GOES-West Split Window: Background: This imagery is created by differencing the 12.0 and 10.7 (m infrared channels on the GOES-West imager. 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: * 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. * Areas of very cold water (e.g. west of South America) can affect the split window algorithm and produce a false positive "SAL" signal. These regions can be easily identified using the JAVA movie because they tend not to move or change form for several consecutive days. Meteosat-8 Split Window: Background: This imagery is created by differencing the 12.0 and 10.8 (m 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: * 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. Meteosat-8/GOES-West Split Window (merged): Background: This product is created by combining the split window imagery from the GOES-West and Meteosat-8 satellites (for more details, see "Product Information" for each satellite). The algorithm for each 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. 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: * 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 the split window imagery that is similar to that of the Saharan Air Layer. 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. * Since one of the infrared channels on the Met-8 satellite is slightly different from the equivalent GOES-West channel, the Met-8 split window algorithm is also slightly different. However, both the GOES-West and Met-8 algorithms produce nearly identical imagery and are merged at ~65 W. Meteosat-8 TruColor Imagery: Background: This product is created by combining the 0.6, 0.8, 1.6, and 3.9 (m channels on the Meteosat-8 satellite. The 0.6, 0.8, and 1.6 (m channels are used as a proxy for the blue, green, and red regions of the visible spectrum and are combined into a single image. The resulting merged "color" image closely mimics what an actual color photo of the Earth would look like from space. These channels can only be used during the day, so an algorithm is used to track the position of the solar terminator (sunset/sunrise line) in each image. For portions of the image that are dark, the 3.9 (m shortwave infrared channel is used. Uses: This imagery is useful for monitoring the position of aerosols (e.g. suspended mineral dust in the Saharan Air Layer). Animations of the imagery are useful for tracking suspended mineral dust and can also help identify the source of the dusty air that is indicated in the imagery. Notes: * The visible portion of the TruColor image is subject to sun glint (solar reflectance off the ocean surface). This effect can make it look "dusty", when in fact, it may not be. This area of sun glint is easily identifiable as it rapidly moves across the basin in successive images. * Low sun angles (relative to the position of the satellite) can make it easier to see suspended mineral dust because scattering by the aerosols is greater. * Saharan mineral dust can often be seen as far west as the Windward Islands (far western edge of the picture) in this imagery and looks like a brown haze. * Cold clouds appear to have a bluish tint in this imagery. This is because the three visible channels being used to create the TruColor imagery are only proxies for the blue, green, and red portions of the visible spectrum. Meteosat-8 Upper-Level Water Vapor Imagery: Background: This product uses the 6.2 (m channel on the Meteosat-8 satellite, which is sensitive to moisture in the middle to upper levels of the atmosphere. Uses: The 6.2 (m 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: * 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). Meteosat-8 Mid-Level Water Vapor Imagery: Background: This product uses the 7.3 (m channel on the Meteosat-8 satellite, which is sensitive to moisture in the lower to middle levels of the atmosphere. Uses: The 7.3 (m 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: * 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.