Atmosphere + Weather Flashcards
(2.1) What is an energy budget?
- refers to the amount of energy entering a system, the amount leaving the system + the transfer of energy within the system
- commonly considered at a global scale (macro-scale) + local scale (micro-scale)
(2.1) What does microclimate mean?
A term sometimes used to describe regional climates - e.g. those associated with large urban areas, coastal areas + mountainous regions
(2.1) What are the components of a daytime budget?
- incoming (shortwave) solar radiation
- reflected solar radiation
- surface absorption
- sensible heat transfer
- long-wave radiation
- latent heat (evaporation + condensation)
(2.1) How to express the earth’s surfaces gain of energy?
Energy available at surface = incoming solar radiation - (reflected solar radiation + surface absorption + sensible heat transfer + long-wave radiation + latent heat transfer)
(2.1) What components does the night time budget consist of?
- long-wave radiation
- latent heat transfer
- absorbed energy returned to earth
- sensible heat transfer
(2.1) What affects incoming (SW) solar radiation?
- latitude
- season
- cloud coverage
(2.1) How do clouds affect incoming solar radiation?
- the less cloud coverage there is, and/or the higher the cloud -> the more radiation reaches the earth’s surface
(2.1) What is albedo?
- the proportion of energy that is reflected back to the atmosphere
- albedo varies with colour - light materials are more reflective than dark materials
- grass has an average albedo of 20-30% - so it reflects back 20-30% of the radiation it receives
(2.1) What is surface absorption *
- energy that reaches the earths surface has the potential to heat it
- much depends on the nature of the surface
- the heat transferred to the soil + bedrock during the day may be released back to the surface at night - partly offsetting the night-time cooling at the surface
(2.1) What is sensible heat transfer?
- refers to the movement of parcels of air into + out of the area being studied
- e.g. air that is warmed by the surface may begin to rise (convection) + be replaced by cooler air = convection transfer —> very common in warm areas in early afternoon
- it is also part of the night time budget - cold air moving into an area may reduce temps - whereas warm air may supply energy + raise temps.
(2.1) What is long wave radiation?
- the radiation of energy from the earth (a cold body) into the atmosphere + some of it eventually into space
- however there is a downward movement of long wave radiation from particles in the atmosphere
- the difference between the two flows is the net long-wave balance
(2.1) Explain net long wave radiation
- during the day - outgoing long wave radiation transfer is greater than the incoming long wave radiation transfer = net loss of energy from surface
- during cloudless night (common in deserts) - little return of long wave radiation from the atmosphere due to lack of clouds = net loss of energy from surface
- cloudy night - clouds return some long wave radiation to the surface = overall loss of energy reduced
(2.1) What is latent heat transfer?
- when liquid water is turned to water vapour, heat energy is used up
- when water vapour becomes a liquid, heat is released
- therefore when water is present at a surface, a proportion of the energy available will be used to evaporate it + less energy will be available to raise local energy levels + temp.
(2.1) Latent heat transfer at night
- during night - water vapour in the air close to the surface condenses to form water (cuz air has been cooled by surface)
- water condenses = latent heat released
- this affects the cooling process at the surface
(2.1) What is dew + when does it occur?
- condensation on a surface
- the air is saturated because the temperature of the surface has dropped enough to cause condensation
- occasionally condensation occurs because more moisture is introduced - e.g. sea breeze - while the temp. remains constant
(2.1) What happens to absorbed energy back into the earth?
- insulation received by the earth will be reradiated as long wave radiation
- some of this will be absorbed by water vapour + other greenhouse gases
- thereby raising temperatures
2.1 Why do surface temperatures change?
- during the day - the ground heats the air by radiation, conduction + convection
- the ground radiates energy + as the air receives more radiation than it emits, the air is warmed
- air close to the ground is also warmed through conduction - air movement at the surface is slower due to friction with the surface so there is more time for it be heated
- the combined effect of radiation + conduction makes the air warmer + makes it rises due to convection
- at night - the ground is cooled as a result of radiation
- heat is transferred from the air to the ground
(2.2) What can incoming solar radiation be referred to as?
Insolation
(2.2) what is convection?
Transfer of heat by the movement of a gas or liquid
(2.2) what is conduction?
The transfer of heat by contact
(2.2) How much insolation gets absorbed by the Earth’s surface?
- only 46%
because…
- 19% is absorbed by atmospheric gases
- 23% is reflected by clouds + water droplets
- 8% is reflected by atmosphere
- 6% reflected by earth’s surface
(2.2) how much energy received by Earth is re-radiated?
- 8% reflected by atmosphere
- 14% re-radiated as long wave
- 22% of latent heat transfer (evaporation + condensation)
= 32%
(2.2) What causes an energy imbalance?
- an excess of radiation (positive budget) in the tropics
- a deficit of radiation (negative balance) at higher latitudes
- neither of these regions are getting hotter or colder so energy transfers equalise this energy imbalance
- this results in a second energy budget in the atmosphere —> horizontal transfer between low latitudes + high latitudes to compensate for differences in global insolation
Latitudes diagram
Energy budget diagram
How is heat transferred?
- ocean currents —> warm ocean currents move heat from the tropics to the poles + cold ocean currents work in the opposite direction
- trade winds —> transfer large amounts of heat from the tropics to the poles
- storms —> tropical cyclones transfer large amounts of heat energy from the tropics to the subtropics + temperate zones
(2.2) what are wind belts?
- air blows from high pressure (over 1013 mb) to low pressure (below 1013mb) + redistributes heat around the earth - sensible heat transfer
- winds between tropics converge on inter tropical convergence zones
- winds blow inwards + rise (forming low pressure) —> rising air stimulates latent heat, causing convection
(2.2) What are annual temperature patterns
- January = highest temps over land (above 30°c) found in Australia + Southern Africa, lowest temps (below -40) are found over Siberia, Greenland + Canadian artic
- July = maximum temp found over the Sahara, Near East, northern India, southern USA + Mexico
(2.2) what causes annual temperature patterns?
- there is little season variation at the equator
- but in mid or high latitudes - larger seasonal variation occurs due to decrease in insolation from the equator to the poles
- there is also a time lag between overhead sun + period of maximum insolation - because the air is heated from below not above
- over oceans the lag time is greater - due to differences in specific heat capacities
(2.2) what influences atmospheric transfer?
- pressure variations —> air blows from high pressure to low pressure = redistributing heat globally
- ocean currents —> warm currents raise the temp of overlying air, cold currents cool the air above
What do pressure variations imply?
- Decline in pressure indicates poorer weather
- rising pressure means better weather
What is surface pressure?
- low pressure in equatorial regions, as warm air rises + leaves the surface
- warm air spreads + gets denser + cooler = sinks
- higher pressures seen in polar regions, where cool air descends onto the surface + meets warm air from equator
Why are surface wind belts uneven?
- uneven due to seasonal variation in insolation
- summer in the northern hemisphere causes cooling in the southern hemisphere
- therefore increasing difference between polar + equatorial air
(2.2) what do atmospheric transfers (winds) do?
- the winds follow the tri-cellular model (Hadley, Ferrell, polar)
- as the Hadley cell starts at the ICTZ (thermal equator) which shifts north in July, moving winds with it
- in India this causes a reversal of winds from southerlies in July to northerlies in January
- this causes the monsoon as southerly winds are moist from the Bay of Bengal
- where as northerly winds came from the himalaya
(2.2) How are ocean currents made?
- created by differences in salt concentration + temperature
- the water warms in the Gulf of Mexico + drifts north into the Atlantic - hitting the UK
- sea ice starts to form, which is fresh water
- this means remaining water is saltier + cleaner + sinks to the bottom, dragging more warm water under to replace it
- this mechanism drives the current - called the Thermo-halide current
(2.2) Land temperature distribution
- low reflectivity = more absorption of radiation
- lower specific heat capacity = set amount of energy raises land temp by more than
- less water = less energy lost by evaporation
(2.2) sea temperature distribution
- high reflectivity = less absorption of radiation
- sun rays penetrate deep = convection current distribute heat deeply
- high specific heat capacity = set amount of energy raises temp by less
- large amounts of energy used for evaporation
(2.2) general air movements
- air flows from high pressure areas to low pressure areas
- the Coriolis effect deflects winds - air is deflected to the right in the northern hemisphere + to the left in the southern hemisphere
- these wind patterns form the General Circulation Model
Diagram of Coriolis effect
What does the General Circulation Model show?
- between the Hadley + Ferrel cells there are significant differences in air pressure
- this creates strong, permanent waves of air about 10 km up (100-300kph) - jet streams
- there are 2 jet streams in each hemisphere -> one between 20°-30° + one 30°-50°
- jet streams are in waves -> e.g. Rossby waves moves around major mountain ranges - Andes, himalaya, alps etc.
(2.2) General circulation diagram
(2.2) Rossby wave diagram
(2.3) atmospheric moisture states
- evaporation, condensation + sublimation
- energy is taken in (latent heat) by evaporation + released by condensation
- hoar frost is an example of sublimation (vapour to solid)
(2.3) Factors effecting evaporation
- Initial humidity of the air —> if the air is very dry then strong evaporation occurs; if it saturated then very little occurs
- supply of heat —> the hotter the air, the more evaporation
- wind strength —> under calm conditions the air becomes saturated rapidly
(2.3) factors affecting condensation
- adiabatic cooling —> decrease in pressure, expand + cool
- radiative cooling of the air
- contact cooling of air when it rests over a cold surface
(2.3) Characteristics of mist + fog
- cloud at ground level (cloud=collection of water droplets)
- mist occurs when visibility is between 1000m + 5000m
- fog is thicker - occurs where visibility is below 1000m
(2.3) why does mist/fog form at ground level?
- air can only hold a certain amount of moisture
- colder air can hold less moisture than warmer air
- once this maximum amount of moisture is reached - air is saturated + water vapour in the air turns to liquid
- this causes clouds to form
(2.3) How do clouds of fog/mist form?
-
air must be cooled close to the ground
—> e.g. advection fog = as warm, moist air passes over a cold surface it is chilled = condensation
—> e.g. radiation fog = when ground loses at heat at night by long wave radiation + therefore the air above is cooled causing condensation + fog -
more water vapour must have been added to the atmosphere close to the ground
—> can occur over warm, wet surfaces e.g. large lakes = water is evaporated from the warm surface of the lake + condenses in the cold air above to form fog
—> for mist or fog to form, condensation nuclei are needed (e.g. dust or salt particles) - more common in urban or coastal areas so more mist/fog occurs there
(2.3) How does dew form?
- dew is the condensation of water on a surface —> water vapour in the air has turned into water droplets on a surface
- normally occurs because the surface is cold + has caused the air to cool + therefore become more saturated (reach dew point) + so condensation has occurred
(2.3) What is temperature inversions?
- normally air temp decreases with altitude - however there are some situations where there is a abnormal layer of warm air above the colder air in the troposphere
- this often happens at night in calm conditions - so sometimes called nocturnal inversions
(2.3) Why do temperature inversions occur?
- during the day the ground is heated by the sun’s short wave radiation + then after a short time, it heats the air above it when it emits long wave radiation
- at the night the ground surface + air lose the heat energy they have absorbed during the day - however the ground loses heat energy faster than air as it is more efficient conductor of heat
- by the end of the night the ground is very cold + the air directly above it will be cool too due to close proximity to surface
- however, the air layer above thus will still be warm as it has cooled slower than the ground surface - causing a temp inversion
(2.3) What impact can temperature inversions have?
- temp inversions will act as a lid on pollutants
- causing them to remain in the lower atmosphere next to the earth’s surface
(2.3) What is a sea breeze?
- on a warm summer day along the coast, the differential heating of land + sea leads to the development of local winds = sea breeze
- the land is heated quicker than the sea + so the air above the land is warmer than the air above the sea during the day
- as air above is heated by radiation from the sun it expands + begins to rise, being lighter then the surrounding air
- to replace the rising air, cooler air is drawn in from above the surface of the sea - this is a sea breeze
(2.3) What is land breeze?
- occurs at night when the land cools faster then the sea
- this creates a situation which is the opposite to day time - air above the sea is warmer than air above land
- the warmer air above the sea rise + expands - pulling in air from the cooler land surface
(2.3) how do clouds form?
- air rises + cools (adiabatic cooling)
- humidity increases to 100% + saturation occurs
- air which is still warmer than the surrounding air will continue to rise —> creating to tall (thunder) clouds - this air is unstable
(2.3) what are the types of clouds?
- cumulo = heaped
- nimbus = rain
- strato = layer
- alto = high
- cirrus = highest
(2.3) what is classed as precipitation?
- rain
- dew
- hail
- fog
- snow
(2.3) how does rain form?
- condensation occurs due to cooling onto condensation nuclei’s (or ground dew)
- droplets grow in size until heavy enough to fall through rising air
(2.3) why does precipitation vary?
- heat
- initial moisture
- atmospheric temperature
(These all effect condensation)
(2.3) what is the Bergeron theory?
- all rain + snow form in clouds with temps below 0°C (often -40°C)
- snow will often melt as it falls to form rain
(2.3) how do thunderstorms form?
- as clouds form, latent heat released causes further uplift
- pulled air brings more moisture
- different movements of air generate static energy
(2.3) how does hail form?
- rain forms updraughts preventing it falling so it freezes to form hail
- if updraughts continue, hail will grow
(2.3) how does snow form?
- water vapour sublimates to create crystals
- mostly air so very light
(2.3) when does heaviest snowfall occur?
- when warm, moist air is forced over mountains
- or warm moist air is forced to mix with cold air on a front
- rapidly cooling in both cases
(2.3) which season is fog common?
- summer + winter due to high pressure conditions (clear skies)
- clear skies allows cooling of ground to be rapid at night + cools air above
(2.3) why does fog disperse as sun rises?
temp rises + reabsorbs moisute into air as humidity falls
(2.3) what is smog?
- inversion traps pollution in the lower layer
- where it mixes with fog to form smog
(2.3) what are the types of rainfall?
- frontal rain
- orographic rain
- conventional rain
(2.3) what is frontal rain?
- when cold air meets warm air in a ‘weather front’
- warm air rises so bumps into the cold air + rises above it
- the warm air gets cooler as it rises + the water vapour condenses into water
- this forms a cloud + eventually falls as raindrops
(2.3) What is orographic rain?
- when wind pushes air towards a hill + forces it upwards
- when it reaches the top of the hill it cools down
- if it has enough moisture, the water vapour will condense into water to form a cloud + eventually fall as raindrops
(2.3) what is conventional rain?
- when the sun shines on the ground + heats a shallow layer of air close to it
- this is air now warmer than the surrounding air, so it rises up into the atmosphere
- warm air gets cooler as it rises up higher
- as a result the water vapour condenses into water, forms a cloud + eventually falls as raindrops
(2.3) what is conventional rain also known as?
- showers - produces smaller areas of rainfall
- they are much smaller + more unpredictable because the ground surface varies
- this means the air close to the ground is heated at different rates - which is why showers can pop up anywhere + be blown around in different directions by the wind
- tarmac (a darker surface) will heat air more quickly than grass (lighter surface) or water (lake)
(2.4) how do urban areas affect their climate?
- anthropogenic heat (people), pollution, cars, acid rain, impermeable surfaces, heat capacity of buildings, reflection etc.
- in general they increase temperature + can increase rainfall
- the effect is know as the urban heat island
Urban heat island diagram
How do buildings affect climate?
- heat stored by buildings + re-radiated
- ground heated by insolation - low albedo of tarmac so less reflected
- streets collect radiated heat
- low humidity - lack of vegetation = less evaporation
What is the greenhouse effect?
- SW radiation passes through atmosphere
- LW radiation trapped by clouds formed by pollution
- small proportion absorbed by ‘green house gases’
- an increase in the quantity of ‘greenhouse gases’ causes more energy to be trapped + an increase in global average temps
Arguments against global warming
Naturally causes
- changed by variations in tilt + elipicity of our orbit
- variations in solar output
- change in ocean currents/ continental drift
- volcanic activity
Effects of global warming?
- rising sea levels - Netherlands/Bangladesh/Maldives = up to 200 million displaced by 1m rise
- 1/20 (400 mil) threatened by floods from glacial melting
- increase in high category hurricanes
- change in agricultural plan
- 400 mil at risk of drought if temps rise by 2°C