Zoe Shoosmith - highest clouds have the coolest IR...

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Radiation is used by meteorologists to distinguish between the height, thickness and precipitation potential of clouds within the atmosphere. Below are images of the US for 20 October 2011 14.45 UTC (9.45 local). VIS Imagery IR (color) Imagery Water Vapor Imagery NCAR, Available at: http://weather.rap.ucar.edu/satellite/ (Last accessed 23/10/11) VIS imagery shows the amount of radiation reflected by clouds via Mei scattering, using the electromagnetic spectrum between 0.4 and 0.7 microns as cloud droplets have a similar radius of around 10 microns. Therefore, the tone of the image shows the albedo of the surface or cloud; white means more of the radiation is being scattered by the cloud and therefore more is reflected back to the satellite, indicating a thicker cloud. Infra-red radiation (11 microns) can indicate the height of a cloud due to the fact that clouds emit at the same temperature as the molecules that make it up. Therefore, the
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Unformatted text preview: highest clouds have the coolest IR reflectivity (shown by the cloud top) and appear blue. The water vapor satellite measures the wavelength of radiation that is readily absorbed by the water vapor molecules, 6.7 microns. This shows patterns in water vapor movement where clouds may not be seen. Red is very dry, purple and blue are moist but as the satellite is measuring the water vapor over the whole atmosphere column; there could be water vapor at the very surface. So using these theories, meteorologists can establish what type of cloud is being seen. Thin wispy on VIS but cold high blue clouds on IR are likely to be Cirrus such as over Western Canada, whereas other high blue clouds on the IR such as the system running along the East coast are thicker on the VIS suggesting cumulonimbus clouds due to the highest water vapor content shown on the 3 rd image....
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This note was uploaded on 01/08/2012 for the course MPO 551 taught by Professor Zhang,c during the Summer '08 term at University of Miami.

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