Polar Night Observations of O3, NO2, and NO3 by GOMOS on Envisat

GOMOS (Global Ozone Monitoring by Occultation of Stars) on ESA's Envisat-satellite measures transmission spectra of light through the Earth's limb using the stellar occultation method. From spectra it is possible to retrieve profiles of O3, NO2, NO3, H2O, O2, neutral density, and aerosols in the stratosphere and mesosphere. GOMOS has an UVIS spectrometer at 248-690 nm and two IR spectrometers at 750-776 nm and 916-956 nm. The spectrometers use 0.5 sec integration time, which provides 1.6 km or better vertical sampling resolution. Two photometers (1 KHz) record fast fluctuations of light (scintillations) caused by small-scale turbulence in the stratosphere. During 24 h GOMOS measures 300-500 occultations leading to a good global coverage. During the first three years of operation GOMOS has measured about 300 000 occultations. An extensive validation program has shown that ozone profiles agree well with various validating data. Using available GOMOS data it is now possible to build global nighttime profile distributions of some key constituents. GOMOS provides a unique view to the development of the ozone layer during the polar night. During the winter months in 2003 ozone was strongly depleted (compared to climatological values) over the southern and northern polar areas. The depletions were associated with strong increases of NO2. The development in the Arctic stratosphere was found to be linked with strong solar proton events in October-November 2003 (Seppälä et al., GRL, 2004 ) but no such an explanation was evident for the Antarctic case.