Parametric Decay of Alfven Waves in the Solar Wind
Abstract
We explore the parametric decay instability of finite amplitude Alfvén waves in the solar wind. Parametric coupling between large amplitude Alfvén waves and compressive fluctuations leads to the growth of both forward propagating compressive waves and backwards propagating Alfvén waves. This three wave coupling, observed in simulations of the solar wind, explains compressive signatures of the solar wind, and additionally provides a mechanism to seed backwards propagating fluctuations necessary for the non-linear turbulent interactions. In MHD, growth rates for PDI depend only on wave amplitudes and , which are both measureable quantities. We compare analytical growth rates for PDI with observations from the NASA Wind mission. We show that the distribution of magnetic fluctuations is bounded by high PDI growth rates and that periods of solar wind which should undergo more than one iteration of parametric decay show enhanced density fluctuations consistent with PDI daughter waves.
- Publication:
-
Solar Heliospheric and INterplanetary Environment (SHINE 2018)
- Pub Date:
- July 2018
- Bibcode:
- 2018shin.confE..11B