Funnel‐shaped, low‐frequency radiation, as observed in frequency time spectrograms, are frequently found at the Earth's magnetic equator. At the equator the radiation often extends from the proton cyclotron frequency up to the lower hybrid frequency. Ray‐tracing calculations can qualitatively reproduce the observed frequency‐time characteristics of these emissions if the waves are propagating in the fast magnetosonic mode starting with wave normal angles of ∼88° at the magnetic equator. The funnel‐shaped emissions are consistent with generation by protons with a ring‐type velocity space distribution. A ring‐shaped region of positive slope in the velocity space density distribution of protons is observed near the Alfvén velocity, indicating that the ring protons strongly interact with the waves. Ray‐tracing calculations show that for similar equatorial wave normal angles lower‐frequency fast magnetosonic waves are more closely confined to the magnetic equator than higher‐frequency fast magnetosonic waves. For waves refracted back toward the equator at similar magnetic latitudes, the lower‐frequency waves experience stronger damping in the vicinity of the equator than higher‐frequency waves. Also, wave growth is restricted to higher frequencies at larger magnetic latitudes. Wave damping at the equator and wave growth off the equator favors equatorial wave normal angle distributions which lead to the funnel‐shaped frequency time characteristic.

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The IMAGE spacecraft uses photon and neutral atom imaging and radio sounding techniques to provide global images of Earth's inner magnetosphere and upper atmosphere. Auroral imaging at ultraviolet wavelengths shows that the proton aurora is displaced equatorward with respect to the electron aurora and that discrete auroral forms at higher latitudes are caused almost completely by electrons. Energetic neutral atom imaging of ions injected into the inner magnetosphere during magnetospheric disturbances shows a strong energy-dependent drift that leads to the formation of the ring current by ions in the several tens of kiloelectron volts energy range. Ultraviolet imaging of the plasmasphere has revealed two unexpected features-a premidnight trough region and a dayside shoulder region-and has confirmed the 30-year-old theory of the formation of a plasma tail extending from the duskside plasmasphere toward the magnetopause.

Reconnection is accepted as an important process for driving the solar wind/magnetospheric interaction although it is not fully understood. In particular, reconnection for northward interplanetary magnetic field (IMF) at high‐latitudes tailward of the cusp, has received little attention in comparison with equatorial reconnection for southward IMF. Using Hawkeye data we present the first direct observations of reconnection at the high‐latitude magnetopause (75°) during northward IMF in the form of sunward flowing protons. This flow is nearly field aligned, approximately Alfvénic, and roughly obeys tangential momentum balance. The magnetic field shear is large at the magnetopause and there is a non‐zero BN component suggesting the existence of a rotational discontinuity and reconnection. The Hawkeye observations support several recent simulations at least qualitatively in terms of flow directions expected for high‐latitude reconnection during northward IMF.

[1] Using the sounding measurements from the radio plasma imager on IMAGE and a plasma density inversion algorithm, we derive the plasma density profiles along the magnetic field in a few L shells every 14 hours at magnetic local noon before, during, and after the 31 March 2001 magnetic storm. An empirical model of the plasmaspheric plasma density distribution is derived as a reference using the measurements before the storm. During the storm the equatorial plasma was substantially depleted in a range of L shells. The flux tubes were refilled after the storm. The filling ratio, the equatorial plasma density normalized by its quiet time value before the storm, is introduced to assess the time evolution of the depletion and refilling processes. The depletion, more than two thirds of the quiet time content, appeared to occur rather quickly after the storm onset, as determined by the limited temporal resolution of the measurements. The refilling proceeded, although more slowly than the depletion process, significantly faster than the theoretical prediction of a 3-day timescale. Dynamic structures are observed in situ and confirmed by the extreme ultraviolet imager (EUV) measurements.