A Kinematic Model for Understanding Rain Formation Efficiency of a Convective Cell
Abstract
A pure theoretical investigation of convective rain formation processes and formation efficiency (FE) is performed using a kinematic one-dimensional time-dependent model with warm rain microphysics. FE is defined as the ratio of total cloud-to-rainwater conversion to total condensation. FE is a component of precipitation efficiency, which is an important but poorly understood parameter in idealized climate models. This model represents a cloud by a cylindrical thermal bubble rising at constant velocity. The model focuses on the interaction between auto-conversion, collection, and lateral mixing about which no theory has been proposed. Taking the auto-conversion threshold into account, a criterion for rain formation and a semianalytical approximate solution of FE are found. The auto-conversion threshold limits the temporal and spatial extent of the "vigorous rain formation region" where most of the rain is produced. The collection and auto-conversion compete with lateral mixing to determine the strength of rain formation within this region. The FE is predicted to be most sensitive to auto-conversion threshold, fractional entrainment rate, and initial bubble water vapor density.
- Publication:
-
Journal of Advances in Modeling Earth Systems
- Pub Date:
- December 2019
- DOI:
- 10.1029/2019MS001707
- Bibcode:
- 2019JAMES..11.4395F
- Keywords:
-
- rain formation efficiency;
- lateral mixing;
- auto-conversion;
- collection;
- kinematic model