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Airflow and Precipitation Structure of Two Leading Stratiform Mesoscale Convective Systems Determined from Operational Datasets

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  • 1 Atmospheric Science Department, Colorado State University, Fort Collins, Colorado
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Abstract

An analysis of the airflow and precipitation structure of two leading stratiform (LS) mesoscale convective systems (MCSs) is presented. Leading stratiform systems are defined as linear MCSs that consist of a convective line with leading stratiform rain. Case studies of LS systems on 7 May 1997 and 30 April 2000 were conducted using the available operational datasets. Several of the features observed, though not all, appear as a mirror image of those seen in trailing stratiform (TS) mesoscale convective systems. Their horizontal reflectivity structure has similar aspects, with convective cells that are sometimes elongated and canted with respect to the convective line, a transition zone of lower reflectivity, and an area of enhanced stratiform rain. The 30 April case shows a leading mesolow that resembles a TS wake low, but its propagation characteristics (and presumably dynamics) differ. A descending leading inflow jet, the counterpart of a rear-inflow jet in a TS system, can be detected in both cases underneath a layer of strong ascending rear-to-front flow aloft.

A few features of these LS systems are distinctive from TS systems. Cells in the convective line appear to be more discontinuous, and are elongated more than those of a TS system, although more work is needed to quantify these distinctions. Rear-feeding from an elevated equivalent potential temperature maximum behind the system is a distinguishing feature of these LS MCSs, since TS MCSs are typically fed from the boundary layer. Unlike the rear-inflow jet in TS systems, neither case shows a reversal in the leading inflow jet as it descends to low levels near the convective line. Both cases exhibit front-to-rear storm-relative surface flow throughout the LS systems.

Finally, a conceptual model is presented that illustrates the structure observed in the two cases, based heavily on a single-Doppler radar analysis of 7 May 1997.

Current affiliation: Atmospheric Technology Division, National Center for Atmospheric Research, Boulder, Colorado

Corresponding author address: Crystalyne R. Pettet, ATD/NCAR, P.O. Box 3000, Boulder, CO 80307. Email: pettet@atd.ucar.edu

Abstract

An analysis of the airflow and precipitation structure of two leading stratiform (LS) mesoscale convective systems (MCSs) is presented. Leading stratiform systems are defined as linear MCSs that consist of a convective line with leading stratiform rain. Case studies of LS systems on 7 May 1997 and 30 April 2000 were conducted using the available operational datasets. Several of the features observed, though not all, appear as a mirror image of those seen in trailing stratiform (TS) mesoscale convective systems. Their horizontal reflectivity structure has similar aspects, with convective cells that are sometimes elongated and canted with respect to the convective line, a transition zone of lower reflectivity, and an area of enhanced stratiform rain. The 30 April case shows a leading mesolow that resembles a TS wake low, but its propagation characteristics (and presumably dynamics) differ. A descending leading inflow jet, the counterpart of a rear-inflow jet in a TS system, can be detected in both cases underneath a layer of strong ascending rear-to-front flow aloft.

A few features of these LS systems are distinctive from TS systems. Cells in the convective line appear to be more discontinuous, and are elongated more than those of a TS system, although more work is needed to quantify these distinctions. Rear-feeding from an elevated equivalent potential temperature maximum behind the system is a distinguishing feature of these LS MCSs, since TS MCSs are typically fed from the boundary layer. Unlike the rear-inflow jet in TS systems, neither case shows a reversal in the leading inflow jet as it descends to low levels near the convective line. Both cases exhibit front-to-rear storm-relative surface flow throughout the LS systems.

Finally, a conceptual model is presented that illustrates the structure observed in the two cases, based heavily on a single-Doppler radar analysis of 7 May 1997.

Current affiliation: Atmospheric Technology Division, National Center for Atmospheric Research, Boulder, Colorado

Corresponding author address: Crystalyne R. Pettet, ATD/NCAR, P.O. Box 3000, Boulder, CO 80307. Email: pettet@atd.ucar.edu

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