【摘要】：本文利用區(qū)域海洋模式ROMS(Regional Ocean Modelling System)及其自帶的四維變分同化模塊，建立了渤黃東海三維風暴潮數(shù)值模式。四維變分同化能夠保持水動力過程的協(xié)調(diào)穩(wěn)定，通過積分切線性模式和伴隨模式，并且運用梯度下降算法，使模擬結(jié)果在同化窗口內(nèi)最大程度的靠近觀測。 采用隨水深變化的底摩擦系數(shù)，對潮汐進行了數(shù)值模擬，分析了四個主要分潮（M2，S2，K1，O1）的同潮時圖。結(jié)果顯示該模式具備較好的潮汐模擬能力，無論無潮點的位置還是等振幅、等遲角線都和前人的模擬結(jié)果非常接近。同時，大部分海洋站點的潮汐模擬結(jié)果和觀測吻合較好。 選定兩次溫帶風暴潮作為研究對象，通過將海洋站觀測水位同化到模式中，很大程度上改進了風暴潮的模擬結(jié)果。設(shè)計了5組孿生敏感性試驗對影響同化模擬結(jié)果的要素進行研究，結(jié)果表明，風應(yīng)力對風暴潮的模擬質(zhì)量起著決定性的作用，初始場只在短時間內(nèi)影響模擬結(jié)果，風速越大，影響時間越短。因此，將風應(yīng)力和初始場同時作為控制變量可以到的最優(yōu)的模擬結(jié)果。同化模擬不僅能夠提高參與同化海洋站的風暴潮模擬精度，還能改善其周圍的模擬結(jié)果。在同化模擬的過程中，迭代次數(shù)是一個非常重要的參數(shù)，它決定了目標函數(shù)—模式結(jié)果和觀測之間距離的下降程度。迭代次數(shù)越多，風暴潮的模擬結(jié)果就會與觀測吻合越好，但同時，也要付出更加高昂的計算代價。 同化模擬一段時間之后，，能夠得到一個與觀測吻合較好的最優(yōu)預(yù)報初始場和最優(yōu)的風應(yīng)力拖曳系數(shù)，分別用最優(yōu)的拖曳系數(shù)和常數(shù)拖曳系數(shù)（0.0026）對風暴潮進行數(shù)值預(yù)報。結(jié)果表明，最優(yōu)預(yù)報初始場對預(yù)報結(jié)果的改進存在不確定性。減水個例的改進效果不明顯，前期預(yù)報結(jié)果產(chǎn)生了較大誤差，可能是因為模式對減水過程的物理描述還不完善，在大風條件下，誤差顯著的表現(xiàn)出來；增水個例的改進效果可以從預(yù)報起始時刻一直持續(xù)到觀測增水的峰值附近，表明最優(yōu)初始場可以提高臨近預(yù)報的準確度。 同化模擬反演的最優(yōu)拖曳系數(shù)能否進一步改善預(yù)報結(jié)果，取決于兩個方面的因素。一方面是同化窗口和預(yù)報窗口風速的誤差變化情況，如果風速誤差在同化前后差異很大，最優(yōu)拖曳系數(shù)適用性一定會變差；另一方面是不同風速條件下拖曳系數(shù)的變化幅度，即在不同風速條件下，如果實際拖曳系數(shù)變化幅度很大，最優(yōu)拖曳系數(shù)的適用性同樣會受到挑戰(zhàn)。
[Abstract]:In this paper, the regional ocean model ROMS (Regional Ocean Modeling system) and its own four-dimensional variational assimilation module are used to establish a three-dimensional storm surge numerical model in the Bohai Sea, Yellow Sea and East China Sea. Four-dimensional variational assimilation can keep the coordination and stability of hydrodynamic process. By means of integral tangent linear model and adjoint model and gradient descent algorithm, the simulated results can be observed in the assimilation window as close as possible. With the bottom friction coefficient varying with the depth of water, the tide is numerically simulated, and the isotidal time diagrams of four main tidal components (M2S2K1O1) are analyzed. The results show that the model has good tidal simulation ability, and the isobaric angle line is very close to the previous simulation results, regardless of the position of no tide point or the equal amplitude. At the same time, the tidal simulation results of most ocean stations are in good agreement with observations. Two temperate storm surges were selected as the research object. By assimilating the observed water levels of ocean stations to the model, the simulation results of storm surges were improved to a great extent. Five sets of twin sensitivity tests were designed to study the factors that affect the simulation results of assimilation. The results show that wind stress plays a decisive role in the simulation quality of storm surge, the initial field only affects the simulation results in a short time, and the wind speed increases. The shorter the influence time is. Therefore, the wind stress and the initial field are taken as the optimal simulation results for the control variables. Assimilation simulation can not only improve the accuracy of storm surge simulation, but also improve the simulation results around it. In the process of assimilation simulation, the number of iterations is a very important parameter, which determines the degree of decrease of the distance between the objective function-model result and the observation. The more iterations, the better the simulation result of storm surge will be, but at the same time, it will be more expensive to calculate. After a period of assimilation simulation, an optimal prediction of initial field and an optimal drag coefficient of wind stress can be obtained. The optimal drag coefficient and constant drag coefficient (0.0026) are used to predict storm surge numerically, respectively. The results show that the improvement of the initial field of the optimal prediction is uncertain. The improvement effect of water reduction case is not obvious, and the result of early forecast has a big error, which may be because the physical description of water reduction process is not perfect, and the error is obvious under the condition of strong wind. The improved effect of water increasing example can be continued from the beginning of prediction to near the peak value of observed water increase, which indicates that the optimal initial field can improve the accuracy of near prediction. Whether the optimal drag coefficient of assimilation simulation inversion can further improve the prediction results depends on two factors. On the one hand, the variation of wind speed error in assimilation window and forecast window, if the error of wind speed is very different before and after assimilation, the applicability of the optimal drag coefficient will certainly become worse; on the other hand, the variation range of drag coefficient under different wind speed conditions, In other words, the applicability of the optimal drag coefficient will also be challenged if the actual drag coefficient varies greatly under different wind speeds.
【學(xué)位授予單位】：國家海洋環(huán)境預(yù)報中心
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2014
【分類號】：P731.23

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