TOMS - Total Calibration Error

The Version 8 algorithm is now used for all TOMS data. For data beginning in year 2000, the calibration has been stabilized relative to NOAA-16 SBUV/2 in the equatorial zone. Because of continuing changes in the optical properties of the front scan mirror that are not well understood, we are now seeing a latitude dependent error that cannot be corrected by a simple calibration correction. The calibration appears to be stable near the equator. But by 50 degrees latitude, there is now a -2% to -4% error in TOMS, a bit larger in the northern hemisphere than in the southern hemisphere. Because of this error, data since 2002 should NOT be used for trend analysis.