Unit 2.2: Atmospheric Pressure and Winds

Question 1

What is atmospheric pressure?

Answer 1

Force exerted by molecules of air against a surface; exists because air is pulled by gravity.

Question 2

List 5 characteristics of atmospheric pressure.

Answer 2

1. measured by a barometer in units of kg/cm squared
2. increases exponentially as it gets closer to the surface and gains mass.
3. air pressure is greatest at sea level
4. high pressure is associated with fair conditions
5. warm air is associated with low pressure

Question 3

What are isobars?

Answer 3

Lines that connect points of equal pressure around the world. The closer the bars are, the more rapid the pressure changes therefore air flows fast between those lines due to pressure gradient.

Question 4

What is wind? What is it measured by?

Answer 4

Air motion with respect to Earth’s surface; mostly horizontal. Measured with anemometers, records speed and direction.

Question 5

Winds are named from…

Answer 5

the direction they come from.

Question 6

Wind is created by a combination of what 3 forces?

Answer 6

Pressure gradient force, Coriolis force, and friction.

Question 7

Define pressure gradient force. List some of its characteristics.

Answer 7

Difference in atmospheric pressure between 2 locations. Winds move from high to low pressure, greater pressure gradient means greater winds, and it contributes to wind speed and direction.

Question 8

Define Coriolis force. List some of its characteristics.

Answer 8

Deflection of air caused by rotation of the Earth, it travels in a curved line instead of a straight line. Deflected to right in northern hemisphere a left in southern, greatest at poles and decreases to 0 at equator, fast winds get deflected stronger, and it only contributes to wind direction.

Question 9

What is friction?

Answer 9

It slows winds at surface, only a factor near the surface.

Question 10

What is the difference between a cyclone and an anticyclone? What is a similarity they both have?

Answer 10

Cyclone: areas of low pressure where air is being forced into it. Air converges at centre which causes it to rise and creates cloudy, stormy conditions.
Anticyclone: area of high pressure with air being forced out. Air diverges at centre which results in clear skies and dry conditions.
Similarity: air both converges/diverges at an angle due to coriolis force.

Question 11

What are 4 consistent features over space due to surface pressure?

Answer 11

1. Intertropical convergenze zone (ITCZ): Low pressure cell that circles equator and migrates with sub polar point. results in rising air and creates unstable atmosphere with plenty of precipitation. (Cyclonic)
2. Subtropical high pressure zones (STHP): High pressure areas around 30o N&S. Air rises from ITCZ and migrates poleward and subsides here, has stable, arid conditions (anticyclonic)
3. Subpolar low: Discontinuous zone of low pressure, forms at 60oN&S. Unstable and wet conditions. (cyclonic)
4. Polar high: High pressure area over both polar regions that is created by cold&dense air. Area is cold and dry.

Question 12

What are trade winds?

Answer 12

Winds from the STHP to the ITCZ, moves toward the equator then flows along it. Northern hemisphere = northeast trade winds and Southern Hemisphere = southeast trade winds. They are mostly found over oceans and weak inland.

Question 13

Define doldrums.

Answer 13

Winds at equator neat the ITCZ where the trade winds meet. Wind goes up, not horizontal.

Question 14

What are westerlies?

Answer 14

Found in both hemispheres, flows from STHP toward polar low and goes from west-east.

Question 15

What are polar easterlies?

Answer 15

Found in both hemispheres, flows from polar high to sub polar low. Typically cold and dense air and goes from east-west.

Question 16

What are 3 upper level winds?

Answer 16

1. Geostrophic winds: wind whose speed and direction is determined by pressure gradient and Coriolis force, it does not cross isobars.
2. Polar jet stream: narrow band of fast wind between 35&60o N&S in a westerly direction.
3. Rossby waves: winds that move up and down latitudes and bring warm air from south to north and cold air from north the south. Completely circles around the earth.

Question 17

Explain sea & land breeze.

Answer 17

In coastal regions during the day, there is low pressure on land, high pressure over sea. This causes winds to go from sea to land which is a SEA BREEZE.
During nighttime, the pressure levels are opposite which causes wind to go from land to sea which is a LAND BREEZE.

Question 18

Explain mountain and valley breezes.

Answer 18

During to day, mountain side facing sun gets hot and has lower pressure than valley, this causes wind to go from valley to mountain which is called VALLEY BREEZE.
The opposite happens in the nighttime and valley has lower pressure than the mountain side which causes wind to go from mountain to valley. This is called MOUNTAIN BREEZE.

Question 19

What are monsoon winds?

Answer 19

It is created by the migration of ITCZ.
In the summer, found in northern India. Wind is from the southwest from the ocean over to the continent and causes wet and unstable conditions.
In winter, found in southern India. Wind is from northeast and flows from the continent to the ocean and makes dry conditions.

Question 20

What are chinook winds?

Answer 20

Created by an interaction with a barrier. On the side of the wind, it is forced up the barrier and cools of which creates wet conditions. As it goes down opposite side it gains pressure and creates dry conditions.

Question 21

What are onshore and offshore winds?

Answer 21

Onshore: from sea to land
Offshore: from land to sea

Question 22

What are prevailing winds?

Answer 22

Direction of wind that occurs most frequently in a time period.