Observed Momentum Transport in Monsoon Convective Cloud Bands

Gandikota V. Rao Saint Louis University, St. Louis, Missouri

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Tai-Hwa Hor Saint Louis University, St. Louis, Missouri

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Abstract

With an aim to examining the exchanges of momentum and kinetic energy between the low-level flow and convection in the Arabian Sea a composite structure of bands and deep convection was constructed using the kinematic and thermodynamic data gathered by the NCAR’s Electra on 24 June 1979. Based on the 1-s data that resolves 200-m scales of motion, the composite structure was constructed and momentum fluxes u′,w prime; and v′,w prime; were computed at various levels from 320 to 4900 m in the eastern Arabian Sea (EAS). The direction of propagation of these bands was chosen as the x direction. It was found that vertical shear and buoyancy were responsible for causing changes in momentum flux.

Results further revealed that u′,w prime; was predominantly countergradient in the cloud bands up to 3 km. The v′,w prime; was however along the vertical gradient of v. A study of kinetic energy transfers showed that there was a net transfer of kinetic energy from larger-scale to band-scale motion.

Abstract

With an aim to examining the exchanges of momentum and kinetic energy between the low-level flow and convection in the Arabian Sea a composite structure of bands and deep convection was constructed using the kinematic and thermodynamic data gathered by the NCAR’s Electra on 24 June 1979. Based on the 1-s data that resolves 200-m scales of motion, the composite structure was constructed and momentum fluxes u′,w prime; and v′,w prime; were computed at various levels from 320 to 4900 m in the eastern Arabian Sea (EAS). The direction of propagation of these bands was chosen as the x direction. It was found that vertical shear and buoyancy were responsible for causing changes in momentum flux.

Results further revealed that u′,w prime; was predominantly countergradient in the cloud bands up to 3 km. The v′,w prime; was however along the vertical gradient of v. A study of kinetic energy transfers showed that there was a net transfer of kinetic energy from larger-scale to band-scale motion.

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