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44 Cards in this Set
- Front
- Back
troposphere |
lowest layer of the atmosphere |
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Planetary Boundary Layer |
(in troposphere) well-developed mixing, friction, convection; depth varies diurnally: is thicker (2 km) during the day, thinner at night |
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Turbulent Surface Layer |
(in troposphere) intense small scale turbulence due to surface convection, roughness thicker during the day (50m), thinner at night; time scale: seconds;
To understand the transfers in the turbulent surface layer we will use the principles of the laminar layer.
The major difference is that we will use the
eddy diffusivity instead of the molecular diffusivity since the transfer is largely
due to eddy activity rather than molecular activity.
The eddy diffusivities are not constant like the molecular.
Rather, they vary over time and space. |
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Roughness Layer |
(in troposphere) depends on height of roughness element--> buildings, trees, etc.; can be 1-3 times the height of roughness element;
Exchanges of heat mass and momentum occur but they
are dif>icult to express.
Flows are very complex.
We will generalize as Necessary. |
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Laminar Boundary Layer |
(in troposphere) depends on wind speed |
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Energy |
ability/capacity to do work |
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Work |
force applied over distance or movement of matter over distance (Newton meter, Nm) |
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Force |
Mass X acceleration (Newton, N) |
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Acceleration |
rate of change of speed (meters/secondsecond) |
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Thermal Energy |
Mechanical energy converted to calories (1 calorie= 4.186 Joules; Joule=Nm) |
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Kinetic energy |
motion |
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Gravitational Potential Energy |
associated with the height of an object above a surface |
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Sensible Heat |
internal energy which may be sensed or measured, for ex: by thermometer |
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Latent Heat |
energy involved with the changes of state of water |
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Latent heat of condensation – Latent heat of evaporation – Latent heat of sublimation – Latent heat of fusion – |
-released when water vapor changes to liquid -absorbed when water changes from liquid to gas (vapor) -absorbed when ice changes to water vapor -released when ice changes to liquid |
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Blackbody |
emits radiation at the maximum possible intensity for every wavelength and temperature to the emitance of an ideal blackbody at the same wavelength and temperature |
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Absorptivity |
the ratio of the amount of radiant energy absorbed to the total amount incident upon that surface. The emissivity of a blackbody is unity (1) |
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Radiant flux |
rate of flow of radiation (Js-1) |
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Radiant flux density |
radiant flux per unit area (Js-1m-2) |
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Irradiance |
radiant flux density incident upon a surface |
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Emittance |
radiant flux density emitted by a surface |
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Quantity depends on... |
1. intensity of the sun's emittance (radiant flux density emitted by a surface) 2. time of day 3. time of year 4. atmospheric transparency |
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Intensity of sun's emittance |
– Stefan-Boltzman and Wien's Laws - Solar Constant 1370 Watts per square meter - angle of incidence affects the radiant intensity of the flux of energy |
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path length of radiation through the atmosphere |
time of day - It is longest near sunrise and sunset and shortest near noon. time of year - It is shortest at summer solstice and longest at winter solstice. |
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Scatter |
occurs when gas molecules intercept and “knock out” parts of the Electromagnetic spectrum. |
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Rayleigh scatter |
occurs in the blue part (very small wavelengths) of the EM spectrum |
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Mie scatter |
occurs across all wavelengths e.g. in clouds |
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Turbidity |
any condition of the atmosphere that reduces its transparency to radiation - dust, aerosols, pollen, haze |
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Quality (of solar radiation) |
Some gases remove some wavelengths of solar energy e.g. ozone and oxygen remove UV radiation in the visible part of the spectrum there is not much absorption except at the longer (red) wavelengths where water vapour and carbon dioxide absorb energy. |
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Diffuse Radiation |
This is the radiation that reaches the earth after being scattered from the direct beam by atmospheric gases. It is very important at high latitudes (longer path length) and during winter (same reason) before sunrise and after sunset. |
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Shortwave reflection |
Some of the solar radiation that reaches the surface of the earth is reflected. The amount of energy reflected depends on the albedo of the surface. |
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albedo |
is the capacity of a surface to reflect shortwave radiation. It is described as a percentage. |
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Long wave radiation |
energy emitted at longer wavelengths by cooler bodies |
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Convection |
vertical exchange of air – occurs in liquids and gases. It involves the actual movement of air and its properties from one place to another. It is the most effective form of transfer and mixing in the atmosphere. - Eddies, thermals. Latent and Sensible Heat are transferred in this manner. |
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Conduction |
occurs via the collision of molecules. Is important in the laminar layer. Energy is transferred by contact |
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ENERGY BALANCE |
Top of Atmosphere: I = O Atmosphere I > O Earth Surface I > O |
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Active surface |
is a plane, infinitesimally thin. It has no mass and no energy but it is the chief site of the exchanges of energy and mass in the system. It is here that energy is absorbed, reflected, emitted and major energy conversions take place. |
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Specific Heat – |
a property of mass (kg) – is the amount of energy it takes to raise the temperature of one unit mass of a substance by 1 degree Kelvin |
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Heat capacity |
a property of volume (m^3) – is the amount of energy it takes to raise the temperature of one unit volume of a substance y 1 degree Kelvin. |
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Subsurface layer |
exchanges are mostly molecular with energy flowing from areas of high concentration to areas of low concentration. The rate of flow depends on the temperature difference between the two locations and the thermal diffusivity since most of the transfer occurs by molecular collisions transferring kinetic energy. |
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lapse |
temperature decrease with height |
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inversion |
temperature increase with height |
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Ks |
are the molecular diffusion coef/icients and are very small.
This means that transfer is slow.
In this way the laminar layer
insulates the surface from most of the atmosphere. The slowness
of transfer also means that gradients tend to be steep in the laminar layer. |
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Outer Layer: |
This is dominated by free convection - large eddies, thermals and heat plumes. It is of variable depth depending on turbulence at the ground. On sunny days it is at 1 - 2km but at night it can be as shallow as 100m. It may also be called the mixed layer. Climatic properties in this layer vary very little with height |