geography, weather

A Look at GOES Water Vapor Imagery (H. Michael Mogil, CCM, CBM, NWA-DS*)

This feature is about GOES (Geostationary Operational Environmental Satellite) Water Vapor (WV) imagery. This type of satellite imagery (just one of many) is based on a specific band of data within the infrared radiation (IR) spectrum. It is collected from a geostationary satellite positioned roughly 22,000 miles above the Equator near the longitude of Florida and a longitude just west of the U.S. West Coast. With the satellites racing around their larger orbit path at an angular speed that matches that of the Earth’s surface, the satellite never sees the earth moving (hence, geo- or Earth- stationary). As a result, animations show cloud and/or moisture movement only. These two U.S.-operated satellites are part of a global network of satellites supported by several Nations and/or organizations.

I’m a big fan of WV imagery because it allows meteorologists and others to see the motions (called animations) of clouds and locations of moist/dry areas. Even when the image is not color-enhanced, the various white to black grey shades provide important discrimination. Thunderstorms, with cold, high, cloud tops appear as the brightest white; cirrus (ice crystal) clouds are white, but typically not as bright. Moist areas are generally grey; dry areas are black (see scaling, warm to cold, at lower left of Fig. 1). It would be easy to see this representation as something similar to a topographic or relief map, with thunderstorms representing the mountains and dry zones representing dried lake beds.

In this image (Fig. 1) and associated animation, there is a lot to see. For example, there is a bright area that develops across eastern Oklahoma and moves into southeast Missouri. To its north, it is easy to see a small-scale swirl in the clouds and moisture areas. Further northwest, a larger swirl (the center of the main storm system) was moving into southwestern Minnesota.

Since the WV imagery is based on IR (temperature) data, it is easy to ascertain ground-based features when very dry air covers a region (such as west Texas, New Mexico, Colorado, and western Kansas). Notice the roughly north-line that separates a light grey region to the west and a dark area to the east. This marks the front-range of the Rocky Mountains, with snow-covered, colder mountains to the west and low-altitude, warmer, plains to the east (Fig. 2).Near the end of the animation, a cloud rapidly develops over far west Texas, just to the northeast of El Paso. The western edge of the cloud stays locked in place, as nearby clouds continue to move by from the west. This cloud feature formed as moist air bumped into the Guadalupe Mountains (and Guadalupe Peak, 8751 feet elevation) and was forced to rise (Fig. 3). Rising air cools by expansion (lower pressure as one goes up in the atmosphere) and this often leads to condensation and cloud formation. Since the feature causing the cloud to form doesn’t move, the cloud feature continually reforms on its western edge. From the ground, this would likely appear as a standing wave cloud,

Finally, across New Mexico, notice that some grey clouds move over the snow-covered, colder ground areas. These clouds are warmer than the underlying ground and provide some information about the vertical atmospheric temperature profile in the area.

The bottom line to all of this is that GOES weather satellite imagery allows meteorologists and others to view larger geographic regions and both large- and small-scale weather features.

And this limited perspective of satellite capabilities is just with current GOES capabilities and just one IR channel. Wait until GOES R, launched last November, gets fully checked out and starts to deliver operational data and images. The WOW factor will likely be incredible!

© 2017 H. Michael Mogil

Originally posted 3/1/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.