• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.335-340
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• 2015

Using the Total Electron Content (TEC) data from the Global Navigation Service System (GNSS) site in Jeju, operated by the Korea Astronomy and Space Science Institute (geographic location: $33.3^{\circ}N$, $126.5^{\circ}E$; geomagnetic location: $23.6^{\circ}N$) for 2002-2014 in Korea, the results of the statistical analysis of positive and negative ionospheric storms are presented for the first time. In this paper, ionospheric storms are defined as turbulences that exceed 50% of the percentage differential Global Positioning System (GPS) TEC ratio (${\Delta}TEC$) with monthly median GPS TEC. During the period of observations, the total number of positive ionospheric storms (${\Delta}TEC$ > 50%) was 170, which is greater than five times the number of negative ionospheric storms (${\Delta}TEC$ < - 50%) of 33. The numbers of ionospheric storms recorded during solar cycles 23 and 24 were 134 and 69, respectively. Both positive and negative ionospheric storms showed yearly variation with solar activity during solar cycle 23, but during solar cycle 24, the occurrence of negative ionospheric storms did not show any particular trend with solar activity. This result indicates that the ionosphere is actively perturbed during solar cycle 23, whereas it is relatively quiet during solar cycle 24. The monthly variations of the ionospheric storms were not very clear although there seems to be stronger occurrence during solstice than during equinox. We also investigated the variations of GPS positioning accuracy caused by ionospheric storms during November 7-10, 2004. During this storm period, the GPS positioning accuracies from a single frequency receiver are 3.26 m and 2.97 m on November 8 and 10, respectively, which is much worse than the quiet conditions on November 7 and 9 with the accuracy of 1.54 m and 1.69 m, respectively.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.47.3-48
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• 2015

We present environmental effects on the galaxy evolution in the Virgo cluster focusing on intracluster medium - interstellar medium (ICM-ISM) interactions and gravitational interactions. We identify signatures of these environmental effects for 21 massive late-type galaxies based on the visual inspection of high resolution HI data from VLA Imaging of Virgo spirals in Atomic gas (VIVA) survey comparing with multi-wavelength data. We classify galaxies into three subgroups showing different environmental effects. First and second groups includes galaxies influenced by ongoing/active and past ram pressure stripping effect, respectively. Third group consists of galaxies undergoing gravitational interactions. Additionally, we define neighbor galaxies for each VIVA galaxies utilizing kinematic data from Extended Virgo Cluster Catalog. Assuming that neighbor galaxies share similar levels of environmental effects with host VIVA galaxies, we investigate environmental effects on galaxy properties in different subgroups using SDSS optical and GALEX ultraviolet photometric data. We find that dwarf neighbor galaxies in first and second groups show rapid quenching of their star formation (SF), while massive counterparts are still in SF activity. On the other hand, most third group galaxies show hints of SF activity regardless of their mass. We conclude that SF and evolution of galaxy in the cluster environment is closely linked to ICM-ISM interactions and dwarf galaxies seem to be more sensitive to this effect compared to massive counterparts.

• Journal of Astronomy and Space Sciences
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• v.23 no.3
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• pp.227-236
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• 2006

The fractal dimension is a quantitative parameter describing the characteristics of irregular time series. In this study, we use this parameter to analyze the irregular aspects of solar activity and to predict the maximum sunspot number in the following solar cycle by examining time series of the sunspot number. For this, we considered the daily sunspot number since 1850 from SIDC (Solar Influences Data analysis Center) and then estimated cycle variation of the fractal dimension by using Higuchi's method. We examined the relationship between this fractal dimension and the maximum monthly sunspot number in each solar cycle. As a result, we found that there is a strong inverse relationship between the fractal dimension and the maximum monthly sunspot number. By using this relation we predicted the maximum sunspot number in the solar cycle from the fractal dimension of the sunspot numbers during the solar activity increasing phase. The successful prediction is proven by a good correlation (r=0.89) between the observed and predicted maximum sunspot numbers in the solar cycles.

• Journal of Astronomy and Space Sciences
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• v.31 no.2
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• pp.149-157
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• 2014

As the prediction of geomagnetic storms is becoming an important and practical problem, conditions in the Earth's magnetosphere have been studied rigorously in terms of those in the interplanetary space. Another approach to space weather forecast is to deal with it as a probabilistic geomagnetic storm forecasting problem. In this study, we carry out detailed statistical analysis of solar wind parameters and geomagnetic indices examining the dependence of the distribution on the solar cycle and annual variations. Our main findings are as follows: (1) The distribution of parameters obtained via the superimposed epoch method follows the Gaussian distribution. (2) When solar activity is at its maximum the mean value of the distribution is shifted to the direction indicating the intense environment. Furthermore, the width of the distribution becomes wider at its maximum than at its minimum so that more extreme case can be expected. (3) The distribution of some certain heliospheric parameters is less sensitive to the phase of the solar cycle and annual variations. (4) The distribution of the eastward component of the interplanetary electric field BV and the solar wind driving function BV2, however, appears to be all dependent on the solar maximum/minimum, the descending/ascending phases of the solar cycle and the equinoxes/solstices. (5) The distribution of the AE index and the Dst index shares statistical features closely with BV and $BV^2$ compared with other heliospheric parameters. In this sense, BV and $BV^2$ are more robust proxies of the geomagnetic storm. We conclude by pointing out that our results allow us to step forward in providing the occurrence probability of geomagnetic storms for space weather and physical modeling.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.99-106
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• 2007

Statistical analyses were performed to investigate the relative success and accuracy of daily maximum X-ray flux (MXF) predictions, using both multilinear regression and autoregressive time-series prediction methods. As input data for this work, we used 14 solar activity parameters recorded over the prior 2 year period (1989-1990) during the solar maximum of cycle 22. We applied the multilinear regression method to the following three groups: all 14 variables (G1), the 2 so-called 'cause' variables (sunspot complexity and sunspot group area) showing the highest correlations with MXF (G2), and the 2 'effect' variables (previous day MXF and the number of flares stronger than C4 class) showing the highest correlations with MXF (G3). For the advanced three days forecast, we applied the autoregressive timeseries method to the MXF data (GT). We compared the statistical results of these groups for 1991 data, using several statistical measures obtained from a $2{\times}2$ contingency table for forecasted versus observed events. As a result, we found that the statistical results of G1 and G3 are nearly the same each other and the 'effect' variables (G3) are more reliable predictors than the 'cause' variables. It is also found that while the statistical results of GT are a little worse than those of G1 for relatively weak flares, they are comparable to each other for strong flares. In general, all statistical measures show good predictions from all groups, provided that the flares are weaker than about M5 class; stronger flares rapidly become difficult to predict well, which is probably due to statistical inaccuracies arising from their rarity. Our statistical results of all flares except for the X-class flares were confirmed by Yates' $X^2$ statistical significance tests, at the 99% confidence level. Based on our model testing, we recommend a practical strategy for solar X-ray flare predictions.

• Journal of Astronomy and Space Sciences
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• v.26 no.1
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• pp.25-30
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• 2009

We report the relation between the solar activity and terrestrial climate change with the solar north-south asymmetry. For this purpose, we calculate sliding correlation coefficients between sunspot numbers and earth's mean annual temperature anomalies. Then, we compare the epoch that the sign of correlation changes with the epoch that the sign of the solar north-south asymmetry changes. We obtain that corresponding times are 1907 and 1985, respectively. Further more, these two epoches are well consistent with those of signs of the solar north-south asymmetry changes. We also obtain that the plot between sunspot numbers and temperature anomalies could be classified by 1907 and 1985. We conclude that temperature anomalies are shown to be negatively correlated with sunspot numbers when the southern solar hemisphere is more active: and vice versa.

• Journal of the Korean Wood Science and Technology
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• v.42 no.5
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• pp.624-633
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• 2014

This study separated the crude extract (70% ethanol) of and its three fractions (hexane, chloroform and ethyl acetate extracts) on the basis of polarity indexes, and examined for their insecticidal activities against aphid (Uroleucon lactucicola). For crude extraction, the 70% ethanol extract showed the best extract yield (58.0%) and insecticidal activity (69.0%) among the various concentrations tested (water, 30% ethanol, 50% ethanol, 70% ethanol and 95% ethanol). The major chemical compounds of different fractions (hexane, chloroform and ethyl acetate extracts) were identified as eugenol by head space-GC-MS analysis. The hexane extract showed the highest eugenol content (43.7%) and insecticidal activity (80.0%). The insecticidal activity is accordingly believed to be attributable to the eugenol component. This may provide a useful starting point for the development of bio-pesticides.

• Applied Microscopy
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• v.12 no.1
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• pp.11-21
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• 1982

A number of recent ultrastructural studies have shown marked differences between the two lining cell types in adult liver sinusoids, endothelial cells and Kupffer cells. In the present study, the ultrastructural features and electron microscopic cytochemistry of sinusoidal lining cells in the fetal liver were studied through fetal period to neonate in the rat. At fetal period, the sinusoid, which contains various blood component, in lined by the endothelial cells, the Kupffer cells and the fat storing cells that located in the space of Disse. As gestation proceeded, these eel's are arranged as adult liver sinusoids. The sinusoidal wall appears to be discontinuous with open fenestration between endothelial cells, but no basal lamina can observed. It seems to be morphologically and functionally distinct at the early gestation between the endothelial cells and the Kupffer cells, the latter showing marked phagocytized activity. The fat storing cells, which contain several fat droplets, are located in the space of Disse. Ultrastructural localization of the acid and alkaline phosphatase activity were noted on the sinusoidal lining cells.

• Journal of Astronomy and Space Sciences
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• v.36 no.4
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• pp.225-234
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• 2019

We explore the associations between the total sunspot area, solar north-south asymmetry, and Southern Oscillation Index and the physical characteristics of clouds by calculating normalized cross-correlations, motivated by the idea that the galactic cosmic ray influx modulated by solar activity may cause changes in cloud coverage, and in turn the Earth's climate. Unlike previous studies based on the relative difference, we have employed cloud data as a whole time-series without detrending. We found that the coverage of high-level and low-level cloud is at a maximum when the solar north-south asymmetry is close to the minimum, and one or two years after the solar north-south asymmetry is at a maximum, respectively. The global surface air temperature is at a maximum five years after the solar north-south asymmetry is at a maximum, and the optical depth is at a minimum when the solar north-south asymmetry is at a maximum. We also found that during the descending period of solar activity, the coverage of low-level cloud is at a maximum, and global surface air temperature and cloud optical depth are at a minimum, and that the total column water vapor is at a maximum one or two years after the solar maximum.

• Journal of Astronomy and Space Sciences
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• v.14 no.1
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• pp.59-66
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• 1997

The relationship between Mg II emission line and light variation of V711 Tau has been derived to investigate the chromospheric activity on V711 Tau. First, a shape of an optical light curve was compared with that of ultraviolet constructed from the IUE low resolution spectra. Second, the intensities of Mg II k emission lines have been reduced from IUE high resolution spectra. The intensity of Mg II k line was compared with brightness of the UV light curve at given phase. The Mg II line intensity is maximum at the phase $O.^{P}4$ where the light is minimum. The evidence of chromosperic activity is indicated by the intensity variation of the MgII emission line with orbital phase for V711 Tau.