Effects of aerosols on the Tropical Cyclone genesis as seen from simulations using spectral bin microphysics model (the HAMP contribution)

Genesis of TC Debby (2006) is investigated using the nested grid WRF model with spectral bin microphysics. Two simulations of an initially weak tropical depression (TD) under different aerosol conditions are compared. In the first simulation, aerosol concentration over the entire computational area was assumed typical of a clean maritime atmosphere (with CCN concentration of 100 cm-3). In the second simulation aerosols (desert dust) with high CCN concentration (up to 2000 cm-3) was initially located over Africa, with a low aerosol concentration (with CCN concentration of 100 cm-3) over the ocean. The TD was triggered by small Gaussian heating in the center of the depression. Aerosols were transferred westward by a background wind and the wind component related to the depression. According to results of simulation convection in the zone of the tropical depression was stronger and lightning was more intense. As a result, the “coherent” structure typical of TC is developed earlier in case of high aerosol concentration. The aerosol effects on the microphysical structure of clouds within the zone of the evolving TC, on the spatial distribution of rain as well as on lightning distributions are calculated for different aerosol conditions. The vertical profiles of aerosol concentration are compared with observations. It is shown that aerosols are transported by TC westwards for large distances.