航海英语(16).docx

Unit 16 Tide and Tidal Currents 1. FEATURES OF TIDE 潮流特点1.1 General Features 一般特点At most places the tidal change occurs twice daily. The tide rises until it reaches a maximum height, called high tide or high water, and then falls to a minimum level called low tide or low water. 在大多数地区潮汐一天变化两次，潮水上涨,直到它达到最大高度,称为高潮或大潮，然后跌落到最低水平称为低潮The rate of rise and fall is not uniform. From low water, the tide begins to rise slowly at first, but at an increasing rate until it is about halfway to high water. The rate of rise then decreases until high water is reached, and the rise ceases. The falling tide behaves in a similar manner. The period at high or low water during which there is no apparent change of level is called stand. The difference in height between consecutive high and low waters is the range. 涨潮和落潮的速度并不一致。直到大约一半的高潮潮位时涨潮速度开始缓慢上升.过了半个高潮潮位后涨潮速度才慢慢下降，直到达到高潮潮位，这时涨潮结束，落潮也表现出相似的方式，连续的高潮或者低潮潮位的水位没有发生明显改变的期间被称为稳定时期。连续不断的高潮或低潮差就是这个的适用范围。2 Types of Tide 潮流的类型A body of water has a natural period of oscillation, dependent upon its dimensions. None of the oceans is a single oscillating body; rather each one is made up of several separate oscillating basins. As such basins are acted upon by the tide-producing forces, some respond more readily to daily or diurnal forces, others to semidiurnal forces, and others almost equally to both. Hence, tides are classified as one of three types, semidiurnal, diurnal, or mixed, according to the characteristics of the tidal pattern.水域都有一个自然的摆动周期，依靠水域的尺寸。所有的海洋都不是单一的水域。每一个海洋都由几个分开的流域组成。因此流域扮演了产生潮流的能量的角色。一些表现为一天或者半天变化一次。另外一些表现为半天变化一次，其他的变化也都和这二者一样。因此，根据潮汐涨退模式特点潮汐分为三种类型半天的一天的还有两种形式混合的。In the semidiurnal tide, there are two high and two low waters each tidal day, with relatively small differences in the respective highs and lows. Tides on the Atlantic coast of the United States are of the semidiurnal type.在半日潮，潮汐每天有两次高潮和两次低潮，相对地和各自的高和低有小小的区别。美国大西洋海岸的潮流特点是半日潮类型的。In the diurnal tide, only a single high and single low water occur each tidal day. Tides of the diurnal type occur along the northern shore of the Gulf of Mexico, in the Java Sea, the Gulf of Tonkin, and in a few other localities. The tide curve for Pei-Hai, China, is an example of the diurnal type.在日周潮里，每天只有唯一一次高潮和低潮发生，沿着墨西哥海湾北部海岸线、爪哇海东京湾和另外一些地区的潮流都是属于日周潮类型的。中国北海湾的潮汐类型也是属于日周潮类型的。In the mixed tide, the diurnal and semidiurnal oscillations are both important factors and the tide is characterized by a large inequality in the high water heights, low water heights, or in both. There are usually two high and two low waters each day, but occasionally the tide may become diurnal. Such tides are prevalent along the Pacific coast of the United States and in many other parts of the world. At Los Angeles, it is typical that the inequalities in the high and low waters are about the same. At Seattle the greater inequalities are typically in the low waters, while at Honolulu it is the high waters that have the greater inequalities. 在混合潮中，日周潮和半日潮摆动都是重要的因素，其潮流特征是高潮高度和低潮高度不等量或者两者都有吧。，通常每天有两个高潮和低潮，但偶尔这种类型的潮流也可能变成日周潮。这样的潮汐在美国太平洋沿岸和世界上其他的许多地方都是普遍存在的。在洛杉矶不高不低的潮位是典型的不均等，西雅图是低潮潮位存在巨大不均等的典型。然而在檀香山却在高潮上存在巨大的不均等.3 Special Tidal Effects特殊潮汐的影响As a wave enters shallow water, its speed is decreased. Since the trough is shallower than the crest, it is retarded more, resulting in a steepening of the wave front. In a few estuaries, the advance of the low water trough is so much retarded that the crest of the rising tide overtakes the low, and advances upstream as a breaking wave called a bore. Bores that are large and dangerous at times of large tidal ranges may be mere ripples at those times of the month when the range is small. Examples occur in the Petitcodiac River in the Bay of Fundy, and at Haining, China, in the Tsientang Kaing. The tide tables indicate where bores occur.当海浪进入浅水时，速度减小，由于海槽比波峰浅，使得速度的减少变得更加的缓慢。导致了波峰变得更加的陡峭。在一些河口湾，前进中的低水槽减小的太多以至于高潮流赶上了低潮，变成了有破坏性的前进的逆流被称为波涛，大潮的时候的巨大的波涛有时候表现出来的仅仅只是波痕或者每月的相应的出现小的范围。这样的例子常发生在加拿大当芬迪海湾泊蒂克河和中国海宁的钱塘江。潮汐表能够预测波涛在什么地方发生。4 Tidal Cycles 潮汐周期Other special features are the double low water (as at Hoek Van Holland) and the double high water (as at Southampton, England). At such place there is often a slight fall or rise in the middle of the high or low water period. The practical effect is to create a longer period of stand at high or low tide. The tide tables list these and other peculiarities where they occur.其他特殊的特点就是双低潮双高潮，在这样的地方，通常在高潮或者低潮中间时期会有轻微的下跌或上升。实际效果是创造本了一个更长时间段的维持在高潮位或者低潮位。潮汐表列出了这些和其他特性会在哪里发生。Tidal oscillations go through a number of cycles. The shortest cycle, completed in about 12 hours and 25 minutes for a semidiurnal tide, extends from any phase of the tide to the next recurrence of the same phase. During a lunar day (averaging 24 hours and 50 minutes) there are two highs and two lows (two of the shorter cycles) for a semidiurnal tide. The moon revolves around the earth with respect to the sun in a synodical month of about 29 1/2 days, commonly called the lunar month. The effect of the phase variation is completed in one-half a synodical month or about 2 weeks as the moon varies from new to full or full to new. The effect of the moons declination is also repeated in one-half of a tropical month of 27 1/3 days or about every 2 weeks. The cycle involving the moons distance requires an anomalistic month of about 27 1/2 days. The suns declination and distance cycles are respectively a half year and a year in length. An important lunar cycle, Called the nodal period, is 18.6 years(usually expressed in round figures as 19 years). For a tidal, particularly a range, to be considered a true mean, it must be either based upon observations extended over this period of time , or adjusted to take account of variations known to occur during the nodal period. 潮汐振荡通过许多周期。半日潮完成一次最短的周期大约12个小时25分，对于半日潮而言它的一个潮汐日平均24小时50分钟会出现两次高潮和两次低潮也就是两次短的循环，月球绕地球转动就像地球绕太阳转动的会合月大约为29天半，通常称为一个潮汐月，潮流完成半个会合月或2周的相位变化效果就像月亮从新月到满月或者从满月到新月别的变化过程。月亮的赤纬大约要27又3分之一天回归月的一半或者每量星期完成一次循环，太阳赤纬或者距离周期分别是半年及1年的长度。一个重要的月亮运行周期，叫做节点周期是18.6年通常被认为是19周年，因此潮汐，特别是范围，被认为是真理的话，它必须是基于观察扩展到这段时间,或考虑到了已知的变化发生在节点的时期。5 Time of Tide潮汐的时间 Since the lunar tide-producing force has the greatest effect in producing tides at most places, the tides “follow the moon.” Because the earth rotates, high water lags behind both upper and lower meridian passage of the moon. The tidal day, which is also the lunar day, is time between consecutive transits of the moon, Or 24 hours and 50 minutes on the average. Where the tide is largely semidiurnal in type, the lunitidal interval (the interval between the moons meridian transit and a particular phase of tide) is fairly constant throughout the month, varying somewhat with the tidal cycles. There are many places, however, where solar or diurnal oscillations are effective in upsetting this relationship. The interval generally given is the average elapsed time from the meridian transit (upper or lower) of the moon until the next high tide. This may be called mean high water lunitidal interval or corrected (or mean) establishment. The common establishment is the average interval on days of full or new moon, and approximates the mean high water lunitidal interval.因为在大多数地方月亮对潮汐生成的影响最大。潮汐跟着月亮变化。由于地球的转动，高潮落后于月亮轨迹的上下两部分。潮汐一天,这也是太阴日之间,月球连续运行,或平均24个小时,50分钟的。在很大程度上半日潮的类型。月潮间隙在相对稳定的条件下，整个月有些和潮周期的变化有关。有些地方，然而太阳系或者全日的摆动打破了他们之间的关系。通常月亮这间隔的时间会持续到下次高潮来临之前。这可以被称为平均高潮位月潮间隙或者更正措施。满月或者新月是常见的完整的平均月潮间隙时间。In the ocean, the tide may be in the nature of a progressive wave with the crest moving forward, a stationary or standing wave which oscillates in a seesaw fashion, or a combination of the two. Consequently, caution should be used in inferring the time of tide at a place from tidal for nearby places. In a river or estuary, the tide enters from the sea and is usually sent upstream as a progressive wave so that the tide occurs progressively later at various places ostream.2. TIDAL DATUMS潮汐基准1 Low Water Datums低水位基准面A tidal datum is a level from which tides are measured. There are a number of such levels of reference that are important to the mariner. 潮汐数据在一定水平上潮汐的进行了实验研究。有很多这种程度的参考，这些参考对海员来说非常重要。The most important level of reference to the mariner is the sounding datum shown on charts. Since the tide rises and falls continually while soundings are being taken during a hydrographic survey, the tide is recorded during the survey so that soundings taken at all stages of the tide can be reduced to a common sounding datum. Soundings on charts show depths below a selected low water datum (occasionally mean sea level), and tide predictions in tide tables show heights above and below the same level. The depth of water available at any time is obtained by adding algebraically the height of the tide at the time in question to the charted depth.对于海员来说最重要的参考水平是海图深度基准面。在调查期间因为潮水持续不断的涨落所以声纳被用来测量记录。在调查期间记录潮汐，被调查的所有潮汐流可以减少到一个共同的测量基准面。调查结果显示深层的海图选择低潮数据偶尔是海平面，与潮汐表的预测与显示高度的上方或下面是同样的水准，任何时刻水深数据的获取增加了潮流的高度。By international agreement, the level used as chart datum should be low enough so that low waters do not fall very far below it. At most places, the level used is one determined from a mean of a number of low waters(usually over a 19 year period) ; therefore , some low waters can be expected to fall bellow it. The following are some of the datums in general use.根据国际协议，作为海图水平基准应该有足够低不至于低潮水位太低。在很多地方，在很多地方,使用的是一个实验测定水平从一个平均的一些低水域(通常为19年周期),因此,一些低水下面将下降。很多都是不经过这个基准通用。 Mean low water (MLW) is the average height of all low waters at a given place. About half of the low waters fall below it , and half above.平均低潮面是各种低潮潮位的某一点上的平均高度，大约是一半的低潮高度，或者低于一半以上。 Mean low water springs (MLWS) , usually shortened to low water springs, is the average level of the low waters that occur at the times of spring tides .低潮平均低潮是平均低潮的简称。是春潮的低潮平均高度。 Mean lower low water (MLLW) is the average height of the lower low waters of each tidal day .平均低低潮潮面是每一个潮汐日的低低潮平均高度。 Tropic lower low water (TcLLW) is the average height of the lower low waters (or of the single daily low waters if the tide becomes diurnal ) that occur when the moon is near maximum declination and the diurnal effect is most pronounced . this datum is not in common use as a tidal reference .回归低低潮是发生当月亮的偏斜并且在最大效果最显著的平均潮面高度。这个数据是使用非通常潮汐参考。 Indian spring low water (ISLW) , sometimes called Indian tide plane or harmonic tide plane , is a low water datum that includes the spring effect of the semi-diurnal portion of the tide and the tropic effect of the diurnal portion . It is about the level of lower low water of mixed tides at the time that the moons maximum declination coincides with the time of new or full moon . 印度春天低潮(ISLW),有时叫做印地安潮流或谐波潮流,是一种低水位数据,包括热带地区春天影响的一部分半日潮的影响。混合潮低低潮是月亮最大倾斜时新月或满月时的水平面。 Mean lower low water springs (MLLWS) is the average level of the lower of the two low waters on the days of spring tides .春季低低潮是春潮每天两次的低潮潮面的评价你高度。 Some still lower datums used on charts are determined from tide observations and some are determined arbitrarily and later referred to the tide. Most of them fall close to one or the other of the following two datums. 一些在海图上应用的静低潮数据，来自于观测者对潮汐的观察，其中有些是任意确定的，然后 就被用做潮汐的参考数据。大多数与其中之一或两者之一的数据相接近。 Lowest normal low water is a datum that approximates the average height of monthly lowest low waters, discarding any tides disturbed by storms. Lowest low water is an extremely low datum. It conforms generally to the lowest tide observed, or even somewhat lower. Once a tidal datum is established, it is sometimes retained for an indefinite period, even though it might differ slightly from a better determination from later observations. When this occurs, the established datum may be called low water datum, lower low water datum, etc. These datums are used in a limited area and primarily for river and harbor engineering purposes. Examples are Boston Harbor Low Water Datum and Columbia River Lower Low Water Datum. 大潮最低低潮是水位的一项数据，是每月的平均低低潮水位高度，舍弃潮汐受到的任何风暴的影响，最低低潮是一项极低的数据。它通常符合最低潮的观察，甚至更低，一旦潮高基准面是既定的，有时候保留了很长一段时间里，尽管它可能从不同方面可以更好的确定自己后来的观察。当这种情况发生时,所建立的数据可以被称为低水位数据,较低的低水位数据,等。这些基准是用在限定区域,主要河流和港口工程的目的。的例子是波士顿港低水位基准,哥伦比亚河较低的低水位的数据。In some areas where there is little or no tide. Such as the Baltic Sea level (MSL) is used as chart datum. This is the average height of the sea for all stages of the tide over a 19 year period. This may differ slightly from half-tide level, which is the level midway between mean high water and mean low water. 在一些地区,那里有很少或没有潮流。例如波罗的海沿岸海平面(潮位作为海图的数据。这是19年来统计的海上潮汐的平均高度。这对于半个潮流水平高度可能略有不同。这是介于平均高潮潮位和平均低潮潮位水平中间的。Inconsistencies of terminology are found among charts of different countries and between charts issued at different times.在不同国家不同时期发行的海图上都有术语上的矛盾。Large-scale charts usually specify the datum if soundings and may contain a tide note giving mean heights of the tide at one or more places on the chart. These heights are intended merely as a rough guide to the change in depth to be expected under the specified conditions. They should not be used for the prediction of heights on any particular day, which should be obtained from tide tables.大型海图上通常会有指定水深点数据如果并能含有浪潮给意味着海图上一个或多个地方。那些数据仅仅只是打算用来作为一种粗略深度变化在指定的状况下。因此不能用潮汐表得到的资料来预测任一天的潮高。2.2 High Water Datums高潮水位资料Heights of terrestrial features are usually referred on nautical charts to a high water datum. This gives the mariner a margin of error when passing under bridges, overhead cables, and other obstructions. The one used on charts of the United States, its territories and possessions, and widely used elsewhere, is mean high water (MHW) , which is the average height of all high waters over a 19 year period. Any other high water datum in use on charts is likely to be higher than this. Other high water datums are mean high water springs (MHWS) , which is the average level of the high waters that occur at the time of spring tides; mean higher high water (MHWS), which is the average height of the height of the higher high waters of each tidal day; and tropic higher high water (TcHHW), which is the average height of the higher high waters (or the single daily high waters if the tide becomes diurnal) that occur when the moon is near maximum declination and the diurnal effect is most pronounced. A reference merely to “high water” levels some doubt as to the specific level referred to, for the height of high water varies from day to day. Where the range is large, the variation during a 2 week period may be considerable.地球高度数据通常在航海海图上高潮资料上被查阅，这给船员在通过桥梁线路和别的障碍物时提供一个误差界限。这个用在美国海图上它的领土和主权广泛的应用到别的地方，是平均高潮潮位，它是过去19年所有的高潮水位的平均值。任何别的高潮水位用于海图都可能高于平均高潮潮位。其他的高潮水位数据是平均大潮高潮，他是发生在高高潮时候水位平均值，平均较高高潮，是每个潮汐日较高高潮水位的平均高度，回归高高潮是平均较高高潮高度，或者一天高潮如果这是全日潮。它发生在当月球接近最大赤纬和一昼夜效应最显著的时候，很少引用高潮使一些人怀疑这涉及到的特殊水位，因为高潮水位日益变化，当范围很大时这两周内的变化值可供参考。Because there are periodic and apparent secular trends in sea level, a specific 19 year cycle (the National Tidal Datum Epoch) is issued for all United States datums. The National Tidal Datum Epoch officially adopted by the National Ocean Service is presently 1960 through 1978. the Epoch is periodically reviewed for revision.因为海平面有周期性和面向长期性的趋势，是一个明细的19年周期由美国新世纪国家潮汐资料官方现采用的国家海洋管理从1978年来的数据，它是为修正做定期性的复审。III. TIDAL CURRENTS潮流1 Tidal and nontidal Currents交汇流Horizontal movement of water is called current. It may be either “tidal ” and “nontidal ”. Tidal current is the periodic horizontal flow of water accompanying the rise and fall of the tide. Nontidal current includes all currents not due to the tidal movement. Nontidal currents includes the permanent currents in the general circulatory system of the oceans as well as temporary currents arising from meteorological conditions. The current experienced at any time is usually a combination of tidal and nontidal currents. 水平水运动的被称为潮流。它可以是“潮”和“非潮流。潮流是周期水平的水流陪同兴衰的潮流。目前非潮流包括所有流不应有的潮汐运动。非潮流包括永久潮流一般循环系统的海洋以及因临时电流的气象条件。目前在任何时间通常经验相结合的潮汐和非潮流。2 General Features一般特点Offshore, where the direction of flow is not restricted by any barriers, the tidal current is rotary; that is, it flows continuously, with the direction changing through all points of the compass during the tidal period. This rotation is caused by the earths rotation, and unless modified by local conditions, is clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The speed usually varies throughout the tidal cycle, passing through two maximums in time and direction. 海洋,那里的水流方向不受任何障碍的影响，潮流是旋转的，也就是说，它的流动是持续不断的，潮汐周期期间在指南针上的潮流方向是向各个方向的。这个旋转是由于地球自转,除非被当地条件下减缓了,潮流在北半球是顺时针旋转的在北半球是逆时针。不同的速度通常在潮汐周期,穿过两个最大值在时间和方向。不同的方向,从零速度在潮最大洪水和强度,称为衰退的中间,长裤。扭转电流可以显示图形化显示,由箭,代表流的速度在每小时。洪水通常是如上图所示,吃水线不景气的变化下方。曲线的潮流可当前的两端形成的具有相同特点的箭头从形式的潮流曲线。在插图,为实现一定的其他用途很方便符合规定的箭,只显示曲线。In rivers or straits, or where the direction of flow is more or less restricted to certain channels, the tidal current is reversing; that is, it flows alternately in approximately opposite directions with an instant or short period of little or no current, called slack water, at each reversal of the current. During the flow in each direction, the speed varies from zero at the time of slack water to a maximum, called strength of flood or ebb, about midway between the slacks. Reversing currents can be indicated graphically, by arrows that represent the speed of the current at each hour. The flood is usually depicted above the slack waterline and the ebb below it. The tidal currents current curve formed by the ends of the arrows has the same characteristic since form as the tide curve. In illustrations and for certain other purposes it is convenient to omit the arrows and show only the curve. 在河流或海峡,或在水流方向或多或少是限制在渠道,潮流是扭转;也就是说,它向用大约相反的方向,或者瞬间短的很少或目前没有,潮,在每一个被称为逆转的潮流。扭转潮流可以图形化显示,代表流每小时的速度。洪水通常是如上图所示,吃水线不景气的变化下方。曲线的潮流可当前的两端形成的具有相同特点的箭头从形式的潮流曲线。在插图,为实现一定的其他用途很方便符合规定的箭,只显示曲线。A slight departure from the sine from is exhibited by the reversing current in a strait, such as East River, New York, that connects two tidal basins. The tides at the two ends of a strait are seldom in phase or equal in range, and the current, called hydraulic current, is generated larg