Lecture 5 Flashcards
Sea and land breeze is another type of…
Thermal circulation
In the daytime, does land heat up more quickly/slowly than the sea?
Quickly, and a thermal circulation forms with a sea breeze
In the night time, sea and land breeze thermal circulations are reversed, why is this?
Because the land surface cools down quicker and to lower temperatures
What is the Urban heat island effect?
Significant increase in air temperatures in a metropolitan area in comparison to the surrounding rural area
What causes the urban heat island effect?
Release (and reflection) of heat from industrial and domestic buildings
Absorption of heat by concrete, brick and Tarmac during the day and it’s release into lower atmosphere at night
Enhanced cloud formation due to pollution = trapped heat
Absence of water = less evapotranspiration and more is available to heat atmosphere
Absence of strong winds to disperse heat/bring in cooler air
Mountain and valley breeze
Day = sloped valley walls receive more insulation
Air above valley walls is heated more efficiently + a gentle upslope wind, valley breeze formed.
Night = cool (dense) air glides downhill into valley, providing a mountain breeze
How is night time inversion caused?
By orography - cold air and pollutants drain downhill and settle in low-lying valleys
Increased pollution caused by subsidence inversion
- form when air above a deep anticyclone (high pressure) slowly subsides + warms due to compression
- colder air at the surface is prevented from mixing with the sinking war, air
- thick layer of polluted air = trapped in valley
- top of the polluted air marks the base of a subsidence inversion
Thermal circulation
Local circulations brought on by changes in air temp.
What is the adiabatic process
When an air parcel cools + warms, /expands + compresses, without exchange of matter + energy with the surrounding air
Does air pressure and density increase/decrease with altitude?
Decrease
When an air parcel is moved to lower altitudes with higher surrounding pressure, what happens to the air?
The surrounding air molecules compress the boundaries of the air parcels –> this increases kinetic energy (average speed) of molecules inside, therefore air gets warmed.
Vice versa - inside the air parcel, molecules compress = lower temperature
What is the environmental lapse rate?
Rate at which temperature decreases with altitude
Crucial in determining the extent of vertical motion in the atmosphere
Atmospheric stability refers to a condition of equilibrium with respect to vertical motion. It the air is stable it will…
Resist vertical motion
If air is in an unstable equilibrium it will…
Given a slight dislocation, move farther away from its original position
The dry adiabatic only applies to
Unsaturated air (has a relative humidity less than 100%)
What does the dry adiabatic lapse rate assess?
In unsaturated air, the rate of warming and cooling due to vertical motion remains constant
Rate of temperature change = approximately 10 degrees c for 1000m of change in elevation
Seen in saturation vapour pressure curve (shows saturation)
What is the moist adiabatic lapse rate? (MALR)
As the rising air cools to its dew point temperature the RH reaches 100% and air = saturated.
Rate of temperature change = 6 degrees c for 1000m of change in elevation
Is the moist adiabatic lapse rate constant?
Not constant, as it varies with temperature and moisture content of the air.
How is atmospheric stability determined?
By comparing the rate of a rising air parcels temperature change with the ambient environmental lapse rate
If the air parcel cools faster than environment, what happens?
It will be more dense (and heavier) and therefore sink back to original altitude
= stable, resists vertical movement
If the rising air parcel cools down slower than its environment, where will it go?
It will continue to rise as it will be warmer (and lighter) than surrounding air.
Air = unstable and enhances an initial vertical displacement
If air is forced to rise in an absolutely stable atmosphere, what occurs?
It will resist vertical movement and spread horizontally.
- Reflected in Stratford (layered) clouds/horizontally spreading radiation fog
- Steady winds, poor visibility due to pollution accumulation
Signs of an unstable atmosphere
When vertical temperature gradient (ELR) is large then the atmosphere is often absolutely/conditionally unstable
Clouds grow vertically and plumes rise to great heights
Cumulus/cumulonimbus type clouds
Upwards and downwards currents, gusty turbulent winds
Good visibility
Dust whirls
Pollutants rise, mix and disperse downwards during the…
Afternoon - atmosphere is most unstable
At night, what happens to pollutants?
Radiation inversion exists
Shorter stacks = trapped
Taller stacks = able to rise and disperse downwards
LA - type photochemical ozone smog occurs because…
There is increased pollution during inversion.
During weather periods with stable stratification pollutants can accumulate to values well above safe air quality standards.
