Analysis of nighttime E-region winds and ionization production


  • M. A. Geller,

  • L. G. Smith,

  • H. D. Voss


Two sets of rocket measurements of nighttime E-region electron densities at Wallops Island are analyzed. One is a series of five electron density profiles that were taken during the night of February 22, 1968, and the other is a collection of electron density profiles that were taken near midnight under varying conditions of geomagnetic activity. The method of analysis uses the steady-state continuity equation for electrons and gives information on the height-averaged ionization production rate and the vertical profile of the ion drift. Conclusions drawn from this analysis include the following: The more marked intermediate layer observed under geomagnetically quiet conditions is most likely a straightforward consequence of lesser ionization rates. Small values of vertical ion drift (about 10 m sec−1) are sufficient to give rise to a marked intermediate layer. Electron production in the E region is minimum near midnight. The production rate below 130 km (probably HI Lβ) increases sharply between 0130 and 0300 EST whereas the production rate in the region above remains relatively constant. The ionization rate in the nighttime E region varies strongly with κp, suggesting the importance of energetic electrons even under moderate and quiet conditions. The intermediate layer may be a result of electron redistribution by the tidal winds of the (2,4) mode of the solar semidiurnal tide.