week 4 Flashcards
(31 cards)
describe differential heating by latitude
latitude affects:
- angle
- area over which radiation is spread
-> solar irradiance (W/m^2)
- global average 1367 W/m^2 at the top of the atmosphere
- insolation is irradiance integrated over time
where does the energy in earth’s atmosphere come from
almost all of the energy in the atmosphere comes from the sun, though there are also other factors
describe earth’s orbit
- earth has an elliptical orbit- varying earth-sun distance results in seasons
weather vs climate
weather refers to short-term changes in the atmosphere
climate describes the average weather conditions in a specific area over a long period of time - 30 years or more
describe the vertical pressure gradient force and gravity
- the molecules of air are trying to move toward the earth because of gravity
- imagine a parcel of air, like a balloon. the vertical pressure gradient force is the difference between the force of the air molecules pushing downwards and the force of the air molecules pushing upwards
- also acting on the mass of the parcel/balloon and trying to move it downward is gravity. when the vertical pressure gradient force, (directed upward), and gravity, (directed downward), are in balance, the parcel moves neither up nor down. it is in hydrostatic equilibrium
what is the hydrostatic equation
*see lecture 4 slide 17
- change in pressure with height is proportional to air density and the gravitational acceleration:
dP/dz = - pg
- density of air is a function of temperature and moisture content -> increasing water vapour or air temperature will cause the density to decrease
- thus dP/dz is large in cold air (the change in pressure with height is large -> the pressure decreases rapidly in cold air and the thickness of a cold air mass is small)
- warm air expands and takes up larger volume
describe the movement of air
- air moves from high to low pressure
- air moves out of the tropics
- since pressure is related with weight of the atmosphere, less air means lower pressure
- high in the atmosphere, air from the region of high pressure moves toward the lower pressure i.e. warm air at the equator creates higher pressure that moves air towards the polar regions
- at sea level, air is moving from the high pressure in the cooler column toward the lower pressure in the warmer column
what is the coriolis effect
the coriolis effect is the curving of the path of objects or fluids due to the earth’s rotation
what is the coriolis equation
f = 2wsinphi (coriolis parameter)
w is the angular velocity of earth’s rotation
phi is the latitude
how does the coriolis parameter (f) differ from the equator to the poles
sin (0) = 0, sin (90) = 1, thus the effect is maximum at the poles
how fast does air move
- consider a parcel of air at the equator, how fast does this parcel of air move?
- because the earth is moving, we can compute the speed of the parcel by:
- distance around the earth = 2piRearth = 2pi(6371) = 40031.7km
- rate of motion = 40031.7km/24 hrs = 1668 km/hr
- at 30 degrees N:
- r=cos(30)Rearth or sin(60)Rearth
- radius of motion = 5517.65km
- distance travelled = 2pi(5517.65)km = 34668.5km in 24 hours
- rate of motion = 34668.5 km/24hrs = 1444.5 km/hr
describe the circulation cells and pressure
- air falls at the top of the polar cell forming deserts
- warms air rises and cools at the top of the ferrell cell. cool air can hold less moisture, leading to rain.
- air falls at the top of the hadley cell, forming deserts
- at the bottom of the hadley cell, warm air rises and cools. cool air can hold less moisture leading to rain and rainforests
what is the conservation of angular momentum
relative speed of air increases as it moves away from the equator
what are jet streams
- fast-flowing air currents > 300 km/h
- 9-16km above the surface
- ribbon-like: hundreds of km wide, a few km deep
- stronger in winter than summer
what is net radiation/ net flux
- it is the balance between incoming and outgoing energy at the top-of-the-atmosphere (TOA)
Rtoa = SWin (1-a) - LWout
describe the poleward energy flux
the time rate change of energy content of the climate system is the balance of the net incoming radiation at the TOA and the divergence of the horizontal energy flux in the atmosphere and ocean
dEao/dt = Rtoa - deltaFao
what does differential solar heating lead to
- differential solar heating between low and high latitudes gives rise to a circulation of the atmosphere and ocean that transports heat poleward.
- as a result of these transports poleward of about 38 degrees in both hemispheres, longwave radiation emission to space exceeds shortwave (solar) radiation gain. without this transport, the polar regions would be colder than observed.
- transports are of sensible heat, latent heat, geopotential and kinetic energy
what is the dry adiabatic lapse rate
- an adiabatic process is one which involves no transfer of heat to or from the system
- if a parcel of dry air is lifted from the surface to altitude it will cool
- the rate at which the temperature of such a dry air parcel falls with altitude is call the dry adiabatic lapse rate
Ld = -9.8 degrees C/km - arises from decline of pressure with altitude
what is specific heat
specific heat is the amount of heat required to warm something:
- for water this is 4.2 kJ kg^-1 K^-1
- for air it is 1.0 kJ kg^-1 K^-1
what is latent heat
latent heat is the heat exchanged when the phase of matter changes:
- it takes 336 kJ kg^-1 to melt ice
- it takes 2230 kJ kg^-1 to evaporate water
energy of water when it changes phase
- water carries lots of energy when it changes phase
- evaporating 1kg of water takes as much energy as warming 1kg by 530K would
- the energy released by condensing water drives many of the extremes of weather
what is the moist adiabatic lapse rate
- the warmer an air parcel is, the more water vapour it can hold
- as a moist air parcel rises, it cools and its saturation water vapour content drops
- as it cools, water vapour condenses, releasing energy and offsetting some of the cooling
- the moist adiabatic lapse rate is therefore lower than the dry one:
Lm = -3.5 to -6.5 degrees C/km
Ld = -9.8 degrees C/km - make sure to mention the air is saturated not moist
describe convection in theory
- consider a dry parcel of air that doesn’t exchange heat/mass with its surroundings
- if this air parcel is warmed, it will expand (ideal gas law)
- the density of the air parcel will be lower than surrounding air and so it will be pushed up
- as it rises, the pressure of its surrounding will drop so it will cool but will still be relatively warm and less dense and continue to rise
describe convection in reality
- in reality, a warmed air parcel will exchange heat and mass with its surroundings
- as the warm air parcel from the surface rises, it will warm the air throughout the atmospheric column
- after some time the atmospheric column will reach a new equilibrium temperature profile
