It is well known that electromagnetic ion cyclotron (EMIC) waves play an important role in controlling particle dynamics inside the Earth's magnetosphere, especially in the outer radiation belt. In ...order to understand the results of wave‐particle interactions due to EMIC waves, it is important to know how the waves are distributed and what features they have. In this paper, we present some statistical analyses on the spatial distribution of EMIC waves in the low Earth orbit by using Swarm satellites from December 2013 to June 2017 (~3.5 years) as a function of magnetic local time, magnetic latitude, and magnetic longitude. We also study the wave characteristics such as ellipticity, wave normal angle, peak frequency, and wave power using our automatic wave detection algorithm based on the method of Bortnik et al. (2007, https://doi.org/10.1029/2006JA011900). We also investigate the geomagnetic control of the EMIC waves by comparing with geomagnetic activity represented by Kp and Dst indices. We find that EMIC waves are detected with a peak occurrence rate at midlatitude including subauroral region, dawn sector (3–7 magnetic local time), and linear polarization dominated with an oblique propagating direction to the background magnetic field. In addition, our result shows that the waves have some relation with geomagnetic activity; that is, they occur preferably during the geomagnetic storm's late recovery phase at low Earth orbit.
Key Points
A statistical analysis of EMIC waves using Swarm satellites is performed
EMIC waves are observed mainly at midlatitude including the subauroral region and dawn sector at low Earth orbit
Approximately 50% of EMICs are related to geomagnetic storms and occur mainly during the storm recovery phase
Low Earth orbit satellites frequently encounter Pc1 pulsations, but most have been observed with limited latitudinal extent or short lifetime. In this study we analyze two large‐scale Pc1 pulsations ...(both latitudinally wide and long‐lasting) generated by ionospheric ducting effect using Swarm and ground magnetometers on 25 June and 3 September 2015. Swarm observed the 25 June pulsations on both dayside and nightside during the storm time substorm (a strong geomagnetic storm on 23 June with Dst = − 204 nT). We found the Pc1 pulsations were pervasive in both magnetic local time sectors of dayside and nightside for at least 2 hr. Another large Pc1 pulsation on 3 September was observed during a nonstorm substorm period. We conclude that (1) ionospheric ducting can transmit Pc1 waves to a wide range of L shells, (2) geomagnetic storm is not a prerequisite for such large‐scale ducting, and (3) wave intensity can abruptly decrease across sharp gradients in the ionospheric plasma density.
Plain Language Summary
The observation of Pc 1 waves in low Earth orbit satellites has frequently been reported. This wave is a kind of plasma waves that plays a very important role in the acceleration and loss mechanisms of the Earth's Van Allen belt. We have found very special Pc 1 waves that cover broad MLT sector with long duration. Combining Swarm constellation satellites' data and a variety of ground magnetometer data, we report the interesting characteristics of this particular wave and relationship with geomagnetic conditions.
Key Points
We analyze two large Pc1 pulsations by ionospheric ducting effect using Swarm satellites and multiple ground magnetometer networks
Pc1 pulsations are pervasive in both MLT sectors of dayside and nightside for at least 2 hr via two different source regions
Wave intensity can abruptly decrease across sharp gradients or irregularities in the ionospheric plasma density
We report the first observation of plasma density oscillations coherent with magnetic Pc1 waves. Swarm satellites observed compressional Pc1 wave activity in the 0.5–3 Hz band, which was coherent ...with in situ plasma density oscillations. Around the Pc1 event location, the Antarctic Neumayer Station III (L ~ 4.2) recorded similar Pc1 events in the horizontal component while NOAA‐15 observed isolated proton precipitations at energies above 30 keV. All these observations support that the compressional Pc1 waves at Swarm are oscillations converted from electromagnetic ion cyclotron (EMIC) waves coming from the magnetosphere. The magnetic field and plasma density oscillate in‐phase. We compared the amplitudes of density and magnetic field oscillations normalized to background values and found that the density power is much larger than the magnetic field power. This difference cannot be explained by a simple magnetohydrodynamic (MHD) model, although steep horizontal/vertical gradients of background ionospheric density can partly reconcile the discrepancy.
Plain Language Summary
Electromagnetic ion cyclotron (EMIC) wave is known to be generated in the inner magnetosphere in the ultralow frequency (ULF) Pc1 range (0.2–5 Hz). The EMIC Pc1 waves propagate as shear Alfvén mode from the magnetospheric source toward the ionosphere. On arriving at ionospheric altitudes, they undergo mode conversion to the compressional Alfvén mode due to the Hall conductivity. According to the ideal magnetohydrodynamics (MHD) theory, the compressional ULF wave can be accompanied by density perturbation of ionospheric plasmas. In this paper, we report the first observation of ionospheric plasma density oscillations driven by EMIC Pc1 waves based on the observation by the Swarm satellites. Simple MHD equations cannot fully explain the amplitude and phase relationship between plasma density and magnetic Pc1 pulsations, while steep horizontal/vertical gradients of background ionospheric plasma density may in part reconcile the discrepancy.
Key Points
We report the first observation of ionospheric plasma density oscillation correlated with electromagnetic ion cyclotron (EMIC) Pc1 wave
Simple MHD theory cannot explain the observed amplitude and phase relationships between the plasma density oscillation and the Pc1 wave
The EMIC Pc1 wave was also accompanied by localized proton precipitation
A lunar vehicle radiation dosimeter (LVRAD) has been proposed for studying the radiation environment on the lunar surface and evaluating its impact on human health. The LVRAD payload comprises four ...systems: a particle dosimeter and spectrometer (PDS), a tissue-equivalent dosimeter, a fast neutron spectrometer, and an epithermal neutron spectrometer. A silicon photodiode sensor with compact readout electronics was proposed for the PDS. The PDS system aims to measure protons with 10–100 MeV of energy and assess dose in the lunar space environment. The manufactured silicon photodiode sensor has an effective area of 20 mm × 20 mm and thickness of 650 μm; the electronics consist of an amplifier, analog pulse processor, and a 12-bit analog-to-digital converter for signal readout. We studied the responses of silicon sensors which were manufactured with self-made electronics to gamma rays with a wide range of energies and proton beams.
Accurate knowledge of the global distribution of magnetospheric chorus waves is essential for radiation belt modeling because it provides a direct link to understanding radiation belt losses and ...acceleration processes. In this paper, we report on newly developed models of the global distribution of chorus amplitudes based on in situ measurements of interplanetary magnetic field (IMF) and solar wind parameters as well as geomagnetic indices using an artificial neural network technique. We find that solar wind speed and IMF BZ are the most influential parameters that affect the evolution of the magnetospheric chorus. The variations of chorus amplitudes in the outer (L ≥ 7) and in the inner (5 ≤ L < 7) regions, respectively, are well correlated with the variations of solar wind speed and IMF BZ. In addition, the solar wind parameter‐based chorus model generally results in a slightly higher correlation between measured and modeled chorus amplitudes than any other models including geomagnetic indices AE, Kp, and Dst. The developed model shows that the chorus is amplified near the prenoon sector during the geomagnetically disturbed conditions. With increasing southward IMF BZ the location of peak chorus amplitude moves from the prenoon sector to the midnight sector, which is due to the enhanced electron injection near midnight. We also present a comparison of diffusive transport simulations for radiation belt electrons interacting with two newly developed chorus models, solar wind parameter‐based and geomagnetic index‐based chorus models. The comparison between two models shows that the modeling outside the plasmapause can affect the dynamic even inside the plasmasphere because the populations outside the plasmapause can act as seed population to radiation belt particles inside the plasmapause. One weakness of our chorus modeling is that it is trained during the early phase of solar cycle 24 where very few strong storms occurred. Therefore, our model might not be valid in reproducing the chorus activity under extremely disturbed conditions, which should be updated in the future once chorus measurements for such conditions become available.
Key Points
Model global distribution of chorus amplitudes with solar wind parameters.
Solar wind speed and IMF Bz are associated with evolution of chorus wave.
Significant difference between solar wind‐based and Kp‐dependent chorus model.
Electromagnetic ion cyclotron (EMIC) waves are closely related to precipitating loss of relativistic electrons in the radiation belts, and thereby, a model of the radiation belts requires inclusion ...of the pitch angle diffusion caused by EMIC waves. We estimated the pitch angle diffusion rates and the corresponding precipitation time scales caused by H and He band EMIC waves using the Tsyganenko 04 (T04) magnetic field model at their probable regions in terms of geomagnetic conditions. The results correspond to enhanced pitch angle diffusion rates and reduced precipitation time scales compared to those based on the dipole model, up to several orders of magnitude for storm times. While both the plasma density and the magnetic field strength varied in these calculations, the reduction of the magnetic field strength predicted by the T04 model was found to be the main cause of the enhanced diffusion rates relative to those with the dipole model for the same Li values, where Li is defined from the ionospheric foot points of the field lines. We note that the bounce‐averaged diffusion rates were roughly proportional to the inversion of the equatorial magnetic field strength and thus suggest that scaling the diffusion rates with the magnetic field strength provides a good approximation to account for the effect of the realistic field model in the EMIC wave‐pitch angle diffusion modeling.
Key Points
Diffusion rates and precipitation time scales due to EMIC waves are calculated using the T04 model
The rates increase by up to several orders of magnitude compared to those based on the dipole model
The enhancement in the rates is mainly due to a decrease in the magnetic field strength
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