Resonant Alfven Waves in the Lower Ionosphere During an Active Aurora-Observations by Electric and Magnetic Field Probes on a Dual Sounding Rocket Experiment
Abstract
During the "Auroral Jets" experiment from Poker Flat, Alaska on March 2, 2017, two NASA sounding rockets were simultaneously launched into an active auroral ionosphere with instrumentation to measure DC and AC electric fields, magnetic fields, energetic electrons, plasma density, and neutral winds, achieving apogees of 190 and 330 km. A prominent feature of the electric and magnetic field observations is the presence of localized, large-amplitude Alfvén wave structures observed in both the electric field and magnetometer data at altitudes as low as 150 km in the vicinity of up- and downward current regions. For one group of waves observed near 200 km altitude, the electric field and magnetic field wave components were +/- 40 mV/m and +/- 50 nT, respectively, corresponding to an E/B wave velocity of 800 km/sec. We interpret the oscillations as representing standing waves associated with the ionospheric Alfvén resonator between the ionosphere and the lower magnetosphere. Indeed, the combined electric and magnetic field measurements show both upgoing and downgoing Poynting Flux, consistent with this interpretation. Furthermore, the electric field components of the Alfvén waves reveal signatures of wave steepening in correlation with large variations of the background plasma density that may result from a nonlinear evolution of the ionospheric feedback instability associated with small scale currents. The results are compared to predictions of previously published numerical studies of Alfven waves in the lower, auroral ionosphere, as well with other sounding rocket observations.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSA0220006A
- Keywords:
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- 2431 Ionosphere/magnetosphere interactions;
- IONOSPHERE;
- 2447 Modeling and forecasting;
- IONOSPHERE;
- 2494 Instruments and techniques;
- IONOSPHERE;
- 2776 Polar cap phenomena;
- MAGNETOSPHERIC PHYSICS