Statistical Signature of NEIALs in International Polar Year PFISR Data

Naturally Enhanced Ion Acoustic Lines (NEIALs) in Incoherent Scatter Radar (ISR) spectral data are characterized by strong enhancements in either or both ion acoustic lines above thermal level over an extended altitude region. The occurrence of NEIALs is associated with plasma turbulence, particle precipitation and strong shears, and typically occurs at the edges of auroral arcs and in the polar cusp. The Poker Flat ISR (PFISR) is located under the auroral oval at about 67-degree invariant latitude, and since the beginning of the International Polar Year (IPY) in March of 2007 the radar has been running continuously, producing a unique dataset very well suited for the study of trends. In this paper we present a statistical study of the occurrence of NEIALs in the IPY dataset from PFISR. The study includes seasonal, and diurnal occurrence frequency of NEIALs, duration of NEIAL events, altitude extent and correlation to geophysical activity and optical aurora occurrence.