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The EOS MLS data describe a piecewise linear representation of vertical profiles of gas phase chemical abundances, temperature, and cloud ice density. The vertical coordinate is log10 (atmospheric pressure) with, typically, 6 breakpoints per decade pressure (. . ., 3.16, 2.15, 1.47, 1.00, 0.68, 0.46, 0.32 hPa, . . .). The vertical range of usefulness depends upon the specific data product and the data version. Some of the MLS observations are "noisy" in nature, with the consequence that negative values are reported - these should not be masked or ignored, as failure to include them (in the averages that are required of these data) will lead to an artificial positive bias.

It is essential that users of MLS data understand and apply the data quality and status indicators available in the data files. These are described, for each released version of MLS data, by MLS Data Quality Documents. These documents also describe the expected precision, resolution, and known artifacts of each product for that data version - and improvement priorities for future data versions. They are available for MLS Version 4.2 (v4.2) data at the MLS Data Documentation page.

The MLS team very strongly encourages users to contact us with any questions on the data and if you find features that seem unreasonable. Although we have done our best to produce a reasonably sound data set within one year of becoming operational, we have no misconceptions that all the data artifacts have been identified. Feedback from users is of great benefit for improving the quality of the next data version. We also welcome, and encourage, users to just inform us that you are using MLS data. By knowing who you are, we can contact you with new data issues as we find them (the MLS team inspects all daily data, and reviews the findings on a weekly basis). Contacts can be made via e-mail to or to the individual(s) listed in the table below.

** MLS FTP Server Shutdown ** The MLS FTP server is scheduled to be shutdown on June 29, 2018. Data availalbe on that server will now be availalbe through HTTPS. The links to these data products have been updated on their appropriate pages under "Special Products" in the navigation to the left. If you have any qustions, please contact the MLS team.

MLS v4.2 data are available from the NASA Goddard Space Flight Center Earth Sciences (GES) Data and Information Services Center (DISC). The following data resources are available at the MLS website:

The v4.2 standard data products and the status, useful vertical range and MLS contact person for each product is given in the following table. All product data files also contain values for the column above the tropopause determined from MLS temperature using the WMO tropopause definition. The temperature file also contains the inferred tropopause pressure.

EOS MLS Version 4.2 Data
(Products with a * require significant averaging over most
or all of their vertical range in order to obtain a useful signal-to-noise ratio.)
product useful vertical range / hPa MLS contact
*BrO 10 - 3.2 Luis Millan Valle
*CH3Cl 147 - 4.6 Michelle Santee
*CH3CN 46 - 1.0 Michelle Santee
CH3OH Not to be used pending further validation Michelle Santee
ClO 147 - 1.0 Michelle Santee
CO 100 - 0.0046
215 - 146
troposhpere: Michael Schwartz
stratosphere / mesosphere: Hugh Pumphrey
geopotential height 83 - 0.001
261 - 100
Michael Schwartz
H2O 83 - 0.002
316 - 100
troposphere: Bill Read
stratosphere / mesosphere: Alyn Lambert
HCl 100 - 0.32 Lucien Froidevaux
*HCN 21 - 0.1 Hugh Pumphrey
HNO3 215 - 1.5 Gloria Manney
*HO2 22 - 0.046 Luis Millan Valle
*HOCl 10 - 2.2 Lucien Froidevaux
Ice water content 215 - 83 Alyn Lambert
Ice water path N/A Alyn Lambert
N2O 68 - 0.46 Alyn Lambert
O3 100 - 0.02
261 - 121
troposphere: Michael Schwartz
stratosphere / mesosphere: Lucien Froidevaux
OH 32 - 0.0032 Luis Millan Valle
Relative Humidity 316 - 0.002 Bill Read
SO2 215 - 10 Bill Read
Temperature 83 - 0.001
261 - 100
Michael Schwartz

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