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Abstract Ultra low frequency (ULF; 1 mHz ‐ several Hz) waves are key to energy transport within the geospace system, yet their contribution to Joule heating in the upper atmosphere remains poorly quantified. This study statistically examines Joule heating associated with ionospheric ULF perturbations using Super Dual Auroral Radar Network (SuperDARN) data spanning middle to polar latitudes. Our analysis utilizes high‐time‐resolution measurements from SuperDARN high‐frequency coherent scatter radars operating in a special mode, sampling three “camping beams” approximately every 18 s. We focus on ULF perturbations within the Pc5 frequency range (1.6–6.7 mHz), estimating Joule heating rates from ionospheric electric fields derived from SuperDARN data and height‐integrated Pedersen conductance from empirical models. The analysis includes statistical characterization of Pc5 wave occurrence, electric fields, Joule heating rates, and azimuthal wave numbers. Our results reveal enhanced electric fields and Joule heating rates in the morning and pre‐midnight sectors, even though Pc5 wave occurrences peak in the afternoon. Joule heating is more pronounced in the high‐latitude morning sector during northward interplanetary magnetic field conditions, attributed to local time asymmetry in Pedersen conductance and Pc5 waves driven by Kelvin‐Helmholtz instability. Pc5 waves observed by multiple camping beams predominantly propagate westward at low azimuthal wave numbers , while high‐m waves propagate mainly eastward. Although Joule heating estimates may be underestimated due to assumptions about empirical conductance models and the underestimation of electric fields resulting from SuperDARN line‐of‐sight velocity measurements, these findings offer valuable insights into ULF wave‐related energy dissipation in the geospace system. 

Abstract The offset between Earth's magnetic and rotational axes introduces a diurnal dependence in the high‐latitude EUV exposure of the northern hemisphere (NH) and southern hemisphere (SH). This variation raises the question: Does the Universal Time (UT) of geomagnetic storm onset impact its geospace consequences? To address this question, we used the Multiscale Atmosphere‐Geospace Environment (MAGE) model to simulate the 10 October 2024, geomagnetic storm—the year's second strongest (SYM‐H minimum of −346 nT). Since the storm occurred near equinox, we did not expect, but found, significant interhemispheric asymmetries in magnetosphere‐ionosphere‐thermosphere (M‐I‐T) coupling parameters such as the cross‐polar cap potential, hemispherically integrated field‐aligned current, and hemispheric power of electron precipitation. Controlled simulations show that interplanetary magnetic field (IMF) and solar wind have negligible effects on these asymmetries, whereas the EUV variation arising from the diurnal dipole tilt produces noticeable interhemispheric differences. Coincidentally, during this storm, IMFB_zturned southward when the SH was tilted toward the Sun, and it maintained this orientation for 12 hr. A controlled simulation with storm onset shifted by 12 hr exhibits a substantial reduction in interhemispheric asymmetry. Differences in integrated Joule heating power and the SML/SMU indices also occurred with the shifted onset, underscoring the importance of UT in stormtime magnetosphere‐ionosphere coupling. 

Abstract Ultra‐low frequency (ULF) waves are a ubiquitous carrier of energy in geospace. However, their efficiency in transferring solar wind energy into the upper atmosphere remains a fundamental and not well‐understood question. This is due to their global presence, which cannot be fully quantified by spatially limited observations, and the need for self‐consistent global modeling to account for their dependence on dynamic, inhomogeneous magnetic fields and plasma densities. In this study we use a purely global magnetohydrodynamic model to investigate energy inputs to the ionosphere in the form of Poynting flux. Oscillations in solar wind dynamic pressure excite field line resonances in the magnetosphere. The total Alfvénic Poynting flux entering the ionosphere can be comparable to the total quasi‐steady Poynting flux under northward interplanetary magnetic field. The efficiency of this energy transfer via ULF waves depends on the driving frequency of the solar wind and the ionospheric Pedersen conductance.