• Bulletin of the Korean Space Science Society
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• 2010.04a
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• pp.39.1-39.1
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• 2010

We have investigated interplanetary (IP) structures of 82 intense geomagnetic storms (Dst $\leq$ -100 nT) that occurred from 1998 to 2006. According to their interplanetary origins, we classified them as four groups: 20 sMC events (IP shock and MC), 19 SH events (sheath field), 12 SH+MC events (Sheath field and MC), and 8 nonMC events (non-MC type ICME). For each group, we examined the relationships between Dst index and solar/IP parameters, namely, direction parameter (DP), CME speed ($V_{CME}$), solar wind speed ($V_{SW}$), minimum of IMF $B_z$ component($Bz_{min}$), and maximum of $E_y$ component ($Ey_{max}$).We found that the relationships strongly depend on their IP source. Our main results can be summarized as follows: 1) The correlation between Dst and DP is the best for the SH+MC events (r = -0.61). 2) The relationship between Dst and $V_{CME}$ gives the best correlation for the sMC events (r = -0.56). 3) There is the best correlation between Dst and $V_{SW}$ for the sMC events (r = -0.61), while there is a very weak correlation (r=-0.17) for the SH events. 4) The relationship between Dst and $Bz_{min}$ gives the best correlation (r = -0.87) for the SH+MC events. 5) The correlation between Dst and $Ey_{max}$ is the best for the SH+MC events (r = -0.87). Summing up, the sMC and SH+MC events give us good correlations, but the SH events, weak correlations. From this study, we suggest that this tendency should be caused by the characteristics of IMF southward components, e.g., smooth field rotations for the MC events and highly IMF fluctuations for the SH events.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.1
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• pp.82-90
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• 2014

In this paper, the effect of Lorentz force on the stability of attitude orientation of a charged spacecraft moving in an elliptic orbit in the geomagnetic field is considered. Euler equations are used to derive the equations of attitude motion of a charged spacecraft. The equilibrium positions and its stability are investigated separately in the pitch, roll and yaw directions. In each direction, we use the Lorentz force to identify an attitude stabilization parameter. The analytical methods confirm that we can use the Lorentz force as a stabilization method. The charge-to-mass ratio is the main key of control, in addition to the components of the radius vector of the charged center of the spacecraft, relative to the center of mass of the spacecraft. The numerical results determine stable and unstable equilibrium positions. Therefore, in order to generate optimum charge, which may stabilize the attitude motion of a spacecraft, the amount of charge on the surface of spacecraft will need to be monitored for passive control.

• International Journal of Aeronautical and Space Sciences
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• v.8 no.2
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• pp.17-27
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• 2007

Minimum-time attitude maneuvers of three-axis stabilized spacecraft are presented to study the feasibility of using three magnetic torquers perform large angle maneuvers. Previous applications of magnetic torquers have been limited to spin-stabilized satellites or supplemental actuators of three axis stabilized satellites because of the capability of magnetic torquers to produce torques about a specific axes. The minimum-time attitude maneuver problem is solved by applying a parameter optimization method for orbital cases to verify that the magnetic torque system can perform as required. Direct collocation and a nonlinear programming method with a constraining method by Simpson's rule are used to convert the minimum-time maneuver problems into parameter optimization problems. An appropriate number of nodes is presented to find a bang-bang type solution to the minimum-time problem. Some modifications in the boundary conditions of final attitude are made to solve the problem more robustly and efficiently. The numerical studies illustrate that the presented method can provide a capable and robust attitude reorientation by using only magnetic torquers. However, the required maneuver times are relatively longer than when thrusters or wheels are used. Performance of the system in the presence of errors in the magnetometer as well as the geomagnetic field model still good.

• Journal of Astronomy and Space Sciences
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• v.19 no.2
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• pp.133-140
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• 2002

Space Physics Sensor onboard the KOMPSAT-1, which was launched at 1999, had transmitted ionospheric data during the solar maximum from June 2000 to August 2001. When the KOMPSAT-1 has passed the equatorial region, equatorial bubbles, in which the electron density abruptly decreases, had frequently been detected. Statistical analysis of the data obtained during the entire operational period shows equatorial bubbles frequently occur across the Atlantic region where the geomagnetic field strength is weak. Also, equatorial bubbles occur more frequently for lower Kp index. The results are in good agreement with the previous observations by DMSP satellites and radio experiments at the Peruvian sector The correlation between electron density and the electron temperature shows various behaviors from event to event.

• Journal of Astronomy and Space Sciences
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• v.20 no.1
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• pp.53-62
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• 2003

SPS(Space Physics Sensor) onboard the KOMPSAT-I, which was launched at 1999, had transmitted ionospheric plasma density and electron temperature during the solar maximum from June 2000 to August 2001, SPS IMS onboard KOMPSAT-I occasionally detected abrupt plasma density enhancement in low-latitude region, in which the plasma density abruptly increases in a narrow region. Statistical analysis of the data obtained during the entire operational period shows that the occurrence probability of these events has its peak value at the Atlantic region and at the Hawaiian region where the geomagnetic field strength is weak. And the occurrence frequency has no correlation with Dst index or F10.7 index. The correlation between plasma density and the electron temperature shows a wide variety, but the anti-correlated cases are dominant.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.74.2-74.2
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• 2014

We have presented a classic two-ribbon filament eruption occurred in the east side of NOAA active region 11850 at 21:00 UT on 29 September 2013. Interestingly, this filament eruption was not accompanied by any flares and just there was a slight brightening in X-rays, C1.2, associated with the eruption. An accompanying huge CME was appeared at 22:12 UT in the LASCO C2 field of view and it propagates into the interplanetary space with a speed of about 440 km/s. And the related solar proton event (S2) started at 05:05 UT and peaked at 20:05 UT on 30 September 2013. The CME arrival was recorded by the ACE spacecraft around 01:30 UT on 2 October 2013. Around the CME arrival time, the solar-wind speed reached at about 640 km/s and IMF Bz showed southward component (-27 nT). Finally, the filament eruption and the CME cause geomagnetic storm (G2) at 03:00 UT on 2 October 2013. We described the detailed evolution of the filament eruption and its related phenomena such as CME, proton event, geomegnetic storm and so on. In addition, we will discuss about the activation mechanism of the filament eruption without flares.

• Journal of the Korea Institute of Military Science and Technology
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• v.18 no.4
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• pp.350-357
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• 2015

Many countries have been developing and operating an underwater surveillance system in order to protect their oceanic environment from infiltrating hostile marine forces which intend to lay mines, conduct reconnaissance and destroy friendly ships anchored at the harbor. One of the most efficient methods to detect unidentified submarine approaching harbor is sensing variation of magnetism of target by magnetic sensors. This measurement system has an advantage of high possibility of detection and low probability of false alarm, compared to acoustic sensors, although it has relatively decreased detection range. The contents of this paper mainly cover the analysis of possible effectiveness of magnetic sensors. First of all, environmental characteristics of surveillance area and magnetic information of simulated targets has been analyzed. Subsequently, a signal processing method of separating target from geomagnetic field and methods of estimating target location has been proposed.

• Economic and Environmental Geology
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• v.17 no.3
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• pp.215-230
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• 1984

Petrological, paleomagnetic, geomorphological and structural studies on the southern part of, so called, Chugaryeong rift valley, have been carried out in order to clarify the nature of the rift valley. Three stages of volcanic activities characterized by Jijangbong acidic volcanic rocks and tholeiitic and andesitic basalt of Cretaceous age(?), and Jongok Quaternary olivine basalt occurred along the Dongducheon fault line. Jijangbong acidic volcanic rocks distributed in the central part of the studied area consist of rhyodacite, acidic tuff and tuff breccia, which are bounded by Dongsong fault on the east and Daegwangri fault on the west. The Jongok basalt differs from those of Ulrung and Jeju islands in mineralogy, chemical composition and differentiation. Jongok basalt distributed along the Hantan river dilineates the vesicles curved toward downstream direction and increment of numbers and thickness of lava flow toward upstream direction. These facts suggest that lava flowed from upstream side of the river. Rectangular drainage patterns also support the presence of the Dongducheon, Pocheon, Wangsukcheon and Kyonggang faults which were previously known. LANDSAT image, however, does not show any lineaments which could be counted as a graben or rift valley. Displacement of Precambrian quartzite and Jurassic Daedong supergroup along the southwestern extension of the Dongducheon fault shows the right lateral movement. The Paleomagnetic study of the tholeiitic and andesitic basalts from Baegeuri, Jangtanri and Tonghyeonri located at 2. 3km east, 0km east, and 1.5km west of Dongducheon fault respectively shows that their VGP(Virtual Geomagnetic Pole) being to intermediate geomagnetic field of short duration which suggests that they formed in almost same period. Mean VGP of Jongok basalt is located 82.4N and 80.6E. This is in good coincidence with worldwide VGP of Plio-Pleistocene indicating that Jongok basalt was extruded during Plio-Pleistocene epoch, and suggesting that the studied area has been tectonically stable since then. From the present study, the tectonic episode of the region is concluded as following three stages. 1. The 1st period is worked by the Daebo orogeny of Jurassic during which granodiorite was intruded in Precambrian basement. 2. The 2nd period is the time when right lateral strike-slip fault of NNE-SSW direction was formed probably during late Cretaceous to Paleogene and the Jijangbong acidic volcanic rocks and the older basalts were extruded. 3. The 3rd period is the time when the fault was rejuvenated during Pliocene or Pleistocene accompanied by the eruption of Jongok basalt. As a conclusion, geologic structure of the studied area is rather fault line valley than graben or rift valley, which is formed by differential erosion along the Dongducheon fault suggesting a continuation of the Sikhote-Alin fault. The volcanic rocks including the Jijangbong acidic rocks, tholeiitic-andesitic basalt and olivine basalt are associated with this fault line.

• Bulletin of the Korean Space Science Society
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• 2008.10a
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• pp.33.3-34
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• 2008

As an activity of building Korean Space Weather Prediction Center (KSWPC), we has studied of radiation effect on the spacecraft components. High energy charged particles trapped by geomagnetic field in the region named Van Allen Belt can move to low altitude along magnetic field and threaten even low altitude spacecraft. Space Radiation can cause equipment failures and on occasions can even destroy operations of satellites in orbit. Sun sensors aboard Science and Technology Satellite (STSAT-1) was designed to detect sun light with silicon solar cells which performance was degraded during satellite operation. In this study, we try to identify which particle contribute to the solar cell degradation with ground based radiation facilities. We measured the short circuit current after bombarding electrons and protons on the solar cells same as STSAT-1 sun sensors. Also we estimated particle flux on the STSAT-1 orbit with analyzing NOAA POES particle data. Our result clearly shows STSAT-1 solar cell degradation was caused by energetic protons which energy is about 700 keV to 1.5 MeV. Our result can be applied to estimate solar cell conditions of other satellites.

• Economic and Environmental Geology
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• v.26 no.4
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• pp.519-539
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• 1993

A total of 264 independently oriented core samples were collected from 26 sites in the southwestern part (the Naktong Trough) of the Cretaceous $Ky{\check{o}}ngsang$ Basin in south Korea. The sampled formations comprise the sedimentary Shindong and the Hayang Groups of the Lower Cretaceous age. Alternating field and thermal demagnetizations were conducted. Characteristic remanent magnetization (ChRM) was relatively easily isolated in each formation except in the Chinju formation, from which only remagnetization circles were observed. Even though an extensive use of the fold test was not possible due to the nearly homoclinal nature of the strata in the area, we believe that the ChRM of each formation is of primary origin based on the following grounds: The in-situ ChRM direction of each formation is different from the present geomagnetic field direction. Fisherian precision parameter becomes enhanced through the tilt correction in all formations, closely to the values required for a positive fold test. Three out of the five studied formations pass the reversal test. The mean palaeomagnetic pole position from the studied area is found to be statistically different from the contemporary pole from the Chinese block exclusive of the Shandong area. The difference in magnetic declination suggests a $14.5^{\circ}$ (${\pm}10.5^{\circ}$) clockwise rotation of the studied area relative to the Chinese block comprising the west of the Tan-Lu fault. On the other hand, any significant difference in magnetic inclination and concurrent palaeolatitude is not observed between the studied area and China as well as the other area (Taegu-Andong area) in the $Ky{\check{o}}ngsang$ Basin. The dual nature of the magnetic polarity confirmed in all formations suggests an older than 124 Ma (Neocomian or older) age of the studied sedimentary strata.