• Ocean and Polar Research
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• 제29권2호
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• pp.113-121
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• 2007

The sound wave in the sea propagates under the effect of water depth, sound speed structure, sea surface roughness, bottom roughness, and acoustic properties of bottom sediment. In shallow water, the bottom sediments are distributed very variously with place and the sound speed structure varying with time and space. In order to investigate the seasonal propagation characteristics of low-frequency sound wave in the Yellow Sea, propagation experiments were conducted along a track in the middle part of the Yellow Sea in spring, summer, and autumn. In this paper we consider seasonal variations of the sound speed profile and propagation loss based on the measurement results. Also we quantitatively investigate variation of bottom loss by dividing the propagation loss into three components: spreading loss, absorption loss, and bottom loss. As a result, the propagation losses measured in summer were larger than the losses in spring and autumn, and the propagation losses measured in autumn were smaller than the losses in spring. The spreading loss and the absorption loss did not show seasonal variations, but the bottom loss showed seasonal variations. So it was thought that the seasonal variation of the propagation loss was due to the seasonal change of the bottom loss and the seasonal variation of the bottom loss was due to the change of the sound speed profile by season.

• Journal of Astronomy and Space Sciences
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• 제30권4호
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• pp.231-239
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• 2013

To identify seasonal and latitudinal variations of F2 layer during magnetic storm, we examine the change of daily averages of foF2 observed at Kokubunji and Hobart during high (2000~2002) and low (2006~2008) solar activity intervals. It is found that geomagnetic activity has a different effect on the ionospheric F2-layer electron density variation for different seasons and different latitudes. We, thus, investigate how the change of geomagnetic activity affects the ionospheric F2-layer electron density with season and latitude. For this purpose, two magnetic storms occurred in equinox (31 March 2001) and solstice (20 November 2003) seasons are selected. Then we investigate foF2, which are observed at Kokubunji, Townsville, Brisbane, Canberra and Hobart, Dst index, Ap index, and AE index for the two magnetic storm periods. These observatories have similar geomagnetic longitude, but have different latitude. Furthermore, we investigate the relation between the foF2 and the [O]/[$N_2$] ratio and TEC variations during 19-22 November 2003 magnetic storm period. As a result, we find that the latitudinal variations of [O]/[$N_2$] ratio and TEC are closely related with the latitudinal variation of foF2. Therefore, we conclude that the seasonal and latitudinal variations of foF2 during magnetic storm are caused by the seasonal and latitudinal variations of mean meridional circulation of the thermosphere, particularly upwelling and downwelling of neutral atmosphere during magnetic storm.

• 한국수산과학회지
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• 제27권6호
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• pp.733-753
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• 1994

해수면의 장주기변동을 알기 위하여 우리나라, 일본, 러시아의 103개 조위관측점의 월평균 해수면을 분석하였다. 기압보정에는 조위관측점 부근의 기상관측점에서 관측된 월평균 해수면기압을 사용하였다. 계절변화는 대부분의 해역에서 지배적이며, 대마해류역 해안에서 가장 크고 러시아 해안에서 가장 작다. 계절변화의 상호상관관계는 대마해류역 해안 사이에서 가장 크다. 이 부속해에서는 계절변화가 대마해류와 관계를 갖고 있는 것으로 보인다. 계절변화는 남쪽에서 북쪽 뿐만 아니라 서쪽에서 동쪽으로도 전파되고 있다. 반면에, 계절변화보다 장주기의 변화는 태평양 연안에서 가장 큰 진폭과 가장 빠른 위상을 보여, 장주기의 변화는 태평양에서 부터 전파되어 오는 것을 보여준다. 계절변화보다 짧은 주기의 변화는 일반적으로 상관관계가 낮다. 이들의 상관관계 값들은 해역사이에 특별한 차이를 보이지 않으며, 거리에 반비례하는 공통적인 경향을 보이고 있다. 이것은 짧은 주기의 파들이 전해역에 걸쳐 발생하여 모든 방향으로 전파되고 있으며 빨리 소멸한다는 것을 의미한다. 1965부터 1985년 동안 이 해역에서 해수면변화의 경향은 일반적으로 태평양연안에서 음의 기울기를 다른 해역이 양의 기울기를 갖는다. 이러한 경향으로 인해 제주와 Sasebo사이의 평균 해수수송량은 이 기간동안 약 1 Sv의 유량이 줄어들 수 있다. 해수면 차이로부터 계산한 수송량의 계절변화는 대한해협에서 2 Sv 정도로 이미 발표된 다른 연구 보고와 비슷하다.

• Ocean and Polar Research
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• 제30권1호
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• pp.33-46
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• 2008

In order to investigate seasonal variations of the physical environments in the region of Jinhae Bay-Nakdongpo, we carried out hydrographic surveys from November 2000 to November 2001. Horizontal and vertical distribution of salinity and temperature shows large seasonal variations. Water column is well mixed in winter and stratified in summer. Low-salinity water is distributed in the form of patches because of the drainage control at the Nakdong River. Seasonal variations in the sea near Gadeok-Sudo are affected by topography, river discharge and tidal current. Currents have been measured using a bottom mounted ADCP and DCM12 between November 2000 and August 2001 in the Gadeok-Sudo. The current in the Gadeok-Sudo shows a distinct two-layer structure with reversed current. Low-pass filtered time series of wind, sea elevation and current are coherent for the period of 1-2 days and are attributed to Ekman-like dynamics. Spatial and temporal circulation pattern shows a slight different. The subtidal current in Jinhae Bay goes northward, however is reversed in the Gadeok-Sudo mouth.

• 한국환경과학회지
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• 제9권2호
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• pp.131-136
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• 2000

The seasonal data obtained at National Fisheries Research and Development Institute from 1989 to 1994 were analyzed to investigate the seasonal variations of temperature and salinity in incheon coastal area. In the tidal flats covering from Incheon harbor to Sorae, the mean temperatures are higher, the amplitudes of flats, the mean salinities are lower, its amplitudes are larger, and its phases are later than those of outer tidal flats. These suggest that Inchion coastal area may be divided into two areas: the tidal flats from Incheon harbor to Sorae, which is largely influenced by the seasonal variation of solar heating, precipitation and evaporation and the outer tidal flats, which is slightly influenced by the effects of seasonal variation of salinity.

• 생약학회지
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• 제24권1호
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• pp.47-53
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• 1993

The seasonal variations of the major six flavonol glycosides(kaempferol 2,6-dirhamnosyl glucoside, quercetin 3-O-rutinoside, kaempferol 3-O-rutinoside, isorhamnetin 3-O-rutinoside, quercetin 3-O-coumaroyl glucorhamnoside and kaempferol 3-O-coumaroyl glucorhamnoside) in Ginkgo biloba leaves were investigated. The contents were determined by HPLC on reversed phase $C_{18}$ column. This result showed that the percentage of six flavonol glycosides decreased during the season from 1.57% in May to 0.39% in November. The content of each flavonol glycoside indicated a similar tendency to decrease. However, the contents of rutinosides of kaempferol, quercetin and isorhamnetin fluctuated markedly than those of coumaroyl glucorhamnosides of kaempferol and quercetin and kaempferol 2,6-dirhamnosyl glucoside.

• International Journal of Industrial Entomology and Biomaterials
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• 제4권2호
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• pp.109-115
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• 2002

With the objective of selecting suitable breeding resource material, 10 polyvoltine and 10 bivoltine breeds were drawn from the germplasm collection of Central Sericultural Research and Training Institute, Mysore, and evaluated for 3 seasons comprising one year (6 trials). Data were collected on seven traits of economic importance such as fecundity, pupation rate, cocoon yield, cocoon weight, cocoon shell weight, cocoon shell ratio and filament length, and statistically analysed with two-way classification, Joint scoring method and evaluation index. Significant seasonal variations (P < 0.01) were observed in both polyvoltine and bivoltine breeds. Polyvoltines BL27, BL36 and BL54 and bivoltines CSR2, CSR4 and Daizo scored highest ranking values in all the three methods. Hybridization was initiated based on larval markings and cocoon shapes. Seasonal variations were discussed.

• 한국환경과학회지
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• 제10권6호
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• pp.423-429
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• 2001

Satellite data, with sea surface temperature(557) by NOAA and sea level(SL) by Topex/poseidon, are used to estimate characteristics on the variations and correlations of 557 and SL in the East Asian Seas from January 1993 through May 1998. We found that there are two climatic characteristics in the East Asian seas the oceanic climate, the eastern sea of Japan, and the continental climate, the eastern sea of China, respectively. In the oceanic climate, the variations of SL have the high values in the main current of Kuroshio and the variations of 557 have not the remarkable seasonal variations because of the continuos compensation of warm current by Kuroshio. In the continental climate, SL has high variations in the estuaries(the Yellow River, the Yangtze River) with the mixing the fresh water and the saline water in the coasts of continent and 557 has highly the seasonal variations due to the climatic effect of continents. In the steric variations of summer, the eastern sea of Japan, the East China Sea and the western sod of Korea is increased the sea level about 10~20cm. But the Bohai bay in China have relatively the high values about 20~30cm due to the continental climate. generally the trends of SST and SL increased during all periods. That is say, the slopes of 557 and SL Is presented 0.29$^{\circ}C$/year and 0.84cm/year, respectively. The annual and semi-annual amplitudes have a remarkable variations in the western sea of Korea and the eastern sea of Japan. In the case of the annual peaks, there appeared mainly In the western sea of Korea and the eastern sea of .Japan because of the remarkable variations of SL associated with Kuroshio. But in the case of the semi-annual peaks, there appeared in the eastern sea of Japan by the influence of current, and in the western sea of Korea by the influence of seasonal temperature, respectively. From our results, it should be believed that 557 and SL gradually Increase in the East Asian seas concerning to the global warming. So that, it should be requested In the international co-operation against In the change of the abnormal climate.

• Journal of the korean society of oceanography
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• 제38권2호
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• pp.68-79
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• 2003

Although seagrasses are relatively abundant, few studies have been conducted on seagrass physiology and ecology in Korea. Zostera marina is the most abundant seagrass species, widely distributed throughout all coastal areas of the Korean peninsula. To examine seasonal dynamics and spatial variations of eelgrass, Zostera marina distributed on the coast of Korea, morphological characteristics, biomass, tissue nutrient constituents, leaf productivity and environmental factors were monitored monthly from the eelgrass beds in Kabae Bay and Kosung Bay on the south coast of the Korean peninsula from June 2001 to June 2002. Eelgrass density, biomass, morphological characteristics, leaf productivities, and tissue nutrient constituents exhibited clear seasonal variations, and these seasonal trends reflected seasonal changes in water temperature. Eelgrass shoot density and biomass at Kabae Bay site showed more obvious seasonal trends than Kosung Bay. No strong seasonality in Kosung Bay site appeared to be caused by high water temperature ($>30{\circ}C$) during summer months at this site. Despite differences in nutrient availabilities between two study sites, eelgrass biomass and leaf productivities were not significantly different between study sites, and this lack of spatial variations implies that the ambient nutrient availabilities at the present study sites are in excess of seagrass nutrient demand. Eelgrass tissue N content and sediment pore water DIN concentrations exhibited reverse relationship at the present study. This reverse relationship suggests in situ nutrient concentrations are not good indicator of nutrient availabilities, and regeneration and turnover rates of sediment nutrients are also important factors to determine nutrient availabilities at the site.

• Environmental Analysis Health and Toxicology
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• 제22권4호
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• pp.329-337
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• 2007

This study considers the characteristics of nitrogen dioxide ($NO_2$), ozone ($NO_3$) and sulfur dioxide ($SO_2$) in three cities of Daegu-Gyeongbuk Area (Daegu, Pohang, and Gumi), which have different city or industrial characteristics, over a time period of 2 years. The diurnal, weekly, monthly and seasonal concentration variations of criteria air pollutants were attributed to compounds or city types. However, the seasonal variations of $O_3$ concentrations were dependent on compounds, but not on city types. Lower $O_3$ concentrations were observed in July when comparing with other summer months. For $SO_2$ and $NO_2$, the concentrations were higher in Daegu when compared to Pohang and Gumi, while the concentrations of $O_3$ were higher in Pohang and Gumi. $SO_2$ exhibited higher levels in the morning hours, while $O_3\;and\;NO_2$ exhibited higher levels in the afternoon hours for all cities. For $O_3$, the concentrations observed during Sunday were higher than those of other week or weekend days. Furthermore, the monthly and seasonal concentration variations of air pollutants depended on compounds or city types. It if noteworthy that the current monthly and seasonal variations were consistent with several prey ious studies.