The Life Cycle of an Extratropical Marine Cyclone. Part II: Mesoscale Structure and Diagnostics

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  • 1 NOAA/ERL Wave Propagation Laboratory, Boulder, Colorado
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Abstract

This is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) field program. Part I describes the 24-h frontal-cyclone evolution through 6-h horizontal analyses of observations taken by specially deployed observing systems from air, land, and sea. Part II presents frontal-scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone's life cycle. Horizontal analyses at 350 m above ground level describe the cyclone's mesoscale frontal baroclinic structure and associated flow patterns. The vertical structure and evolution of the cyclone's cold front, warm front, and bent-back front are illustrated in cross-sectional analyses of potential temperature, wind velocity, potential vorticity (PV), front-relative transverse flow vectors, diabatic heating, and PV tendencies. Of particular interest are the lower-tropospheric positive PV anomalies within the warm front and within its bent-back extension westward into the polar airstream. Airborne radar reflectivities and Doppler velocities provide a detailed account of the precipitation elements and associated wind flow patterns in the vicinity of the fronts, including mesoconvective radar reflectivities of greater than 50 dBZ and cross-frontal convergent flow exceeding −20 × 10−4 s−1. Time series traces of the 1-s aircraft observations show large and rapid changes in meteorological variables as the aircraft crossed the narrow frontal zones.

Abstract

This is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) field program. Part I describes the 24-h frontal-cyclone evolution through 6-h horizontal analyses of observations taken by specially deployed observing systems from air, land, and sea. Part II presents frontal-scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone's life cycle. Horizontal analyses at 350 m above ground level describe the cyclone's mesoscale frontal baroclinic structure and associated flow patterns. The vertical structure and evolution of the cyclone's cold front, warm front, and bent-back front are illustrated in cross-sectional analyses of potential temperature, wind velocity, potential vorticity (PV), front-relative transverse flow vectors, diabatic heating, and PV tendencies. Of particular interest are the lower-tropospheric positive PV anomalies within the warm front and within its bent-back extension westward into the polar airstream. Airborne radar reflectivities and Doppler velocities provide a detailed account of the precipitation elements and associated wind flow patterns in the vicinity of the fronts, including mesoconvective radar reflectivities of greater than 50 dBZ and cross-frontal convergent flow exceeding −20 × 10−4 s−1. Time series traces of the 1-s aircraft observations show large and rapid changes in meteorological variables as the aircraft crossed the narrow frontal zones.

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