Conjugate Observations of Quasiperiodic Emissions by the Van Allen Probes Spacecraft and Ground‐Based Station Kannuslehto. Issue 6 (17th June 2020)

• Record Type: Journal Article
• Authors: Bezděková, B.; Němec, F.; Manninen, J.; Hospodarsky, G. B.; Santolík, O.; Kurth, W. S.; Hartley, D. P.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 6(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-06-17
• Subjects: Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2020JA027793
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Whistler mode waves observed in the Earth's inner magnetosphere at frequencies between about 0.5 and 4 kHz which exhibit a nearly periodic time modulation of the wave intensity are called quasiperiodic (QP) emissions. Conjugate measurements of QP events at several different locations can be used to estimate their spatial extent and spatiotemporal variability. Results obtained using conjugate QP measurements provided by the ground‐based station Kannuslehto ( L ≈5.5) and the Van Allen Probes spacecraft ( L shells between about 1.1 and 6.5) between September 2012 and November 2017 are presented. Altogether, 26 simultaneously detected events were analyzed. The event modulation periods and frequency‐time structures were generally the same at all observation points. Spatial separations of the spacecraft and the ground‐based station during conjugate observations are typically within about 40° in azimuth and from about 1 to 3 in L shell. RBSP consistently observes events at lower L shells than Kannuslehto, with the event occurrence primarily inside of the plasmasphere. Ratios of Poynting fluxes observed by the spacecraft and on the ground are used to evaluate event intensity variations related to the spacecraft position. It is found that the intensity decreases considerably both at low L shells and outside of the plasmasphere. Finally, an event containing a gap in its frequency‐time structure related to a sudden change of its properties is analyzed in detail. Key Points: Spatial separations during conjugate observations are typically within 40° in azimuth and from about 1 to 3 in L shell Spacecraft and ground‐based intensity ratios demonstrate an intensity decrease both close to the plasmapause and at low L shells Event with a gap and spectral structure change was explained as two immediately following events