Phase and amplitude structure of Pc 3 magnetic pulsations as determined from multipoint observations

Abstract

Abstract. To identify the propagation mode of ULF waves in the magnetosphere, observational determination of their amplitude and phase structure is necessary. Despite the fact that Pc 3 pulsations are observed at various latitudes, no systematic studies of the phase and amplitude structure of Pc 3 over a wide range of latitudes have been done. Using magnetic field data from the Western Pacific magnetometer array centered at 210 ø geomagnetic longitude and from the Geotail satellite, we present the latitudinal structure of a Pc 3 pulsation event that occurred on October 17-18, 1992. During this event, Geotail was located in the dayside magnetosphere at a radial distance of -8 Re and observed tailward propagating fast-mode magnetosonic waves in the Pc 3 band [Takahashi et al., 1994b]. Pulsations observed at the ground stations, also on the dayside, exhibit dynamic spectra similar to those observed from Geotail. Spectral analyses of the ground data reveal that the pulsations are often coherent from L -1 to L -6. Furthermore, the phase of the pulsations varies with L in a complex manner: at low-latitude stations in the L range between 1.1 and 2.9, there is little phase delay; at a high-latitude station (L -5.5) the phase relative to low latitudes is -180ø; and at an equatorial station (L = 1.01), the phase relative to low latitudes is -150 ø . The pulsation amplitude is at an overall maximum at the highest-latitude station of the magnetometer array, but two additional maxima occur at L -1 and L -2.1. We discuss these observations in terms of MHD wave propagation effects in the magnetosphere.

ULF waves: 1997 IAGA division 3 reporter review

“…An explanation of single-frequency low-latitude Pc 3 pulsations which is consistent with the Vellante et al (1996) result has been o ered by Matsuoka et al (1997). Instead of introducing the cavity resonance, Matsuoka et al (1997) attribute the in-phase oscillations observed at L < 2.8 to an evanescent mode associated with upstream waves that propagate into the deep magnetosphere.…”

“…Feng et al (1995) and Matsuoka et al (1997) observe single-frequency Pc 3 events at low latitude v`2 using latitudinal arrays of magnetometers. Figure 6 shows an event represented by Feng et al (1995).…”

Near-equatorial Pi2 and Pc3 waves observed by CHAMP and on SAMBA/MAGDAS stations

“…Matsuoka et al (1997) found a significant phase shift $150°of dayside equatorial (L < 1.01) Pc3 pulsations as compared with those at low-latitude stations. Our ground observations have revealed equatorial enhancement of amplitude $2 times, but no phase peculiarities at equatorial MAGDAS stations.…”

“…The latitudinal distribution in the top-side ionosphere showed that dayside compressional power in the Pc3 band was most pronounced in two regions: near noon, 09-14 LT at near-equatorial latitudes (±15°from the geomagnetic equator), and at high latitudes $75° (Heilig et al, 2007). However, the overall Pc3 amplitude/phase spatial structure cannot be explained by a simple propagation of fast mode (Matsuoka et al, 1997). Besides resonant conversion into Alfven field line oscillations, the excitation of some cavity mode may be possible.…”

“…However, because of its large horizontal scale, even an evanescent fast mode can convey significant wave energy towards the Earth. Commonly, the earthward propagation of compressional fast mode was described in the frameworks of 1D (Pekrides et al, 1997;Matsuoka et al, 1997) or 2D (Allan et al, 1996) models. In reality, the spatial distribution of wave power is determined by the diffraction of an incident large-scale FMS mode on a relatively small conductive sphere (Earth).…”