First simultaneous measurements of waves generated at the bow shock in the solar wind, the magnetosphere and on the ground

Abstract

Abstract. On 5 September 2002 the Geotail satellite observed the cone angle of the Interplanetary Magnetic Field (IMF) change to values below 30 • during a 56 min interval between 18:14 and 19:10 UT. This triggered the generation of upstream waves at the bow shock, 13 R E downstream of the position of Geotail. Upstream generated waves were subsequently observed by Geotail between 18:30 and 18:48 UT, during times the IMF cone angle dropped below values of 10 • . At 18:24 UT all four Cluster satellites simultaneously observed a sudden increase in wave power in all three magnetic field components, independent of their position in the dayside magnetosphere. We show that the 10 min delay between the change in IMF direction as observed by Geotail and the increase in wave power observed by Cluster is consistent with the propagation of the IMF change from the Geotail position to the bow shock and the propagation of the generated waves through the bow shock, magnetosheath and magnetosphere towards the position of the Cluster satellites. We go on to show that the wave power recorded by the Cluster satellites in the component containing the poloidal and compressional pulsations was broadband and unstructured; the power in the component containing toroidal oscillations was structured and shows the existence of multi-harmonic Alfvénic continuum waves on field lines. Model predictions of these frequencies fit well with the observations. An increase in wave power associated with the change in IMF direction was also registered by ground based magnetometers which were magnetically conjunct with the Cluster satellites during the event. To the best of our knowledge we present the first simultaneous observations of waves created by backCorrespondence to: L. B. N. Clausen (lbnc1@ion.le.ac.uk) streaming ions at the bow shock in the solar wind, the dayside magnetosphere and on the ground.

ULF wave activity during the 2003 Halloween superstorm: multipoint observations from CHAMP, Cluster and Geotail missions

“…These studies revealed that toroidal and poloidal mode field line resonances together with compressional Pc5 waves account for most of the observed coherent pulsations observed in the outer magnetosphere (Anderson et al, 1990). Multipoint observations show that upstream ULF waves in the Pc3-4 bands are generated in the foreshock region and entering and propagating through the magnetosphere as compressional waves (Sakurai et al, 1999;Constantinescu et al, 2007;Heilig et al, 2007;Clausen et al, 2009).…”

“…The four Cluster spacecraft, therefore, represent a valuable tool for the analysis of magnetospheric ULF pulsations, as shown by a plethora of recent studies (e.g., Eriksson et al, 2005;Schäfer et al, 2007;Clausen et al, 2009). For this purpose, the Cluster spacecraft were originally placed in a 4 × 19.6 R E elliptical polar .…”

Spectral structure of Pc3–4 pulsations: possible signatures of cavity modes

“…The dependence of Pc3 activity on solar wind density suggests that UWs are the predominant source of midlatitude Pc3s. A multi-instrument study by Clausen et al (2009) clearly illustrates the transfer of ULF energy from an upstream source. Simultaneous observations made aboard spacecraft in the solar wind (Geotail) and in the magnetosphere (Cluster), and by magnetometers on the ground showed (i) the excitation of ULF waves in the magnetometers 10 min after the IMF direction changed to a parallel orientation, and (ii) a broad, unstructured band of frequencies in the poloidal and compressional field components, driving multiple harmonics of FLRs in the toroidal field component.…”

A solar-wind-driven empirical model of Pc3 wave activity at a mid-latitude location

“…According to Clausen et al (2009) the propagation of compressional waves through the magnetosheath that drive pul-sations in the magnetosphere can be calculated using the process described by Khan and Cowley (1999). Propagation through the sheath is determined by sheath width, solar wind speed (V sw ), plasma flow speed into the magnetopause (V mp ) and the shock jump ratio…”

“…It is assumed that the fast mode wave is responsible for carrying ULF energy through the magnetosphere at the Alfvén speed V A toward the Earth (Clausen et al, 2009). The Alfvén speed in the magnetosphere, based on electron density measurements, varies between about 1000 km s −1 in the inner magnetosphere (L ≈ 3 − 6) (Fraser et al, 1988) and about 3000 km s −1 in the outer magnetosphere (L ≈ 6-10) (e.g.…”