Deep Convective Cloud Ensemble Properties and Aerosol Influences
| Tianle Yuan | University of Maryland |
Category: Cloud Properties
Example of latitudinal dependence of CER-BT profile slopes. The upper panel is for different areas over Asia and the lower for North America
We define deep convective clouds (DCC) based on moderate-resolution imaging spectroradiometer data and examine their ensemble optical and structural properties over different geographic regions. Cloud optical depth distribution of DCC systems, including their convective cores and thick anvil clouds, is stable for individual regions and has variations depending on geographic locations and topography. The cloud preferential detraining level shows similar characteristics. Cloud top crystal effective radius (CER) is universally and positively correlated with cloud top brightness temperature. It is also affected by other environmental factors like surface elevation, aerosol concentration, and composition. DCCs developed over elevated areas tend to have smaller CER at the cloud top. We attribute this to a colder cloud base and a thinner cloud depth for mountainous regions. Simultaneous observations of aerosols and clouds made by the National Aeronautics and Space Administration’s A-Train provide direct evidence of aerosol-DCC interactions. An increased level of smoke and anthropogenic aerosols reduces CER because of more activated droplets, delayed coalescence processes, and possibly homogeneous freezing of numerous small droplets. On the other hand, an increase of CER is observed for clouds developed near a dust source. We argue that activating large dust particles, for example, a giant CCN and/or heterogeneous freezing ice nuclei, may lead to early glaciations and thus a larger CER. Systematically delayed freezing is observed based on ensemble data. CER’s dependence on temperature for DCCs has a systematic latitudinal dependence, which may be explained through a simple thermodynamic argument. We find a strong connection between the DCC frequency pattern and precipitation pattern for several parts of the world. General properties of DCCs presented in this study and their variations may be useful for cloud parameterization in GCM models and our findings of aerosol influence on cloud top properties provide new insight into the aerosol-cloud-precipitation interaction. Implications of our results are important for cirrus clouds and moisture exchange between the stratosphere and troposphere.
This poster will be displayed at ARM Science Team Meeting.
