Contrasting dynamic characteristics of shear turbulence and Langmuir circulation in the surface mixed layer

Large eddy simulation （LES） is used to investigate contrasting dynamic characteristics of shear turbulence （ST） and Langmuir circulation （LC） in the surface mixed layer （SML）. ST is usually induced by wind forcing in SML. LC can be driven by wave-current interaction that includes the roles of wind, wave and vortex forcing. The LES results show that LC suppresses the horizontal velocity and greatly modifies the downwind velocity profile, but increases the vertical velocity. The strong downweUing jets of LC accelerate and increase the downward transport of energy as compared to ST. The vertical eddy viscosity Km of LC is much larger than that of ST. Strong mixing induced by LC has two locations. They are located in the 26s-36s （Stokes depth scale） and the lower layer of the SML, respectively. Its value and position change periodically with time. In contrast, maximum Km induced by ST is located in the middle depth of the SML. The turbulent kinetic energy （TKE） generated by LC is larger than that by ST. The differences in vertical distributions of TKE and Krn are evident. Therefore, the parameterization of LC cannot be solely based on TKE. For deep SML, the convection of large-scale eddies in LC plays a main role in downward transport of energy and LC can induce stronger velocity shear （S2） near the SML base. In addition, the large-scale eddies and Sz induced by LC is changing all the time, which needs to be fully considered in the parameterization of LC.

Statistical characteristics of the surface ducts over the South China Sea from GPS radiosonde data

Based on the global position system （GPS） radiosonde data near the sea surface, the surface duct characteristics over the South China Sea （SCS） were statistically analyzed. The annual surface duct occurrence over the SCS was about 64%. Of the observed surface ducts, duct heights mainly distributed between 18 and 42 m, with M slopes in the range of -0.3 to -0.2 M units/m. Those ducts accounted for about 80% of the ducting cases. For the total profiles, the duct occurrences in a day changed slowly and were more than 60% in all times. The surface ducts formed more easily in the daytime than in the nighttime and most of the duct height were at bellow about 32 m. Additionally, The seasonal variation of the SCS ducts appeared to be evident, except that the mean duct thickness was almost constant, about 33 m for all seasons. The highest occurrence was about 71% in the autumn, followed by in the summer, spring and winter. In spring, their top-height existed more often at a height of more than 48 m. Their mean duct strength became stronger trend from spring to winter, with the M-slope in the range between -0.26 and -0.18 M units/m. Those results agreed well with other studies, provided considering the data resolution. The statistical analysis was reliable and gave the duct estimation for the SCS. Such duct climatology not only has important implications for communication systems and the reliability of the radar observation, but also can provide useful information to improve the accuracy of the meteorological radar measurements.

Comparison of summer chlorophyll a concentration in the South China Sea and the Arabian Sea using remote sensing data

The South China Sea（SCS） and the Arabian Sea（AS） are both located roughly in the north tropical zone with a range of similar latitude（0°–24°N）. Monsoon winds play similar roles in the upper oceanic circulations of the both seas. But the distinct patterns of chlorophyll a（Chl a） concentration are observed between the SCS and the AS.The Chl a concentration in the SCS is generally lower than that in the AS in summer（June–August）; the summer Chl a concentration in the AS shows stronger interannual variation, compared with that in the SCS; Moderate resolution imaging spectroradiometer（MODIS）-derived data present higher atmospheric aerosol deposition and stronger wind speed in the AS. And it has also been found that good correlations exist between the index of the dust precipitation indicated by aerosol optical thickness（AOT） and the Chl a concentration, or between wind and Chl a concentration. These imply that the wind and the dust precipitation bring more nutrients into the AS from the sky, the sub-layer or coast regions, inducing higher Chl a concentration. The results indicate that the wind velocity and the dust precipitation can play important roles in the Chl a concentration for the AS and the SCS in summer. However aerosol impact is weak on the biological productivity in the west SCS and wind-induced upwelling is the main source.

Synoptic-scale disturbances over the northern South China Sea and their responses to El Nio

Using surface and aerological meteorological observations obtained at the Xisha Automatic Weather Station and three moored buoys along the continental slope, characteristics of the synoptic-scale disturbances over the northern South China Sea （NSCS） are extensively studied. The power spectra of surface and aerological observations suggest a synoptic feature with a pronounced energy peak at a period of 5–8 d and a weak peak at 3–4 d. The standard deviation of the synoptic temperature component derived at Xisha Station from 1976 to 2011 indicates that the strongest variability normally exists in August all through the whole troposphere. At the interannual scale, it is found that El Nin o plays an important role in regulating the synoptic disturbances of atmosphere. The vertical synoptic disturbances have a double active peak following El Nin o condition. The first peak usually occurs during the mature phase of El Nin o, and the second one occurs in the summer of decay year. Comparing with the summer of developing years, the summer of the decaying year of El Nin o has more active and stronger synoptic disturbances, especially for the 5–8 d period variations.

Assimilating temperature and salinity profiles using Ensemble Kalman Filter with an adaptive observation error and T-S constraint

Temperature （T） and salinity （S） profiles from conductivity-temperature-depth data collected during the Northern South China Sea Open Cruise from August 16 to September 13, 2008 are assimilated using Ensemble Kalman Filter （EnKF）. An adaptive observational error strategy is used to prevent filter from diverging. In the meantime, aiming at the limited improvement in some sites caused by the T and S biases in the model, a T-S constraint scheme is adopted to improve the assimilation performance, where T and S are separately updated at these locations. Validation is performed by comparing assimilated outputs with independent in situ data （satellite remote sensing sea level anomaly （SLA）, the OSCAR velocity product and shipboard ADCP）. The results show that the new EnKF assimilation scheme can significantly reduce the root mean square error （RMSE） of oceanic T and S compared with the control run and traditional EnKF. The system can also improve the simulation of circulations and SLA.

不同型线的螺杆转子热力耦合分析研究

以不同类型螺杆真空泵转子为研究对象,建立了梯形齿转子和矩形齿转子的三维数模和有限元模型,在综合考虑热膨胀、气体压力、转子运动、温度等多因数作用下,进行转子的热力耦合分析,得到转子的温度场和热形变分布情况,并分析比较不同温度环境下不同类型转子的变形程度。研究结果表明:梯形齿型转子的多种形变量均相对较小,且分析得到的形变量可应用于螺杆转子冷态设计的热补偿中,为螺杆真空泵各处间隙的设计提供理论依据。

Diffusion Characteristics of Swells in the North Indian Ocean

Research on the diffusion characteristics of swells contributes positively to wave energy forecasting, swell monitoring, and early warning. In this work, the South Indian Ocean westerly index(SIWI) and Indian Ocean swell diffusion effect index(IOSDEI) are defined on the basis of the 45-year(September 1957–August 2002) ERA-40 wave reanalysis data from the European Centre for Medium-Range Weather Forecasts(ECMWF) to analyze the impact of the South Indian Ocean westerlies on the propagation of swell acreage. The following results were obtained: 1) The South Indian Ocean swell mainly propagates from southwest to northeast. The swell also spreads to the Arabian Sea upon reaching low-latitude waters. The 2.0-meter contour of the swell can reach northward to Sri Lankan waters. 2) The size of the IOSDEI is determined by the SIWI strength. The IOSDEI requires approximately 2–3.5 days to fully respond to the SIWI. The correlations between SIWI and IOSDEI show obvious seasonal differences, with the highest correlations found in December–January–February(DJF) and the lowest correlations observed in June–July–August(JJA). 3) The SIWI and IOSDEI have a common period of approximately 1 week in JJA and DJF. The SIWI leads by approximately 2–3 days in this common period.

践行“一带一路”新发展理念推动“中国-斯里兰卡联合科教中心”高质量发展

中国科学院完整准确全面贯彻新发展理念,布局“一带一路”科技合作,开拓性建设了10个海外中心,开展了一系列开创性的国际科技合作,与“21世纪海上丝绸之路”参与国家合作创新研究、培养科技创新人才,兼顾国际学术前沿与当地民生发展。文章以中国科学院中国-斯里兰卡联合科教中心高质量发展为例,阐述了共建“一带一路”10年来中斯科教融合高质量发展的成果,并对中斯科教合作的未来发展方向进行思考和提出建议。