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An Observational Comparison of Level of Neutral Buoyancy and Level of Maximum Detrainment in Tropical Deep Convective Clouds
Author(s) -
Wang Dié,
Jensen Michael P.,
D'Iorio Jennifer A.,
Jozef Gina,
Giangrande Scott E.,
Johnson Karen L.,
Luo Zhengzhao Johnny,
Starzec Mariusz,
Mullendore Gretchen L.
Publication year - 2020
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd032637
Subject(s) - convective available potential energy , convection , atmospheric sciences , environmental science , troposphere , neutral buoyancy , entrainment (biomusicology) , buoyancy , climatology , radiosonde , atmospheric convection , geology , meteorology , physics , quantum mechanics , rhythm , acoustics , thermodynamics
Tropical deep convective clouds are important drivers of large‐scale atmospheric circulation representing the main vertical transport pathway through the depth of the troposphere for heat, momentum, water, and chemical species. The strength and depth of this transport are impacted by the convective updraft size and intensity that are driven by buoyancy, dynamical forcing, and mixing of environmental air, that is, entrainment. In this study, we identify tropical deep convective systems with well‐defined forward anvils using Atmospheric Radiation Measurement (ARM) ground‐based profiling radars, at three ARM fixed sites in the Tropical Western Pacific (TWP; i.e., Manus, Nauru, and Darwin) and three ARM Mobile Facility deployments in Niamey, Niger; Gan Island, Maldives; and Manacapuru, Brazil. We use the difference between the level of neutral buoyancy (LNB) and the level of maximum detrainment (LMD) as a proxy for the effective bulk convective entrainment ( ε p r o x y ). The LNB, the theoretical height that a parcel raised above the level of free convection would reach with no mixing, is calculated based on preconvection radiosonde measurements using parcel theory. The LMD is the height of the maximum reflectivity observed in forward anvil clouds by profiling radars. Deep convective systems over the TWP show higher LNBs that extend to 16.3 km on average and larger ε p r o x y (median value of LNB minus LMD up to 6.5 km) compared to their continental counterparts in the Amazon and West Africa. Oceanic conditions show larger convective available potential energy (CAPE) coupled with higher moisture at low levels, which favors larger ε p r o x y . In contrast, continental cases initiate and develop, under high convective inhibition, steeper environmental lapse rate, and high wind shear conditions, which show smaller offset between LNB and LMD. Deep convective cases that promote significant cold pools at the surface experience less ε p r o x y . Using a Random Forest regression algorithm, CAPE is associated with the highest feature importance score for predicting convective ε p r o x y , followed by low‐level relative humidity. For continental cases, the low‐level wind shear also indicates higher importance.