High-resolution Poynting Flux Statistics from the Swarm Mission: How Much is Being Underestimated at Larger Scales?

Abstract

Underestimation of the transfer of energy between the magnetosphere and ionosphere, the Poynting flux, is a persistent issue in space weather studies and the high-latitude ionospheric models. Thought to be due to the inability to resolve smallscale fluctuations of the ionospheric electric field, this underestimation could lead to significant further underestimations in parameters such as the thermospheric mass density and consequential satellite drag. Utilising 16Hz ion velocity and magnetic field measurements from the Swarm satellite mission, we examine the observed Poynting flux due to electric field fluctuations on very small spatial scales (˜1km), and then artificially smooth the data to increase the observed scale. We quantify the decrease of integrated Poynting flux, poleward of 60/-60 degrees geomagnetic latitude, with increasing spatial scale. The decrease can be underestimated by as much as 15% by increasing scale from 1km to only 8.6km, or 16Hz to 2Hz equivalent, with upward Poynting flux decreasing significantly faster. Our results thus point to a significant Alfvén wave driven component of the Poynting flux on kilometre scales. Additionally, we observe a northern hemisphere preference for increased Poynting flux, of which we examine its dependence on scale size and interplanetary magnetic field.

Statistical studies of plasma structuring in the auroral ionosphere by the Swarm satellites

“…This indicates that the increased integrated power we obtain gives a measure on the downward Poynting flux dominated by Alfvénic energy. In recent years, studies with the Swarm satellites have been conducted to present maps of the Poynting flux in the northern and southern hemisphere (Ivarsen et al, 2020;Billett et al, 2022). The climatology we present of the B y integrated power maps onto the Poynting flux within these studies adequately with an overall increase in Poynting flux in a circular shape around the magnetic pole and a further increase within the cusp.…”