A statistical study of spatial distribution and source region size of chorus waves using Van Allen Probes data

Abstract

Abstract. Spatial distribution and source region size of chorus waves are important parameters in understanding their generation. In this work, we analyze over 3 years of continuous wave burst mode data from Van Allen Probes and build a data set of rising and falling tone chorus. For the L shell range covered by Van Allen Probes data (3.5 ≤ L ≤ 7), statistical results demonstrate that the sector where rising tones are most likely to be observed is the dayside during geomagnetically quiet and moderate times and the dawnside during active times. Moreover, rising tone chorus waves have a higher occurrence rate near 5 the equatorial plane, while the falling tone chorus waves have a higher possibility to be observed at lower L-shell and higher magnetic latitude. By analyzing the direction of Poynting wave vector, we statistically investigate the chorus source region size along a field line, and compare the results with previous theoretical estimates. Our analysis confirms previous conclusions that both rising tone and falling tone chorus waves are generated near the equatorial plane, and shows that previous theoretical estimates roughly agree with the observation within a factor of two. Our results provide important insights into further 10 understanding of chorus generation.

Two‐Dimensional gcPIC Simulation of Rising‐Tone Chorus Waves in a Dipole Magnetic Field

“…The whistler mode waves are first excited by an anisotropic electron distribution around the magnetic equator (∣ λ ∣ ≤ 3°,). Such latitudinal range is consistent with previous satellite observations (Santolik et al, ; Teng et al, ). After the whistler mode waves leave the source region and obtain a sufficiently large amplitude, they begin to have a frequency chirping and evolve into rising‐tone chorus waves.…”

Observation of Unusual Chorus Elements by Van Allen Probes

“…v ⊥ is the perpendicular velocity of electrons. Considering that chorus waves are generated near the equator (Teng et al., 2018), the second term of the right side in Equation is approximate 0 because the magnetic field (or gyro‐frequency Ω e ) barely varies along the position h .…”

A Statistical Analysis of Duration and Frequency Chirping Rate of Falling Tone Chorus

“…The general method of wave event identification from burst‐mode data is similar to the one used by Teng et al. (2018): we set a threshold (up to 10 −4 nT 2 /Hz) for the wave magnetic field power spectral density and visually inspect the power spectrogram of each event. For each event, the location parameters such as magnetic local time (MLT), magnetic latitude (MLAT) and L shell are derived from the TS04D magnetic field model (Tsyganenko & Sitnov, 2005) provided by the data analysis software SPEDAS (Angelopoulos et al., 2019).…”