Cross comparisons of O3 and NO2 measured by the atmospheric ENVISAT instruments GOMOS, MIPAS, and SCIAMACHY

Abstract

Vertical profiles of O 3 and NO 2 abundances from the atmospheric instruments GOMOS (Global Ozone Monitoring by the Occultation of Stars), MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and SCIAMACHY (Scanning Imaging Spectrometer for Atmospheric Chartography) all on-board the recently launched European Space Agency (ESA) Environmental Satellite (ENVISAT) are intercompared. These comparisons contribute to the validation of these data products by detecting systematic deviations, for example, wrong tangent height determinations, spectroscopic errors, and others. The cross comparison includes GOMOS data products retrieved by the GOMOS prototype processor from ACRI (Sophia Antipolis, France), the scientific SCIAMACHY data products from the Institute of Environmental Physics at University of Bremen (IUP) and the scientific MIPAS data products from the Institute for Meteorology and Climate Research in Karlsruhe (IMK) and Institute of Astrophysics in Andalusia (IAA). Coincident measurements were identified by limiting the time difference to 100 min (duration of one orbit) and less than 500 km between two observation points. When lower stratospheric ozone is strongly depleted during polar spring, a homogeneity condition was further imposed on the satellite measurements by requiring an upper limit on the potential vorticity difference at the 475 K isentrope between both observations. Since geographically coincident NO 2 measurements of the three instruments are performed during different times of the day and NO 2 has a rather strong diurnal variability, matches of NO 2 profiles were compared only where the solar zenith angle difference was below 5°. First results of the cross comparison show an agreement within 15% between 21 and 40 km altitude for O 3 profiles and an agreement within 20% between 27 and 40 km altitude for NO 2 profiles among the GOMOS, MIPAS and SCIAMACHY measurements.

Validation of ozone measurements from the Atmospheric Chemistry Experiment (ACE)

“…Between 14 and 64 km, the differences were found to be 2.5-7.5% with GOMOS measuring less ozone than the comparison instrument. In comparisons with MIPAS and SCIAMACHY, the agreement for GOMOS dark limb profiles was −5% from 20-50 km and +1% from 20-40 km, respectively (Bracher et al, 2005). The level 2 data product used for these comparisons was version 6.0a.…”

Global ozone monitoring by occultation of stars: an overview of GOMOS measurements on ENVISAT

“…Water vapour plays an important role in the photo-chemistry, and in particular is the major scavenger of ozone (by HO x catalytic reaction cycle) at altitudes greater than 40 km (Brasseur and Solomon, 2005). The strongest absorption band of H 2 O in the silicon CCD domain is in the Near Infra Red (NIR), around 936 nm (Fig.…”

“…This conclusion was demonstrated to be independent of the star temperature and magnitude and the latitudinal region of the GOMOS observation, with the exception of a slightly larger bias in the polar regions at altitudes between 35 and 45 km. GOMOS, MIPAS and SCIAMACHY measurements of O 3 and NO 2 have been compared by Bracher et al (2005). In the mesosphere and lower thermosphere only satellite data are available for validation purposes.…”

“…Both gases participate in the NO x family, involved in a catalytic cycle that provides the major loss processes for odd oxygen (O 3 and O) in the stratosphere (Crutzen, 1971;Brasseur and Solomon, 2005). NO 2 has an extended absorption band in the visible, with conspicuous peaks at 430-450 nm (Fig.…”

“…The photochemical lifetimes of oxygen and hydrogen radicals in the mesosphere are only a few hours (Brasseur and Solomon, 2005), and the ozone concentration should reflect a rapid photochemical equilibrium. In spite of this relatively simple situation, there are some significant discrepancies between observations (relatively scarce before GOMOS) and the prediction of current modeling.…”