The Microwave Limb Sounder (MLS) Level 3AT data product consists of daily, 65.536 second interval time-ordered vertical profiles of temperature, geopotential height, concentrations of O3, H2O, CH3CN, ClO, HNO3, and SO2, as well as upper tropospheric humidity (UTH). The insrument measures in the microwave spectral region at frequencies of 63, 183 and 205 GHz. MLS was flown on NASA's Upper Atmosphere Research Satellite (UARS) and designed to measure the chemical composition of the stratosphere and mesosphere, relationship between chlorine monoxide and ozone destruction. Limb measurements were made in the altitude range between 10 and 85 km at about 2.5 km resolution. Data were collected between latitude 34S and 80N and 80S and 34N, alternating each satellite yaw cycle of about 36 days. The MLS Level 3AT data were processed with the version 5 algorithm, except H2O which is version 6, and SO2 and UTH which are version 4.

Note: H2O and O3 at 183 GHz data are available only through April 15, 1993 when
the 183 GHz radiometer failed.

The MLS level 3AT product consists of 10 granules per day. A data granule is one MLS species or subtype per day.  The following subtypes are available:


 1) CH3CN - methyl cyanide            [vmr]
 2) CLO - chlorine monoxide           [vmr]
 3) H2O - water vapor                 [vmr]
 4) HNO3 - nitric acid                [vmr]
 5) O3_183 - ozone at 183 GHz         [vmr]
 6) O3_205 - ozone at 205 GHz         [vmr]
 7) SO2 - sulfur dioxide              [vmr]
 8) GPH - geopotential height         [m]
 9) TEMP - atmospheric temperature    [Kelvin]
10) UTH - upper tropospheric humidity [%]

*vmr = volume mixing ratio

MLS data are on the UARS standard pressure levels (in mbars) given by:

P(i) =  1000 * 10**(-i/6)  for i = 0, 1, 2, ...

Each of the 10 MLS granules is accompanied by an additional parameter file, designated as level 3TP.  The parameter file, contains the additional ancillary and quality information, as well as total column amounts not found in the 3AT files. The data files are available in a binary record oriented format.