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Park J.,Korea Astronomy and Space Science Institute Daejeon South Korea | Luhr H.,Helmholtz Center Potsdam | Nishioka M.,Japan National Institute of Information and Communications Technology | Kwak Y.-S.,Korean University of Science and Technology
Journal of Geophysical Research A: Space Physics | Year: 2015

Plasma density undulations in the dayside low-latitude/midlatitude ionospheric F region were often attributed to thermospheric gravity waves (TGWs). However, the relationship between the former and the latter has been at best indirectly evidenced. In this study we investigate daytime fluctuations in neutral mass density (ρ) and plasma density (ne) measured onboard CHAMP from 2001 to 2010. A significant amount of daytime fluctuations in ne is strongly correlated with in situ fluctuations of ρ, which we term "TGW-related ne fluctuations." The TGW-related ne fluctuations are (1) stronger in the winter hemisphere than in the summer hemisphere and (2) strongest in the South American sector during June solstice months. These climatological features are in general agreement with those of TGWs reported previously, especially at midlatitudes. On the other hand, the relative amplitude of TGW-related ne fluctuations does not depend strongly on solar activity. ©2015. American Geophysical Union. Source


Hwang J.,Korean University of Science and Technology | Choi E.-J.,Korea Advanced Institute of Science and Technology | Park J.-S.,Kyung Hee University | Fok M.-C.,NASA | And 5 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

We investigate an electron flux dropout during a weak storm on 7-8 November 2008, with Dst minimum value being -37nT. During this period, two clear dropouts were observed on GOES 11>2MeV electrons. We also find a simultaneous dropout in the subrelativistic electrons recorded by Time History of Events and Macroscale Interactions during Substorms probes in the outer radiation belt. Using the Radiation Belt Environment model, we try to reproduce the observed dropout features in both relativistic and subrelativistic electrons. We found that there are local time dependences in the dropout for both observation and simulation in subrelativistic electrons: (1) particle loss begins from nightside and propagates into dayside and (2) resupply starts from near dawn magnetic local time and propagates into the dayside following electron drift direction. That resupply of the particles might be caused by substorm injections due to enhanced convection. We found a significant precipitation in hundreds keV electrons during the dropout. We observe electromagnetic ion cyclotron and chorus waves both on the ground and in space. We find the drift shells are opened near the beginning of the first dropout. The dropout in MeV electrons at GEO might therefore be initiated due to the magnetopause shadowing, and the followed dropout in hundreds keV electrons might be the result of the combination of magnetopause shadowing and precipitation loss into the Earth's atmosphere. © 2015. American Geophysical Union. All Rights Reserved. Source


Kim J.-H.,Chungbuk National University | Lee D.-Y.,Chungbuk National University | Cho J.-H.,Chungbuk National University | Shin D.-K.,Chungbuk National University | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

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 5years, 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 2h 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 ~1.5years, 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. © 2015. American Geophysical Union. All Rights Reserved. Source


Kim K.-C.,Korea Astronomy and Space Science Institute Daejeon South Korea | Lee D.-Y.,Chungbuk National University | Shprits Y.,University of California at Los Angeles
Journal of Geophysical Research A: Space Physics | Year: 2015

Accurate knowledge of the global distribution of plasmaspheric hiss is essential for the radiation belt modeling because it provides a direct link to understanding the radiation belt loss in the slot region. In this paper, we study the dependence of hiss activity on solar wind parameters and geomagnetic activity indices using Time History of Events and Macroscale Interactions during Substorms hiss measurements made from 1 July 2008 to 30 June 2012 based on a correlation analysis. We find that hiss amplitudes are well correlated with the preceding solar wind speed VSW, interplanetary magnetic field (IMF) BZ, and interplanetary electric field (IEF) EY with delay times of 5-6h for VSW and 3-4h for IMF BZ and IEF EY, while the best correlation with the geomagnetic indices, AE, Kp, and SYM-H, occurs at a delay time of 2-3h for AE and SYM-H and 3-4h for Kp. Of the solar wind parameters, the dawn-to-dusk component of IEF EY yields the best correlation with the variation of hiss wave. More interestingly, the global distribution of hiss waves shows a significant dependence on the VSW and IMF BZ: the most intense hiss region tends to occur at prenoon sector for a more southward IMF BZ, while the tendency is opposite with increasing VSW. This implies different origins of hiss activity. Also, we employ an artificial neural network technique to develop models of the global distribution of hiss amplitudes based on the solar wind parameters and geomagnetic indices. The solely solar wind parameter-based model generally results in a higher correlation between the measured and modeled hiss amplitudes than any other models based on the geomagnetic indices. Finally, we use the solar wind parameter-based model to investigate hiss activity during storm events by distinguishing between coronal mass ejection-driven storms and corotating interaction region-driven storms. The result shows that in spite of the differences in the behavior of solar wind parameters between the two storm groups, the different types of storms lead to the similar evolution of hiss waves in overall appearance even though the detailed behavior of hiss activations are different. ©2015. American Geophysical Union. Source


Park J.,Korea Astronomy and Space Science Institute Daejeon South Korea | Luhr H.,Helmholtz Center Potsdam | Kervalishvili G.,Nodia Institute of Geophysics | Rauberg J.,Helmholtz Center Potsdam | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

Previous studies suggested that electric and/or magnetic field fluctuations observed in the nighttime topside ionosphere at midlatitudes generally originate from quiet time nocturnal medium-scale traveling ionospheric disturbances (MSTIDs). However, decisive evidences for the connection between the two have been missing. In this study we make use of the multispacecraft observations of midlatitude magnetic fluctuations (MMFs) in the nighttime topside ionosphere by the Swarm constellation. The analysis results show that the area hosting MMFs is elongated in the NW-SE (NE-SW) direction in the Northern (Southern) Hemisphere. The elongation direction and the magnetic field polarization support that the area hosting MMFs is nearly field aligned. All these properties of MMFs suggest that they have close relationship with MSTIDs. Expectation values of root-mean-square field-aligned currents associated with MMFs are up to about 4 nA/m2. MMF coherency significantly drops for longitudinal distances of ≥1{ring operator}. ©2015. American Geophysical Union. Source

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