Ocean Atmosphere System
The Earth's ocean and atmosphere are locked in an embrace. winds push against the surface of the ocean, creating currents that help control. Chapter 4: Global Energy Transfer, Atmosphere and Ocean Circulation, Climate that maintains ocean and atmosphere circulation and helps to drive erosion. Climate change caused by ocean, not just atmosphere, study finds .. And how much, how distributed, when, where, the relationships with local changes maybe this will help you understand: omarcafini.info omarcafini.info
But, because of the Coreolis Effect, such winds, again will be deflected toward the right in the northern hemisphere and create a general clockwise rotation around the high pressure center. In the southern hemisphere the effect is just the opposite, and winds circulate in a counterclockwise rotation about the high pressure center. Such winds circulating around a high pressure center are called anticyclonic winds.
The rising moist air at the equator creates a series of low pressure zones along the equator. Water vapor in the moist air rising at the equator condenses as it rises and cools causing clouds to form and rain to fall. After this air has lost its moisture, it spreads to the north and south, continuing to cool, where it then descends at the mid-latitudes about 30o North and South. Descending air creates zones of high pressure, known as subtropical high pressure areas.
Because of the rotating Earth, these descending zones of high pressure veer in a clockwise direction in the northern hemisphere, creating winds that circulate clockwise about the high pressure areas, and giving rise to winds that blow from the northeast back towards the equator. These northeast winds are called the trade winds. In the southern hemisphere the air circulating around a high pressure center is veered toward the left, causing circulation in a counterclockwise direction, and giving rise to the southeast trade winds blowing toward the equator.
Air circulating north and south of the subtropical high pressure zones generally blows in a westerly direction in both hemispheres, giving rise to the prevailing westerly winds. These westerly moving air masses again become heated and start to rise creating belts of subpolar lows.
Meeting of the air mass circulating down from the poles and up from the subtropical highs creates a polar front which gives rise to storms where the two air masses meet. In general, the surface along which a cold air mass meets a warm air mass is called a front. The position of the polar fronts continually shifts slightly north and south, bringing different weather patterns across the land.
In the summer months, the polar fronts shift northward, and warmer subtropical air circulates farther north. Effect of Air Circulation on Climate Atmospheric circulation is further complicated by the distribution of land and water masses on the surface of the Earth and the topography of the land.
If the Earth had no oceans and a flat land surface, the major climatic zones would all run in belts parallel to the equator. But, since the oceans are the source of moisture and the elevation of the land surface helps control where moist air will rise, climatic zones depend not only on latitude, but also on the distribution and elevation of land masses. The atmosphere picks up most of its moisture and heat from the oceans and thus weather patterns and climate are controlled by the oceans.
Global Energy Transfer, Atmosphere, Climate
The oceans vary considerably in their depth. The deepest part of the ocean is called the abyssal plain. As the seafloor starts to rise toward continental margins it is called the continental rise. The continental slope is the steep slope rising toward continual margins. The gently sloping area along the margin of a continent is called the continental shelf.
In addition, deep trenches that occur along zones where oceanic lithosphere descends back into the mantle are called oceanic trenches. These features all effect the circulation of the oceans and the ecosystems that inhabit the oceans. Coastal Zones A coastal zone is the interface between the land and water.
These zones are important because a majority of the world's population inhabit such zones. Coastal zones are continually changing because of the dynamic interaction between the oceans and the land. Waves and winds along the coast are both eroding rock and depositing sediment on a continuous basis, and rates of erosion and deposition vary considerably from day to day along such zones.
The energy reaching the coast can become high during storms, and such high energies make coastal zones areas of high vulnerability to natural hazards. Thus, an understanding of the interactions of the oceans and the land is essential in understanding the hazards associated with coastal zones. Tides, currents, and waves bring the energy to the coast, and thus we start with these three factors.
Tides Tides are due to the gravitational attraction of Moon and to a lesser extent, the Sun on the Earth. Because the Moon is closer to the Earth than the Sun, it has a larger effect and causes the Earth to bulge toward the moon.
At the same time, a bulge occurs on the opposite side of the Earth due to inertial forces this is not explained well in the book, but the explanation is beyond the scope of this course.
These bulges remain stationary while Earth rotates. The tidal bulges result in a rhythmic rise and fall of ocean surface, which is not noticeable to someone on a boat at sea, but is magnified along the coasts.
Usually there are two high tides and two low tides each day, and thus a variation in sea level as the tidal bulge passes through each point on the Earth's surface. Along most coasts the range is about 2 m, but in narrow inlets tidal currents can be strong and fast and cause variations in sea level up to 16 m Because the Sun also exerts a gravitational attraction on the Earth, there are also monthly tidal cycles that are controlled by the relative position of the Sun and Moon.
The highest high tides occur when the Sun and the Moon are on the same side of the Earth new Moon or on opposite sides of the Earth full Moon. The lowest high tides occur when the Sun and the Moon are not opposed relative to the Earth quarter Moons. These highest high tides become important to coastal areas during hurricane season and you always hear dire predications of what might happen if the storm surge created by the hurricane arrives at the same time as the highest high tides.
Fluctuations in Water Level While sea level fluctuates on a daily basis because of the tides, long term changes in sea level also occur. Such sea level changes can be the result of local effects such as uplift or subsidence along a coast line.
But, global changes in sea level can also occur.
Such global sea level changes are called eustatic changes. Eustatic sea level changes are the result of either changing the volume of water in the oceans or changing the shape of the oceans. For example, during glacial periods much of the water evaporated from the oceans is stored on the continents as glacial ice. This causes sea level to become lower. As the ice melts at the end of a glacial period, the water flows back into the oceans and sea level rises.
Thus, the volume of ice on the continents is a major factor in controlling eustatic sea level. Global warming, for example could reduce the amount of ice stored on the continents, thus cause sea level to rise. Since water also expands increases its volume when it is heated, global warming could also cause thermal expansion of sea water resulting in a rise in eustatic sea level.
Oceanic Currents The surface of the oceans move in response to winds blowing over the surface. The winds, in effect, drag the surface of oceans creating a current of water that is usually no more than about 50 meters deep. Thus, surface ocean currents tend to flow in patterns similar to the winds as discussed above, and are reinforced by the Coreolis Effect.
But, unlike winds, the ocean currents are diverted when they encounter a continental land mass. In the middle latitudes ocean currents run generally eastward, flowing clockwise in the northern hemisphere and counterclockwise in the southern hemisphere. Such easterly flowing currents are deflected by the continents and thus flow circulates back toward the west at higher latitudes. Because of this deflection, most of the flow of water occurs generally parallel to the coasts along the margins of continents.
Only in the southern oceans, between South America, Africa, Australia, and Antarctica are these surface currents unimpeded by continents, so the flow is generally in an easterly direction around the continent of Antarctica. Ocean Waves Waves are generated by winds that blow over the surface of oceans. In a wave, water travels in loops.
But since the surface is the area affected, the diameter of the loops decreases with depth. The diameters of loops at the surface is equal to wave height h.
This depth is called wave base. In the Pacific Ocean, wavelengths up to m have been observed, thus water deeper than m will not feel passage of wave.
But outer parts of continental shelves average m depth, so considerable erosion can take place out to the edge of the continental shelf with such long wavelength waves. When waves approach shore, the water depth decreases and the wave will start feeling bottom. In addition the currents are influenced by the Coriolis Force and the tides.
A general pattern of ocean current is shown in the map below. The currents are also influenced by the position of landmasses. Whereas in the Pacific we have currents that more or less correspond to the patterns of the surface winds, current patterns look more complex in the Indian Ocean and the Atlantic.
In the North Atlantic, the Gulfstream moves warm equatorial surface waters northward, and a return current of cold arctic water moves southward across the Atlantic seafloor. Decades of research on ocean currents have revealed that there is a large scale oceanic circulation system.
The Gulfstream that moves into the North Atlantic finally sinks as it cools and returns south across the Atlantic seafloor, flows as a bottom current into the South Atlantic, and then rises to the surface again in the Indian Ocean and the Eastern Pacific, only to warm up absorbing heat from overlying air masses and turn west to feed back into the Gulfstream.
Actually, the sinking of the Gulf Stream is not so much a consequence of cooling and density increase, but one of salinity. Equatorial surface waters are more saline high evaporationand the waters of the North Atlantic are less saline because they mix with meltwater [low salinity] from icebergs and from the Greenland ice cap.
Thus, once the Gulfstream cools sufficiently it is heavier that the lower salinity North Atlantic seawater and sinks. A complete run through this current system is estimated to take about years. At the moment this current system appears very stable, but comparatively minor changes may upset the delicate balance of temperature differences and prevailing winds.
For example, scientists have speculated that melting of the Greenland icecap could introduce so much meltwater of low salinity and low density to the North Atlantic that the Gulfstream is prevented from sinking and returning as a southward flowing bottom current.
This would interrupt the current system and cause equatorial waters and regions to get warmer, and northern Europe to get colder. Atmospheric and oceanic circulation are closely coupled. Specific examples for this kind of interaction are weather phenomena knows as El Nino and La Nina these will be discussed later. The net result of all these interactions, when averaged over periods of decades to centuries, is the Earth System's overall "condition", a state of dynamic equilibrium.
The global climate is a major expression of this "condition".
Climate change caused by ocean, not just atmosphere, study finds
Although circulation of air masses and ocean waters as outlined above plays a significant role in determining global heat exchange and average world temperatures, there are several other, more fundamental, controls on climate. The basic items that determine Earth climate are: The movement of the continents across Earth's surface modulates the global climate on very long time scales by changing wind patterns, ocean currents, and the ease with which ice can accumulate.
Under some configurations of continents and oceans the heat exchange may be severely impeded, leading to hot tropics and ice covered polar regions. Also, when we have all the landmasses bunched up in the polar regions the warm ocean current may not get far enough north and we end up with glaciated continents.
Conversely, when we have all the continents hanging around the equator, the polar regions have very good oceanic heat exchange and world temperatures would be more uniform. Item 3 Greenhouse Effect will be discussed at some length later in this lecture. Basically, this is where linkage to the biosphere comes in. Item 1 Astronomical Parameterswill be surveyed now, because we have already set the stage by going over the origin of the solar system.
Earth's rapid rotation about its axis compared to the time for one orbit around the Sun determines day and night, spreads the incoming solar radiation more or less uniformly around circles of latitude, and strongly affects circulation patterns in the oceans and atmosphere. The eccentricity of Earth's orbit modulates the intensity of the incoming solar radiation through the course of the year.
The tilt of Earth's axis with respect to the ecliptic plane results in the seasons.
Note, that it is summer in the northern hemisphere when the Earth is closest to the sun perihelion, January 3rd, million kmand winter when it is farthest away aphelion, July 4th, million km.
Thus, the tilting of the northern hemisphere towards the sun in summer longer days, more solar energy input and the tilting away from the sun in the winter shorter days, less solar energy input are more important than the actual distance to the sun. The relationship between the eccentricity of Earth's orbit and the orientation tilt of the planet's axis of rotation vary systematically over time.
This causes cyclic shifts of solar energy input that can produce climate modulations repetitive temperature variations. But certain gases and other contaminants in the atmosphere have different effects on different wavelengths of radiation. In addition trace gases have an effect, the most important of which are the greenhouse gases.
Greenhouse Gases Energy coming from the Sun is carried by electromagnetic radiation. Some of this radiation is reflected back into space by clouds and dust in the atmosphere.
The rest reaches the surface of the Earth, where again it is reflected by water and ice or absorbed by the atmosphere. Greenhouse gases in the atmosphere absorb some of the longer wavelength infrared radiation and keep some of it in the atmosphere.
This keeps the atmospheric temperature relatively stable so long as the concentration of greenhouse gases remains relatively stable, and thus, the greenhouse gases are necessary for life to exist on Earth. Venus, which has mostly CO2 in its atmosphere, has temperature of about oC also partly due to nearness to Sun. The CO2 concentration in the atmosphere has been increasing since the mid s. The increase correlates well with burning of fossil fuels.
Thus, humans appear to have an effect. Methane concentration in the atmosphere has also been increasing. Naturally this occurs due to decay of organic matter, the digestive processes of organisms, and leaks from petroleum reservoirs.
Humans have contributed through domestication of animals, increased production of rice, and leaks from gas pipelines and gasoline. Volcanic Effects Volcanoes produce several things that result in changing atmosphere and atmospheric temperatures.
CO2 produced by volcanoes adds to the greenhouse gases and may result in warming of the atmosphere. Sulfur gases produced by volcanoes reflect low wavelength radiation back into space, and thus result in cooling of the atmosphere. Dust particles injected into the atmosphere by volcanoes reflect low wavelength radiation back into space, and thus can result in cooling of the atmosphere. Chlorine gases produced by volcanoes can contribute to ozone depletion in the upper atmosphere.
Volcanism in the middle Cretaceous produced large quantities of basalt on the seafloor and released large amounts of CO2. The middle Cretaceous was much warmer than present, resulting in much higher sea level. The Carbon Cycle In order to understand whether or not humans are having an effect on atmospheric carbon concentrations, we must look at how carbon moves through the environment. Carbon is stored in four main reservoirs.
In the atmosphere as CO2 gas. From here it exchanges with seawater or water in the atmosphere to return to the oceans, or exchanges with the biosphere by photosynthesis, where it is extracted from the atmosphere by plants.Ocean & Atmospheric Interactions
CO2 returns to the atmosphere by respiration from living organisms, from decay of dead organisms, from weathering of rocks, from leakage of petroleum reservoirs, and from burning of fossil fuels by humans. In the hydrosphere oceans and surface waters as dissolved CO2.
From here it precipitates to form chemical sedimentary rocks, or is taken up by organisms to enter the biosphere. CO2 returns to the hydrosphere by dissolution of carbonate minerals in rocks and shells, by respiration of living organisms, by reaction with the atmosphere, and by input from streams and groundwater.
In the biosphere where it occurs as organic compounds in organisms. CO2 enters the biosphere mainly through photosynthesis.
From organisms it can return to the atmosphere by respiration and by decay when organisms die, or it can become buried in the Earth. In the Earth's lithosphere as carbonate minerals, graphite, coal, petroleum. From here it can return to the atmosphere by weathering, volcanic eruptions, hot springs, or by human extraction and burning to produce energy.
Cycling between the atmosphere and the biosphere occurs about every 4. Cycling between the other reservoirs probably occurs on an average of millions of years. For example, carbon stored in the lithosphere in sedimentary rocks or as fossil fuels only re-enters the atmosphere naturally when weathering and erosion expose these materials to the Earth's surface.
Climate change caused by ocean, not just atmosphere, study finds
When humans extract and burn fossil fuels the process occurs much more rapidly than it would occur by natural processes. With an increased rate of cycling between the lithosphere and the atmosphere, extraction from the atmosphere by increased interaction with the oceans, or by increased extraction by organisms must occur to balance the input. If this does not occur, it may result in global warming.
Global Warming Average global temperatures vary with time as a result of many processes interacting with each other. These interactions and the resulting variation in temperature can occur on a variety of time scales ranging from yearly cycles to those with times measured in millions of years.
Such variation in global temperatures is difficult to understand because of the complexity of the interactions and because accurate records of global temperature do not go back more than years. But, even if we look at the record for the past years, we see that overall, there is an increase in average global temperatures, with minor setbacks that may have been controlled by random events such as volcanic eruptions.
Records for the past years indicate that average global temperatures have increased by about 0. While this may not seem like much, the difference in global temperature between the coldest period of the last glaciation and the present was only about 5oC.
In order to predict future temperature changes we first need to understand what has caused past temperature changes. Computer models have been constructed to attempt this. Although there is still some uncertainty, most of these models agree that if the greenhouse gases continue to accumulate in the atmosphere until they have doubled over their pre values, the average global temperature increase will be between 1 and 5oC by the year This is not a uniform temperature increase. Most models show that the effect will be greatest at high latitudes near the poles where yearly temperatures could be as much as 16oC warmer than present.
Effects of Global Warming Among the effects of global warming are: Global Precipitation changes - A warmer atmosphere leads to increased evaporation from surface waters and results in higher amounts of precipitation.
Equatorial regions will be wetter than present, while interior portions of continents will become warmer and drier than present. Changes in vegetation patterns - because rainfall is distributed differently, vegetation will have to adjust to the new conditions. Mid latitude regions become more drought prone, while higher latitude regions become wetter and warmer, resulting in a shift in agricultural patterns.
Increased storminess - A warmer, wetter atmosphere favors tropical storm development. Tropical Cyclones will be stronger and more frequent. Changes in Ice patterns - Due to higher temperatures, ice in mountain glaciers will melt. This is now being observed. But, because more water will be evaporated from the oceans, more precipitation will reach the polar ice sheets causing them to grow.
Reduction of sea ice - Sea ice is greatly reduced due to higher temperatures at the high latitudes, particularly in the northern hemisphere where there is more abundant sea ice.
Ice has a high albedo reflectivityand thus reduction of ice will reduce the albedo of the Earth and less solar radiation will be reflected back into space, thus enhancing the warming effect.
Thawing of frozen ground - Currently much of the ground at high latitudes remains frozen all year. Increased temperatures will cause much of this ground to thaw.