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The collapse of the midnight ionosphere and behavior of meridional neutral winds at Townsville over a full solar cycle
Author(s) -
Dandenault P. B.,
Richards P. G.
Publication year - 2015
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2015ja021842
Subject(s) - equinox , midnight , solstice , ionosphere , atmospheric sciences , zonal and meridional , physics , thermosphere , climatology , meteorology , geology , geophysics , astronomy , latitude
This paper investigates the causes of the sudden descent (midnight collapse) of the ionosphere at Townsville, Australia, during the equinox periods of years between 1970 and 1980. The collapse of h m F 2 at midnight is found to occur on 89% of the 330 equinox nights that are investigated, and the mean magnitude of the midnight collapse is 84 km in the March equinox periods and 99 km in the September equinox periods. Observations of h m F 2 are used to determine equivalent meridional neutral winds using a first principles physics model. Harmonic analysis of these derived winds reveals the existence of significant diurnal (24 h), semidiurnal (12 h), and terdiurnal (8 h) tidal components. The contribution of wind harmonics to the midnight collapse is determined by band‐pass filtering the winds to only allow certain tides and then modeling their effect on h m F 2 near midnight. The results indicate that the diurnal, semidiurnal, and terdiurnal components of the meridional neutral wind all play a significant role at various times, but the effect of the 6 h wind component is minimal. The spectral analysis also reveals that the terdiurnal wind component becomes dominant during solar maximum. Electric fields do not appear to be responsible for the midnight h m F 2 collapse because it is seldom seen at the near‐conjugate station of Akita, Japan.