Version 8 IMK/IAA MIPAS measurements of CH4: Dataset

General The data set contains global distributions of methane (CH4) in the middle atmosphere (approx. 10-100 km altitude), covering the time period from July 2002 to April 2012, which were retrieved from infrared limb emission spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European Space Agency satellite platform Envisat. This data set comprises results of the retrieval of CH4 volume mixing ratios (VMRs) from MIPAS infrared spectra with the level-2 research data processor developed and operated by the Karlsruhe Institute of Technology's Institute of Meteorology and Climate Research (KIT-IMK, Karlsruhe, Germany) in cooperation with the Institute de Astrofísica de Andalucía (IAA-CSIC, Granada, Spain). A thorough description of the data set can be found in https://doi.org/10.5194/amt-17-2849-2024. Data representation The data are vertical profiles of CH4 volume mixing ratios. There are two representations of these profiles: CH4 and corresponding pressure and temperature profiles are given on a fixed altitude grid. The altitude grid width is less than the vertical resolution. Hence, for comparison with other data sets, the proper application of the respective averaging kernels is mandatory. These kernel matrices are available as a separate data set. CH4 values are given on a fixed pressure grid and, additionally, as layer-means. The pressure grid is chosen such that application of averaging kernels is not necessary (so-called "coarse grid representation", marked with "cg" in the file names). File names and contents The archive file names are MIPAS-E_IMK.<YYYY>.<CitationVersion>[OptionalCoarseGridSpecifier].tgz, with: <YYYY> are four digits representing the year <CitationVersion> is a string of the form V8<SpecResIndicator>_CH4_<Baseline>, where <SpecResIndicator> is either "H" (high spectral resolution measurement period of MIPAS, 2002-2004) or "R" (reduced spectral resolution measurement period of MIPAS, 2004-2012). <Baseline> refers to the version of the retrieval setup and is a number with two (for the V8H period) or three digits (for the V8R period). In the latter case, the first of the three digits indicates the MIPAS measurement mode: 1 upper troposphere - lower stratosphere mode, altitude range ~5 to 50 km 2 nominal mode, altitude range ~7 to 70 km 5 middle atmosphere mode, altitude range ~18 to ~102 km 6 upper atmosphere mode, altitude range ~40 to ~115 km 7 noctilucent cloud mode, altitude range ~37 to ~105 For the V8H period only nominal measurement mode data is available (~7 to 70 km). There are two different middle atmosphere datasets for each year, marked by the baseline numbers 561 and 562. The dataset 561 is designed for compatibility with the 161 and 261 datasets, while 562 is optimized for combination with 662 and 762 datasets. The OptionalCoarseGridSpecifier is "cg". Its presence indicates, that the file contains the coarse grid representation of the data (see above section Data representation, No.2) In publications which use a part of this data set, the full <CitationVersion> string shall be used to identify the used MIPAS data set (e.g., "V8R_CH4_161cg"). Each of the archive data files contains a set of monthly NetCDF data files with the naming conventions just as for the archive files, except that the year string is changed to a year+month string <YYYYMM>. E.g., MIPAS-E_IMK.2009.V8R_CH4_261.tgz contains MIPAS-E_IMK.200901.V8R_CH4_261.nc, MIPAS-E_IMK.200902.V8R_CH4_261.nc, MIPAS-E_IMK.200903.V8R_CH4_261.nc, etc. Important note: The vertical range of valid/meaningful CH4 VMRs is generally different from profile to profile. For the data representation on the coarse pressure grid/layer the invalid data values are already set to NaN. For the fixed altitude grid data the data user has to calculate the valid altitude range for each vertical profile individually, by combining the information given by the global attributes "use_data_only_in_altitude_range" and "restrict_altitude_range": the greater of the corresponding two lower and the lesser of the corresponding two upper values define the actual validity altitude boundaries.