Estimates of absolute scattering coefficients of radar aurora

Data available in the literature and obtained with the Homer, Alaska 398 MHz phased-array radar have been used to obtain estimates of scattering coefficients of radar aurora over a frequency range of 30-1,210 MHz, and to express them in terms of a wave-packet scattering model. At any one frequency these scattering coefficients typically range over 4 or 5 orders of magnitude. Between 50 MHz and 850 MHz the frequency dependence of the strongest echoes seems to be described quite well by a scattering coefficient per unit volume of {sigma}{sub {nu}} = 3 {times} 10{sup {minus}7} (K){sup {minus}2.25} m{sup {minus}1}, where k is the wave number of the fluctuations in the plasma. This expression is thought to describe scattering from primary instabilities whose propagation vectors are perpendicular to the magnetic field, and parallel to the electrojet current. There is evidence that at 30 MHz the largest scattering coefficients are significantly larger than predicted by this expression, while at 1,210 MHz they are significantly smaller. At 50 MHz the strongest auroral scattering coefficient appears to be more than an order of magnitude greater than what is obtained in the equatorial electrojet. From the scattering coefficients, estimates of the mean fractional electron densitymore » fluctuation amplitude, {delta}N/N, have been made and compared with previous results.« less

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