A study on the energetic electron precipitation observed by CSES

High energy particles are the main target of satellite space exploration; particle storm events are closely related to solar activity,cosmic ray distribution, and magnetic storms. The commonly seen energetic particle(electron) precipitation anomalies include mainly the inner and outer Van Allen radiation belts, the South Atlantic Anomaly, and the anomalous stripes excited by artificial electromagnetic waves. The China Seismo-Electromagnetic Satellite(CSES), launched in February of 2018, provides a platform for studying ionospheric particle disturbances. This paper reports the first studies of electron precipitation phenomenon based on high energy particle data from the CSES. We find that the global distribution of electron fluxes in the low energy band(0.1–3 MeV) can relatively well reflect the anomalous precipitation belt, which is consistent with results based on the DEMETER satellite, indicating that the quality of the lowenergy band payload of the CSES is good. In addition, this paper makes an in-depth study of the electron precipitation belt excited by the NWC artificial VLF electromagnetic transmitter located in Australia, which appears as a typical wisp structure on the energy spectrum. The magnetic shell parameter L corresponding to the precipitation belt ranges from 1.44 to 1.74, which is close to the L value(～1.45) of the NWC transmitter; the energy of the precipitation electrons is between 100 keV and 361.57 keV, among which the precipitation of 213.73 keV electrons is most conspicuous.

A simulation study of the influence of soft precipitatingelectrons on the polar ionosphere

Calculation of the influence of soft precipitating electrons on the polar ionosphere was carried out. The primary results are: (1) During summer time when the sunlight is the main source of upper atmosphere ionization, the additional soft electron precipitation can increase the NmF2. The daily variation of NmF2 is mainly controlled by solar EUV radiation. (2) At wintertime, when only soft electron precipitation ionization is considered, a peak at the height of F2 layer also appears. The altitude profile of electron density is different frorn that when the sunlit ionization is taken into account.

A conjugate study of the polar ionospheric F2-layer and IRI-2007 at 75 ° magnetic latitude for solar minimum

Long-duration conjugate observations by the EISCAT Svalbard Radar （ESR） and the ionosonde at Zhongshan station from the International Polar Year （IPY） during solar minimum conditions are analyzed, with respect to variability in the F2-1ayer peak parameters. A comparison between International Reference Ionosphere- 2007 （IRI-2007） and observation data clearly demonstrates good agreement in summer, but greater deviations in winter. The IRI model reproduces the F2 peak parameters dominated by solar photoionization reasonably well, but it does not address the effect of electron precipitation. Hence, the discrepancies become large in the winter auroral ionosphere.

The Auroral Station in Adventdalen, Svalbard

This paper describes the Auroral Station in Adventdalen near Longyearbyen, Svalbard (78°N, 15°E). The main instruments at the site are for optical observation of aurora and airglow, but magnetic and radar observations are also carried out. Emission spectra show the difference between the dayside and nightside optical aurora. A newly compiled mesospheric temperature series from the station is also presented, derived through 20 years of spectral measurements of the hydroxyl airglow layer.

Pulsating aurora - a review

In this review, the observational facts about pulsating aurorae are summarized and discussed in the frame of the recent develpment of the theories which intend to explain the mechanism of auroral pulsations. Although new data are available some key observations in the magnetosphere are still missing in order to identify the wave mode to precipitate electrons into the atmosphere and in order to understand the role of magnetospheric plasma in producing pulsating aurora. It apters that the Coroniti-Kennel or micropulsation theory needs to be re-visited although the so-called flow cyclotron maser model seems to explain many of the characteristics of auroral pulsations.

Artificial modification of Earth's radiation belts by ground-based very-low-frequency(VLF)transmitters

Wave-particle interactions play a fundamental role in the dynamic variability of Earth’s donut-shaped radiation belts that are highly populated by magnetically trapped energetic particles and characteristically separated by the slot devoid of high energetic electrons.Owing to the continuous accumulation of high-quality wave and particle measurements from multiple satellites in geospace,the important contribution of ground-based very-low-frequency(VLF)transmitter waves to the electron dynamics in the near-Earth space has been unprecedently advanced,in addition to those established findings of the significant effects of a variety of naturally occurring magnetospheric waves.This paper focuses on the artificial modification of Earth’s inner radiation belt and slot by artificial VLF transmitter emissions.We review the global distributions of VLF transmitter waves in geospace,their scattering effects on radiation belt electrons in terms of both theoretical and observational analyses,and diffusion simulation results of wave-particle interactions along with data-model comparisons.We start with a brief review of the radiation belt electron dynamics and an introduction of anthropogenic VLF transmitter waves.Subsequently,we review the global morphology of in situ VLF transmitter waves corresponding to different transmitter locations,including their day-night asymmetry,geographic distributions,seasonal and geomagnetic activity dependence,and wave propagation features.Existed theoretical and observational analyses of electron scattering effects by VLF transmitter waves are then reviewed to approach the underlying physics that can modulate the spatio-temporal variations of the electron radiation belts.Further Fokker-Planck electron diffusion simulations and their comparisons with realistic satellite observations clearly indicate that VLF transmitter emissions can effectively remove energetic electrons to produce a radially bifurcated electron belt,thereby quantitatively confirming the direct link between operations of VLF transmitters at ground and changes of the energetic electron environment in space.We finally discuss the unsolved problems and possible future research in this area,which has important implications for potential mitigation of the natural particle radiation environment with active means.

Heat-treatable Mg-9Al-6Sn-3Zn extrusion alloy

Mg-9Al-6Sn-3Zn （wt%） alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg17Al12 precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg17Al12 nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.

Relationship Between the Strengthening Effect and the Morphology of Precipitates in Al–7.4Zn–1.7Mg–2.0Cu Alloy

The morphological evolution of the precipitates in Al–7.4Zn–1.7Mg–2.0Cu（wt%） alloy was studied by highresolution transmission electron microscopy（HRTEM）. Statistics reveal that the hardness of the alloy changes accordingly with the change of the average thickness–diameter ratio of precipitates. The GPII zones are mainly responsible for the first and also the highest hardness peak. They grow in diameter and keep 7-atomic-layer in thickness. Once the thickness changes, the phase transformation from GPII zone to g0 or g-precursor would occur. The resultant metastable g0 and g-precursor precipitates grow in both diameter and thickness, but much faster in the former. After the first hardness peak,the metastable g0 precipitates and g-precursor, coexisting with part of GPII zones, are counted as the main hardening precipitates.