Samson M Hagos — Pacific Northwest National Laboratory
Zhe Feng — Pacific Northwest National Laboratory
Chidong Zhang — NOAA/PMEL
Matus Martini — Pacific Northwest National Laboratory
Casey Dale Burleyson — Pacific Northwest National Laboratory
Category
Convective organization and regime transitions
Description
Hovmöller diagram of the difference in precipitation (mm hr-1) between the control and no-diurnal cycle simulations. The Blue oval shows the weakened MJO signal and the red ovals indicate enhanced precipitation over Sumatra and Borneo
The influence of diurnal cycle of convection on the propagation of MJO across the Maritime Continent (MC) is examined using cloud permitting regional model simulations and observations. A pair of ensembles of control and no-diurnal cycle simulations of the November 2011 MJO episode is performed. In the no-diurnal cycle experiment, the incoming shortwave radiation at the top of the atmosphere is maintained at its daily mean value. In the simulation with the diurnal cycle, the MJO signal propagating across the MC is weakened compared to the no-diurnal cycle experiment, with much of the convection stalling over the large islands of Sumatra and Borneo. The propagating MJO signal is weakened by the diurnal cycle while the stationary convection over the islands is enhanced, resulting in an apparent stalling of MJO signal. Examination of the surface energy fluxes in the model and observations indicates that the presence of the diurnal cycle of cloudiness enhances the mean surface downwelling radiation as clouds form in the afternoon. Analysis of ARM and TRMM observations also shows that this modulation of surface downwelling shortwave radiation by clouds negatively projects on the MJO intra-seasonal cycle and therefore weakens it. In addition, the diurnal cycle limits the maximum size and lifetime of clouds in the model, further enhancing the downwelling shortwave radiation and precipitation over the islands.
