Impact of resolution on simulation of closed mesoscale cellular convection identified by dynamically guided watershed segmentation

被引:5
作者
Martini, Matus N. [1 ]
Gustafson, William I., Jr. [1 ]
Yang, Qing [1 ]
Xiao, Heng [1 ]
机构
[1] Pacific NW Natl Lab, Atmospher Sci & Global Change Div, Richland, WA 99352 USA
基金
美国海洋和大气管理局;
关键词
STRATOCUMULUS CLOUDS; PACIFIC; MODEL; PRECIPITATION; AEROSOLS;
D O I
10.1002/2014JD021962
中图分类号
P4 [大气科学(气象学)];
学科分类号
0706 ; 070601 ;
摘要
Organized mesoscale cellular convection (MCC) is a common feature of marine stratocumulus clouds that forms in response to interactions among dynamic, microphysical, and radiative processes at the mesoscale. Cloud resolving models begin to resolve some of these processes, but using high resolutions is extremely costly. To understand the impact of limited resolution on MCC, we use the Weather Research and Forecasting model with chemistry and fully coupled cloud-aerosol interactions to simulate MCC over the southeast Pacific during the Variability of the American Monsoon Systems Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx). A suite of experiments with 3 and 9 km grid spacing indicates that the simulations with finer grid spacing have smaller liquid water paths and cloud fractions, while cloud tops are higher. The observed diurnal cycle is reasonably well simulated. To isolate organized MCC characteristics, we develop a new automated method that uses the watershed segmentation combining the detection of cloud boundaries with coincident vertical velocities. This ensures that the detected cloud fields are dynamically consistent for closed MCC, a common feature within the VOCALS-REx region. We demonstrate that the 3 km simulation is able to reproduce the scaling between horizontal cell size and boundary layer depth seen in satellite observations for the conditions of 900-1400m deep boundary layers. However, the 9 km simulation is unable to resolve smaller circulations corresponding to shallower boundary layers, instead producing MCC with an invariant horizontal scale for all simulated boundary layers depths. The results demonstrate that the grid spacing needed for proper simulation of the MCC structure in marine stratocumulus regions depends on the boundary layer depth.
引用
收藏
页码:12674 / 12688
页数:15
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