Early calibration problems detected in TOMS Earth-Probe aerosol signal

TOMS ( version 8) ozone and aerosol data are analyzed in order to extract characteristic temporal patterns on a near global scale. A clear annual cycle of the global average for the ozone is apparent in the measured intervals (Nimbus-7: 1978 - 1993, Earth-Probe: 1996 - 2005), however a similar initial periodicity disappears for the aerosol index in the Earth-Probe records. A detailed spectral analysis revealed significant asymmetries in the Nimbus-7 aerosol signal for the two hemispheres, which is not present in Earth-Probe data. The available record from the Ozone Monitoring Instrument ( one and a half years) shows a return to the seasonal variability seen by Nimbus-7 in both hemispheres. This suggests that calibration difficulties of the Earth-Probe instrument started earlier than mid 2000, when it became apparent from many indications.