Geophysical validation of temperature retrieved by the ESA processor from MIPAS/ENVISAT atmospheric limb-emission measurements

Abstract

Abstract. The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) has been operating since March 2002 onboard of the ENVIronmental SATellite of the European Space Agency (ESA). The high resolution (0.035 cm −1 full width half maximum, unapodized) limb-emission measurements acquired by MIPAS in the first two years of operation have very good geographical and temporal coverage and have been re-processed by ESA with the most recent versions (4.61 and 4.62) of the inversion algorithms. The products of this processing chain are pressures at the tangent points and geolocated profiles of temperature and of the volume mixing ratios of six key atmospheric constituents: H 2 O, O 3 , HNO 3 , CH 4 , N 2 O and NO 2 . As for all the measurements made with innovative instruments and techniques, this data set requires a thorough validation. In this paper we present a geophysical validation of the temperature profiles derived from MIPAS measurements by the ESA retrieval algorithm. The validation is carried-out by comparing MIPAS temperature with Correspondence to: M.Ridolfi (Marco.Ridolfi@unibo.it) correlative measurements made by radiosondes, lidars, insitu and remote sensors operated either from the ground or stratospheric balloons.The results of the intercomparison indicate that the bias of the MIPAS profiles is generally smaller than 1 or 2 K depending on altitude. Furthermore we find that, especially at the edges of the altitude range covered by the MIPAS scan, the random error estimated from the intercomparison is larger (typically by a factor of two to three) than the corresponding estimate derived on the basis of error propagation.In this work we also characterize the discrepancies between MIPAS temperature and the temperature fields resulting from the analyses of the European Centre for Mediumrange Weather Forecasts (ECMWF). The bias and the standard deviation of these discrepancies are consistent with those obtained when comparing MIPAS to correlative measurements; however, in this case the detected bias has a peculiar behavior as a function of altitude. This behavior is very similar to that observed in previous studies and is suspected to be due to vertical oscillations in the ECMWF temperature.Published by Copernicus Publications on behalf of the European Geosciences Union. M.Ridolfi et al.: MIPAS temperature validationThe current understanding is that, at least in the upper stratosphere (above ≈10 hPa), these oscillations are caused by a discrepancy between model biases and biases of assimilated radiances from primarily nadir sounders.

Analysis of SAGE II ozone of the middle and upper stratosphere for its response to a decadal-scale forcing

“…The top SSU channel covers a rather broad atmospheric region and its weighting function is centered at about 1.5 hPa, while that of AMSU-A is narrower and centered at about 2.5 hPa. Several recent, middle atmosphere temperature validation studies have indicated that the operational temperatures are too warm above 45 km and by as much as 5 to 10 K in the lower mesosphere at the low latitudes (Ridolfi et al, 2007;Gille et al, 2008;Masiello et al, 2010). It is suspected that there is also a warm bias for the SAGE II temperatures, especially after mid-2001.…”

Technical Note: Intercomparison of ILAS-II version 2 and 1.4 trace species with MIPAS-B measurements

“…Besides a high performance and flexibility of the pointing system the suitability of MIPAS-B to validate instruments like ILAS-II is based mainly on its high spectral resolution (about 0.07 cm −1 after apodization) allowing the separation of individual spectral lines from continuum-like emissions in combination with a high radiometric accuracy. A comprehensive overview and description of the instrument is given by Friedl-Vallon et al (2004) Cortesi et al, 2007;Höpfner et al, 2007;Ridolfi et al, 2007;Wang et al, 2007;Wetzel et al, 2007). The flight duration of more than 15 h from 18:22 UTC (20 March) to 09:38 UTC (21 March) also permitted a good match of the sunrise measurement of the ILAS-II sensor aboard ADEOS-II.…”

MIPAS: an instrument for atmospheric and climate research

“…The bias and the standard deviation of these discrepancies are consistent with those obtained when comparing MIPAS data to correlative measurements; however, the detected bias to ECMWF data has a peculiar altitude dependence. But this seems to be a problem of the ECMWF temperature distribution (see Ridolfi et al, 2007).…”