This is a 12-month animation of color-enhanced images from NOAA’s GOES East geostationary weather satellite. It covers all of 2009 except for brief periods when my internet connection or my computer were down. The date and time of each image is at the upper left, if it survives YouTube’s reencoding of the video. This is a bit long, but here it is for the record:
This video is made from infrared images, which measure heat radiation, so what you see here is basically temperature. The color is artificial (obviously!) and is used to enhance the contrast between different temperatures. The temperature is significant because severe weather is usually associated with convective systems which generate tall clouds, and the tops of tall clouds are colder than the tops of low clouds. But that daily pulsing you see isn’t necessarily clouds, as discussed below.
Note that the credits at the end of the video have an error in the URL of the original images, which should be http://www.goes.noaa.gov/GIFS/ECI7.JPG.
Monchrome infrared satellite image
The advantage that infrared (IR) imaging has over visual is that you can still take the picture when it gets dark — the clouds “glow” in the IR wavelenghts based on their heat, whereas visual imaging requires reflected light from an external source, such as the sun. So we can “see” the clouds from space at night by sensing the IR glow.
But it’s not just the clouds that emit IR radiation — the ground, seas, and lakes do, too. The ground and oceans are usually warmer than clouds, and therefore stand out from them. But they warm up more during the day and cool off at night. That’s the source of the daily pulsing you see. The black, white, and to a certain extent, the light blue are seen in the images used for this animation usually are areas not covered by clouds. You’ll notice the black and white surge farther north in the summer.
You’ll also notice that the Great Lakes stay blue while the land around them turn white or black. That’s because the deep waters of Lake Michigan, e.g., have a more steady temperature than the land surface which heats significantly under the midday sun.
Color-enhanced infrared satellite image
NOAA has colorized these images for greater contrast. They have different formulas for doing that, and you can see the same view colorized different ways on NOAA’s site, as well as the monochrome view.
These IR images show differences in the amount of radiated heat. Because clouds can rise high into the atmosphere where the temperatures are lower, this is a good way to detect the sorts of high clouds associated with thunderstorms and hurricanes. But not all clouds are high with cold tops. There are times when the current b/w image makes it appear that it should be sunny where I am, but in reality it’s solidly overcast. In that situation the overcast is low clouds without high tops that are at a temperature not too much lower than the surface.
What would be cool to do would be to overlay the current national composite radar image on the current IR satellite photo. That would show where it actually rains and snows in the weather systems we see in these images. I don’t know where I’d find satellite images that are projected and georeferenced in such a way that I could get the two to line up properly, though. The transparent, georeferenced weather radar images are there, as discussed previously.
Thanks to Dan O’Connor at DanoSongs.com for the liberally licensed music used as a sound track here. This video is can be reused under the terms of the CC-BY-3.0-US Creative Commons license. That license simply requires attribution for reuse. The video can be credited to EGB13.net. See DanoSongs.com for how to credit the audio.
