Publication Date

2014-07-28

Availability

Open access

Embargo Period

2014-07-28

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Meteorology and Physical Oceanography (Marine)

Date of Defense

2014-05-29

First Committee Member

Paquita Zuidema

Second Committee Member

Brian Mapes

Third Committee Member

Ping Zhu

Fourth Committee Member

Bruce Albrecht

Abstract

Observations of organized precipitating trade-wind cumuli show convective invigoration at their cold pool boundaries. Convection and cold pools are studied using nested-WRF simulations of a day from the Rain in Cumulus over the Ocean experiment. The sub-cloud updrafts downwind and near the cold pool boundaries are statistically compared to updrafts not associated with cold pools. Cold pools affect cloud growth through altering the thermodynamic properties of the updrafts to include moister, cooler air and by enhancing the updraft speed; the latter is particularly important for encouraging deeper, high-liquid water path clouds. It is examined in this study how different microphysics schemes affect the characteristics of simulated trade-wind cumulus convection and cold pools. The initial simulation is compared to an additional nested-WRF simulation using a different microphysics scheme. The differences in autoconversion and accretion rate lead to different precipitation production. The parameterization of raindrop terminal fall speed causes the discrete evaporation efficiencies and different surface cold pool properties under the same surface rainrate. The shallow cumulus cold pools observed in trade-wind region are compared to observation over the tropical Indian Ocean. Data from the Dynamics of the Madden-Julian Oscillation field campaign is analyzed to identify and characterize shallow cumulus cold pools. For the same surface temperature depression in the cold pools, the cold pools in the tropical Indian Ocean show smaller changes in surface specific humidity and wind speed. The comparisons of cold pool characteristics between these two regions help understand the sensitivity of cold pool generation to environmental conditions.

Keywords

shallow convection; cold pool; precipitation; convective invigoration; boundary layer; WRF simulation; RICO; DYNAMO

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