Directly-driven oscillations: Current status, open questions, and how they inform us about magnetic reconnection (Invited)

Abstract:

There exists strong evidence that periodic number density structures in the solar wind drive discrete, global magnetospheric oscillations through a quasi-static 'forced breathing'. These oscillations have periods in Earth's rest frame of 15 minutes up to several hours, and several studies have shown the distribution of frequencies to closely align with the 'magic frequencies' that were originally attributed to global cavity modes. In addition, there is strong evidence that some nightside Pi2 pulsations are directly-driven by periodicities inherent to magnetotail flow bursts. Although seemingly different, both types of pulsations may derive from the same physical process: highly modulated magnetic reconnection. In this talk, I first briefly review the current understanding of both types of directly-driven oscillations, including new multi-point observations of directly-driven Pi2 made by THEMIS, and high-resolution charge-state measurements of solar wind oscillations made by ACE. For both types of directly-driven oscillations, the new observations push the source region closer to the reconnection site. For the forced-breathing oscillations, this links global magnetospheric oscillations to processes occurring near the solar surface. I conclude by discussing how we might use measurements of these directly-driven oscillations in both the solar wind and magnetosphere to probe magnetic reconnection.