sensible heat flux and vertically integrated moisture flux convergence peaks 3 to 6 h earlier compared to the phase of DC of rainfall estimated from TRMM rainfall. The early development of convection in the model may result in the inappropriate representation of condensation and evaporation cycle and hence DC of rainfall. The study emphasize that improvement in the phase of triggering of convection by cumulus parameterization schemes is essential to improve DC rainfall simulated by regional climate models.