MIPAS reduced spectral resolution UTLS-1 mode measurements of temperature, O3, HNO3, N2O, H2O and relative humidity over ice: retrievals and comparison to MLS

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Chauhan, S. ; Höpfner, M. ; Stiller, G. P. ; Clarmann, T. ; Funke, B. ; Glatthor, N. ; Grabowski, U. ; Linden, A. ; Kellmann, S. ; Milz, M. ; Steck, T. ; Fischer, H. ; Froidevaux, L. ; Lambert, A. ; Santee, M. L. ; Schwartz, M. ; Read, W. G. ; Livesey, N. J. (2009)

During several periods since 2005 the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat has performed observations dedicated to the region of the upper troposphere/lower stratosphere (UTLS). For the duration of November/December 2005 global distributions of temperature and several trace gases from MIPAS UTLS-1 mode measurements have been retrieved using the IMK/IAA (Institut für Meteorologie und Klimaforschung/Instituto de Astrofísica de Andalucía) scientific processor. In the UTLS region a vertical resolution of 3 km for temperaure, 3 to 4 km for H<sub>2</sub>O, 2.5 to 3 km for O<sub>3</sub>, 3.5 km for HNO<sub>3</sub> and 3.5 to 2.5 km for N<sub>2</sub>O has been achieved. The retrieved temperature, H<sub>2</sub>O, O<sub>3</sub>, HNO<sub>3</sub>, N<sub>2</sub>O, and relative humidity over ice are intercompared with the Microwave Limb Sounder (MLS/Aura) v2.2 data in the pressure range 316 to 0.68 hPa, 316 to 0.68 hPa, 215 to 0.68 hPa, 215 to 3.16 hPa, 100 to 1 hPa and 316 to 10 hPa, respectively. In general, MIPAS and MLS temperatures are biased within &plusmn;4 K over the whole pressure and latitude range. Systematic, latitude-independent differences of &minus;2 to &minus;4 K (MIPAS-MLS) at 121 hPa are explained by previously observed biases in the MLS v2.2 temperature retrievals. Temperature differences of &minus;4 K up to 12 K above 10.0 hPa are present both in MIPAS and MLS with respect to ECMWF (European Centre for Medium-Range Weather Forecasts) and are likely due to deficiencies of the ECMWF analysis data. MIPAS and MLS stratospheric volume mixing ratios (vmr) of H<sub>2</sub>O are biased within &plusmn;1 ppmv, with indication of oscillations between 146 and 26 hPa in the MLS dataset. Tropical upper tropospheric values of relative humidity over ice measured by the two instruments differ by &plusmn;20% in the pressure range ~146 to 68 hPa. These differences are mainly caused by the MLS temperature biases. Ozone mixing ratios agree within 0.5 ppmv (10 to 20%) between 68 and 14 hPa. At pressures smaller than 10 hPa, MIPAS O<sub>3</sub> vmr are higher than MLS by an average of 0.5 ppmv (10%). General agreement between MIPAS and MLS HNO<sub>3</sub> is within the range of &minus;1.0 (&minus;10%) to 1.0 ppbv (20%). MIPAS HNO<sub>3</sub> is 1.0 ppbv (10%) higher compared to MLS between 46 hPa and 10 hPa over the Northern Hemisphere. Over the tropics at 31.6 hPa MLS shows a low bias of more than 1 ppbv (&gt;50%). In general, MIPAS and MLS N<sub>2</sub>O vmr agree within 20 to 40 ppbv (20 to 40%). Differences in the range between 100 to 21 hPa are attributed to a known 20% positive bias in MIPAS N<sub>2</sub>O data.
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