Validation of version-4.61 methane and nitrous oxide observed by MIPAS

Abstract

The ENVISAT validation programme for the atmospheric instruments MIPAS, SCIAMACHY and GOMOS is based on a number of balloon-borne, aircraft, satellite and ground-based correlative measurements. In particular the activities of validation scientists were coordinated by ESA within the ENVISAT Stratospheric Aircraft and Balloon Campaign or ESABC. As part of a series of similar papers on other species [this issue] and in parallel to the contribution of the individual validation teams, the present paper provides a synthesis of comparisons performed between MIPAS CH₄ and N₂O profiles produced by the current ESA operational software (Instrument Processing Facility version 4.61 or IPF v4.61, full resolution MIPAS data covering the period 9 July 2002 to 26 March 2004) and correlative measurements obtained from balloon and aircraft experiments as well as from satellite sensors or from ground-based instruments. In the middle stratosphere, no significant bias is observed between MIPAS and correlative measurements, and MIPAS is providing a very consistent and global picture of the distribution of CH₄ and N₂O in this region. In average, the MIPAS CH₄ values show a small positive bias in the lower stratosphere of about 5%. A similar situation is observed for N₂O with a positive bias of 4%. In the lower stratosphere/upper troposphere (UT/LS) the individual used MIPAS data version 4.61 still exhibits some unphysical oscillations in individual CH₄ and N₂O profiles caused by the processing algorithm (with almost no regularization). Taking these problems into account, the MIPAS CH₄ and N₂O profiles are behaving as expected from the internal error estimation of IPF v4.61 and the estimated errors of the correlative measurements.