海水运动 Seawater in motion

1. 海水运动 Seawater in motion • 波浪 wave • 潮汐 tide • 海流 oceanic current

2. 海水的结构 • Shallow surface mixed zone (upper 450 m) • mixed by wind and currents • Uniformly warm • Generally higher salinity (surface evaporation) • Transition zone (< 1500 m thick) • Temperature decreases rapidly –thermocline (the layer of rapidly changing temperature, is present only in the low latitudes) • Salinity decreases rapidly –halocline (layer of water in which a high rate of change in salinity in vertical dimensions) • Pycnocline zone • Deep zone • Very cold, near freezing < 4˚C • Relatively low salinity

3. 大海永远不是宁静的……

4. The Ocean in Motion • Winds generate surface currents 风 • Density differences create deep-ocean circulations 密度差异 • The Sun and Moon produce tides 引力 • Waves carry storm energy to land and act as erosion agents

5. 波浪

7. Basic Parts of a Wave wavelength crest trough 波基面 wave base = 1/2 wavelength

8. 质点运动

9. 不同水深的波浪运动½波长的意义

10. 一些重要的波浪类型和驱动力 湖面波动 海啸

11. 海洋中的波浪 • 形成原因：海面上的风应力，海底及海岸附近的火山、地震，大气压力的变化，日、月的引潮力等； • 波动的周期从零点几秒到数十小时以上，波高从几毫米到几十米，波长可以从几毫米到几千公里； • 风引起的波浪多1-30s的周期能量最大；30-50s为长周期的重力波，呈长涌或先行涌形式，多风暴引起；5min到数小时的多风暴、地震引起；而更长的12-24h的波动多潮力引起。

12. 波浪破碎 冲浪带 破浪带 碎/激浪带

13. 波浪破碎 • Breaker zone：The portion of the nearshore zone where wave velocity and wavelength decrease and the waves get higher and become progressively asymmetrical. • Surf zone：The portion of the nearshore zone where oversteeped waves topple over and crash onto the beach.

19. 沿岸流 离岸流

20. wave - pushes sand up at an angle 沿岸流 gravity - sand rolls straight down

21. 波浪侵蚀 海蚀洞 海蚀穹/拱 海蚀柱

23. 波浪侵蚀与海岸发育 弯曲海岸 平直海岸

24. 潮汐：自然的力量！

25. 潮汐的产生

27. Sun and Moon’s gravitational pull on Earth causes “bulges” in water masses 日月的引力与离心力相互作用使得海水膨胀隆起 • Earth rotates through/under the bulges • Results: two high tides and two low tides per day

28. 月相图 下弦 塑 望 上弦

29. 大潮spring tide、小潮neap tide

30. 典型月的潮汐记录

31. 潮汐测量

32. 不同的潮汐类型 半日潮 日潮 混合潮

34. 世界上不同潮汐类型的分布

35. Tidal Currents • Horizontal flow of water due to rise and fall of tides • 落潮流Ebb current - falling tide • 涨潮流Flood current - rising tide • 平潮Slack water - little or no current in between • Not important in open sea

36. Tidal Currents • Important in narrow places such as bays, rivers and estuaries • Can be large, 40 ft (12m) change, currents at 12 mph • Cause of erosion • Example: Bay of Fundy, Nova Scotia, Canada • 钱塘江：7-8米 • 长江口：2-3米 • 黄河口：1米左右

39. 热带风暴产生地区

42. Hurricane Andrew

43. 美国历史上的风暴损失

45. 海流

46. Surface ocean currents are parts of huge, slowly moving, circular whirls, or gyres, that begin near the equator in each ocean. • Wind is the driving force for the ocean’s surface currents. Where wind is in contact with the ocean, it passes energy to the water through friction and causes the surface layer to move. • The most significant factor other than wind that influences the movement of ocean waters is the Coriolis effect, the deflective effect of Earth’s rotation that causes free-moving objects to be deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. Because of the Coriolis effect, surface currents form clockwise gyres in the Northern Hemisphere and counterclockwise gyres in the Southern Hemisphere.

48. 北半球的海岸上升流和沉降流