UARS MLS Version 5 Data

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Announcement of UARS MLS Version 5 Data Availability

UARS MLS Version 5 data are now becoming available at the UARS CDHF.
The following UARS months are on the CDHF at time of writing this message (29 April 1999):

92_07
93_03
94_02
96_02

Barring unforeseen circumstances, processing of MLS V5 data for the entire UARS mission is expected to be completed by Oct-Nov 1999.

There are 9 atmospheric parameters produced by MLS Version 5 processing and put in L3AT/L3AL files (however, no L3AL files are produced for UTH - see below). These parameters, and the MLS scientist responsible for their validation, are:

temperature (TEMP) - D.L. Wu, dwu@mls.jpl.nasa.gov
O3 from 205 GHz (O3_205) - L. Froidevaux, lucien@mls.jpl.nasa.gov
O3 from 183 GHz (O3_183) - L. Froidevaux, lucien@mls.jpl.nasa.gov
stratospheric water vapor (H2O) - H.C. Pumphrey, hcp@met.ed.ac.uk
The H2O files also contain troposphere H2O mixing ratios at 147, 215, 316 and 464 hPa for which W.G. Read is responsible. However it should be emphasized that the tropospheric H2O and the stratospheric H2O in these files are from different radiometers, and that consistency between these two data sets in the region of the tropopause has not been achieved. The 'Level 2' ASCII file (described below) is recommended for upper trop H2O data because it contains more information for screening bad data points.
chlorine monoxide (ClO) - J.W. Waters, joe@mls.jpl.nasa.gov
nitric acid (HNO3) - M.L. Santee, mls@mls.jpl.nasa.gov
upper tropospheric humidity (UTH) - W.G. Read, bill@mls.jpl.nasa.gov
However, as mentioned above, the 'Level 2' ASCII file described below is recommended for UTH since it contains additional info for screening bad data.
methyl cyanide (CH3CN) - N.J. Livesey, livesey@mls.jpl.nasa.gov
geopotential height (GPH) - D.L. Wu, dwu@mls.jpl.nasa.gov

In addition to the Level 3 files for UTH (which give upper tropospheric humidity in terms of relative humidity with respect to ice at 147, 215, 315 and 464 hPa - using NCEP temperatures), a "Level 2" UTH ASCII file is available which gives the corresponding water vapor mixing ratios, NCEP temperatures, and other information useful for diagnosing the MLS UTH data. The header to the ASCII file contains information that should be sufficient for understanding its contents. Besides CH3CN and GPH, which are new products still being validated, the primary changes in MLS Version 5 data from earlier versions are:

retrieved values are produced at the full resolution of the UARS surfaces, six points per decade change in pressure, over most of the useful vertical range for each parameter,
improved treatment of coupled temperature and tangent point retrievals
refinements in spectroscopy and estimated instrument sideband responses for some bands,
iterative retrievals in some bands (also done in the previously released "V4.90" UTH data)

The main changes in retrieved geophysical parameters, from those in previous MLS Data Versions, are:

a generally wider range of pressures for reliable results
useful temperature data now extend into the mesosphere, but with a gap between ~0.46 and ~0.2 hPa where values are not reliable,
O3_205 data have better accuracy, particularly in the lower stratosphere - the biases in Version 4 have generally been removed,
ClO data are generally improved in the lower stratosphere, although there still may be some remaining biases at the ~0.1-0.2 ppbv abundance level,
HNO3 data are improved, and now cover the range from 100 to 10 hPa,
Stratospheric H2O data are now useful down to 68 hPa (100 hPa values given in the files are not reliable),
O3_183 data have more sensitivity in the lower stratosphere but the 68 hPa and 100 hPa values are not considered reliable at low latitudes (mainly 20S-20N) because of remaining systematic bias artifacts.

The major difference between the V5 UTH values and the previously-released V4.90 data is that empirical parameters in the V5 H2O continuum emission expressions are determined using coincident Vaisala sonde H2O profiles, whereas V4.90 assumed 100% relative humidity for certain situations where maximum radiances were used in deriving the empirical parameters. This leads to the V5 relative humidities being, on the average, lower than V4.90, by the follwoing amounts:

22% at 147 hPa
12% at 215 hPa
14% at 316 hPa
14% at 464 hPa

In addition to noting the caveats mentioned earlier in this message, and the single-profile estimated precisions included in the data files, screeening for bad data in the files should follow the same procedures as in previous MLS data versions:

only use data from records for which the corresponding MMAF_STAT (in the appropriate L3PT/L3PL files) equals "G", "T", or "t",
only use data where the estimated precision (in the L3AT/L3AL files) has a positive value,
only use data where the quality indicator (in the L3PT/L3PL files), e.g. "QUALITY_CLO", has value "4". The following additions apply to the new data products
use "QUALITY_CLO" as the quality indicator for CH3CN as it is from the same spectral band as ClO,
use "QUALITY_TEMP" (quality indicator for temperature) as the quality indicator for geopotential height. There may be additional screening for geopotential height that will be needed due to spacecraft attitude effects, but these have not been included in the data set and users of this product should keep in close communication with the MLS team in regards to potential bad data which are not indentified by our existing flags,
for UTH:
- clip all data at ~120% relative humidity to reduce the effects of clouds
- reject 316 hPa and 464 hPa values when "single_layer_rh" (a quantity given in the Level 2 ASCII file) minus the retrieved relative humidity value is greater than 5.0.

More information on remaining known systematic artifacts and details for each parameter will be discussed in a "Data Quality Document" to be prepared by the MLS team, and expected to be available in summer 1999. A publication describing the Version 5 data and its quality is also planned on a somewhat longer time scale.

Sulfur dioxide is not produced in Version 5 due to complications of the CH3CN retrieval, and Version 5 CH3CN values will be contaminated by Pinatubo SO2 for the period of ~Sep-Nov 1991, and the Lascar volcano SO2 for a local region over South America on 21 and 22 April 1993.

Temperature variances at gravity-wave scales have also been produced as a special product, but are not being produced as part of routine reprocessing. Contact Dong Wu (dwu@mls.jpl.nasa.gov) for information on these data.

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UARS MLS Version 5 Data

Announcement of UARS MLS Version 5 Data Availability

This page maintained by Joe Waters (joe@mls.jpl.nasa.gov). Last updated 29 April 1999.