Large‐amplitude GPS TEC variations associated with Pc5–6 magnetic field variations observed on the ground and at geosynchronous orbit

Abstract

Large‐amplitude variations in GPS total electron content (TEC) at Pc5–6 (<6.67 mHz) frequencies have been observed, using a high data rate Global Positioning System (GPS) receiver of the Canadian High Arctic Ionospheric Network. TEC variations with peak‐to‐peak amplitudes of 2–7 TEC units (1 TECU = 1016 el m−2) were observed over a 2.5 h period in the postnoon sector on 9 September 2011, during a period of high auroral activity within a moderate geomagnetic storm. TEC observations were from the Sanikiluaq, Nunavut (56.54°N, 280.77°E) GPS receiver located in the auroral region. Over this same time period, compressional Pc5–6 magnetic field variations were observed by the geosynchronous GOES 13 magnetometer and the ground‐based Sanikiluaq magnetometer. GOES 13 has a northern magnetic footprint in close proximity to Sanikiluaq. Cross‐correlation analysis indicates that magnetic field and TEC variations were possibly linked. No natural hazards or nuclear explosions capable of exciting TEC perturbations were reported on this day. Using a triangulation technique involving TEC measurements of multiple GPS satellites, the propagation velocity of TEC variations in the ionosphere was also calculated. This calculation revealed two distinct events: lower frequency (~0.9 mHz) TEC variations that propagated westward, consistent with the westward propagation of compressional Pc5 waves observed by GOES 13 and 15 satellites, and higher‐frequency (~3.3 mHz) TEC variations that propagated southward. This is the first report of variations in ionospheric TEC linked to satellite observations of Pc5–6 ULF waves.

Modulation of the ionosphere by Pc5 waves observed simultaneously by GPS/TEC and EISCAT

“…However, GPS observations have revealed that the depth of periodic TEC modulation is sometimes even somewhat larger (e.g., in the event of October 31, 2003, ΔN T /N T ~ 2.5 %) than the geomagnetic field modulation (ΔB/B 0 ~ 1 %). In principle, ULF modulation of energetic electron precipitation, inducing an additional periodic ionization of the lower ionosphere, can cause periodic TEC variations with much higher depth than geomagnetic field variations (Watson et al 2015). However, during the event under consideration no periodic electron precipitation occurred as evidenced by simultaneous riometer observations.…”

“…The radar observations showed that Pc5 waves can noticeably modulate the ionospheric plasma: the electric field E, plasma convection velocity V, E-layer electron density N e and the ionosphere conductance Σ, and electron T e and ion T i temperatures in both F-and E-layers (see references in Pilipenko et al 2014b). Recent observations by Pilipenko et al (2014a) and Watson et al (2015) have demonstrated that Pc5 waves are capable to modulate TEC as well.…”

“…Early results, during the era of Faraday technique with geostationary beacons, reported TEC fluctuations related to geomagnetic variations in the Pc3-4 range (30-to 50-s period) (Davies and Hartman 1976;Okuzawa and Davies 1981). The TEC modulation by intense Pc5 pulsations was found by Pilipenko et al (2014a) and Watson et al (2015). Thus, the standard TEC/GPS technique is sufficiently sensitive to detect ULF waves in some cases.…”

“…Additional periodic ionization and consequently TEC variations may occur owing to the ULFmodulated precipitation of energetic electrons into the ionosphere (Watson et al 2015). Other possible mechanisms of TEC modulation by incident MHD waves comprise (a) plasma compression by evanescent fast compressional mode wave arising from the interaction of an Alfven wave with the anisotropic ionosphere (Pilipenko and Fedorov 1995); (b) periodic advection across a lateral gradient of the ionospheric plasma (Waters and Cox 2009); (c) periodic vertical shift and reconfiguration of the plasma vertical profile (Poole and Sutcliffe 1987); (d) frictional heating of ionospheric ions owing to periodic dragging through neutrals, and (e) field-aligned plasma transport by an Alfven wave (Pilipenko et al 2014a).…”

Geomagnetic and ionospheric response to the interplanetary shock on January 24, 2012

“…For an examination of the ionospheric response to solar wind pressure pulses, Jayachandran et al (2011) suggested using the GPS global navigation satellite system. This technique that provides information on total electron content (TEC) along a radio path satellite-ground receiver is sensitive enough to detect the ionospheric response to transient and periodic disturbances in the ULF band (Watson et al 2015;Belakhovsky et al 2016). The case study of a TEC response to an IP shock by Jin et al (2016) suggested that a shock-generated TEC variation is a "duplication" of the shock aurora observed by UV sensors onboard the Defense Meteorological Satellite Program (DMSP) satellites.…”