Abstract
Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared limb emission spectrometer on the Envisat platform. From 2002 to 2012, it performed pole-to-pole measurements during day and night, producing more than 1000 profiles per day. The European Space Agency (ESA) recently released the new version 7 of Level 1B MIPAS spectra, in which a new set of time-dependent correction coefficients for the nonlinearity in the detector response functions was implemented. This change is expected to reduce the long-term drift of the MIPAS Level 2 data. We evaluate the long-term stability of ozone Level 2 data retrieved from MIPAS v7 Level 1B spectra with the IMK/IAA scientific level 2 processor. For this, we compare MIPAS data with ozone measurements from the Microwave Limb Sounder (MLS) instrument on NASA's Aura satellite, ozonesondes and ground-based lidar instruments. The ozonesondes and lidars alone do not allow us to conclude with enough significance that the new version is more stable than the previous one, but a clear improvement in long-term stability is observed in the satellite-data-based drift analysis. The results of ozonesondes, lidars and satellite drift analysis are consistent: all indicate that the drifts of the new version are less negative/more positive nearly everywhere above 15 km. The 10-year MIPAS ozone trends calculated from the old and the new data versions are compared. The new trends are closer to old drift-corrected trends than the old uncorrected trends were. From this, we conclude that the nonlinearity correction performed on Level 1B data is an improvement. These results indicate that MIPAS data are now even more suited for trend studies, alone or as part of a merged data record.
Highlights
The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared (IR) limb emission spectrometer onboard the Envisat platform
The vertical resolution derived from the full-width at half maximum (FWHM) of rows of the averaging kernel matrix for the old and the new versions is shown in Fig. 4: it varies between 2 and 3 km in the troposphere, varies between 3 and 5 km in the stratosphere, and goes up to 5 km at 50–65 km altitudes
Around 35 km, the new version demonstrates an improvement with respect to ACE-FTS for which the bias is reduced from 2 % to almost 0 %
Summary
The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) was an infrared (IR) limb emission spectrometer onboard the Envisat platform. Laeng et al.: On the improved stability of the version 7 MIPAS ozone record spectra (von Clarmann et al, 2003) Another major improvement is the implementation of a new set of time-dependent correction coefficients for the nonlinearity (NL) in the detector response functions. The correction coefficients were taken from preflight studies and were not time dependent, but the instrument is aging and the detector response function is changing (Eckert et al, 2014) This improvement of the Level 1B spectra is expected to have a major impact on MIPAS Level 2 data, by reducing the instrument drift. In addition to each target species, microwindow-dependent continuum radiation profiles and microwindow-dependent, but height-independent, zero-level calibration corrections are jointly fitted
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