Lecture 5

Question 1

Sea and land breeze is another type of…

Answer 1

Thermal circulation

Question 2

In the daytime, does land heat up more quickly/slowly than the sea?

Answer 2

Quickly, and a thermal circulation forms with a sea breeze

Question 3

In the night time, sea and land breeze thermal circulations are reversed, why is this?

Answer 3

Because the land surface cools down quicker and to lower temperatures

Question 4

What is the Urban heat island effect?

Answer 4

Significant increase in air temperatures in a metropolitan area in comparison to the surrounding rural area

Question 5

What causes the urban heat island effect?

Answer 5

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

Question 6

Mountain and valley breeze

Answer 6

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

Question 7

How is night time inversion caused?

Answer 7

By orography - cold air and pollutants drain downhill and settle in low-lying valleys

Question 8

Increased pollution caused by subsidence inversion

Answer 8

• 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

Question 9

Thermal circulation

Answer 9

Local circulations brought on by changes in air temp.

Question 10

What is the adiabatic process

Answer 10

When an air parcel cools + warms, /expands + compresses, without exchange of matter + energy with the surrounding air

Question 11

Does air pressure and density increase/decrease with altitude?

Answer 11

Decrease

Question 12

When an air parcel is moved to lower altitudes with higher surrounding pressure, what happens to the air?

Answer 12

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

Question 13

What is the environmental lapse rate?

Answer 13

Rate at which temperature decreases with altitude

Crucial in determining the extent of vertical motion in the atmosphere

Question 14

Atmospheric stability refers to a condition of equilibrium with respect to vertical motion. It the air is stable it will…

Answer 14

Resist vertical motion

Question 15

If air is in an unstable equilibrium it will…

Answer 15

Given a slight dislocation, move farther away from its original position

Question 16

The dry adiabatic only applies to

Answer 16

Unsaturated air (has a relative humidity less than 100%)

Question 17

What does the dry adiabatic lapse rate assess?

Answer 17

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)

Question 18

What is the moist adiabatic lapse rate? (MALR)

Answer 18

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

Question 19

Is the moist adiabatic lapse rate constant?

Answer 19

Not constant, as it varies with temperature and moisture content of the air.

Question 20

How is atmospheric stability determined?

Answer 20

By comparing the rate of a rising air parcels temperature change with the ambient environmental lapse rate

Question 21

If the air parcel cools faster than environment, what happens?

Answer 21

It will be more dense (and heavier) and therefore sink back to original altitude

= stable, resists vertical movement

Question 22

If the rising air parcel cools down slower than its environment, where will it go?

Answer 22

It will continue to rise as it will be warmer (and lighter) than surrounding air.

Air = unstable and enhances an initial vertical displacement

Question 23

If air is forced to rise in an absolutely stable atmosphere, what occurs?

Answer 23

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

Question 24

Signs of an unstable atmosphere

When vertical temperature gradient (ELR) is large then the atmosphere is often absolutely/conditionally unstable

Answer 24

Clouds grow vertically and plumes rise to great heights
Cumulus/cumulonimbus type clouds
Upwards and downwards currents, gusty turbulent winds
Good visibility
Dust whirls

Question 25

Pollutants rise, mix and disperse downwards during the…

Answer 25

Afternoon - atmosphere is most unstable

Question 26

At night, what happens to pollutants?

Answer 26

Radiation inversion exists

Shorter stacks = trapped
Taller stacks = able to rise and disperse downwards

Question 27

LA - type photochemical ozone smog occurs because…

Answer 27

There is increased pollution during inversion.

During weather periods with stable stratification pollutants can accumulate to values well above safe air quality standards.