Earth’s Energy Budget

Modes of Energy Travel Heat Energy can be transferred in three specific ways: Conduction Convection Radiation

Heat Transfer Conduction - transfers heat via direct molecular collision. An area of greater kinetic energy will transfer thermal energy to an area with lower kinetic energy. Conduction is the most common form of heat transfer and occurs via physical contact. Examples would be to place your hand against a window or place metal into an open flame. 

Heat Transfer Convection – is heat transfer by mass motion of a fluid such as air or water when the heated fluid is caused to move away from the source of heat, carrying energy with it. As the immediate hot air rises, it pushes denser, colder air down.

Heat Transfer Radiation – atoms emit electromagnetic waves. All materials radiate thermal energy based on their temperature. The hotter an object, the more it will radiate. The sun is a clear example of heat radiation that transfers heat across the solar system.

Solar Energy 71% absorbed 29% reflected When radiant solar energy reaches the Earth, 2 different interactions occur: Reflection – the radiation is reflected back into space unchanged Absorption – the radiation is absorbed by the atmosphere of the Earth’s surface. 71% absorbed 29% reflected

Breakdown

Earth’s “Constant” Temperature The Earth retains a relatively constant temperature. To do this, it must lose as much energy back to space as it absorbs from the Sun. So we need to reradiate 71% of that energy back into space.

Balancing at the surface For the energy budget at the Earth’s surface to balance, processes on the ground must get rid of the 48 percent of incoming solar energy that the ocean and land surfaces absorb. Energy leaves the surface through three processes: evaporation, convection, and emission of thermal infrared energy.

Cont. About 25 percent of incoming solar energy leaves the surface through evaporation. An additional 5 percent of incoming solar energy leaves the surface through convection. The atmosphere is warmer near the surface and colder at higher altitudes, and under these conditions, warm air rises, shuttling heat away from the surface.

About 17 percent of incoming solar energy leaves the surface as thermal infrared energy (heat) radiated by atoms and molecules on the surface.

Energy and Water Most of the sun’s energy hits water on earth (earth is 70% water) Interactions between the sun’s energy and water have a major influence on weather but it depends on what state the water is in White snow and ice reflect the vast majority of solar energy in the water world.

Energy and Water Liquid water reflects only about 7% (i.e. it absorbs about 93%!!!) Therefore the sun’s energy drives the water cycle, and in turn our weather.

Water in the Air The incoming radiation from the sun causes ~23% of liquid water to evaporate Evaporation occurs from all bodies of water but mostly the oceans Water exists in the air as water vapour When the air becomes saturated, condensation of the water vapour occurs (forms liquid water droplets) – this is called the DEW POINT The amount of water vapour in the air is measured by humidity

Assignment Using your notes, draw your own picture that shows the water cycle. Include the following terms: Evaporation Evapotranspiration Condensation Surface Runoff Groundwater flow Precipitation Also add in the heat energy transfer you recorded in your notes – include incoming radiation and re-radiation of energy

Heating Earth Why is it that when you are at the beach, the sand can be scorching hot while the water is cool? After all they are getting the same amount of solar radiation

Specific Heat Capacity Water is cooler because it has a higher specific heat capacity – meaning that it can absorb more heat before changing its temperature. Specific heat is the amount of energy needed to raise the temperature of a certain mass by 1 degree Celsius.

Heating Dry Land vs Water All sunlight that hits the sand or earth is absorbed in the top few cm making it 5 times as hot as water All sunlight that hits water can be absorbed in layers much deeper thus making it cooler (think convection and conduction!).

Heating the Air The first step is radiation – the sun’s energy warms the surface of the earth. The second step is conduction Conduction heats the air by hot (energized) water and land molecules transferring their heat (energy) to the surrounding air The air directly above the land or water then becomes a similar temperature to the temperature of the water or land

Heating the Air The third step is convection As the lower layers of air warm, it expands becoming less dense Since it is less dense and warm, it rises and cooler air takes the place closer to the ground Other substances in the air such as CO2 and H2O (g) can absorb sunlight and can cause temperature in the air to fluctuate

Heating the Air Uneven heating of the air causes wind When cold air is located near warm air it pushes it upwards and creates wind

Sea Breeze

Sea Breeze Occur during the day Travel from sea to land How it works: The land warms up faster than the water This is due to water’s high specific heat capacity – it needs a lot of energy to warm up water The warm air over the land rises while the cooler air over the water sinks down and moves in to replace it. This cool air moving to the land causes the sea breeze!

Land Breeze

Land Breeze Occur at night Travel from land to sea How it works: dry land cools faster than water This is due to water’s large specific heat capacity (meaning it holds heat longer) The air above the water is now warmer than the air above land. This warm air rises, while the cool air above the land falls and rushes over the water to take the place of the rising warm air. The cycle continues, creating a land breeze.