Impact of Shallow Cumulus on Surface Energy Budget and Convective Cloud Populations over the Amazon

 
Poster PDF

Authors

Zhe Feng — Pacific Northwest National Laboratory
Samson M Hagos — Pacific Northwest National Laboratory
Larry Berg — Pacific Northwest National Laboratory
Casey Dale Burleyson — Pacific Northwest National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory
Scott Giangrande — Brookhaven National Laboratory
Courtney Schumacher — Texas A&M University
Joseph Olson — National Oceanic and Atmospheric Administration

Category

Convective clouds, including aerosol interactions

Description

Simulation of convective cloud processes and their associated radiative feedbacks remains one of the largest sources of uncertainty in climate models. In this study, we examine the representation and impact of shallow cumulus clouds on the population of convective clouds over Amazon using model simulations and data collected during the GoAmazon2014/5 field campaign. Our recent observation-based study (Giangrande et al. 2017) found that shallow cumulus clouds dominate surface cloud radiative effects for both wet and dry seasons. Convection-Permitting Model (CPM, x=2 km) WRF simulations show that the model largely underestimates the frequency of shallow cumulus clouds during daytime, resulting in large positive bias in downwelling shortwave radiative flux at the surface. Such biases could potentially have a significant impact on the simulated diurnal timing of deep convection and amount of precipitation in this region, which are poorly simulated in most current climate models. We examine a new multi-plume mass-flux scheme coupled with the Mellor-Yamada-Nakanishi-Ninno (MYNN) Planetary Boundary Layer parameterization, which is primarily designed to better represent sub-grid clouds for CPMs. The impact of the sub-grid scale parameterization on simulated shallow cumulus, their surface radiative effects and boundary layer thermodynamics will be quantified using field campaign observations. We also examine the effect of sub-grid-scale cumulus clouds on shallow-to-deep convection transitions and the diurnal cycle of convection using a new geostationary-satellite-based approach developed using GoAmazon2014/5 ground-based radar observations (see Burleyson et al. abstract). Reference Giangrande, S. E., et al. (2017), Cloud characteristics, thermodynamic controls and radiative impacts during the Observations and Modeling of the Green Ocean Amazon (GoAmazon2014/5) experiment, Atmos. Chem. Phys., 17(23), 14519-14541, doi: 10.5194/acp-17-14519-2017.