Structure of the magnetopause: Observations and implications for reconnection

This paper deals with dynamic processes caused by irregularities close to the magnetopause as discussed by several authors in the recent literature. The problem of plasma entry is tackled theoretically by assuming individual filaments appearing at the magnetopause with an excess inward momentum. The conditions under which entry is possible are derived in a two‐dimensional model. With ideal MHD, entry is essentially confined to the cases of near magnetic field alignment. The consequences of nonideal MHD processes are discussed qualitatively. The results support the possibility of the presence of an irregular distribution of ‘merging patches’ on the magnetopause, giving better agreement with recent observations than the classical steady state reconnection picture. All entry mechanisms discussed are potential candidates for the processes that form the plasma boundary layer.

Section: Discussionmentioning

confidence: 99%

On the role of irregularities in plasma entry into the magnetosphere

Schindler¹

1979

“…In this initial study we neglect the effects of dipole tilting. The field within the magnetosheath is assumed to be current-free [e.g., Fairfield, 1979] 2.5.2. Geomagnetic field at the magnetopause boundary.…”

Section: Coordinate Systemmentioning

confidence: 99%

Role of the magnetosheath flow in determining the motion of open flux tubes

Cooling¹,

Owen²,

Schwartz³

2001

141

220

Abstract. We have constructed a model which examines the motion of reconnected magnetic flux tubes over the surface of the magnetopause. For a given interplanetary magnetic field (IMF) we first determine the draping and strength of the magnetosheath magnetic field, flow velocity, and density over the entire surface of a paraboloid magnetopause. For a given magnetopause location we apply a test for steady state reconnection occurring between the magnetosheath field and a modeled magnetospheric field at that point. We trace the subsequent motion of these tubes along the surface of the magnetopause and into the magnetotail. Results are shown for a range of cases. The model has applications in testing various hypotheses about the location of reconnection events and, for example, IMF By effects. In particular, it highlights the dominance of the magnetosheath flow model in determining the motion of the tubes and the necessity of sub-Alfv6nic magnetosheath flows for the occurrence of steady state reconnection poleward of the cusp during periods of northward IMF. Our model may also be used to identify likely reconnection sites on the dayside and near-Earth nightside magnetopause and to identify possible locations for steady state reconnection.

“…The structure of the magnetopause has been the subject of many studies, experimental as well as theoretical, during this past decade [see reviews by Willis, 1971Willis, , 1975Sonnerup, 1976;Roederer, 1977;Fairfield, 1979]. Curiously, an extensive study of magnetopause polarization has not been undertaken.…”

Section: Introductionmentioning

confidence: 99%

Magnetic field rotation through the magnetopause: ISEE 1 and 2 observations

Berchem¹,

Russell²

1982

110

ISEE 1 and 2 magnetic field data obtained during dayside magnetopause crossings have been analyzed using a minimum variance technique in order to determine the characteristics of the rotation of the magnetic field across the magnetopause. Only a small fraction of the magnetopause crossings examined present a sufficiently coherent structure that they can be compared with theoretical predictions, and only a few of the hodograms of the magnetic field at the crossings show the ideal rotation expected for a rotational discontinuity structure. Observed senses of rotation are not consistent with the predictions of the electron whistler polarization theory. Rotations greater than 180° are very seldom observed; they usually occur across multiple crossings, either as 360° rotation about the minimum variance direction or, occasionally, in more complicated patterns associated with ‘S’‐shaped hodograms. These observations suggest that the sense of the magnetic field rotation through the magnetopause is controlled by the relative orientation of the magnetosheath and magnetospheric field and that the angular rotation is minimized when the magnetic field changes from one orientation to the other.