Estimating Bulk Entrainment With Unaggregated and Aggregated Convection. Issue 1 (15th January 2018)

• Record Type: Journal Article
• Authors: Becker, Tobias; Bretherton, Christopher S.; Hohenegger, Cathy; Stevens, Bjorn
• Is Part Of: Geophysical research letters. Volume 45:Issue 1(2018)
• Page Start: 455
• Page End: 462
• Publication Date: 2018-01-15
• Subjects: convective organization -- convective aggregation -- bulk entrainment rate -- convective parameterization -- radiative‐convective equilibrium -- moist shell; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2017GL076640
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: To investigate how entrainment is influenced by convective organization, we use the ICON (ICOsahedral Nonhydrostatic) model in a radiative‐convective equilibrium framework, with a 1 km spatial grid mesh covering a 600 by 520 km 2 domain. We analyze two simulations, with unaggregated and aggregated convection, and find that, in the lower free troposphere, the bulk entrainment rate increases when convection aggregates. The increase of entrainment rate with aggregation is caused by a strong increase of turbulence in the close environment of updrafts, masking other effects like the increase of updraft size and of static stability with aggregation. Even though entrainment rate increases with aggregation, updraft buoyancy reduction through entrainment decreases because aggregated updrafts are protected by a moist shell. Parameterizations that wish to represent mesoscale convective organization would need to model this moist shell. Key Points: Against expectation, bulk entrainment rate increases when convection aggregates in convection‐permitting RCE simulations Aggregated updrafts have high bulk entrainment rates because they are densely packed, generating a lot of shear and turbulence Aggregated updrafts are protected by a moist shell and therefore experience less buoyancy reduction through entrainment