Eight Miles High

by Eric Ellman

Damon Wells Professor of Geophysics Ron Smith is spending most of this summer at 40,000’ elevation, flying straight into a phenomenon that controls global weather. For the months of June and July he directs a crew of over 50 people who rotate night shifts aboard an instrument-laden Gulfstream V from NCAR in coordination with another specially equipped plane and team from Germany studying gravity waves in the stratosphere.

Based in Christchurch, New Zealand, the NSF-funded Project DEEPWAVE has been over 5 years in preparation.  It seeks to unlock the mysteries of Brewer-Dobson circulation, named for the British meteorologists who first proposed its existence based on observations of mid-latitude dryness and high-latitude ozone accumulation that otherwise defied explanation in the years leading up to and following World War II.  While nuclear fall-out in Polar Regions following atmospheric tests in the tropics confirmed the existence of high-altitude global circulation, direct measurements that might explain what drives it and which might aid in predicting how it influences weather have escaped study until now.

Gravity waves drive the circulation, says Dr. Smith.  A result of density differences in air or water, gravity waves, or as they are sometimes known, buoyancy waves, result from a packet of fluid floating upward in search of equilibrium, over-compensating, and descending again.  The ocean is “loaded” with these oscillations, he says. In the atmosphere they can propagate up to 100 kilometers in elevation. They begin when a current encounters an obstacle, roughness on the ocean floor, or a mountain projecting into the sky. The latter makes New Zealand’s Alps, square in the middle of the “Roaring 40’s”, a prime spot for study.

“This is the first time we’ll be able to measure them as they propagate deeply into the atmosphere,” says Dr. Smith.  The waves reach towering heights, he explains, become unstable, and crash “just like waves on the beach”.  In the process he believes they drive the giant circulation cells that stretch from polar to equatorial regions. Though confined to the stratosphere, they influence conditions all the way to the surface of the earth, and are likely just as important a control over weather as the better-known Hadley Cell circulation in the tropics.  Direct study of the phenomenon is now possible using a NCAR’s Gulfstream V, which has an altitude ceiling of 51,000 feet, and new upward pointing LIDARs and infrared mappers that allows them to peer even more deeply into the heights.  As powerful as the new instrumentation is, however, it can’t compete with the sun, thus necessitating nocturnal observations.

Accompanying Dr. Smith from Yale are postdoctoral researcher Campbell Watson, graduate students Christopher Kruse, Alison Nugent, Azusa Takeishi and undergraduate research assistant Christine Tsai. 

Team members were recently interviewed by a Christchurch news team, which you can view here: http://www.3news.co.nz/Scientists-use-planes-as-flying-weather-labs/tabid/1216/articleID/349606/Default.aspx