First Observation of Lion Roar Emission in Saturn's Magnetosheath

0487612 - ÚFA 2018 RIV US eng J - Článek v odborném periodiku
Píša, David - Sulaiman, A. H. - Santolík, Ondřej - Hospodarsky, G. B. - Kurth, W. S. - Gurnett, D. A.
First Observation of Lion Roar Emission in Saturn's Magnetosheath.
Geophysical Research Letters. Roč. 45, č. 2 (2018), s. 486-492. ISSN 0094-8276. E-ISSN 1944-8007
Grant CEP: GA ČR GA17-08772S; GA ČR GJ16-16050Y
Grant ostatní: AV ČR(CZ) AP1401
Program: Akademická prémie - Praemium Academiae
Institucionální podpora: RVO:68378289
Klíčová slova: Cassini spacecraft * Magnetosheath * Saturn * lion roar emissions * bow shock * propagation * particle * plasma * waves
Obor OECD: Fluids and plasma physics (including surface physics)
Impakt faktor: 4.578, rok: 2018
http://onlinelibrary.wiley.com/doi/10.1002/2017GL075919/abstract

We present an observation of intense emissions in Saturn's magnetosheath as detected by the Cassini spacecraft. The emissions are observed in the dawn sector (magnetic local time similar to 06:45) of the magnetosheath over a time period of 11 h before the spacecraft crossed the bow shock and entered the unshocked solar wind. They are found to be narrow-banded with a peak frequency of about 0.16 f(ce), where f(ce) is the local electron gyrofrequency. Using plane wave propagation analysis, we show that the waves are right hand circularly polarized in the spacecraft frame and propagate at small wave normal angles (<10 degrees) with respect to the ambient magnetic field. Electromagnetic waves with the same properties known as ´lion roars´ have been reported by numerous missions in the terrestrial magnetosheath. Here we show the first evidence such emission outside the terrestrial environment. Our observations suggest that lion roars are a solar-system-wide phenomenon and capable of existing in a broad range of parameter space. This also includes 1 order of magnitude difference in frequencies. We anticipate our result to provide new insight into such emissions in a new parameter regime characterized by a higher plasma beta (owing to the substantially higher Mach number bow shock) compared to Earth.
Trvalý link: http://hdl.handle.net/11104/0282290