University of Crete Island of Crete

The equatorial E region and its plasma instabilities: A tutorial

D. T. Farley

Cornell University, Ithaca, NY, USA (

Since this a tutorial, we first briefly review the basic physics of the E region of the equatorial ionosphere, with emphasis on the strong electrojet current system that drives plasma instabilities that generate strong plasma waves that are easily detected by radars and rocket probes. We then discuss the instabilities themselves, both the theory and some examples of the observational data. These instabilities have now been studied for about half a century (!), beginning with the IGY, particularly at the Jicamarca Radio Observatory in Peru. The linear fluid theory of the important processes is now well understood, but there are still questions about some kinetic effects, not to mention the considerable amount of work to be done before we have a full quantitative understanding of the limiting nonlinear processes that determine the details of what we actually observe. As our observational techniques, especially the radar techniques, improve, we find some answers, but also more and more questions. One difficulty with studying natural phenomena, such as these instabilities, is that we cannot perform active cause-and-effect experiments; we are limited to the inputs and responses that nature provides. The one hope here is the steadily growing capability of numerical plasma simulations. If we can accurately simulate the relevant plasma physics, we can control the inputs and measure the responses in great detail. Unfortunately, the problem is inherently three-dimensional, and we still need more computer power than is currently available, although we have come a long way. Let us hope that Moore’s Law remains valid for at least a few more years!

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Jicamarca Radio Observatory

Arecibo Observatory

MU Radar

Equatorial Atmosphere Radar

Gadanki Radar

Imaging Radars


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