Multiscale Analysis of a Mature Mesoscale Convective Complex

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  • 1 NOAA/ERL/National Severe Storms Laboratory, Mesoscale Research Division, Boulder, Colorado
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Abstract

A multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex (MCC) observed during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central (PRE-STORM) experiment. This midlatitude system was the second in a series of four MCCs that developed and traveled along a quasi-stationary frontal zone over the central United States on 3–4 June 1985. Objectively analyzed mesoscale upper-air soundings encompassing the MCC are interpreted in tandem with more detailed dual-Doppler radar measurements that disclose the storm's internal airflow and precipitation structure. The mature MCC is found to include a variety of local environments and associated weather, ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains. A corresponding spectrum of mesoscale ver6cW-motion profiles is documented. These findings are related to previous composite-based portrayals of MCCs, as well as detailed case studies of simpler squall-type convective systems.

A hallmark of this storm was its “open-wave” precipitation pattern, in which two convective bands intersected so as to resemble a miniature developing frontal cyclone. This resemblance proves superficial, however, since 1) anticyclonic lower-tropospheric flow was observed in place of the expected cyclonic circulation near the convective apex, and 2) the accompanying wavelike lower-tropospheric temperature pattern was strongly influenced by moist processes intrinsic to the MCC (e.g., evaporative cooling), as opposed to horizontal advection about a developing vortex. The storm's intriguing organization is instead postulated to have resulted from the superposition of two preferred convective modes: one aligned with the mean vertical wind-shear vector, accompanied by marked cross-band thermal contrast and deformation through a deep layer, and another oriented perpendicular to the low-level shear, which exhibited a shallow gust front and mesoscale cold pool as found in squall-line systems. Highly three-dimensional airflow within the mature MCC and a pronounced modulation of convective instability across an embedded frontal-like zone further promoted the storm's asymmetric precipitation pattern.

Abstract

A multiscale analysis reveals diverse atmospheric structure and processes within a mesoscale convective complex (MCC) observed during the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central (PRE-STORM) experiment. This midlatitude system was the second in a series of four MCCs that developed and traveled along a quasi-stationary frontal zone over the central United States on 3–4 June 1985. Objectively analyzed mesoscale upper-air soundings encompassing the MCC are interpreted in tandem with more detailed dual-Doppler radar measurements that disclose the storm's internal airflow and precipitation structure. The mature MCC is found to include a variety of local environments and associated weather, ranging from tornadic thunderstorms to more linear convective bands and widespread chilling rains. A corresponding spectrum of mesoscale ver6cW-motion profiles is documented. These findings are related to previous composite-based portrayals of MCCs, as well as detailed case studies of simpler squall-type convective systems.

A hallmark of this storm was its “open-wave” precipitation pattern, in which two convective bands intersected so as to resemble a miniature developing frontal cyclone. This resemblance proves superficial, however, since 1) anticyclonic lower-tropospheric flow was observed in place of the expected cyclonic circulation near the convective apex, and 2) the accompanying wavelike lower-tropospheric temperature pattern was strongly influenced by moist processes intrinsic to the MCC (e.g., evaporative cooling), as opposed to horizontal advection about a developing vortex. The storm's intriguing organization is instead postulated to have resulted from the superposition of two preferred convective modes: one aligned with the mean vertical wind-shear vector, accompanied by marked cross-band thermal contrast and deformation through a deep layer, and another oriented perpendicular to the low-level shear, which exhibited a shallow gust front and mesoscale cold pool as found in squall-line systems. Highly three-dimensional airflow within the mature MCC and a pronounced modulation of convective instability across an embedded frontal-like zone further promoted the storm's asymmetric precipitation pattern.

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