Marc has taught Bachelor level students climate science and has a PhD in climate science.
Energy Transfer on a Small Scale
Atmosphere and Ocean
Have you ever felt a sea breeze on the beach during the day? I'm sure you have also felt the hot sand beneath your feet and the warmth of the Sun's rays as you were sunbathing.
If so, you have experienced all three processes of heat transfer: convection, conduction, and radiation. These processes are the three basic modes of heat transport in Earth system physics.
Once an object such as your feet makes contact with the warmer ground below, the transfer of heat takes place. Energy transfer by the physical contact of a warmer object to a cooler object, and through vibrating molecules, is known as conduction. This usually occurs before convection takes place if a warmer object or medium comes into contact with a cooler object.
Convection is a macroscopic process or one that involves the movement of fluid or air, as in our example of the sea breeze. The occurrence of the sea breeze is mainly due to the difference in the heat capacity of the water or ocean versus the land. The heat capacity is the ability of an object to hold heat. The water has a higher heat capacity than the land, so it takes longer for the temperature of the water to change.
With the Sun shining during the day, the land heats up faster than the ocean, and so the air is warmer above the land compared to the ocean. As a result, a low pressure system over the land and a high pressure system over the ocean develop. This creates an imbalance of pressure with the the flow of air blowing from the high pressure system (ocean) to the low pressure system (land). This is the process of convection and is a special case called a daytime sea breeze that we may feel on a bright sunny day at the beach. We can also call this process that occurs during a sea breeze convection currents.
Using this same example of our day at the beach, the third process called radiation occurs when we may be uncomfortable lying on the very hot sand to get a sun tan. Because the sand's surface has been heating up all day from the Sun's rays, heat in the form of infrared radiation is emitted from the surface.
Energy Transfer on a Large Scale
Atmosphere and Ocean
From our sea breeze example there exists a strong coupling between the atmosphere and ocean through the link of the temperature difference of the land and ocean and the surrounding air. On a much larger scale, or one that involves the whole ocean or Earth system, we can extend this smaller scale sea breeze to a well known weather phenomenon known as El Niño. An El Niño occurs when the water warms in the Pacific Ocean off the coast of South America.
Recall how in our sea breeze example the wind blows from cooler air over the ocean to warmer air over the land. The same situation occurs during an El Niño with winds blowing from the cooler ocean in the western Pacific to the warmer ocean in the central and eastern tropical Pacific. This event can last a year or even more and can occur every two to seven years. It is know to affect weather and ocean patterns throughout the world.
In order to understand how the radiation transfer of heat occurs on a large scale, we can think of the Sun as a great big driver of all the Earth's processes. One example of this is when the incoming radiation has been reflected from the surface or clouds in the atmosphere, and is then either emitted from the surface as infrared radiation as we saw on the beach, or is re-radiated back downwards towards the surface from the clouds.
This re-radiation is one of the most important components in climate change research as it regulates the surface temperature of the Earth with changes over time. This concept is also known as the greenhouse effect.
Similar to our day at the beach with the warm land surface and cooler ocean, conduction and convection also occur deep in the Earth's interior. By conduction the surface of the Earth or lithosphere can become hot because of melted rock deep in the interior that escapes through cracks of the surface. Events where melted rock flows through the surface of the Earth are called plumes.
Once the hot rock rises towards the surface, cooler rock flows downward to the core of the Earth where it is then heated. This then causes circulation of warm and cold material within the interior. This is convection occurring in the deep interior of the Earth and is similar to the processes that occur in our sea breeze example.
Energy is transferred in the atmosphere, ocean, and Earth's interior system by three processes: convection, conduction, and radiation.
These processes can all occur at the same time on either a small or large scale. There is also a strong coupling found between the atmosphere and ocean. Large scale phenomenon involving these energy transfer processes can affect weather worldwide.
Convection and conduction also occur deep inside the interior of the Earth through processes similar to events in the atmosphere and ocean.
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