A comparative study of POAM II and electrochemical concentration cell ozonesonde measurements obtained over northern Europe

Ozone profiles measured by the Polar Ozone and Aerosol Measurement (FOAM II) instrument (version 5 retrievals) flown on the SPOT 3 spacecraft are compared with coincident electrochemical concentration cell (ECC) ozonesonde profiles at 11 stations over polar northern regions. The comparison study extends from December 1993 to March 1996 and contains about 500 coincidences. The satellite and ozonesonde profile coincidences are averaged separately for winter and nonwinter periods and for winter coincidences occurring inside and outside of the polar vortex. The mean differences versus altitude show a dependence on the latitude separation between the sondes and the FOAM II measurements. The best estimate of the biases between the FOAM II and the ECC ozone measurements is obtained after removal of the latitudinal gradient effect on the relative mean differences for the dynamically quiet nonwinter periods. The biases are negative at all altitudes indicating that the FOAM version 5 retrievals are low relative to the ECC sondes. The magnitude of this bias ranges from 2-3% near the lowest and highest altitudes of profile overlap (17 and 30 km) to 7.6% from 21 to 24 km, which is comparable to the evaluated errors of both instruments.