Atmosphere and Weather Flashcards
What is the atmosphere?
A mix of gases held to Earth by gravity; it increases in density, and therefore pressure, towards the Earth’s surface and is divided into zones based on temperature variations.
Name the layers of the atmosphere and their cut off points in order.
Troposphere, Tropopause, Stratosphere, Stratopause, Mesosphere, Mesopause, Thermosphere, Exosphere.
Where does the troposphere range from?
The Earth’s surface to 7km at the poles and 17km at the equator.
Why does the range of the troposphere differ between the poles and the equator?
The spin of the earth means that the atmosphere around the equator gets thrown out wider than at the poles due to the spinning motion.
What is the troposphere?
An unstable layer containing the majority of earth’s climate and weather.
How much of the total mass of the atmosphere and water vapour is found in the troposphere?
99% of the total mass of the atmopshere; 50% below 5.6km and contains 99% of water vapour.
What is the tropopause?
An isothermal layer at the top of the troposphere creating a temperature inversion which prevents air rising into the atmosphere.
What does the Stratosphere include?
The ozone layer which is concentrated at 15-35km in the stratosphere. The stratosphere extends to 51km above the Earth’s surface.
What is at the end of the stratosphere?
The stratopause where a temperature inversion happens
What does the mesosphere include?
Extends to 85km above the earth’s surface. Most meteors burn up here.
What is at the end of the mesopshere?
The mesopause is where another temperature inversion occurs as not many gases but some that reflect so temperature decreases.
What does the thermosphere include?
Extends over 640km from the earth’s sruface. The ISS orbits at around 350km.
What is the lapse rate?
The decrease of temperature with height.
What is the lapse rate in the tropsophere?
The temperature decreases by 6.4C every 1000m.
What does diurnal refer to?
The differences between day and night
What does the energy budget refer to?
The difference between incoming solar radiation and outgoing terrestrial radiation, added to the total amount lost by scattering, reflection and absorption by clouds.
What is the only input into the energy budget?
Incoming solar radiation (insolation0
What is wind?
Large bodies of air which have almost uniform moisture and temperature characteristics within the air mass.
What is geogstrophic wind?
A wind that flows parallel to isobars, resulting from a balance between pressure gradient force and the Coriolis force.
Where do air masses gain their characteristics from?
Contact with the ground or sea surface in the regions where they originate.
How much transferred energy is done by ocean currents and by wind?
20% by ocean currents, 80% by the winds.
What is an ocean gyre?
A large system of circular ocean currents formed by global wind patterns and forces created by the Earth’s rotation.
What are the 3 forces that cause the circulation of a gyre?
Earth’s global wind patterns, Earth’s rotation and Earth’s landmasses.
What is Thermohaline Circulation?
The slow circulation of water at depth which transfers energy as a result of convection and the differences in the salinity of the water affects the density of it.
What are the 6 main influences on temperature?
No seasonal variations= NSV
- Latitude
- Distribution of land and sea NSV does not change
- Ocean currents NSV does not change
- Altitude NSV does not change
- Cloud
- Wind
What is wind created by?
By air moving from high pressure to low pressure.
What is the speed of the air movement/wind determined by?
The pressure gradient- i.e. how big the difference is between high and low and how fast it changes.
Why do surface winds vary over the course of the year?
Influence of land and sea on temperature
Disruption by mountains and other landforms
Upper air movements
What are the upper westerlies?
Fast moving winds between 30 and 50°N and S, at the top of the troposphere that are essentially horizontal unlike those in the cells.
What do the upper westerlies result from?
o A high temperature gradient from N to S creating a strong pressure gradient (the polar front)
o The Coriolis force increasing as the air flows towards the poles, causing the air to take a path towards the East and become geostrophic (balance between pressure gradients and Coriolis forces)
What are Rossby waves?
- Deviation to the upper westerlies creates large waves (three to six in each hemisphere) which move slowly from west to east, much slower than the air moving through them
How are Rossby waves (deviations) caused?
By disturbance in the airflow created by a very high mountain range (e.g. Tibetan plateau) which compresses the air above it and creates wave troughs and ridges. Waves can be ‘pinched’ off to form cyclones/depressions of cold air.
What are the characteristics of jet streams?
- A narrow ribbon of fast-moving air running through the centre of the Rossby waves.
- Speeds can reach 250km/h.
- They are discontinuous, meander from W to E and can be thousands of km long.
How much water does the atmosphere contain and how much does this make up on earth?
- The atmosphere contains 12900km3 of water, primarily as gas (vapour).
- This only makes up 0.4% of the total water on Earth, but any changes to this has a profound effect on human life.
What is water vapour?
A greenhouse gas, so any changes can be a direct cause of climate change.
How does atmospheric water exist as a gas?
water vapour above 100°C but can exist at all temperatures down to below freezing point
How does atmospheric water exist as a liquid?
water is the stable phase between 0°C and 100°C but exists above that as super-heated water and below that as super-cooled water down to -40°C (which leads to freezing rain)
How does atmospheric water exist as a solid?
ice is the stable phase below 0°C
What are the changes that result from a decrease in temperature causing molecules to lose energy and lose speed releasing latent heat to the atmosphere?
condensation, freezing and deposition.
What are the changes that result from an increase in temperature giving molecules more energy and so more speed causing absorption and storage of heat from the atmosphere?
melting, evaporation, sublimation
What does humidity refer to?
How moist the air is because of the water vapour it contains.
What is absolute humidity?
the actual amount of water vapour in a given volume of air
What is relative humidity (more useful)?
Measures how near the air is to saturation, compared to the maximum amount that can be held at that temperature and pressure (fully saturated air)
What is the relative humidity % equation?
Actual moisture content x 100 _______________________________________________
The maximum saturation moisture content at the same temperature and pressure
When is air saturated?
when it has 100% relative humidity
What type of air can hold more moisture and what does this mean?
- Warm air can hold more moisture than cold so has a higher maximum amount
- As a result air over poles dry whereas air over tropics very humid.
When does evaporation occur?
when energy from the sun hits the surface of the water/land and causes water to change from liquid to gas
What do the rates of evaporation depend on?
-The amount of solar energy
–Availability of water
–Humidity of the air - The more humid the air the closer to saturation point the air is so less evaporation will occur.
–Temperature of the air – Warmer air can hold more water than cold air.
What is condensation?
- As air cools it holds less vapour. If cooled sufficiently, then air will reach saturation – known as the dew point.
- Excess water in the air is then converted back to liquid water
What is the dew point?
When air reaches saturation
What happens when condensation occurs?
Heat is released as the structure of the molecules becomes more organised from gas to liquid.
What do vapour molecules require to condense?
- Small particles to condense on (e.g. smoke, salt, dust). These are known as condensation nuclei and are hygroscopic (have an affinity for water)
- Surfaces that are colder than the dew point temperature (e.g. leaves, grass, windows). If colder than freezing point, then the vapour deposits to form hoar frost.
What 3 ways can the coolingof the air in order for the air to become saturated occur?
- Conduction (contact) cooling coming into contact with a cold object below dew point temperature
- Radiation cooling by loss of long-wave radiation from clouds and gases in the atmosphere to space
- Expansion (adiabatic) cooling as air rises, gases expand, so their temperature falls.
Describe the temperature inversion at the earth’s surface?
Normally air temperature decreases with increasing altitude but under certain weather conditions, the opposite occurs and temperature increases with height so that a layer of warmer air overlies a colder layer.
What is precipitation?
Moisture deposited on Earth’s surface in liquid or solid from the atmosphere.
What has to happen for precipitation to occur?
Air has to cool to below dew point temp., either by vertical movement or conduction
What can vertical movement be triggered by?
- Convection
- Frontal uplift (frontal rainfall)
- Orographic/relief uplift
- Radiation cooling
When does convectional rainfall occur?
When the Sun’s thermal energy heats the Earth’s surface, causing the air near the ground to warm, expand, and become less dense, making it rise.
When does orographic/relief rainfall occur?
When prevailing winds carry moist air that collides with a mountain or area of high relief.
When does frontal rainfall occur?
When warm air and cold air meet at a front, the boundary between the two air masses.
What are the 3 types of cloud according to type?
Stratus, Cumulus and Cirrus.
What are stratus clouds?
Layer clouds over a wide area where there is little vertical uplift.
What are cumulus clouds?
Heaped clouds with flat bases and globular upper surfaces, where there is more vertical but localised uplift.
What are cirrus clouds?
Where condensation occurs at very high altitude forming wispy clouds of ice.
How are clouds subdivided by height?
Into either:
Cirro- prefix for very high
Alto- prefix for mid level
(only apply to stratus and cumulus not cirrus)
What is collision theory with precipitation?
Different sized water droplets have different falling rates and are moved in both rising and falling air currents within cumulonimbus clouds.
When droplets collides with other to form a larger drop what 3 processes occur?
Aggregation, Coalescence and Accretion.
What is aggregation?
When two ice crystals join together to form snow
What is coalescence?
When two water droplets collide and join together – main process in forming rain
What is accretion?
When an ice crystal collects a water droplet, leading to the formation of hail
What is carbon concentration measured in?
ppm= parts of gas per million
What is a microclimate?
Climate within a small area that differs significantly from the climate of the surrounding area.
