IMK/IAA MIPAS temperature retrieval version 8: nominal measurements

• Published in: Atmospheric measurement techniques 2021-06, Vol.14 (6), p.4111-4138
• Main Authors: Kiefer, Michael, von Clarmann, Thomas, Funke, Bernd, García-Comas, Maya, Glatthor, Norbert, Grabowski, Udo, Kellmann, Sylvia, Kleinert, Anne, Laeng, Alexandra, Linden, Andrea, López-Puertas, Manuel, Marsh, Daniel R, Stiller, Gabriele P
• Format: Article
• Language: English
• Subjects: Altitude; Analysis; Atmospheric models; Atmospheric sounding; Atmospheric temperature; Calibration; Carbon dioxide; Climate and population; Climate models; Constraints; Data; Error analysis; Fourier transforms; Information retrieval; Latitude; Line shape; Local thermodynamic equilibrium; Michelson interferometers; Mixing ratio; Noise; Noise measurement; Nonlinear systems; Nonlinearity; Numerical integration; Radiance; Radiative transfer; Resolution; Robustness (mathematics); Scaling; Sensors; Spectra; Spectral resolution; Spectroscopy; Stratopause; Summer; Systematic errors; Temperature differences; Temperature distribution; Temperature fields; Temperature gradients; Temperature profile; Temperature profiles; Thermodynamic equilibrium; Tropical climate; Uncertainty; Vertical profiles; Wave phase
• ISSN: 1867-8548; 1867-1381; 1867-8548
• DOI: 10.5194/amt-14-4111-2021

A new global set of atmospheric temperature profiles is retrieved from recalibrated radiance spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Changes with respect to previous data versions include a new radiometric calibration considering the time dependency of the detector nonlinearity and a more robust frequency calibration scheme. Temperature is retrieved using a smoothing constraint, while tangent altitude pointing information is constrained using optimal estimation. ECMWF ERA-Interim is used as a priori temperature below 43 km. Above, a priori data are based on data from the Whole Atmosphere Community Climate Model Version 4 (WACCM4). Bias-corrected fields from specified dynamics runs, sampled at the MIPAS times and locations, are used, blended with ERA-Interim between 43 and 53 km. Horizontal variability of temperature is considered by scaling an a priori 3D temperature field in the orbit plane in a way that the horizontal structure is provided by the a priori while the vertical structure comes from the measurements. Additional microwindows with better sensitivity at higher altitudes are used. The background continuum is jointly fitted with the target parameters up to 58 km altitude. The radiance offset correction is strongly regularized towards an empirically determined vertical offset profile. In order to avoid the propagation of uncertainties of O3 and H2O a priori assumptions, the abundances of these species are retrieved jointly with temperature. The retrieval is based on HITRAN 2016 spectroscopic data, with a few amendments. Temperature-adjusted climatologies of vibrational populations of CO2 states emitting in the 15 µm region are used in the radiative transfer modeling in order to account for non-local thermodynamic equilibrium. Numerical integration in the radiative transfer model is now performed at higher accuracy. The random component of the temperature uncertainty typically varies between 0.4 and 1 K, with occasional excursions up to 1.3 K above 60 km altitude. The leading sources of the random component of the temperature error are measurement noise, gain calibration uncertainty, spectral shift, and uncertain CO2 mixing ratios. The systematic error is caused by uncertainties in spectroscopic data and line shape uncertainties. It ranges from 0.2 K at 20 km altitude for northern midlatitude summer conditions to 2.3 K at 12 km for tropical conditions. The estimated total uncertainty amounts to va