Sept. 18, 2006 — Tropical thunderstorms can affect near-Earth space weather, say researchers. That conclusion comes from a new computer simulation that was developed to explain a mysterious thickening in two bands of our planet’s very thin outermost atmosphere during spring and fall equinoxes.
"The two bands straddle Earth’s magnetic equator," said researcher Thomas Immel of University of California at Berkeley about the thickening in the ionosphere over the tropics . Immel and his colleagues have published the results of their new model of the bands in a recent issue of Geophysical Research Letters.
The ionosphere is formed by solar x-rays and ultraviolet light, which break apart atoms and molecules in the upper atmosphere, creating a layer of electrically-charged gas known as plasma. The densest part of the ionosphere forms two bands of plasma close to the equator, which look like parallel ribbons encircling Earth some 250 miles above the ground.
Four locations along the ribbons have been seen getting exceptionally bright, as seen by NASA’s IMAGE satellite. Those bright spots, it turns out, were above the steamy Amazon Basin, the Congo Basin, Indonesia and the Pacific Ocean around spring and fall equinoxes, says Immel, when the sun is highest in the sky and thunderstorms are strongest and most persistent.
That discovery made many researchers suspicious that biggest tropical thunderstorms that form in those places are somehow the cause of the ion ribbons. The problem, however, is that there has never been any known physical connection between thunderstorms way down in the lower atmosphere and "tides" of ions out at the edge of space.
That’s changed, thanks to the Global Scale Wave Model, developed by Immel and his team.
The model has simulated the situation and revealed that the most powerful thunderstorms can pour energy up as high as 62 to 75 miles above the equator, several times higher than the storms themselves. That means the storms can alter a layer of the ionosphere that gets partially electrified every day just from the Sun shining on it.
When electrified air is moved by winds from below, it is also moving within Earth’s magnetic field, which creates a giant electrical generator and an electrical field. It's that airborne electrical field which is felt by the ions much higher up, in the outer reaches of the ionosphere. They respond to that field by forming the glowing bands.
