Ionospheric Behavior during the 10 June 2021 Annular Solar Eclipse and Its Impact on GNSS Precise Point Positioning  
[PERSON]  
1 Space and Planetary Exploration Laboratory (SPEL), Faculty of Physical and Mathematical Sciences, University of Chile, Av. Tupper 2007, Santiago 8370451, Chile; [EMAIL_ADDRESS] (J.C.V.-A. ); [EMAIL_ADDRESS] (Y.S.-S.)  
[PERSON]  
1 Space and Planetary Exploration Laboratory (SPEL), Faculty of Physical and Mathematical Sciences, University of Chile, Av. Tupper 2007, Santiago 8370451, Chile; [EMAIL_ADDRESS] (J.C.V.-A. ); [EMAIL_ADDRESS] (Y.S.-S.)  
[PERSON]  
3 Centro de Instrumentacion Cientifica, Universidad Adrentista de Chile, km 12 Camino a Tanilvoro, Chillan 3780000, Chile; [EMAIL_ADDRESS] (J.C.V. The ionosphere is directly affected since this atmospheric layer is produced by solar radiation. The total electron content (TEC) is a measure of the electron density in the ionosphere integrated along the line of sight, thus, an indication of its ionization. TEC can be obtained using a radio link between a satellite and the ground. Nowadays, the most common system delivering TEC measurements is the Global Navigation Satellite Systems (GNSS), which requires TEC measurements to improve the precision of position estimation. TEC is expressed in TEC units (TECu), where 1 TECu = 10\({}^{16}\) e/m\({}^{2}\). The perturbation of the ionosphere can be analyzed through the variations of TEC. The main parameters of the TEC variations during the eclipses are the delay value (\(\tau\)) relative to the maximum phase of the eclipse; its amplitude (A), which generally is a decrease; and the duration (\(\Delta T\)) of the perturbation [4]. Since the Moon's shadow moves rapidly from west to east across the Earth at supersonic speed, the total eclipse lasts just a few minutes anywhere [5; 6; 7]. Previous works have reported the depletion of TEC after the onset of the partial solar eclipse and have presented values of A in percent (A[%]) that can reach up to \(-64\%\) with \(\tau\) from \(-30\) to 180 min [8; 9; 10; 11]. This delay has been interpreted as an indicator of the combined effect of the photochemical processes and plasma dynamics [1; 12]. Some works have reported \(\Delta T\) from 50 to 240 min [4; 13]. However, some studies have reported even longer effects [14; 15]. A historical summary of ionospheric responses to solar eclipses since 1920 can be found in the Appendix in [PERSON] et al. [16]. Recent studies have shown that the effects of a solar eclipse on the ionosphere are not only local but can affect other geographic regions outside the umbra/penumbra of the eclipse [15; 17; 18; 19; 20]. These effects may be due to transport between hemispheric magnetic conjugates, alteration of the equatorial fountain effect, generation of a disturbed dynamo, and/or Atmospheric Gravity Waves (AGWs) that generate Traveling Atmospheric Disturbances (TADs) and/or Traveling Ionospheric Disturbances (TIDs). An annular solar eclipse took place on 10 June 2021. The first external contact (P1 time) and the last external contact (P4 time) of the solar eclipse were at 08:12:22 UT and 13:11:22 UT, respectively. The partial solar eclipse was seen from the following geographic regions: in parts of the eastern United States and northern Alaska, Canada and parts of the Caribbean, Europe, Asia, and northern Africa. The annular eclipse was visible from parts of northeastern Canada, Greenland, and the Arctic Ocean, passing through the North Pole, and ending in Russian territory. It maximum magnitude was 0.944: this is the fraction of the angular diameter of a celestial body being eclipsed.