Different types of low-latitude boundary layer as observed by Interball Tail probe

Interball Tail probe crossed dayside magnetopause during late winter to mid dle autumn months. The high-latitude magnetopause was crossed outbound orbi t, while the low-latitude magnetopause was crossed inbound. We analyze 31 l ow-latitude magnetopause/low-latitude boundary layer (LLBL) crossings recor ded in 1996 in the fast mode of SCA-1 ion spectrometer. Data from the MIF/F M-3 magnetometers and ELECTRON spectrometer are also used. The majority of magnetopause/LLBL crossings fall into two categories: (1) highly structured LLBL (14 cases) and (2) weakly structured LLBL (9 cases). The highly struc tured LLBL usually consists of short-time (0.5-5 min) transients including fast-moving (of an order of magnetosheath velocity) plasma as well as densi ty transients that are nearly stationary relative to the magnetospheric pla sma. The observed ensemble of transients shows evolution of plasma paramete rs from magnetosheath-like to magnetosphere-like. Fast-moving transients fr equently have flux transfer event (FTE) magnetic signatures. This type of L LBL is usually accompanied by various reconnection signatures and is more f requently observed when the interplanetary magnetic field (IMF) and/or magn etosheath magnetic field has a negative B, component. The weakly structured LLBL shows a significantly smaller variation of number density and hotter plasma temperature. Strong velocity shear is frequently observed at the mag netopause in the weakly structured case. Dispersed ion signatures are often seen within this type of LLBL. The ion and electron temperatures within th e weakly structured LLBL are more elevated in respect to the magnetosheath values compared to the highly structured LLBL. The weakly structured LLBL h as a tendency to occur at positive IMF and/or magnetosheath magnetic field B,. 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 high ly structured LLBL. While the highly structured LLBL originates at low lati tudes, the weakly structured LLBL is most probably formed at high latitudes .