Reverse engineering the tropical precipitation-buoyancy relationship

Reverse engineering the tropical precipitation-buoyancy relationship AbstractThe tropical precipitation-moisture relationship, characterized by rapid increases in precipitation for modest increases in moisture, is conceptually recast in a framework relevant to plume buoyancy and conditional instability in the tropics. The working hypothesis in this framework links the rapid onset of precipitation to integrated buoyancy in the lower troposphere. An analytical expression that relates the buoyancy of an entraining plume to the vertical thermodynamic structure is derived. The natural variables in this framework are saturation and subsaturation equivalent potential temperatures, which capture the leading order temperature and moisture variations respectively. The use of layer averages simplifies the analytical and subsequent numerical treatment. Three distinct layers: the boundary layer, the lower-free troposphere and the mid-troposphere adequately capture the vertical variations in the thermodynamic structure. The influence of each environmental layer on the plume is assumed to occur via lateral entrainment, corresponding to an assumed mass flux profile. The fractional contribution of each layer to the mid-level plume buoyancy, i.e. the layer weight, is estimated from TRMM 3B42 precipitation and ERA-I thermodynamic profiles. The layer weights are used to “reverse-engineer” a deep inflow mass flux profile that is nominally descriptive of the tropical atmosphere through the onset of deep convection. The layer weights—which are nearly the same for each of the layers—constitute an environmental influence function and are also used to compute a free tropospheric integrated buoyancy measure. This measure is shown to be an effective predictor of onset in conditionally averaged precipitation across the global tropics—over both land and ocean. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Reverse engineering the tropical precipitation-buoyancy relationship

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0469
D.O.I.
10.1175/JAS-D-17-0333.1
Publisher site
See Article on Publisher Site

Abstract

AbstractThe tropical precipitation-moisture relationship, characterized by rapid increases in precipitation for modest increases in moisture, is conceptually recast in a framework relevant to plume buoyancy and conditional instability in the tropics. The working hypothesis in this framework links the rapid onset of precipitation to integrated buoyancy in the lower troposphere. An analytical expression that relates the buoyancy of an entraining plume to the vertical thermodynamic structure is derived. The natural variables in this framework are saturation and subsaturation equivalent potential temperatures, which capture the leading order temperature and moisture variations respectively. The use of layer averages simplifies the analytical and subsequent numerical treatment. Three distinct layers: the boundary layer, the lower-free troposphere and the mid-troposphere adequately capture the vertical variations in the thermodynamic structure. The influence of each environmental layer on the plume is assumed to occur via lateral entrainment, corresponding to an assumed mass flux profile. The fractional contribution of each layer to the mid-level plume buoyancy, i.e. the layer weight, is estimated from TRMM 3B42 precipitation and ERA-I thermodynamic profiles. The layer weights are used to “reverse-engineer” a deep inflow mass flux profile that is nominally descriptive of the tropical atmosphere through the onset of deep convection. The layer weights—which are nearly the same for each of the layers—constitute an environmental influence function and are also used to compute a free tropospheric integrated buoyancy measure. This measure is shown to be an effective predictor of onset in conditionally averaged precipitation across the global tropics—over both land and ocean.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Mar 6, 2018

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