Physical Processes Driving the Response of the F2-region Ionosphere to the 21 August 2017 Solar Eclipse at Millstone Hill

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Friday, May 4, 2018

The high-resolution thermosphere-ionosphere-electrodynamics general circulation model (TIEGCM) was used to investigate the cause of F2-region electron density (Ne) responses to the Great American Solar Eclipse on 21 August 2017 at Millstone Hill (42.610N, 71.480W).

UT and altitude variations of electron densities image
UT and altitude variations of electron densities from incoherent scatter radar observations (a) and TIEGCM simulations (b) at Millstone Hill on 21 August 2017. The vertical dashed lines show the time of maximum eclipse at the location, the horizontal bars indicate the duration of the eclipse. Figures 1c-1f give electron density profiles from observations (black squares and grey dots) and model simulations with the eclipse (red) and without the eclipse (blue) at four UTs.

Diagnostic analysis of model results shows that eclipse-induced disturbance winds cause F2-region Ne changes directly by transporting plasma along field lines, indirectly by producing enhanced O/N2 ratio that contribute greatly to the recovery of the ionosphere near and below the F2 peak after the maximum obscuration. Ambipolar diffusion reacts to plasma pressure gradient changes and modifies Ne profiles. Wind transport and ambipolar diffusion take effect from the early phase of the eclipse and show strong temporal and altitude variations. The interplay of chemical processes involving dimming solar radiation and changing composition with wind transport and ambipolar diffusion causes the time delay and asymmetric characteristic of the F2-region response seen by Millstone Hill incoherent scatter radar observations.

Publication Name: Geophysical Research Letters