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UARS MLS Data

Overview

The primary MLS data products, which are produced in all versions of MLS data, are stratospheric profiles of:
  • ozone, O3
  • chlorine monoxide, ClO
  • water vapor, H2O
  • temperature


Additional data products that have been obtained from UARS MLS include:
  • Sulfur Dioxide, SO2, injected into the stratosphere by volcanic eruptions (Version 4 data only),
  • Lower Stratospheric Nitric Acid, HNO3, (Versions 4 and 5 data)
  • Upper Tropospheric Humidity, UTH, (Versions 4.9 and 5 data)
  • Methyl Cyanide, CH3CN, (Version 5 data only)
  • Geopotential Height, GPH, (Version 5 data only)
  • Temperature variances associated with atmospheric gravity wave activity. Contact Dr. Dong Wu, now at NASA Goddard Space Flight Center, for these data.


Users of MLS data are advised to study the MLS data validation papers appearing in the Journal of Geophysical Research special issue on Evaluation of the UARS data [vol. 101, No. D6, 30 April 1996]. Those papers described validation of the MLS Version 3 data, but contain useful general information on the MLS data products. A paper on validation of the upper tropospheric humidity is in preparation, and expected to be submitted to JGR around March 2000. A paper on validation of the MLS Version 5 data is planned to be submitted to JGR around fall 2000. The "quality documents", with links below, describe the expected quality of products in each version of the data.

The Version 5 data are publicly available through NASA Earthdata Search.


Data Collection and Usage

UARS MLS atmospheric observations started on 19 September 1991, within one week of launch. The MLS stratospheric H2O and mesospheric O3 measurements ceased in April 1993 due to failure of the 183 GHz radiometer after 18 months of excellent data had been obtained. After 2.3 years in orbit (in late December 1993) the antenna scanning mechanism, which had only a two-year design lifetime, began to exhibit signs of wear. At that time measurement coverage started to become more intermittent - exacerbated by problems with the UARS power system.

Starting 13 July 1997, in order to reduce power consumption after failure of UARS battery 1, MLS begin operating in a mode using only filter bank 2 ( which gives ClO, UTH, CH3CN and SO2) and filter bank 4 (which gives O3 and HNO3). Pointing information for this mode of operation is obtained from the O3 linewidth variation with atmospheric pressure, but useful measurements of atmospheric temperature are not produced. Tests have shown this mode of operation produces scientifically-useful data. Because of the special software required to produce data in this mode of operation, and due to the MLS team needing to ensure its pedigree, these data are temporarily being catalogued only at JPL, and will be placed on the UARS CDHF and GSFC DAAC starting with MLS Version 5. Version 4 data for this period can be obtained now by contacting the MLS team.

Problems with the MLS antenna scan intensified greatly after 29 June 1998, and a much more limited number of good profiles are obtained during each day of operation after that date. It was decided, in August 1999, to "mothball" MLS and save its remaining lifetime for overlapping measurements with the next-generation MLS instrument to be launched on the EOS CHEM satellite with operations scheduled to start in early 2003, or for attempting observations of "special events" before that time.

Anyone using MLS data for scientific purposes should be thoroughly familiar with the contents of the appropriate validation paper and with the "quality documents" produced for that version of the data, as well as the quality indicators and estimated uncertainties available electronically with the data. Data should be used for scientific analyses only if the quality indicators indicate it is acceptable to do so; the estimated uncertainties and documented known artifacts in the data should be considered before drawing scientific conclusions. The MLS team should be contacted if there are any questions on the data or their quality.


Documentation

See Livesey, et al., 'The UARS MLS version 5 dataset: Theory, characterization and validation,' JGR, 2003 for the best description of the MLS Version 5 data. You can also read a supplement to this paper for additional information. A daily calendar of MLS measurement coverage from 1991 through 1999 is given in an appendix of this paper.

  • Data quality document
  • Level 1 data from Version 4 were used to produce the Level 2 and Level 3 data for Version 5. No Version 5 Level 1 files are produced.
  • No Standard Formatted Data Unit (SFDU) documents were produced for MLS Version 5 data. The formats for the Level 3 files (L3AT, L3AL, L3PT, L3PL) are identical to those for Version 4, and the Version 4 SFDU documents listed below can be consulted, if needed. The Level 2 file for UTH, containing valuable UTH diagnostic information, is an ASCII file whose header contains sufficient information for understanding the contents of that file. Users wishing to examine the "overall" MLS Level 2 file (L2OUT), whose format has changed significantly in Version 5, should contact the MLS Science Team for information on its contents.