Buoyancy of Convective Clouds in TOGA COARE

Dingying Wei Department of Physics and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, New Mexico

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Alan M. Blyth Department of Physics and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, New Mexico

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David J. Raymond Department of Physics and Geophysical Research Center, New Mexico Institute of Mining and Technology, Socorro, New Mexico

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Abstract

The buoyancy of convective clouds in TOGA COARE was calculated from the NCAR Electra in situ measurements of temperature, humidity, liquid water content, and two-dimensional images of raindrops. Most of the measurements were made at 700 mb (10°C) although some were made at 850 (18°C) and 600 mb (2°C). The temperature was measured with the Ophir radiometer, which does not have the wetting problem that has degraded many previous measurements of in-cloud temperature in warm clouds.

On average, the in-cloud virtual temperature excess was found to be less than the adiabatic value by about 2 K, while the negative influence of total water content on buoyancy was less than 0.5 K. Furthermore, the total water content was highly variable and much smaller than the adiabatic value. The authors conclude, therefore, that entrainment and mixing was usually a much larger factor in reducing the buoyancy than water loading.

The average buoyancy in downdrafts was positive and similar to the value in updrafts.

Corresponding author address: Alan Blyth, Department of Physics, New Mexico Institute of Mining and Technology, Socorro, NM 87801.

Email: blyth@kestrel.nmt.edu

Abstract

The buoyancy of convective clouds in TOGA COARE was calculated from the NCAR Electra in situ measurements of temperature, humidity, liquid water content, and two-dimensional images of raindrops. Most of the measurements were made at 700 mb (10°C) although some were made at 850 (18°C) and 600 mb (2°C). The temperature was measured with the Ophir radiometer, which does not have the wetting problem that has degraded many previous measurements of in-cloud temperature in warm clouds.

On average, the in-cloud virtual temperature excess was found to be less than the adiabatic value by about 2 K, while the negative influence of total water content on buoyancy was less than 0.5 K. Furthermore, the total water content was highly variable and much smaller than the adiabatic value. The authors conclude, therefore, that entrainment and mixing was usually a much larger factor in reducing the buoyancy than water loading.

The average buoyancy in downdrafts was positive and similar to the value in updrafts.

Corresponding author address: Alan Blyth, Department of Physics, New Mexico Institute of Mining and Technology, Socorro, NM 87801.

Email: blyth@kestrel.nmt.edu

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