A study of Pc-5 ULF oscillations

Abstract

Abstract.A study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic magnetic field spectrograms have been used to survey ULF pulsation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were examined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probability of occurence of toroidal mode oscillations on the dawn and dusk sides of the magnetosphere inside geosynchronous orbit, while poloidal mode oscillations occur predominantly along the dusk side, consistent with high azimuthal mode number excitation by ring current ions.Pc-5 pulsations following Storm Sudden Commencements (SSCs) were examined separately. The spatial distribution of modes for the SSC events was consistent with the statistical study for the lifetime of CRRES. The toroidal fundamental (and harmonic) resonances are the dominant mode seen on the dawn-side of the magnetosphere following SSCs. Power is mixed in all three components. In the 21 dusk side SSC events there were only a few examples of purely compressional (two) or radial (one) power in the CRRES study, a few more examples of purely toroidal modes (six), with all three components predominant in about half (ten) of the events.

Magnetohydrodynamic modeling of three Van Allen Probes storms in 2012 and 2013

“…A1b, when it was already at higher L. Both spacecraft see approximately the same peak frequency 3.3 mHz by 22:01 UT, with power significantly lower at spacecraft B at that time and reduced further as it passes by 22:16 UT and moves further duskward. Figure 5 shows that the mHz ULF wave PSD attenuates away from the dayside, particularly clear for spacecraft B in panel (d), which has moved more duskward than A, as has been seen in many studies, with concentration of toroidal-mode power along the flanks of the magnetosphere and compressional in B (poloidal E φ ) power across the dayside; see, for example, Anderson et al (1992a, b) for a review of AMPTE CCE magnetometer measurements, Lessard et al (1999) for analysis of the local time distribution of AMPTE IRM magnetometer data, Hudson et al (2004) for CRRES magnetometer, Liu et al (2009) for THEMIS data, and Engebretson et al (1998) for ground magnetometer studies. Other LFM CME-shock event studies (Elkington et al, 2002 have confirmed the predominance of wave power on the dayside in the poloidal E φ component and discussed the need to include that longitudinal asymmetry in any prescribed ULF wave model of effects on radial transport and acceleration of electrons.…”

A long‐duration narrowband Pc5 pulsation

“…Similarly to the definition used by Hudson et al [2004], here we characterize as narrowband Pc5 pulsations all magnetospheric oscillations with Df < 2 mHz at a given time, where bandwidth Df is the full width at half maximum. Such pulsations can be attributed either to the solar wind, acting as an external driver, or to internal plasma anisotropies, and are characterized by their azimuthal wave number, m [Dungey, 1954;Green, 1976], which is often indicative of the excitation mechanism.…”

The interaction of ultra-low-frequency pc3-5 waves with charged particles in Earth’s magnetosphere

“…These results have been confirmed by statistical analysis of GOES magnetic field data at geosynchronous orbit . Although excitation of ULF Pc4-5 waves has been traditionally attributed to the K-H instability, waves generated by this instability show minimum activity around noon near the subsolar stagnation region compared with the dawn and dusk sector (e.g., Anderson et al 1990;Zhu and Kivelson 1991;Lessard et al 1999;Hudson et al 2004;Takahashi and Ukhorsky 2007). The observations reported here, on the other hand, show that poloidal ULF waves associated with solar wind dynamic pressure pulses exhibit a maximum at local noon.…”

“…Sudden density or velocity increases in the solar wind produced by IP shocks lead to a step-like enhancement of the solar wind dynamic pressure and a sudden compression of Earth's dayside magnetosphere. The resulting magnetosonic waves launched into the magnetosphere (Wilken et al 1982;Kepko and Spence 2003;Hudson et al 2004;Claudepierre et al 2009) excite FLRs around magnetic local noon (Zong et al 2009a, b;) and interact with charged particles. Fig.…”