AVHRR SST Calibration Problems (August 2000 to present) AVHRR SST appears to be too cool (0.2 - 0.8C depending on the time and location) compared to ship and buoy observations in parts of the equatorial regions and southern hemisphere. An in-depth analysis of AVHRR aerosol optical depths has revealed slightly enhanced aerosols over the global latitudinal band -5 to -10S, likely due to increased biomass burning over the period. These do not appear significant enough to be the sole cause of the AVHRR SST bias. During the past two months the calibration channel 3 on the NOAA-14 AVHRR (which is used in the NLSST equations) appears to be negatively effected by stray light occasionally contaminating the blackbody (probably due to the geometry of the satellite compared to the sun) over the tropical latitudes. This happened with NOAA-11 at the end of its lifetime as well. Although there is an "automatic" threshold fix in the processing stream to fix the drops in counts due to stray light, based on NOAA-11, it appears to be insufficient to correct our current negative SST offset (we are in "uncharted territory."). We will attempt to develop corrections for this negative offset, but they may have to be carried out manually for several months until NOAA-16 is producing our "new/improved" SSTs. We hope to go operational with NOAA-16 in December 2000. AES and SST Cal/Val Team October 17, 2000