Ionospheric Storms


(movie courtesy of A. Burns, T. Killeen and W. Wang at the University of Michigan)

Is there an ionospheric storm in progress now?

About the movie:

You are viewing a 24-hour long simulation of the total electron content in a column above the Earth's surface (between 100 and 400 km altitude) during the April 10-11, 1997 ionospheric storm event. This storm occurred in association with a magnetic storm that began in near-Earth space at ~21 UT on April 10 due to the arrival of a coronal mass ejection from the Sun. The storm subsided at around 9 UT on April 11 but the changes to the ionosphere lasted much longer.

Major Features of the Disturbed Ionosphere:

  • Bands of enhanced density that appear at high latitudes during the storm but disappear rapidly as it subsides are due to the high velocity particles that precipitate into the atmosphere, smashing into the neutral atmospheric gases and knocking electrons free. These same high velocity particles produce the auroral lights.
  • The overall enhanced densities at lower latitudes, that appear immediately as the storm begins and persist long after it is over, are called positive storm effects. Deep depletions in density are called negative storm effects.
  • Large-scale alterations in the neutral wind system and composition and temperature changes in the high altitude atmosphere during ionospheric storms are responsible for these dramatic changes in the ionosphere.
  • The pattern of positive and negative storm effects vary from storm to storm in a complicated way. The dynamic processes that produce these complex variations are not well-understood yet but are the subject of vigorous theoretical and observational research programs.

The Effects on Radio Waves

Depressions in the ionospheric density cause major communications problems because radio frequencies that previously had been reflecting off the ionosphere, now punch through. The maximum useable frequency (MUF) can be decreased by a factor of 2 during an ionospheric storm event. Storm effects are more pronounced at high latitudes.

How Long Do Ionospheric Storm Effects Last?

Deep depressions in the ionosphere produced during ionospheric storms can last typically for a day or so.


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