High-beta plasma blobs in the morningside plasma sheet

[摘要] Equator-S frequently encountered, i.e. on 30%of the orbits between 1 March and 17 April 1998, strong variations of themagnetic field strength of typically 5–15-min duration outside about 9R_Eduring the late-night/early-morning hours. Very high-plasma beta values werefound, varying between 1 and 10 or more. Close conjunctions between Equator-Sand Geotail revealed the spatial structure of these "plasma blobs" andtheir lifetime. They are typically 5–10^° wide in longitude and havean antisymmetric plasma or magnetic pressure distribution with respect to theequator, while being altogether low-latitude phenomena
(≤ 15^°). They drift slowly sunward, exchange plasma acrossthe equator and have a lifetime of at least 15–30 min. While their spatialstructure may be due to some sort of mirror instability, little is known aboutthe origin of the high-beta plasma. It is speculated that the morningsideboundary layer somewhat further tailward may be the source of this plasma. Thiswould be consistent with the preference of the plasma blobs to occur duringquiet conditions, although they are also found during substorm periods. Therelation to auroral phenomena in the morningside oval is uncertain. The energydeposition may be mostly too weak to generate a visible signature. However,patchy aurora remains a candidate for more disturbed periods.

Key words. Magnetospheric physics (plasma convection;plasma sheet; plasma waves and instabilities)

[学科分类] 地球科学(综合)