Understanding wave-particle interactions in Earth's polar cusps

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. Some of the wave-particle interactions resemble those observed elsewhere in Earth's ionosphere, such as in the nightside aurora. However, not enough measurements have been made in the cusp to determine how the its wave-particle processes differ. Together with collaborators at several other universities, we are leading an effort to launch a rocket into the cusp in November-December, 2015. This experiment, called the Cusp Alfven and Plasma Electrodynamics Rocket (CAPER), will measure waves and particles in several frequency ranges, from Hz to MHz, with sufficient resolution to determine the phase relation between them, and hence the nature of their interaction including direction of energy flow. By making the most advanced measurements of this type ever made in the cusp, we expect to answer the question of whether wave-particle interactions there are identical to those in other space plasma environments or have their own special characteristics due to unique aspects of the particle distribution functions in the cusp.

A further pair of sounding rockets will be launched into the polar cusp in November-December, 2018. The primary focus of this pair of rockets is to measure low-altitude signatures of magnetic reconnection, an important plasma physics process which occurs approximately 60,000 km above the Earth where Earth's magnetic field lines interact with those of the sun. Dartmouth instrumentation will contribute to this experiment by measuring the plasma density on both rockets. In addition to the main goal of measuring reconnection signatures, this experiment will provide a second opportunity to measure details of wave-wave and wave-particle interactions in the cusp.