Session 16A.3 (To be presented at 9:00 am) High resolution observations of a cold front on 10 June 2002

Friday, 8 October 2004: 8:30 AM
Nettie R. Arnott, Penn State University, University Park, PA; and Y. P. Richardson and J. Wurman

Presentation PDF (2.0 MB)

The fine scale structure and evolution of a cold front are examined using over-determined dual-Doppler syntheses of mobile radar data collected on 10 June 2002 during the International H2O project (IHOP). Linear reflectivity maxima, which may be horizontal convective rolls or gravity waves, and open cellular convection intersect the cold front, causing spatial variations in convergence along the front. Small scale vertical vorticity maxima (misocyclones) often are coincident with these intersections and are associated with vertical velocity maxima.

During the deployment, trajectory analysis indicates that parcels entering the frontal circulation have a strong horizontal along-front component of motion. Upward motion, however, is nearly continuous spatially along the front during the first hour of the deployment. Because of this, parcels remain in regions of upward motion as they advect along the front, and many eventually ascend to cloud base. Parcels in vertical velocity maxima associated with misocyclones, however, ascend nearly vertically, not with a significant along-front component. A line of cumulus congestus developed along the cold front and appeared promising for convection initiation.

During the second hour of the deployment, however, misocyclones caused large kinks in radar reflectivity and fractures in upward motion. Except for those parcels remaining in the vertical velocity maxima associated with misocyclones, most parcels did not dwell long enough in the fractured upward motion to ascend to the top of the multi-Doppler domain. Furthermore, parcels may encounter downward motion, and thus descend, as they advect along the front. Simultaneously, enhanced warming behind the cold front observed by aircraft and ground based mobile mesonet probes indicates a weakening of the cold front. As a result of the fracturing in upward motion and weakening of the cold front, the cumulus clouds become more scattered.

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