Large-scale characteristics of the 1993 United States midwestern great flood and its simulation by the MM5 mesoscale model

Abstract

The record-breaking flood of 1993 provides an excellent opportunity to address many issues to the interest of GCIP-Mississippi: the large-scale characteristics of the hydrometeorology, the predictability of ECMWF model, and the sensitivity of mesoscale simulation. The effects of meridional and zonal vapor transport on precipitation production have been examined in the observation as well as in the ECMWF/TOGA and ERA data. Components of atmospheric and terrestrial water balance were compared. Cloud water change/flux activity, convection feature, diurnal variation, and land-atmospheric interaction were investigated, and intercompared among the three data sets. The intercomparison has demonstrated partial improvement from TOGA to ERA. It also indicates possible internal inconsistencies in the ERA, the ability and inability of simulating large-scale or mean fields and fine-scale extremes. It reveals the impacts of the new soil hydrology and boundary layer schemes in ERA in warmer and winter times, and the possible influence on surface hydrology. A 9.5-day (28 June to 7 July 1993) simulation study by the Penn State/NCAR MM5 mesoscale model, with the help of enhanced IR images from GOES satellite data was carried out. The sensitivity of MCS simulations to different cumulus parameterization schemes and explicit moisture schemes was investigated. The model is considerably skillful in the environmental steering wind direction, but greatly limited in the orthogonal direction. The model could not reproduce the "last-hour" rain--an extraordinary MCC, indicating that the model lacks representation of the mechanisms responsible for modifying the environmental controls on the evolution of long-lived MCSs, particularly after the system reaches its maximum extent.