CONVECTIVE SCALE INTERACTION: ARC CLOUD LINES AND THE DEVELOPMENT AND EVOLUTION OF DEEP CONVECTION (SATELLITE METEOROLOGY, THUNDERSTORMS)

Information from satellite data and research aircraft data are used to provide new understanding concerning the mesoscale development and evolution of deep convection in an atmosphere typified by weak synoptic-scale forcing. The major topic covered is the importance of convective scale interaction in the development and evolution of deep convection. This interaction is shown to manifest itself as the merger and intersection of thunderstorm outflow boundaries (arc cloud lines) with other convective lines, areas or boundaries.; Using geostationary satellite visible and infrared data convective scale interaction is shown to be responsible for over 85% of the intense convection (colder than -42(DEGREES)C) over the southeast United States by late afternoon (6 pm local), and an overwhelming majority of that area's afternoon rainfall.; Using satellite image and sounding data, as well as research aircraft information, it is shown how variations in a local environment's ability to support strong convection may be determined. Using this information, coupled with information about the arc cloud line's life cycle, four distinct properties of convective scale interaction are analyzed. (1) Thunderstorm outflow boundaries may maintain their identity as arc cloud lines for several hours after they have moved away from their parent source. (2) The arc cloud line outflow boundary can, and often does, cause deep convection to develop along it at distances well over 150 km from its point of generation. (3) Deep convective development along an outflow boundary is a selective process--it only occurs where the arc cloud line merges with a cumulus region or intersects another boundary. When the arc cloud line moves into clear skies no deep convection develops. (4) As the cumulus regime evolves on a given day, and much of the cumulus field dies away, the majority of new thunderstorms are confined to arc cloud line intersection points.