IMF Control of Alfvénic Energy Transport and Deposition at High Latitudes

Abstract

©2017. American Geophysical Union. All Rights Reserved. We investigate the influence of the interplanetary magnetic field (IMF) clock angle ϕ IMF on high-latitude inertial Alfvén wave (IAW) activity in the magnetosphere-ionosphere transition region using Fast Auroral SnapshoT (FAST) satellite observations. We find evidence that negative IMF B z coincides with nightside IAW power generation and enhanced rates of IAW-associated electron energy deposition, while positive IMF B z coincides with enhanced dayside wave and electron energy deposition. Large ((Formula presented.) nT) negative IMF B y coincides with enhanced postnoon IAW power, while large positive IMF B y coincides with enhanced but relatively weaker prenoon IAW power. For each ϕ IMF orientation we compare IAW Poynting flux and IAW-associated electron energy flux distributions with previously published distributions of Alfvénic Poynting flux over ∼2–22 mHz, as well as corresponding wave-driven electron energy deposition derived from Lyon-Fedder-Mobarry global MHD simulations. We also compare IAW Poynting flux distributions with distributions of broad and diffuse electron number flux, categorized using an adaptation of the Newell et al. (2009) precipitation scheme for FAST. Under negative IMF B z in the vicinity of the cusp (9.5–14.5 magnetic local time), regions of intense dayside IAW power correspond to enhanced diffuse electron number flux but relatively weaker broadband electron precipitation. Differences between cusp region IAW activity and broadband precipitation illustrate the need for additional information, such as fields or pitch angle measurements, to identify the physical mechanisms associated with electron precipitation in the vicinity of the cusp.