The importance of Alfvén waves in energy transport inside the magnetosphere has been demonstrated over the last two decades. Generated in various magnetospheric regions, much of their energy carried to the auroral zone is deposited inside the auroral acceleration region (AAR) via particle acceleration. In this report, we present the integrated contributions of Alfvén wave power to the nightside auroral zone during different levels of auroral activity, as measured by the auroral electrojet (AE) index. Data were collected from an ideal vantage point, namely, above the nominal AAR, over a 6-year period of Polar satellite operation. We provide functional forms for the total inflowing and outflowing Alfvén wave powers, both of which are linear—at least up to an AE index of 700 nT. For all AE values the power inflow is significantly larger than the power outflow; therefore, the estimated net wave power flowing into the AAR is sufficient to account for the integrated precipitating Alfvénic electron power in the nightside auroral zone below the AAR. The estimated global Alfvén wave absorption (by electrons) and reflection are, respectively, 56% and 33% (upper limit), while an excess wave power of 11% (lower limit) is available for other energy conversion processes, such as Joule heating and Alfvénic ion outflow.
Bibliographical noteFunding Information:
This research was supported by the NSF grant AGS‐1613134 and the NASA grants NNX16AG67G and NNX10AL03G. All data needed to evaluate the conclusions in the paper are presented in the paper. Relevant survey Polar data, including description of caveats, can be found at NASA's Coordinated Data Analysis Web ( https://cdaweb.sci.gsfc.nasa.gov ). Calibrated data, used in this study, can be obtained by request from the instrument principal investigators ( www‐istp.gsfc.nasa.gov/istp/polar/principal_inv.html ). The AE and Dst indices can be downloaded from the World Data Center in Kyoto ( http://wdc.kugi.kyoto‐u.ac.jp/aedir ).
- AE dependence
- Alfvén wave
- Alfvénic electrons
- M-I coupling
- wave-particle interaction