Traveling Ionospheric Disturbances and Ionospheric Perturbations Associated With Solar Flares in September 2017. Issue 7 (10th July 2019)

• Record Type: Journal Article
• Authors: Zhang, Shun‐Rong; Coster, Anthea J.; Erickson, Philip J.; Goncharenko, Larisa P.; Rideout, William; Vierinen, Juha
• Is Part Of: Journal of geophysical research. Volume 124:Issue 7(2019)
• Page Start: 5894
• Page End: 5917
• Publication Date: 2019-07-10
• Subjects: solar flare -- traveling ionospheric disturbance -- acoustic‐gravity wave -- GNSS TEC -- incoherent scatter radar observation -- midlatitude ionosphere; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA026585
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Solar flares provide strong impulsive radiation and energy injection to the sunlit upper atmosphere. The impact on the ionosphere is immense in spatial scale, and therefore, it is not immediately evident if dramatically elevated neutral heating can lead to excitation of acoustic gravity waves. Using primary observations from Global Navigation Satellite System differential TEC (total electron content) over the continental United States, this paper presents postflare ionospheric observations associated with three X‐class flares on 6, 7, and 10 September 2017. Postflare ionospheric changes had two significant morphological characteristics: (1) A few minutes after the X9.3 flare peak on 6 September, clear traveling ionospheric disturbance (TID) fronts emanated near the sunrise terminator with alignment parallel to its direction—TIDs propagated predominantly eastward into the dayside with a 150 m/s phase speed and a ∼30‐min period; (2) synchronized differential TEC oscillations over continental United States with ∼60‐min periodicity and damping amplitude over time, following all three X‐class flares. Postflare ionospheric oscillation spectra exhibited significantly enhanced amplitudes and changes of periodicities (including the appearance of the 60‐min oscillations). The Millstone Hill incoherent scatter radar observed large ionospheric up‐welling occurring nearly simultaneously as detected TIDs at the X9.3 flare peak, with up to 80 m/s enhancements in vertical drift at 500 km lasting for ∼30 min. Results suggest that significant solar flare heating and associated dynamical effects may be an important factor in TID/acoustic gravity wave excitation. Plain Language Summary: A solar flare injects a sudden and strong energy input to the sunlit upper atmosphere at a range of radiation wavelengths important for ionospheric photochemistry and thermospheric dynamics. Impulsive energy inputs from flares are well known to generate sudden ionospheric density enhancements with subsequent quick decay. This study addresses another type of flare‐associated ionospheric perturbation, known as traveling ionospheric disturbances (TIDs), in the form of propagating waves in space and time as well as synchronized temporal oscillations over the continental United States. Our study provides likely direct observations pointing to a previously unconfirmed TID excitation mechanism associated with solar flare impacts near the sunrise terminator. We observed TIDs with a dense network of Global Navigation Satellite System receivers, yielding detection of differential ionospheric electron content with high fidelity and excellent spatiotemporal resolution. We also used incoherent scatter radar observations at Millstone Hill to reveal ionospheric expansion/up‐welling associated with flare impact. These results address fundamental questions regarding solar flare influences on initiation of atmospheric and ionospheric waves. Key Points: Postflare TIDs emanating near sunrise terminator propagated predominantly eastward with 150 m/s zonal phase speed and 30‐min period Synchronized differential TEC oscillations occurred over the continental United States with 60‐min period and decreasing amplitude over time Rapid and significant ionospheric up‐welling developed in the topside immediately after onset of X‐class flare