Journal of Geophysical Research
American Geophysical Union
During the last solar maximum period several observations of anomalously high F region peak altitudes have been made by the high latitude incoherent scatter radars. The observations indicate that there are several distinctive features associated with these high hmF2 ionospheric profiles: (1) they are observed near midnight with the plasma flowing out of the polar cap, (2) NmF2 ranges from 105 to 106 cm−3, (3) hmF2 ranges from 400 to 500 km, (4) below 300 km the profile is devoid of ionization, and (5) the observations are for solar maximum conditions. In an effort to explain these radar observations, a time-dependent high latitude ionospheric model was used to study transport effects for a wide range of solar cycle, seasonal, magnetic activity, and neutral wind conditions. The model results indicate that high hmF2 values in the midnight sector of the polar region can be generated without the need for ionization due to auroral precipitation. For solar maximum, all of the observed features of the high hmF2 density profiles are reproduced by the model if the neutral wind across the polar cap is greater than 400 m/s. Such wind speeds have been frequently measured during the last solar maximum period. The study also shows general results for the influence of transport in the polar cap for different seasonal and solar cycle conditions. NmF2 and hmF2 are lower for solar minimum than solar maximum. However, the seasonal dependences are strongly coupled with both the strength of the convection and the neutral wind speed.
Sojka, J. J., and R. W. Schunk (1985), Theoretical Study of Anomalously High F Region Peak Altitudes in the Polar Ionosphere, J. Geophys. Res., 90(A8), 7525–7532, doi:10.1029/JA090iA08p07525.