SMALL-SCALE STRUCTURE OF A COASTAL FRONT AS REVEALED BY DUAL-DOPPLER RADAR

The analysis of the rainband structure and wind fields associated with a coastal front along the North Carolina shoreline is described. Dual -Doppler radar and the augmented GALE (Genesis of Atlantic Lows Experi ment) ensemble of in situ stations depict shallow, convective rainband s that overtake the front from the warm-ah sector and intensify at the surface front location. Clockwise band rotation is shown to be caused by the difference in alignment between the echo motion and the rainba nd axes and by new development ahead of the front. Radar measurements depict the circulation systems associated with a portion of one rainba nd in the cold air ahead of the front. Here shallow precipitation core s are vertically tilted due to the frontal wind shear. Circulation cel ls and most precipitation cores are centered just above the frontal in version, as inferred by the wind shift line aloft. This feature is nea rly horizontal in the cross-frontal direction but slopes downward in a direction roughly parallel to the front. Ahead of the front main updr afts in and above the cold air are found near the upwind portion of pr ecipitation cores and along two well-defined lines aligned roughly per pendicular to the front. These lines propagate northward and affect se veral nearby surface sites prior to frontal passage. The speed of nort hward propagation is consistent with gravity wave theory, while on the larger scale the front appears to behave as the lending edge of a den sity current. The major features found in this case are compared and c ontrasted with those of a synoptic-scale warm front.