An explanation for intense frontal updrafts and narrow cold-frontal rainbands

Abstract

Measurements with Doppler radar, and instrumented aircraft and towers, have revealed that surface cold fronts often have cross-frontal circulations organized on a scale of a kilometer or less. These circulations include intense updrafts (1 to 20 m s-1) that result in a narrow band of heavy rainfall. We used a nonhydrostatic model to investigate the mechanism for these updrafts and to isolate those characteristics of the prefrontal environment that result in intense updrafts and narrow bands of heavy rainfall. The conditions for intense updrafts and heavy rainfall in our simulations were: 1) strong deep cold pools, 2) a prefrontal environment that contains deep layers of air that are nearly saturated with a lapse rate that is nearly neutral to moist ascent, and 3) intense low-level vertical shear in the cross-frontal component of the horizontal wind. -from Author