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Frontal and Radar Refractivity Analyses of the Dryline on 11 June 2002 during IHOP

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  • 1 National Center for Atmospheric Research, * Boulder, Colorado
  • | 2 Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, California
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Abstract

An analysis of a dryline that did not initiate convection during the observational period is presented. The dryline was the weakest kinematic boundary observed during the International H2O Project (IHOP), but was associated with a large moisture gradient. Detailed dual-Doppler wind syntheses from an airborne Doppler radar were combined with radar refractivity measurements providing a rare opportunity to examine both the kinematic and moisture characteristics of this boundary. The radar thin line denotes the approximate kinematic position of the dryline and was quasi-linear on this day. In contrast, the moisture pattern across the dryline was more complex than was suggested by the characteristics of the thin line. Prominent in the horizontal plots was the presence of narrow (few kilometers wide) channels of moisture extending 15–20 km into the dry air mass. Past studies have suggested that echo thin lines observed in the clear air can be used as a proxy for delineating the moisture contrast across the dryline. In contrast, the “moisture extrusions” were present even though the thin line was quasi-linear and were located in weak-echo regions along the thin line. It is hypothesized that transverse rolls developed at an angle to the boundary layer winds and intersected the dryline. The kinematic airflow associated with these rolls could have protected the moist tongues from the eroding effect of the dry flow west of the dryline. The moisture extrusions appear to diminish with time as they mix with the surrounding dry air.

Corresponding author address: Roger M. Wakimoto, NCAR/EOL, P.O. Box 3000, Boulder, CO 80307. Email: wakimoto@ucar.edu

This article included in the International H2O Project (IHOP_2002) special collection.

Abstract

An analysis of a dryline that did not initiate convection during the observational period is presented. The dryline was the weakest kinematic boundary observed during the International H2O Project (IHOP), but was associated with a large moisture gradient. Detailed dual-Doppler wind syntheses from an airborne Doppler radar were combined with radar refractivity measurements providing a rare opportunity to examine both the kinematic and moisture characteristics of this boundary. The radar thin line denotes the approximate kinematic position of the dryline and was quasi-linear on this day. In contrast, the moisture pattern across the dryline was more complex than was suggested by the characteristics of the thin line. Prominent in the horizontal plots was the presence of narrow (few kilometers wide) channels of moisture extending 15–20 km into the dry air mass. Past studies have suggested that echo thin lines observed in the clear air can be used as a proxy for delineating the moisture contrast across the dryline. In contrast, the “moisture extrusions” were present even though the thin line was quasi-linear and were located in weak-echo regions along the thin line. It is hypothesized that transverse rolls developed at an angle to the boundary layer winds and intersected the dryline. The kinematic airflow associated with these rolls could have protected the moist tongues from the eroding effect of the dry flow west of the dryline. The moisture extrusions appear to diminish with time as they mix with the surrounding dry air.

Corresponding author address: Roger M. Wakimoto, NCAR/EOL, P.O. Box 3000, Boulder, CO 80307. Email: wakimoto@ucar.edu

This article included in the International H2O Project (IHOP_2002) special collection.

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