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SAL: Background: This imagery is created by differencing the 12.0 and 10.8µm infrared channels on the Meteosat-8 satellite.
The algorithm is sensitive to the presence of dry and/or dusty air in the lower atmosphere (~600-850 hPa or ~4,500-1,500 m) and is denoted by the yellow to red shading.
Uses:
This imagery is useful for monitoring the position and movement of dry air masses such as the Saharan Air Layer (SAL). Animations of the imagery are useful for tracking these features and can also help identify the source of the dry and/or dusty air that is indicated in the imagery.
Notes:
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Dry air and suspended aerosols (e.g. mineral dust) both contribute to a positive "SAL" signal in this imagery, but the relative contribution of each cannot be determined from this imagery alone.• Polar air originating from the mid-latitudes produces a positive signal in this imagery that is similar to that of the SAL. This is because both air masses contain substantial dry air in the lower to middle troposphere. The JAVA movie is a useful tool for determining which type of air mass is being indicated in the imagery.
http://cimss.ssec.wisc.edu/tropic2/misc/sal/info.sal.m8split.html-------------------------------------------------------------------------------------------------------
VAPOR DE AGUA EN NIVELES MEDIOS: Background: This product uses the 7.3µm channel on the Meteosat-8 satellite, which is sensitive to moisture in the lower to middle levels of the atmosphere.
Uses: The 7.3µm channel is useful for
detecting moisture in the lower to middle troposphere and is typically most sensitive to moisture at ~600 hPa or ~4,500 m.
Notes:
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This channel is more effective than the upper-level water vapor imagery for tracking the Saharan Air Layer (SAL) because it detects moisture (or lack of) more effectively at levels where the SAL is typically found (~500-850 hPa or 6,000-1,500 m).
• Since this channel is able to detect the lower atmosphere more effectively, caution should be taken in interpreting the imagery, particularly in extremely dry areas over land (e.g. the Sahara Desert). In these regions, rapid heating during the day and cooling at night can affect the satellite retrievals in this channel. Specifically, if the lower to middle atmosphere is extremely dry, this channel "sees" more effectively down to the Earth's surface. Therefore, strong surface heating can produce an enhanced false "dry" signal and surface cooling can produce an enhanced false "moist" signal. However, although this effect can be significant over land areas, it is negligible over the ocean.
http://cimss.ssec.wisc.edu/tropic2/misc/sal/info.sal.wvlower.html---------------------------------------------------------------------------------------------------------
VAPOR DE AGUA EN NIVELES ALTOS Background: This product uses the 6.2µm channel on the Meteosat-8 satellite, which is sensitive to moisture in the middle to upper levels of the atmosphere.
Uses: The 6.2µm channel is useful for
detecting moisture in the middle to upper troposphere and is typically most sensitive to moisture at ~400 hPa or ~7,500 m.
Notes:
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This channel is often not effective for tracking the Saharan Air Layer (SAL) because it detects moisture (or lack of) more effectively at levels above where the SAL is typically found (~500-850 hPa or 6,000-1,500 m).
http://cimss.ssec.wisc.edu/tropic2/misc/sal/info.sal.wvupper.html