Oceans cover over 71% of the Earth’s surface and over 97% of the water on Earth is in the oceans. The oceans affect the weather and the weather affects the oceans.
THE LAYERS OF THE OCEAN
The ocean is divided into multiple layers.
- Also called the sunlight zone.
- It starts at the surface and goes 660 feet (200 m) deep.
- Visible light exists in this area.
- Heating from the Sun causes temperature changes on the surface in latitude and during each season.
- SST ranges from 97°F (36°C) in the Persian Gulf to 28°F (-2°C) around the North Pole.
- The wind combined with the heat of the Sun forces the water and heat to mix.
- The bottom of the sunlight zone marks the beginning of the thermocline, which is where ocean temperatures decrease rapidly.
- The thermocline’s depth and strength vary from year to year and season to season, but it is usually strongest in the tropics and non-existent at the north and south poles in winter.
- The Mesopelagic Zone is beneath the Epipelagic Zone.
- It extends from 660 feet (200 m) below the surface to 3,300 feet (1,000 m) deep.
- Also called the twilight zone because the sunlight is very faint.
- The thermocline is within this layer.
- Bioluminescence begins to appear on lifeforms in this layer and the eyes on fish are larger and they are pointed upward to see the shadows of the other animals for food.
- The Bathypelagic Zone is beneath the Mesopelagic Zone.
- It extends from 3,300 feet (1,000 m) beneath the ocean surface to 13,100 feet (4,000 m) deep.
- It is always dark in this layer, which is why it is nicknamed the midnight zone.
- The temperature of the ocean water in this layer is quite cold, at 39°F (4°C). Nevertheless, the temperature doesn’t go up or down much from 39°F (4°C).
- The pressure in this layer is quite impressive as you get closer to the 13,000 foot mark; it is 5,850 pounds per square inch.
- The Abyss is beneath the Bathypelagic Zone.
- It extends from 13,000 feet (4,000 m) below the surface to 19,700 feet (6,000 m).
- It is pitch black in this layer.
- Over 3/4 of the ocean bottoms out in this layer.
- The name abyss comes from the Greek word meaning “no bottom.”
- Only a few animals can be found living this deep in the ocean.
- The water temperature here hovers just over 32°F (0°C).
- This is the deepest that the ocean can go.
- It extends from 19,700 feet (6,000 m) below the ocean surface to the very bottom of the Mariana Trench, at 36,070 feet (10,994 m).
- The water temperature is 33°F (1°C).
- The weight of all of the water above the Mariana Trench is eight tons per square inch.
The ocean is not made up of freshwater. Rather, it is made up of salt water. The salinity of the salt water is indicated as a ratio of salt (in grams) to liters of water. In ocean water, there is usually around 35 grams of dissolved salts in each liter. This is commonly written as 35‰. The average range of the salinity of the ocean is between 33 and 27 grams per liter.
Just like the atmosphere has areas of high and low pressure, the oceans have areas of high and low salinity. The Atlantic Ocean tends to be the saltiest. As you get closer to the equator and the north and south poles, the ocean salinity drops.
The reason that the ocean is less salty near the equator and at the poles is because there is a higher concentration of fresh water within those areas of the ocean. The sea ice at north pole melts some in the Northern Hemisphere summer, while the ice at the south pole melts some in the Southern Hemisphere summer. The melted ice is made up of fresh water. Once the ice melts, the freshwater mixes with the salt water, lowering the salinity of the sea water. Thus, at the equator, the tropics receive more rain than anywhere else on Earth. Due to the amount of fresh water falling into the ocean, the salt water loses some salinity. Between the equator and either poles, there is more evaporation due to ocean currents. When evaporation occurs, fresh water is extracted from the ocean and the salt grains remain. The lack of fresh water in those areas of the ocean allow the ocean to become saltier.
The temperature at which ocean water freezes depends on the amount of salt in the sea water. The addition of salt lowers the freezing temperature. Water salinity at 17 grams per liter freezes at 30°F (-1°C) and at 35‰, water freezes at 28.5°F (-2°C).
The temperature and salinity of ocean water determines the water’s density. When the ocean water’s temperature decreases, the density increases. As the salt water gains salt, the density goes up. The increase in salinity lowers the freezing point of the water. This is vital information for when you are talking about sea ice formation.
Nevertheless, water is unique. As the temperatures of the water decreases to about 40°F (4°C), the water molecules begin sticking together and they start to slow down. As the water temperature falls below 40°F (4°C), the molecules really start bonding together, which causes the water to expand, decreasing the density. When the water temperature reaches the freezing point (32°F or 0°C), the molecules become locked together in a crystalline structure. This results in a 9% increase in size. The decrease in density and the expansion of the water is what causes ice to float.
Just like the atmosphere moves and balances the Sun’s energy around the globe, so do the oceans. In the oceans, the energy moves with ocean currents, such as the Gulf Stream. These ocean currents are shallow. They exist because of the Sun’s heating of the Earth. The Sun’s energy has placed semi-permanent pressure centers on the ocean surface. When wind blows over the surface and over the pressure centers, waves are formed by transferring some of the wind energy, in the form of momentum from the atmosphere to the ocean surface. These ocean currents are driven by trade winds, salinity of the ocean water, and changes in SST (sea surface temperature). There are a set of currents, called counter-currents, which do not move with the trade winds. These currents are located along the equator and they exist because they are where trade winds are weak. The water returns east after it is pushed west by equatorial currents.
Along the west coasts of continents, ocean currents flow toward the equator. These currents are called cool currents, because they pull cold water toward the equator, from either pole. The most well-known cold current is the California Current, which flows along the U.S. Pacific Coast. Along the east coasts of continents, ocean currents flow toward the poles. These currents are called warm currents, because they pull warm water toward the pole, from the equator. The Gulf Stream is a warm current and it is one of the longest and strongest ocean currents in the world with a speed around 3 mph (5 kph).
These currents largely impact the climate system and global weather patterns. Northwestern Europe’s climate is much milder than places at the same latitude because of the Gulf Stream.
There is also a deep-ocean circulation called the Great Ocean Conveyor or thermohaline circulation. It is driven by the density of the water which is controlled by the ocean temperature (thermal) and the salinity (haline) of the sea water. The Great Ocean Conveyor slowly flows southward. It flows into the Atlantic Ocean, then it flows around South Africa and into the Indian Ocean. From there, the water flows into the Pacific.
In the North Atlantic Ocean, the water flows northward toward the north pole. As the water approaches the Arctic, it cools, which increases the water’s density. When the water drops to 32°F (0°C), sea ice will form because the salt is extracted from the frozen water, making the water underneath more dense. The salt water, because it is denser, will sink to the ocean floor. Since the cool water sinks in the North Atlantic, the warmer water will likely rise in the North Pacific. It has been estimated, that the water that sinks will not rise again in the Pacific for over 1,000 years.
The wind also produces waves. As wind blows across the water, the friction between the air and the water stretch the surface. The surface becomes rough as waves are generated. This makes it easy for wind to strengthen the waves.
In order to understand how waves are formed and how they work, we need to understand the parts of a wave. The top of a wave is known as the crest. The bottom is known as the trough. The height of a wave from bottom to top is the vertical change. The distance from crest to crest or trough to trough is called the wavelength, just like in radio waves.
There is an orbital motion of the water which causes objects to bob up and down, forward and backward, and side to side as wave passes underneath the object. However, these orbital motions are not completely circular. Waves have an almost closed circular motion because of the tiny forward motion associated with each passing wave. These tiny forward motions become lesser and flatter as the water increases in depth. This is why you will be pushed around more swimming in a body of water where there are waves or people jumping into the water, generating waves. If you go underneath the surface, you will not feel the motion as much than if you were at the top.
The speed that a wave moves in the water depends on the wavelength and the water depth. The longer the wavelength and the deeper the water, the faster a wave will move. The shallower the water, and the shorter the wavelength, the slower the wave will move. Because tsunamis have wavelengths of 60 miles (100 km) or more, they generally move at a pace of 550 mph (900 km/h). When a deep water wave approaches the shoreline, the depth of the water will be one-half of the wavelength. The wave will begin to “feel” the bottom, which will cause the wave to decelerate, increase in height, and break forward. The reason a wave breaks forward is because the wave is moving faster than the water underneath, which causes the wave to become unstable.
Storms of equal size and intensity may generate large waves in the Pacific. These waves can be much larger than the ones in any other ocean because of how open the Pacific Basin is. The size of these wind waves depend upon three important things; the wind strength, the wind duration, and the fetch.
- Wind Strength | The wind must be blowing faster than the wave for the energy to be transferred.
- Wind Duration | The wind must be strong and it must last for a good amount of time in order to assist in the formation of big waves.
- Fetch | The distance the wind blows without changing direction.
If the wind blows long enough, and if the wind is strong enough, a wave’s vertical distance should increase. As the wave increases in height, the wave will eventually begin to move faster and break.
In a fully developed sea, waves outrun the storm that formed the waves. This reduces the height of the wave and it also lengthens the wavelength. These waves are called swells. They appear in groups and they may travel many thousands of miles before changing in height or speed. As we discussed above, the longer the wavelength, the faster the wave will move. When the waves leave the storm which created them, they will organize with the longer waves ahead of the shorter waves (length). The energy will be evenly distributed across a large area.
Just like other waves, swells will begin to feel the bottom of the shallow ocean as it approaches the shoreline. The direction of the wave may change due to sandbars and the shape of the land. The wave will start moving faster than the water underneath, which will make the wave’s vertical distance increase, and with the force of gravity, it will cause the wave to break. In Hawaii, there is good winter surfing waves due to the swell waves generated from winter storms, which form off of the northern Pacific Ocean.
Rouge waves or extreme storm waves are large waves which appear out of nowhere. They are not predictable and they have been responsible for a large number of ship wrecks over the years. They tend to not flow with the wind patterns. One of these waves struck and almost capsized the R.M.S. Queen Mary right after WWII as it was passing the southern tip of Newfoundland.
What causes these large waves? According to the National Weather Service,
“Generally, they form because of swells, while travelling across the ocean, do so at different speeds and directions. As these swells pass through one another their crests, troughs, and lengths happen to coincide and reinforce each other, combining them to form unusually large waves that tower then disappear. If the swell are travelling close to the same direction, these mountainous waves may last for several minutes before subsiding.”
Tides are a change in the water levels of the ocean. These water levels go from high to low and they usually change twice a day, six hours apart. These are called semi-diurnal tides. The change from high tide to low tide is called “ebb tide” and the change from low tide to high tide is called “flood tide.”
The main cause for tides is from gravity on Earth, between the Earth and the moon, and between the Earth and the Sun. The gravitational pull between the Earth and the Sun is 178 times stronger than the pull between the Earth and the moon. However, the tidal pull between the Earth and moon is much stronger than the pull between the Earth and Sun.
According to the National Weather Service,
“The result of this tidal pull is a bulge in the ocean water almost inline with the position of the moon; one bulge toward the moon and one on the opposite side of the Earth, away from the moon. When we observe the tides what we are actually seeing is the result of the Earth rotating under this bulge.”
The reason for a bulge on the opposite side of Earth, facing away from the moon at the time,
“…is obviously not gravity that is doing it but rather, it is the difference in gravitational force across the Earth that causes the bulge. This difference in gravitational force comes from the moon’s pull at various points on the Earth.”
“Because the pull of gravity becomes stronger as the distance decreases between two objects, the moon pulls a little harder at point “C” (closest point to the moon) than it does at point “O” (in the center of the Earth), and the pull is weaker still at point “F” (farthest point from the moon). If it were not for the Earth’s gravity, the planet would be pulled apart (figure 2).”
“Yet also because of the Earth’s gravity which pulls us toward the center of the planet we can mathematically subtract the moon’s pull at the center of the Earth from the moon’s pull at both point “C” and “F.” When this vector-based subtraction occurs, we are left with two smaller forces; one toward the moon and one on the opposite side point away from the moon (figure 3) producing two bulges.”
When the Earth rotates every 24 hours, we pass under areas where the tidal force pulls water away from Earth’s surface, which is when we experience high tide. The bulge across Earth is constantly the same because of the evenly distributed gravitational force. The water level during high or low tide at any given location may differ because of the shape and depth of shorelines. This may cause a given location to have only one high and low tide a day, which is referred to as a diurnal tide. Other causes for differences in tides are orbital patterns in the moon and the Earth around the Sun. These orbits are by no means circular. They are elliptical. There are changes in orbital patters of the Earth, the Sun, and the moon. The distance from the Earth and moon may change by as much as 13,000 miles (31,000 km). Every 28 days, or once a month, the moon will reach its closest point to Earth. This causes the tides to be considerably higher than normal. Between the Earth and the Sun, we go from our closest and farthest point over the course of a year.
The bulge in the ocean also changes in the Northern and Southern Hemisphere. According to the National Weather Service,
“As the moon completes one orbit around the Earth (about every 28 days), there are two times in each orbit when the Earth, moon, and the Sun are in line with each other, and two times when the Earth, moon, and Sun are at right angles… When all three angles are in line (around full and new moons), the combined effect of the moon’s and Sun’s pull on the Earth’s water is at its greatest resulting in the greatest ranges between high and low tide. This is called a “spring” tide (from the water springing or rising up).”
“Seven days after either a full or new moon, the Earth moon, and Sun are at right angles to each other. At this time, the pull of the moon and the pull of the Sun partially cancel each other out. The resulting tide, called a “neap” tide, has the smallest range between high and low tide.”
THE SEA BREEZE
The ocean is able to absorb and store a lot of energy from the Sun for two reasons. The first reason is because the transparency of the water allows the rays from the Sun to penetrate deep into the ocean water. How far the rays go depends on how clear the water is. Near tropical islands, the sunlight may reach a depth of 500 to 650 feet (150 to 200 m). This means that it takes a great amount of solar radiation to increase the water temperature. The second reason is because of the continuous turbulence of the wind and the weather mixing the water. This distributes the surface heating of the ocean surface.
Over land, most of the Sun’s energy gets reflected rather than absorbed because the Sun’s rays do not penetrate the soil like it does the water. Most of the energy from the Sun gets confined to the top few inches of the soil. This is part of what causes large temperature fluctuations on a daily basis between day and night on the surface rather than over bodies of water. The difference between how much the surface and water are heated have a huge impact on the weather in coastal areas, because of the formation of land and sea breezes.
The circulation of the sea breeze is made up of two opposing flows. One is at the surface (2), called the sea breeze. The other is above (5), which is called the return flow. These result in a difference in the density of the air between the land and the sea caused by the Sun’s energy.
The Sun warms the surface and the ocean at the same rate. However, the ground’s heat remains in the top inches of the soil. It gets reflected back into the atmosphere, which warms the air. The density of the air increases as the air warms. This forms a weak low pressure area known as a thermal low (1). The cooler and denser air moves inland off of the water (2). As the cooler air moves inland, it forces the less dense warm air to rise (3). Between the warm and cool air is a boundary called a sea breeze front, which the same as your typical cold front, which is formed because of the difference in air temperature on either side of the front (land & water). As the front moves through, the air temperature may drop more than 20°F (11°C) in the coastal area. The skies clear after the sea breeze passes by. This also may increase the humidity, change the wind speed and/or direction.
On land, as the warm air is forced up, the sea breeze front will begin to cool the rising warm air. This increases the density of the air, which forms an area of high pressure (4). This occurs around 3,000 to 5,000 feet (1,000 to 1,500 m) in elevation. Because the air is at 3,000 to 5,000 feet (1,000 to 1,500 m), the air pressure and the air density are greater than the same elevation over the water. This forces the air to flow back over the water (5). As the air is over the water, the air cools, which increases the density of the air, which allows the air to sink (6). High pressure will form at the ocean surface (7). The process will continue to repeat. The sea breeze doesn’t have to just occur on the ocean, it may also occur on large bodies of water such as bays, harbors, large rivers, land large lakes.
Sea breezes generally occur in a local area. However, they may affect weather across a much larger area if there are larger atmospheric conditions occurring. With these sea breeze fronts, thunderstorms may develop, just as with cold fronts. The number of thunderstorms that will occur depend on the weather pattern across the region.
Light west winds of 5 to 10 mph (8 to 16 km/h) keep the sea breeze front confined to the eastern coast, but also make for more widespread thunderstorms along the boundary. Stronger winds from the west can prevent the sea breeze front from moving onshore or forming at all, thus no thunderstorms will occur. Winds blowing east can help push the sea breeze front and thunderstorms as much as halfway across the region.
On small peninsulas, such as at the northern tip of New Zealand, sea breezes from opposite coasts may collide. The collision of the two lines may result in the formation of a single but intense, short-lived line.
The opposite of a sea breeze is a land breeze. While sea breezes occur during the day, land breezes occur at night. Despite this temporal difference in occurrence of land and sea breezes, the formation of land breezes is basically the same as that of sea breezes, however, the role of the ocean and land is reversed.
At night, land temperature falls below that of the ocean resulting in an increase in air density. Gravity’s downward pull moves air downhill spilling it onto the water (1). This more-dense air undercuts the lighter, warmer air over the water (2) forcing it up into the atmosphere (3). This rising air forms a weak low pressure area (4).
The rising air accumulates aloft forming an area of higher pressure (5). Relative to the land at the same elevation, air flows back toward land from high pressure to low pressure (6). Once back over land, the air cools, increases in density and then sinks causing an increase in density and high pressure (7). Gravity pulls the dense air offshore again completing the circulation.
Land breezes are weaker than sea breezes but not because of the difference in heating. Daytime heating and nighttime cooling occur at about the same rate so the potential for both land and sea breezes to be the same strength exists. At night however, the cooling ground inhibits vertical motion, which, in turn, weakens the land breeze circulation. Nighttime cooling produces a shallower change in temperature so land breeze circulation is shallower and terrain, vegetation, and buildings stop the flow of air from land to water.
THE MARINE LAYER
The marine layer is similar to a sea breeze because it also represents a difference between warm and cool air. The marine layer can persist for days or weeks along the west coasts of any continent. It most noticeably occurs along the coasts of central and southern California.
In the summertime, when someone drives from the Golden Gate Bridge in San Francisco, California, temperatures will be in the upper 50s to low 60s with fog. However, once you go to the top of Mount Tamalpais, just a few miles to the north, the skies will be clearer and temperatures will be in the 80s or low 90s. This is because of you rising above the marine layer, which is cool.
The reason for the marine layer is because the U.S. west coast’s ocean water comes from the Gulf of Alaska, in which the currents pull warm cold water into the area. In the Atlantic, the water can be up to 30°F (17°C) warmer than the water along the Pacific coast. The same goes for the west coasts of other continents, but the cool water comes from the Arctic and Antarctic. The cool water makes the air above cooler, which makes the air denser, which sinks and forces the warm air to rise.
The height of the marine layer differs from day to day. It all depends upon atmospheric Conditions across the entire region. If the cool, dense air is sinking with high pressure overhead at elevations of 15,000 to 30,000 feet (4,500 to 9,000 m), the sinking air under pressure will squash the marine layer. If the downward forcing of the air is really strong, the marine layer will be very small in height/depth. There will be a lot of low clouds and fog that will be confined around the beaches. However, just about a mile inland, it will be sunny and clear. If the downward forcing is weaker, then foggy conditions will lift and spread further inland because the marine layer will have a greater depth. If there is further lifting, the marine layer will push the cool air further inland and over the coastal mountains into the valleys.
Due to this phenomenon, the Sacramento and San Joaquin Valleys often have extreme temperature swings in the summer.
Bakersfield, CA is located in the southern half of the San Joaquin Valley. It is surrounded by mountains on three sides. These mountains break up weather systems, which is why Bakersfield only receives an average of 6.49 inches of rain per year and they block out the cool air from the marine layer. However, with the occasional lifting of the marine layer, cool air is able to spill into the area for a couple of days, thus causing wild temperature swings from the 100s to 70s and back again.
Rip currents are powerful currents of water. They flow away from the shore. These generally extend from the beach shoreline out past where the waves break. They can happen at any beach and they may occur in other large bodies of water such as the Great Lakes.
Usually, rip currents will form in low spots or breaks in sandbars. They may also form around piers. They tend to be very narrow in width and they tend to extend out by hundreds and hundreds of feet from the shoreline. Rip currents form when incoming waves create sandbars (1) and the waves push lots of water in between the sandbar and the shore (2) until part of this sandbar collapses, which allows water to rush backward at 1 to 2 feet per second toward the sea (3). After the water flows back through the gap, it begins to spread out (4), which weakens the rip current.
Surprising to many, rip currents are the biggest surf threat to humans, not sharks and not jellyfish. 100 estimated people die each year from these rip currents, as people get pulled away from the shore. The reason people drown in rip currents is because they are not able to swim, which may be due to fear, shock, panic, or just simply the ability to not know how to swim (but why would you be in the ocean if you don’t know how to swim?).
Read about Rip Current Safety here.
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