Characteristics of plasma structuring in the cusp/cleft region at Svalbard

Satellite scintillation, all-sky optical imager, and digisonde observations were coordinated during a cusp campaign conducted at Ny Alesund, Svalbard (78.9 degrees N, 11.8 degrees E; 75.7 degrees N corrected geomagnetic latit ude, over the period January 4-15, 1997. This paper is focused on a study o f the distribution and dynamics of mesoscale (tens of kilometers to tens of meters) electron density irregularities in the dayside auroral region. Thi s study has been performed at Ny Alesund, Svalbard, by measuring the effect s of these irregularities on the amplitude scintillation of 250-MHz transmi ssions from a quasi-stationary polar satellite as well as the amplitude and phase scintillation of 1.6-GHz signals from Global Positioning System (GPS ) satellites. These GPS scintillation measurements were augmented by the us e of dual-frequency (1.2 and 1.6 GHz) GPS phase data acquired at the same s tation by the Jet Propulsion Laboratory for the International GPS Geodynami c Service (IGS). The continuous 250-MHz scintillation observations explored the daytime auroral ionosphere 2 degrees poleward of Ny Alesund and showed that the scintillation spectra are often broad, as may be expected for irr egularities in a turbulent flow region. Such irregularity dynamics were det ected poleward of the nominal cusp region over the interval of 0600-1500 ma gnetic local time. The period of observations included the magnetic storm o f January 10-11, 1997, when GPS observations of the IGS detected polar cap patches with total electron contents of 3 x 10(16) m(-2) and large-scale (t ens of kilometers) phase variations at the GPS frequency of 1.6 GHz that co rresponded to temporal gradients of 2 x 10(16) m(-2) min(-1). However, ampl itude scintillations at the GPS frequency of 1.6 GHz could not be detected in association with these large-scale phase variations, indicating that the irregularities with wavelengths less than the Fresnel dimension of 400 m w ere below the detectable limit. This is shown to be consistent in the conte xt of enhanced ionospheric convection determined by digisonde and scintilla tion spectra.