Energetic electron precipitation (EEP) associated with pulsating aurora can transfer greater than 30 keV electrons from the outer radiation belt region into the upper atmosphere and can deplete atmospheric ozone via collisions that produce NOx and HOx molecules. Our knowledge of exactly how EEP occurs is incomplete. Previous studies have shown that pitch angle scattering between electrons and lower‐band chorus waves can cause pulsating aurora associated with EEP and that substorms play an important role. In this work, we quantify the timescale of chorus wave decay following substorms and compare that to previously determined timescales. We find that the chorus decay e‐folding time varies based on magnetic local time (MLT), magnetic latitude, and wave frequency. The shortest timescales occur for lower‐band chorus in the 21 to 9 MLT region and compares, within uncertainty, to the energetic pulsating aurora timescale of Troyer et al. (2022,
Earth's slot region, lying between the outer and inner radiation belts, has been identified as due to a balance between inward radial diffusion and pitch angle (PA) scattering induced by waves. However, recent satellite observations and modeling studies indicate that cosmic ray albedo neutron decay (CRAND) may also play a significant role in energetic electron dynamics in the slot region. In this study, using a drift‐diffusion‐source model, we investigate the relative contribution of all significant waves and CRAND to the dynamics of energetic electrons in the slot region during July 2014, an extended period of quiet geomagnetic activity. The bounce‐averaged PA diffusion coefficients from three types of waves (hiss, lightning‐generated whistlers [LGW], and very low frequency [VLF] transmitters) are calculated based on quasi‐linear theory, while the CRAND source follows the results in Xiang et al. (2019,
- Award ID(s):
- 1834971
- NSF-PAR ID:
- 10375025
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 125
- Issue:
- 9
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract https://doi.org/10.3389/fspas.2022.1032552 ) for energetic pulsating aurora. We are able to further support this connection by modeling our findings in a quasi‐linear diffusion simulation. These results provide observations of how chorus waves behave after substorms and add additional statistical evidence linking energetic pulsating aurora to substorm driven lower‐band chorus waves. -
more » « less
Abstract The very‐low frequency (VLF) and low frequency (LF) waves from ground transmitters propagate in the ionospheric waveguide, and a portion of their power leaks to the Earth's inner radiation belt and slot region where it can cause electron precipitation loss. Using Van Allen Probes observations, we perform a survey of the VLF and LF transmitter waves at frequencies from 14 to 200 kHz. The statistical electric and magnetic wave amplitudes and frequency spectra are obtained at 1 <
L < 3. Based on a recent study on the propagation of VLF transmitter waves, we divide the total wave power into ducted and unducted portions, and model the wave normal angle of unducted waves with dependences onL shell, magnetic latitude, and wave frequency. At lower frequencies, the unducted waves are launched along the vertical direction and the wave normal angle increases during the propagation until reaching the Gendrin angle; at higher frequencies, the normal angle of unducted waves follows the variation of Gendrin angle. We calculate the bounce‐averaged pitch angle and momentum diffusion coefficients of electrons due to ducted and unducted VLF and LF waves. Unducted and ducted waves cause efficient pitch angle scattering atL = 1.5 and 2.5, respectively. Although the wave power from ground transmitters at frequencies higher than 30 kHz is low, these waves can cause the pitch angle scattering of lower energy (2–200 keV atL = 1.5) electrons, which cannot resonate with the VLF transmitter waves at frequencies below 30 kHz, lightning generated whistlers, or plasmaspheric hiss. -
more » « less
Abstract Atomic oxygen (O) in the mesosphere and lower thermosphere (MLT) results from a balance between production via photo‐dissociation in the lower thermosphere and chemical loss by recombination in the upper mesosphere. The transport of O downward from the lower thermosphere into the mesosphere is preferentially driven by the eddy diffusion process that results from dissipating gravity waves and instabilities. The motivation here is to probe the intra‐annual variability of the eddy diffusion coefficient (k
zz ) and eddy velocity in the MLT based on the climatology of the region, initially accomplished by Garcia and Solomon (1985,https://doi.org/10.1029/JD090iD02p03850 ). In the current study, the intra‐annual cycle was divided into 26 two‐week periods for each of three zones: the northern hemisphere (NH), southern hemisphere (SH), and equatorial (EQ). Both 16 years of SABER (2002–2018) and 10 years of SCIAMACHY (2002–2012) O density measurements, along with NRLMSIS®2.0 were used for calculation of atomic oxygen eddy diffusion velocities and fluxes. Our prominent findings include a dominant annual oscillation below 87 km in the NH and SH zones, with a factor of 3–4 variation between winter and summer at 83 km, and a dominant semiannual oscillation at all altitudes in the EQ zone. The measured global average kzz at 96 km lacks the intra‐annual variability of upper atmosphere density data deduced by Qian et al. (2009,https://doi.org/10.1029/2008JA013643 ). The very large seasonal (and hemispherical) variations in kzz and O densities are important to separate and isolate in satellite analysis and to incorporate in MLT models. -
more » « less
Abstract MMS3 spacecraft passed the vicinity of the electron diffusion region of magnetotail reconnection on 3 July 2017, observing discrepancies between perpendicular electron bulk velocities and
drift, and agyrotropic electron crescent distributions. Analyzing linear wave dispersions, Burch et al. (2019, https://doi.org/10.1029/2019GL082471 ) showed the electron crescent generates high‐frequency waves. We investigate harmonics of upper‐hybrid (UH) waves using both observation and particle‐in‐cell (PIC) simulation, and the generation of electromagnetic radiation from PIC simulation. Harmonics of UH are linearly polarized and propagate along the perpendicular direction to the ambient magnetic field. Compared with two‐dimensional PIC simulation and nonlinear kinetic theory, we show that the nonlinear beam‐plasma interaction between the agyrotropic electrons and the core electrons generates harmonics of UH. Moreover, PIC simulation shows that agyrotropic electron beam can lead to electromagnetic (EM) radiation at the plasma frequency and harmonics. -
more » « less
Abstract To investigate the role of atmospheric collisions and cosmic ray albedo neutron decay (CRAND) in the dynamics of energetic electrons in the Earth's inner radiation belt during geomagnetic quiet times, a drift‐collision‐source model that includes azimuthal drift, pitch angle diffusion from elastic collision, energy loss from inelastic collision, and a CRAND source is developed. In the model, the bounce‐averaged pitch angle diffusion coefficients and energy loss rates are calculated based on scattering of electrons with neutrals given by the NRLMSISE‐00 model and with ions and electrons given by International Reference Ionosphere (IRI) 2012 model. The electron source rate from CRAND follows the recently developed drift‐source model in Xiang et al. (2019). For 304‐keV quasi‐trapped electrons at
L = 1.25, simulation results with CRAND show good agreement with Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions satellite observations, confirming that CRAND is the main source for these quasi‐trapped electrons, in contrast to the previous understanding that these quasi‐trapped electrons were formed by wide‐angle scattering of the trapped populations. For trapped electrons, 153, 304, and 509 keV atL < 1.3, the simulation results with only azimuthal drift and atmospheric collisions show a much quicker decrease than observations, while simulation results including a CRAND source are generally comparable to the observations, suggesting that CRAND is an important source of trapped hundreds of kiloelectron‐volt electrons atL < 1.3 during quiet times and provides a baseline for the electron flux even during active times as well. Furthermore, these results suggest that actual radial diffusion rates in the inner belt are lower than previous estimates in which CRAND contributions were not considered.
