Extended Abstract (28K)2.2
Impact of adjustments in the Kain-Fritsch Convective Scheme on QPF of Elevated Convection
Christopher J. Anderson, Iowa State University, Ames, IA; and W. A. Gallus, R. W. Arritt, and J. S. Kain
Elevated convective systems in the central United States present a difficult QPF problem for mesoscale models. Often, episodes of elevated convection are missed altogether in model forecasts despite reasonably accurate predictions of wind and thermodynamic fields. In such cases it is reasonable to suspect that the deficiency may lie in the model's criteria for initiation of deep convection. Convective parameterization schemes in mesoscale models are often linked to boundary layer characteristics which may not be appropriate for convective initiation in elevated mixed layers.
We will report on modifications to the Kain-Fritsch convective parameterization scheme as it is implemented in the workstation Eta model. These modifications are tested in the Eta model QPF in simulations of elevated convective systems. At this time, three modifications are being investigated: one modification links the convective trigger function to turbulent vertical velocity in elevated mixed layers; another links the convective trigger function to lapse rates of layers adjacent to elevated nearly moist adiabatic layers; and the third relates parameterized downdraft mass flux to grid-resolved relative humidity and lapse rate. Results from case studies and from a quasi-operational implementation during the summer of 2002 will be discussed at the conference.
Session 2, Case Studies II
Monday, 12 August 2002, 1:30 PM-3:00 PM
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