Ionospheric Response over Europe during the Solar Eclipse of 20 March 2015

Abstract

The solar eclipse on 20 March 2015 was a fascinating event for people in Northern Europe. From a scientific point of view the solar eclipse can be considered as an in situ experiment on the Earth’s upper atmosphere with a well-defined switching off and on of the solar irradiation. Due to the strong changes in solar radiation during the eclipse dynamic processes were initiated in the atmosphere and ionosphere causing a measurable impact e.g. on the temperature and ionization. We analyzed the behavior of the total ionospheric ionization over Europe by reconstructing the total electron content (TEC) maps and differential TEC maps. Investigating the large depletion zone around the shadow spot we found a TEC reduction of up to 6 TEC units. The total plasma depletion reached over 60% which is much higher than those reported earlier for 1999 and 2005 solar eclipses. During the solar eclipse ionospheric plasma redistribution processes significantly affect the shape of the electron density profile which is seen in the equivalent slab thickness derived by combining vertical incidence sounding (VS) and TEC measurements. We found enhanced slab thickness values revealing on the one hand an increased width of the ionosphere around the maximum phase and on the other hand evidences for a delayed depletion of the topside ionosphere. Additionally, we investigated VLF (Very Low Frequency) signal strength measurements and found immediate amplitude changes due to ionization loss at the lower ionosphere during eclipse time. We found that the magnitude of the TEC depletion is linearly dependent on the Sun’s obscuration function. By modelling the TEC depletion and knowing the Sun’s obscuration function in advance, Global Navigation Satellite System (GNSS) operators may improve the broadcast ionospheric correction during a solar eclipse day.