Radiation astronomy/Hydrometeors

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Def. precipitation products of the condensation of atmospheric water vapour are called hydrometeors.

"Condensation or sublimation of atmospheric water vapor produces a hydrometeor. It forms in the free atmosphere, or at the earth's surface, and includes frozen water lifted by the wind. Hydrometeors which can cause a surface visibility reduction, generally fall into one of the following two categories:

  1. Precipitation. Precipitation includes all forms of water particles, both liquid and solid, which fall from the atmosphere and reach the ground; these include: liquid precipitation (drizzle and rain), freezing precipitation (freezing drizzle and freezing rain), and solid (frozen) precipitation (ice pellets, hail, snow, snow pellets, snow grains, and ice crystals).
  2. Suspended (Liquid or Solid) Water Particles. Liquid or solid water particles that form and remain suspended in the air (damp haze, cloud, fog, ice fog, and mist), as well as liquid or solid water particles that are lifted by the wind from the earth’s surface (drifting snow, blowing snow, blowing spray) cause restrictions to visibility. One of the more unusual causes of reduced visibility due to suspended water/ice particles is whiteout, while the most common cause is fog."[1]


Quill satellite radar image is shown of the flooded Eel River outflow current. Credit: oldteched, U. S. National Reconnaissance Office, and U. S. Geological Survey.

On the right, the Quill satellite radar image is shown of the flooded Eel River outflow current debris field in gray.

"Colored content is USGS-derived base map. Gray overlay is derived from a "Quill" satellite radar image made during the December 1964 flooding of California's Eel River. Accurate registration of the overlay onto the map is demonstrated by the excellent match of the stream-valley features in each."[2]

Rain gauges[edit]

The image shows a standard rain gauge. Credit: Bidgee.

Rain is measured in units of length per unit time, typically in millimeters per hour, [3] or in countries where imperial units are more common, inches per hour.[4] The "length", or more accurately, "depth" being measured is the depth of rain water that would accumulate on a flat, horizontal and impermeable surface during a given amount of time, typically an hour.[5] One millimeter of rainfall is the equivalent of one liter of water per square meter.[6]

The standard way of measuring rainfall or snowfall is the standard rain gauge, which can be found in 100-mm (4-in) plastic and 200-mm (8-in) metal varieties.[7] The inner cylinder is filled by 25 mm (0.98 in) of rain, with overflow flowing into the outer cylinder. Plastic gauges have markings on the inner cylinder down to 0.25 mm (0.0098 in) resolution, while metal gauges require use of a stick designed with the appropriate 0.25 mm (0.0098 in) markings. After the inner cylinder is filled, the amount inside it is discarded, then filled with the remaining rainfall in the outer cylinder until all the fluid in the outer cylinder is gone, adding to the overall total until the outer cylinder is empty.[8]


  1. Lua error in Module:Citation/CS1 at line 3723: bad argument #1 to 'pairs' (table expected, got nil).
  2. Lua error in Module:Citation/CS1 at line 3723: bad argument #1 to 'pairs' (table expected, got nil).
  3. http://www.wmo.int/pages/prog/www/IMOP/publications/CIMO-Guide/CIMO%20Guide%207th%20Edition,%202008/Part%20I/Chapter%206.pdf
  4. 5 - Principal Hazards in U.S.doc Chapter 5 - Principal Hazards in U.S.doc Check |url= value (help). p. 128.
  5. Rain gauge and cubic inches
  6. FAO.org. FAO.org. Retrieved 2011-12-26.
  7. National Weather Service Office, Northern Indiana (2009). 8 Inch Non-Recording Standard Rain Gauge. Retrieved 2009-01-02.
  8. Chris Lehmann (2009). 10/00. Central Analytical Laboratory. Retrieved 2009-01-02.