Observations and numerical simulations of the transition of a banded nocturnal MCS to a daytime squall line
S. B. Trier, NCAR, Boulder, CO; and J. H. Marsham
On 13 June 2002 a banded nocturnal mesoscale convective system (MCS) located over the southern Great Plains (SGP) of the United States evolved into a highly organized squall line near the beginning of the subsquent diurnal heating cycle. In the current study, numerical simulations are examined for mechanisms responsible for the "elevated" banded structure within the MCS and its subsequent reorganization into a squall line characterized by a single leading edge of large radar reflectivity oriented approximately perpendicular to the environmental low-level shear. Although not widely studied, this type of transition is believed to frequently occur in MCSs that are able to persist beyond sunrise over the SGP. One mechanism that could account for a such a reorganization is the development of a surface-based cold pool resulting from penetrative downdrafts (which are favored as the environmental PBL destabilizes during the morning) and its interaction with the vertical shear. However, the reorganization to a squall line commences while the air with greatest CAPE is located well above the surface. Moreover, sensitivity studies that exclude latent cooling processes exhibit a similar reorganization suggesting additional factors could be critical to the evolution of the observed MCS.
Session 2, Mesoscale Convective Systems: Initiation and Structure
Monday, 11 October 2010, 10:45 AM-12:00 PM, Grand Mesa Ballroom F
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