Total electron content data at three GPS stations in Yellowstone National Park

Total electron content (TEC) data—a measure of activity in the ionosphere—at three GPS stations in Yellowstone. Each line color is a measurement using a different satellite passing overhead. Note how the data are steady until the evening of May 10, 2024, when the signals start to fluctuate wildly due to the arrival of the Coronal Mass Ejection. A spectacular aurora was visible across large parts of the United States that evening. (Credit: Pin-hsuan Cheng, University of Colorado Boulder)