NCERT Class 11 Part 1 Chapter 14: Movement of Ocean Water YouTube Lecture Handouts

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NCERT Class 11 Part 1 Geography Chapter 14: Movement of Ocean Water

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Waves

Image of a Waves

Image of a Waves

Image of a Waves

  • Ocean water is influenced by temperature, salinity, density and winds. Horizontal movement is current (water moves) and waves (water does not move, move only in wave trains); vertical movement is tides (rise and fall of waters) – it includes upwelling and sinking

  • Waves: Energy that moves. Wind causes waves to travel and energy is released. Approach beach, wave slows due to friction.

  • When depth of the water is half the wavelength, wave breaks. Largest waves are seen in open oceans. Wind continue to move as they absorb energy from wind.

  • Breeze of 2 knots or less blow over calm waters

  • Steep waves are young and are formed by local winds.

  • Maximum wave height is determined by wind strength – how long it blows and area over which it blows in single direction

  • Gravity pulls crest downwards while falling water pushes trough upwards. Wave Motion is circular.

Components of Waves

  • Crest and Trough

  • Wave height – from bottom of trough to top of crest

  • Wave amplitude – half of height

  • Wave period – time interval between two crest

  • Wavelength – distance b/w two crests

  • Wave speed – rate of movement through water

  • Wave frequency – number of waves passing in one second time interval

Tides

Image of a Tides

Image of a Tides

Image of a Tides

  • Tide: Rise and fall of sea level due to attraction of sun and moon (caused by moon’s gravitational pull, centrifugal force)

  • Surge: Movement of water by meteorological effects

  • On side of earth facing moon – tidal bulge appears while on other side there is centrifugal force

  • Tide generating force is difference b/w gravitational attraction of moon and centrifugal force

  • On surface nearest to moon – attractive force is greater than centrifugal force and causes bulge towards moon

  • Horizontal tide generating forces are important than vertical tide generating forces

  • Where continental shelf is wide, bulge is higher; it is low when it hits mid-oceanic islands

  • Shape of bay and estuary intensify tide. Funnel shaped bays have more magnitude.

  • Tidal current: When tide is channeled between islands or bays

  • Highest tide in world – Bay of Fundy, Canada with bulge of 15-16m

  • There are 2 high and 2 low tides every 24 hours

Types of Tides

Image of a Types of Tides

Image of a Types of Tides

Image of a Types of Tides

  • Perihelion on 3rd Jan – earth closest to sun – unusually high and unusually low tides

  • Aphelion on 4th July – tidal range is less

  • Ebb- time b/w high tide and low tide when water level is falling

  • Flow or flood: time b/w low tide and high tide when water level is rising

  • Importance of Tide – can be predicted, help navigators and fishermen, harbors have shallow bars at entrance which prevent boats from entering into harbor. Help to desilt sediment, remove polluted water from estuary and generate electrical power. 3MW tidal power project at Durgaduani in Sunderbans

Ocean Currents

  • Two forces – primary force that initiate water movement and secondary force that influence current to flow

  • Primary force influencing currents are heating by solar energy, wind (pushes), gravity (pulls to pile and create gradient variation) and Coriolis force (right in north hemisphere and left in south hemisphere)

  • Heating causes expansion of water. Near equator water is 8 cm higher than middle latitudes – causes slight gradient and water tends to flow down the slope

  • Gyre: accumulation of water and flow around them – creates circular currents in large basins

  • Currents are strongest near surface at 5 knots; at depth speed is slow at 0.5 knots

  • Strength of current refers to speed of current

  • Fast current is strong. Current is strongest at surface and decreases with depth.

  • Difference in density affect vertical mobility

  • Cold dense water sinks at poles and light water rises (cold water at pole sinks and moves towards equator)

  • Warm water travel from equator to poles to replace sinking waters

Types of Ocean Currents

  • Based on Depth

    • Surface – 10% of all; found in upper 400 m

    • Deep water – 90% water; move around ocean basins due to variations in density and gravity

  • Based on Temperature

    • Cold Current – cold water to warm areas on west of continents on low and mid latitude & to east in higher latitudes in North Hemisphere

    • Warm Current – warm water to cold areas on east of continents on low and mid latitude & to west in higher latitudes in North Hemisphere

Major Ocean Currents

  • Currents are influenced by prevailing wind and Coriolis force

  • Ocean circulation corresponds to air circulation

  • Air circulation over ocean in mid latitude is anticyclonic (ocean circulation is also similar)

  • Transportation of heat from one latitudinal level to another takes place

  • Effects of ocean currents – West coast in tropical and subtropical latitude are bordered by cool waters – low average temperature, narrow range of temperature with fog

  • West coast of continent in middle and higher latitude are bordered by warm waters causes distinct marine climate – cold summer, warm winter with narrow range of temperature

  • Warm current flows parallel to east coast in tropical and subtropical latitude – lead to warm and rainy climate – lie on west margin of subtropical anti-cyclones

  • Mixing of warm current and cold current replenish oxygen and favor growth of planktons (best fishing grounds in world)

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