Change in Deep Convective Ice Water Content and Rainrate as Cbserved from AURA MLS, CloudSat, Aqua MODIS, and ISCCP Datasets.

Abstract:

The influence of aerosols on ice water content (IWC) and rainrate has been suggested by some numerical simulations and observational studies. This is often complicated by a lack of contextual information regarding the dynamic structure and life cycle of the cloud systems. We investigate IWC and rainrate from deep convections (DC) using datasets from AURA Microwave Limb Sounder, CloudSat, Aqua Moderate Resolution Imaging Spectroradiometer, and International Satellite Cloud Climatology Project over the Congo, the Amazon, and South Asia during three different stages of lifecycle. We use measurements from AURA MLS to investigate the change in water content associated with the smaller sized ice crystals at anvil level and CloudSat to derive the relation between the amounts of larger sized ice crystals and rainrate with ambient aerosol loadings. We integrate reflectivity above freezing level (IZ) to calculate the amount of ice and differentiate reflectivity (DZ) with respect to altitude below the freeing level to estimate the attenuated rainfall under the cloud. Our analysis using the reflectivity data shows that IZ and DZ don’t change with aerosols loadings during the growing stage. However, IZ increases and DZ decreases, suggesting a delayed precipitation and increase of ice formation, during the matured stage. During the decaying stage, DZ increases, leading to a loss in larger ice particles or as shown by a decrease of the IZ above freezing level.

IWC within the anvils of the DCs during their growing stage shows no significant relations with the ambient aerosol concentration over the Congo and South Asia. However, anvil IWC decreases during the matured stage over the South Asia and increase over the Congo as aerosol optical depth surrounding the DCs increases. Aerosol’s concentration plays an important role during the decaying stage and is significantly and positively correlated with the IWC of the anvils, suggesting an increase of smaller ice particles in convective anvils with aerosols.

Together with the result of CloudSat, our results supports the hypothesis that an increase of aerosols tend to invigorate large mesoscale deep convection by delaying precipitation and increasing both large and smaller ice particles in convective anvils during the mature phase, and increase precipitation during the decay phase.