Cool Islands in the Sky

SkyIslandKittPeakDec2015.crop_edited-2 (1)

The photo above was taken at the Kitt Peak National Observatory in southern Arizona, at an elevation of about 7,000 ft (2134 m), approximately 2,000 ft (610 m) above the surrounding desert. While trees and snow patches are visible on the ground here, the desert in the distance is warmer, drier and relatively barren. Kitt Peak is a classic example of an Arizona sky island -- an isolated mountain and not part of a mountain range.

In the desert southwest of the U.S., the temperature often has little to do with latitude; that is distance north of the equator. For example, traveling south from Phoenix, Arizona into Mexico, the climate becomes progressively cooler as the land elevation gradually increases. Why? When air rises, it expands, releasing the energy the atmospheric pressure uses to compress the air. So as it rises, the air cools at a rate of about 5 1/2 degrees F/1000 feet or about 10 degrees C/1000 meters.

If the air contains moisture in the form of water vapor, this expansion leads to condensation (cloud formation) and precipitation. Thus, at higher elevations not only is the air cooler, but precipitation (rain or snow) is more likely than at the surface, so it's not unusual to see snow-capped mountains looming above a desert landscape. Photo taken on December 14, 2015.

Photo Details: Camera Model: Canon EOS REBEL T5; Lens: EF-S18-55mm f/3.5-5.6 IS II; Focal Length: 18.0mm; Aperture: ƒ/10.0; Exposure Time: 0.0040 s (1/250); ISO equiv: 100; Software: Adobe Photoshop Elements 9.0 Macintosh.

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