Observations of strong gyro line spectra at Arecibo near dawn

Experiments performed near dawn during the PARS Summer School at Arecibo in August 2004 show clear evidence of the gyro line in the incoherent scatter radar (ISR) spectra with only six minutes of signal integration. A very weak gyro line was first observed by Behnke and Hagen (1978) requiring two hours of signal integration. Electrons that resonate with the gyro wave mode are well within the thermal distribution. At this point we know of no theory to explain the magnitude of the gyro lines we have detected although it seems clear that the presence of photoelectrons is related to it. We present the experimental results and a comparison with an incoherent scatter numerical model based on the theory developed by Trulsen and Bjorna (1978), which shows a very good correlation. From this comparison, and by combining the gyro line and the plasma line techniques, it is possible to make electron temperature measurements.