Model Validation of Observed Secondary Circulation in FIFE-1989 IFC-5 Dataset Using Coupled Mesoscale-SVATS Modeling System

A 2-part observational study of an extended secondary circulation throughout the late summer intensive field campaign (IFC-5) of the FIFE-1989 field experiment documented a persistent boundary layer secondary circulation; see Smith et al. (1994) and Wai and Smith (1998). This circulation feature was thought to be maintained by relatively large surface gradients of vegetation and soil moisture, created by antecedent rainfall conditions. Somewhat surprising was the persistence of the circulation through a sequence of weak to strong synoptic events that disturbed but did not destroy the overall vertical structure of the circulation. Various questions concerning the horizontal scale over which the circulation developed and to what degree organized surface heating gradients must be maintained to drive the circulation could not be answered in the observational analysis because of the limited domain over which the FIFE datasets were taken.

This study extends the observational work by simulating the circulation using a high resolution, nested, non-hydrostatic mesoscale model coupled to a detailed SVATS model. Model results to be discussed focus on the horizontal scales over which significant gradients of vegetation-soil moisture induce and maintain the circulation consistent with what was observed from the 1989 dataset, and what particular features of cloudiness arise as the surface forcing is modulated. The issue of cloudiness was not well-addressed in the observational studies given the nature of the FIFE observations).

Smith, E.A., M.M.-K. Wai, H.J. Cooper, M.T. Rubes, and A. Hsu, 1994: Linking boundary circulations and surface processes during FIFE 89. Part 1: Observational analysis. J. Atmos. Sci., 51, 1497-1529.

Wai, M.M.-K., and E.A. Smith, 1998: Linking boundary circulations and surface processes during FIFE 89. Part 2: Maintenance of secondary circulation. J. Atmos. Sci., 55, 1260-1276.