Forrest M. Mimms III, who has provided us with insightful, critically important information on atmospheric water vapor; see
has published a new paper with Lin Chambers and David Brooks:
Forrest M. Mims III,Lin Hartung Chambers, and David R. Brooks, 2011: Measuring Total Column Water Vapor by Pointing an Infrared Thermometer at the Sky. Bulletin of the American Meteorological Society 2011 ; doi: 10.1175/2011BAMS3215.1
The abstract reads
A 2-year study affirms that the temperature indicated by an inexpensive ($20 to $60) IR thermometer pointed at the cloud-free zenith sky (Tz) is a proxy for total column water vapor (precipitable water or PW). Tz was measured at or near solar noon, and occasionally at night, from 8 September 2008 to 18 October 2010 at a field in South-Central Texas. PW was measured by a MICROTOPS II sun photometer. The coefficient of correlation (r2) of PW and Tz was 0.90, and the rms difference was 3.2 mm. A comparison of Tz with PW from a GPS site 31 km NNE yielded an r2 of 0.79, and an rms difference of 5.8 mm. An expanded study compared Tz from eight IR thermometers with PW at various times during the day and night from 17 May to 18 October 2010, mainly at the Texas site and 10 days at Hawaii’s Mauna Loa Observatory. The best results were provided by two IR thermometers that yielded an r2 of 0.96 and an rms difference with PW of 2.7 mm. The results of both the ongoing 2-year study and the 5-month comparison show that IR thermometers can measure PW with an accuracy (rms difference/mean PW) approaching 10%, the accuracy typically ascribed to sun photometers. The simpler IR method, which works day and night, can be easily mastered by students, amateur scientists and cooperative weather observers.
Capsule: A $20 infrared thermometer pointed at the cloud-free zenith sky can measure precipitable water vapor about as well as a sun photometer–and it can do so day or night.
As they write in the conclusion
“…an IR thermometer provides a very inexpensive instrument for meteorologists, cooperative weather observers and students to measure PW and to better understand the role of water vapor in weather and as the dominant greenhouse gas.”
Since the atmospheric water vapor increases are required in order to amplify radiative warming from anthropogenically added CO2, this inexpensive instrumentation can provide a much wider survey of actual water vapor trends. As we reported in our paper
Wang, J.-W., K. Wang, R.A. Pielke, J.C. Lin, and T. Matsui, 2008: Towards a robust test on North America warming trend and precipitable water content increase. Geophys. Res. Letts., 35, L18804, doi:10.1029/2008GL034564.
at least for North America, there has not been a positive feedback od added water vapor when the troposphere warms.