Evidence of component merging equatorward of the cusp

The Polar spacecraft passed through a region near the dayside magnetopause on May 29, 1996, at a geocentric distance of similar to 8 R-E and high, nor thern magnetic latitudes. The interplanetary magnetic field (IMF) was north ward during the pass. Data from the Thermal Ion Dynamics Experiment reveale d the existence of low-speed (similar to 50 km s(-1)) ion D-shaped distribu tions mixed with cold ions (similar to 2 eV) over a period of 2.5 hours. Th ese ions were traveling parallel to the magnetic field toward the Northern Hemisphere ionosphere and were convecting primarily eastward. The D-shaped distributions are distinct from a convecting Maxwellian and, along with the magnetic field direction, are taken as evidence that the spacecraft was in side the magnetosphere and not in the magnetosheath. Furthermore, the absen ce of ions in the antiparallel direction is taken as evidence that low-shea r merging was occurring at a location southward of the spacecraft and equat orward of the Southern Hemisphere cusp. The cold ions were of ionospheric o rigin, with initially slow field-aligned speeds, which were accelerated upo n reflection from the magnetopause. These observations provide significant new evidence consistent with component magnetic merging sites equatorward o f the cusp for northward IMF.