Cloud-resolving simulations using the WRF model driven by large-scale forcings
Authors
Yangang Liu — Brookhaven National Laboratory
Wuyin Lin — Brookhaven National Laboratory
Satoshi Endo — Brookhaven National Laboratory
Gang Liu — Brookhaven National Laboratory
Category
Modeling
Description
Time series of cloud properties in the ARM SGP case. (a) Maximum height of cloud top (solid line) and minimum height of cloud base (dash line). (b) Total (solid line) and maximum (dash line) cloud fractions. (c) Liquid water path. Blue and orange lines indicate WRF-FASTER and KNMI-LES, respectively.
Cloud-resolving model (CRM) and large-eddy simulation (LES) have been demonstrated to be effective tools in the evaluation and development of parameterizations of various fast processes in climate models. The Weather Research and Forecasting (WRF) model can be used as a LES model. However, the default WRF-LES is not suited for the cloud-resolving simulation with large-scale forcings. Under the Fast-Physics System Testbed and Research (FASTER) project, we extend the capability of WRF-LES to simulate clouds with time-varying large-scale and surface forcings and evaluate simulations by the modified WRF (WRF-FASTER) against observations and other models’ results. First, the WRF-FASTER is evaluated by a well-tested continental cumulus case at ARM’s Southern Great Plains (SGP) site in GCSS model intercomparison studies. The shallow cumulus clouds produced by WRF-FASTER have very similar properties to another LES model in terms of the diurnal variation (see figure) and vertical profiles of mean state and turbulent moments. Second, the simulations with continuous forcings are tested using the data in the Cloud IOP in March 2000 at ARM SGP. WRF-FASTER roughly follows the time variation of observed cloud pattern but also shows mis- and over-predictions of cloud fraction, which also have been seen in the previous simulations of other CRMs. Further evaluation will be performed using a nocturnal drizzling stratocumulus case based on the second research flight of the DYCOMS-II project.
