Different types of LLBL as observed by Interball Tail probe

Vaisberg, O. L.^1,2, Smirnov, V. N.², Avanov, L A.², Waite, J. H., Jr.³, Burch, J.L.³ Gallagher D. L.¹, Borodkova, N. L.²

¹ SD50, NASA Marshall Space Flight Center, Huntsville, Alabama , USA

²� Space Research Institute, Profsoyuznaya 84/32, Moscow, 117810 Russia,

3 Southwest Research Institute, P.O. Drawer 28510, San Antonio, TX� 78228-0510, USA

Abstract

Interball-Tail probe crossed dayside magnetopause during late winter-middle autumn months. The high-latitude magnetopause was crossed outbound orbit while the low-latitude magnetopause was crossed inbound. We analyze 31 low-latitude magnetopause/LLBL crossings recorded in 1996 in the fast mode of SCA-1 ion spectrometer. Data from the MIF/FM-3 magnetometers and ELECTRON spectrometer are also used. The majority of Magnetopausemagnetopause/LLBL crossings fall into 4two categories: 1. Magnetopause without a boundary layer (1 case); 2. Highly structured LLBL (14 cases), and 32.Weakly-structured LLBL (9 cases), 4. LLBL at oscillating magnetopause (1 case). The highly-structured LLBL usually consists of short-time (0.5- 5 min) transients including fast-moving (of an order of magnetosheath velocity) plasma as well as density transients that are nearly stationary relative to the magnetospheric plasma. The observed ensemble of transients shows evolution of plasma parameters from magnetosheath-like to magnetosphere-like. Fast-moving transients frequently have FTE magnetic signatures. This type of LLBL is usually accompanied by various reconnection signatures, and is more frequently observed when the IMF and/or magnetosheath magnetic field has a� negative Bz component. The weakly-structured LLBL shows a significantly smaller variation of number density and hotter plasma temperature. Strong velocity shear and the density drop areis frequently observed at the magnetopause in the weakly-structured case. Dispersed ion signatures are often seen within this type of LLBL. The ion and electron temperatures within the weakly-structured LLBL are more elevated in respect to the magnetosheath values compared to the highly-structured LLBL. The weakly-structured LLBL has a tendency to occur at positive IMF and/or magnetosheath magnetic field Bz. The cause of significant differences between the two kinds of LLBL lies, apparently, in the significantly larger distance of the plasma entry site from the observation point, for weakly-structured LLBL, as opposed to highly-structured LLBL. While the highly-structured LLBL originates at low latitudes, the weakly structured LLBL is most probably formed at high latitudes.