Pentad averages of HIRS channel 12 brightness temperatures and upper
tropospheric humidity estimates have been produced from January 1979 through
December 1995.  HIRS is an infrared water vapor sounder and channel 12 is
sensitive to moisture in the upper troposphere (~300 to 500 mb).

Anomalies of upper tropospheric water vapor produced from HIRS channel 12
brightness temperatures have been produced for a 16 year period. The resulting
anomalies are from cloud-cleared scenes. In regions with a moist upper
troposphere the weighting function for this channel peaks around 200-300 mb,
while for drying regions the peak moves down to around 300-400 mb. Details of
the retrieval and discussion of the 16 year climatology are given in references
listed below.

hm  -> HIRS channel 12 pentad brightness temperature composites
ha  -> HIRS channel 12 pentad brightness temperature anomalies
um  -> Pentad means of upper tropospheric humidity 

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HIRS   -> High-resolution Infrared Sounder

References:

Bates, J. J., X. Wu, and D. L. Jackson, 1996: Interannual variability of
  upper-tropospheric water vapor band brightness temperature, J. Climate,
  Vol 9, pp. 427-438. 

Wu, X., J. J. Bates, and S. J. S. Khalsa, 1993: A climatology of the water
  vapor band brightness temperatures from NOAA operational satellites, J.
  Climate, Vol 6, pp. 1282-1300