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Choi J.-M.,Chungnam National University | Kil H.,Johns Hopkins University | Kwak Y.-S.,Korean University of Science and Technology | Park J.,Korean University of Science and Technology | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2017

The quasi-periodic occurrence of equatorial plasma bubbles is understood in terms of seeding mechanisms in the bottomside F region. However, no quantitative investigation has been conducted to identify how often quasi-periodic bubbles occur. This study investigates the wave property in the bubble occurrence (or spacing between bubbles) using the measurements of the plasma density in 2008-2012 by the Planar Langmuir Probe on board the Communication/Navigation Outage Forecasting System (C/NOFS) satellite. The wave property is investigated using the Lomb-Scargle periodograms derived from 664 segments of series of bubbles. In the majority of segments, the spacing between bubbles is represented by the combination of several wave components. Periodic bubbles whose property is represented by a few pronounced wave components are rare events. These results indicate that the spacing between bubbles is generally irregular. The manner of bubble occurrence does not show any notable variation with longitude and season. Because a consistent wave property does not exist in the occurrence of bubbles and the appearance of bubbles in the topside is affected by many factors, the manner of bubble occurrence in satellite observations does not provide a precise diagnostic of seeding mechanisms. © 2017. American Geophysical Union. All Rights Reserved.


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.


Lee Y.-S.,Korea Astronomy and Space Science Institute Daejeon South Korea | Kirkwood S.,Swedish Institute of Space Physics | Kwak Y.-S.,Korean University of Science and Technology | Shepherd G.G.,York University | And 3 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2015

We report interannual variations of the correlation between the reflectivity of polar mesospheric summer echoes (PMSEs) and solar wind parameters (speed and dynamic pressure), and AE index as a proxy of geomagnetic disturbances, and cosmic noise absorption (CNA) in the declining phase (2001-2008) of solar cycle 23. PMSEs are observed by 52MHz VHF radar measurements at Esrange (67.8°N, 20.4°E), Sweden. In approaching the solar minimum years, high-speed solar wind streams emanate from frequently emerging coronal holes, leading to 7, 9, and 13.5day periodicities in their arrival at Earth. Periodicities of 7 and/or 9days are found in PMSE reflectivity in 2005-2006 and 2008. Periodicity-resolved correlations at 7 and 9days of both D region ionization observed by cosmic noise absorption (CNA) and PMSE with solar wind speed and AE index vary from year to year but generally increase as solar minimum is approached. PMSEs have a higher periodicity-resolved correlation with AE index than the solar wind speed. In addition, cross correlation of PMSE reflectivity with AE index is mostly higher than with CNA in solar minimum years (2005-2008). This can signify that high-speed solar wind stream-induced high-energy particles possibly have strong influence on CNA, but not as much as on PMSE, especially for the years of significant periodicities occurring. © 2015. American Geophysical Union. All Rights Reserved.


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.


Lee H.-B.,Chungnam National University | Kim Y.H.,Chungnam National University | Kim E.,Chungnam National University | Hong J.,Chungnam National University | Kwak Y.-S.,Korea Astronomy and Space Science Institute Daejeon South Korea
Journal of Geophysical Research A: Space Physics | Year: 2016

Topside ionospheric profiles have been measured by Alouette 1 and ISIS 1/2 in the periods of 1962-1972 and 1972-1979, respectively. The profiles cover from the orbital altitude of 1000km to the F2 peak and show large variations over local time, latitude, and seasons. We here analyze these variations in comparison with plasmaspheric total electron contents (pTECs) that were measured by Jason-1 satellite from the altitude of 1336km to 20,200km (GPS orbit). The scale heights of the profiles are generally smaller in the daytime than nighttime but show large day-to-day variations, implying that the ionospheric profiles at 1000km are changing dynamically, rather than being in diffusive equilibrium. We also derived transition heights between O+ and H+, which show a clear minimum at dawn for low-latitude profiles due to decreasing O+ density at night. To compare with pTEC, we compute topside ionospheric total electron content (tiTEC) by integrating over 800-1336km using the slope of the profiles. The tiTEC varies in a clear diurnal pattern from ~0.3 to ~1 and ~3total electron content unit (TECU, 1TECU=1016elm-2) for low and high solar activity, respectively, whereas Jason-1 pTEC values are distributed over 2-6TECU and 4-8TECU for low and high solar activity, respectively, with no apparent diurnal modulation. Latitudinal variations of tiTEC show distinctive hemispheric asymmetry while that of Jason-1 pTEC is closely symmetric about the magnetic equator. The local time and latitudinal variations of tiTEC basically resemble those of the ionosphere but are characteristically different from those of Jason-1 pTEC. Based on the difference between tiTEC and pTEC variations, we propose that the region above ~1300km should be considered as the plasmasphere. Lower altitudes for the base of "plasmaspheric TEC," as used in some studies, would cause contamination of ionospheric influence. ©2016. American Geophysical Union.


Ryu K.,Korea Advanced Institute of Science and Technology | Kwak Y.,Korea Astronomy and Space Science Institute Daejeon South Korea | Kim Y.H.,Chungnam National University | Park J.,Korea Astronomy and Space Science Institute Daejeon South Korea | And 2 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2016

Using the ionospheric measurements of CHAMP, DEMETER, and DMSP F15, the seasonal and spatial variations of the topside ionosphere during the last solar minimum period were investigated and compared with ionospheric models. In all the satellite measurements, equatorial ionization anomaly (EIA) shows clearly longitudinal asymmetry with wave number -3 or -4 patterns. Anomalous increases of Ne in the nighttime surpassing daytime Ne, known as the Weddell Sea anomaly (WSA) or midlatitude summer nighttime anomaly (MSNA), were also observed in the global Ne distribution with differences in detailed geometry of the geomagnetic field according to the altitude. In the nighttime ionosphere, the reduced Te in the equatorial region at the DMSP altitude, identified as the equatorial plasma temperature anomaly (EPTA), was ascribed to the leftover of the prereversal enhancement of the upward plasma drift. Though the EIA, WSA, MSNA, and EPTA are all associated with the upward plasma movement, the difference in the thermal evolution is ascribable to the geometry of drift in which the plasma moves across the geomagnetic field line for the EIA and the EPTA, while along the field line for the WSA and the MSNA. ©2016. American Geophysical Union.


Cho J.-H.,Chungbuk National University | Lee D.-Y.,Chungbuk National University | Noh S.-J.,Chungbuk National University | Shin D.-K.,Chungbuk National University | And 6 more authors.
Journal of Geophysical Research A: Space Physics | Year: 2016

Magnetospheric compression due to impact of enhanced solar wind dynamic pressure Pdyn has long been considered as one of the generation mechanisms of electromagnetic ion cyclotron (EMIC) waves. With the Van Allen Probe-A observations, we identify three EMIC wave events that are triggered by Pdyn enhancements under prolonged northward interplanetary magnetic field (IMF) quiet time preconditions. They are in contrast to one another in a few aspects. Event 1 occurs in the middle of continuously increasing Pdyn while Van Allen Probe-A is located outside the plasmapause at postmidnight and near the equator (magnetic latitude (MLAT)~-3°). Event 2 occurs by a sharp Pdyn pulse impact while Van Allen Probe-A is located inside the plasmapause in the dawn sector and rather away from the equator (MLAT~12°). Event 3 is characterized by amplification of a preexisting EMIC wave by a sharp Pdyn pulse impact while Van Allen Probe-A is located outside the plasmapause at noon and rather away from the equator (MLAT~-15°). These three events represent various situations where EMIC waves can be triggered by Pdyn increases. Several common features are also found among the three events. (i) The strongest wave is found just above the He+ gyrofrequency. (ii) The waves are nearly linearly polarized with a rather oblique propagation direction (~28° to ~39° on average). (iii) The proton fluxes increase in immediate response to the Pdyn impact, most significantly in tens of keV energy, corresponding to the proton resonant energy. (iv) The temperature anisotropy with T⊥>T|| is seen in the resonant energy for all the events, although its increase by the Pdyn impact is not necessarily always significant. The last two points (iii) and (iv) may imply that in addition to the temperature anisotropy, the increase of the resonant protons must have played a critical role in triggering the EMIC waves by the enhanced Pdyn impact. © 2016. American Geophysical Union. All Rights Reserved.


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.


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.


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.

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