D. A. Lorentzen

Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of back-ground fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.

Magnetopause surface eigenmodes were suggested as a potential source of dayside high-latitude broadband pulsations in the Pc5-6 band (frequency about 1–2 mHz). However, the search for a ground signature of these modes has not provided encouraging results. The comparison of multi-instrument data from Svalbard with the latitudinal structure of Pc5-6 pulsations, recorded by magnetometers covering near-cusp latitudes, has shown that often the latitudinal maximum of pulsation power occurs about 2–3° deeper in the magnetosphere than the dayside open-closed field line boundary (OCB). The OCB proxy was determined from SuperDARN radar data as the equatorward boundary of enhanced width of a return radio signal. The OCB-ULF correspondence is further examined by comparing the latitudinal profile of the near-noon pulsation power with the equatorward edge of the auroral red emission from the meridian scanning photometer. In most analyzed events, the “epicenter” of Pc5-6 power is at 1–2° lower latitude than the optical OCB proxy. Therefore, the dayside Pc5-6 pulsations cannot be associated with the ground image of the magnetopause surface modes or with oscillations of the last field line. A lack of ground response to these modes beneath the ionospheric projection of OCB seems puzzling. As a possible explanation, we suggest that a high variability of the outer magnetosphere near the magnetopause region may suppress the excitation efficiency. To quantify this hypothesis, we consider a driven field line resonator terminated by conjugate ionospheres with stochastic fluctuations of its eigenfrequency. A solution of this problem predicts a substantial deterioration of resonant properties of MHD resonator even under a relatively low level of background fluctuations. This effect may explain why there is no ground response to magnetopause surface modes or oscillations of the last field line at the OCB latitude, but it can be seen at somewhat lower latitudes with more regular and stable magnetic and plasma structure.

The Investigation of Cusp Irregularities 2 sounding rocket was launched 5 December 2008 at 1035 UT. We present an overview of the associated solar wind and auroral conditions, and we look in detail at the relationship between poleward moving auroral forms (PMAFs) and the creation of polar cap patches using ground‐based optical and radar data as well as in situ data from the rocket payload. The solar wind was found to be dominated by a stable interplanetary magnetic field (IMF) B_z < 0 and by an IMF B_y > 0 situation. The aurora was characterized by a series of PMAFs throughout the period of interest. Associated with each PMAF were polar cap patches seen to emerge from the most poleward location of the PMAFs. On the basis of the available data, we present a conceptual model explaining the creation of the polar cap patches under the given solar wind and ionospheric conditions.

We report a study of ion upflow as seen by the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR), initiated by a rotation from interplanetary magnetic field (IMF) B_Z negative to IMF B_Z positive, under the influence of a strongly negative IMF B_Y. We combine ground‐based instruments, such as meridian scanning photometers (MSP), all‐sky imager (ASI) data, and radars, with solar wind data from the Advanced Composition Explorer (ACE) spacecraft and low‐altitude particle precipitation data from the Defense Meteorological Satellite Program (DMSP) F‐13 spacecraft as well as wave data from the Svalbard EISCAT Rocket Study of Ion Outflows (SERSIO) sounding rocket flight. Following a coronal mass ejection, the solar wind data showed high dynamic pressures (up to 20 n Pa) and a strongly varying IMF. The observed ion upflow was seen to be of a pulsed nature and sustained by pulsed soft electron precipitation. The data findings indicated pulsed lobe reconnection as the mechanism funneling energy and momentum down to the northern polar hemisphere.

In this study we present optical ground‐based signatures of drifting airglow patches in the polar ionospheric F‐layer, in the evening/nighttime MLT sector. The patches were observed under predominately IMF B_Z < 0, IMF B_Y > 0 conditions, which are favorable for high‐density sunlit plasma to be entrained into the polar cap with the large afternoon cell in the northern hemisphere. The patch morphology, such as altitude, meridional convection speed, and repetition rate was investigated using a meridian scanning photometer, and put into the context of activity changes in the auroral substorm. It was found that the meridional patch speed was modulated by the ongoing substorms, and that the patches crossed the open/closed field line boundary (OCB), even during late recovery, and subsequent growth phase. We take this as an indication of ongoing tail reconnection, and we therefore propose that the patches can be used as a tracer for tail reconnection when they cross the OCB and enter the nighttime auroral oval.

Using a collision by collision model from Lorentzen et al., the latitudinal and longitudinal dispersion of single auroral protons are calculated. The proton energies varies from 1 to 50 keV, and are released into the atmosphere at 700 km altitude. The dipole magnetic field has a dip-angle of 8 degrees. Results show that the main dispersion region is at high altitudes (300-350 km) and occurs during the first few charge exchange collisions. As the proton travels further down the atmosphere the mean free path becomes smaller, and as a result the spreading effect will not be as pronounced. This means that the first few charge exchange collisions fully determines the width of both the latitudinal and longitudinal dispersion. The volume emission rate was calculated for energies between 1 and 50 keV, and it was found that dayside auroral hydrogen emissions rates were approximately 10 times weaker than nightside emission rates. Simulations were also performed to obtain the dependence of the particle dispersion as a function of initial pitch-angle. It was found that the dispersion varies greatly with initial pitch-angle, and the results are summarized in two tables; a main and an extreme dispersion region.Key words. Ionosphere (auroral ionosphere; · particle precipitation) · Space plasma physics · (transport processes)