P74 Impact of biomass burning aerosols on the diurnal cycle of convective clouds and precipitation over a tropical island

Hodzic, Alma, National Center for Atmospheric Research (NCAR), Jean Philippe Duvel, The French National Center for Scientific Research, France, Pablo Saide, and Greg Thompson, NCAR

A simplified version of the weather-aerosol model (WRF-Chem) is used to study the effect of biomass-burning aerosols on the diurnal evolution of deep convection over the tropical island of Borneo during the boreal summer of 2009. Simulations are performed at the cloud-resolving scale (4km) for 40 days and include interactive fire emissions and an explicit treatment of radiative and microphysical effects of aerosols. Intense burning occurred daily in the southern part of the island, and smoke propagated northwards to regions of deep convection. The model captures well the diurnal cycle and intensity of precipitation and high cloud cover observed by MTSAT and TRMM. Deep convection and rain maximum develop at 16LST due to boundary layer heating, and at 2LST due to high altitude updrafts. The dominant average effect of smoke aerosols is to enhance convective instability and increase precipitation in the main convective band parallel to the Borneo Northwest coast, and to suppress the convection elsewhere. The origin and diurnal patters of these effects will be discussed in details. The robustness of the model results to uncertainties in aerosol optical properties will also be explored.