Thursday, 4 December 2014
Broadband Meter-Wavelength Observations of Ionospheric Scintillation
This week, the first KAIRA paper detailing the ionospheric scintillation observations we've been performing, and the "scintillation arc" phenomenon we've noted in the KAIRA blog (http://kaira.sgo.fi/2014/07/ionospheric-scintillation-arcs.html) was accepted for publication in the Journal of Geophysical Research. The image shown is of a poster presented at the recent European Space Weather Week which summarises this work, along with a few more recent results taken with LOFAR. The abstract of the paper follows and the full work can already be found online (http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014JA020406/).
Intensity scintillations of cosmic radio sources are used to study astrophysical plasmas like the ionosphere, the solar wind, and the interstellar medium. Normally these observations are relatively narrow band. With Low Frequency Array (LOFAR) technology at the Kilpisjarvi Atmospheric Imaging Receiver Array (KAIRA) station in northern Finland we have observed scintillations over a 3 octave bandwidth. “Parabolic arcs”, which were discovered in interstellar scintillations of pulsars, can provide precise estimates of the distance and velocity of the scattering plasma. Here we report the first observations of such arcs in the ionosphere and the first broad-band observations of arcs anywhere, raising hopes that study of the phenomenon may similarly improve the analysis of ionospheric scintillations. These observations were made of the strong natural radio source Cygnus-A and covered the entire 30-250 MHz band of KAIRA. Well-defined parabolic arcs were seen early in the observations, before transit, and disappeared after transit although scintillations continued to be obvious during the entire observation. We show that this can be attributed to the structure of Cygnus-A. Initial results from modeling these scintillation arcs are consistent with simultaneous ionospheric soundings taken with other instruments, and indicate that scattering is most likely to be associated more with the topside ionosphere than the F-region peak altitude. Further modeling and possible extension to interferometric observations, using international LOFAR stations, are discussed.