The movement of energy within our earth's one connected system is paramount for the life on this planet to thrive. There are many places this global energy travels, and before speaking of the waves I will explain our systems high in the sky. Our atmosphere can be divided into four distinct layers that each have a different physical makeup and qualities. Starting with the lowest layer we have the troposphere maxing out from sea level at ten kilometers high. Air pressure and temperature lowers as you climb this layer, and almost all weather is formed in this later due to the abundance of water vapor and dust particles. Next, we have the stratosphere, which rises up almost forty kilometers from the top of the troposphere. Interestingly, temperatures actually warm as you ascend while within the stratosphere, due to the ozone-rich ozone layer residing within this layer. Above that, we have the mesosphere, which takes up thirty-five kilometers of space from the top of the stratosphere. Temperatures once again grow cold as altitude goes up, and it is now nigh impossible to breathe due to the air pressure of less than one percent. Finally, we then see the thermosphere, which reaches over ninety kilometers in the sky from sea level. Moreso space than atmosphere, the excess of UV radiation causes the temperatures to reach over nine hundred degrees Fahrenheit right before entering the final frontier. One thing all of these layers have in common is their previously mentioned physical makeup, which also explains why it gets hard to breathe up there. The total composition of the entire atmosphere is seventy-eight percent nitrogen and twenty-one percent oxygen, with the remaining percent being other gasses. The reason why we can breathe fine down here is that oxygen molecules are heavier than nitrogen molecules, causing them to pool at the bottom (Layers of Earth's Atmosphere). The atmosphere and its layers are important for keeping the molecules we need to live where we need them, but it also traps something else. Heat is trapped by our atmosphere while also being released by it and the earth, and there's a way to measure this. The heat budget is the balance of how much heat the earth is releasing and absorbing at the same time, and the goal is for the heat taken to equal the heat released. There are multiple natural factors on our planet that absorb, release, or reflect heat given by the sun, and each by different amounts. For absorption, the land and ocean combined take about forty-seven percent of *the sun's* heat budget, and twenty-three percent is absorbed by dust, clouds, and gasses. Almost all surfaces reflect some amount of heat, and the remaining thirty percent of the budget is reflected by the surface and clouds or just scattered to space. The heat released from the earth isn't actually all from the sun and is a combination of solar heat, latent heat, and heat from greenhouse gases. Of this heat, around sixty percent of it is released by clouds and gasses such as CO2 in the atmosphere. and the remaining percent is released latently from the earth through processes such as longwave radiation and conduction. One more important factor with heat budget is that it is not spread across the earth equally. Due to the earth being a sphere, heat is spread out more in different areas than others, causing those spread-out locations to be colder than where the heat is more concentrated (8.1 Earth's Heat Budget). The curvature of the earth has a drastic effect on how heat energy reaches the planet, but it alongside our earth's rotation also has an effect on the wind. This phenomenon is now well known and documented, and is one part of the very large picture of earth's circulation. To preface, the differing levels of pressure between the equator and poles cause air to move in a cycle. As there is also a temperature difference between these areas, this also allows heat from the equator to reach up to the poles which get less heat budget. Secondly, due to the earth's spherical nature latitudes closer to the poles actually rotate slower than areas near the equator. These two factors combined together form the Coriolis effect, a phenomenon that causes airborne objects in motion to swerve left or right. The Coriolis effect has a pronounced effect on our wind circulation as it travels globally from the equator to the poles, changing a cycle that would've been stacked on top of itself into more of a circle. This circle is called a gyre, and there are two gyres for each hemisphere that circle in opposite directions. The north gyre circles clockwise, going east or "right", while the south gyre circles counterclockwise, going west or "left" (Evers). These two gyres are key to the circulation of the earth and its currents, however, it gets more complicated than just two circles. There are individual parts of these gyres and of our global oxygen supply that each have an important effect on the entire system. The air cells are the most important of these with three being mirrored for each hemisphere, and all providing their own current. From the equator to thirty degrees latitude we have the Hadley cell, which contains the northeastern and southeastern trade winds for each respective hemisphere. The winds flow in opposite directions much like their respective gyres, and the northeastern tradewinds are what allowed easy commerce between Europe and the Americas. From thirty degrees latitude to sixty degrees latitude is the Ferrel cell, which contains the westerlies in both hemispheres. An important impact the westerlies have had on us is it's powering of the Gulf stream, a current of warm water that prevents Europe from freezing over. Finally, from sixty degrees latitude to the poles, we have the Polar cell, which contains the polar jet stream. Frigid air from the poles makes its way toward the equator thanks to the atmospheric currents present within the polar cell, completing the full cycle of the gyres (Otsego). The equator has been mentioned countless times as a factor in the circulation of the currents, but the one in the middle of the earth isn't actually the center in question. There is actually a second equator that ties to meteorological currents that shifts around depending on the time of year. The meteorological equator or equatorial trough is the true point where the two Hadley cells meet, and is most often positioned five degrees above or below the geographic equator. The reason it moves is because of differing levels of heat absorption between the earth's land and its oceans. Water is much more absorbent than soil or rock, so the northern hemisphere is colder on average than the southern hemisphere. This affects the position of the meteorological equator and means it will be five degrees north during the northern summer, and five degrees south during the southern summer (Rydell). The earth's second equator is unique with its ability to move along the earth's latitude, but other weather phenomena also change depending on their location. The more intense weather occurrences such as hurricanes and cyclones are found all around the world and have different qualities depending on their spot. With cyclones, the two main classifications are tropical and extra-tropical, with the difference being their core temperatures. Tropical cyclones always have warm cores and spread temperature equally throughout the storm, while extratropical cyclones have cold cores and have much more stratified temperatures throughout. As for locations, extratropical cyclones are most often found within the Ferrel air cell outside of tropical areas (Tropical, subtropical, or extratropical?). Tropical cyclones, which include typhoons and hurricanes as well, can be in a multitude of different locations. Typhoons are found in the northwest Pacific Ocean, cyclones range between the south Pacific and Indian Oceans, and hurricanes from the Atlantic Ocean to the northeast Pacific (Hurricanes, Typhoons, and Cyclones). These large storms can be found in many different oceans across the world, but those areas are prone to increase. Because of recent changes in climate due to human activity, the intensity and amount of these deadly storms are growing. The warming of both the atmosphere and the ocean has been shown to increase the power behind large tropical storms such as hurricanes and cyclones in multiple ways. Rises in sea levels mean that storms can reach farther inland than before, while also increasing the amount of rain they bring within the clouds. Meanwhile, the overall intensity of hurricanes will increase significantly due to warmer air, with more category four and five storms being predicted in the future (Knutson). However, despite their increases in size, there is actually one natural factor that works to dampen the intensity of tropical storms, and it comes in the form of Saharan dust. Winds blow dust from the Saharan desert all the way to the eastern coast of the United States, and this dust absorbs water vapor vital to hurricane formation. While only a partial blocker, hurricane season only starts after most of this dust has dissipated, meaning these particles likely put in a lot of work we just can't see (Beitler). That was everything to do with atmospheric circulation, however, its influence spreads further than just the skies. The ocean has currents of its own as well, some provided by existing atmospheric currents, and others it creates completely by itself.
Our earth's oceans possess their own set of currents and cycles which are equally as important for life to exist on the planet. One of these currents is the surface current, which is provided by the wind and is found within a mere 10% of the earth's total water. However, while the base amount of water affected by surface currents is small, its influence spreads far below the waves. When surface water is moved by the wind, it drags on the water layer below it, this layer in turn pulls on the water layer below *it*, and so on and so forth. The catch is that the direction and power of this drag change as depth increases, with the intensity decreasing for each layer until it hits zero. In addition, each layer of water hit changes the angle the energy is going in by fifteen degrees from the layer above it. This entire process is called an Ekman spiral, and the direction the angle shift goes in is directly tied to the Coriolis effect (The Ekman Spiral). Speaking of the Coriolis effect, it and the global winds also have a large-scale effect on ocean currents through the formation of five unique ocean gyres. These ocean gyres are comprised of boundary currents, which as the name suggests flow around the boundaries of different ocean basins around the world. One boundary current of note is the Gulf stream, which I previously mentioned when talking about atmospheric currents. While the atmospheric gyre powers the system, the oceanic gyre and Gulf stream represent the actual warm water being transported (Boundary Currents). All gyres transport large amounts of water across the world, however, the gyres do not move the same way throughout the whole cycle. Depending on which direction a point in the gyre is flowing, it can actually increase the speed it transports water exponentially. This occurrence is called westward intensification, a phenomenon where the western sides of a gyre are much more intense than the eastern sides of a gyre. The reason this happens is because of a special quality of the Coriolis effect, specifically two areas closer to the poles have a greater difference in rotation speed than two areas near the equator of the same distance apart. The greater the difference in force between two points, the greater the effects of the Coriolis effects are. Because the westward sides of gyres are heading toward the poles in both the southern and northern hemispheres, it causes the water flow to be thinner and faster in those areas. Conversely, because the eastern sides of gyres are heading toward the equator, they are much wider and slower than on the east side. This difference in speed also causes the "center" of the gyre to be positioned more toward the left side of it rather than in the center of the rough circle (9.4 Western Intensification). That was almost every different quality of the general circulation of our planet's water, but there are a few more individual systems that have yet to be discussed yet. These systems all relate to the previous Coriolis effect and surface currents, but their importance lies in what gets transported alongside the water. The first of these events are upwelling and downwelling, which primarily happen alongside the coast and have drastic effects on nutrient transport. With upwelling, the wind blows away from the beach and carries surface water with it, causing nutrient-rich deep waters to rise up and take its place. These upwelling zones are highly productive, and great communities both under and above the waves often sprouted up next to them. On the other side of the spectrum is downwelling, where the wind blows toward the beach, which causes water to pile up and push down on the liquid beneath it. This allows surface water to sink to deeper parts of the ocean, and due to not being as rich in nutrients the surrounding areas are much less active (9.5 Currents, Upwelling and Downwelling). The next two occurrences are related to the weather, with this first one being much less intense than the second. Both atmospheric and oceanic currents transport weather phenomena all over the world. Winds heading to the poles bring warm water and precipitation to higher latitude areas, while winds heading in the opposite direction bring cold water down from the poles back to the equator. The main benefit of this heat transport is to balance out the uneven distribution of the heat budget across our earth, meaning certain areas won't be too hot or cold to live in (How does the ocean affect climate and weather on land?). Finally, we have the two extremely large climate events, El Niño and La Niña, which have drastic effects on how the gyres flow. During a La Niña or "cold" event, the eastbound trade winds increase in speed significantly, transporting large amounts of water toward Asia. This causes large amounts of upwelling on the west coast of North America, making northern parts of the country colder, western areas wetter, and southern areas much drier. The colder temperatures on the west coast mean certain aquatic species will arrive there for the season such as squid and salmon, while the dry south means crops won't grow as well. During an El Niño or "warm" event, the trade winds die down almost to a halt, and warm waters will start to flow back toward North America. This reduces upwelling in these areas significantly, and the reduced nutrients can hurt phytoplankton and fish populations significantly. The shift in the jet stream also causes northern areas to be much drier than normal and southern areas to get heavily increased precipitation, which could have drastic effects on crops (What are El Niño and La Niña). That was the entirety of the Coriolis effect and its many different methods for circulating water around the world, and yet there is one more way for it to be transported. This method of circulation is almost entirely unique, unaffected by wind and instead powered by two other factors. Thermohaline circulation is a system where water is transported around the equator and poles due to differences in temperature and salinity. When the water reaches the poles, some of it freezes into ice and leaves its salt behind in the existing water, increasing its density. This increase causes the saltier water to sink to the deep, becoming bottom water. The cold water sinking leaves a gap which is then again filled by warmer surface waters, and the now bottom water will go down towards the equator again. The equator possesses a lot of upwelling zones, which allows the bottom water to rise up, shaking its salt off and warming up. This water then heads back towards the poles to fill the gaps left by sinking water, fully completing the cycle often described as a treadmill due to the warm water passing directly above the deep cold water (Thermohaline Circulation).
Cited Sources:
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