Observations of penetrated solar wind plasma elements in the plasma mantle |
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| Authors: | R Lundin B Aparicio |
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| Institution: | Kiruna Geophysical Institute, Box 704, S-981 27 Kiruna, Sweden |
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| Abstract: | PROGNOZ-7 observations of intense “magnetosheath-like” plasma deep inside the high latitude boundary layer, the plasma mantle, indicates that solar wind plasma elements may occasionally penetrate the magnetopause and form high density regions in the plasma mantle. These “magnetosheath-like” regions are usually associated with strong flow of solar wind ions (e.g. H+ and He2+) and the presence of terrestrial ions (e.g. O+). The magnetosheath-like structures may roughly be classified as “newly injected” or “stagnant”. The newly injected structures have characteristics very similar to those found in the magnetosheath, i.e. strong antisunward flow and magnetosheath ion composition and density. The magnetic field characteristics may, however, differ considerably from those found further out in the magnetosheath. The “stagnant” structures are characterized by a reduced plasma flow, a lower density and a different ion composition as compared to that in the magnetosheath. In a few cases newly injected structures were even found in the innermost part of the mantle (i.e. forming a “boundary region” adjacent to the lobe). These cases were also associated with fairly strong fluxes of O+ ions in the outer mantle. Whilst the newly injected type of magnetosheath-like structure contained almost no O+ ions, the stagnant regions were intermixed by an appreciable amount of ionospheric ions. The newly injected and stagnant penetration regions had both in common a diamagnetic decrease of the ambient magnetic field. The newly injected structures, however, were also associated with a considerable reorientation of the magnetic field vector. A common feature for penetration regions well separated from the magnetopause is that they are mainly observed for a southward IMF. A third category of plasma mantle penetrated events, denoted “open magnetopause” events, usually occurred when the IMF was away and northward. Characteristics for these events were a smooth transition/rotation of the magnetic field vector near the magnetopause, and fairly high ion densities in the mantle and the transition region. |
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