Relating remotely‐sensed vegetation and soil moisture indices to surface energy fluxes in vicinity of an atmospheric dryline

Abstract

A physical‐statistical method for optimal estimation of daily surface heat flux and Bowen ratio on the mesoscale is applied to a portion of the US southern Great Plains, where a strong surface/atmosphere moisture gradient (dryline) was present. The method, previously tested over the central US, is based on observations of daytime planetary boundary layer (PBL) growth from the operational rawinsonde network and diurnal land‐surface temperature amplitude measured from geostationary (GOES) satellite. The mesoscale patterns of these heat fluxes are compared with an AVHRR based vegetation index and a surface‐based antecedent precipitation index. The derived heat flux is found to decrease by nearly an order of magnitude with the transition from prairie to forest eastward across Oklahoma. A subtle maximum in heat flux in the Texas panhandle is observed upwind of an eastward bulge in the dryline where enhanced downward mixing of dry air was occurring. Relationships for surface heat flux are formulated in terms of the vegetation and antecedent precipitation indices using: (1) a simple polynomial, and (2) a physical approach where soil moisture and partitioning of fluxes between bare soil and canopy are considered.