Unifying Models of Chorus Wave Frequency Chirping

A new model of chorus wave electron interaction attempts to explain how observations can support two seemingly contradictory mechanisms of frequency chirping.

Determining the global coherence of chorus waves in the magnetosphere

<p>Whistler mode chorus waves play a vital role in the Earth’s outer radiation belt dynamics through the cyclotron resonant pitch angle diffusion.     Recent numerical studies have shown that the temporal and spatial variability of wave growth parameters have universal importance for the diffusion process, which should be much larger than those in the traditional averaged diffusion model.       In the present study, we analyzed both the temporal and spatial coherence of chorus wave in a statistical method using data from the EMFISIS instrument onboard the Van Allen Probes A&B from November 2012 to July 2019. In total, we find 3,875 chorus wave events to calculate the correlation of wave amplitudes between Van Allen Probes A&B.      The results show that both the spatial and temporal correlation of chorus waves decrease significantly with increasing spacecraft separation and time lag, and the spatial and temporal coherence of chorus wave only last ~433 km and ~12 s. We also find that the spatial coherence of chorus waves is higher at L>6, on the dayside, or with a lower geomagnetic index (AL*), while the temporal coherence of chorus waves does not depend on the L-shell, geomagnetic index (AL*) or magnetic local time (MLT). Our results will increase the accuracy of modeling wave-particle interactions due to chorus waves.</p>

Conjugate pulsating aurora and chorus waves: case study at high temporal resolution

<p>Studies have shown a broad correlation between pulsating aurora, chorus waves, and electron scattering, but most studies have used either low time resolution waveform data, high time resolution waveform data over short periods of time, or waveform data without direct crossover of an all sky camera field of view. For the present study, we analyze three nights in Oct 2016 with conjugate Van Allen Probe (VAP) chorus wave observations and HAARP all sky camera (ASC) pulsating aurora observations. We use VAP burst mode waveform data collected for about an hour at 16,000 samples/s during direct VAP crossover of the HAARP ASC FOV in Gakona, AK. Our high-resolution analysis indicates a more complicated relationship between individual aurora pulsations and chorus wave elements.</p><p>We show in previous study that for each VAP ASC crossover event on October 16 2016, the chorus wave elements observed by VAP do not correspond well to the detailed dynamics of the pulsating aurora. We compare the individual chorus wave elements to the extracted all sky camera optical intensity fluctuations along the mapped magnetic footpoint determined by four separate field line models. Our Poynting flux analysis shows chorus wave propagation towards the northern hemisphere. Based on previous results using THEMIS data, we would expect to see good correlation between the observed chorus waves above the magnetic equator and the pulsating aurora dynamics in the northern hemisphere. However, observed chorus waves may be distorted during propagation away from the generation region or non-linear wave effects may play a role.</p><p>In this study we extend our analysis to the VAP ASC crossover events on October 13 and 19 2016. We expand our methodologies for optical intensity extraction of ASC images. We seek to draw connections between the characteristics of the individual chorus wave elements and the correlation to pulsating aurora dynamics to better identify particular chorus wave electron resonance conditions.</p>

Chorus and hiss scales in the inner magnetosphere: statistics from high-resolution filter bank (FBK) Van Allen Proves multi-point measurements

<p>The spatial scales of whistler-mode waves, determined by their generation process, propagation, and damping, are important for assessing the scaling and efficiency of wave-particle interactions affecting the dynamics of the radiation belts. We use multi-point wave measurements in 2013-2019 by two identically equipped Van Allen Probes spacecraft covering all MLTs at L=2-6 near the geomagnetic equator to investigate the spatial extent of active regions of chorus and hiss waves, their wave amplitude distribution in the source/generation region, and the scales of chorus wave packets, employing a time-domain correlation technique to the spacecraft approaches closer than 1000 km, which happened every 70 days in 2012-2018 and every 35 days in 2018-2019. The correlation of chorus wave power dynamics using two spacecraft measurements is found to remain significant up to inter-spacecraft separations of 400 km to 750 km transverse to the background magnetic field direction, consistent with previous estimates of the chorus wave packet extent, but indicating the likely presence of two different scales of about 400 km and 750 km. Our results further suggest that the chorus source region can be slightly asymmetrical, more elongated in either the azimuthal or radial direction, which could also explain the aforementioned two different scales. An analysis of average chorus and hiss wave amplitudes at separate locations similarly reveals different radial and azimuthal extents of the corresponding wave active regions, complementing previous results based on THEMIS spacecraft statistics mainly at larger L>6. Both the chorus source region scale and the chorus active region size appear smaller inside the outer radiation belt (at L< 6) than at higher L-shells.</p>