Abstract
Abstract. Based on a case study we test the cavity mode model of the magnetosphere, looking for eigenfrequencies via multi-satellite and multi-instrument measurements. Geotail and ACE provide information on the interplanetary medium that dictates the input parameters of the system; the four Cluster satellites monitor the magnetopause surface waves; the POLAR (L=9.4) and LANL 97A (L=6.6) satellites reveal two in-situ monochromatic field line resonances (FLRs) with T=6 and 2.5 min, respectively; and the IMAGE ground magnetometers demonstrate latitude dependent delays in signature arrival times, as inferred by Sarafopoulos (2004b). Similar dispersive structures showing systematic delays are also extensively scrutinized by Sarafopoulos (2005) and interpreted as tightly associated with the so-called pseudo-FLRs, which show almost the same observational characteristics with an authentic FLR. In particular for this episode, successive solar wind pressure pulses produce recurring ionosphere twin vortex Hall currents which are identified on the ground as pseudo-FLRs. The BJN ground magnetometer records the pseudo-FLR (alike with the other IMAGE station responses) associated with an intense power spectral density ranging from 8 to 12 min and, in addition, two discrete resonant lines with T=3.5 and 7 min. In this case study, even though the magnetosphere is evidently affected by a broad-band compressional wave originated upstream of the bow shock, nevertheless, we do not identify any cavity mode oscillation within the magnetosphere. We fail, also, to identify any of the cavity mode frequencies proposed by Samson (1992). Keywords. Magnetospheric physics (Magnetosphereionosphere interactions; Solar wind-magnetosphere interactions; MHD waves and instabilities)
Highlights
In the single-fluid field line resonance (FLR) model (Southwood, 1974; Chen and Hasegawa, 1974) compressional mode magnetic waves propagating in the near-Earth magnetosphere couple into transverse magnetic standing waves on closed magnetic field lines
This work deals with a case study of day 181, 2001, that incorporates measurements obtained (a) in the solar wind plasma regime (Geotail and ACE satellites), (b) at the magnetopause surface, (c) well-inside the magnetosphere (POLAR and LANL satellites), and (d) on the Earth’s surface
We examine the Pc5 frequency pulsations of plasma density and magnetic field that occur during a pass of the POLAR satellite along the dawn meridian and close to the geomagnetic equator; an interval of two hours (03:45 to 05:45 UT) of day 181, 2001, is under study
Summary
In the single-fluid field line resonance (FLR) model (Southwood, 1974; Chen and Hasegawa, 1974) compressional. Sarafopoulos (2004b) observed latitude-dependent delays in signature arrival times at the dawnside ground magnetograms and demonstrated that these structures are directly dictated by successive exo-magnetosphere pressure pulses applied along the magnetopause He established (using ground and satellite data, together with results from the Tsyganenko T96 model of the magnetosphere) the conditions under which a compression wave travelling tailward along the magnetopause surface will produce poleward moving signatures in ground. Under the Sarafopoulos (2004b, 2005) perspective the observation that all the auroral ground stations show the same frequency, which is associated with successive twin-vortex current systems imposed by a magnetopause surface wave, has nothing to do with the cavity mode The latter is the subject for this study, which further extends this author thinking. This work tests the cavity mode model using a case study
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