ORCID Profile
0000-0001-6179-4666
Current Organisations
Princeton Plasma Physics Laboratory
,
Andrews University
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Publisher: AIP Publishing
Date: 03-2013
DOI: 10.1063/1.4793726
Abstract: Linear mode conversion (LMC) is the linear transfer of energy from one wave mode to another in an inhomogeneous plasma. It is relevant to laboratory plasmas and multiple solar system radio emissions, such as continuum radiation from planetary magnetospheres and type II and III radio bursts from the solar corona and solar wind. This paper simulates LMC of waves defined by warm, magnetized fluid theory, specifically the conversion of Langmuir/z-mode waves to electromagnetic (EM) radiation. The primary focus is the calculation of the energy and power conversion efficiencies for LMC as functions of the angle of incidence θ of the Langmuir/z-mode wave, temperature β=Te/mec2, adiabatic index γ, and orientation angle ϕ between the ambient density gradient ∇N0 and ambient magnetic field B0 in a warm, unmagnetized plasma. The ratio of these efficiencies is found to agree well as a function of θ, γ, and β with an analytical relation that depends on the group speeds of the Langmuir/z and EM wave modes. The results demonstrate that the energy conversion efficiency ϵ is strongly dependent on γβ, ϕ and θ, with ϵ∝(γβ)1/2 and θ∝(γβ)1/2. The power conversion efficiency ϵp, on the other hand, is independent of γβ but does vary significantly with θ and ϕ. The efficiencies are shown to be maximum for approximately perpendicular density gradients (ϕ≈90°) and minimal for parallel orientation (ϕ=0°) and both the energy and power conversion efficiencies peak at the same θ.
Publisher: Wiley
Date: 07-10-2022
Publisher: American Geophysical Union (AGU)
Date: 24-02-2023
DOI: 10.1029/2022GL102467
Abstract: Juno satellite observations have illustrated substantial ex les of broadband electron energization up to 10 5 –10 6 eV levels. In order to explain these observations, we use a hybrid gyrofluid kinetic‐electron model in an untilted dipolar topology to illustrate energization to high levels in weak current conditions by inertial Alfvén waves close to the Jupiter ionosphere for ambient plasma densities and magnetic field perturbations inferred from Juno satellite observations. The key to the high energization is the extremely low densities evident in the observations which necessitates the acceleration of electrons to very high velocities in order to carry the field‐aligned current.
Publisher: American Physical Society (APS)
Date: 22-08-2014
Publisher: American Geophysical Union (AGU)
Date: 05-2014
DOI: 10.1002/2013JA019364
Publisher: American Geophysical Union (AGU)
Date: 09-2023
DOI: 10.1029/2023JA031596
Publisher: American Geophysical Union (AGU)
Date: 2013
DOI: 10.1029/2012JA018083
Publisher: Authorea, Inc.
Date: 04-04-2023
DOI: 10.22541/ESSOAR.168057588.83872371/V1
Abstract: The nonthermal continuum radiation (NTC) beaming angle is computed over the entire Van Allen Probes A mission when the spacecraft was in the dawn sector. The conditions in the dawn sector are favorable for the wave vector to lie near/in the spacecraft’s spin plan allowing a favorable estimate of the beaming angle, and the dawn sector is also advantageous in that previous studies show NTC occurrence to peak in this sector. We found that scatter plots, over the entire mission, of beaming angle versus magnetic latitude form a distinct inverted V pattern, with the apex at/near the magnetic equator. This pattern was sharpest for frequencies (f) ≲ 100 kHz. Using the NTC beaming formula from LMCT, we show that such an inverted V pattern is expected due to the large variation in the plasmapause location over the entire mission. The theoretical derived pattern qualitatively reproduces the observed pattern but not quantitatively. The lack of quantitative agreement is discussed and is attributed to several factors, one factor is off centered emissions from the radio window. The qualitative agreement strongly supports LMCT as being the dominant mechanism generating NTC for f ≲ 100 kHz. For f ≳ 100 kHz the inverted V pattern becomes less distinct, and strong near equatorial beaming is observed. After considering contamination of our selections by left-handed polarized AKR, our study suggests that besides LMCT another unidentified NTC generation mechanism becomes important for f ≳ 100 kHz.
Publisher: American Geophysical Union (AGU)
Date: 06-01-2016
DOI: 10.1002/2015GL066978
Publisher: American Geophysical Union (AGU)
Date: 08-2011
DOI: 10.1029/2011GL048621
Publisher: Springer Berlin Heidelberg
Date: 2006
Publisher: American Geophysical Union (AGU)
Date: 04-2019
DOI: 10.1029/2019JA026532
Publisher: American Geophysical Union (AGU)
Date: 14-07-2015
DOI: 10.1002/2015GL064531
Publisher: AIP Publishing
Date: 28-04-2005
DOI: 10.1063/1.1896285
Abstract: Linear mode conversion of ordinary and extraordinary waves into upper hybrid waves has been investigated by adopting a time-dependent numerical model. In order to solve the wave equations as an initial-valued problem, the finite difference method is used in both time and space. It is examined how wave coupling occurs in a cold magnetized plasma, where inhomogeneity lies perpendicular to the ambient magnetic field, by analyzing time histories of both electric and magnetic field components. The results show that electromagnetic energy of ordinary and extraordinary waves is transferred into electrostatic energy when the resonant condition at upper hybrid resonances is satisfied.
Publisher: Frontiers Media SA
Date: 14-01-2022
DOI: 10.3389/FSPAS.2021.785413
Abstract: The Kelvin–Helmholtz (KH) instability of magnetohydrodynamic surface waves at the low latitude boundary layer is examined using both an eigenfrequency analysis and a time-dependent wave simulation. The analysis includes the effects of sheared flow and Alfvén velocity gradient. When the magnetosheath flows are perpendicular to the ambient magnetic field direction, unstable KH waves that propagate obliquely to the sheared flow direction occur at the sheared flow surface when the Alfvén Mach number is higher than an instability threshold. Including a shear transition layer between the magnetosphere and magnetosheath leads to secondary KH waves (driven by the sheared flow) that are coupled to the resonant surface Alfvén wave. There are remarkable differences between the primary and the secondary KH waves, including wave frequency, the growth rate, and the ratio between the transverse and compressional components. The secondary KH wave energy is concentrated near the shear Alfvén wave frequency at the magnetosheath with a lower frequency than the primary KH waves. Although the growth rate of the secondary KH waves is lower than the primary KH waves, the threshold condition is lower, so it is expected that these types of waves will dominate at a lower Mach number. Because the transverse component of the secondary KH waves is stronger than that of the primary KH waves, more efficient wave energy transfer from the boundary layer to the inner magnetosphere is also predicted.
Publisher: American Geophysical Union (AGU)
Date: 08-2019
DOI: 10.1029/2019JA026849
Abstract: A hybrid gyrofluid‐kinetic electron model is adapted and used to simulate poloidal standing modes for different electron temperatures and azimuthal mode numbers. As in previous studies of toroidal standing modes, mirror force effects lead to increased parallel potential drops, monoenergetic electron energization, and wave energy dissipation as the ambient electron temperature is increased. A similar trend is also observed when the electron temperature is held fixed and the azimuthal mode number increased—owing to the narrowing of the azimuthal flux tube width, which necessitates more electron energization to carry the increased parallel current density. In both cases, the increase in electron energization eventually leads to more rapid decreases in the parallel current with time because of the dissipation of wave energy.
Publisher: American Geophysical Union (AGU)
Date: 14-03-2023
DOI: 10.1029/2022GL101544
Abstract: We examine coupling of fluctuations in the solar wind with electromagnetic ion cyclotron (EMIC) waves in the magnetosphere using an advanced full‐wave simulation code, Petra‐M. Dipole tilt dramatically affects the coupling process. While very little wave power can reach the inner magnetosphere without tilt effects, a tilted dipole field dramatically increases the efficiency of the coupling process. Solar wind fluctuations incident at high magnetic latitude effectively reaches the ground along the field line and mode‐convert to linearly polarized field‐aligned propagating waves at the Alfvén and IIH resonances. Therefore, solar wind compressions efficiently drive linearly polarized EMIC waves when the dipole angle is tilted toward or away from the Sun‐Earth direction.
Publisher: AIP Publishing
Date: 2020
DOI: 10.1063/5.0013580
Publisher: American Geophysical Union (AGU)
Date: 07-2022
DOI: 10.1029/2022JA030262
Abstract: In the present study, we explore the observational characteristics of Electromagnetic Ion Cyclotron (EMIC) wave propagation from the source region to the ground. We use magnetometers aboard Geostationary Operational Environment Satellite (GOES) 13, the geosynchronous orbit satellite at 75°W, and at Sanikiluaq ground station (SNK, 79.14°W and 56.32°N in geographic coordinates, and L ∼ 6.0 in a dipole magnetic field) which is located in northern Canada. Using these magnetically conjugate observatories, simultaneous EMIC wave observations are carried out. We found a total of 295 coincident and 248 non‐coincident EMIC wave events between GOES 13 and the SNK station. Our statistical analysis reveals that the coincident events are predominantly observed on the dayside. The wave normal angles are slightly higher for the non‐coincident events than for coincident events. However, the coincidence of the waves is mostly governed by the intensity and duration of the wave. This is confirmed by the geomagnetic environment which shows higher auroral electrojet (AE) and Kp indices for the coincident events. We also found that some events show high‐frequency ( f 0.4 Hz) wave filtering. The statistics of the high‐frequency filtered and non‐filtered wave events show that there are clear magnetic local time (MLT) and F10.7 index differences between the two groups, as well as in ionospheric electron density measurements. In addition, we also found differences in the wave properties which possibly indicate that the propagation in the magnetosphere also plays an important role in the wave filtering.
Publisher: American Geophysical Union (AGU)
Date: 02-2016
DOI: 10.1002/2015JA021851
Publisher: American Geophysical Union (AGU)
Date: 10-2012
DOI: 10.1029/2012JA017982
Publisher: American Geophysical Union (AGU)
Date: 12-2003
DOI: 10.1029/2003GL017918
Publisher: AIP Publishing
Date: 2023
DOI: 10.1063/5.0164070
Publisher: American Physical Society (APS)
Date: 06-07-2007
Publisher: AIP Publishing
Date: 10-2008
DOI: 10.1063/1.2994719
Abstract: Linear mode conversion of Langmuir waves to radiation near the plasma frequency at density gradients is potentially relevant to multiple solar radio emissions, ionospheric radar experiments, laboratory plasma devices, and pulsars. Here we study mode conversion in warm magnetized plasmas using a numerical electron fluid simulation code with the density gradient parallel to the ambient magnetic field B0 for a range of incident Langmuir wavevectors. Our results include: (1) both o- and x-mode waves are produced for Ω=(ωL∕c)1∕3(ωc∕ω)≲1, contrary to previous ideas. Only the o mode is produced for Ω≳1.5. Here ωc is the (angular) electron cyclotron frequency, ω is the angular wave frequency, L is the length scale of the (linear) density gradient, and c is the speed of light. A WKB-style analysis accounts semiquantitatively for the production and relative conversion efficiencies of the o and x modes in the simulations. (2) In the unmagnetized limit, equal amounts of o- and x-mode radiation are produced. (3) The mode conversion window narrows as Ω increases. (4) As Ω increases the total electromagnetic field changes from linear to circular polarization, with the o- and x-mode signals remaining circularly polarized. (5) The conversion efficiency to the x mode decreases monotonically as Ω increases while the o-mode conversion efficiency oscillates due to an interference phenomenon between incoming and reflected Langmuir/z modes. (6) The maximum total conversion efficiencies for wave power from the Langmuir/z mode to radiation are of order 50%–70%. They depend strongly on the wave frequency when close to the background plasma frequency but weakly on the electron temperature T0 and β=T0∕mc2. The corresponding energy conversion efficiencies are favored since they allow separation into o and x modes, use directly measured experimental quantities, and generalize easily for wave packets. The total energy conversion efficiency differs from the power conversion efficiency by the ratio of the group speeds for each mode, is less than 10% for the value of β=0.01 simulated, and decreases linearly with β. Since β≈10−5–10−4 in the solar wind and corona, this β dependence is important in applications. (7) The interference effect and the disappearance of the x mode at Ω≳1 can be accounted for semiquantitatively using a WKB-type analysis. (8) Constraints on density turbulence are developed for the x mode to be generated and be able to propagate from the source. (9) Standard parameters for the corona and the solar wind near 1 AU suggest that linear mode conversion should produce both o- and x-mode radiation for solar and interplanetary radio bursts. It is therefore possible that linear mode conversion under these conditions might explain the weak total circular polarizations of type II and III solar radio bursts.
Publisher: AIP Publishing
Date: 2020
DOI: 10.1063/5.0013978
Publisher: American Geophysical Union (AGU)
Date: 09-2023
DOI: 10.1029/2023JA031426
Publisher: EDP Sciences
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 05-2013
Publisher: AIP Publishing
Date: 06-2019
DOI: 10.1063/1.5091579
Abstract: We perform numerical simulations of high harmonic fast waves (HHFWs) in the scrape-off-layer (SOL) of National Spherical Torus Experiment (NSTX)/NSTX-U using a recently developed 2D full wave code. We particularly show that a realistic NSTX SOL boundary can significantly affect HHFW propagation and power losses in the SOL. In NSTX SOL boundaries, HHFW is easily localized near the antenna and propagates less to the SOL, and thus, less power is lost to the SOL. We also show that the lower SOL power losses occur when the SOL volume is smaller and the distance between the last closed flux surface and the antenna is shorter. We investigate the effect of electron density in front of the antenna and the ambient magnetic field strengths on the SOL power losses as well. Showing consistency with the experiments, SOL losses are minimized when the SOL density is near the critical density where the fast wave cutoff is open, and the plasma is strongly magnetized.
Publisher: American Geophysical Union (AGU)
Date: 11-2008
DOI: 10.1029/2008JA013310
Publisher: AIP Publishing
Date: 12-2013
DOI: 10.1063/1.4837515
Publisher: American Geophysical Union (AGU)
Date: 03-2021
DOI: 10.1029/2019JA027698
Abstract: Understanding the physical mechanisms responsible for the cross‐scale energy transport and plasma heating from solar wind into the Earth's magnetosphere is of fundamental importance for magnetospheric physics and for understanding these processes in other places in the universe with comparable plasma parameter ranges. This paper presents observations from the Magnetosphere Multiscale (MMS) mission at the dawn‐side high‐latitude dayside boundary layer on February 25, 2016 between 18:55 and 20:05 UT. During this interval, MMS encountered both the inner and outer boundary layers with quasiperiodic low frequency fluctuations in all plasma and field parameters. The frequency analysis and growth rate calculations are consistent with the Kelvin‐Helmholtz instability (KHI). The intervals within the low frequency wave structures contained several counter‐streaming, low‐ (0–200 eV) and mid‐energy (200 eV–2 keV) electrons in the loss cone and trapped energetic (70–600 keV) electrons in alternate intervals. The counter‐streaming electron intervals were associated with large‐magnitude field‐aligned Poynting fluxes. Burst mode data at the large Alfvén velocity gradient revealed a strong correlation between counter streaming electrons, enhanced parallel electron temperatures, strong anti‐field aligned wave Poynting fluxes, and wave activity from sub‐proton cyclotron frequencies extending to electron cyclotron frequency. Waves were identified as Kinetic Alfvén waves but their contribution to parallel electron heating was not sufficient to explain the eV electrons.
Publisher: American Geophysical Union (AGU)
Date: 08-2015
DOI: 10.1002/2015JA021092
Publisher: Wiley
Date: 28-06-2020
Publisher: American Geophysical Union (AGU)
Date: 27-08-2018
DOI: 10.1029/2018GL079278
Publisher: American Geophysical Union (AGU)
Date: 06-2015
DOI: 10.1002/2014JA020910
Location: United States of America
No related grants have been discovered for Eun-Hwa Kim.