Magnetospheric responses to sudden and quasiperiodic solar wind variations

Abstract

On April 13 (day 103), 2001, 0700–1400 UT, the Polar satellite experienced different plasma regimes (i.e., magnetosphere, magnetosheath, and solar wind) because of the solar wind dynamic pressure variations and its high orbital inclination near the subsolar magnetopause meridian. When Polar was in the magnetosheath, quasiperiodic spacecraft potential (SP) variations, corresponding to density variations, with a recurrence time of ∼3–10 min were observed. Using simultaneous solar wind observations, it was confirmed that the magnetosheath SP variations were inherent in the solar wind. We observed an almost one‐to‐one correspondence between the SP variations and the geomagnetic field perturbations at lower latitudes (L = 1.1–2.8) on the nightside. At higher latitudes (L = 2.9–6.1) on the dayside, however, the field perturbations are more complicated than the magnetosheath SP variations. This suggests that if the magnetospheric perturbations produced by the external source (solar wind/magnetosheath pressure variations) deeply penetrate into the magnetosphere, the lower‐latitude data on the nightside are important to monitor the external source variations. In addition, we observed the radial electric field oscillations excited nearly simultaneously with the magnetic field enhancement, associated with a sudden increase in the solar wind dynamic pressure, when Polar was in the magnetosphere. These oscillations may be considered as transient standing Alfvén waves excited by externally applied pressure changes as reported by previous studies.

Non-triggered auroral substorms and long-period (1–4 mHz) geomagnetic and auroral luminosity pulsations in the polar cap

“…ULF power in the outer magnetosphere and at high geomagnetic latitudes on the ground surface is influenced by steep and quasi-periodic variations of solar wind dynamic pressure (Kepko et al, 2002;Kim et al, 2002). Global ULF enhancements following such dramatic changes in solar wind dynamic pressure as a sudden commencement (SC) and sudden impulse (SI) have been studied for almost 50 years, beginning with the early report by Saito and Matsushita (1967).…”

Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

“…Impulsive or quasi-periodic variations of the solar wind dynamic pressure can cause Pc5-6 oscillations that are highly coherent throughout all the high-latitude region (Kim et al, 2002). A positive correlation between the amplitude of the geomagnetic pulsations on the ground and solar wind dynamic pressure oscillations in the Pc5/6 frequency range exists not only for high-amplitude events, but permanently at any amplitude of the pressure oscillations (Yagova et al, 2007).…”

Pc5 waves generated by substorm injection: a case study

“…The satellites' data, given in the GSE coordinate system (http://cdaweb.gsfc.nasa.gov/), were transformed into the mean-field-aligned coordinate system: the x-and ycoordinates are directed outward (radial coordinate) and eastward (azimuthal coordinate), and z-coordinate is directed along the averaged magnetic field (defined by taking the 40-min boxcar running averages of the 60-s data (Kim et al, 2002). Hence, the transformed B x (t), B y (t), and B z (t) variations approximately describe the poloidal, toroidal and fieldaligned components of magnetic field vector B, respectively.…”