An upper E region quarterdiurnal tide at Arecibo?

Abstract

Studies of the time‐height trajectories of ionosphere E region layers at Arecibo have revealed not only the usual diurnal sporadic‐E and semidiurnal intermediate layer structures but also that on occasion, extra layers form and descend through the E region. In particular, during January 1981, four layers per day were observed to descend through the upper E region. This four‐per‐day layer system was remarkably coherent over the 3 days of observation and suggests the existence of a 6‐hour period or quarterdiurnal tidal wind system in the upper E region. Numerical simulations of ion trajectories in a realistic model atmosphere with diurnal, semidiurnal, and quarterdiurnal tidal wind systems of appropriate amplitude and phase structures confirm that the presence of a quarterdiurnal tide is sufficient to explain the observations.