Coupling the Solar-Wind/IMF to the Ionosphere Through the High Latitude CUSPS

Abstract

Magnetic merging is a primary means for coupling energy from the solar wind into the magnetosphere-ionosphere system. The location and nature of the process remain as open questions. By correlating measurements from diverse locations and using large-scale MHD models to put the measurements in context, it is possible to constrain our interpretations of the global and meso-scale dynamics of magnetic merging. Recent evidence demonstrates that merging often occurs at high latitudes in the vicinity of the cusps. The location is in part controlled by the clock angle in the interplanetary magnetic field (IMF) Y-Z plane. In fact, B Y bifurcates the cusp relative to source regions. The newly opened field lines may couple to the ionosphere at MLT locations of as much as 3 hr away from local noon. On the other side of noon the cusp may be connected to merging sites in the opposite hemisphere. In fact, the small convection cell is generally driven by opposite hemisphere merging. B X controls the timing of the interaction and merging sites in each hemisphere, which may respond to planar features in the IMF at different times. Correlation times are variable and are controlled by the dynamics of the tilt of the interplanetary electric field phase plane. The orientation of the phase plane may change significantly on time scales of tens of minutes. Merging is temporally variable and may be occurring at multiple sites simultaneously. Accelerated electrons from the merging process excite optical signatures at the foot of the newly opened field lines. All-sky photometer observations of 557.7 nm emissions in the cusp region provide a ''television picture'' of the merging process and may be used to infer the temporal and spatial variability of merging, tied to variations in the IMF.

Magnetosheath Interaction with the High Latitude Magnetopause

“…Savin et al (2002a) accounted for the difference of the power for Polar and Interball spectra of about one order of magnitude by the average magnetic field annihilation in a patchy reconnection (cf. Maynard, 2003). Similar reasoning for 29 May 1996 has been proposed by Savin et al (2004).…”

“…Savin et al (1998bSavin et al ( , 2001Savin et al ( , 2002aSavin et al ( , b, 2004 and Maynard (2003) provide relevant references and results.…”

“…This is in agreement with the cross-correlation of B y at 07:30-10:10 UT being <0.5; at 09:30-10 UT the cross-correlation is 0.23, with a time lag for Geotail of 12 min, with Geotail V x =)478 km/s. Considering possible different tilts for SW disturbances (Maynard, 2003) would hardly improve the correlation substantially. Greater resolution of these variations is presented in Figure 4, which will be discussed in detail in Section 2.…”

Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms

“…In such cases magnetic mapping between merging sites and the conjugate northern and southern cusps remains intelligible, albeit more complicated. However, the temporal and spatial properties of energetic electron tails are similar (Maynard et al, 2005). Cowley and Lockwood (1992) suggested that merging is intermittent, occurring in bursts, separated by quiescent gaps at particular locations.…”

“…Particle measurements acquired during a fortuitous DMSP overflight of an auroral structure above Svalbard showed that electrons with energies between 0.5 and a few keV were the sources of 557.7 nm emissions. Maynard et al (2005) used Polar data to show that electrons with similar energies constitute the high-energy tails of the suprathermal electron distributions found on field lines connected to active merging sites.…”