Adam Adkins
EF3
On water vapor satellite imagery, when you get to clear air there is very little to display however sometimes a red color is displayed. What is this? Thanks, I could not seem to find an answer elsewhere!
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Simple Question
- Thread starter Adam Adkins
- Start date
rdale
EF5
It depends on the color table you use, the one I have doesn't show any reds at all. Do you have a sample? Is there a legend on that map?
Rich Thompson
EF3
Adam,
If you're looking at one of the standard enhancements, the red areas are "dry". The satellite sensor for water vapor imagery is sensitive to water vapor (and clouds) in the middle parts of the atmosphere, usually higher than about 700 mb. Any moisture closer to the ground won't really be detected.
If you get water vapor satellite data from either the RAP site (www.rap.ucar.edu/weather/satellite), the COD site (weather.cod.edu/analysis), or the NWS site linked in the left menu bar (http://www.goes.noaa.gov/ECWV1.html), then you'll see red on the colder end of the color table for water vapor satellite. Below is the current national water vapor image from the COD site:
This particular source does not show the color table values, but others do. The reds and oranges essentially correspond to drier air. Water vapor imagery shows mid-upper tropospheric water vapor content and is not a function of light or "clearness" of the air. Thus even when clouds are not present over a location, there will still be plenty of useful information gained from water vapor imagery. Usually drier air in the mid-upper troposphere implies some sort of adiabatic subsidence (because that might be what it takes to get that dry).
Note that in all reality, what's being plotted is brightness temperature, which is a function of many things, but mainly in the channel shown (probably 22 GHz) it is a function of precipitable water (i.e., vertically integrated moisture content). Lower brightness temperatures would be due mainly to drier conditions.
ADD: I see Rich and I are on the same wavelength here (haha...get it? wavelength...yeah, I know that was bad)
This particular source does not show the color table values, but others do. The reds and oranges essentially correspond to drier air. Water vapor imagery shows mid-upper tropospheric water vapor content and is not a function of light or "clearness" of the air. Thus even when clouds are not present over a location, there will still be plenty of useful information gained from water vapor imagery. Usually drier air in the mid-upper troposphere implies some sort of adiabatic subsidence (because that might be what it takes to get that dry).
Note that in all reality, what's being plotted is brightness temperature, which is a function of many things, but mainly in the channel shown (probably 22 GHz) it is a function of precipitable water (i.e., vertically integrated moisture content). Lower brightness temperatures would be due mainly to drier conditions.
ADD: I see Rich and I are on the same wavelength here (haha...get it? wavelength...yeah, I know that was bad)
