2.2 Controls on Deep-Convective Precipitation and the Dialogue with the Mesoscale

Monday, 7 January 2019: 10:45 AM
North 232AB (Phoenix Convention Center - West and North Buildings)
J. David Neelin, Univ. of California, Los Angeles, Los Angeles, CA; and F. Ahmed, K. A. Schiro, Y. H. Kuo, and C. Martinez-Villalobos

Over recent decades, a wealth of data on precipitation processes from satellite retrievals and field campaigns has been available to the community. The challenge has been in boiling this down to information most useful for improving model representations of convection, particularly in presence of mesoscale organization. Selected aspects of this area will be reviewed, including the role of lower free tropospheric moisture as a control on the onset of deep convection, and elements of the mesoscale literature that appear to be highly relevant to this. Complimentary approaches for estimating the precipitation-buoyancy relationship are compared including mixing constrained by estimates of mass flux growth in the lower troposphere, forward calculations of buoyancy under different entrainment assumptions, and a "reverse-engineering" approach that infers what the weighting must be to yield the observed pickup of precipitation. The inferred incorporation of mass through a deep lower-tropospheric layer for the convective entities yielding intense precipitation has intriguing similarities to inflow into coherent updrafts that have long been pointed out in the mesoscale community. Apparent similarities between mesoscale-convective systems and less-organized convection under these measures are noted. Conversely, relatively simple models constructed to explore the consequences of variations across a sharp pickup of precipitation with lower-tropospheric water vapor provide hypotheses for how a number of features of precipitation statistics arise, including aspects of mesoscale organization.
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