Editorial Type:
Article
Article Type:
Research Article

The “Footprint” under a Decaying Tropical Mesoscale Convective System

Mark F. Geldmeier Department of Meteorology, University of Hawaii, Honolulu, Hawaii

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Gary M. Barnes Department of Meteorology, University of Hawaii, Honolulu, Hawaii

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Print Publication:
01 Nov 1997
DOI:
https://doi.org/10.1175/1520-0493(1997)125<2879:TFUADT>2.0.CO;2
Page(s):
2879–2895
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Abstract

On 10 February 1993, during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, the two NOAA WP-3Ds and the NCAR Electra flew under the anvil region of a decaying mesoscale convective system (MCS). Satellite and radar observations show that the MCS had a lifetime of 16 h and deep convection had essentially ceased along the leading edge at the time of sampling. The two NOAA aircraft flew at 35-m altitude over a 150 km × 300 km area to map conditions in the wake of this MCS and estimate the fluxes at the air–sea interface using the bulk aerodynamic approximation. A 20000-km2 area of divergence greater than 5 × 10−5 s−1 characterizes the wake, which is 2°C cooler and 0.5 g kg−1 drier than the environment. Sensible heat fluxes are three times greater and latent fluxes are double that found in the nearby undisturbed environment. These higher fluxes are to the east of the divergence center as a result of the superposition of the MCS fields on the westerly flow. Mixed-layer heights are suppressed and a surface mesolow (0.5 mb) is found more than 100 km behind the leading edge. SST is depressed nearly 0.4°C and is coincident with a divergent stress field and the coolest air in the wake. These fields demonstrate that MCSs stabilize the atmosphere at a given location long after the convective cells have either decayed or moved away. Highest surface fluxes occur in response to convective and mesoscale modification.

Corresponding author address: Prof. Gary M. Barnes, Department of Meteorology, University of Hawaii at Manoa, 2525 Correa Road, Honolulu, HI 96822.

Abstract

On 10 February 1993, during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Response Experiment, the two NOAA WP-3Ds and the NCAR Electra flew under the anvil region of a decaying mesoscale convective system (MCS). Satellite and radar observations show that the MCS had a lifetime of 16 h and deep convection had essentially ceased along the leading edge at the time of sampling. The two NOAA aircraft flew at 35-m altitude over a 150 km × 300 km area to map conditions in the wake of this MCS and estimate the fluxes at the air–sea interface using the bulk aerodynamic approximation. A 20000-km2 area of divergence greater than 5 × 10−5 s−1 characterizes the wake, which is 2°C cooler and 0.5 g kg−1 drier than the environment. Sensible heat fluxes are three times greater and latent fluxes are double that found in the nearby undisturbed environment. These higher fluxes are to the east of the divergence center as a result of the superposition of the MCS fields on the westerly flow. Mixed-layer heights are suppressed and a surface mesolow (0.5 mb) is found more than 100 km behind the leading edge. SST is depressed nearly 0.4°C and is coincident with a divergent stress field and the coolest air in the wake. These fields demonstrate that MCSs stabilize the atmosphere at a given location long after the convective cells have either decayed or moved away. Highest surface fluxes occur in response to convective and mesoscale modification.

Corresponding author address: Prof. Gary M. Barnes, Department of Meteorology, University of Hawaii at Manoa, 2525 Correa Road, Honolulu, HI 96822.

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