GNSS Observations of Ionospheric Variations During the 21 August 2017 Solar Eclipse

On 21 August 2017, during daytime hours, a total solar eclipse with a narrow similar to 160km wide umbral shadow occurred across the continental United States. Totality was observed from the Oregon coast at similar to 9:15 local standard time (LST) (17:20 UT) to the South Carolina coast at similar to 13:27 LST (18:47 UT). A dense network of Global Navigation Satellite Systems (GNSS) receivers was utilized to produce total electron content (TEC) and differential TEC. These data were analyzed for the latitudinal and longitudinal response of the TEC and for the presence of traveling ionospheric disturbances (TIDs) during eclipse passage. A significant TEC depletion, in some cases greater than 60%, was observed associated with the eclipse shadow, exceeding initial model predictions of 35%. Evidence of enhanced large-scale TID activity was detected over the United States prior to and following the large TEC depletion observed near the time of totality. Signatures of enhanced TEC structures were observed over the Rocky Mountain chain during the main period of TEC depletion.