2013 Vol. 32, No. 11

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2013, 32(11): .
2013, 32(11): .
Acta Oceanologica Sinica (AOS) is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.
The diel verticalmigration of sound scatterers observed by an acoustic Doppler current profiler in the Luzon Strait from July 2009 to April 2011
YANG Chenghao, LIAO Guanghong, YUAN Yaochu, CHEN Hong, ZHU Xiaohua
2013, 32(11): 1-9. doi: 10.1007/s13131-013-0371-8
Acoustic Doppler current profiler (ADCP) receives echoes from sound scatterers, then their speed is calculated by the Doppler effect. In the open ocean, most of these backscatterers are from the plankton. The sound scatterers descend down to depth at around dawn, their mean speed is 2.9 cm/s, then they ascend up to the surface layer at around dusk with a mean speed of 2.1 cm/s, in the Luzon Strait. The descending speed is faster, which suggests that this zooplankton population may accelerate its downward migration under the action of the gravity. The vertical distribution of a mean volume backscattering strength (MVBS) in the nighttime has two peaks, which locate near the upper and lower boundary layers of halocline, respectively. However, the backscatterers only aggregate near the surface layer in the daytime. The diel vertical migration (DVM) of sound scatterers has several characteristic patterns, it is stronger in summer, but weaker in winter, and the maximum peak occurs in September. The DVM occurrence is synchronous with the seawater temperature increasing at around dawn and dusk, it may affect the ocean mixing and water stratification.
Rainfall effect on wind waves and the turbulence beneath air-sea interface
ZHAO Dongliang, MA Xin, LIU Bin, XIE Lian
2013, 32(11): 10-20. doi: 10.1007/s13131-013-0372-7
Rainfall effects on wind waves and turbulence are investigated through the laboratory experiments in a large wind-wave tank. It is found that the wind waves are damped as a whole at low wind speeds, but are enhanced at high wind speeds. This dual effect of rain on the wind waves increases with the increase of rain rate, while the influence of rainfall-area length is not observable. At the low wind speed, the corresponding turbulence in terms of the turbulent kinetic energy (TKE) dissipation rate is significantly enhanced by rainfall as the waves are damped severely. At the high wind speed, the augment of the TKE dissipation rate is suppressed while the wind waves are enhanced simultaneously. In the field, however, rainfall usually hinders the development ofwaves. In order to explain this contradiction of rainfall effect on waves, a possibility about energy transfer fromturbulence to waves in case of the spectral peak ofwaves overlapping the inertial subrange of turbulence is assumed. It can be applied to interpret the damping phenomenon of gas transfer velocity in the laboratory experiments, and the variation of the TKE dissipation rates near sea surface compared with the law of wall.
Impacts of sea spray on the boundary layer structure of Typhoon Imbudo
TANG Jie, LI Weibiao, CHEN Shumin, WANG Lei
2013, 32(11): 21-26. doi: 10.1007/s13131-013-0373-6
High winds in a typhoon over the ocean can produce substantial amounts of spray in the lower part of the atmospheric boundary layer, which can modify the transfer of momentum, heat, and moisture across the air-sea interface. However, the consequent effects on the boundary layer structure and the evolution of the typhoon are largely unknown. The focus of this paper is on the role of sea spray on the stormintensity and the structure of the atmospheric boundary layer. The case study is Typhoon Imbudo in July 2003. The results show that sea spray tends to intensify storms by increasing the sea surface heat fluxes. Moreover, the effects of sea spray are mainly felt in boundary layer. Spray evaporation causes the atmospheric boundary layer to experience cooling and moistening. Sea spray can cause significant effects on the structure of boundary layer. The boundary-layer height over the eyewall area east to the center of Typhoon Imbudo was increased with a maximum up to about 550 mdue to sea spray, which is closely related with the enhancements of the heat fluxes, upwardmotions, and horizontalwinds in this region due to sea spray.
First six months quality assessment of HY-2A SCAT wind products using in situ measurements
WANG He, ZHU Jianhua, LIN Mingsen, HUANG Xiaoqi, ZHAO Yili, CHEN Chuntao, ZHANG Youguang, PENG Hailong
2013, 32(11): 27-33. doi: 10.1007/s13131-013-0374-5
The first Chinese microwave ocean environment satellite HY-2A, carrying a Ku-band scatteromenter (SCAT), was successfully launched in August 2011. The first quality assessment of HY-2A SCAT wind products is presented through the comparison of the first 6 months operationally released SCAT products with in situ data. The in situ winds fromtheNationalData Buoy Center (NDBC) buoys, R/V Polarstern, Aurora Australis, Roger Revelle and PY30-1 oil platform, were converted to the 10 m equivalent neutral winds. The temporal and spatial differences between the HY-2A SCAT and the in situ observations were limited to less than 5 min and 12.5 km. For HY-2A SCAT wind speed products, the comparison and analysis using the NDBC buoys yield a bias of -0.49 m/s, a root mean square error (RMSE) of 1.3 m/s and an increase negative bias with increasing wind speed observation above 3m/s. Although less accurate of HY-2A SCAT wind direction at low winds, the RMSE of 19.19° with a bias of 0.92° is found for wind speeds higher than 3 m/s. These results are found consistent with those fromR/Vs and oil platformcomparisons. Moreover, the NDBC buoy comparison results also suggest that the accuracy of HY-2A SCAT winds is consistent over the first half year of 2012. The encouraging assessment results over the first 6 months show that wind products from HY-2A SCAT will be useful for scientific community.
An oil slick spectral experiment of nearshore sea water in the East China Sea
WANG Difeng, PAN Delu, GONG Fang, WANG Tianyu, ZHAN Yuanzeng
2013, 32(11): 34-40. doi: 10.1007/s13131-013-0375-4
Alongwith the rapid advance in global industrialization,oil spill events caused by offshoreoperations, transportation and accidents are increasing. Compared with ship surveys, monitoring oil spills through remote sensing has real-time, comprehensive, low-cost advantages,which can effectively guide cleaning and evaluation, and reduce themarine ecological destruction resulting fromoil spills. Therefore, studying the remote sensing mechanism used to monitor marine oil spills is of great significance for ecological environmental protection. This paper describes an experiment and corresponding analysis based on the above-water method, using the East China Sea coastal turbid water. The analysis shows that "upward short-wave" in ultraviolet and blue-purple bands and its displacement, along with the changing thickness, are important characteristics for distinguishing between the oil slick and the sea water, and also to differentiate oil slicks of different thicknesses. Fromblue to near-infrared bands, the spectrumof lube oil is flatter than that of diesel, and the diesel spectrumrises faster than the lube spectrumon the right side of the trough at 400 nm. These two features forman important basis for differentiating diesel fromlube oil. These analyses will further the development of oil spill remote sensing in the East China Sea.
A comparison of summer precipitation structures over the South China Sea and the East China Sea based on tropical rainfall measurementmission
LI Jiangnan, YANG Chaofeng, LI Fangzhou, HE Qihua, LI Weibiao
2013, 32(11): 41-49. doi: 10.1007/s13131-013-0376-3
The three-dimensional structures of summer precipitation over the South China Sea (SCS) and the East China Sea (ECS) are investigated based on tropical rainfall measurement mission (TRMM). The primary results are as follows. First, both the convective and stratiformprecipitationrates in the SCS aremuch higher than those of the ECS. The contribution of the convective cloud precipitation to the surface precipitation is primarily over the SCS and the ECS with a proportion of about 70%, but the contribution of convective cloud precipitation is slightly larger in the SCS than the ECS. The contribution of stratus precipitation is slightly larger in the ECS than that in the SCS. Second, the content of cloud particles and precipitation particles in the ECS in June was greater than that in the SCS, while in July and August, the content of cloud and precipitation particles in the ECS was less than that in the SCS. Third, the latent heat profile of the ECS is quite different fromthat of the SCS. In June, the peak values of evaporation and condensation latent heating rates in the ECS are greater than those in the SCS. In July and August, however, the peak values of evaporation and condensation latent heating rates in the ECS are about 0.05°/h less than those in the SCS.
Discrete elementmodeling of ice loads on ship hulls in broken ice fields
JI Shunying, LI Zilin, LI Chunhua, SHANG Jie
2013, 32(11): 50-58. doi: 10.1007/s13131-013-0377-2
Ice loads on a ship hull affect the safety of the hull structure and the ship maneuvering performance in ice-covered regions. A discrete element method (DEM) is used to simulate the interaction between drifting ice floes and a moving ship. The pancake ice floes are modelled with three-dimensional (3-D) dilated disk elements considering the buoyancy, drag force and additional mass induced by the current. The ship hull is modelled with 3D disks with overlaps. Ice loads on the ship hull are determined through the contact detection between ice floe element and ship hull element and the contact force calculation. The influences of different ice conditions (current velocities and directions, ice thicknesses, concentrations and ice floe sizes) and ship speeds are also examined on the dynamic ice force. The simulated results are compared qualitatively well with the existing field data and other numerical results. This work can be helpful in the ship structure design and the navigation security in ice-covered fields.
Geographical distribution and age composition of Euphausia superba larvae (Crustacea:Euphausiacea) in the South Shetland Islands region and southern Scotia Sea in relation to environmental conditions
GAO Qian, XU Zhaoli, HUANG Hongliang, CHEN Xuezhong, FENG Chunlei, LI Lingzhi
2013, 32(11): 59-67. doi: 10.1007/s13131-013-0377-2
Spatial distribution patterns of the different life stages of Euphausia superba in the region of the South Shetland Islands and southern Scotia Sea (Antarctica) were assessed based on scientific survey data collected in January and February of 2010. Adults, eggs, nauplii, metanauplii, calyptopis Ⅰ-Ⅲ, and furcilia Ⅰ-Ⅱ were found in the investigation. The abundance of larvae averaged 1 172.8 ind./m2, with calyptopis Ⅰ and Ⅱ as the dominant stages. Habitat occupancy patterns varied among Euphausia superba at different stages, and three sub-regionswere identified by cluster analysis. The degree of larval development increased fromwest to east. Larvae were not observed north of the South Shetland Islands. Calyptopis I was predominant in the water between Elephant Island and the South Orkney Islands, which featured no thermocline. Older stages, including calyptopis Ⅱ and Ⅲ and furcilia Ⅰ and Ⅱ, were common in north and northeast of the South Orkney Islands, which were characterized by high temperature and high chlorophyll concentration. Distribution and abundance of the early life stages of E. superba were associatedwith specific environmental conditions. According to Biota-Environment matching (BIOENV), the distributions of E. superba larvae were correlated with a combination of temperature at the surface and 200m, and 0-100 mintegrated chlorophyll a concentration.
Research Notes
The physical simulation of wave groups and their variations in a wave flume
LIU Si, ZHANG Yongliang, LIU Shuxue, LI Jinxuan, XIA Zhisheng
2013, 32(11): 68-73. doi: 10.1007/s13131-013-0379-0
The physical simulation method of wave groups in a wave flume is proposed and verified by the experiments. The experimental results demonstrate that random waves with desired wave groupiness, which simultaneously includes the wave group height and length, can be generated satisfactorily at the specified position in a wave flume using the proposed method. Furthermore, the transformation properties of the wave groupiness along the flat-bottomed wave flume are investigated based on the physically simulated waves. Associated proposals with the physical simulation of wave groups are given.
The watermass variability and southward shift of the Southern Hemispheremid-depth supergyre
DUAN Yongliang, HOU Yijun, LIU Hongwei, LIU Yahao
2013, 32(11): 74-81. doi: DOI: 10.1007/s13131-013-0380-7
The Southern Hemisphere subtropical supergyre at intermediate depths connects all three ocean basins and plays a significant role in responding and conveying the climate-change-related variations in the global ocean. On the basis of the Simple Ocean Data Assimilation (SODA) ocean reanalysis, the thermohaline variability and southward shift of themid-depth supergyre are demonstrated. The steric height of the subsurface relative to 1 500 m (400-1 500 m) from the SODA depicts exactly the flow patterns and variability of the oceanic supergyre. During 1958-2007 the water masses in the gyre interiors become cooler/fresher, with the significant exceptions of the Agulhas Current system and Agulhas leakage. The results also exhibit a pronounced strengthening of the inter-basin connection of the supergyre, and the strongest southward shift, by about 2.5° over the whole period, occurs in the central-south Pacific, which is associated with the changes in the basin-scale wind forcing.
The validation of the significant wave height product of HY-2 altimeter-primary results
CHEN Chuntao, ZHU Jianhua, LIN Mingsen, ZHAO Yili, HUANG Xiaoqi, WANG He, ZHANG Youguang, PENG Hailong
2013, 32(11): 82-86. doi: 10.1007/s13131-013-0381-6
The HY-2 satellite was successfully launched on 16 August 2011. The HY-2 significant wave height (SWH) is validated by the data fromthe South China Sea (SCS) field experiment, National Data Buoy Center (NDBC) buoys and Jason-1/2 altimeters, and is corrected using a linear regressionwith in-situmeasurements. Compared with NDBC SWH, the HY-2 SWH show a RMS of 0.36 m, which is similar to Jason-1 and Jason-2 SWH with the RMS of 0.35mand 0.37mrespectively; the RMS of corrected HY-2 SWH is 0.27m, similar to 0.27 m and 0.23 mof corrected Jason-1 and Jason-2 SWH. Therefore the accuracy of HY-2 SWH products is close to that of Jason-1/2 SWH, and the linear regression function derived can improve the accuracy of HY-2 SWH products.
The validation of HY-2 altimetermeasurements of a significant wave height based on buoy data
WANG Jichao, ZHANG Jie, YANG Jungang
2013, 32(11): 87-90. doi: 10.1007/s13131-013-0382-5
HY-2 has been launched by China on August 16, 2011 which assembles multi-microwave remote sensing payloads in a body and has the ability of monitoring ocean dynamic environments. The HY-2 satellite data need to be calibrated and validated before being put into use. Based on the in-situ buoys fromthe National Data Buoy Center (NDBC), Ku-band significant wave heights (SWH, hs) of HY-2 altimeter are validated. Eleven months of HY-2 altimeter Level 2 products data are chose from October 1, 2011 to August 29, 2012. Using NDBC 60 buoys yield 902 collocations for HY-2 by adopting collocation criteria of 30 min for temporal window and 50 km for a spatial window. An overall RMS difference of the SWH between HY-2 and buoy data is 0.297 m. A correlation coefficient between these is 0.964. An ordinary least squares (OLS) regression is performed with the buoy data as an independent variable and the altimeter data as a dependent variable. The regression equation of hs is hs(HY-2)=0.891×hs (NDBC)+0.022. In addition, 2016 collocations are matched with temporal window of 30min at the crossing points of HY-2 and Jason-2 orbits. RMS difference of Ku-band SWH between the two data sets is 0.452 m.