Hydrodynamic effect of the regulation project of Yangtze River deepwater channel downstream of Nanjing

A two-dimensional flow numerical model of the tidal reaches, which total length is more than 700 km, is established from Datong to the Yangtze River estuary. The tidal levels, velocities, diversion ratios and dynamic axes before and after the separate regulation of each reach and combined regulation of all reaches are obtained. The comparative analysis shows that the regulation project of a separate reach basically has no impact on velocity distributions and variations of diversion ratios of upper and lower reaches, the variations of dynamic axes are only within the local scope of the project. The regulation project of a separate reach also has less impact on the water level in the lower adjacent reaches, but will make the water levels in the upper reaches rise. After the implementation of the regulation projects for all reaches, the rise of water level in the upstream reaches will have a cumulative impact.     

历次核试验进入海洋的~(137)Cs对中国近海影响的模拟研究

1945年以来,世界各主要核国家进行了数千次核试验,这些核试验产生的绝大部分放射性物质通过多种途径进入海洋,对海洋环境造成放射性污染。本文建立了一个准全球海洋的放射性物质输运和扩散数值模式,通过数值模拟手段评估了历史核试验释放的放射性物质137 Cs对中国近海海洋环境的影响。本文借助前人工作评估了核试验释放137Cs进入海洋的途径和总量;通过比较模拟结果与观测资料,表明本文建立的放射性物质模式能够较好地模拟出137Cs在中国近海及其邻近海域的分布情况和随时间演变特征;模拟结果表明中国近海里的137Cs浓度在20世纪50年代中期达到最大,其中吕宋海峡海域137Cs浓度最高,达80.99Bq/m3;进一步分析了2011年3月份日本福岛核事故前中国近海137Cs浓度分布状况,2011年整个中国近海137Cs浓度介于1.0~1.6Bq/m3间,且其浓度垂向分布较均匀,相对封闭的南海浓度略高于其他海域。     

吕宋海峡内波吸引子的三维数值模拟

Internal waves propagate along wave beams that are inclined with respect to the horizontal plane. It is conjectured that the internal waves generated in the Luzon Strait may be confined between the double ridges in the strait and concentrate to a closed trajectory, the so-called internal wave attractor, due to the reflection of wave beams from the lateral boundaries, sea surface and bottom. This work carried out two experiments using a three dimensional non-hydrostatic general circulation model, MITgcm, to investigate the possibility that the ridges in the Luzon Strait allows for internal wave attractors. Baroclinic current in both of the experiments demonstrate the forming of ring-like patterns in some section around 20° and 21°N, indicating that the development of the internal wave attractors are allowed in the Luzon Strait. The different resolutions and initial conditions in the two experiments also reveal that the internal-wave-attractor phenomenon is robust in this region.     

Simulation of the extreme waves generated by typhoon Bolaven (1215) in the East China Sea and Yellow Sea

Record-breaking high waves occurred during the passage of the typhoon Bolaven (1215) (TYB) in the East China Sea (ECS) and Yellow Sea (YS) although its intensity did not reach the level of a super typhoon. Winds and directional wave measurements were made using a range of in-situ instruments mounted on an ocean tower and buoys. In order to understand how such high waves with long duration occurred, analyses have been made through measurement and numerical simulations. TYB winds were generated using the TC96 typhoon wind model with the best track data calibrated with the measurements. And then the wind fields were blended with the reanalyzed synoptic-scale wind fields for a wave model. Wave fields were simulated using WAM4.5 with adjustment of C_d for gust of winds and bottom friction for the study area. Thus the accuracy of simulations is considerably enhanced, and the computed results are also in better agreement with measured data than before. It is found that the extremely high waves evolved as a result of the superposition of distant large swells and high wind seas generated by strong winds from the front/right quadrant of the typhoon track. As the typhoon moved at a speed a little slower than the dominant wave group velocity in a consistent direction for two days, the wave growth was significantly enhanced by strong wind input in an extended fetch and non-linear interaction.     

High-contrast coronagraph for ground-based imaging of Jupiter-like planets

We propose a high-contrast coronagraph for direct imaging of young Jupiter-like planets orbiting nearby bright stars. The coronagraph employs a steptransmission filter in which the intensity is apodized with a finite number of steps with identical transmission in each step. It should be installed on a large ground-based telescope equipped with a state-of-the-art adaptive optics system. In this case, contrast ratios around 10-6 should be accessible within 0.1 arcsec of the central star. In recent progress, a...     

Modeling Research of the 27-day Forecast of 10.7 cm Solar Radio Flux (I)

Adopting the autoregressive method for time-series modeling, we have made a study on the medium-term forecast of solar 10.7 cm radio flux (F10.7). The result of forecast experiments and the error analysis indicate that when the solar activity is at a rather low level and the 27-day periodicity of F10.7 is apparent, the autoregressive forecast method has a high accuracy and relatively ideal effectiveness, but when a large active region appears or disappears on the solar dusk, the forecast effectiveness is not ideal. This means that the autoregressive method for the time-series modeling can reflect well the 27-day periodicity of F10.7, and that it has certain applicability for building a mediumterm forecast model of F10.7. By comparing the forecast results in the period from 21th September 2005 to 7th June 2007, it is demonstrated that the accuracy of the autoregressive forecast method is equivalent to that of the forecast made by the American Air Force.     

The improvement of the one-dimensional Mellor-Yamada and K-profile parameterization turbulence schemes with the non-breaking surface wave-induced verticalmixing

Both the level 2.5 Mellor-Yamada turbulence closure scheme(MY) and K-profile parameterization(KPP) are popularly used by the ocean modeling community.The MY and the KPP are improved through including the non-breaking surface wave-induced vertical mixing(Bv),and the improved schemes were tested by using continuous data at the Papa ocean weather station(OWS) during 1961–1965.The numerical results showed that the Bv can make the temperature simulations fit much better with the continuous data from Papa Station.The two improved schemes overcame the shortcomings of predicting too shallow upper mixed layer depth and consequently overheated sea surface temperature during summertime,which are in fact common problems for all turbulence closure models.Statistical analysis showed that the Bv effectively reduced the mean absolute error and root mean square error of the upper layer temperature and increased the correlation coefficient between simulation and the observation.Furthermore,the performance of vertical mixing induced by shear instability and the Bv is also compared.Both the temperature structure and its seasonal cycle significantly improved by including the Bv,regardless of whether shear instability was included or not,especially for the KPP mixing scheme,which suggested that Bv played a dominant role in the upper ocean where the mean current was relatively weak,such as at Papa Station.These results may provide a clue to improve ocean circulation models.     

FIO-ESM v2.0 CORE2-forced experiment for the CMIP6 Ocean Model Intercomparison Project

We introduced the Coupled Model Intercomparison Project Phase 6 (CMIP6) Ocean Model Intercomparison Project CORE2-forced (OMIP-1) experiment by using the First Institute of Oceanography Earth System Model version 2.0 (FIO-ESM v2.0), and comprehensively evaluated the simulation results. Unlike other OMIP models, FIO-ESM v2.0 includes a coupled ocean surface wave component model that takes into account non-breaking surface wave-induced vertical mixing in the ocean and effect of surface wave Stokes drift on air-sea momentum and heat fluxes in the climate system. A sub-layer sea surface temperature (SST) diurnal cycle parameterization was also employed to take into account effect of SST diurnal cycle on air-sea heat ?uxes to improve simulations of air-sea interactions. Evaluations show that mean values and long-term trends of significant wave height were adequately reproduced in the FIO-ESM v2.0 OMIP-1 simulations, and there is a reasonable fit between the SST diurnal cycle obtained from in situ observations and that parameterized by FIO-ESM v2.0. Evaluations of model drift, temperature, salinity, mixed layer depth, and the Atlantic Meridional Overturning Circulation show that the model performs well in the FIO-ESM v2.0 OMIP-1 simulation. However, the summer sea ice extent of the Arctic and Antarctic is underestimated.     

Characteristics of sea ice kinematics from the marginal ice zone to the packed ice zone observed by buoys deployed during the 9th Chinese Arctic Expedition

Sea ice growth and consolidation play a significant role in heat and momentum exchange between the atmosphere and the ocean. However, few in situ observations of sea ice kinematics have been reported owing to difficulties of deployment of buoys in the marginal ice zone (MIZ). To investigate the characteristics of sea ice kinematics from MIZ to packed ice zone (PIZ), eight drifting buoys designed by Taiyuan University of Technology were deployed in the open water at the ice edge of the Canadian Basin. Sea ice near the buoy constantly increased as the buoy drifted, and the kinematics of the buoy changed as the buoy was frozen into the ice. This process can be determined using sea ice concentration, sea skin temperature, and drift speed of buoy together. Sea ice concentration data showed that buoys entered the PIZ in mid-October as the ice grew and consolidated around the buoys, with high amplitude, high frequency buoy motions almost ceasing. Our results confirmed that good correlation coefficient in monthly scale between buoy drift and the wind only happened in the ice zone. The correlation coefficient between buoys and wind was below 0.3 while the buoys were in open water. As buoys entered the ice zone, the buoy speed was normally distributed at wind speeds above 6 m/s. The buoy drifted mainly to the right of the wind within 45° at wind speeds above 8 m/s. During further consolidation of the ice in MIZ, the direct forcing on the ice through winds will be lessened. The correlation coefficient value increased to 0.9 in November, and gradually decreased to 0.7 in April.     

哈拉湖岩芯XRF扫描元素统计分析及其环境意义

青藏高原东北缘高山湖泊哈拉湖是位于季风与西风影响的交汇带的封闭深水湖泊,是区域环境和气候变化的良好记录载体。目前对该湖的研究还较少,缺乏对沉积物中元素环境意义的系统认识。通过高分辨率XRF岩芯扫描,用相关、聚类和因子分析的方法对哈拉湖沉积岩芯地球化学元素进行分析。结果显示Ti、K、Si、Al、Fe、Mn等元素变化一致,相关性高,归为同一类,即径流输入的陆源碎屑组分,反映了流域水文状况如径流量的变化。Sr、Zr元素相关性高,为赋存在粗颗粒沉积物中的元素,根据哈拉湖实际,应为冬季湖泊冰面风力搬运,反映了湖区冬季风力强度的变化。Ca元素既与径流输入元素总体变化一致,也与Sr、Zr元素显著相关,且在第一和第二主成分(径流和风力)上的载荷相当,表明哈拉湖沉积物中的碳酸盐既有粗颗粒的外源碎屑,也有湖泊自生的组分,这在利用碳酸盐进行地球化学研究时应重视,注意去除外源碎屑碳酸盐的影响。可溶元素S和Cl可能反映了入湖水量与蒸发对比情况,与湖泊盐度有关。