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Statistical Study of the Non-thermal Continuum Radiation Beaming Angle measured by the High Frequency Receiver on Van Allen Probes-A
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  • Scott A. Boardsen,
  • Eun-Hwa Kim,
  • James L Green,
  • Chio Z Cheng,
  • Iver H. Cairns,
  • Jay Robert Johnson
Scott A. Boardsen

Corresponding Author:[email protected]

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Eun-Hwa Kim
Princeton Plasma Physics Laboratory, Princeton University
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James L Green
Space Science Endeavors LLC
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Chio Z Cheng
Princeton Plasma Physics Laboratory, Princeton University
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Iver H. Cairns
University of Sydney
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Jay Robert Johnson
Andrews University
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The nonthermal continuum radiation (NTC) beaming angle is computed over the entire Van Allen Probes A mission when the spacecraft was in the dawn sector. The conditions in the dawn sector are favorable for the wave vector to lie near/in the spacecraft’s spin plan allowing a favorable estimate of the beaming angle, and the dawn sector is also advantageous in that previous studies show NTC occurrence to peak in this sector. We found that scatter plots, over the entire mission, of beaming angle versus magnetic latitude form a distinct inverted V pattern, with the apex at/near the magnetic equator. This pattern was sharpest for frequencies (f) ≲ 100 kHz. Using the NTC beaming formula from LMCT, we show that such an inverted V pattern is expected due to the large variation in the plasmapause location over the entire mission. The theoretical derived pattern qualitatively reproduces the observed pattern but not quantitatively. The lack of quantitative agreement is discussed and is attributed to several factors, one factor is off centered emissions from the radio window. The qualitative agreement strongly supports LMCT as being the dominant mechanism generating NTC for f ≲ 100 kHz. For f ≳ 100 kHz the inverted V pattern becomes less distinct, and strong near equatorial beaming is observed. After considering contamination of our selections by left-handed polarized AKR, our study suggests that besides LMCT another unidentified NTC generation mechanism becomes important for f ≳ 100 kHz.
30 Mar 2023Submitted to ESS Open Archive
04 Apr 2023Published in ESS Open Archive