Energy Balance in the Troposphere Flashcards
What is the greenhouse effect?
“The process whereby radiatively active gases (carbon dioxide, water vapour, methane, and CFCs) absorb and emit the energy at longer wavelengths, which are retained longer, delaying the loss of infrared to space. Thus, the lower troposphere is warmed through the radiation and re-radiation of infrared wavelengths. The approximate similarity between this process and that of a greenhouse explains the name.”
In Chapter 2, we characterised Earth as a cooler blackbody radiator than the Sun, emitting energy in longer wavelengths from its surface and atmosphere toward space. However, some of this longwave radiation is absorbed by carbon dioxide, water vapour, methane, nitrous oxide, chlorofluorocarbons (CFCs), and other gases in the lower atmosphere and then emitted back, or reradiated, toward Earth. This process affects the heating of Earth’s atmosphere. The rough similarity between this process and the way a greenhouse operates gives the process its name—the greenhouse effect. The gases associated with this process are collectively termed greenhouse gases.
What are greenhouse gasses?
Gases in the lower atmosphere that delay the passage of longwave radiation to space by absorbing and reradiating specific wavelengths. Earth’s primary greenhouse gases are carbon dioxide, water vapour, methane, nitrous oxide, and fluorinated gases, such as chlorofluorocarbons (CFCs)
What is cloud-albedo forcing?
“An increase in albedo (the reflectivity of a surface) caused by clouds due to their reflection of incoming insolation.”
Low, thick stratus clouds reflect about 90% of insolation. The term cloud-albedo forcing refers to an increase in albedo caused by such clouds, and the resulting cooling of Earth’s climate (because albedo effects exceed greenhouse effects,
What is Cloud-greenhouse forcing?
High-altitude, ice-crystal clouds reflect only about 50% of incoming insolation. These cirrus clouds act as insulation, trapping longwave radiation from Earth and raising minimum temperatures. This is cloud-greenhouse forcing, which causes warming of Earth’s climate (because greenhouse effects exceed albedo effects.
An increase in greenhouse warming caused by clouds because they can act like insulation, trapping longwave (infrared) radiation.
What are Jet contrails?
“Condensation trails produced by aircraft exhaust, particulates, and water vapour can form high cirrus clouds, sometimes called false cirrus clouds”
Jet contrails (condensation trails) produce high cirrus clouds stimulated by aircraft exhaust—sometimes called false cirrus clouds, or contrail cirrus (Figure 4.8c and d). Contrails both cool and warm the atmosphere, and these opposing effects make it difficult for scientists to determine their overall role in Earth’s energy budget. Recent research indicates that contrail cirrus trap outgoing radiation from Earth at a slightly greater rate than they reflect insolation, suggesting that their overall effect is a positive radiative forcing, or warming, of climate. When numerous contrails merge and spread in size, their effect on Earth’s energy budget may be significant.
How is the solar energy arriving at the top of the atmosphere distributed?
Out of 100% of the solar energy arriving at the top of the atmosphere, 31% is reflected back to space—this is Earth’s average albedo. This includes scattering (7%), reflection by clouds and aerosols (21%), and reflection by Earth’s surface (3%). Another 21% of arriving solar energy is absorbed by the atmosphere—3% by clouds, 18% by atmospheric gases and dust. Stratospheric ozone absorption accounts for another 3%. About 45% of the incoming insolation transmits through to Earth’s surface as direct and diffuse shortwave radiation. In sum, Earth’s atmosphere and surface absorb 69% of incoming shortwave radiation: 21% (atmosphere heating) + 45% (surface heating) + 3% (ozone absorption) = 69%. Earth eventually emits this 69% as longwave radiation back into space.
How much dose the atmosphere radiate absorbed energy back into space?
In total, the atmosphere radiates 58% of the absorbed energy back to space, including the 21% absorbed by clouds, gases, and dust; 23% from convective and latent heat transfers; and another 14% from net longwave radiation that is reradiated to space. Earth’s surface emits 8% of absorbed radiation directly back to space, and stratospheric ozone radiation adds another 3%. Note that atmospheric energy losses are greater than those from Earth. However, the energy is in balance overall: 61% atmospheric losses + 8% surface losses = 69%.
Summarize the earths-atmosphere energy budget system by latitude.
Between the tropics, the angle of incoming insolation is high and daylength is consistent, with little seasonal variation, so more energy is gained than lost—energy surpluses dominate.
In the polar regions, the Sun is low in the sky, surfaces are light (ice and snow) and reflective, and for up to 6 months during the year no insolation is received, so more energy is lost than gained—energy deficits prevail.
At around 36° latitude, a balance exists between energy gains and losses for the Earth-atmosphere system.
How dose the tropical surplus and polar deficit drive global circulation patterns?
The imbalance of energy from the tropical surpluses and the polar deficits drives a vast global circulation pattern. The meridional (north–south) transfer agents are winds, ocean currents, dynamic weather systems, and other related phenomena. Dramatic examples of such energy and mass transfers are tropical cyclones (hurricanes and typhoons) discussed in Chapter 8. After forming in the tropics, these powerful storms mature and migrate to higher latitudes, carrying with them water and energy that redistributes across the globe.
