A137-08
Role of large-scale forcing on the development of nonprecipitating continental convective clouds revealed from LASSO large-eddy simulations

Friday, 11 December 2020: 21:23
Virtual
Hyeyum Hailey Shin1, Lulin Xue1, Weiwei Li2, Grant Firl1, Yufei Chu3 and Zhien Wang4, (1)National Center for Atmospheric Research, Boulder, CO, United States, (2)National Center for Atmospheric Research, Developmental Testbed Center, Boulder, CO, United States, (3)University of Colorado Boulder, Boulder, CO, United States, (4)University of Colorado at Boulder, Boulder, CO, United States
Recorded Presentation
Abstract:
The role of large-scale forcing (LSF) on the development of nonprecipitating continental convective clouds at the ARM SGP site is investigated using large-eddy simulations (LES) provided by the DOE’s LES ARM Symbiotic Simulation and Observation (LASSO) project (Gustafson et al. 2020). We selected two LASSO cases that show large sensitivities of LES cloud skill scores (SS) to LSF, 2016-06-11 and 2018-06-06 cases, and compared the highest SS and lowest SS simulations for each case in order to understand how differences in LFS impact on cloud simulations by altering low-level mean vertical structure and turbulence statistics.

The comparison of mean temperature and moisture profiles for the 2016 case shows that the major differences in large-scale forcing between the two simulations selected for this case are the strength of the inversion layer overlying the atmospheric boundary layer (ABL) and the moisture advection in the free atmosphere (FA). The analysis of vertical structure of high-order turbulence statistics and dominant length scales of vertical velocity, moisture, and cloud fields reveals that the inversion strength controls the formation of boundary-layer clouds by modulating the penetration of surface-driven updrafts which transport moisture from the ABL, while the large-scale moisture advection in the FA controls the formation of high-level clouds which are decoupled from the surface-driven low-level clouds. For the 2018 case, it is found that the large-scale subsidence in the low SS simulation for this case is about one order of magnitude smaller than in the high SS simulation, leading to a deeper surface-driven cloud layer by facilitating the development of boundary layer.

Reference Gustafson, W. I., A. M. Vogelmann, Z. Li, X. Cheng, K. K. Dumas, S. Endo, K. L. Johnson, B. Krishna, T. Fairless, and H. Xiao, 2020: The Large-Eddy Simulation (LES) Atmospheric Radiation Measurement (ARM) Symbiotic Simulation and Observation (LASSO) Activity for Continental Shallow Convection. Bull. Amer. Meteor. Soc., 101(4), E462–E479.

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