[1] The origin of whistler mode radiation in the plasmasphere is examined from 3 years of plasma wave observations from the Dynamics Explorer and the Imager for Magnetopauseto-Aurora Global Exploration spacecraft. These data are used to construct plasma wave intensity maps of whistler mode radiation in the plasmasphere. The highest average intensities of the radiation in the wave maps show source locations and/or sites of wave amplification. Each type of wave is classified on the basis of its magnetic latitude and longitude rather than any spectral feature. Equatorial electromagnetic (EM) emissions ($30-330 Hz), plasmaspheric hiss ($330 Hz to 3.3 kHz), chorus ($2-6 kHz), and VLF transmitters ($10-50 kHz) are the main types of waves that are clearly delineated in the plasma wave maps. Observations of the equatorial EM emissions show that the most intense region is on or near the magnetic equator in the afternoon sector and that during times of negative B z (interplanetary magnetic field) the maximum intensity moves from L values of 3 to <2. These observations are consistent with the origin of this emission being particle-wave interactions in or near the magnetic equator. Plasmaspheric hiss shows high intensity at high latitudes and low altitudes (L shells from 2 to 4) and in the magnetic equator with L values from 2 to 3 in the early afternoon sector. The longitudinal distribution of the hiss intensity (excluding the enhancement at the equator) is similar to the distribution of lightning: stronger over continents than over the ocean, stronger in the summer than in the winter, and stronger on the dayside than on the nightside. These observations strongly support lightning as the dominant source for plasmaspheric hiss, which, through particle-wave interactions, maintains the slot region in the radiation belts. The enhancement of hiss at the magnetic equator is consistent with particle-wave interactions. The chorus emissions are most intense on the morningside as previously reported. At frequencies from $10 to $50 kHz, VLF transmitters dominate the spectrum. The maximum intensity of the VLF transmitters is in the late evening or early morning with enhancements all along L shells from 1.8 to 3.

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Abstract. A new technique is introduced that remotely measures the plasma density profile in the plasmasphere. Radio plasma imager (RPI) echo observations provide echo delay time as function of frequency, from which the plasma density as function of position along the magnetic field line can be calculated. An example from the nightside plasmasphere (L--3) shows the density having its minimum value near the equator and rapidly increasing densities along the field line above 40 ø magnetic latitude. The density increases at a faster rate toward the ionosphere than the field strength. The index of the power law of the density as a function of field strength increases from a few tenths near the equator to close to unity near 40 ø and greater than 2 near the ionosphere.

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.