Relative Influence of the Meteorological and Aerosol Conditions on Rainrate and Latent Heating of Mesoscale Convective Systems Through Their Lifecycle over Tropical Continents

We use a suite of co-located geostationary and polar orbital satellite measurements to infer relative influence of aerosols and other meteorological conditions on rain rates (RR), cloud ice water content (IWC), and latent heat (LH) profiles through the life cycle of large mesoscale convective systems (MCSs) over the tropical South America, Africa and South Asia for the period of January 2003- June2008. Under similar lower tropospheric humidity (RH₈₅₀) and vertical wind shear (VWS) conditions, a higher aerosol optical depth (AOD) is associated with lower RR and LH, and higher cloud ice in the convective cores and anvils at different phases of the convective lifecycle. In particular, an increase of AOD by one standard deviation (1s) is associated with a decrease of RR during the convective lifecycle, especially during the growing phase and decay phases when VWS is high at the rates of -0.43 mm/h and -0.54 mm/h, respectively.  Consequently, LH released by the MCSs increases as it is dominated by RR during these two phases. However, RR increases up to 0.29 mm/h, except under dry conditions (RH₈₅₀ <40%) when RR decreases by -0.24 mm/h due to a 1s increase in AOD during the mature phase. Multiple linear regression analysis suggests that AOD explain 16%, 23%, and 29% of RR’s variance during the growing, mature and decaying phases, respectively, over the global tropical continents. By comparison, increases of convective available potential energy (CAPE), and relative humidity at the 850 hPa (RH₈₅₀) by 1s for each of these variables is associated with an increase of RR up to 0.32 mm/h and 0.42 mm/h, respectively.  These three meteorological variables together explain 47%, 77%, and 45% of the total variance of the RR during the growing, mature, and decaying phases, respectively.

IWC of the MCSs increases with aerosols during all three phases of convective lifecycle, as expected from the increase of smaller cloud particles and reduced RR. With increasing aerosol concentrations, total integrated reflectivity of the larger sized cloud ice particles, as detected by CloudSat, increases up to 10 and 21 dBZ in the convective core regions during the growing and decaying phases, respectively. During the mature phase IZ decreases by -13 dBZ since RR increases with a 1s increase in AOD. The IWC detected by Aura Micro-Limb Sounder at 216 hPa, mainly comprised of small ice particles at the top of the convective anvils, also increases by 0.48, 1.35, and 0.79 mg /m³  during the growing, mature, and decaying phases, respectively.  Thus, these three independent satellite sensors measuring convective ice cloud and precipitation particles consistently suggest that an increase of aerosol can reduce RR and increase cloud ice in the convective cores and anvils