Lecture 21: Weather

Question 1

What is weather?

Answer 1

Gives the conditions of the atmosphere at a specific place and time on the planet.

Question 2

What is climate?

Answer 2

Defines the average weather that occurs at a location over a period of time (decades, centuries, or more).

Question 3

What is does pressure-gradient flow mean?

Answer 3

Air has a lower density around the equator which causes lower pressure because it is hotter, and the opposite at the poles.
And air tends to flow in from zones of higher pressure to take the place of the hotter rising air.
-Near the equator, this occurs in the Inter Tropical Convergence Zone (ITCZ).

Question 4

What are isobars?

Answer 4

Lines of constant pressure.

Question 5

What controls the wind speed?

Answer 5

The pressure gradient

• If isobars are far apart, there is a low pressure gradient and a low wind speed.
• If isobars are close together, there is a steeper pressure gradient and higher wind speed.

The Coriolis effect and friction with the Earth’s surface also affects wind speed.

Question 6

What is geostrophic flow?

Answer 6

When flow becomes parallel to isobars the pressure-gradient is exactly balanced by the Coriolis Effect.

Question 7

What is the hadley cells?

Answer 7

Are driven by pressure-gradient flow, located near the equator.

Question 8

What is the ferrel cells?

Answer 8

Are poorly defined, with circulation driven by the movement of adjacent cells.

Question 9

What is the polar cells?

Answer 9

Are driven by pressure-gradient flow, located near the poles.

Question 10

How is near-surface flow different from winds at high altitudes?

Answer 10

Friction along the Earth’s surface reduces the Coriolis Effect on pressure-gradient flow.
-In the northern hemisphere, wind is deflected counterclockwise relative to isobars and the opposite direction in the southern hemisphere.

Question 11

How are ekman spirals formed?

Answer 11

They are caused by modification of pressure-gradient flow by the Coriolis force.

Question 12

Where is there high pressure on the Earth?

Answer 12

• Between Hadley and Ferrel cells

- At the poles

Question 13

Where is there low pressure?

Answer 13

• Between Ferrel and Polar cells

- Near the equator (the ITCZ)

Question 14

What are easterlies?

Answer 14

Persistent winds that dominate the equatorial zones (winds from the East).

Question 15

What are westerlies?

Answer 15

Persistent winds that dominate zones above the subtropical high pressure zones (winds from the West)

Question 16

What are trade winds?

Answer 16

Persistent wind patterns

Question 17

What is a jet stream and how are they formed?

Answer 17

Strong westerly geostrophic flow and are formed because the mid-latitude change in altitude of tropopause creates a steep pressure gradient.

Question 18

What are rossby waves?

Answer 18

The result of large fluctuations in the position of the polar fronts.

Question 19

What are air massses?

Answer 19

Large volumes of air that have internally consistent properties, including pressure, humidity and, temperature.

Question 20

What are the five major types of air masses and what is the air like in it?

Answer 20

1. Continental Artic (bitterly cold, dry)
2. Continental Polar (cold, dry)
3. Maritime Polar (cool, moist)
4. Continental Tropical (hot, dry)
5. Maritime Tropical (hot, moist)

Question 21

How are monsoons formed?

Answer 21

The seasonal migration of pressure belts reverses wind directions near the equator, impacting India, Australia, and Western Africa.

Question 22

How does the winds change in the winter due to monsoons?

Answer 22

Dry NW winds come from land and the ITCZ lies south of India.

Question 23

How does the winds change in the summer due to monsoons?

Answer 23

SW winds from the ocean brings heavy rain and the ITCZ migrates north.

Question 24

What causes sea breeze?

Answer 24

During the day, the land heats faster than the sea, causing air to rise over land and create a region of low pressure. A sea breeze then blows towards land.

Question 25

What causes land breeze?

Answer 25

At night, the land cools faster than the sea, causing air to rise over the sea creating a zone of low pressure. A land breeze blows towards the sea.

Question 26

How does the temperature of a valley change daily?

Answer 26

Warm air rises up the valley during the day making it hotter.
Cold air sinks down the valley at night making it colder.

Question 27

Why does the B.C side of the Rocky Mountains have more vegetation than the Alberta side?

Answer 27

Due to chinooks. Regional atmospheric flow forces air over the mountains and as they rise the water in the clouds condense and fall out in precipitation. Then on the other side the dry warm air descends.

Question 28

What kind of air do thunderstorms typically form?

Answer 28

In warm moist air masses, during daytime heating, especially along cold fronts where mT (maritime Tropical) air contacts cP (continental Polar) air.

Question 29

How does lightning occur?

Answer 29

Strong air currents cause the ionization of air molecules, such that the anvil (top) of the cloud becomes positively charged and the base of the cloud becomes negatively charged. An electrical discharge occurs to balance this separation of charge (lightning) and heat the air explosively.

Question 30

Where and how do tornados form?

Answer 30

In thunderstorms and are initiated in spiral updrafts by the collision of mT air with cP air which causes an instability in the atmosphere.
Are tightly rotating centers that typically rotate in the direction of the larger air mass.

Question 31

Where do tropical cyclones form?

Answer 31

5-10° north or south of the equator in the ITCZ.

Question 32

What does a tropical cyclone need to form?

Answer 32

1. The air needs to be warm and moist (>26° over the sea)
2. Condensation to supply latent heat for continued density lifting
3. The Coriolis effect to drive rotation

Question 33

When does a cyclone reach hurricane status?

Answer 33

When the winds are >119km/h.

Question 34

What are three effects of a tropical cyclone and how do they occur?

Answer 34

• Low pressure in the center of a cyclone can rise sea level up to 9m.
• Wind may drive this raised water on shore, causing a storm surge.
• Very high rainfall (>250mm) often occurs, causing flooding.