It's low tide at Robin Hood's Bay, North Yorkshire, which is a popular scenic area of the Northeast coast of England. PHOTOS BY R A KEARTON/GETTY IMAGES
這是北約克郡羅賓漢灣的低潮，北約克郡是英格蘭東北海岸的熱門風景區。 KEARTON / GETTY影象的照片
Tides have caused a lot of trouble recently. During high tide periods, low-lying areas that border the ocean now flood way more often than they used to. Between 2000 and 2017, the average frequency of "high tide flooding" across the United States increased by 50 percent. Floods of this sort block roadways, harm infrastructure, and back up storm drains.
潮汐最近造成了很多麻煩。在漲潮時期，與海洋接壤的低窪地區比以往更多地氾濫成災。在2000年至2017年之間，全美國“高潮洪災”的平均發生率增加了50％。這種洪水會阻塞道路，損害基礎設施，並排洩雨水。
Around 40 percent of the global population lives within 62 miles (100 kilometers) of a coastline. Recent flood trends must have a lot of these people wondering about tidal science. How do tides happen? Why do some areas get more dramatic tides than others? And why can't the sea level just stay constant everywhere, all the time? Today we're going to look at the physics and idiosyncrasies of planet Earth's tides.
全球人口的約40％生活在海岸線的62英里（100公里）內。最近的洪水趨勢肯定使許多人對潮汐科學感到好奇。潮汐如何發生？為什麼有些地區的潮流比其他地區更具戲劇性？為什麼海平面不能一直到處保持恆定呢？今天，我們將研究地球潮汐的物理學和特質。
Pushing Water推水
Check out the diagram below. In the picture, you will notice that our planet is sitting inside a blob of ocean water that's kind of shaped like a rugby ball. There's a bulge in the ocean on each side of the planet. Observe that one bulge is protruding from the half of the globe that's facing the moon while the other is located on Earth's opposite end.
檢視下圖。在圖片中，您會注意到我們的星球正坐在一團海水中，海水的形狀類似於橄欖球球。在地球的每一側海洋中都有一個凸起。觀察到一個凸起從面對月球的地球的一半伸出，而另一個則位於地球的另一端。
Why do these bulges exist? In a nutshell, they're primarily caused by the moon's gravitational pull upon the Earth. That force can have two separate components. It can pull matter "vertically," by which we mean perpendicularly to the Earth's surface. And it can also pull things "horizontally" — i.e.: in a direction that runs parallel to the face of our planet.
為什麼這些凸起存在？簡而言之，它們主要是由月球對地球的引力引起的。該力可以具有兩個單獨的分量。它可以“垂直”拉動物質，即垂直於地球表面的意思。而且它還可以“水平”拉動物體，即：沿平行於我們星球表面的方向拉動物體。
Now, the spot on the globe that sits right beneath the moon at any given time is called the sublunar point. Meanwhile, the spot on the other side of our planet that is directly opposite the sublunar point is known as the antipodal point. It's no coincidence that the ocean bulges are highest right over those two spots. At the sublunar point and the antipodal point, the moon's gravitational pull lacks a horizontal component — something that is also missing at the two corners of the world that are located 90 degrees away from these spots.
現在，地球上在任何給定時間都位於月球下方的點稱為月下點。同時，我們行星另一側與月底下點直接相對的點稱為對映點。在這兩個地點上，海浪最高是絕非偶然的。在月球下和對映點，月球的引力缺乏水平分量-在與這些點相距90度的世界兩個角上也缺少這種分量。
Those four areas are unique in that regard; every other location on Earth experiences a horizontal force that pushes water molecules in the ocean toward either the sublunar point (where the moon's gravitational force is at its strongest) or the antipodal point (where the moon's gravitational pull is at its weakest). This is why the ocean bulges up over those two areas.
在這方面，這四個領域是獨特的；地球上所有其他位置都受到水平力的作用，該力將海洋中的水分子推向月球下點（月球的引力最強）或對極點（月球的引力最弱）。這就是為什麼海洋在這兩個區域隆起的原因。
Here Comes The Sun太陽來了
Once every 24 hours, Earth completes a full rotation around its axis. During this process, any given spot on the planet's surface (like, say, Long Island or Australia) will pass right through both of those ocean bulges. So — in most areas — when your home is directly under a bulge, the local tide should be high. But as it enters the space between the bulges, the tide in your area should get lower. This isn't always the case, as you'll learn next.
每隔24小時，地球會繞其軸完成一次完整的自轉。在此過程中，地球表面上的任何給定點（例如長島或澳大利亞）都將直接穿過這兩個海洋凸起。因此-在大多數地區-當您的房屋正處於隆起之下時，當地的潮流應該很高。但是當它進入凸起之間的空間時，您所在地區的潮汐應該會降低。情況並非總是如此，接下來您將學習。
For now, let's discuss another factor that influences our tides. The sun also exerts a gravitational pull on the oceans, but because our solar companion is further away, its effects on the tides are less pronounced than the moon's. Still, the big ball of gas and plasma does noticeably enhance tidal bulges on a regular basis.
"The tides are [at their] largest ... when the sun and moon line up," Duncan Agnew, a geophysicist at the University of California, San Diego, says in an email. He notes that this happens during two separate lunar phases: Full moons and new moons. Astronomers and Earth scientists refer to these plus-sized tides as spring tides. (Note that the name has nothing to do with the spring season; indeed, spring tides occur throughout the year.)
加利福尼亞大學聖地亞哥分校的地球物理學家鄧肯·阿格紐夫（Duncan Agnew）在一封電子郵件中說：“潮汐處於[最大]……當太陽和月亮排成一行時。”他指出，這發生在兩個單獨的月球階段：滿月和新月。天文學家和地球科學家將這些特大潮汐稱為春季潮汐。 （請注意，這個名稱與春季無關；實際上，春季潮全年都會發生。）
During spring tides, the "high" tides are really high and the "low" tides are unusually low. Things get less extreme when the sun and moon sit at right angles to each other (relative to Earth). Such an arrangement will produce a neap tide; a period in which the difference between high and low tides is minimal.
在春季潮汐期間，“高”潮確實很高，而“低”潮卻異常低。當太陽和月亮彼此成直角（相對於地球）時，事情變得不那麼極端了。這樣的安排將產生浪潮。高潮和低潮之間的差異最小的時期。
When Continents Interfere當大陸干涉
Brace yourself: Things are about to get even more complex. Earth may be a "blue planet," but 29 percent of our world's surface is covered by land. Coves, cliffs and other geographic features can interfere with the tides, too, intensifying them in some locales and weakening them in others.
振作起來：事情將變得更加複雜。地球可能是“藍色星球”，但地球的29％被土地覆蓋。海灣，懸崖和其他地理特徵也可能會干擾潮汐，在某些地區加劇潮汐，在其他地區減弱潮汐。
Most coastal areas receive two high tides per day, with a new one coming every 12 hours and 25 minutes. Yet exceptions to the rule aren't hard to find. "Ocean tides are a complicated process that involves the tidal force acting on water that is, as it were, also free to slosh around in the ocean basins," Agnew says. Many beaches on the Gulf of Mexico only receive one high tide per day, a byproduct of restricted water flow. Elsewhere, water that enters the V-shaped Bay of Fundy in Nova Scotia is pushed upward as it moves inland. This results in huge height disparities between low and high tides there called bore tides.
大多數沿海地區每天都會收到兩次漲潮，每12個小時25分鐘就會有一次新的漲潮。但是，不難發現該規則的例外情況。阿格紐說：“海潮是一個複雜的過程，涉及的潮汐力作用於水，儘管如此，水也同樣可以在海盆中自由晃動。”墨西哥灣的許多海灘每天僅收到一次漲潮，這是水流受限的副產品。在其他地方，進入新斯科舍省的V形芬迪灣的水在向內陸移動時被向上推。這導致在稱為潮汐潮的低潮和高潮之間存在巨大的高度差異。