Isinglass
April 2, 2014
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It has long been known that the aurora emit radio waves at the second and third harmonics of the electron cyclotron frequency. A detailed theory explaining these emissions has been developed and tested in many experiments. However, recently (in 2012) the fourth and fifth harmonics were observed for the first time. While it is possible that the same theoretical explanation applies to them, there is some evidence that their polarization may be inconsistent with the mechanism that generates the lower harmonics.
[more]The polar cusps are two funnel-like regions near the poles of Earth's approximately dipolar magnetic field, one in each hemisphere, where the Earth's magnetic field may directly connect to that of the solar wind. The interaction of the solar wind and its magnetic field with Earth's magnetic field gives rise to unusual effects in the cusp leading to particular distributions of accelerated and non-accelerated charged particles, which in turn generate plasma waves and interact with pre-existing plasma waves.
[more]For almost twenty years, bursty radio emissions at 1.5-4.5 MHz, originating in Earth's high latitude ionosphere, have been described and probed with multiple experiments. The emission mechanism remains a mystery, though recently a theory has been proposed. We have set up arrays of antennas attached to sensitive digital receivers at several Arctic and Antarctic locations, to perform measurements needed to test the theory. In addition, we are investigating signals similar to the burst emissions detected by NASA satellites.
[more]Auroral Kilometric Radiation is the most powerful natural radio emission from Earth's environment, carrying away up to a percent of the energy of the aurora. Our group and others have found evidence that the radiation is not only beamed away from the Earth, as previously known, but occasionally leaks to low altitudes.
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