First edition! May 2012
The Sun The
Earth
The
Atmosp here
The sun is responsible for certain phenomena that occur in our atmosphere. Here is how and why. Ocean currents exist all over the oceans, at different depths and in different directions. These currents move along usually the same paths. Although currents are affected by the rotation of the Earth, the sun is also responsible for their movement. First of all, the sun heats up our atmosphere and winds. When the atmosphere is warm, winds are created, and they move the surface of the ocean with friction. Winds don’t affect the ocean much deeper than 100 meters. The sun doesn’t only heat the atmosphere, but the ocean itself as well. When the temperature of the water changes, so does its density. Cold water is denser than hot water, since hot water is closer to being a gas and cold water is closer to being a solid. The sun can also heat the ocean to evaporation point, which makes it become saltier, and, therefore, denser. Thermohaline circulation, or densitydependent currents, occurs when the water column becomes unstable because of density changes caused by the sun.
The water cycle is the process through which water changes state from liquid, solid, and gas, and location from the atmosphere, the land, and the ocean. Although it is an everlasting circle of events, one could say that the cycle begins when water from natural bodies of water like oceans, lakes, and rivers is evaporated by the sun. The liquid water is turned into water vapor that rises into our atmosphere. Water vapor can also be formed by snow and ice through sublimation and transpiration, which is when plants release water through their leaves after absorbing it from the ground. When the vapor in the atmosphere gets colder, it turns into small water drops through condensation (gas to liquid), and clouds are formed by these droplets. As more drops combine with each other, clouds grow and are eventually too heavy to stay in the atmosphere, so they are released as precipitation (rain, snow, sleet) in order to return to the ground. The water that falls back down to the ground either becomes a part of water bodies, sinks into the ground or, in the case of snow and ice, becomes part of a glacier and stays at the surface.
There is much more to plants than meets the eye. Plants grow because of a process called photosynthesis. Photosynthesis is performed exclusively by plants and some types of algae. Photosynthesis literally means “making by light”. Plants absorb and use the sun’s energy, with their chlorophyll, to split the water’s hydrogen from its oxygen. The leftover hydrogen is combined with carbon dioxide, which they take from the air, and this combination turns into glucose. Plants use glucose as fuel to make other substances within it, and they need glucose in order to survive and grow. Some plants even change their growth patterns in order to absorb more light, since the sun is what triggers photosynthesis and they couldn’t live without it. There are certain types of plants that can live covered by shadows, but it is because they need a smaller amount of sunlight to create the chemical reaction to create glucose and grow. Even so, every single plant in the world needs even a small amount of sunlight to use that energy and produce its own fuel using photosynthesis.
Wind is the horizontal movement of air from a place with high pressure to a place with low pressure. Winds are described by their direction and speed. Winds are caused by differences in air pressure and temperature in our planet. Since some places receive direct sunlight and others receive indirect sunlight and have colder climates, there is an unequal heating of the atmosphere. In places that receive direct heat from the sun, the air warms up and becomes less dense, and therefore, it rises. Cool air, which is denser, flows underneath warm air. Think of it as a convection current that flows all over the globe. Cool air replaces the warm air that has risen. This movement of cold and warm air is what makes winds blow. Every wind that blows in our atmosphere is part of a global circulation system that is acting to even out temperature and air pressure all over the world. Since the globe receives constant sunlight, in different amounts for each different part of it, constant patterns of wind are formed. For example, since the Equator is the warmest part of the Earth, this part of the atmosphere has low air pressure and winds from the Equator blow towards places with high pressure, like the North and South poles, since these are the coldest places in the planet. In their turn, cold, dense winds from the poles sink and blow towards the Equator.
However, winds don’t only blow from North to South. Winds are deflected by the Earth’s rotation to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This happens because, underneath the blowing winds, the Earth is rotating to the East at a high speed, yet the wind continues to move on a straight path. Consider, instead of a wind, an airplane. From the surface of the Earth, it would appear that the airplane is deflecting to the side, but from the airplane, it seems as though it is moving straight forward. This happens the most near the North Pole, where the Earth’s rotation is the fastest, but in the Equator, it doesn’t have any effect.
Contrary to popular belief, the seasons are not a result of the Earth’s orbit around the sun. The Earth’s rotation axis isn’t perpendicular, but it is tilted at a 23,45 degree angle to perpendicular. This tilt makes different parts of the planet receive the Sun’s rays at a more direct angle in different times of the year. Each hemisphere, Northern and Southern, has its own seasons at separate times of the year because, for instance, during summer for the Northern Hemisphere, the Earth’s tilt makes it be closer to the sun, therefore receiving direct sunlight, while the Southern Hemisphere is tilted away from the sun and living wintertime. Some countries have more pronounced seasons than other. For example, Alaska has 24 hour long sunlight during the summertime, since it is located so far north of the globe and is tilted towards the sun at all time, so the rotation of the Earth doesn’t change the amount of sunlight it gets. Countries located on or near the Equator often have only two seasons, rainy and dry, as they are located in the center of the planet and the tilt doesn’t affect these countries that much. The tilt of the planet is also responsible for the summer and winter solstices. These happen in the Northern Hemisphere. December 21 or 22 is the winter solstice, which marks the beginning of winter, and is the shortest day of the year. The summer solstice is the longest day of the year, June 21, and is the beginning of summer. These events occur because these are the times in which the sun is at its furthest northern or southern declination, or the times in which the Northern Hemisphere is closest or furthest away from the sun.
Almost all the energy in our atmosphere comes from the sun. It reaches the Earth as electromagnetic waves, mostly as visible light, infrared rays, and some UV (ultraviolet) rays. Sometimes, particles can affect the incoming radiation from the sun, and this happens because of absorption and scattering. Some of the energy coming into the Earth can be absorbed by molecules from water vapor, carbon dioxide, and ozone in the atmosphere. This is called absorption. Scattering, on the other hand, happens when dust particles reflect the incoming sunlight in every direction. When light is scattered, the light looks bluer. This is why the sky looks blue! There are three types of scattering. They are known as Rayleigh, Mie, and nonselective scattering. Rayleigh scattering happens when the wavelength of the incoming radiation is much bigger than the particles that are making in scatter, such as dust and nitrogen or oxygen molecules. This type of scattering makes longer wavelengths scatter less than shorter ones. Rayleigh scattering is the main type of scattering in the upper atmosphere. Mie scattering happens when wavelengths and particles have the same size. Particles that cause Mie scattering can be water vapor, pollen and smoke. This scattering occurs mostly in the lower part of the atmosphere, where bigger particles are located. Nonselective scattering is the opposite of Rayleigh scattering, since it happens when the particles are much bigger than the wavelengths of the radiation. Large particles like rain water droplets
scatter every wavelength about equally. This phenomenon causes clouds to appear white, since red, green, and blue light are scattered equally, and red, green, and blue light sum up to create white light. The ozone layer in our atmosphere absorbs the harmful UV rays coming from the sun that would otherwise burn our skin. If it weren’t for the ozone layer, living in the earth would probably be impossible for us because of the sun’s dangerous rays. Energy that comes through to the surface of the Earth and is absorbed by humans, objects, and, basically, everything on the planet, is eventually returned to the atmosphere. Matter that has absorbed the sun’s energy radiates infrared rays. Some of these rays make it back out of the atmosphere, but others don’t, since they are absorbed by gases in the bottom layers of the atmosphere, mostly water vapor and carbon dioxide. This is known as the “greenhouse effect”. This process makes the planet remain warm and in comfortable living conditions for living beings, but in parts of the globe in which carbon dioxide in the atmosphere is accumulated, it leads to global warming and changes in the Earth’s temperature.
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