On the direction of the Poynting flux related to the mesoscale electromagnetic turbulence at high latitudes

Up to now, several tens of theories for inverted‐ V structure and discrete arc formation have been proposed. In about half of them the source of auroral structuring is supposed to be in the ionosphere, whereas a magnetospheric origin is inferred in others. In order to discriminate between these two classes of mechanisms, we have examined the observed direction of the high‐latitude Poynting flux δ P = δ E × δ B associated with the structured electric δ E and magnetic δ B fields. The upward direction of δ P would indicate an ionospheric generator of these fields, while downward δ P is a signature of a magnetospheric mechanism at work. The analysis was performed for scales ranging from 3.8 km to a few hundreds of kilometers in the ionosphere, meaning that the irregularities under study can be identified with discrete auroral features. The electric and magnetic field measurements of the Dynamics Explorer 2 satellite (altitudes from 300 to 1000 km) for a period of one and a half years were used. We have found that in about 95% of cases the relative orientation of δ E and δ B is such that δ P points downward, suggesting a magnetospheric origin of electromagnetic field structuring at high latitudes. Being averaged over the polar cap, δ P exhibits a steady growth with northward B z interplanetary magnetic field (IMF) increasing, while, averaged over the auroral oval, δ P grows with increasing southward B z IMF.