Varney, R. H., Nicolls, M. J., Heinselman, C. J., & Kelley, M. C. (2009). Observations of polar mesospheric summer echoes using PFISR during the summer of 2007. Journal of atmospheric and solar-terrestrial physics, 71(3-4), 470-476.
The Poker Flat Incoherent Scatter Radar (PFISR) has been running nearly continuously throughout the summer of 2007, which permits an unprecedented, long-term study of polar mesospheric summer echoes (PMSE) at UHF. When not being used for other operations, PFISR runs in its International Polar Year (IPY) mode. 176 examples of PMSE have been identified in the IPY dataset during the summer of 2007 on 42 different days. IPY data were examined from March through mid-September. The first event was observed on May 27, and the last on August 10. During the four months from May 14 through September 14 the IPY mode was run 57% of the time and PMSE was detected 3.3% of the time the mode was running. Thirty-eight percent of the days with data during these four months had at least one PMSE event. Seventy-three percent of the events occurred during the daytime, and of the 48 events at night, 31 were accompanied by auroral precipitation. The events that did not occur with aurora show a strong correlation with solar zenith angle, which suggests a dependence on background ionization. Events were observed in range gates centered at 81.2 and 85.5 km, with 141 of the 176 events in the lower gate. The events have a mean duration of 19.6 min, but events lasting as long as 106 min have been observed. The events have a mean reflectivity of 1.3×10-17m-1, which is a lower bound due to the possibility that the beam is not filled. A Lorentzian power spectrum was assumed to fit for the half-power half-width (HPHW) of the measured autocorrelation functions. The HPHWs which could be measured have a mean of 14.8 m/s, with a standard deviation of 11.1 m/s.