Survey of Ionospheric GPS TEC Signatures of Pc3-6 Geomagnetic Pulsations in the Auroral Region

Abstract:

Several case studies have revealed fluctuations in ionospheric total electron content (TEC) associated with ultra-low frequency (ULF) magnetic field variations observed using satellite and ground magnetometers. At this point, the TEC response to ULF waves is considered unpredictable and intermittent, and the mechanisms that drive the variations in TEC are still unresolved. We have conducted a survey of the TEC response to ULF waves in the Pc3-6 (up to 200 mHz) frequency range using a high-data-rate Global Positioning System (GPS) receiver located in Sanikiluaq, Nunavut (56.54⁰N, 280.77⁰E), which is located in the auroral region. The GPS receiver if part of the Canadian High Arctic Ionospheric Network (CHAIN). In-situ ULF activity was monitored using magnetometer measurements of the GOES 13 satellite, which has a magnetic footprint in close proximity to Sanikiluaq, while corresponding ULF activity on the ground was monitored by the Sanikiluaq ground magnetometer.

A preliminary survey during the year 2017 revealed 920 narrow-band Pc3-6 ULF waves observed by the GOES 13 magnetometer, during periods where simultaneous GPS TEC and ground magnetometer measurements were available. Cross-spectral analysis of GOES 13 magnetic field with GPS TEC and ground magnetic field was used to determine whether variations observed in the respective measurements were linked. Discrete peaks in GOES 13 ULF wave occurrence were observed in the morning, afternoon, and nighttime sectors, with peak seasonal occurrence around December solstice. Coherent fluctuations in GPS TEC were observed in 24% of GOES 13 ULF wave events. Of these TEC events, 89% were accompanied by coherent variations in ground magnetic field, while 11% had no corresponding magnetic field variations on the ground. Primary factors governing the TEC response to ULF activity were ULF wave amplitude and frequency, with TEC variation intensity typically increasing with ULF wave amplitude and decreasing the ULF frequency ULF. There were exceptions, however. For example, significant TEC variations occasionally accompanied small amplitude ULF waves in the Pc3 frequency band. Other potential factors governing the TEC response to ULF activity, such as season, local time, background ionospheric conditions, and energetic particle flux at GOES 13, will also be discussed.