On October 24, 1995, and March 9, 1997, two solar eclipse events occur. It is therefore of interest to investigate how the ionosphere responded to the eclipses. Five global positioning system (GPS) ground-based receivers are specifically designed to observe large-scale ionospheric variations over the geomagnetic equatorial, equatorial anomaly crest, and midlatitude regions. Two-dimensional images of ionospheric total electron content (TEC) during the two eclipse periods are constructed. The deviations in the TEC images on eclipse days from those on reference days show that during the eclipse days the ionosphere experienced some large-scale changes. Four features of the TEC deviations, pre-ascension (PA), major depression (MD), sunset ascension (SA), and secondary depression (SD) have been observed. A detailed study shows that in geomagnetic low latitudes, PAs are possibly related to the locations of the equatorial anomaly crest. The latitudinal location, amplitude, and occurrence time of MDs suggest that the fountain effect is essential. SAs and SDs occurring in geomagnetic equatorial and low latitudes and appearing respectively before/around and after local sunset indicate that the prereversal enhancement plays an important role.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999JA900001

Ionospheric total electron content response to solar eclipses

A modelling study is presented which investigates in-situ generated changes of the thermosphere and ionosphere during a solar eclipse. Neutral temperatures are expected to drop by up to 40 degrees K at 240 km height in the totality footprint, with neutral winds of up to 26 m/s responding to the change of pressure. Both temperatures and winds are found to respond with a time lag of 30 min after the passing of the Moon's shadow. A gravity wave is generated in the neutral atmosphere and propagates into the opposite hemisphere at around 300 m/s. The combined effects of thermal cooling and downwelling lead to an overall increase in [O], while [N(2)] initially rises and then for several hours after the eclipse is below the "steady state" level. An enhancement of [NmF2] is found and explained by the atmosphere's contraction during, and the reduced [O]/[N(2)] ratio after the eclipse.

/pdf/effects-of-a-mid-latitude-solar-eclipse-on-the-thermosphere-1t4dxomgu1.pdf

Effects of a mid‐latitude solar eclipse on the thermosphere and ionosphere ‐ A modelling study

This paper provides the overview of an inte- grated, multi-disciplinary effort to study the effects of the 29 March 2006 total solar eclipse on the environment, with special focus on the atmosphere. The eclipse has been visible over the Eastern Mediterranean, and on this occasion several research and academic institutes organised co-ordinated ex- perimental campaigns, at different distances from eclipse to- tality and at various environments in terms of air quality. De- tailed results and findings are presented in a number of com- ponent scientific papers included in a Special Issue of Atmo- spheric Chemistry and Physics. The effects of the eclipse on meteorological parameters, though very clear, were shown to be controlled by local factors rather than the eclipse mag- nitudes, and the turbulence activity near surface was sup- pressed causing a decrease in the Planetary Boundary Layer. In addition to the above, the decrease in solar radiation has caused change to the photochemistry of the atmosphere, with night time chemistry dominating. The abrupt "switch off" of the sun, induced changes also in the ionosphere (140 up to 220 km) and the stratosphere. In the ionosphere, both photochemistry and dynamics resulted to changes in the re- flection heights and the electron concentrations. Among the most important scientific findings from the experiments un- dertaken has been the experimental proof of eclipse induced thermal fluctuations in the ozone layer (Gravity Waves), due to the supersonic movement of the moon's shadow, for the first time with simultaneous measurements at three altitudes namely the troposphere, the stratosphere and the ionosphere.

/pdf/the-total-solar-eclipse-of-march-2006-overview-3dantmcz8s.pdf

J.A. Klobuchar

Papers

A multi-station satellite radio beacon study of ionospheric variations during total solar eclipses