Reconstruction of the magnetopause and low-latitude boundary layer topology using Cluster multi-point measurements

Abstract

Abstract. Multi-spacecraft data from Cluster allow for a more detailed magnetopause and boundary layer structure determination than ever before. Reconstruction methods, in which the time variability observed during a pass is interpreted as being due to boundary motion and/or spatial structure, are particularly well suited for this task. Such methods rely on the availability of plasma and field data and adopt the tangential discontinuity hypothesis to determine the motion, acceleration, boundary structure, boundary curvature and surface wave speed over an extended time interval. In this paper one-and two-dimensional reconstruction methods are applied to multi-spacecraft data for the first time.

Magnetopause and Boundary Layer

“…The two-dimensional reconstructions in Figure 8.38a-d represent the spatial distribution of a few quantities in the comoving frame (see De Keyser et al, 2004a, for other quantities). Colour-coded reconstructions of ion density (CIS/HIA, C1 and Figure 8.38a) and of the perpendicular magnetic ULF wave intensity (STAFF, 0.3-10 Hz, all spacecraft, Figure 8.38b) outline the undulating shape of the wave.…”

“…De Keyser et al (2004a) have applied a two-dimensional empirical reconstruction technique to a subset of the data: two wave periods between 01:53 to 02:15 UT (wave period is 11 minutes). The result of this analysis is a two-dimensional picture of the surface waves (the wave structure can be shown to be essentially invariant in one direction, the z direction) in a reference frame that slides along the boundary with the wave, shown in Figure 8.38.…”

Empirical reconstruction and long-duration tracking of the magnetospheric boundary in single- and multi-spacecraft contexts

“…-The method gives information about the thickness of and possible density structure inside the LLBL (see also De Keyser et al, 2004). This is important for understanding mass transport across the magnetopause.…”

“…It is implicitly assumed that x mpbl (t) is a single-valued function, which might not be true in the nonlinear stage of the evolution of surface waves (Otto and Fairfield, 2000) or in the presence of isolated magnetosheath plasma entities inside the magnetosphere (Lemaire and Roth, 1991). If the plasma near the MP/BL moves collectively back and forth as a planar structure, without plasma flow across the MP/BL, the locally measured plasma velocity v x (or v ⊥x ) can be used as a substitute for the boundary velocity (Paschmann et al, 1990;De Keyser et al, 2004). Alternatively, one may use the electric drift or the velocity of a single plasma component.…”

“…Straightforward application of this idea has limited success because the errors grow rapidly as the analysis interval becomes longer. De Keyser et al (2004) have applied this idea in the multi-spacecraft case: Combining plasma velocity data from all spacecraft can reduce the errors. It has also been shown that problems due to inaccurate boundary velocity information can be remedied by using an optimization approach, in which a model boundary motion profile is matched to the observed boundary motion proxy while simultaneously fitting other parameters to prescribed spatial profiles (De Keyser et al, 2002).…”