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Convective Momentum Transport Observed during the TOGA COARE IOP. Part I: General Features

Convective Momentum Transport Observed during the TOGA COARE IOP. Part I: General Features The momentum budget residual X = ( X, Y ) is estimated with objectively analyzed soundings taken during the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intense observing period (IOP; November 1992–February 1993) to study the effects of convective momentum transport (CMT) over the western Pacific warm pool. The time series of X and Y exhibit multiscale temporal behavior, showing modulations by the Madden–Julian oscillation (MJO) and other disturbances. The power spectra of X, Y, and I T BB (an index of convective activity) are remarkably similar, showing peaks near 10, 4–5, and 2 days, and at the diurnal period, suggesting a link between deep cumulus convection and the acceleration–deceleration of the large-scale horizontal motion, via CMT, which is being modulated by various atmospheric disturbances. The temporal behavior of X and Y can be described as fractals from 1/4 to ∼20 and from 1/4 to ∼16 days, respectively. Their fractal characteristics are reflected in the very large standard deviations around the small IOP means. From the analyses of the quantities u X /| u |, υ Y /| υ |, and v · X , the IOP-mean vertical distributions of the frictional force due to subgrid-scale eddies and the rate of kinetic energy transfer ( E = − v · X ) are determined. The frictional deceleration and downscale energy transfer take place in a deep tropospheric layer from the surface to 300 hPa. In addition, a concentration of large friction and energy transfer exists in a layer just below the tropopause, suggesting the contribution of momentum detrainment from the top of deep cumuli. The IOP-mean frictional deceleration and downscale energy transfer in the lower troposphere are ∼0.5–1.0 m s −1 day −1 and ∼1.0 × 10 −4 m 2 s −3 , respectively. The product of eddy momentum flux with the large-scale vertical wind shear shows that the momentum transport is, on the average, downgradient; that is, kinetic energy is converted from the large-scale motion to convection and turbulence. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Atmospheric Sciences American Meteorological Society

Convective Momentum Transport Observed during the TOGA COARE IOP. Part I: General Features

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References (69)

Publisher
American Meteorological Society
Copyright
Copyright © 2001 American Meteorological Society
ISSN
1520-0469
DOI
10.1175/1520-0469(2002)059<1857:CMTODT>2.0.CO;2
Publisher site
See Article on Publisher Site

Abstract

The momentum budget residual X = ( X, Y ) is estimated with objectively analyzed soundings taken during the Tropical Ocean and Global Atmosphere Coupled Ocean–Atmosphere Response Experiment (TOGA COARE) intense observing period (IOP; November 1992–February 1993) to study the effects of convective momentum transport (CMT) over the western Pacific warm pool. The time series of X and Y exhibit multiscale temporal behavior, showing modulations by the Madden–Julian oscillation (MJO) and other disturbances. The power spectra of X, Y, and I T BB (an index of convective activity) are remarkably similar, showing peaks near 10, 4–5, and 2 days, and at the diurnal period, suggesting a link between deep cumulus convection and the acceleration–deceleration of the large-scale horizontal motion, via CMT, which is being modulated by various atmospheric disturbances. The temporal behavior of X and Y can be described as fractals from 1/4 to ∼20 and from 1/4 to ∼16 days, respectively. Their fractal characteristics are reflected in the very large standard deviations around the small IOP means. From the analyses of the quantities u X /| u |, υ Y /| υ |, and v · X , the IOP-mean vertical distributions of the frictional force due to subgrid-scale eddies and the rate of kinetic energy transfer ( E = − v · X ) are determined. The frictional deceleration and downscale energy transfer take place in a deep tropospheric layer from the surface to 300 hPa. In addition, a concentration of large friction and energy transfer exists in a layer just below the tropopause, suggesting the contribution of momentum detrainment from the top of deep cumuli. The IOP-mean frictional deceleration and downscale energy transfer in the lower troposphere are ∼0.5–1.0 m s −1 day −1 and ∼1.0 × 10 −4 m 2 s −3 , respectively. The product of eddy momentum flux with the large-scale vertical wind shear shows that the momentum transport is, on the average, downgradient; that is, kinetic energy is converted from the large-scale motion to convection and turbulence.

Journal

Journal of the Atmospheric SciencesAmerican Meteorological Society

Published: Feb 15, 2001

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