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

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 small-scale 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. Utilizing 16 Hz 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 (similar to 1 km), 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 1 km to only 8.6 km, or 16-2 Hz equivalent, with upward Poynting flux decreasing significantly faster. Our results thus point to a significant Alfven wave driven component of the Poynting flux on kilometer 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.