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The systematic study of ionospheric storms has been conducted primarily with\udgroundbased data from the Northern Hemisphere. Significant progress has been\udmade in defining typical morphology patterns at all latitudes; mechanisms\udhave been identified and tested via modeling. At higher mid-latitudes (sites\udthat are typically sub-auroral during non-storm conditions), the processes\udthat change significantly during storms can be of comparable magnitudes, but\udwith different time constants. These include ionospheric plasma dynamics\udfrom the penetration of magnetospheric electric fields, enhancements to\udthermospheric winds due to auroral and Joule heating inputs, disturbance\uddynamo electrodynamics driven by such winds, and thermospheric composition\udchanges due to the changed circulation patterns. The ~12° tilt of\udthe geomagnetic field axis causes significant longitude effects in all of\udthese processes in the Northern Hemisphere. A complementary series of\udlongitude effects would be expected to occur in the Southern Hemisphere. In\udthis paper we begin a series of studies to investigate the\udlongitudinal-hemispheric similarities and differences in the response of the\udionosphere's peak electron density to geomagnetic storms.\ud\ud \ud\udThe ionosonde stations at Wallops Island (VA) and Hobart (Tasmania) have\udcomparable geographic and geomagnetic latitudes for sub-auroral locations,\udare situated at longitudes close to that of the dipole tilt, and thus serve\udas our candidate station-pair choice for studies of ionospheric storms at\udgeophysically-comparable locations. They have an excellent record of\udobservations of the ionospheric penetration frequency (foF2) spanning\udseveral solar cycles, and thus are suitable for long-term studies. During\udsolar cycle #20 (1964–1976), 206 geomagnetic storms occurred that had Ap≥30 or Kp≥5 \udfor at least one day of the\udstorm. Our analysis of average storm-time perturbations (percent deviations\udfrom the monthly means) showed a remarkable agreement at both sites under a\udvariety of conditions. Yet, small differences do appear, and in systematic\udways. We attempt to relate these to stresses imposed over a few days of a\udstorm that mimic longer term morphology patterns occurring over seasonal and\udsolar cycle time spans. Storm effects versus season point to possible\udmechanisms having hemispheric differences (as opposed to simply seasonal\uddifferences) in how solar wind energy is transmitted through the\udmagnetosphere into the thermosphere-ionosphere system. Storm effects versus\udthe strength of a geomagnetic storm may, similarly, be related to patterns\udseen during years of maximum versus minimum solar activity

Ionospheric storms at geophysically-equivalent sites – Part 1: Storm-time patterns for sub-auroral ionospheres