Lithium Red Sky
Red sky at night: scientist's delight
Natural blood-red sky at night is comparatively rare. Perhaps once a decade, huge flares on the sun generate red auroras that spread over much of the earth's surface and sometimes cause the sky to appear red.
In recent years, artifically red nighttime skies have been created over limited parts of the earth. Rocket-borne releases of a few pounts of the element lithium make markers in the sky that can be easily photographed to measure winds in the high atmosphere.
Many Alaskans and Yukoners are familiar with the barium releases made aboard rockets launched from the Poker Flat rocket range near Fairbanks. These releases create two types of cloud. One is a neutral green cloud that moves with the wind. The other is a bluish purple cloud that striates like a rayed aurora and moves under the influence of the electric field in the high atmosphere.
In somewhat similar fashion it is possible to slowly spew out lithium metal from a rocket to produce a long, visible red trail. Sunlight shining on the lithium atoms cause them to be excited so that they glow with a red light. Unllke the barium, lithium released in the high atmosphere yields only a neutral gas tracer. The neutral tracer is useful only for measuring the direction and speed of the wind in the high atmosphere at altitudes well above 100 km.
This week scientists from NASA's Goddard Space Flight Center are at Poker Flat attempting to fly two rockets that will release both lithium and barium. These releases are high enough to be visible to all persons with clear sky in Alaska, eastern Siberia and northwestern Canada.
The red lithium trails are easy to see and do persist for a long time. Lithium is such a light element that it remains aloft for hours drifting with the wind. Eventually the lithium becomes invisible as it disperses and combines with other elements in the air.
The overall objective of the research using chemical releases at high altitude is to understand how energy is transferred from one level to another in the atmosphere and the near-earth regions of space above. That energy transfer may have some influence upon climate.
