Editorial Type:
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Article Type:
Research Article

A Wintertime Gulf Coast Squall Line Observed by EDOP Airborne Doppler Radar

G. M. Heymsfield NASA/Goddard Space Flight Center, Greenbelt, Maryland

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J. B. Halverson Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, Maryland

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I. J. Caylor Joint Center for Earth Systems Technology, University of Maryland Baltimore County, Baltimore, Maryland

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Print Publication:
01 Dec 1999
DOI:
https://doi.org/10.1175/1520-0493(1999)127<2928:AWGCSL>2.0.CO;2
Page(s):
2928–2950
Restricted access

Abstract

An extensive wintertime squall line on 13 January 1995 occurring along the U.S. Gulf of Mexico coastline is examined using airborne radar observations combined with conventional data analysis. Flight tracks with the ER-2 Doppler radar (EDOP) mounted on the high-altitude (20 km) ER-2 aircraft provided a unique view of the vertical structure of this line. In this paper, the authors document the squall line structure, and compare and contrast this structure with other published cases.

The squall line had several prominent features that differ from previous studies: 1) the stratiform region was wide in comparison to more typical systems that are 50–100 km wide; 2) the trailing stratiform region consisted of two to three separate embedded trailing bands rather than one continuous band; 3) vertical motions in the trailing stratiform region were nearly twice as strong as previously reported values, with mean values approaching 1 m s−1 between 7- and 9-km altitude, and larger values (1.5 m s−1) in the embedded bands; 4) reflectivities were large with mean stratiform values of about 38 dBZ, and maximum convective values of about 55 dBZ; 5) the squall line rear inflow descended to the surface well behind the leading edge (∼200 km); 6) the convective and squall line inflow region exhibited unique microphysics with small graupel or hail falling out of the tilted squall line updraft, and a wavy, elevated melting region associated with the inflow; and 7) the squall-scale transverse circulation was directly coupled with a jet streak thermally direct circulation, and the ascending branch of this direct circulation may have enhanced production of widespread stratiform rainfall. A conceptual model is presented highlighting the features of this squall line and the coupling of the squall line to the larger-scale flow.

Corresponding author address: Gerald M. Heymsfield, NASA/GSFC, Code 912, Greenbelt, MD 20771.

Email: gerald.heymsfield@gsfc.nasa.gov

Abstract

An extensive wintertime squall line on 13 January 1995 occurring along the U.S. Gulf of Mexico coastline is examined using airborne radar observations combined with conventional data analysis. Flight tracks with the ER-2 Doppler radar (EDOP) mounted on the high-altitude (20 km) ER-2 aircraft provided a unique view of the vertical structure of this line. In this paper, the authors document the squall line structure, and compare and contrast this structure with other published cases.

The squall line had several prominent features that differ from previous studies: 1) the stratiform region was wide in comparison to more typical systems that are 50–100 km wide; 2) the trailing stratiform region consisted of two to three separate embedded trailing bands rather than one continuous band; 3) vertical motions in the trailing stratiform region were nearly twice as strong as previously reported values, with mean values approaching 1 m s−1 between 7- and 9-km altitude, and larger values (1.5 m s−1) in the embedded bands; 4) reflectivities were large with mean stratiform values of about 38 dBZ, and maximum convective values of about 55 dBZ; 5) the squall line rear inflow descended to the surface well behind the leading edge (∼200 km); 6) the convective and squall line inflow region exhibited unique microphysics with small graupel or hail falling out of the tilted squall line updraft, and a wavy, elevated melting region associated with the inflow; and 7) the squall-scale transverse circulation was directly coupled with a jet streak thermally direct circulation, and the ascending branch of this direct circulation may have enhanced production of widespread stratiform rainfall. A conceptual model is presented highlighting the features of this squall line and the coupling of the squall line to the larger-scale flow.

Corresponding author address: Gerald M. Heymsfield, NASA/GSFC, Code 912, Greenbelt, MD 20771.

Email: gerald.heymsfield@gsfc.nasa.gov

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