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Albedo
Albedo
Albedo is the fraction of light that a surface reflects. If it is all reflected, the albedo is equal to 1. If 30% is reflected, the albedo is 0.3. The albedo of Earth's surface (atmosphere, ocean, land surfaces) determines how much incoming solar energy, or light, is immediately reflected back to space.
Ambient temperature
Ambient temperature
Ambient temperature is the average temperature of an environment.
Conduction
Conduction
A type of heat transfer. Conduction is when heat moves from one object to another object through direct touch. Conduction transfers heat to cooler air that directly touches the hot surface.
Convection
Convection
A type of heat transfer. Convection occurs when air warmed by the surface rises upward, moving heat away from the surface. Convection from hot pavement is the reason that the air above a hot road on a summer day appears to shimmer.
Emissivity
Emissivity
Emissivity is a measure of how efficiently an object radiates heat, i.e. how well the surface of an object “tells the truth” about its temperature. Emissivity values range from 0 (a theoretically perfect mirror that reflects all energy) to 1 (a theoretical object called a blackbody that perfectly absorbs and radiates all energy).
Evaporative cooling
Evaporative cooling
Cooling of a surface that occurs when liquid, usually water, absorbs heat and changes into gas (vapour). This occurs because the liquid gains heat energy and escapes into the air as vapour, leaving the remaining liquid cooler.
Infrared radiation
Infrared radiation
Infrared radiation (IR), or infrared light, is a type of radiant energy that's invisible to human eyes but that we can feel as heat. All objects in the universe emit some level of IR radiation.
Land surface temperature
Land surface temperature
Land surface temperature is how hot the “surface” of the Earth would feel to the touch in a particular location. From a satellite’s point of view, the “surface” is whatever it sees when it looks through the atmosphere to the ground. It could be snow and ice, the grass on a lawn, the roof of a building, or the leaves in the canopy of a forest.
Mean radiant temperature
Mean radiant temperature
Mean radiant temperature (MRT) is a measure of the average temperature of all surfaces surrounding a person, including walls, floors, and objects. Unlike air temperature, MRT considers the radiant heat exchange between the human body and its surroundings.
Relative humidity
Relative humidity
Relative humidity (RH) is the amount of moisture in the air as a percentage of the amount the air can actually hold. Warmer air can hold more moisture than cooler air, which means that for a given amount of atmospheric moisture, RH will be lower if air is warm than it would be if the air is cool.
Solar radiation
Solar radiation
All of the energy from the Sun that reaches the Earth arrives as solar radiation, part of a large collection of energy called the electromagnetic radiation spectrum. Solar radiation includes visible light, ultraviolet light, infrared, radio waves, X-rays, and gamma rays.
Thermal cameras and infrared energy
Thermal cameras and infrared energy
All objects emit infrared energy, known as a heat signature. An infrared camera (also known as a thermal imager) detects and measures the infrared energy of objects. The camera converts that infrared data into an electronic image that shows the apparent surface temperature of the object being measured.
Transpiration
Transpiration
The process of water moving through plants and being released through aerial parts. When solar energy is absorbed by plants, much of the energy is released by evaporative cooling through transpiration.
Urban greenhouse effect
Urban greenhouse effect
Solar energy absorbed at Earth’s surface is radiated back into the atmosphere as heat. As the heat makes its way through the atmosphere and back out to space, greenhouse gases absorb much of it. Why do greenhouse gases absorb heat? Greenhouse gases are more complex than other gas molecules in the atmosphere, with a structure that can absorb heat. They radiate the heat back to the Earth's surface, to another greenhouse gas molecule, or out to space.
There are several different types of greenhouse gases. The major ones are carbon dioxide, water vapor, methane, and nitrous oxide. These gas molecules all are made of three or more atoms. The atoms are held together loosely enough that they vibrate when they absorb heat. Eventually, the vibrating molecules release the radiation, which will likely be absorbed by another greenhouse gas molecule. This process keeps heat near the Earth’s surface.
Air pollution and increases in CO2 increase the urban greenhouse effect. Nitrogen and oxygen, cannot absorb heat and contribute to the greenhouse effect.
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