Fluctuation of Lower Ionosphere Associated with Energetic Electron Precipitations during a Substorm

Tongxing Fu,Zhixu Wu,Xin Zhang,Peng Hu

doi:10.3390/atmos12050573

Abstract

In this paper, using the combined observations of the NOAA 16, LANL-01A, IMAGE satellites, VLF radio wave, and ground-based riometers, we study the fluctuation of lower ionosphere-associated precipitating energetic electrons during a geomagnetic storm on 8 November 2004. Associated with the substorm dispersion injection observed by the LANL-01A satellite, the riometers observed obvious enhancements of ionospheric absorption within the electron isotropic zone, which they attributed to the tail current sheet scattering (TCS) mechanism. Through observations of the NOAA 16 satellite, we found a sharp enhancement of the precipitating electron flux within the anisotropic zone, which entailed an obvious separation of energetic electron precipitation at high latitudes. This energetic electron precipitation within the anisotropic zone leads to the significant enhancement of electron density in the D region, thus resulting in the variations of VLF radio wave amplitudes, which propagate in the middle latitudes. Since the projection of the electron precipitation region within the anisotropic zone is at the inner edge of the plasmapause observed by the IMAGE EUV, the precipitation of energetic electrons should be attributed to the ELF hiss-ring current electron interaction. As a result, the energetic electron precipitations due to the tail current sheet scattering mechanism and wave-particle interaction in the inner magnetosphere were both observed and analyzed as they were associated with a substorm during a geomagnetic storm.

Highlights

Gvozdevsky et al [1] have summarized that when low-altitude NOAA spacecraft cross into the ionosphere from high to low latitudes, they detected an isotropic flux distribution in higher latitudes and subsequently detected anisotropic flux distribution in lower latitudes.The boundary between zones of isotropic and anisotropic fluxes is called the isotropic boundary (IB)
Since the two riometers were located in the isotropic zone and very close to midnight (GIL was at 1.85 MLT, ISL was at 1.92 MLT on the onset of substorm injection), the energetic electrons within the isotropic zone precipitated into the atmosphere and cause additional ionization, which led to enhancements of ionospheric absorption
Since the particle gyroradius is comparable with the field line curvature radius in the equatorial plane, the energetic electrons from the substorm injection can be scattered into the loss cone and precipitate into the high-latitude ionosphere [34], which leads to an increase of the ionospheric absorption

Summary

Introduction

Gvozdevsky et al [1] have summarized that when low-altitude NOAA spacecraft cross into the ionosphere from high to low latitudes, they detected an isotropic flux distribution in higher latitudes and subsequently detected anisotropic flux distribution in lower latitudes. Clilverd et al [26] have estimated seasonal changes of the precipitating flux of the outer radiation belt energetic electrons into the atmosphere by the observations of NOAA satellite and VLF radio waves. We used the riometers at high latitudes (L > 4.5) to detect fluctuations of the lower ionosphere due to energetic electron precipitation within the isotropic zone, which are caused by the TCS mechanism. VLF radio wave receivers at middle latitudes (L < 4) are used to depict the fluctuation of the lower ionosphere due to energetic electron precipitation within the anisotropic zone, which is caused by the wave-particle interaction in the inner magnetosphere. The effect of energetic electron precipitation within the anisotropic zone on the profile of lower ionospheric electron density and VLF radio wave propagation are discussed in this paper

Instrumentations

Observations

November

Discussion and Conclusions

Background