The Atmosphere Flashcards
What is the structure and composition of the atmosphere?
Troposphere
- 8-10km at poles, 15-17km at Equator
- Where weather and other related processes occur e.g. precipitation and surface winds
- Warmed by heat from the earth’s surface
- The top is called the tropopause, which is -40˚ - -80˚C
Stratosphere
- 10-50 km above
- Warmed by absorption of solar radiation
- Lower stratosphere temperatures are relatively constant, but upper stratosphere temperatures increase with altitude
- The top is around 0˚C
Mesophere
- 80km above max
- No water vapour, cloud or dust to absorb incoming radiation
- Wind speeds reach 3000km/h, strongest in atmosphere
- -90˚C
Thermosphere
- 80km+
- Thins out as it reaches higher elevation
- Increasing concentrations of atomic oxygen (single oxygen atoms), which, like the ozone, absorb incoming solar radiation
What is insolation?
- Short wave solar radiation
- The earth’s primary source of energy
What factors affect insolation?
Distance from the Sun
- Elliptical orbit accounts for a 6% variation
Latitude
- Higher and lower latitudes have up to two times a larger area to be heated, less concentrated
- Equatorial areas have a smaller areas to be heated, more concentrated and closer to the sun
Length of Day and Night
- 23.5% tilt
- Seasonal variation for day and night
- The shorter the day, the less incoming solar radiation is absorbed
What actually happens to incoming solar radiation as it reaches earth? What effect does this contribute to?
Majority of incoming solar radiation do not even reach the earth’s surface. Instead, most are either reflected or absorbed by:
- ozone
- water vapour
- CO2
- dust and ice particles
- clouds
- 24% reaches the earth’s surface
- 21% reaches the earth’s surface as diffused radiation
- After reaching the surface, radiation is transformed in infra-red energy. 94% of this energy is absorbed by water vapour and CO2 in the atmosphere. This creates the natural greenhouse effect.
This contributes to albedo.
What is albedo?
“The ratio between incoming radiation and the amount reflected back in space, expressed as a percentage, is known as albedo.”
- 10% oceans and dark soil
- 25% grasslands
- 40% desert sands
- 85% snow
What are horizontal heat transfers?
Surface winds and ocean currents. 80% (wind) and 20% (ocean) of heat transfer between them. This transfers heat from the equator to the poles and vice versa for cold.
What are vertical heat transfers?
This refers to the air masses in the atmosphere. These also assist in regulating temperatures in the tropics and poles.
- Heated air rises at the Equator in the Hadley Cell and begin to move to the poles once reaching the tropopause.
- At 30˚ N and S, the air descends, creating a Subtropical High Pressure Belt. Some of the air returns as surface windsto the Equator to create the Hadley Cell.
- The warm and cold air meets at the Polar Front (60˚ latitude). The warm air is lifted over the cold.
- The area of low pressure forms the Polar Cell.
Describe high pressure.
- Also called anticyclones
- Air descends
- As the air descends, it gains moisture in the warmth, creating a draw weather condition
- Stable conditions, clear skies, low wind velocities
Describe low pressure.
- Also called cyclones
- Air rises
- As the air rises into cooler parts of the atmosphere, the moisture it carries condensates and produces precipitation.
- Unstable conditions, cloudy skies and rain, high wind velocities
What are isobars on synoptic charts?
- Lines that join equal barometric pressure
- Barometric pressure is measured in hectopascals hPa
- To determine pressure, you need to refer to the values given to each isobar
- The closer together, the lower the pressure
What are pressure systems on synoptic charts?
- Defined patterns formed by isobars
- High pressure: where barometric pressure increases towards the centre, isobars are further apart
- Low pressure: where barometric pressure decreases towads the centre, isobars closer together
What are cold fronts on synoptic charts?
- Represented by a line with triangles
- Where cold air cuts over warm air
- Associated with rain fall
What is a warm front on synoptic charts?
- Represented by a patterned curved line
- A slow, gradual undercut of cold air by warm air
- Slower but longer periods of precipitation
What are wind speed on synoptic charts?
- The closer the isobars, the higher the wind velocity
- Some synoptic charts include wind velocity and direction
What is wind direction on a synoptic chart?
- Winds are named from the direction from which they come from e.g. a southerly wind originated from the south
- Direction is determined by location. In the Southern Hemisphere, winds travel anti-clockwise out of the centre from high pressure, winds in low pressure travel clockwise towards the centre.
What is rainfall on synoptic charts?
- Areas which have had rainfall in the pass 24 hours are shaded
Define the different features of air masses over different locations and their general names.
- Air masses over oceans contain more moisture than those over land.
- High pressure air masses at the tropics form warm air masses.
- High pressure air masses at the poles form cold air masses.
- Maritime air masses form over oceans.
- Continental air masses form over land.
- Arctic air mass (Ac)
- Antarctic air mass (Aac)
- Tropical maritime (Tm)
- Polar maritime (Pm)
- Tropical continental (Tc)
- Polar continental (Pc)
- Equatorial (E)
The point where two air masses meet is called a front.
What is a warm front?
This is a gradual undercut of cold air by warm air. It produces long and slow periods of precipitation.
What is a cold front?
This is where cold air cuts through warm air. This produces sudden and possibly violent periods of precipitation.
How do storms develop?
Moist air
- creates condensation, which forms clouds
- heat energy is released which makes rising air more buouyant and forms more clouds
Unstable atmosphere
- allows clouds to rise higher
Mechanism to initiate development
- fronts, troughs and low pressure areas
- land forms such as mountains
Severity depends on how rapid clouds rise.
Multi-cellular storms are formed when storm cells of the same storm system are each at different life stages.
A long-lived thunderstorm is called a supercell. It is more severe and intense.
How do lightning and thunder develop in storms?
- When electrical energy is discharged from clouds
- Lightning is produced when the difference in charges between the clouds and earth are great enough: top of clouds are positive, the middle and bottom are negative, and the earth is positive
- Forked lightning: where lightning flashes between clouds and earth
- Sheet lightning: where lightning flashes within the cloud
- Thunder is the sound produced by electrical discharge (sound travels faster than light). Thunder occurs after discharge.
How are hailstorms formed?
- Hail starts as a small ice crystal or is covered in tiny frozen cloud droplets.
- As the nucleus falls to the warmer portion of the thunderstorm, it collects cloud droplets which freeze slowly over it.
- As the nucleus returns to the cold, it collects more cloud droplets which freeze on impact.
- The number of layers - which are usually around 15-20 - are determined by how many cycles the it undergoes in the storm.
- The hail falls off once it becomes too heavy to support.
How does orographic rainfall occur?
Also called “rain shadow” effect.
- Warm, moist air is forced to rise to cooler altitudes as it moves over the mountain.
- As it rises, the moisture condenses and precipitation occurs.
- Cool, dry air results as the air mass drifts over the mountain.
- As the air descends on the other side, it warms but remains dry.
Water only reached one side of the mountain.
What is Foehn wind?
Warm, dry air that descends most mountain ranges as a result of orographic rainfall.
How is conventional rainfall formed?
- Warm air rises, then cools and precipitates when a large cumulonimbus cloud is formed.
- This produces heavy rains, thunder and lightning
How is frontal rainfall formed?
- Warm air meets cold air
- War air is forced over cold
- Where the two air masses meet, precipitation occurs
How does insolation differences affect global climate patterns?
Different concentrations of insolation on the earth’s surface are responsible for the rotation of air in the atmosphere.
Where there is a higher concentration of solar radiation, the temperature is warmer, and the air rises. Where there is a lower concentration of solar radiation, temperatures are cooler and the air descends.
This is why it is warmer near the equator and colder at the poles.
How does the earth’s axis affect global patterns?
Due to the 23.5% tilt, earth receives its seasonal changes as it orbits around the sun.
Alternating seasons occur in hemispheres depending on how much insolation a hemisphere receives. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, as it receives more insolation.
How does the distribution of land and water affect global climate patterns?
- Ocean currents can help define how much water a land mass receives
- Warm ocean currents have high rates of evaporation. Coastal areas adjacent to them are likely to have frequent rainfalls.
- Cold ocean currents have low rates of evaporation and thus drier. Land masses adjacent to them are usually drier as well. Majority of the world’s deserts are caused by cold ocean currents.
How does topography affect global climate patterns?
- The higher the altitude, the colder the climate
- Orographic rainfall and anabatic and katabatic winds.
How are land and sea breezes caused?
- Occurs when there is a difference in heat temperatures between the land and sea.
- Land heats up faster; ocean retains heat longer.
Day
- Land heats more rapidly than ocean, thus, it is much warmer. This forms low pressure.
- Warm air rises and cools as it reaches higher altitudes. A cloud curtain may be formed.
- Warm air cools as it drifts out to sea.
- The cool air descends over the sea, creating high pressure.
- A sea breeze blows from the high pressure, to the low pressure.
Night
- The sea retains heat for longer, and thus, it is warmer.
- The warm ocean air rises and creates low pressure.
- The warm air cools as it reaches higher altitudes.
- The cooling air mass drifts over to the land, where it is cooler, and descends, creating high pressure.
- The land breeze blows from the high pressure to the low pressure.
How are anabatic and katabatic winds formed?
These wind types are formed from temperature variations throughout the day and night in a valley or hilly land area.
Day - Anabatic flow
- The air warms with the land and rises, creating low pressure.
- The rising air follows the gradients of the hills, creating strong uphill winds.
- Updrafts may result in the formation of clouds
Night - Katabatic flow
- Air cools as the valley cools and descends, creating high pressure.
- The cool wind follows the gradient of the hills.
- If there is enough moisture, fog may develop due to the temperature inversion.
What are the features of an urban microclimate?
- Creates more particles for water droplets to form on (e.g. dust).
- Generates more heat.
- Alters radiation pattern, composition and moisture content in the air
- Alters air flow
Sunlight
- Urban areas have higher temperatures, yet they receive less sunlight and have more cloud cover
- Atmospheric particles may absorb and reflect up to 50% of insolation, especially in winter as the sun is lower in the sky
Humidity
- Relatively lower
- Lack of evapotranspiration
Cloud Formation and Precipitation
- Increased rate of cloud formation and higher precipitation due to increased moisture content in the atmosphere and higher convection currents from warmer temperatures
- Cloud cover up to 10% heavier
- Strong thermal currents create a 25% greater chance of thunder and up to 400% greater chance of hail
Wind
- Generally lower due to obstruction of buildings and other urban structures
- Large buildings can form “canyons” where winds have higher velocities to travel in
- Buildings can also create eddies
What are aspect-induced microclimates?
- Microclimates formed due to the gradient of slopes and the direction they face
- Slopes that face the equator have a northerly aspect in the Southern Hemisphere, a southerly aspect in the Northern Hemisphere. These slopes receive more direct sunlight than slopes facing the poles
- Slopes with an easterly aspect receive direct sunlight during the morning, when temperatures are cooler
- Slopes with a westerly aspect receive sunlight later int he day, when temperatures are at their peak
- Slopes that are not exposed to direct sunlight are cooler and moister
- Slopes with a southerly aspect are is shadow for a high majority of the year
- Slopes with a northerly aspect receive sun throughout the entire year and are only in shadow for a few weeks of winter
With a forested area as an example, what are the features of microclimates in different land surfaces?
- Absorb and trap larger amounts of insolation in comparison to exposed areas. The canopy acts like a blanket to retain the heat absorbed
- Thus, there is only a small diurnal range of temperature (the difference between the max and min daily temperature range) is created
- Higher relative humidity
- Lower wind velocities
What is the Coriolis Effect?
This refers to how winds never travel in straight lines because of the earth’s constant rotating. Instead, they travel in swirls from the poles to the Equator.
How does the composition of the atmosphere affect global climate patterns?
The atmosphere affects the earth’s temperature and, thus, its climate.
CO2 and water vapour in the troposphere regulate temperatures by permitting in radiant sun and preventing a portion of it from returning to space. This creates the natural greenhouse effect. Without it, life on earth would not exist and the earth would have an average temperature of -18˚C.
Describe the movement of surface winds.
- As the N and S winds meet at the Equator, the North are deflected to the right, the South to the left. This is the Coriolis Effect and creates the North-East and South-East trade winds.
- North winds at the poles are deflected to the right and South winds to the left.
- Westerlies cover the area in between the poles and tropics.
- There are no surface winds at the Equator due to rising air (Equatorial Doldrums).
- The 30˚ region is also calm (Horse Latitude).
- At the 40˚-49˚ latitudes is the Roaring Forties.
