Ionospheric and geomagnetic effects of the solar eclipse of 18 March 1988 in East Asia

Abstract

Effects due to the transit of a solar eclipse through SE Asia on 18 March 1988 have been investigated using ionograms, electron content measurements, magnetograms and microbarograph recordings, provided by a chain of stations situated roughly parallel to the path of totality. In corresponding time sequence depletions of foE and foFl were observed, while in the F2-region the only affected parameter of hpF2, at equatorial anomaly crest locations, showed well-defined maxima. Electron density-height profiles revealed a ‘deep hollowed-out valley’ of electron density within the height range 200–300 km. Estimations of ionization and production loss rates demonstrated that the equatorial anomaly diffusion process was considerably reduced. Even though the eastward electric field E overhead the magnetic equator, providing the ( E × B) upward diffusion for the equatorial anomaly mechanism, was enhanced on this day it is clear that the local depletion in electron density caused by the solar eclipse succeeded in greatly reducing the transport of ionization to higher latitudes. As a consequence of the depletion of electron density in the E-region at the magnetic equator the northward movement of electrons forming the S q , current was halted, this showing up as a drop in magnetic declination at S q current-focus latitude locations. Afterwards, the resurgence of ionization diffusion down magnetic field lines, associated with the equatorial anomaly, caused a secondary peak in the magnetic declination. Direct evidence for the production of acoustic gravity waves by the moving bow wave front of the solar eclipse is afforded by the observation of waves with periods of 30–33 min on ionosonde sounding virtual heights and a microbarograph, lower atmosphere, pressure recording.