The August 21, 2017 Total Eclipse and the Ionosphere

UNAVCO collected 5-Hz GPS data from stations within the PBO network that were in the path of 90% totality. Demián Gómez, a postdoc at Ohio State with Mike Bevis, has taken the 15-second RINEX files inside the totality path and calculated the Total Electron Content (TEC) at each station-satellite pair for each epoch recorded during the day of the eclipse. These calculations result in TEC observations at the ionospheric piercing points (IPP), the intersection of the station-satellite line-of-sight (LOS) and the peak electron density of the ionospheric F layer at a height of ~300 km. Using the estimated TEC at each IPP, he produced a video showing the TEC change during the passage of the umbra and penumbra of the eclipse over North America over a period of one hour. The video shows that as the moon’s shadow passes and the sunlight is blocked, the TEC drops due to the recombination of the ionized particles.

The ionosphere is part of the upper atmosphere and is ionized by solar and cosmic radiation. Ultraviolet light, X-rays, and high-energy radiation strip electrons from atoms, creating an ionized environment. The sun is the largest contributor of ionizing radiation, so the atmosphere is strongly ionized during the daytime. At night cosmic rays from distant sources such as supernovae, black holes, etc. ionize the atmosphere more weakly. The ionosphere is dispersive, so that radio waves (such as from GPS satellites) traveling through will have a phase velocity dependent on their frequencies. The phase difference between the two GPS carrier frequencies is used to estimate the TEC along the column of atmosphere of the LOS between a station-satellite pair, characterized by the number of electrons per square meter in that column. This technique is exploited by researchers to study ionospheric structure and disturbances, as in the case of the 2017 total eclipse.

#TotalEclipse2017 #PBO #IonosphereGPS

Eclipse highlight at UNAVCO:
https://www.unavco.org/highlights/2017/eclipse2017.html

The ionosphere and total electron content:
http://www.swpc.noaa.gov/phenomena/ionosphere
http://www.swpc.noaa.gov/phenomena/total-electron-content
https://scied.ucar.edu/ionosphere

Sample papers:
Virtual array beamforming of GPS TEC observations of coseismic ionospheric disturbances near the Geomagnetic South Pole triggered by teleseismic megathrusts
http://onlinelibrary.wiley.com/doi/10.1002/2015JA021725/full

A new technique for mapping of total electron content
using GPS network in Japan
https://www.jstage.jst.go.jp/article/eps1998/54/1/54_1_63/_pdf

A global mapping technique for GPS-derived
ionospheric total electron content measurements
http://onlinelibrary.wiley.com/doi/10.1029/97RS02707/pdf

Application of ionospheric tomography to real-time
GPS carrier-phase ambiguities resolution, at scales of
400-1000 km and with high geomagnetic activity
http://onlinelibrary.wiley.com/doi/10.1029/1999GL011239/pdf

Spatial information used to plot the umbra and penumbra:
https://svs.gsfc.nasa.gov/4518

Shapefile reference
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 8.0.0.0.0

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