Determination of Appropriate Microphysical Time Scales and Parameterization of Cloud Entrainment-Mixing Mechanisms
Abstract
Cloud-climate feedbacks are identified to be one of the largest uncertainties in simulations/projections of climate change, and one important reason is related to the poor understanding and parameterization of turbulent entrainment-mixing processes. There are still disagreements on the appropriate microphysical time scales used in study of entrainment-mixing mechanisms, which hinders parameterization of entrainment-mixing mechanisms in models.
This study aims at tackling this crucial problem by analysis of the aircraft observations from the RACORO campaign and numerical simulations with the Explicit Mixing Parcel Model (EMPM). It is found that the appropriate time scale to use depends on the specific objectives of entrainment-mixing studies. First, if the focus is on the variations of liquid water content and saturation deficit, phase relaxation time of water vapor is the most appropriate. Second, if one focuses on the variations of droplet size and number concentration, time for droplet complete evaporation is the most appropriate. Third, time scales are equivalent under certain microphysical and thermodynamic conditions. After determination of the most appropriate microphysical time scales, a parameterization of entrainment-mixing mechanism is developed based on 12000 EMPM simulations with initial inputs from the observations over the Tibetan Plateau. The new parameterization is incorporated into WRF Morrison scheme and shows improvement in probability density function of precipitation rate.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.A23B..06L
- Keywords:
-
- 0319 Cloud optics;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0320 Cloud physics and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 3310 Clouds and cloud feedbacks;
- ATMOSPHERIC PROCESSESDE: 3360 Remote sensing;
- ATMOSPHERIC PROCESSES