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30 June 2018, Volume 30 Issue 2 Previous Issue    Next Issue

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Classification of auroral images based on convolutional neural network Wang Fei, Yang Qiuju 2018, 30 (2):  123-131.  DOI: 10.13679/j.jdyj.20170038 Abstract ( 726 )   PDF (5787KB) ( 862 )   Auroral light is the result of charged particles interacting with the magnetosphere and ionosphere. Proper classification of complex morphological all-sky auroral images is meaningful for studying the relationship between electromagnetic activity and energy coupling. To address these issues, a method of deep learning based on a convolutional neural network was proposed to explore the feature space of auroral data and to achieve automatic auroral recognition. The representation method was used in automatic recognition of four primary categories of aurora observed in 2003 at the Yellow River Station. The supervised classification accuracy rates on labeled data between dataset1 and dataset2 were 93.17% and 91.5%, respectively. The occurrence distributions of the four categories obtained through automatic classification of data from 2004–2009, were consistent with the spectral energy distribution excited by three bands. The experimental results showed that the presented representation method is effective for automatic auroral image recognition. Related Articles | Metrics

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Climatological characteristics of planetary boundary layer height at Jan Mayen, Arctic Zhang Xiang, Zhang Yehui, Han Jingbo, Zhang Le, Shi Wanrong 2018, 30 (2):  132-139.  DOI: 10.13679/j.jdyj.20170042 Abstract ( 648 )   PDF (1383KB) ( 741 )   Based on 43 years’ data of twice-daily radiosonde observations, this study investigated the temporal variability of the planetary boundary layer height (PBLH) at Jan Mayen, Norway, based on the Bulk Richardson Number method. It was found that the PBLH during daytime was higher than at night for most months. In addition, the monthly averaged PBLH in summer (around 262 m) was found much lower than in spring or winter (about 600 m). The PBLH variations showed good anticorrelation with surface relative humidity. Because of the influence of the Gulf Stream, the annual temperature difference at the Jan Mayen station is quite small and the surface temperature shows little seasonal variation. Surface relative humidity exhibits considerable seasonal variation, with a maximum value in summer and a minimum value in winter. The higher humidity in summer causes higher latent heat flux that restrains the convective process in the boundary layer, which leads to the lower summer PBLH. The long-term changes in PBLH at the studied station also revealed some interesting results. The annual mean PBLH decreased from 1973 to 1988, increased rapidly between 1988 and 1995, and then fluctuated between 500 and 600 m after 1995. Related Articles | Metrics

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Characteristics of katabatic winds in Terra Nova Bay, Antarctica Sun Qizhen, Zhang Zhanhai, Ding Zhuoming, Shen Hui, Zhang Lin, Meng Shang 2018, 30 (2):  140-153.  DOI: 10.13679/j.jdyj.20170026 Abstract ( 1321 )   PDF (25216KB) ( 613 )   Terra Nova Bay (TNB), Antarctica, is one of the confluence zones where strong katabatic winds are intense. In this paper, data from the high-resolution Antarctic mesoscale prediction system (AMPS) and automatic weather station (AWS) Manuela on Inexpressible Island in TNB are used to analyze the characteristics of katabatic winds in these areas. The AMPS shows good capability in simulating wind speed and air temperature at Inexpressible Island; however, the simulated wind direction is about 30° further westward than measured. The wind speed at Inexpressible Island increases rapidly from January and it is maintained at a high level during April–September. Data from the Manuela AWS indicate the strongest winds lag the lowest temperatures by about 3 h in January, and in winter, the measured wind direction is mostly west-southwest. Katabatic winds in TNB and the surrounding area are derived from the higher ice sheet to the west, and the spatial distribution of the wind direction rarely changes with season. The wind speed shows considerable seasonal variation; winds are generally a breeze during November–January, before increasing during March–September. In winter, katabatic winds form confluence zones at several glaciers near the coast of TNB, and Inexpressible Island is affected by katabatic winds from the Reeves Glacier. Boundaries are clear in the upper, northern, and southern sides of the katabatic winds areas of the Reeves Glacier. Strong katabatic winds extend from the surface to 650–800 m above ground level (AGL), and the core of the maximum wind speed is located at about 50–200 m AGL. Strong katabatic winds can be weakened because of the terrain of Inexpressible Island. The surface potential temperature differs little from the inland plateau to the coastal area near TNB, indicating a dry adiabatic process within the march of the katabatic winds in these areas. Related Articles | Metrics

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Variation of sea ice motion velocity in the Ross Sea (1979–2015) Liu Yige, Ke Changqing, Zhang Jie 2018, 30 (2):  154-160.  DOI: 10.13679/j.jdyj.20170021 Abstract ( 1134 )   PDF (1329KB) ( 937 )   Using data of monthly mean sea ice motion velocity and sea ice concentration, provided by the National Snow and Ice Data Center, we established the temporal variation of sea ice motion velocity in the Ross Sea (1979–2015). The interannual and seasonal variational characteristics of sea ice motion velocity were revealed, as was the relationship between sea ice motion velocity and sea ice extent. Finally, the factors influencing the variation of sea ice motion velocity were analyzed. The results showed that sea ice motion velocity in the Ross Sea increased during 1979–2015; the rate of increase was fastest in autumn, followed by winter, spring, and summer. The average motion velocity of sea ice in winter was highest, followed by autumn, spring, and summer. The sea ice motion velocity and sea ice extent both showed increasing trends over the 37-year period. Although the variation of sea ice motion velocity lagged sea ice extent by 1–2 months, significant positive correlation was found between them, and the increase of sea ice motion velocity caused the extent of sea ice to expand, affecting the distribution of Antarctic sea ice. Significant positive correlation was found between sea ice motion velocity and wind speed in the Ross Sea, indicating that the wind field was a factor contributing directly to the variation of sea ice motion velocity. In addition, sea ice motion was also affected by the pressure field, ocean currents, and ocean drag coefficient. Related Articles | Metrics

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Analysis of spatiotemporal variability of sea ice in the Beaufort Sea using passive microwave remote sensing data Liu Yue, Pang Xiaoping, Zhao Xi, Su Chuqin, Ji Qing 2018, 30 (2):  161-172.  DOI: 10.13679/j.jdyj.20170036 Abstract ( 815 )   PDF (7331KB) ( 711 )   Based on daily and monthly sea ice concentration data, obtained from the National Snow and Ice Data Center, the 15% sea ice concentration limit in the Beaufort Sea was used as a threshold to determine the location of the sea ice edge. After extracting the sea ice edge, we calculated the sea ice concentration, sea ice extent, and sea ice area. We then analyzed the spatiotemporal variabilities and trends of the retreat of the ice edge in the Beaufort Sea through interannual and seasonal changes. The results showed that sea ice concentration, sea ice extent, and sea ice area in the Beaufort Sea during 1978–2015 all had significant trends of reduction. During the study period, sea ice concentration decreased by an average of about 0.3%·a–1, sea ice extent decreased by an average of 3 235 km2·a–1, and sea ice area decreased by an average of 5 084 km2·a–1. Sea ice concentration during 1979–1996 showed no significant trend of decrease, although a trend of reduction was evident during 1996–2015. The sea ice extent in the Beaufort Sea is at its maximum between November and May (full ice coverage) and at its minimum in September. The sea ice area reaches its minimum in September and its maximum in December or January. The time of minimum sea ice extent appears to have become delayed. The state of total ice cover has tended to begin later, end earlier, and its duration (average: 212 d) has become shorter. Related Articles | Metrics

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Research on the navigability of the Arctic Northeast Route based on sea ice conditions during the passage of M/V Yong Sheng Ma Long, Li Zhenhua, Chen Guanwen, Li Yilin 2018, 30 (2):  173-185.  DOI: 10.13679/j.jdyj.20170017 Abstract ( 893 )   PDF (2854KB) ( 880 )   Sea ice condition is critical in developing and using Arctic passages. In this study, sea ice concentration products (2006–2015) from The University of Bremen in Germany were considered, and the sea ice regime along the route of M/V Yong Sheng in 2013 was extracted (route navigational window, spatial distribution of daily sea ice concentration, and monthly standard deviation of sea ice concentration). Then, the basic conditions of the navigational window of the route from 2006 to 2015 were analyzed. The general navigable conditions, main locations of ice barriers from 2006 to 2015, and fluctuations of sea ice concentration of the waters from July to October were established. Furthermore, the key areas affecting the navigability of the Arctic Northeast Passage were determined, and the trends of the navigational window of the route of M/V Yong Sheng and the key areas were determined. Related Articles | Metrics

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Study on drying characteristics of Antarctic krill Zhang Junwen, Zheng Xiaowei, Shen Jian, Ouyang Jie, Gao Xiang, Zhou Chunsheng, Tan Jiayu 2018, 30 (2):  186-191.  DOI: 10.13679/j.jdyj.20170025 Abstract ( 791 )   PDF (508KB) ( 762 )   Antarctic krill is rich as a resource and rich in nutrients. It is considered the reserve protein bank for human survival. Therefore, the question of how to ensure efficient use of this resource has become a focus of current scientific and technological research. Both the drying curve and the drying rate curve of Antarctic krill were studied under the condition of a constant temperature of 120℃, and hot air drying was undertaken to simulate the conditions of the Antarctic sea area. The results showed that under constant drying conditions, the drying rate was 0.497 g·cm–2·min–1, the critical water content was 0.56, and constant drying time accounted for about 1/3 of the total time. When the moisture content was lower than a critical value, the material entered the drying stage. In addition, the drying rate of Antarctic krill was found related to both the drying temperature and the drying surface area of the material. The drying rate and the surface area of Antarctic krill are accelerated by an increased drying rate, which has important implications and significance regarding equipment design and the actual production of Antarctic krill as a food resource. Related Articles | Metrics

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Identification of Antarctic fish from the sea adjacent to Yelcho Station based on DNA barcoding Li Yuan, Zhang Ran, Song Puqing, Li Hai, Chen Jian, Lin Longshan 2018, 30 (2):  192-197.  DOI: 10.13679/j.jdyj.20170010 Abstract ( 739 )   PDF (907KB) ( 651 )   As an important part of the Antarctic Ocean ecosystem, Antarctic fish play a role in material cycling and the energy flow within the food web. Individual Antarctic fish specimens were collected from the sea adjacent to Yelcho Station during the 32nd Chinese National Antarctic Research Expedition, and morphological analysis and DNA barcoding were employed in their identification. After running blast searches in NCBI, sequence similarity results showed that only two individuals were identifiable to the species level, while six individuals were unmatched. Combined with a homologous sequence from GenBank, phylogenetic analysis was performed and four groups were unambiguously identified from the NJ tree. There was clear overlap (barcoding gap) between intraspecific and interspecific variabilities in each species, as the smallest interspecific divergences were well below 2%, while the largest intraspecific divergences were above 2%. Three valid species were detected from eight individuals, encompassing seven Nototheniidae fish and one Harpagiferidae fish. Finally, all results further confirmed that notothenioid fish were dominant in terms of species diversity and biomass in the investigated seas. Related Articles | Metrics

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Reality and influence of Antarctic search and rescue system and the response of China Dong Yue, Ge Longwen 2018, 30 (2):  199-209.  DOI: 10.13679/j.jdyj.20170028 Abstract ( 729 )   PDF (2726KB) ( 713 )   With the increase of various activities in Antarctic, such as scientific research, tourism, and fishing, the questions of how best to avoid and reduce emergency cases and to improve rescue activities have become of great importance. IMO and ICAO divide the globe based on search and rescue plans, the five countries nearest Antarctica (Australia, New Zealand, Chile, Argentina, and South Africa) have developed Antarctic search and rescue system. The search and rescue responsibilities of states are governed by the standards and recommended practices contained in 4 conventions. Based on five countries’ own search and rescue systems and extensive international cooperation, this system has been working successfully and contributing. Under the current framework of the Antarctic Treaty System, it is important to note that search and rescue activities in Antarctica will contribute substantially to Antarctic security. Besides, increasing participation in Antarctic activities will also definitely expand the presence of the relevant countries in Antarctica. As one of the main participants in Antarctic activities, China has important regional interests. Therefore, it is necessary for China to strengthen its presence and influence in Antarctica via increasing its participation in Antarctic search and rescue activities as well as updating relative equipment and abilities. Related Articles | Metrics

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Cold trap technique for collecting atmospheric water vapor and its applications in the study of water stable isotopes Hu Jiaquan, Pang Hongxi 2018, 30 (2):  210-219.  DOI: 10.13679/j.jdyj.20170043 Abstract ( 770 )   PDF (1142KB) ( 788 )   This study systematically introduces the cold trap technique for use in the collection of atmospheric water vapor, including its basic principles, experimental methods, error estimates, and applications in the study of water stable isotopes. Atmospheric water vapor can condense completely in the cold trap by increasing both the condensation surface area (by filling with small glass beads) and the condensation time under conditions of cold temperature (−80℃). The condensed water sublimates or evaporates by heating the cold trap, and then the sublimated or evaporated water vapor re-condenses in a sample bottle under vacuum conditions and cold temperatures (−80℃). The error of the stable isotopic composition in the collected water vapor derives mainly from two aspects: the lost saturated vapor during collection and the ambient air in the bottle mixed with the sampled water. The magnitudes of the above two errors were estimated theoretically in the study. Water vapor collection using a cold trap has important applications in the study of water stable isotopes including achieving high-accuracy δ17O data in atmospheric water vapor, obtaining high-accuracy isotopic composition of atmospheric water vapor in the remote areas of polar ice sheets where vapor concentration is very low, and verifying the isotopic measurements of atmospheric water vapor by laser absorption spectrometers. Related Articles | Metrics