Moving mesoscale plasma precipitation in the cusp

Abstract

On 28 March 2001, when the interplanetary magnetic field was strongly duskward, the DMSP F12 spacecraft observed an ion precipitation burst in a latitudinally narrow region near 1200 MLT. A few minutes earlier, the Low Energy Neutral Atom (LENA) imager on the IMAGE spacecraft, whose field of view (FOV) looks into the high‐altitude cusp, detected an enhancement of energetic neutral atom signals, which are produced by the ion injection. The LENA data suggest that the ion injection moved out of its FOV after approximately 4 min. At this time, the ground‐based magnetometers of the IMAGE chain in Svalbard, located westward of LENA's FOV, began to indicate perturbations. These perturbations immediately reached a peak and then ceased; the perturbations lasted 2–3 min. During this interval, there was an enhanced westward flow over Svalbard, as observed by the SuperDARN radars. The EISCAT Svalbard radar detected an enhancement of electron density and temperature that was concurrent with this flow enhancement, suggesting that a plasma precipitation burst accompanied with the flow. These observations, which cover a longitudinally extending region of the cusp, strongly suggest the existence of moving mesoscale plasma precipitation (MMPP). The MMPP travels westward with a longitudinally elongated form. Its leading and trailing edges should be created by the temporal effect of the cusp. The other edges, which lie along the streamline, would originate in a spatially limited region along the open‐closed line. The boundary of the MMPP form is delineated by both the temporal and spatial structures of the cusp.