This is the time of year when, during the night and early morning, streams run down from the Franklin Mountains, and the Rio Grande Valley fills nearly to its brim. By mid-day, all disappear into thin air. Hadn't noticed it? Obviously, you're insensitive to temperature, for these are bodies of cold air.
If air ranged in color from red when hot to blue when cold, you'd
easily see the blue currents streaming into the valley and coalescing to form a slow
river sliding downstream. But what causes them? Radiation and conduction are at work
here. After nightfall, the barren slopes of the Franklins rapidly radiate the sun's
heat accumulated during the day. The air immediately adjacent to these exposed surfaces
is cooled by conduction, and cool air is heavier than warm air. Weighing more, the air
naturally streams downslope, just as would water. Have some doubts? Look outside on
these wintery mornings. That dense cloud of pollution is trapped in the cold valley air
by the warmer air above. Our old friend, the temperature inversion has arrived!
Listen to the Audio (mp3 format) as recorded by KTEP, Public Radio for the Southwest.
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.