• 한국수자원학회논문집
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• 제46권3호
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• pp.253-265
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• 2013

본 연구에서는 쾨펜의 기후대 구분법을 이용하여 현재 아시아 지역(경도 $55.6^{\circ}{\sim}149.3^{\circ}$, 위도 $-11.5^{\circ}{\sim}53.0^{\circ}$) 기후대를 분석하고, IPCC SRES A2 시나리 오상황에서의 기후대 변화를 전망하였다. 이와 더불어 기후대 구분의 기준이 되는 강수 및 기온자료의 시공간적 변동성을 분석하였다. 기후요소의 변동성을 분석한 결과, 2080년경에는 기준기간(1991~2010)에 비해 기온은 $4.0^{\circ}C$, 강수량은 12% 증가할 것으로 전망되었다. 공간적으로는 기온의 경우 고위도 지역이 저위도 지역보다 기온상승폭이 크게 나타났으며 강수량은 지역적 편중이 심화될 것으로 전망되었다. 기후대 변화를 전망한 결과, 대체로 온난한 기후대의 면적은 증가한 반면, 한랭한 기후대의면적은 감소하는 것으로 분석되었다. 기준기간 대비 2080년경에는 열대 기후대(A)의 경우 7.2%, 건조 기후대(B)는 1.9% 증가하였으며 온대 기후대(C), 냉대 기후대(D), 한대 기후대(E)는 각각 -2.4%, -4.9%, -1.8% 감소하는 것으로 전망되었다. 이러한 결과는 지구온난화에 따른 기온 증가와 사막화의 영향에 기인한 것으로 판단된다.

• Ocean and Polar Research
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• 제26권2호
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• pp.299-309
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• 2004

Conductivity-temperature-depth (CTD) data obtained along a meridional section in the eastern tropical Pacific in July 2003 have been analyzed to identify various water masses, and to examine the hydrographic structure and zonal geostrophic currents in the upper 1000 m. Water mass analysis shows the existence of subtropical and intermediate waters, characterized by layers of subsurface salinity maximum and minimum, originating from both hemispheres of the Pacific. Vertical section of temperature in the upper 200 m shows the typical trough-ridge structure associated with the zonal current system for most of the tropical Pacific. Water with the lowest salinity of less than 33.6 was found in the upper 30 m between $8.5^{\circ}N$ and $10.5^{\circ}N$ in a boundary zone between the North Equatorial Current and North Equatorial Countercurrent. Temporal changes in water properties observed at $10.5^{\circ}N$ over a period of 9 days suggest both the local rainfall and horizontal advection is responsible for the presence of the low-salinity water. Development of a barrier layer was also observed at $10.5^{\circ}N$. In the North Equatorial Current region a local upwelling was observed at $15^{\circ}N$, which brings high salinity and cooler subtropical water to the sea surface. A band of countercurrent occurs in the upwelling region between $13^{\circ}N$ and $15^{\circ}N$.

• Ocean and Polar Research
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• 제38권2호
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• pp.89-102
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• 2016

In this study, we evaluated the model performance with respect to Sea Surface Temperature (SST) and Net Heat Flux (NHF) by considering the characteristics of seasonal temperature variation and contributing factors and by analyzing heat budget terms in the Northwestern Pacific and East Asian Marginal Seas ($110^{\circ}E-160^{\circ}E$, $15^{\circ}N-60^{\circ}N$) using the HadGEM2-AO historical run. Annual mean SST of the HadGEM2-AO is about $0.065^{\circ}C$ higher than observations (EN3_v2a) from 1950 to 2000. Since 1960, the model has simulated well the long-term variation of SST and the increasing rate of SST in the model ($0.014^{\circ}C/year$) is comparable with observations ($0.013^{\circ}C/year$). Heat loss from the ocean to the atmosphere was simulated slightly higher in the HadGEM2-AO than that in the reanalysis data on the East Asian Marginal Seas and the Kuroshio region. We investigated the causes of temperature variation by calculating the heat budget equation in the two representative regions. In the central part of the Kuroshio axis ($125^{\circ}E-130^{\circ}E$, $25^{\circ}N-30^{\circ}N$: Region A), both heat loss in the upper mixed layer by surface heat flux and vertical heat advection mainly cause the decrease of heat storage in autumn and winter. Release of latent heat flux through the heat convergence brought about by the Kuroshio contributes to the large surface net heat flux. Positive heat storage rate is mainly determined by horizontal heat advection from March to April and surface net heat flux from May to July. In the central part of the subtropical gyre ($155^{\circ}E-160^{\circ}E$, $22^{\circ}N-27^{\circ}N$: Region B), unlike Region A, vertical heat advection predominantly causes the decrease of heat storage in autumn and winter. In spring and summer, surface heat flux contributes to the increase of heat storage in Region B and the period is two times longer than the period for Region A. In this season, shoaling of the mixed layer depth plays an important role in the increase of SST.

• Journal of Astronomy and Space Sciences
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• 제28권4호
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• pp.305-310
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• 2011

The total electron content (TEC) using global positioning system (GPS) is analyzed to see the characteristics of ionosphere over King Sejong station (KSJ, geographic latitude $62^{\circ}13'S$, longitude $58^{\circ}47'W$, corrected geomagnetic latitude $48^{\circ}S$) in Antarctic. The GPS operational ratio during the observational period between 2005 and 2009 is 90.1%. The annual variation of the daily mean TEC decreases from January 2005 to February 2009, but increase from the June 2009. In summer (December-February), the seasonal mean TEC values have the maximum of 26.2 ${\pm}$ 2.4 TEC unit (TECU) in 2005 and the minimum of 16.5 ${\pm}$ 2.8 TECU in 2009, and the annual differences decrease from 3.0 TECU (2005-2006) to 1.4 TECU (2008-2009). However, on November 2010, it significantly increases to 22.3 ${\pm}$ 2.8 TECU which is up to 5.8 TECU compared with 2009 in summer. In winter (June-August), the seasonal mean TEC slightly decreases from 13.7 ${\pm}$ 4.5 TECU in 2005 to 8.9 ${\pm}$ 0.6 TECU in 2008, and the annual difference is constantly about 1.6 TECU, and increases to 10.3 ${\pm}$ 1.8 TECU in 2009. The annual variations of diurnal amplitude show the seasonal features that are scattered in summer and the enhancements near equinoxes are apparent in the whole years. In contrast, the semidiurnal amplitudes show the disturbed annual peaks in winter and its enhancements near equinoxes are unapparent. The diurnal phases are not constant in winter and show near 12 local time (LT). The semidiurnal phases have a seasonal pattern between 00 LT and 06 LT. Consequently, the KSJ GPS TEC variations show the significant semidiurnal variation in summer from December to February under the solar minimum between 2005 and 2009. The feature is considered as the Weddell Sea anomaly of larger nighttime electron density than a daytime electron density that has been observed around the Antarctica peninsula.

• Ocean and Polar Research
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• 제37권2호
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• pp.127-140
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• 2015

A continuous series of 60 snow samples was collected at a 2.5-cm interval from a 1.5-m snow pit at a site on the Styx Glacier Plateau in Victoria Land, Antarctica, during the 2011/2012 austral summer season. Various chemical components (${\delta}D$, ${\delta}^{18}O$, $Na^+$, $K^+$, $Mg^{2+}$, $Ca^{2+}$, $Cl^-$, $SO_4{^2-}$, $NO_3{^-}$, $F^-$, $CH_3SO_3{^-}$, $CH_3CO_2{^-}$ and $HCO_2{^-}$) were determined to understand the highly resolved seasonal variations of these species in the coastal atmosphere near the Antarctic Jang Bogo station. Based on vertical profiles of ${\delta}^{18}O$, $NO_3{^-}$and MSA, which showed prominent seasonal changes in concentrations, the snow samples were dated to cover the time period from 2009 austral winter to 2012 austral summer with a mean accumulation rate of $226kgH_2Om^{-2}yr^{-1}$. Our snow profiles show pronounced seasonal variations for all the measured chemical species with a different pattern between different species. The distinctive feature of the occurrence patterns of the seasonal variations is clearly linked to changes in the relative strength of contributions from various natural sources (sea salt spray, volcanoes, crust-derived dust, and marine biogenic activities) during different short-term periods. The results allow us to understand the transport pathways and input mechanisms for each species and provide valuable information that will be useful for investigating long-term (decades to century scale periods) climate and environmental changes that can be deduced from an ice core to be retrieved from the Styx Glacier Plateau in the near future.

• Ocean and Polar Research
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• 제36권2호
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• pp.189-197
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• 2014

The pearl-spot damsel, Chromis notata, is one of the important fishery species in Korea. While C. notata has been commonly harvested in southern Korea, the increasing number of C. notata in higher latitudes has crucial ecological, economic and evolutionary implications under conditions where the climate is rapidly changing. Here we examined the morphological and genetic characteristics of C. notata to assess patterns of geographical variations among the groups from three different sites. The groups were clearly distinguishable in the analysis of morphological characteristics. On the other hand, the groups were genetically indistinguishable. All individuals fell within a single clade in the neighbor-joining tree but appeared scattered in the haplotype network. Several haplotypes are shared among the sampling sites (Jejudo-Ulleungdo; Hap 9, Wangdolcho-Ulleungdo; Hap 28, Hap 33, Hap 34). Although control region markers did not elucidate the spatial patterns in genetic characteristics, Wangdolcho and Ulleungdo groups appear to exhibit a more robust gene flow between the two groups than with Jejudo group. Integrative approaches such as those combining morphological and genetic analyses minimize potential errors caused by limited perspectives of each analysis and can provide useful information for discovering functional DNA regions attributable to morphological characteristics expressions.

• Ocean and Polar Research
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• 제43권1호
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• pp.15-30
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• 2021

In this study, using 16 ORA-IP (Ocean Reanalysis Intercomparison Project) data, we investigated spatial and temporal changes of net surface heat flux in the East Asian seas and presented a new ensemble net surface heat flux index. The ensemble net surface heat flux index is produced considering the data distribution and the standard deviation of each ORA-IP. From the correlation analysis with air temperature averaged over the Korean Peninsula, ensemble net heat flux around the Korea Strait shows the highest correlation (0.731) with a 3 month time lag. For the correlation study regarding precipitation over the Korean Peninsula, it also shows significant correlation especially in winter and spring seasons. Similar results are also found in comparison with climate indices (AO, PDO, and NINO3.4), but ensemble net surface heat flux data in winter season reveals the strongest correlation patterns especially with winter temperature and spring precipitation.

• Ocean and Polar Research
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• 제33권1호
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• pp.55-68
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• 2011

The distribution and inter-annual variation of nutrients (N, P, Si) and dissolved/particulate organic carbon were investigated in the equatorial thermocline ridge ($7^{\circ}{\sim}11.5^{\circ}N$, $131.5^{\circ}W$) of the northeast Pacific. From the Oceanic Nino Index and Multivariate ENSO Index provided by NOAA, normal condition was observed in July 2003 and August 2005 on the aspect of global climate/ocean change. However, La Ni$\~{n}$a and El Ni$\~{n}$o episodes occurred in July 2007 and August 2009, respectively. Thermocline ridge in the study area was located at $9^{\circ}N$ in July 2003, $8^{\circ}N$ in August 2005, $10^{\circ}N$ in July 2007, and $10.5^{\circ}N$ in August 2009 under the influence of global climate/ocean change and surface current system (North Equatorial Counter Current and North Equatorial Current) of the northeast Pacific. Maximum depth integrated values (DIV) of nutrients in the upper layer (0~100 m depth range) were shown in July 2007 (mean 21.12 gN/$m^2$, 4.27 gP/$m^2$, 33.72 gSi/$m^2$) and higher variability of DIV in the equatorial thermocline ridge was observed at $10^{\circ}N$ during the study periods. Also, maximum concentration of dissolved organic carbon (DOC) in the upper 50 m depth layer was observed in July 2007 (mean $107.48{\pm}14.58\;{\mu}M$), and particulate organic carbon (POC, mean $9.42{\pm}3.02\;{\mu}M$) was similar to that of DOC. Nutrient concentration in the surface layer increased with effect of upwelling phenomenon in the equatorial thermocline ridge and La Ni$\~{n}$a episode, which had formed in the central Pacific. This process also resulted in the increasing of organic carbon concentration (DOC and POC) in the surface layer. From these results, it is suggested that spatial and temporal variation of chemical and biological factors were generated by physical processes in the equatorial thermocline ridge.

• Ocean and Polar Research
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• 제42권2호
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• pp.115-131
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• 2020

The effective range of surface current data observed by high-frequency radar (HFR) operated in the northern coastal area of Jeju Island by Korea Institute of Ocean Science and Technology was estimated and the distribution and variability of the M₂ tidal current of the Jeju Strait was analyzed. To evaluate the HFR data, the M₂ tidal current corrected from 25 hours current data observed by the Korea Hydrographic and Oceanographic Agency (KHOA) was compared with the M₂ tidal current in the Jeju Strait analyzed from the surface currents of HFR. The reliability of HFR data was confirmed by analyzing the characteristics of the tide components of these two data sets, and the effective range of HFR data was estimated through temporal and spatial analysis. The observation periods of HFR used in the analysis were from 2012 to 2014, and it was confirmed that there is a difference in the effective range of HFR data according to the observation time. During the analysis periods, the difference between the M₂ current ellipses from the data of KHOA and the HFR was greater in the eastern than in the western part of the Jeju Strait, and represented a high reliability in the western and central parts of the Jeju Strait. The tidal current of the Jeju Strait analyzed using the HFR data revealed a seasonal variability a relatively weak in summer and a strong in winter, about a 17% fluctuations between the summer and winter based on the length of the semi-major axis of tidal ellipse. Appraisals and results of regarding the characteristics and seasonal variability of the M₂ tidal current in the Jeju Strait using HFR data have not been previously reported, so the results of this study are considered meaningful.

• Ocean and Polar Research
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• 제36권2호
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• pp.111-119
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• 2014

이 연구에서는 동해의 해수 중 방사성탄소의 분지별 비교 및 시간에 따른 변화를 이해하고자 하였다. 1999년 동해의 일본분지, 울릉분지, 야마토분지 3개 분지에서 총 5개의 정점에서 채취한 시료로부터 방사성탄소를 분석하였다. 동해의 방사성탄소는 일반적인 대양에서의 분포와 유사하게 표층에서 2000 m 수심까지 가파르게 감소하는 양상을 보이며, 2000 m 보다 깊은 수심에서는 일정한 값을 보였다. 분지별로 방사성탄소의 수직분포를 비교해 보면, 3개의 분지의 표층(<200 m)에서 방사성탄소 값은 63~85‰ 이내로 유사하였으나 200~2000 m의 중층수에서는 분지별로 최대 60‰까지 차이가 나타났다. 중층수의 방사성탄소는 일본분지, 울릉분지, 야마토분지 순으로 높은 값이 나타나는데, 이는 중층수 순환의 형태와 그 분포가 일치한다. 2000 m 보다 깊은 수심의 저층수에서는 방사성탄소가 분지별로 뚜렷한 차이 없이 모든 분지에서 -80~-60‰ 내의 값을 보인다. 동해 표층수에서는 시간에 따라 매년 약 2‰씩 ${\Delta}^{14}C$ 값이 감소하였다. 반면, 동해 심층에서의 방사성탄소는 세개의 분지 모두 시간에 따라 증가하고 있다. 동해 중앙수의 방사성탄소는 매년 약 3.3‰ 증가하고 있는데, 이는 심층수나 저층수보다 시간에 따라 빠르게 증가한다. 심층수와 저층수에서는 방사성탄소가 1990년대 중반까지 증가하다가 1995년 이후로는 거의 증가하지 않고 일정한 값을 보인다. 심층수와 저층수에서의 ${\Delta}^{14}C$ 값의 시간에 따른 변화는 동해의 심층수 형성의 시간적 변화와 연관지어 해석되어야 할 것이다. 향후 동해 해수순환의 변화를 이해하기 위하여 방사성탄소 연구가 지속되어야 할 것이다.