HAO Colloquium - Anthea Coster, MIT Haystack Observatory

Ionospheric Signatures of the 21 August 2017 Solar Eclipse

On 21 August 2017, during daytime hours (16:00--20:00 UTC), a total solar eclipse occurred across the continental United States along a path from Oregon to South Carolina with a narrow ~100-km wide umbral shadow. Outside of this region, a partial solar eclipse associated with the penumbra covered the majority of the continental United States. Haystack Observatory, a multidisciplinary radio science research center run by MIT, was one of several institutions funded by NASA Heliophysics to study eclipse induced ionospheric variations. As part of its many activities, MIT Haystack Observatory coordinated the placement of 7 GNSS receivers in the region of totality at sites in Missouri, South Carolina, Wyoming, Oregon. These receivers were provided by UNAVCO and MIT and collected total electron content (TEC) data at a 1 to 10 second cadence from all GPS and GLONASS satellites in view. In addition, MIT utilized the dense global network of GNSS receivers across North and South America to produce both TEC and differential TEC maps. Five days of GNSS data - the eclipse day, two days prior and two days after - were analyzed for the electron density latitudinal response and for the presence of traveling ionospheric disturbances (TIDs), with the aim of identifying signatures specifically associated with the solar eclipse. Differential TEC techniques were used for TID detections by subtracting a background TEC. In addition, TIDs in the region near totality were examined by comparing the individual line of sight TEC from nearby receivers.

We report here on initial results our GNSS analysis for the 21 August 2017 event. A significant electron density depletion was clearly observed across the US associated with the eclipse shadow. We will provide a preliminary estimate of the time delay and spatial distance between the maximum of the TEC depletion and the center of the eclipse totality. We also report on signatures of gravity waves observed above the Rocky Mountain chain during the eclipse and on observations of weak traveling ionospheric disturbances (TIDs) clearly associated with this eclipse. We will also compare these findings with those made during prior eclipses. Eclipse observations have long been of interest to the upper atmospheric research community, as they are a naturally occurring 'active' experiment that offers a special opportunity for studying both solar ionizing radiation and the earth's ionosphere. Eclipse studies for the 2017 event have benefited from the vast increase in fidelity and coverage of ground-based monitoring tools, especially GNSS monitoring of total electron content (TEC).

Date and time: 
Wednesday, September 13, 2017 - 1:30pm to 2:30pm