• Journal of Astronomy and Space Sciences
• /
• v.36 no.3
• /
• pp.133-147
• /
• 2019

Challenging Minisatellite Payload (CHAMP) satellite magnetic data are used to investigate the latitudinal variation of the storm-time meso-scale field-aligned currents by defining a new metric called the FAC range. Three major geomagnetic storm events are considered. Alongside SymH, the possible contributions from solar wind dynamic pressure and interplanetary magnetic field (IMF) $B_Z$ are also investigated. The results show that the new metric predicts the latitudinal variation of FACs better than previous studies. As expected, the equatorward expansion and poleward retreat are observed during the storm main phase and recovery phase respectively. The equatorward shift is prominent on the northern duskside, at ${\sim}58^{\circ}$ coinciding with the minimum SymH and dayside at ${\sim}59^{\circ}$ compared to dawnside and nightside respectively. The latitudinal shift of FAC range is better correlated to IMF $B_Z$ in northern hemisphere dusk-dawn magnetic local time (MLT) sectors than in southern hemisphere. The FAC range latitudinal shifts responds better to dynamic pressure in the duskside northern hemisphere and dawnside southern hemisphere than in southern hemisphere dusk sector and northern hemisphere dawn sector respectively. FAC range exhibits a good correlation with dynamic pressure in the dayside (nightside) southern (northern) hemispheres depicting possible electrodynamic similarity at day-night MLT sectors in the opposite hemispheres.

• Journal of Astronomy and Space Sciences
• /
• v.6 no.1
• /
• pp.1-15
• /
• 1989

Magnetospheic substorm in the magnetotail region is studied numerically by means of a three dimensional MHD code. The analytic solution for the quiet magnetotail is employed as an initial configuration. The localized solar wind is modeled to enter the simulation domain through the boundaries located in the magnetotail lobe region. As a result of the interaction between the solar wind and the magnetosphere, the magnetic field lines are stretched, and the plasma sheet becomes thinner and thinner. When the current driven resistivity is generated, magnetic reconnection is triggered by this resistivity. The resulting plasma jetting is found to be super-magnetosonic. Although the plasmoid formation and its tailward motion is not quite clear as in the two dimensional simulation, which is mainly because of the numerical model chosen for the present simulation, the rarification of the plasmas near the x-point is observed. Field aligned currents are observed in the late expansive stage of the magnetospheric substorm. These field aligned currents flow from the tail toward the ionosphere on the dawn side from the ionosphere to ward the tail on the dusk side, namely in the same sense of the region 1 current. As the field aligned currents develop, it is found that the cross tail current in the earth side midnight section of the magnetic x-point is reduced.

• The Bulletin of The Korean Astronomical Society
• /
• v.28 no.1
• /
• pp.54-54
• /
• 2003

• Bulletin of the Korean Space Science Society
• /
• 1993.10a
• /
• pp.8-8
• /
• 1993

Field-aligned(Birkeland) currents of the High-latitude polar region are to the linkage between the solar wind-magnetosphere system and the ionosphere. The characteristics of field-aligned currents at an attitude of 1300 km have been investigated from the KiSat-A satellite magnetometer data recorded at SatRec form March to May 1993. It is found that the po1arity of both east-west and south-north magnetic components becomes reversed and distorted across the poleward edge. We suggest that these changes May occur rule to the Region 1 and Region 2 currents. It is also suggested that the current time resolution which is about 30 seconds, should be improved to prove gradual polarity changes in the polar region. In addition, it is shown how the observational results depend on the longitude in the high-latitude region.

• Bulletin of the Korean Space Science Society
• /
• 2001.11a
• /
• pp.45-45
• /
• 2001

• Journal of Astronomy and Space Sciences
• /
• v.36 no.1
• /
• pp.1-9
• /
• 2019

In this paper we present analysis of current density when the Cluster spacecraft pass the nightside auroral region at about $4-5R_E$ from the center of Earth. The analysis is made when the inter-spacecraft separation is within 200 km, which allows all four spacecraft to be situated inside the same current sheet. On 22 February 2002, two field-aligned current (FAC) events were observed in both the southern and the northern hemispheres. The FACs were calculated with magnetic field data obtained by the four spacecraft using the Curlometer method. The scales of the FACs along the spacecraft trajectory and the magnitudes were hundreds of kilometers and tens of $nA/m^2$, respectively, and both events were mapped to the auroral region in the ionosphere. We also examined reliability of the results with some parameters, and found that our results are adequately comparable with other studies. Nevertheless, some limitations that decrease the accuracy of current estimation exist.

• Bulletin of the Korean Space Science Society
• /
• 2003.10a
• /
• pp.40-40
• /
• 2003

When the magnetotail is disturbed by an impulsive input such as the substorm onset, compressional magnetohydrodynamic (MHD) waves play an important role in delivering perturbed energy and exciting various wave modes and currents. The plasmasheet, in which relatively hot plasmas exist, is surrounded by relatively cold plasmas at the plasma sheet boundary layer (PSBL) and the equatorial plasmasphere. Since the Alfven speed significantly varies near these regions, the compressional waves are expected to undergo mode conversion by inhomogeneity at the boundary between cold and hot plasma regions. We investigate how the initial compressional MHD wave energy is reflected, transmitted, and absorbed across that boundary by adopting the invariant imbedding method (IIM) which gives the exact reflection, transmission, and absorption coefficients without any theoretical approximations for given frequencies and wave numbers. The IIM method is very useful in quantifying the reflection and transmission of compressional waves in the sense that we can calculate how much fast mode wave energy is delievered into shear Alfven waves or field-aligned currents. Our results show that strongly localized absorption occurs at the boundary region. This feature suggests that localized field-aligned currents can be impulsively excited at such boundary regions by any compressional disturbances, which is highly associated with impulsive auroral brightening at the substorm onset. We compare our results with previous studies in cold inhomogeneous plasmas.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2005.07b
• /
• pp.1096-1099
• /
• 2005

Multi-walled carbon nanotubes (CNTs) grown on catalyst dots by thermal chemical vapor deposition were vertically aligned with a high population density. Such densely populated CNTs showed poor field emission characteristics due to the electrical screening effect. We reduced the number density of CNTs using an adhesive tape treatment. For dotpatterned CNTs, the tape treatment decreased the CNT density by three orders of magnitude, drastically improved the turn-on electric field from 4.8 to $1.8V/{\mu}m$, and changed the emission image from spotty to uniform luminescence. We also report long-term emission stability of dot-patterned CNTs by measuring the emission currents with time at different duty ratios.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2000.01a
• /
• pp.49-50
• /
• 2000

5.2" microtip field emission displays (FEDs) with high voltage applications are fabricated. Nano-structural analysis on microtips is performed for the reliable operation of FEDs. Chemical compositions on the apex of microtips are fully analyzed. A charging mechanism on spacers is simulated and experimentally confirmed with micro-images. A gas-aging mechanism is also studied with integration step of FEDs. The brightness of more than 300 $cd/m^2$ is achieved. In addition, as a new concept, 9" color carbon nanotube FEDs (CNT-FEDs) are introduced using well-aligned carbon nanotubes on glass substrates by paste squeeze and surface treatment techniques. A number of carbon nanotubes, $5-10/{\mu}m2$, are uniformly distributed over a large area. The turn-on fields of 1 $V/{\mu}m$ and field emission currents of 1.5 mA at 3 $V/{\mu}m$ are acquired. Different mechanisms between microtip FEDs and CNT-FEDs are discussed.

• Proceedings of the KIEE Conference
• /
• 1994.07b
• /
• pp.1609-1611
• /
• 1994

In ECR and helicon reactors for plasma processing, a high density plasma is generated in a source region which is connected to a diffusion region where the processing takes place. Large density and potential gradients can develop at the orifice of the source which drive ion currents into the diffusion region. The average ion velocity may become the order of the sound velocity. Measurements of the ion saturation current to a Langmuir probe are used as a standard method of determining the plasma density in laboratory discharges. However, the analysis becomes difficult in a steaming plasma. We have used the HAMLET plasma simulator to simulate the ion flow to a large langmuir probe in an ECR plasma. The collection surface was aligned with the Held upstream, normal to the field, and downstream. ion trajectories through the electric and magnetic fields were calculated including ion-neutral collisions. We examines the ratio of ion current density to plasma density as a function of magnetic field and pressure.