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Statistical Study of the Properties of Magnetosheath Lion Roars
Univ Sheffield, Automat Control & Syst Engn, Sheffield, S Yorkshire, England..
NASA, Goddard Space Flight Ctr, Heliophys Sci Div, Greenbelt, MD USA..
Southwest Res Inst, San Antonio, TX USA..
Univ Paris Sud, Sorbonne Univ, CNRS, Lab Phys Plasmas,UMR7648,Ecole Polytech,Observ Pa, Paris, France..
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2018 (Engelska)Ingår i: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 123, nr 7, s. 5435-5451Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Lion roars are narrowband whistler wave emissions that have been observed in several environments, such as planetary magnetosheaths, the Earth's magnetosphere, the solar wind, downstream of interplanetary shocks, and the cusp region. We present measurements of more than 30,000 such emissions observed by the Magnetospheric Multiscale spacecraft with high-cadence (8,192 samples/s) search coil magnetometer data. A semiautomatic algorithm was used to identify the emissions, and an adaptive interval algorithm in conjunction with minimum variance analysis was used to determine their wave vector. The properties of the waves are determined in both the spacecraft and plasma rest frame. The mean wave normal angle, with respect to the background magnetic field (B-0), plasma bulk flow velocity (V-b), and the coplanarity plane (V-b x B-0) are 23 degrees, 56 degrees, and 0 degrees, respectively. The average peak frequencies were similar to 31% of the electron gyrofrequency (omega(ce)) observed in the spacecraft frame and similar to 18% of omega(ce) in the plasma rest frame. In the spacecraft frame, similar to 99% of the emissions had a frequency < omega(ce), while 98% had a peak frequency < 0.72 omega(ce) in the plasma rest frame. None of the waves had frequencies lower than the lower hybrid frequency, omega. From the probability density function of the electron plasma beta(e), the ratio between the electron thermal and magnetic pressure, similar to 99.6% of the waves were observed with beta(e) < 4 with a large narrow peak at 0.07 and two smaller, but wider, peaks at 1.26 and 2.28, while the average value was similar to 1.25.

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American Geophysical Union (AGU), 2018. Vol. 123, nr 7, s. 5435-5451
Nationell ämneskategori
Fusion, plasma och rymdfysik
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URN: urn:nbn:se:kth:diva-234638DOI: 10.1029/2018JA025343ISI: 000442664300012Scopus ID: 2-s2.0-85050883426OAI: oai:DiVA.org:kth-234638DiVA, id: diva2:1247439
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QC 20180912

Tillgänglig från: 2018-09-12 Skapad: 2018-09-12 Senast uppdaterad: 2018-09-12Bibliografiskt granskad

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Lindqvist, Per-Arne

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