Exploring conventional tidal prediction schemes for improved coastal numerical forecast modeling

This study provides a practical guide to the use of classical tidal prediction algorithms in coastal numerical forecasting models such as tide and tide-storm-surge models. Understanding tidal prediction parameter formulas and their limitations is key to successfully modifying and upgrading tidal prediction modules in order to increase the accuracy of perpetual interannual simulations and, in particular, storm-surge modeling studies for tide-dominated coastal environments. The algorithms for the fundamental prediction parameters, the five astronomical variables, used in tidal prediction are collated and tested. Comparisons between their estimation using different parameterizations shows that these methods yield essentially the same results for the period 1900–2099, revealing all are applicable for tidal forecasting simulation. Through experiments using a numerical model and a harmonic prediction program, the effects of nodal modulation correction and its update period on prediction accuracy and sensitivity are examined and discussed using a case study of the tidally-dominated coastal regime off the west coast of Korea. Results indicate that this correction needs updating within <30 days for accurate perpetual interannual tidal and mean sea-level predictions, and storm-surge model predictions requiring centimeter accuracy, for tidally-dominated coastal regimes. Otherwise, unacceptable systematic errors occur.     

Numerical analysis of effects of tidal variations on storm surges and waves

This study examines the effects of tides on surges, wave setups and waves, in terms of tidal amplitudes and phases, by using a coupled numerical model of Surge, WAve and Tide (called as SuWAT). The SuWAT model, composed of depth integrated nonlinear shallow water equations and Simulating WAves Nearshore (SWAN) model, is able to simultaneously run with an arbitrary number of nested domains by using the Message Passing Interface. The results for an idealized case indicate that surge and wave setup are increased in the phase of low water and decreased in the high water phase; on the other hand, waves change in a reverse manner. Such changes are enhanced by large tidal variations. The conventional method (e.g., surge plus tide independently) has the possibility of overestimation for the total water level. The hindcast results for Typhoon Ewiniar in 2006 show that the run with tides is more accurate 10% than that without tides in coastal areas of Korea. The nested scheme improves the accuracy up to 40% for the prediction of water levels in the simulations. It is shown that the present coupled model, SuWAT, is capable of predicting both water levels and waves under storm events with reasonable accuracy against the observations.     

珠江口赤潮生成的天气分型研究

赤潮的爆发是生物、化学、物理等多因素综合作用的结果。温度、风力、风向、气压等气象条件,海况、潮汐、海流及海水的理化特征,如海水温度、盐度、营养盐、微量元素等都是赤潮爆发的重要因子或诱导因素。当前由于海洋生态领域的数值预报仍不成熟,国内的赤潮预测主要还是依靠经验和统计方法为主,如气象条件预报法、水文条件预报法、化学条件预报法、生物条件预报法、卫星遥感预报法或是综合预报法等。本文根据2001年～2005年《沿海海洋赤潮专报》中广东省阳江到汕尾沿海(112°～116°E)即珠江口地区发生赤潮的记录,使用NCEP再分析数据,从气象条件诱发赤潮的角度分析得出最易引发珠江口赤潮的5种天气形势,并用相关性分析方法得出其中两种天气形势的典型场,对预测珠江口沿海的赤潮发生具有一定的指导意义,可在实践中加以应用。     

我国潮汐潮流区域预报的发展

简要回顾了我国潮汐潮流区域预报的发展过程。1959—1964年期间按前苏联杜瓦宁方法编制的永久潮流表是第一代预报产品,该产品提供了我国近海若干站点5 m层潮流预报资料。1970—1978年期间按方国洪提出的方法而研制的永久预报图表集是第二代预报产品,提供了基本上覆盖我国近海的多层潮流预报资料;这两代产品均以纸质图表为载体。2005—2006年期间方国洪等研制了第三代预报产品,覆盖了我国近海各海区,分辨率达到5′×5′,垂向10层,并可自动内插到任意点和任意水层。同时介绍了三代产品的研发过程及基本原理。     

2020年西藏波密ML4.9震群活动的潮汐触发特征

2020年7-8月,西藏波密发生显著震群,震群包含25次ML≥4.0地震,最大为7月19日ML4.9地震.震群部分相邻地震具有约24h或12h的时间间隔,这意味着波密震群地震活动可能受不同周期潮汐变化的影响.针对其中20次有震源机制结果的ML≥4.0地震,分别计算地震前后震源机制解在2个节面上的潮汐正应力、剪应力和库仑...     

新岛台地电场的潮汐响应与地震

本文通过采用频谱分析和BAYTAP-G方法对位于日本伊豆群岛的新岛台跨度达三年（1998～2000年）的地电场的观测资料进行了分析研究,对该台地电场的潮汐响应进行了定量提取与分析,得到了地电场潮汐响应的一些主要特征,例如除了存在全日分潮、半日分潮等不同周期的潮汐成分外,还呈现出明显的半月、半年等不同周期的活动规律.进一步的定量分析显示与新岛台若乡（Wakago）关联的测线的潮汐响应在2000年夏季的群发地震前呈现出不同程度的异常变化,而在所分析的另一条测线中并未检测到类似的异常,这也许可以成为地震电磁信号的“选择性”现象的一种新的证据.     

中国大陆经纬链地电场日变化

本文应用中国大陆两条经度链和两条纬度链上共37个地电场台站的观测数据,研究了地电场日变化的时/频域特征,结果认为,绝大多数台站的日变化表现为两次起伏的半日波,紧临午前午后出现;按FFT振幅谱由大到小,其主要周期成分依次为12.4/12、8、24 h等,与潮汐调和分量周期一致;纬度效应主要表现为沿经度链的日变化幅度与纬度高/低有关,日变化相位差与当地时差吻合;Loyd季节的J季节日变化幅度最大、E季节其次、D季节最小.讨论了产生日变化主要周期成分的可能原因,认为月日引潮力引起的地面涡旋电流强度变化和太阳风引起的空间电磁活动共同产生了地电日变化的半日波周期成分.     

2009年1月强爆发性增温期间突发E(Es)层的响应

平流层爆发性增温(SSW)期间,低层大气温度场和风场等的剧烈变化会直接影响潮汐和风剪切作用.此举可能会导致电离层Es的相应变化.本文以2009年1月事件为例,分析了SSW期间Es层的响应.首先,在排除太阳活动和地磁活动对Es层影响的前提下,分析了昆明站附近MLT区域行星波和潮汐波的波动特性,发现此期间存在显著的2日行星波,并伴有日潮汐减弱和半日潮汐增强等波动现象;随后,分析相应时间段内Es层的变化特性发现,重庆和昆明站附近Es层强度明显减弱,且其高度显著抬升.这一现象与低层大气的波动变化具有同步性.最后,通过模拟经典风剪切理论下Es层金属离子的汇聚过程和运动轨迹,再现了SSW期间Es层与低层大气波动的耦合演化过程.该分析结果为研究低层-中层-高层大气的耦合过程提供了一种新的思路.     

Principal component analysis of tsunami buoy record: Tide prediction and removal

Principal component or Empirical Orthogonal Function (EOF) analysis is applied to tsunameter records by treating them as two-dimensional signals, where the second dimension is created by breaking a single time series into cycles and treating the cycle number as a second dimension. Under certain conditions, principal components calculated from different records are shown to determine the same functional space. Signal decomposition into pre-calculated principal components is used to predict or extract the tidal component of a record. This work shows that EOF processing allows for short-term tidal predictions at tsunami buoy locations with the precision of more advanced methods and with minimal a priori knowledge about tidal dynamics. Also shown is that filtering in EOF domain is sensitive to the non-tidal component of a record and therefore presents a tool for early tsunami detection and quantification.