The variability of warm cloud droplet radius induced by aerosols and water vapor in Shanghai from MODIS observations

Abstract

The influence of aerosol optical depth (AOD) on cloud droplet effective radius (CER) is closely related to the liquid water path (LWP) and the total water vapor (WV) in the atmosphere. From a spatial distribution, the interaction between AOD and CER coincided with the anti-Twomey effect in Shanghai. The high-value locations of both the AOD and CER were consistent, both found in central Shanghai. Based on a linear regression analysis of the AOD–CER relationship on a log-log scale, the results showed that the effect of AOD on CER in Shanghai followed not only the Twomey effect but also the anti-Twomey effect. This was mainly due to differing LWPs. When the LWP was less than 50 g/m2, CER decreased with increasing AOD at moderate aerosol loading (AOD < 0.6), and then followed by an increase in CER with increasing AOD. Note that, the role of AOD on CER may be overestimated under this situation. Conversely, when LWP ranged from 50 g/m2 to 150 g/m2, CER decreased with the increase in AOD, agreeing with the Twomey effect. The effect of WV on the interaction between AOD and CER was also investigated and the results indicated that the influence of AOD on CER became larger as WV decreased.