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Abstract In Earth’s low atmosphere, hurricanes are destructive due to their great size, strong spiral winds with shears, and intense rain/precipitation. However, disturbances resembling hurricanes have not been detected in Earth’s upper atmosphere. Here, we report a long-lasting space hurricane in the polar ionosphere and magnetosphere during low solar and otherwise low geomagnetic activity. This hurricane shows strong circular horizontal plasma flow with shears, a nearly zero-flow center, and a coincident cyclone-shaped aurora caused by strong electron precipitation associated with intense upward magnetic field-aligned currents. Near the center, precipitating electrons were substantially accelerated to ~10 keV. The hurricane imparted large energy and momentum deposition into the ionosphere despite otherwise extremely quiet conditions. The observations and simulations reveal that the space hurricane is generated by steady high-latitude lobe magnetic reconnection and current continuity during a several hour period of northward interplanetary magnetic field and very low solar wind density and speed. 

Abstract Using the global Lagrangian version of the piecewise parabolic method‐magnetohydrodynamic (PPMLR‐MHD) model, we simulate two consecutive storms in December 2015, a moderate storm on 14–15 December and a strong storm on 19–22 December, and calculate the radial diffusion coefficients (D_LL) from the simulated ultralow frequency waves. We find that even though the strong storm leads to more enhancedB_zandE_φpower than the moderate storm, the two storms share in common a lot of features on the azimuthal mode structure and power spectrum of ultralow frequency waves. For both storms, the totalB_zandE_φpower is better correlated with the solar wind dynamic pressure in the storm initial phase and more correlated withAEindex in the recovery phase.B_zwave power is shown to be mostly distributed in low mode numbers, whileE_φpower spreads over a wider range of modes. Furthermore, theB_zandE_φpower spectral densities are found to be higher at higherLregions, with a strongerLdependence in theB_zspectra. The estimatedD_LLbased on MHD fields shows that inside the magnetopause, the contribution from electric fields is larger than or comparable to that from magnetic fields, and our event‐specific MHD‐basedD_LLcan be smaller than some previous empiricalD_LLestimations by more than an order of magnitude. At last, by validating against in situ observations from Magnetospheric Multiscale spacecraft, our MHD results are found to generally well reproduce the totalB_zfields and wave power for both storms, while theE_φpower is underestimated in the MHD simulations.