1. Atmosphere and Weather Flashcards
What is weather?
Short-term changes in atmospheric conditions at a particular point in space / time
What is climate?
Climate is the long-term changes in the mean / average atmospheric conditions
How are you gonna remember the 5 layers of the atmosphere?
- Exosphere = Extra
- Thermosphere = Terrstrial
- Mesosphere = Mammals
- Stratosphere = Steal
- Troposphere = Toast
Why is the sun important for atmospheric processes?
Heat from the sun provides the energy to drive all atmospheric processes
What is Albedo?
Albedo is the percentage of light reflected by a surface (the whiteness of the surface) - it refers to the reflection coefficient.
Which albedo levels are (probably) important to remember?
Thick cumulonimbus cloud - 92%
Fresh snow - 80%
Sandy surfaces - 40%
Deciduous forest - 18%
Coniferous forest - 12%
How does insolation heat the atmosphere?
The atmosphere gains very little heat from insolation passing through it - poor conductor of heat
Incoming short-wave insolation can travel through a clear, cloud-free atmosphere
This then heats up the Earth’s surface, which then heats the atmosphere from below via conduction.
What is conduction?
Conduction is the process by which heat energy is transmitted through collisions between neighbouring atoms / molecules
Where does conduction more readily occur?
Conduction occurs more readily in solids and liquids, where the particles are closer together, than in gases.
What is convection?
Convection / convective heat transfer is the transfer of heat from one place to another due to the movement of fluid
What is radiation?
Radiation is the emission / transportation of energy in the form of waves or particles through space or through a material vacuum
What is atmospheric radiation / insolation?
Atmospheric radiation is the flow of electromagnetic energy between the sun and the Earth’s surface.
What is sensible heat transfer?
Sensible heat transfer is direct transfer by conduction / convection
What is latent heat transfer?
Latent heat transfer is heat transfer where energy is used or required as part of a change between states.
What factors affect the Daytime energy budget?
- Incoming short-wave insolation
- Reflection of radiation
- Heat transfer by conduction and convection
- Heat lost via long-wave radiation
- Soil absorbs heat from radiation
- Evaporation more likely
[ENERGY SURPLUS]
What factors affect the nighttime energy budget?
- NO incoming short-wave insolation
- NO reflection of radiation
- Heat transfer by conduction and convection (but may be less convection)
- Heat lost via long-wave radiation
- Ground decreases in temperature as long-wave radiation emits heat
- Condensation more likely
[ENERGY DEFICIT]
Which areas have the highest levels of insolation?
Land masses at the Tropics of Cancer and Capricorn
(where most deserts are)
Which areas have the lowest levels of insolation?
- The Artic and Antartic circles
The equator aslo has a low level of insolation
Why is the climate colder at the poles?
The angle of insolation from the sun means that the heating effect of insolation is spread over a greater area at the poles.
This reduces the concentration of heat resulting in a colder climate overall
Which latitudes have an energy surplus?
Which latitudes have an energy deficit?
Low latitudes
High latitudes
Why do we have seasons?
Seasons exist because the Earth rotates on a fixed axis tilted by 23.5°
As the Earth rotates around the Sun, the tilt of the Earth’s axis means that the North/South hemisphere recieves more direct insolation from the sun, alternating through the course of the year.
Which has a higher albedo (reflectivity) - land or sea? What does this entail?
The land has a higher albedo (reflectivity) which means that less radiation is absorbed by the land than the sea.
Where does heat penetrate further - land or sea? What does this entail?
Heat penetrates further into the sea - heat energy dispersed over a greater body of water, increased by ocean currents.
In contrast, most land surfaces are poor conductors of heat, so heat is confined in these areas to the near surface.
Which retains energy for longer - land or sea?
The sea retains heat for longer, and so is relatively warm in winter.
Which has a higher specific heat capacity - land or sea? What does this mean?
The sea has a higher specific heat capacity - a certain amount of heat will raise temperatures far less than it would raise the temperature of the land.
What defines a maritime climate?
Mild winters and cool summers, influenced by proximity to the sea.
Which holds more moisture - warm air or cold air?
Warm air
How do ocean currents occurr?
Ocean currents form because prevailing surface winds pull surface water with them.
How do ocean currents regulate the world’s temperatures?
Ocean currents carry water at different temperatures and therefore regulate the temperature of the ocean, bringing warm water from warmer regions and cold water from colder regions.
Warm ocean currents warm the air above them, which then rises. Warm air holds more moisture than cold air, causing higher rainfall.
For cold ocean currents, the opposite is true (colder air holds less moisture…)
What is the Inter Tropical Convergence Zone (ITCZ)?
The ITCZ is an area between the tropics where trade winds converge
Why does the ITCZ not follow the thermal equator?
- Proximity to sea - influenced by specific heat capacity of water compared with land and surfaces
- Ocean currents - influenced by cold and warm currents and the resulting temperature and wind pattern variations
- Altitude - atmosphere is thinner and albedo is higher in high-altitude areas
- Aspect - south-facing slopes receive more sunlight than north-facing in the Northern Hemisphere.
- Length of day / night
- Cloud cover
- Prevailing winds
How does the ITCZ affect areas in its regular path?
Areas in the regular route of the ITCZ recieve thousands of mm a year e.g. India, Bangladesh. It is the primary cause of the monsoon season
How does the ITCZ affect areas sometimes within its path?
Areas that only sometimes fall within the ITCZ but are in areas with dry winds, such as the Sahel, experience variable weather e.g. Mali, Niger, Sudan
How are areas outside the ITCZ with dry winds affected?
Areas outside the ITCZ but in areas with dry winds experience little to no rainfall at all e.g. Egypt.
How often do El Niño Southern Oscillation events occur?
El Niño Southern Oscillation (ENSO) events occur every 3-4 years as a result of weather patterns over the Pacific Ocean.
What happens in an El Niño Southern Oscillation event?
- Pressure rises over the western Pacific and decreases on the Eastern side (reverse is normally the case)
- This limits the northward migration of the ITCZ causing it to veer southwards
- Trade winds weaken in strength
- Breakdown of normal climatic conditions which leads to freak weather and disasters.
Some scientists predict that climate change would cause the ITCZ to move 5° further North. What might this affect?
- Wet areas in northern Indonesia, Malaysia and the Phillipines may recieve less ITCZ rain reducing potential for coffee farming
- Sothern Central America / Ecuador would become drier, making some crops like bananas and coffee impossible to cultivate
- Greater droughts in Northern Mexico and Sothern US
- El Salvador may become more humid
What is the thermal equator?
The thermal equator is a theoretical equator based on the pattern of the most intense surface heating, that moves between 23.5 N and 23.5 S through the year.
What are Jet Streams?
Jet streans are a series of high speed air currents that circulate the Earth at approximately 10-15 km above the surface
They are found at the tropopause, the transition zone between the troposphere and the stratopshere
Where do Jet Streams form?
They form near boundaries of adjacent air masses with significant differences in temperature e.g. the polar region and the warmer air from the South.
There are two major jet streams:
- Polar jet stream ~60°N
- Subtropical jet stream (weaker) ~30°N
How do Rossby Waves form in the latitudes betwen 30°-50°N?
The jet streams create fast-moving westerly [W→E] winds (the Westerlies) between 30°-50°N
These are reinforced by a strong North-South temperature gradient
These then meander from a westerly path to create Rossby Waves
What effect do Rossby waves have on the UK?
Rossby waves create pools of warmer air surrounded by colder air, and vice versa
This brings unusual seasonal weather to the UK e.g. a warm winter.
What is the dew point?
The dew point is the temperature to which air must cool for it to become completely saturated with water.
This is because air loses its ability to hold water as it cools, which then condenses, instead of being suspended in the air as vapour.
How does temperature of the dew point influence the volume of vapour held, and what influences the temperature of the dew point?
The higher the dew point, the more water vapour can be held.
The temperature of the dew point is influenced by the humidity of the air - higher humidity results in a higher dew point.
How do raindrops form through collision and coalescence?
Water droplets in a cloud collide with each other and combine / coalesce into larger droplets - movement is caused by convection currents.
Droplets remain suspended in the cloud until they are large enough to drop.
How do raindrops form by the ice crystal theory / Wegener-Bergeron-Findeisen (WBF) process?
Ice crystals form at high altitude in a cold cloud. These are then moved up and down in the cloud by convection currents.
Water vapour then forms around these ice crystals within the cloud through aggregation (ice + ice) and accretion (ice + water), causing the ice crystal to grow.
These ice crystals then fall when they become too heavy to be held by the cloud, and then melt when falling to become rain.
How do raindrops form due to dust / aerosols (condensation nuclei)?
Dust and other particles within clods create a surface for condensation to occur upon.
These dust particles accumulate water and collide with other water droplets, until they form into a raindrop themselves.
These raindrops continue to grow until they are too heavy to be held by the cloud, after which they fall as rain.
What is a (rainfall) front?
A front is the boundary between hot and cold air masses.
How is frontal rain formed?
Warm air is forced to rise along a front over denser cold air
This air is cooled by altitude and the cold front until the dew point is reached and condensation occurs, resulting in heavy rainfall at the front.
How is relief rainfall formed?
Warm, moist air from large water sources (such as the ocean) are blown onto land by prevailing wind
This air is then forced to rise due to hills / mountains, increasing altitude causing it to cool and condense until rain clouds form.
A rain shadow then occurs on the leeward side of the mountain range.
How does convectional rainfall form?
Insolation intensely heats the ground in the area causing the air above it to heat rapidly.
As this air rises, it cools and condenses to form huge cumulonimbus clouds and lots of rain
Often occurs in tropical regions during the afternoons, but can also occur in the UK during heatwaves
How does snow form?
Water vapour in clouds change into ice. When crystals fall the combine and collide (aggregation) into larger and heavier ice crystals, which then fall as snow once heavy enough.
Water vapour can also form straight into a solid (sublimation) as long as the temperature is below zero.
The ground and air temperature must remain below zero for snow to remain, else it becomes rain.
How does hail form?
Hail is formed when ice particles rise and fall inside cumulonimbus clouds, and super-cooled water droplets collide with and freeze around them (accretion). These frozen droplets fall as hail once too heavy to remain suspended in the cloud
Hail falls quickly so it is has little time to melt into rain.
What is fog?
Fog is a cloud in contact with the ground that reduces visibility to less than 1000m
What is absolute humidity?
Absolute humidity is the total mass of water vapour in a given volume of air (g/m3)
What is relative humidity?
Relative humidity is the actual vapour content in comparison with the volume of water possible to hold at a certain temperature (measured as a percentage %)
How does advection fog form?
Advection fog forms when moist, warm air passes over a cold surface.
This causes the air to cool and become more saturated, causing fog to develop and changing the relative humidity
How does valley fog form?
Valley fog forms when cold, dense air sinks and settles into the lower point of the valley, condensing and forming fog.
This is often due to a temperature inversion with warmer air passing above the valley.
How does radiation fog form?
Radiation fog occurs when the ground rapidly loses its heat at night via long-wave radiation.
This cools the air above the ground
This reduced the ability of the air to hold moisture, causing condensation (e.g. around condensation nuclei)
Which factors increase the formation of radiation fog?
- Winter temperatures
- Clear skies and calm conditions
- Night skies - fog dissipates soon after sunrise as ground warms
How does upslope fog form?
Upslope fog forms when winds blow air up a slope.
The air cools adiabatically as it rises, causing moisture inside to condense
The fog is likely to form in areas with a steep relief close to a body of water e.g. the Lake District
What is smog?
Smog is a mixture of smoke and fog.
What is dew?
Dew is the deposition of water droplets on the surface of grass / leaves
This forms because the surrounding air cools to the dew point, causing condensation both in the air and onto these surfaces.
