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EOS MLS Data Frequently Asked Questions

This page attempts to answer common inquiries from MLS data users. If you are not able to find an answer to your question here, please refer to the Data Quality Document or contact the MLS data team at

  1. Q: "My IDL software is having problems reading the MLS data I just received and tells me that the data file is not in HDF format. Is MLS data in HDF format?"

    A: "Yes, all MLS data is in HDF version 5 format -- Level 1 files are in standard HDF format and Level 2 files are in HDF-EOS format. Commonly, users are not using a version of IDL that is equipped to read the file. Please make sure that your version of IDL is able to read HDF version 5 format -- if you are using IDL, you should be using IDL Version 6.1 or higher."

  2. Q: "Why, when reading the temperature file do I have problems (only one 'height level' reported)."

    A: "You didn't ask to specifically read the swath named 'Temperature', and your software instead read the first swath in ASCII order: 'TPPressureWMO'. You should generally request a particular swath from the file (for the mixing ratio files, the first is usually the one you want (i.e., 'O3' rather than 'O3 column')."

  3. Q: "What is the significance of the cXX number (like MLS-Aura_L2GP-BrO_v01-51-c01_2005d281.he5) in MLS data filenames?"

    A: "The cXX numbers make reference to the processing attemps for that day's files. The standard and most common cycle number is c01. However, cycle number increment above c01 when the MLS-SIPS has failed to process the day's data on the first attempt, which can occur due to any number of reasons. Cycle numbers DO NOT indicate any problems with the data."

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