Transpolar auroras, their associated particle precipitation, and their occuurence with respect to the IMF By polarity are examined on the basis of DMSP F6 auroral images and the corresponding particle data. It is found that the transpolar arcs are located in the poleward edge of the soft particle precipitation region extending from either the dawn or dusk part of the auroral oval precipitation; they are not embedded in the polar rain region. This finding suggest that the transpolar arcs are located along the poleward boundary of the closed field line region (or the equatorward boundary of the open region) as suggested by Meng (1981). Further, the appearance of the extended precipitation region from the oval depends on the polarity of the IMF By in the northern hemisphere morning sector for IMF By0. In general, the precipitating particle flux in the extended precipitation region is not high enough to produce appreciable luminosity. Thus only the transpolar arcs (associated with relatively intense precipitation) near the poleward boundary tend to become much more luminous, forming the so-called'' ''theta aurora.'' ¿American Geophysical Union 1991