UARS MLS Version 5 (and 6) Level 3AT data roll ups

README file for NetCDF UARS MLS L3AT compilation March 2026 This file is a NetCDF repackaging of the Version 5 and 6 “Level 3AT” data from the Microwave Limb Sounder (MLS) instrument on NASA’s Upper Atmosphere Research Satellite (UARS). At the time of writing, the quasi-original (see below) data are available from the NASA Goddard Space Flight Center (GSFC) Data and Information Services Center (DISC). Level 3AT was a UARS cross-instrument standard for geophysical products along the instrument measurement track. As such, it is akin to “Level 2” data from more recent instruments, notably Aura MLS (for which the “Level 2 Geophysical Product”, L2GP, files are the direct equivalent). L3AT was by far the most widely used dataset from UARS MLS. Note that the original binary data formats were developed for VAX/VMS systems. Given the multiplicity of approaches for converting such files from the original VMS record-based structure to unix-style files, including issues such as changes in endianness etc., multiple second-generation translations of these data exist in various binary formats that mimic their original VMS-based storage. These new NetCDF files have been generated by the MLS team, drawing from local copies of translated files stored on the Aura MLS Science Computing Facility (SCF). These L3AT data products are described in detail in Livesey, N.J., W.G. Read, L. Froidevaux, J.W. Waters, H.C. Pumphrey, D.L. Wu, M.L. Santee, Z. Shippony, and R.F. Jarnot, "The UARS Microwave Limb Sounder version 5 dataset: Theory, characterization and validation," J. Geophys. Res. 108, D13, 4378, doi:10.1029/2002JD002273, 2003. The original ASCII-format documentation accompanying the UARS MLS Version 5 dataset (dated 21 January 2000) is included, unedited, as the “documentation” attribute in each of these new data files (along with this README). The coordinates and data fields in this NetCDF file are named and annotated in a manner that should make their meaning reasonably self-evident. Beyond the change from binary format to NetCDF, other key differences between the original data files and these new files relate to the file granularity and the storage of quality control information. The original data were stored in daily (midnight-to-midnight universal time) files, with separate files for each geophysical product each day. This NetCDF-based record consists of one file per product for the entire UARS mission. In the original scheme, quality control information (the MMAF_STAT and QUALITY_xxx fields discussed in the “documentation”) were stored in a separate L3TP (“Parameter file”), with one such file per day, giving information on many (but not all) products. In these new files, the “MMAF_STAT” flag is retained, while the “QUALITY_xxx” fields are simply named “quality” and placed in each product-specific file as an additional data array. See the “documentation” for interpretation of these flags.