This paper reports on the design and installation of a thermostat to keep the temperature of the fluxgate magnetometer constant and the data stability evaluation after installation. The thermostat was installed at the Icheon Geomagnetic Observatory operated by the Korean Space Weather Center of National Radio Research Agency. It was designed in consideration of stability of temperature control against safety incident, potential effects on magnetic field measurement, and the temperature control efficiency. After the temperature control device was installed, it was confirmed that the temperature was constantly maintained at the level of 20℃. Delta F and baseline values were used to evaluate geomagnetic data stability, and it was confirmed that delta F and baseline fluctuations were reduced after installation of the thermostat.

We perform a statistical comparison of the global behavior of the THEMIS observed and simulated plasmapause in the geomagnetic equatorial plane. Simulation is based on the interchange instability mechanism. Analyzing plasmapause positions (LPPs) from the period July 2008 to December 2012, we derived formation and propagation characteristics of the main plasmapause, which reflect the most probable global plasmapause behavior. The results suggest a global eastward azimuthal plasmapause propagation and a radial plasmapause motion limited to the 21–07 MLT sector. The formation of the plasmapause takes place with the highest probability at postmidnight. It is likely that the erosion occurs in a range of MLTs simultaneously. On the dayside, the plasmapause moves almost entirely azimuthally. We suggest that the plasmapause propagates azimuthally with a mean angular velocity close to the corotation speed at all MLTs, at least during periods of lower geomagnetic activity. The results also show that the experimental plasmapause characteristics are in accordance with the interchange instability mechanism. Along with the proposed suggestions for future works, this study contributes to making a further step toward resolving some of the long‐lasting, unresolved issues related to plasmapause dynamics.

The cross-correlation analysis is applied to the comprehensive database of THEMIS plasmapause crossings (6840 LPP s) and both solar wind parameters and geomagnetic indices (thereafter LPP indicators). We estimate MLTs of the plasmapause formation and further monitor the motion of the new plasmapause at high MLT resolution. Our results show that plasmapause is firstly formed within 23–07 MLT and then propagates around the Earth with the velocity estimated to amounts for 1.10 and 0.45 of the corotation velocity in sectors 07–15 MLT and 15–23 MLT, respectively. Two branches within 23–07 MLT are identified, one at low time lags (Tlag s) and second at high Tlag s which we relate to the formation of the new plasmapause and to the propagation of the plasmapause formed one MLT-cycle before. This study can be used to improve the current understanding of the plasmapause formation and propagation.

It is well known that the plasmapause is influenced by the solar wind and magnetospheric conditions. Empirical models of its location have been previously developed such as those by O'Brien and Moldwin (2003) and Larsen et al. (2006). In this study, we identified the locations of the plasmapause using the plasma density data obtained from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. We used the data for the period (2008-2012) corresponding to the ascending phase of Solar Cycle 24. Our database includes data from over a year of unusually weak solar wind conditions, correspondingly covering the plasmapause locations in a wider L range than those in previous studies. It also contains many coronal hole stream intervals during which the plasmasphere is eroded and recovers over a timescale of several days. The plasmapause was rigorously determined by requiring a density gradient by a factor of 15 within a radial distance of 0.5L. We first determined the statistical correlation of the plasmapause locations with several solar wind parameters as well as geomagnetic indices. We found that the plasmapause locations are well correlated with the solar wind speed and the interplanetary magnetic field B-z, therefore the y component of the convective electric field, and some energy coupling functions such as the well-known Akasofu's epsilon parameter. The plasmapause locations are also highly correlated with the geomagnetic indices, Dst, AE, and Kp, as recognized previously. Finally, we suggest new model fit functions for the plasmapause locations in terms of the solar wind parameters and geomagnetic indices. When applied to a new data interval outside the model training interval, our model fit functions work better than existing ones. The new model fit functions developed here extend the range of conditions from those used in previous works.

Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) Bz and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF Bz or AE index. Two separate models are developed: one based only on the IMF Bz and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10°, and |MLAT| = 10°–25°. The model performance is measured by the coefficient of determination R2 and the rank‐order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of ~1.5 years, the AE‐based model works slightly better than the IMF Bz‐based model: for the AE‐based model, the mean R2 and ROCC values are ~0.46 and ~0.78 for |MLAT| < 10°, respectively, and ~0.4 and ~0.74 for |MLAT| = 10°–25°, respectively; for the IMF Bz‐based model, the mean R2 and ROCC values are ~0.39 and ~0.74 for |MLAT| < 10°, respectively, and ~0.33 and ~0.70 for |MLAT| = 10°–25°, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models.

Whistler mode chorus wave is considered to play a critical role in accelerating and precipitating the electrons in the outer radiation belt. In this paper we test a conventional scenario of triggering chorus using THEMIS satellite observations of waves and particles. Specifically, we test if the chorus onset is consistent with development of anisotropy in the electron phase space density (PSD). After analyzing electron PSD for 73 chorus events, we find that, for similar to 80 % of them, their onsets are indeed associated with development of the positive anisotropy in PSD where the pitch angle distribution of electron velocity peaks at 90 degrees. This PSD anisotropy is prominent mainly at the electron energy range of <= similar to 20 keV. Interestingly, we further find that there is sometimes a time delay among energies in the increases of the anisotropy: A development of the positive anisotropy occurs earlier by several minutes for lower energy than for an adjacent higher energy.

The Earth's outer radiation belt often suffers from drastic changes in the electron fluxes. Since the electrons can be a potential threat to satellites, efforts have long been made to model and predict electron flux variations. In this paper, we describe a prediction model for the outer belt electrons that we have recently developed at Chungbuk National University. The model is based on a one-dimensional radial diffusion equation with observationally determined specifications of a few major ingredients in the following way. First, the boundary condition of the outer edge of the outer belt is specified by empirical functions that we determine using the THEMIS satellite observations of energetic electrons near the boundary. Second, the plasmapause locations are specified by empirical functions that we determine using the electron density data of THEMIS. Third, the model incorporates the local acceleration effect by chorus waves into the one-dimensional radial diffusion equation. We determine this chorus acceleration effect by first obtaining an empirical formula of chorus intensity as a function of drift shell parameter L*, incorporating it as a source term in the one-dimensional diffusion equation, and lastly calibrating the term to best agree with observations of a certain interval. We present a comparison of the model run results with and without the chorus acceleration effect, demonstrating that the chorus effect has been incorporated into the model to a reasonable degree.

It has long been known that the magnetospheric particles can precipitate into the atmosphere of the Earth. In this paper we examine such precipitation of energetic electrons using the data obtained from low-altitude polar orbiting satellite observations. We analyze the precipitating electron flux data for many periods selected from a total of 84 storm events identified for 2001-2012. The analysis includes the dependence of precipitation on the Kp index and the electron energy, for which we use three energies E1 > 30 keV, E2 > 100 keV, E3 > 300 keV. We find that the precipitation is best correlated with Kp after a time delay of < 3 hours. Most importantly, the correlation with Kp is notably tighter for lower energy than for higher energy in the sense that the lower energy precipitation flux increases more rapidly with Kp than does the higher energy precipitation flux. Based on this we suggest that the Kp index reflects excitation of a wave that is responsible for scattering of preferably lower energy electrons. The role of waves of other types should become increasingly important for higher energy, for which we suggest to rely on other indicators than Kp if one can identify such an indicator.