Combining Ground-based and Space-based Measurements to
Explain Auroral Radio Emissions

Jim LaBelle
Dartmouth College

A loop antenna deployed at ground level in the auroral zone
detects a variety of radio emissions of auroral origin, including
auroral hiss, auroral roar, and auroral MF-burst.
The latter two emission types are believed to result from
mode conversion of high-frequency electrostatic waves, similar to
the generation of terrestrial continuum radiation in the magnetosphere.
In the case of the auroral emissions, ground-level
measurements determine their polarization,
direction of arrival, frequency structure, etc., but rocket-borne
measurements are required to detect the causative electrons and the
electrostatic waves that mediate the radiation process.
The frequency structure of the auroral roar emissions is particularly
interesting and inspires a theoretical model in which
inhomogeneity of the background plasma plays an important role
in the emission process. Sounding rocket observations, including
a recent flight which penetrated the source regions of the auroral roar in the
F-region ionosphere, provide critical data for testing the
theoretical model.