A Parameterization for Cloud Organization and Propagation by Evaporation‐Driven Cold Pool Edges

• Published in: Journal of advances in modeling earth systems Vol. 16; no. 1
• Main Authors: Freitas, Saulo R., Grell, Georg A., Chovert, Angel D., Silva Dias, Maria Assunção F., Lima Nascimento, Ernani
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 01.01.2024; American Geophysical Union (AGU)
• Subjects: Advection; Atmospheric models; cloud organization; Clouds; Cold pools; Convection; convection parameterization; Convective cells; Convective development; Downdraft; Evaporation; Mass flux; mesoscale convective system; Mesoscale convective systems; Moist convection; Moist static energy; numerical modeling; Parameterization; Propagation; Simulation; tropical convection; Vertical wind shear; Wind shear
• ISSN: 1942-2466; 1942-2466
• DOI: 10.1029/2023MS003982

When the negatively buoyant air in the cloud downdrafts reaches the surface, it spreads out horizontally, producing cold pools. A cold pool can trigger new convective cells. However, when combined with the ambient vertical wind shear, it can also connect and upscale them into large mesoscale convective systems (MCS). Given the broad spectrum of scales of the atmospheric phenomenon involving the interaction between cold pools and the MCS, a parameterization was designed here. Then, it is coupled with a classical convection parameterization to be applied in an atmospheric model with an insufficient spatial resolution to explicitly resolve convection and the sub‐cloud layer. A new scalar quantity related to the deficit of moist static energy detrained by the downdrafts mass flux is proposed. This quantity is subject to grid‐scale advection, mixing, and a sink term representing dissipation processes. The model is then applied to simulate moist convection development over a large portion of tropical land in the Amazon Basin in a wet and dry‐to‐wet 10‐days period. Our results show that the cold pool edge parameterization improves the organization, longevity, propagation, and severity of simulated MCS over the Amazon and other different continental areas. Plain Language Summary In nature, cold pools are formed by cold air masses descending from the low to mid‐troposphere in thunderstorms. When these drafts reach the surface, they spread out horizontally. A manifestation of cold pools is the relatively high speed at the gust front, which can lift environmental air producing new convective cells. Moreover, depending on ambient conditions, the cold pools may help organize the new convective cells, increasing their aggregation and forming the so‐called mesoscale convective systems (MCSs). MCSs, which cover hundreds to thousands of km2, significantly impact the global scale circulation, energy budget, hydrological cycle, and population safety. Forecasting MCSs is challenging for global circulation models (GCM) due to the broad spectrum of scales of the involved atmospheric phenomenon. The computational limitations, at present and for some time to come, do not allow running in real‐time GCMs, which explicitly solves all relevant scales of motion. This paper describes a methodology to account for essential interplays between cold pools edges and moist convection to be applied in the GCMs of weather and climate forecasting. We show that the method improves the model simulation of the main types of MCSs over the Amazon Basin and other continental areas. Key Points A model scheme for including effect of cold pools edges in triggering new convective cells and storm propagation is presented The scheme is coupled with a convection parameterization and applied in the modeling of moist convective systems The method improves the organization, longevity, propagation, and severity of the simulated mesoscale convective systems