mod 2
solar energy
insolation: measured in units of watts per square meter therefore varies by latitude and by season
a = as if overhead - insolation at its greatest
b = slanted - same energy spread over larger area
responsible for long shadows in midlatitude summers
insolation varies with the sun’s passage in the sky (ex. passage of the sun at the equator)
equinoxes - at noon the sun is directly overhead
solstices - at noon the sun is at an angle
(ex. passage of the sun at mid latitudes)
equinoxes - at noon the sun is 50 degrees above horizon
solstices - june solstice has a higher angle; december the angle is lower
daily insolation
poleward of artic/antarctic circles, sun is below horizon for part of year
daily insolation at its maximum at the pole during summer solstice
two maxima and two minima in daily isolation at the equator occurring at the equinoxes and solstices respectively
insolation
49% = direct radiation (radiation that goes directly to earth’s surface)
31% = reflected back to space (3% by scatter, 19% by clouds, 9% by ground)
20% = absorbed by atmosphere (3% by clouds, 17% by dust and gases)
22% = scattered by atmosphere (eventually get to earth’s surface as diffuse radiation)
in theory, this could affect the climate (ex: more snow, higher albedo, less energy reaches surface, temp decreases, more snow = ice albedo feedback effect)
radiation balance
in comparison to how much radiation we get, the earth is warmer than it should be
bc it’s harder for longwave radiation to leave, the earth is warmed, longwave is absorbed by gases in the atmosphere
the greenhouse effect
greenhouse gases include carbon dioxide, ozone, water vapor, methane, CFCs
they absorb longwave and then re-radiate it to the surface (counter-radiation)
the earth is warmer (by 35 deg. C or 63 deg. F) than it would be without these gases
this is the greenhouse effect
net radiation
difference between incoming and outgoing radiation
at high latitudes, there is an energy deficit
poleward heat transfer moves surplus energy from low to high latitudes
world latitude zones
globe divided into broad latitude zones that we use to describe climatic and other geographic zones
composition of the atmosphere in the troposhere
constant gases
nitrogen 78% (converted by bacteria in a useful form in soils) oxygen 21% (produced by green plants in photosynthesis and used in respiration)
argon ~1% (inert)
variable gases in the atmosphere
carbon dioxide 0.035% (used by green plants in photosynthesis and produced by respiration, burning of fossil fuels)
gaseous water 0.1-4%
methane (produced by cows, termites, swamps, etc.)
CFCs (entirely human made gas)
dust and particulates (from pollen, sea-salt, volcanic dust, soil, etc.)
the earth’s atmosphere
atmosphere = gaseous envelope surrounding the earth
made up of a series of concentric layers
atmosphere is held down by gravity
most of the atmosphere’s mass is near the surface
structure and science of the atmosphere
the atmosphere consists of several layers with different temperatures, pressures, and compositions
troposphere: warmed by greenhouse gases
stratosphere: warmed by chemicals absorbing light, including ozone & UV
ozone: in the stratosphere, forms the layer, absorbs ultraviolet radiation
mesosphere: atmosphere less dense and gets colder
thermosphere: chemicals highly excited by sunlight
heat balance
sensible heat: heat you can sense (measure using a thermometer)
latent heat: heat used in the evaporation of water or liberated in condensation (cannot be measured by a thermometer)
latent heat transfer: transfers heat from an evaporating surface to the atmosphere
solar energy losses in the atmosphere
shortwave energy absorbed or diverted in different ways
UV absorbed by ozone
scattering produces diffuse radiation
clouds reflect radiation back to space (and also absorb radiation)
counter radiation
surface is also warmed by longwave radiation emitted by the atmosphere
surface emits radiation that goes directly to space
but most is absorbed by the atmosphere
atmosphere emits radiation that goes directly to space
but also radiates energy back to the surface
albedo
radiative energy can either be absorbed (heating) or reflected (no heating)
percentage of solar radiation reflected = albedo
fresh snow = 85-95%
dry sand = 35-40%
tropical forest = ~13%
earth’s albedo = ~30%
Knowt
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Studied by 11 people
