The relationship between E region electron density and the power of auroral coherent echoes at 45 MHz

Data taken during joint observations of the European incoherent scatter (EI SCAT) radar and the Karmaselga auroral coherent radar (46.5 MHz) are combin ed to investigate the dependence of the coherent echo power upon the maximu m electron density in the E region. For electron densities in the range (1- 3)x 10(11) m(-3), an increase in the echo power with the electron density w as found. A few coherent echoes were observed for electron densities larger than 3x10(11) m(-3) but when such echoes occurred, their power was small e ven though the ionospheric electric field was strong, more than 30 mV/m. Th ese measurements agree reasonably well with the model of Uspensky and Willi ams [1988] which takes into account ionospheric refraction and assumes that auroral coherent echo is a superposition of scattering from a thick layer of electrojet irregularities. Results of the comparison indicate that elect ron density at altitudes around 110 km can be roughly estimated solely from coherent radar data.