4 p.m. - 5 p.m. Location: SLC 1.102
Dr. Jean-Pierre St. Maurice (Saskatchewan)
Energetic photons from the sun and the lack of frequent collisions are responsible for the creation of the ionosphere above 90 km altitude. Electrical currents are also flowing in response to winds blowing through the region. As I will quickly illustrate, the currents are enhanced at the magnetic equator through a double-Hall effect. Furthermore, the current divergences give rise to electric fields that impart bulk plasmas motion to the ionosphere. One well-known consequence of this motion is the so-called equatorial fountain effect that feeds a plasma density anomaly well above normal altitudes, a few degrees away from the equator. Another interesting consequence is the formation of separate daytime and nighttime dynamos; I will show how we have recently come to the conclusion that the local zonal (east-west) electric field resulting from this change can produce thin layers of ionization near 110 km, a few degrees away from the equator. In the plasma holes left over by these so-called "sporadic E layers", I will also present observations showing that electrons can be heated by several hundred degrees and argue that the only source of heat can be relatively weak electrical currents flowing along the magnetic field. Other interesting aspects of equatorial electrodynamics can be found at sunset, when the electric field is enhanced prior to undergoing a sign reversal, owing to a change in ionospheric conductivity triggered by the disappearing sunlight. I will discuss why there is no converse enhancement at sunrise. However, I will show that, related to the changing conductivity mechanism, a double electric field reversal was observed at the magnetic equator when a solar eclipse passed over the southern tip of India around the noon hour.