• Journal of Astronomy and Space Sciences
• /
• v.27 no.4
• /
• pp.319-327
• /
• 2010

We examine the ionospheric F2-layer electron density variation by solar activity in middle latitude by using foF2 observed at the Kokubunji ionosonde station in Japan for the period from 1997 to 2008. The semi-annual variation of foF2 shows obviously in high solar activity (2000-2002) than low solar activity (2006-2008). It seems that variation of geomagnetic activity by solar activity influences on the semi-annual variation of the ionospheric F2-layer electron density. According to the Lomb-Scargle periodogram analysis of foF2 and Ap index, interplanetary magnetic field (IMF) Bs (IMF Bz <0) component, solar wind speed, solar wind number density and flow pressure which influence the geomagnetic activity, we examine how the geomagnetic activity affects the ionospheric F2-layer electron density variation. We find that the semi-annual variation of daily foF2, Ap index and IMF Bs appear clearly during the high solar activity. It suggests that the semi-annual variation of geomagnetic activity, caused by Russell-McPherron effect, contributes greatly to the ionospheric F2-layer semi-annual electron density variation, except dynamical effects in the thermosphere.

• Journal of Astronomy and Space Sciences
• /
• v.38 no.4
• /
• pp.229-236
• /
• 2021

We present for the first time the characteristics of upper atmospheric horizontal winds over the Korean Peninsula. Winds and their variability are derived using four-year measurements by the Korea Astronomy and Space Science Institute (KASI) meteor radar. A general characteristic of zonal and meridional winds is that they exhibit distinct diurnal and seasonal variations. Their changes indicate sometimes similar or sometimes different periodicities. Both winds are characterized by either semi-diurnal tides (12 hour period) and/or diurnal tides (24 hour period) from 80-100 km. In terms of annual change, the annual variation is the strongest component in both winds, but semi-annual and ter-annual variations are only detected in zonal winds.

• Fisheries and Aquatic Sciences
• /
• v.3 no.2
• /
• pp.163-171
• /
• 2000

A series of numerical experiments are performed to examine the generation of inter-annual variations by an inertial current in an idealized semi-enclosed basin with dimension comparable to that of the East Sea. Model results indicate that the inter-annual variations dominate the kinetic energy spectrum with a peak around the time scales of 2-3 years. These variations are mostly due to the westward propagating meanders and large eddies induced by the instability of current, indicating their dependency on the eddy-resolving capacity of the model. They are generated in the interior of the basin but their energy is largely confined near the western boundary such that the east-west dimension of the basin cannot be considered as a critical factor as long as the basin covers enough western boundary region. Overall, this study suggests that the inter-annual variation observed in the East Sea is due to the meandering and large eddies induced by the instability of the current.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.17 no.6
• /
• pp.557-565
• /
• 1984

The year-to-year fluctuations of seasonal variation of sea surface temperatures (SST) in the Korea Strait are studied based on monthly SST data for more than 50 years at Mitsushima ana Okinoshima in the strait. The frequency distribution of SST has two peaks at temperatures below and above the multi-year average, but that of SST anomalies has only one peak at the zero anomaly. More than $95\%$ of the anomalies are in the range of ${\pm}2^{\circ}C$. The harmonic constansts of seasonal SST variation vary from year to year. The standard deviations of annual means, annual amplitudes, ana semi-annual amplitudes are less than $1^{\circ}C$, and those of the annual ana semi-annual phases are about $5^{\circ}$ and less than $50^{\circ}$, respectively. The SST in the Korea Strait have a tendency to decrease their amplitudes as the annual means increase. Physical mechanisms responsible for the analyzed results are discussed in this paper.

• Environmental Analysis Health and Toxicology
• /
• v.22 no.2 s.57
• /
• pp.111-118
• /
• 2007

This study was performed to measure gaseous Organochlorine Pesticides (OCPs : heptachlor epoxide, ${\alpha}/{\gamma}-chlordane$, trans-nonachlor, endosulfan, ${\gamma}-HCH$ and p, p'-DDE) concentration using PUF high volume sampler from June, 2000 to June, 2002 in the semi-rural atmosphere. Using monitoring data for two years, we tried to investigate the annual cycles of gaseous OCPs. We considered three functions to describe the annual cycle: Gaussian, Lorentzian and sinusoidal functions. These functions accounted for $54{\sim}91%$ of the variability in concentration for each gaseous OCPs, and the sinusoidal function gave the best fits. It was seen that the gaseous OCPs concentration increased during the warmer weather while decreased during colder weather. The variation of the gaseous OCPs concentration was closely similar to the variations of ambient temperature. The annual cycle of endosulfan was strongly higher than in comparison with other gaseous OCPs, while for ${\gamma}-HCH$, the cycle was weakly high and did not show apparent seasonal variation. The position of the annual maximum exists generally late July to early August. The period that showed levels more than a half maximum was from late June to early September.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• v.9 no.1
• /
• pp.383-386
• /
• 2005

CCW(China Coastal Water) is different each year. It appears clearly from June to October in the neighboring sea of Jeju island. It appears in June, and it's strong most in August, after tat disappears in October. CCW appeared clearly at 1996 and 1999 during investigation period(1995 to 1999). SLA and SST appear annual variations(about 365day), semi-annual variations(about 180day) from power spectral density. After PCA(Principal component analysis), it's different. PCA of SLA shows 43day variations and PCA of SST shows 259day variations. SLA and SST appear annual variation, semi-annual variation and seasonal variation from power spectral density. SLA appeared that summer and fall of 1996 and 1999 is higher than other years. It seem to be being the relationship which is close with the severe rain strom. Temperature distribution of sea surface according to season is different, but clearly water temperature boundary divides this area into Yellow Sea and East China Sea. It considered that CCW follow according to boundary of temperature. The variation which it follows at time of SLA and SST is faster about one month to three month at Yangtz.

• Ocean and Polar Research
• /
• v.31 no.1
• /
• pp.71-76
• /
• 2009

Drastic changes in the water quality and phytoplankton community of the new Saemankeum Lakeduring the first decade following the construction of the Saemankeum Sea Wall has been considered to be unavoidable. Input of eutrophicated water through the Mankyeong River and Dongjin River might produce more direct effects on the water quality and phytoplankton community, which lead us to launch a long-term semi-weekly investigation at the "Mankyeong Bridge" monitoring point to resolve its short-term effect as well as long-term stabilization of the ecosystem in the new Saemankeum Lake. During 15 months starting from June 2006, the water temperature varied in accordance with the typical seasonal variations in temperate on the coasts, and no significant daily variations evoked by tidal cycle could be detected. However, there was an inverse relationship between seasonal precipitation and salinity even though the range in annual variation was drastically reduced right after the construction of the Saemankeum Sea Wall. Species richness in the phytoplankton community was also reduced due to the narrowed annual range of salinity, which would eliminate the mid-high salinity species from the Mankyeong Bridge monitoring point. Similarly, species diversity was decreased with increased dominance of the phytoplankton community after the construction. Between the two summer seasons during the present study, species diversity was higher in 2007 than in 2006, which might indicate the early stage of a gradual stabilization in the ecosystem including the phytoplankton community at the monitoring station. The phytoplankton community thus needs to be monitored on a long-term basis to identify indirect signals that can be used to assess the stability of the ecosystem in the young Saemankeum Lake.

• Proceedings of the National Institute of Ecology of the Republic of Korea
• /
• v.3 no.3
• /
• pp.154-164
• /
• 2022

Understanding temporal variations in wildlife populations is a prerequisite for conservation planning of wide-ranging species such as tigers (Panthera tigris). We determined the temporal variation in abundance, population growth, and sex ratios at different age and sex stages for a tiger population in Ranthambhore Tiger Reserve, India from November 2007 to February 2011 using motion-sensing cameras. We identified 19 male and 21 female tigers from stripe patterns during 16,110 trap nights within an area covering 233 km². The annual abundance of the population varied from 34.9 (mean)±3.8 (SE) to 23.9±1.5, with a declining trend in the mean annual change of abundance (-12%). The density of adult females remained stable across the study duration, but the densities of adult males and non-breeding tigers fluctuated. The sex ratio was female-biased (0.58 males/female) for breeding tigers and male-biased (1.74 males/female) for non-breeding tigers. Our results reinforce the importance of long-term studies for monitoring the naturally occurring processes in populations to develop population indicators and identify reliable baseline information for conservation and management planning of populations.

• Journal of Astronomy and Space Sciences
• /
• v.33 no.4
• /
• pp.287-293
• /
• 2016

The equatorial region of the Earth's ionosphere exhibits large temporal variations in electron density that have significant implications on satellite signal transmissions. In this paper, the first observation results of the variations in the trough of the equatorial ionospheric anomaly at the permanent Global Navigation Satellite System (GNSS) site in Chuuk (Geographic: $7.5^{\circ}N$, $151.9^{\circ}E$; Geomagnetic: $0.4^{\circ}N$) are presented. It was found that the daytime Global Positioning System (GPS) total electron content (TEC) values vary according to the 27 day period of solar rotation, and that these trends show sharp contrast with those of summer. The amplitudes of the semi-annual anomaly were 12.4 TECU (33 %) on $19^{th}$ of March and 8.8 TECU (23 %) on $25^{th}$ of October respectively, with a yearly averaged value of 38.0 TECU. The equinoctial asymmetry at the March equinox was higher than that at the October equinox rather than the November equinox. Daily mean TEC values were higher in December than in June, which could be interpreted as annual or winter anomalies. The nighttime GPS TEC enhancements during 20:00-24:00 LT also exhibited the semi-annual variation. The pre-midnight TEC enhancement could be explained with the slow loss process of electron density that is largely produced during the daytime of equinox. However, the significant peaks around 22:00-23:00 LT at the spring equinox require other mechanisms other than the slow loss process of the electron density.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2006.05a
• /
• pp.485-488
• /
• 2006

SLA and SST is high in summer and fall, it is low in spring and winter. The clearly annual period shows through the power spectrum density. A semi-annual period and seasonal period appeared, In. At sea surface variation of satellite data(Mean Sea Level Anomaly) and in-situ data, coefficient-correlation show 0.323 at Mukho which is located in the coastal. Chujado and Ulleungdo is a 0.685 and 0.780, retentively. A coefficient-correlation of SST show higher than sea surface variation as Mukho-0.920, Chujado-0.894 and Ulleungdo-0.815. A comparison between SST and MSLA show 0.77, SST appeared faster about 1 to 3 months than MSLA.