Earth Science in Space 5: Sprites, auroras and cosmic dust in the upper atmosphere

The Earth is not just a body of rock, and geology is not just about rocks. When you study rocks enough, eventually the questions you ask and the answers you find lead upward into the atmosphere and beyond. Earth extends into space in a literal sense, and instruments based in space are an integral part of geology. So let's put down our rock hammers and go into these uppermost parts of the Earth—the ionosphere and magnetosphere—and trace the continuum from there to the ground.

As the Sun shines on Earth, the atmosphere shields us from a little over half of the incoming radiant energy. Ozone in the stratosphere, you remember, absorbs part of the ultraviolet radiation, and water vapor and carbon dioxide take care of most of the infrared and microwave energy. The upshot is that the outermost atmosphere is a very energized place, and above about 100 kilometers altitude, a significant portion of the air is ionized and conducts electricity. The solid Earth is a conductor too. But in between is a lot of insulating air.

An early picture of a red sprite. For lots more info, see the sprites list. NASA image.
Recently scientists documented some weird electrical beasts that cross this insulating barrier and complete the global circuit. They are forms of lightning that strike upward, the most common ones being red sprites, or just sprites. I think they're the coolest things in the sky.

Go just a little higher up, and the influence of outer space gets stronger. Consider the aurora, which forms where the Earth's magnetic field steers free electrons energized by superheated wind from the Sun. Over most of the planet, this activity happens well above the air, but near the magnetic poles the magnetic field lines lead downward and the electrons put on a show.

The space shuttle snapped this picture of the southern aurora in 1994. The shuttle's tail is in the foreground, flying top toward Earth. NASA image.
The Global Positioning System, better known as GPS, has had revolutionary impacts, but here's one you probably haven't heard of before . . . The satellites are being used to monitor the whole ionosphere, with daily results posted on NASA's GENESIS site.

The part of space where our satellites fly is still part of the Earth—the magnetosphere. This is where radiation from two sources, the Sun and the galaxy, interacts with a protective magnetic bubble that the Earth maintains. Up here things are energetic enough for nuclear reactions to take place, such as the transformation of nitrogen to radiocarbon, as I described in Part 2.

Magnetospheric studies are hard for me to follow, but if the mathematics excites you, then you should find this introduction to the magnetosphere fascinating. And for more alleyways on the Web to lose yourself in, visit NASA's Space Physics Data System or the Today's Space Weather page. The military has its own set of space weather soldiers.

This stuff has some connection, still obscure, to our climate. Something between the Sun and Earth takes the small, 0.1-percent fluctuations of the Sun's energy and amplifies them into definite changes, like a 3-degree latitude shift in north Atlantic storm tracks between high and low points in the sunspot cycle, or changes in the ozone layer. Something makes day-to-day solar activity cause immediate changes in regional meteorology.

Professor Brian Tinsley has suggested a link from sunstorms to rainfall via the solar wind, modulating the global rain of electrons—a sort of invisible aurora—through the stratosphere that causes electric charge to accumulate on high cloud tops. There they trigger "electrofreezing" of supercooled water droplets. Read his recent papers at Tinsley's site.

And let us not forget the possibility that a large amount of water coming into the upper atmosphere from outer space in the form of small comets, which I've written about here. That discovery could not have been made without space-based cameras looking down on us.


Not just gases, ions and radiation are up there—cosmic dust rains down on us, tiny grains of comet stuff. NASA has a program that collects it in the stratosphere and shares it with researchers. Web maestro Amara Graps wrote this dandy piece for the sci.astro newsgroup about cosmic dust.