Precipitable water explained

Precipitable water is the depth of water in a column of the atmosphere, if all the water in that column were precipitated as rain. As a depth, the precipitable water is measured in millimeters or inches. Often abbreviated as "TPW", for Total Precipitable Water.

Measurement

There are different measurement techniques:

• One type of measurement is based on the measurement of the solar irradiance on two wavelengths, one in a water absorption band, and the other not. The precipitable water column is determined using the irradiances in these bands and the Beer–Lambert law.
• The precipitable water can also be calculated by integration of radiosonde data (relative humidity, pressure and temperature) over the whole atmosphere.
• Data can be viewed on a Lifted-K index. The numbers represent inches of water as mentioned above for a geographical location.
• Recently, methods using the Global Positioning System have been developed.^[1]
• Some work has been performed to create empirical relationships between surface specific humidity and precipitable water based on localized measurements (generally a 2nd to 5th order polynomial).^{[2] [3] [4]} However, this method has not received widespread use in part because humidity is a local measurement and precipitable water is a total column measurement.

External links

• Current global map of precipitable water
• Maurellis . A. N. . R. . Lang . W. J. . van der Zande . I. . Aben . W. . Ubachs . 2000 . Precipitable water column retrieval from GOME data . Geophys. Res. Lett. . 27 . 6 . 903–906 . 10.1029/1999GL010897 . 2000GeoRL..27..903M . 1871/23072 . 55326173 .
• Remote Sensing of Water Vapor From GPS Receivers

Notes and References

1. Bevis, M.. GPS Meteorology: Remote Sensing of Atmospheric Water Vapor Using the Global Positioning System . Journal of Geophysical Research . 1992 . 97 . D14 . 15787–15801 . 1992JGR....9715787B . 10.1029/92JD01517 . etal.
2. Liu . Timothy . 27 February 1986 . Statistical Relation between Mean Precipitable Water and Surface-Level Humidity over Global Oceans . Monthly Weather Review . 114 . 8 . 1591–1602 . 10.1175/1520-0493(1986)114<1591:srbmmp>2.0.co;2. 1986MWRv..114.1591L . free .
3. Hsu . S.A. . Blanchard . B.W. . 15 October 1989 . The Relationship Between Total Precipitable Water and Surface-Level Humidity Over the Sea Surface: A Further Evaluation . Journal of Geophysical Research . 94 . C10 . 14539–14545 . 10.1029/JC094iC10p14539 . 1989JGR....9414539H.
4. Guangxiong . Peng . Jing . Li . Yunhao . Chen . Norizan . Abdul . Tay . Liphong . 17 July 2006 . High-resolution Surface Relative Humidity Computation Using MODIS Image in Peninsular Malaysia . Chinese Geographical Science . 16 . 3 . 260–264 . 10.1007/s11769-006-0260-6 . 73558154 . 22 January 2014 . 4 March 2016 . https://web.archive.org/web/20160304044130/http://egeoscien.neigae.ac.cn/fileup/PDF/20060312.pdf . dead .