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

• Main Authors: M. L. Santee, A. Lambert, L. Froidevaux, H. Fischer, T. Steck, M. Milz, S. Kellmann, A. Linden, U. Grabowski, N. Glatthor, B. Funke, T. von Clarmann, G. P. Stiller, M. Höpfner, S. Chauhan, M. Schwartz, W. G. Read, N. J. Livesey
• Format: Article
• Language: English
• Published: Copernicus Publications 2009-07-01
• Series: Atmospheric Measurement Techniques
• Online Access: http://www.atmos-meas-tech.net/2/337/2009/amt-2-337-2009.pdf
• ISSN: 1867-1381; 1867-8548

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 H₂O, 2.5 to 3 km for O₃, 3.5 km for HNO₃ and 3.5 to 2.5 km for N₂O has been achieved. The retrieved temperature, H₂O, O₃, HNO₃, N₂O, 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 ±4 K over the whole pressure and latitude range. Systematic, latitude-independent differences of −2 to −4 K (MIPAS-MLS) at 121 hPa are explained by previously observed biases in the MLS v2.2 temperature retrievals. Temperature differences of −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 H₂O are biased within ±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 ±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 O₃ vmr are higher than MLS by an average of 0.5 ppmv (10%). General agreement between MIPAS and MLS HNO₃ is within the range of −1.0 (−10%) to 1.0 ppbv (20%). MIPAS HNO₃ 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 (>50%). In general, MIPAS and MLS N₂O 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 N₂O data.