2: Atmospheric structure, dynamics and global climate

describe the composition of earths atmosphere

78% Nitrogen

21% Oxygen

1% Argon

400 ppm CO₂

variable components: 0-4% water vapour (0.01ppm at surface, 10ppm at 25km)

Draw and eplain the height-temp graph

3 warm areas:

1. Troposphere: warm air near ground, decreasing with height. heating from greenhouse effect. solar radiation absorbed by ground and emits infrared

2. Stratosphere: O3 + UV → O2 + O + heat

3. Mesosphere: " 50km = hot zone

Thermosphere: more intense radiation from sun

draw and explain the height-pressure graph

• 75% earths weight lies below 10km

• at 50km 99.1% of the earths atmosphere lies below

• pressure decreases rapidly with height

Acronym for composition of the atmosphere

Tropical Storms Mean Terrible Emergencies

Troposphere
Stratosphere
Mesosphere
Thermosphere
Exosphere

describe troposphere and its heat (and heat source)

Region of earths weather systems

temp decreases with height → relatively warm air near ground

• heating from greenhouse effect

• solar radiation is absorbed by the ground which emits infrared which is absorbed by the atmosphere

Heat is generated by:

• intense radiation from the sun

• x-rays and extreme UV

• O and N absorb this radiation, causing them to break into their atomic components, these then react with the radiation, losing electrons and leaving ions (ionosphere)

explain how the earth remains radiative equilibrium - three laws or radiation

1. All objects emit radiation - Plancks law

2. Hotter objects emit more radiation than cooler objects - Stefann-Bolteman law

3. Hotter objects emit their peak radiation at shorter wavelengths - Weins displacement law

explain plancks law

ALL OBJECTS EMIT RADIATION

• the earths climate system maintains a balance between solar energy absorbed and IR energy radiated into space.

• the greenhouse effect distributes the temperature in the atmosphere so that the surface is much warmer than the mean radiative temperature

explain the stefann-bolteman law

HOTTER OBJECTS EMIT MORE RADIATION THAN COOLER OBJECTS

• this law allows scientists to figure out how hot the sun is based on how much power strikes the earth in a square meter - the temp of earth without climate effect can be determined, this is useful for climate models

• more energy will radiate out until net energy balance is zero earths temp will stabilise at another, increased value

• the law acts like a negative feedback to keep earths temperature from changing in one direction only

explain weins displacement law

HOTTER OBJECTS EMIT THEIR PEAK RADIATION AT SHORTER WAVELENGTHS

• the GHG selectively absorb certain frequencies of radiation e.g. H2O and CO2 are strong absorbers

• hot sun emits radiation in shorter wavelengths in visible end of spectrum

• cool earth emits longer waves in infrared section

what if the earth had no atmosphere?

energy of incoming short wave solar radiation = energy of outgoing longwave radiation emitted by earth in order to maintain steady temp.

-18 degrees compared to 15

• atmosphere adds 33 decrees to the temp of earths surface

with earths atmosphere, what happens to radiation and gases

greenhouse gases absorb infrared radiation but are transparent to solar radiation → so we see solar radiation penetrating too and being absorbed by the ground → emission of infrared radiation which is absorbed by the atmosphere

Mars (and venus) vs earth

• lack oxygen in their atmospheres

• do not have ozone layer or stratopause

• different thermal profiles to earth

• mars and earth both have warming near surface, ionisation occurs in both thermospheres byt there is no oxygen in the middle regions of the atmosphere on mars - hence the gap

why is the atmosphere so important?

1. provides swings between day and night

2. protection from harmful radiation

3. transports energy from tropics to poles

4. provides wind and ppt to weather rocks and erode continents - rock cycle

troposphere

• greenhouse effect

• heating from ground

stratosphere → mesosphere

• O3 + UV → O2 + O + heat

• UV comes from above stratosphere where ozone is concentrated

thermosphere

ionisation of atoms

Describe the heat in the stratosphere

• heat comes from the presence of ozone

• O3 + UV → O2 + O + heat

• breaking of the bonds constructing the ozone lead to heat release

what is dewpoint

the temperature the air needs to be cooled to (at constant pressure) in order to achieve a relative humidity (RH) of 100%

what happens when air moves up and down?

• As long as no condensation or evaporation, an air parcel changes temp at a rate of ~10C/Km

• the dewpoint does not change

draw a height graph with temp and dewpoint of air

How does vertical movement of air produce clouds?

• water molecules with enough Ek evaporate into water vapour

• when condensation and evaporation are equal then the pressure due to water vapour is called the saturation vapour pressure

• every 1km height increase results in a 10C decrease

• The base of the cloud forms at the altitude at which the rising air cools and condensation starts. Rising air remains warmer and continues to rise, as it does this more vapour condenses, forming columns

draw the shape of raindrops at different sizes

saturation definition

when air contains the maximum amoint of water vapour for a given temperature

latent heat definition

the energy transferred to a substance while it changes state

latent heat of fusion

what causes water to change state from solid to liquid

latent heat of vapourisation

what causes water to change state from water to vapour

saturation vapour pressure (eˢ) hPa

how much water would be in the atmosphere at equilibrium in a closed container

• this increases with temperature

vapour pressure (absolute)

the partial pressure of water vapour in atmosphere

dew-point temperature (Td) hPa (absolute)

the temp of which air would have to cool to reach saturation (temp at which dew forms)

relative humidity equation

actual pressure (e) / saturation vapour pressure (eˢ) x 100

single cell circulation of a non-rotating earth

• converging air goes up, producing clouds and precipiration

• polar fronts at surface are associated with a jet stream

• jet stream W→E

• the number of cells per hemisphere is a function of rotation rate of a planet and its size

• at some latitudes more energy is recieved by the sun and some areas have surplis. Flow from the poles to the equator in both hemispheres which produce the single-cell atmospheric circulation

Albedo

the measure of reflectivity of a surface, expressed as the percentage of incident light or radiation reflected. Higher albedo indicates more sunlight is reflected back into space.

How does the atmosphere maintain a steady temperature?

energy of incoming shortwave solar radiation must equal energy of outgoing long-wave radiation emitted by earth

• thermal equilibrium at top - more infrared radiation, must be warmer

How is the earths climate regulated?

• amount of oncoming solar radiation

• albedo

• conc of GHG

what is the Intertropical convergence zone?

The Intertropical Convergence Zone (ITCZ) is a region near the equator where trade winds from the Northern and Southern Hemispheres converge, causing frequent thunderstorms and rainfall, and playing a crucial role in tropical climate patterns.

what are subtropical anticyclones?

high-pressure systems formed when air, which has risen in the tropics, subsides in subtropical areas. the air is warmed as it descends making rainfall unlikely. The subtropical anticyclone over the north atlantic (‘Azores’ or the ‘Bermuda high’) influences weather and climate over eastern US, western EU, and north-west africa.

what is the polar front?

represents the boundary between higher latitude cold air and lower latitude warm air

what is the polar jet stream?

a core of strong winds around 5-7 miles above earths surface, blowing from west to east

The jet stream separates _____ air from _____ air.

The jet stream is _______ in the winter hemisphere.

polar, tropical, stronger

what are rain shadows? with examples

Rain shadows are regions with significantly reduced rainfall due to geographical features, such as mountains, blocking moist air from reaching them.

e.g. the Andes rain shadow

The jet stream brings flow from the ocean, up over the range but the other side is baron of vegetation.

e.g. Hawaii

Northeast trade winds are constant over the ocean, but on the downstream side, no vegetation.

describe the Hadley cell

• biggest cell

• at equator

• warmer, less dense air rises to ~18km and spreads out underneath tropopause

• warm air spreads out towards the poles, gradually cooling and sinking - flowing back to the equator

describe the polar cells

• smallest cell

• cold dense air descends in the polar regions, flowing at about 60-70 degrees north

• as it leaves polar regions it will begin to warm and rise, returning to the poles at high levels

describe the ferrel cells

• between hadley and polar cells

• not driven by temp, flow in opposite direction to the others

• transport heat from equator to poles

• result in semi-permanent areas of high and low pressire due to the rising and descending parts of circulation cells giving us our climatic zones

• where air is rising, an area of low pressure is creates, resulting in more rainfall

what are wind barbs

indicate the speed and direction of wind on a weather maps

surface weather maps

T = low, H = high

isobars: lines of constand seal-level pressure

jed stream: closely packed height lines

example of dry and moist adiabatic motion

which is not a component of the earths climate system?
lithosphere
hydrosphere
heliosphere
cryosphere

heliosphere

what is the lowest layer of earths atmosphere?

troposphere

which is the least abundant gas in earths atmosphere?

CO2

where did most of the CO2 in the atmosphere originate from

outgassing

what is not a component of earths atmosphere

suspended dust particles

clouds

infiltration

water vapour

infiltration

how many polar jet streams are there

2

why is the thermosphere hot

ionization

what is the approx value of the dry adiabatic laspe rate

10C per km

when liquid water evaporates to water vapour, the surrounding air…

cools