New Aspects of the Ionospheric Behavior Over Millstone Hill During the 30-Day Incoherent Scatter Radar Experiment in October 2002

The geomagnetic storm-driven ionospheric changes and the involved processes are interesting and challenging topics in understanding and predicting the ionosphere. In this study we investigate the response of the ionosphere to geomagnetic disturbances during the 30-day incoherent scatter radar measurements conducted at Millstone Hill (42.6\textdegreeN, 71.5\textdegreeW) from 4 October to 4 November 2002. During geomagnetically disturbed periods, while the peak electron density of the F2 layer (NmF2) and total electron content deviate remarkably from the quiet time ones in a similar way, the incoherent scatter radar measurements reveal that the changes in electron density are frequently different between low and high altitudes. The electron density is significantly depleted at low altitudes; however, at topside it either changes slightly or sometime is enhanced. The enhanced vertical scale height around 600 km under geomagnetically active conditions implies that the topside electron density profiles become much steeper. The increase in the peak height of F2 layer (hmF2) indicates the upward motions under the action of the storm-driven dynamic processes. Further, sometimes strong differences are shown in total electron content between Millstone Hill and longitude 100\textdegreeW. The competing contributions from dynamic processes and disturbance composition to the storm-time ionospheric changes over Millstone Hill are indicated in the different responses in electron density at the bottomside and topside of the ionosphere.