Coupling between land-surface boundary-layer parameterization and rainfall on local and regional scales: lessons from the wet summer of 1993.

INTRODUCTION

In this paper we discuss the impact of the coupling between the land-surface, boundary-layer (BL) parameterizations and rainfall on two different time and space scales: a local diurnal timescale and a regional seasonal timescale. The catastrophic flooding in the continental mid-West of the US in the summer of 1993 focused our attention on the coupling between soil moisture and rainfall on long-time scales, just as Cycle 48 of the ECMWF model was implemented.

The development of cycle 48 of the ECMWF model was based extensively on the use of local test data-sets, including FIFE-1987 (Betts et al, 1993, Beljaars and Betts, 1992; Beljaars 1993). It included four predictive layers for soil moisture, as well as other changes discussed briefly below. We discovered a large sensitivity of monthly and seasonal precipitation over the US on initial soil moisture. Because of the profound importance of this on long-term rainfall prediction, we are presenting some preliminary results and a brief discussion of some of the feedbacks involved.

This research has been further stimulated by the planning needs of the GCIP and BOREAS field programs, which address respectively the interaction between the surface and atmosphere for the Mississippi basin, and a cross section of the Canadian boreal forest between Saskatchewan and Manitoba.

Further discussions and analysis are found in

Beljaars, A.C.M., P. Viterbo, M.J. Miller and A.K. Betts, 1996: The anomalous rainfall over the United States during July 1993: sensitivity to land surface parameterization and soil moisture anomalies. Mon. Wea. Rev., 124, 362-383.

Betts, A. K., J.H. Ball, A.C.M. Beljaars, M.J. Miller and P. Viterbo, 1996: The land-surface-atmosphere interaction: a review based on observational and global modeling perspectives. J. Geophys. Res. 101, 7209-7225.

Related Topics

• Boundary Layer,
• Climate,
• Convection