Atmosphere II : Climate Flashcards
what is climate
average or typical conditions of the atmosphere
what are the most common components of climate
precipitation and temperature
define proxy measurement
A proxy is an indirect measure of the desired outcome which is itself strongly correlated to that outcome. It is commonly used when direct measures of the outcome are unobservable and/or unavailable.
what does climate average out
climate averages out weather, but not season
define paleoclimate
a climate prevalent at a particular time in the geological past.
do we only have current climate measurements
no we have climate measurements that span modern to past climates (paleoclimate)
what are the three ways that energy can be transferred
through radiation, conduction and convection
define radiation
transfer of energy as waves or particles through air (emission/transmission)
called electromagnetic radiation
what is the electromagnetic spectrum
range of frequencies of em radiation and their wavelengths (or energies)
how is the em spectrum seperated into 2
as longwave (low energy) and shortwave (high energy)
the energy of EM radiation is inversely proportional to what
wavelength
define conduction
heat(energy) transfer from one molecule to next as molecules vibrate
rate of transfer of heat depends on temperature difference (gradient)
e.g. heat moving along a metal bar
occurs in all phases, gas, liquid, solid
define convection
transfers of heat by movement of a fluid (mass transfer)
caused by buoyancy forces due to changes in density that arise from changes in temperature
set up convection cells - these present in the atmosphere as turbulence (fluid mixing) or an instability (uneven heating)
moist convection leads to…
thunderstorms
how do convection cells forms on oceans and land
at night landmass cools quicker than the ocean so creates a cell the other way compared to day time
how does convection lead to rainfall
When the land warms up, it heats the air above it. This causes the air to expand and rise. As the air rises it cools and condenses. If this process continues then rain will fall.
how does the sun transfer heat
by radiation
how does the ground transfer heat
the ground absorbs heat through by conduction, heat moves into atmosphere by radiation
how does the atmosphere transfer heat
convection
what is earths steady state theory
earths climate system, unperturbed, is in a (quasi-) steady state
energy in = energy out
incoming radiation = outgoing radiation
as space is a vacuum, the only form of energy transfer is:
em radiation
convection causes what type of cyclone
a low pressure cyclone
what is blackbody radiation
a perfect blackbody is an object that absorbs all incoming radiation (that is, none is reflected)
radiation emitted by a blacbody depends only what
its temperature
what is plancks law about
plancks law of blackbody radiation defines the relationship how much radiation is emitted at a certain wavelength for a body of a certain temperature
what is isotropic, what does it mean?
blackbody is isotropic (radiation emitted at equal intensity in all directions)
what is radiance
power emitted by a blackbody (w/m^2/sr) sr = ser radian
what is spectral radiance
radiance per unit frequency (w/m^2/sr/Hz)
what waves are radiation from the sun
shortwave (UV/visible)
radiation from the earth is…
longwave (infrared)
the emission of radiation from the sun and earth…
hardly overlap
what is the Stefan-Boltzmann law about
power radiated from a blackbody in terms of its temperature
how to go from kelvin to degrees celsius
k = degree Celsius + 273.15k
what is stefan-boltzmann law
total energy radiated per unit surface area of a blackbody is proportional to T^4
this relationship integrated in all directions over a hemisphere and over all frequencies is:
I = sigma x t^4
where sigma = 5.67 x 10^-8 wm^-2k^-4 is the stefan b constant
I = the blackbody irradiance or energy flux density
what is a radiation modifier example
albedo and transmittance
what is albedo
symbol alpha, a, it is the ratio of reflected radiation to incident radiation (incoming light striking a surface)
0 < a < 1
what is transmittance
transmittance, gamma, y, is the ratio of transmitted radiation (radiation that passes through a fluid) to incident radiation:
0 < y < 1
what is a grey body
a grey body is a body that emits according to plancks formula multiplied by fractional emissivity, epsilon, E
0 < E < 1
tell me what the emissivity value means
where E is a measure of efficiency of emitting thermal radiation (0 for a shiny object, 1 for a blackbody)
what is the global albedo
earth is not a perfect blackbody, clouds, ice, reflective land surfaces like deserts increase a and reduce E
earths colour varies from white to deep blue (nearly blue)
what are the albedo properties of the earth
water = near perfect blackbody
snow = very reflective
albedo varies as a function of properties of surface (land/cloud)
the ocean albedo depends on the angle of the solar radiation striking the surface (sun glint)
the albedo of bare sea ice depends on the density of the air bubbles
earths global average = 0.3
tell me about the global mean energy model (incoming radiation)
energy of incident shortwave solar radiation (solar constant) S(subscript 0) = 1366 w/m^2
s0 = incident solar radiation
how do we calculate the global mean energy model (outgoing radiation)
energy of sun incident on earth = epsilon s0 /4
area of the earth the sun intercepts = pi x r^2
fraction of solar constant received by earth = pir^2/4pir^2 = s0/4 = 342 w/m^2
E = 1 - alpha = 0.7
how can we integrate global mean temperature and the energy of a blackbody
the energy of blackbody is proportional to its temperature
E(out) = sigma x t^4
tell me about the penetration of radiation on the atmosphere
majority of shortwave penetrates the atmosphere, very little longwave escapes
what are the natural greenhouse gases:
water vapour, co2, oxygen and ozone, methane, nitrous oxide
what is the chemical symbol for methane
methane = CH4
what is the chemical symbol for nitrous oxie
N20
what is the grey atmosphere
gray atmoshpere is transparent in shortwave and includes a layer of infrared absorbing gases that intercept outgoing longwave radiation
tell me about uneven heat in the world and its redistribution
equator gets more sun radiation than the poles, uneven heating.
redistribution of heat:
convection plays a role
not as simple as Hadleys 1735 suggestion that convection cell extends from equator to the poles
redistribution does not account for coriolis effect
tell me about tropical Hadley cells
sun heats equator
hot air rises
air masses move towards poles
air masses diverge from north-south path due to coriolis effect
cool dry air sinks at about 30 degree latitude (deserts)
still named hadley cell
air rising (convective uplift) is associated with…
clouds and rain (tropical rainforests)
air sinking (subsidence) associated with…
dry air (deserts)
tell me about convective cells
moist, warm air rises forming clouds
cold, dry air subsides (compresses and warms)
tell me about surface winds bestie
descending branch of cell reaches surfaces, forms surface winds that diverge due to Coriolis effect
poleward and equatorward winds meet, air forced upward, maintains convective cells.
tell me about annual mean surface temperature
warmest at the equator
coldest at the poles
Antarctic colder than arctic (isolated less land mass to redistribute head)
colder at elevation
canada colder than europe
where does rain occur
most rain in intertropical convergence zone (ITCZ) (convective uplift)
little rain at edge of tropics ~ 30 degrees north (subsidence)
more rain over equatorial oceans = storm tracks
why are circulation patterns not always stable
seasonal variation interannual variability north atlantic oscillation el-nino southern oscillation extreme weather longer-timescale variability (not the focus of this module)
tell me about earths seasons
earth is tilted at an angle of 23.5 from its orbital plane
different parts of the earth receive the suns most direct rays
when north pole tilts toward the sun, it is summer in the northern hemisphere
when south pole tilts toward the sun, its winter in the northern hemisphere
