Land surface heterogeneity in 3-dimensional atmospheric simulations.

Also issued as thesis (Ph. D.)--University of Michigan, 1995.

Includes bibliographical references (p. 142-147).

A stand-alone, vectorized version of the Biosphere-Atmosphere Transfer Scheme (VBATS) and a regional climate model (ReGCM2) are used to study the effects of subgrid scale heterogeneity in land surface processes on large scale mean surface fluxes and on mesoscale dynamics, respectively. First, an explicit method (VBATS), which allows for multiple heterogeneities in surface characterization and hydrology, is developed. VBATS is employed to assess the sensitivity of mean large scale (i.e., a Global Climate Model, CGM, grid cell of 300 Km) surface fluxes of latent and sensible heat, and momentum to subgrid scale heterogeneity in land-cover, precipitation and elevation. It is found that the partitioning of energy can be affected by up to 30%, runoff by 50%, and surface stress in excess of 60%. When precipitation is explicitly distributed to the subgrid cells, the Bowen ratio and runoff both increase. An experiment which combines the subgrid scale effects of land-cover, precipitation, and elevation is performed to demonstrate the potential of this method. The second part of this work employs the ReGCM2 at high resolution (10 Km), to study the development of the "inland breeze", which is an atmospheric dynamical response to contrasts in surface thermal forcing. Realistic large scale atmospheric forcing and prescribed surface thermal contrasts are employed in the ReGCM2 during a pair of one month simulations of June 1990. Control and perturbation experiments, wherein homogeneous and heterogeneous land-cover and moisture are specified, are used to isolate the dynamical signal resulting from surface forcing. Inland breezes having strength similar to the land-sea breeze occur on three days during the 30 day integration. The diurnal development of circulations are found to be consistent with previous results. While the mean strength of circulations and vertical transport of heat for the simulated month is not large, the vertical transport of moisture can be important and the dynamics appear to affect large scale precipitation. An 8% increase in precipitation is found downwind from the region of strong upwelling portion of the coherent circulations. A discussion of the forcings and feedbacks between the surface and the large scale atmospheric conditions, which relate to the formation of coherent circulations is presented.