MMM SEMINAR NCAR
"Convective initiation
ahead of the sea-breeze front"
Robert Fovell
UCLA Atmospheric and Oceanic Sciences
A 3D cloud-resolving model is used to explore the interaction between the sea-breeze circulation (SBC) and horizontal convective rolls (HCRs) leading to deep convection. Specifically, a case in which deep convection is spawned above a roll updraft aligned parallel to the sea-breeze front (SBF) is examined. The convection was initiated ahead of the SBF as the front approached, well before the inevitable roll merger. Ostensibly, both the sea-breeze and roll circulations were required for deep convection to be present in this case at all because convection was entirely absent when either phenomenon was removed.
Analysis reveals that the SBC itself was responsible for making the environment into which it was propagating more favorable through gentle yet persistent lifting. The rolls that formed within this environment provided the missing spark responsible for deep convection through their own direct and indirect effects upon their surroundings. The latter consists of vertical moisture advection and the generation of obstacle effect gravity waves.
Once established, deep convection above the roll updraft modulated cloudiness above the approaching SBF, at first suppressing it but subsequently assuring its reestablishment and eventual growth into deep convection, again prior to the front-roll merger. This resulted from the influence of gravity waves excited owing to heating and cooling within the roll cloud.
Thursday, 9 September 2004, 3:30 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane