Lecture 4

Question 1

What causes horizontal pressure variations?

Answer 1

Changes in temperature and air density

Question 2

What do isobars (lines of equal pressure) describe?

Answer 2

Pressure distribution at the surface

Question 3

When representing pressure in e.g. Isobar charts, regions with high pressure will present themselves as?

Answer 3

Ridges.

Low pressures = troughs

Question 4

What is the pressure gradient force?

Answer 4

The force that drives the air from high pressure areas to low pressure areas.

E.g. a warm location, like the equator, and a cold region, like the North Pole. Air at the equator is warmed with more solar energy than the air at the North Pole, so it rises and then moves horizontally toward the North Pole. As it cools, it sinks back down toward the warmer equatorial region. The air pressure difference between the two locations is called the pressure gradient and the force that moves the air = PGF

Question 5

Horizontal transport of air or wind consists of a balance of…

Answer 5

Friction, pressure gradient force, coriolis, centripetal

Question 6

The coriolis effect

Answer 6

Causes wind to deflect due to the earths rotation. (Effects direction not speed)
Northern hemisphere - deflects right
Southern Hemisphere- deflects left
Stronger the wind, greater the deflection

Question 7

The coriolis force increases with latitude, being 0 at the equator. The amount of deflection depends on:

Answer 7

Rotation of the earth
Latitude
Moving objects speed

Question 8

Circumference of lower latitudes are _______ than at higher latitudes

Answer 8

Larger

E.g. The city of Quito ‘travels’ a greater distance within 24hrs compared to Buffalo (located at a higher altitude)

Question 9

Geostrophic wind balance

Answer 9

High altitude (no ground friction influence) Pressure gradient force will result in wind motion until a speed is reached where PGF and Coriolis balance each other out.

Consequently, wind will flow parallel to isobars and won’t accelerate further.

Question 10

Centripetal force (circular motion)

Answer 10

Combination of PGF + coriolis = centripetal force (circular motion)

Question 11

What does the centripetal force cause?

Answer 11

Northern hemisphere=
Wind motion travels anti clockwise around a low pressure system
Clockwise around a high pressure system (anticyclone)

Opposite in Southern H =
Low pressure system flows clockwise

Question 12

Friction influences the atmospheric flow between the surface and 1000m altitude, this lower part of the atmosphere is called…

Answer 12

Planetary boundary layer

Question 13

Friction reduces wind speed and in turn the coriolis force. What does this cause?

Answer 13

An imbalance between coriolis force and pressure gradient force, wind blows across isobars

Question 14

At stable stratification and smooth terrain, how far does the effect of the surface friction extend?

Answer 14

Only a relatively short distance upwards above the ground.

Unstable and terrain is rough =surface friction extends further upwards

Question 15

Explain how trade winds are formed?

Answer 15

Intense heating at equator warms air near the surface causing it to rise high into the atmosphere.
Rising air creates space + the equatorial low pressure zone (which sucks air in from higher latitudes) forms trade winds

This produces trade winds which meet at the inter tropical convergence zone (ITCZ)

Question 16

What is the atmopheric vs ocean heat transport?

Answer 16

Trade winds blowing into ITCZ + climate system = trying to export heat away from equator.
In blowing winds do nothing to help this.

Question 17

Describe the Hadley cell

Answer 17

Adiabatic cooling and advective cooling takes place 
At about 30 degrees N+S it sinks = sub-tropical high pressure zone 
Air sinks (lost most of its moisture, so dries area it sinks onto)
Some sinking air pulled back towards equator = Hadley cell

Question 18

Some of the air at 30 degrees N flows towards the poles, what is this called?

Answer 18

Westerlies

Atmosphere takes over as main poleward of heat

Question 19

When does the poleward movement of warm sub-tropical air cease?

Answer 19

When it meets the air mass at the polar front

Question 20

Why are there high pressures over the poles?

Answer 20

Intense cold at poles causes air to become super chilled and sink
(The polar high + ‘blow out winds’)

Question 21

What occurs when cold air mass meets warmer westerlies at the polar front? And what are the other 2 cells called?

Answer 21

Condensation and precipitation

Forces warm sub-tropical air to rise, as cold polar air = more dense

Rising air completes 2 other cells = Ferrell cell and Polar cell

Question 22

What are the important components of the 3 cells?

Answer 22

High altitude
Fast flowing
Narrow air currents called ‘jet streams’

Question 23

Where do jet streams occur?

Answer 23

Tropopause, driven by spin at the earth and strong differences in temperature

Question 24

What’s the strongest jet stream?

Answer 24

Polar jet

Question 25

What way to jet streams typically flow?

Answer 25

West to east

Question 26

What can happen if a jet stream meanders?

Answer 26

Forms a rossby wave (large kinks in westerly flows)

Question 27

What is an air mass?

Answer 27

Large body of air whose properties of temperature and humidity are fairly similar in any horizontal direction at any given altitude

Question 28

Arctic, polar, tropical, equatorial, maritime and continental are classifications of…

Answer 28

Air masses

Question 29

What controls the flow of air (winds) on earth?

Answer 29

Latitude variation in solar irradiance
Earths tilt and seasons
Mean sea level pressure (MSL)