Numerical experiments on estimating the accuracy of four-dimensional analysis of hydrophysical fields using a quasi-geostrophic model of currents

The relationship between the results of four-dimensional (4-D) analysis and the approximations employed in the assimilation scheme, as well as the initial fields, is studied. The contribution made by a procedure of correcting the horizontal velocities by theT, S data to the increase of the quality of the data obtained is estimated. Numerical experiments were carried out on the data of measurements made in the observation site located in the Newfoundland energy-active zone in August 1985.Translated by Mikhail M. Trufanov.     

Comparison of the Kalman smoothing technique with other ocean diagnostic methods

The use of the Kalman smoothing technique is suggested to handle an ocean diagnosis problem. It is shown that the variety of existing diagnostic techniques may be generalized, for which purpose the smoothing problem from the theory of optimal evaluation may be used.Translated by Vladimir A. Puchkin.     

The use of the Kalman smoothing algorithm for the analysis and processing of oceanographic data. Statement and methods of solution

It is suggested that the algorithm of Kalman smoothing is used to analyse and process oceanographic data. Two methods of solving the Kalman smoothing problem are given: an iteration method and a precise method. Their advantages and disadvantages are considered, as well as different cases and conclusions.Translated by Mikhail M. Trufanov.     

Numerical experiments on estimating the effect of non-linearity on long wave propagation over a seamount

In the context of the nonlinear, theory of long waves, we solve, using numerical techniques, a non-stationary problem on the barotropic wave propagation over an isolated bottom elevation. The time interval during which the wave process over an obstacle sets in is determined. The relative contributions of the non-linear terms to the model equations have been analysed. A practical criterion of applicability of the linear approximation to the problem examined has been formulated.Translated by Vladimir A. Puchkin.     

大连城市发展面临的水问题及解决途径浅析

文章通过对大连水资源的特点及利用现状的分析,总结出大连城市发展面临的水资源问题,短缺问题及水安全问题等;同时分析了缓解上述问题的四种解决途径,并对水资源问题的可缓解程度及其利弊进行了分析,最后提出,从长远观点看,加快海水利用产业的步伐为缓解大连市水资源问题的最佳途径。     

Numerical experiments on double-diffusive intrusions in the ocean and their relation to laboratory experiments

Numerical experiments on double-diffusive intrusions are reviewed briefly. Though the number of studies is very limited at present, they have undoubtedly an advantage that a heat–salt system can be studied without undesired heat loss from the boundaries.Several possibilities for future numerical experiments are summarized.     

Numerical experiments on dynamic stiffening of beams and plates

By introducing continuous or discontinuous variations in the thickness of beams, arches and plates, it is possible in many practical situations to raise the value of the fundamental frequency and, at the same time, to lower the weight of the structural element. This is a beneficial situation, especially in those cases where weight reduction and large dynamic stiffness are of interest. The present paper surveys some recent practical accomplishments in this area.The rigorous procedure consists, from a general structural optimization viewpoint, of minimizing an objective function (for instance, total volume) subject to constraints on the geometry and behavior (natural frequencies, buckling loads, etc.). In many instances it is convenient to reverse the problem: one fixes or limits the weight or volume and constructs some quantity which describes the desired behavior of the system e.g. the fundamental frequency.The problems under study in the present paper are considerably more modest in scope, since the procedure is performed by numerical experiments.     

Comparison of marine insolation estimating methods in the adriatic sea

We compare insolation results calculated from two well-known empirical formulas (Seckel and Beaudry’s SB73 formula and the original Smithsonian (SMS) formula) and a radiative transfer model using input data predicted from meteorological weather-forecast models, and review the accuracy of each method. Comparison of annual mean daily irradiance values for clear-sky conditions between the two formulas shows that, relative to the SMS, the SB73 underestimates spring values by 9 W m^-2 in the northern Adriatic Sea, although overall there is a good agreement between the annual results calculated with the two formulas. We also elucidate the effect on SMS of changing the ‘Sun-Earth distance factor (f)’, a parameter which is commonly assumed to be constant in the oceanographic context. Results show that the mean daily solar radiation for clear-sky conditions in the northern Adriatic Sea can be reduced as much as 12 W m^-2 during summer due to a decrease in thef value. Lastly, surface irradiance values calculated from a simple radiative transfer model (GM02) for clear-sky conditions are compared to those from SB73 and SMS. Comparison within situ data in the northern Adriatic Sea shows that the GM02 estimate gives more realistic surface irradiance values than SMS, particularly during summer. Additionally, irradiance values calculated by GM02 using the buoy meteorological fields and ECMWF (The European Centre for Medium Range Weather Forecasts) meteorological data show the suitability of the ECMWF data usage. Through tests of GM02 sensitivity to key regional meteorological factors, we explore the main factors contributing significantly to a reduction in summertime solar irradiance in the Adriatic Sea.     

Numerical experiments on low-frequency fluctuations on a submerged coastal reef

Low-frequency fluctuations on a reef coast are studied through a numerical model based on nonlinear conservation equations of mass and momentum. The model is used to investigate the long wave generation and propagation phenomena under both breaking and non-breaking incident short wave groups. The effects of incident wave characteristics and reef topography on the long wave phenomena are discussed. The results show that the long wave elevations on reef coasts are substantial, which explains the large water level fluctuations observed at certain occasions.     

Numerical experiments of swash oscillations on steep and gentle beaches

A weakly non-linear Boussinesq model with a slot-type shoreline boundary is used to simulate swash oscillations on beaches. Numerical simulations of swash were compared with laboratory measurements and in general good agreement found (less than 15% root-mean-square error of surface elevation except in regular waves). A series of numerical experiments on shoreline movement were then performed for a range of beach slopes and incident wave conditions. The resulting swash characteristics are then discussed in terms of their physical nature and spectral properties. On steep slopes, both individual bores and infragravity waves are equally significant in driving the swash while infragravity waves alone drive them on mild slopes. Swash excursions on any given slope are found to be highest when individual bores from a partially saturated surf zone ride on top of low-frequency waves. This is confirmed by the relationship found between swash excursion and wave groupiness in the surf zone. Swash excursions increase with increasing incident wave energy, even in fully saturated surf zones. However, a poor correlation is found between swash excursion and the surf similarity parameter due to the involvement of infragravity wave energy in the swash.     

Numerical experiments of internal tides in Suruga Bay

Numerical experiments were performed to explain the observed results of the internal tides in Uchiura Bay. The experiments for the generation of the internal tides in Suruga Bay indicate that the internal tides, generated at the slopes in the bay, are not as large an amplitude as those observed in Uchiura Bay. However, when the semidiurnal internal tides incident through the mouth of Suruga Bay are considered, they are amplified. The amplitude at the head of Uchiura Bay is 6–12 times larger than that at the mouth of Suruga Bay under the summer density structure. Under the fall density structure, the amplitude ratio is approximately 4–6. The amplification of the semidiurnal internal tides in Uchiura Bay is considered to be due to resonance of the longitudinal internal seiche of Uchiura Bay. On the other hand, the calculated diurnal internal tides are not as large as those observed. Therefore, the diurnal internal tides are thought to already have these large amplitudes at the mouth of Suruga Bay. Therefore, from the observations and numerical experiments, it is concluded that the internal tides observed in Uchiura Bay are mostly the internal tides originating from the outer region of Suruga Bay, and the semidiurnal tides are the internal seiche which is resonantly amplified.     

影响黄渤海的温带气旋数值集合预报试验

为了改进温带气旋数值预报的精度,基于WRF(Weather Research and Forecasting)模式,利用GSI(Gridpoint Statistical Interpolation)-EnKF(Ensemble Kalman Filter)系统,设计了一套温带气旋集合预报方法,其具有的2种选择方案通过滤掉质量较差的集合成员从而将集合成员数目控制在10以内,达到了大幅降低集合预报计算量的目的。针对2020年7月一次影响黄海的温带气旋个例,开展了一系列决定性预报与集合预报的数值对比试验。分析结果如下:1)不采取任何择优方案的集合预报效果就已经明显优于决定性预报,而采取择优方案使得预报效果进一步得到提升;2)预报初始时刻择优(直接择优方案)的集合预报效果远不如短时积分3 h后才进行择优(积分择优方案)的预报效果; 3)积分择优方案优于直接择优方案的原因是,初始场集合体中的成员经过短时积分后其误差得以放大而使得择优更加准确。多个例的应用结果进一步表明,本文提出的积分择优方案温带气旋集合预报方法具有较好的业务预报应用前景。     

NaCl 溶液闪蒸效率特性数值研究

盐水闪蒸技术广泛应用于海水淡化及海洋温差能发电,含盐质量分数、给盐液温度和闪蒸压力对闪蒸汽化率和热效率有很大影响。在质量分数为3.5%～20%、给盐液温度为30～95℃和闪蒸压力为1～30 kPa的范围内,对NaCl溶液闪蒸汽化率和热效率等闪蒸效率特性进行了定量计算研究,研究得到了盐水含盐质量分数、给盐液温度和闪蒸压力对闪蒸汽化率以及热效率影响的规律。结果表明,降低含盐质量分数,提高给盐液温度,降低闪蒸压力可提高闪蒸汽化率与热效率;含盐质量分数越高,造成的热损失越大,而提高给盐液温度会增大热损失。     

Numerical simulation and experiments of a probe descending in the sea

A numerical model, based on Reynolds equations, was developed to estimate the drag coefficient of a probe. The relation of the displacement of the probe and time was obtained applying the drag coefficients to equations governing the motion of the probe. Experiments were conducted for verification of the calculations. To count in the influence of probe's weight and seawater's density, numerical analysis were carried out. Results indicate both the change of probe's weight due to wire releasing and the difference of density of the different sea area have accumulated influence on the trace of probe and should not be neglected.     

Numerical experiments on wind-driven circulations and associated transport processes in Suruga Bay

The dynamics of the wind-driven circulations and surface transport processes in Suruga Bay have been examined by performing numerical experiments. While strong winds exist outside the bay, the winds inside the bays are greatly reduced, which generates a strong wind stress curl in winter and autumn. In particular, in winter, a strong positive curl region is located across the bay mouth, and a strong surface circulation with counterclockwise rotation is generated beneath it. The circulation is nearly geostrophic, but is not affected by the bottom topography in the deep bay. It is suggested that intense surface water exchange through the bay mouth occurs in winter, whereas it is not active in the other seasons when no significant vorticity is supplied on the bay mouth from the atmosphere. Moreover, we propose a hypothesis that the atmospheric wind stress curl will cause the frequent appearance of the counterclockwise circulation in winter in the real ocean.     

A comparison of the main methods for estimating probabilities of extreme still water levels

Sea-level return periods are estimated at 18 sites around the English Channel using: (i) the annual maxima method; (ii) the r-largest method; (iii) the joint probability method; and (iv) the revised joint probability method. Tests are undertaken to determine how sensitive these four methods are to three factors which may significantly influence the results; (a) the treatment of the long-term trends in extreme sea level; (b) the relative magnitudes of the tidal and non-tidal components of sea level; and (c) the frequency, length and completeness of the available data. Results show that unless sea-level records with lengths of at least 50 years are used, the way in which the long-term trends is handled in the different methods can lead to significant differences in the estimated return levels. The direct methods (i.e. methods i and ii) underestimate the long (> 20 years) period return levels when the astronomical tidal variations of sea level (relative to a mean of zero) are about twice that of the non-tidal variations. The performance of each of the four methods is assessed using prediction errors (the difference between the return periods of the observed maximum level at each site and the corresponding data range). Finally, return periods, estimated using the four methods, are compared with estimates from the spatial revised joint probability method along the UK south coast and are found to be significantly larger at most sites along this coast, due to the comparatively short records originally used to calibrate the model in this area. The revised joint probability method is found to have the lowest prediction errors at most sites analysed and this method is recommended for application wherever possible. However, no method can compensate for poor data.     

Numerical experiments of HAB inducement in Qingdao adjacent coastal area

A three-dimension ecological dynamic model was established to numerically study the relationship of HAB and environmental conditions.The numerical experiments showed that the growth of diatom,the dominant HAB specie,was mainly restricted by phosphate and silicate.If the concentrations of phosphate and silicate reach 17-25 μg/L and 300-375 μg/L respectively,the water is in a state of eutrophication.When phosphate and silicate up to 26-32 μg/L and 350-500 μg/L respectively,HAB could be induced.The major regions of HAB occurrence are Jiaozhou Bay mouth,coastal bays,and coastal area from Maidao to Shilaoren.To avoid HAB occurrence,concentration of phosphate and silicate should not exceed 17-20 μg/L and 300 μg/L as a whole.Reasonable control of pollutant discharge is a key point to prevent water eutrophication and HAB occurrence.