Evaluation of Satellite-Derived Latent Heat Fluxes

Abstract

A method of determining ocean?atmosphere latent heat flux using the Special Sensor Microwave/Imager (SSM/I) and the Advanced Very High Resolution Radiometer (AVHRR) is presented and evaluated. While sea surface temperatures are retrieved from AVHRR data with an accuracy of 0.5?1.0 K, the near-surface wind speed and the surface air humidity are retrieved from measurements of the SSM/I with accuracies of 1.4 m s?1 and 1.1 g kg?1, respectively. The latent heat flux is then computed with a stability-dependent bulk parameterization model. The derived fluxes are compared to globally distributed instantaneous shipboard and buoy measurements and to monthly averages of 2° ? 2° longitude and latitude bins. The standard error for instantaneous flux estimates is approximately 30 W m?2, and that for monthly averages decreases to 15 W m?2. Additionally, a 1-yr time series of latent heat flux at the weathership M in the North Atlantic and two shorter time series during the Tropical Ocean Global Atmosphere Coupled Ocean?Atmosphere Response Experiment (TOGA COARE) and the Central Equatorial Pacific Experiment (CEPEX) in the tropical Pacific are compared to satellite measurements. The SSM/I-derived parameters, as well as the latent heat flux, are represented very well on the weathership M. During TOGA COARE and CEPEX, the near-surface humidity is sometimes systematically overestimated in the warm pool region, which results in an underestimation of the latent heat flux. Nevertheless, the representation of the latent heat flux is always in the range of the in situ measurements.