First observations of intense GPS L1 amplitude scintillations at midlatitude

First observations of intense GPS L1 amplitude scintillation activity in the midlatitude ionosphere at latitudes corresponding to the northeastern United States have been made. Moderate to severe, these scintillations result from space weather effects due to a disturbed ionosphere. Moderate to severe scintillations can degrade or even disrupt communication and navigation systems relying upon transionospheric radio wave propagation. A modified GPS receiver was used to record GPS satellite signal strength at Cornell University (53.2° magnetic latitude) during a magnetospheric disturbance on September 25-26, 2001 from 0000-0400 UTC. This disturbance (K_p = 6, minimum D_st = -110 nT) prompted the ionospheric trough to move equatorward over the northeastern U.S. and produced large plasma densities and gradients attributed to storm-time effects. This disturbance resulted in intense L-band amplitude scintillations (≥20 dB, S₄ ≈ 0.8) which are highly uncharacteristic at this magnetic latitude. Concurrent measurements of TEC showed steep density gradients (30 TEC/deg) and evidence of irregularity structuring.