Chapter 6 - Notes

Question 1

What are the 4 mechanisms that cause air to rise (mentioned in chapter 4)?

Answer 1

1. Orographic lifting - air is forced to rise over a mountainous barrier.
2. *Frontal wedging *- warmer, less dense air, is forced over cooler, denser air.
3. *Convergence *- a pile-up of horizontal air flow results in upward movement.
4. *Localized convective lifting - *unequal surface heating causes localized pockets of air to rise because of their bouyancy.

Question 2

Why are windward mountain slopes some of the rainiest places on earth?

Answer 2

Because when the air is forced to rise by the mountains, adiabatically cooling often generates clouds and precipitation.

Question 3

What is a **Rain shadow desert **?

Answer 3

A dry area on the lee side of a mountain range.

Question 4

What is a **Front **?

Answer 4

A boundary (discontinuity) separating air masses of differnt densities, one warmer and often higher in moisture content then the other.

Question 5

What storms are weather-producing fronts associated with?

Answer 5

**Middle-latitude cyclones **

Question 6

What is stability when refering to air?

Answer 6

Stability is a property of air that describes its tendancy to remain in its original position (stable) or to rise (unstable)

Question 7

What are the 3 fundamental conditions of the atmospere?

Answer 7

1. Absolute stability - The condition of air that has an environmental lapse rate that is less than the wet adiabatic rate (1°C per 100 meters).
2. Absolute instability - The condition of air that has an environmental lapse rate that is greater than the dry adiabatic rate (1°C per 100 meters).
3. Conditional instability - The condition of moist air with an environmental lapse rate between the dry and wet adiabatic rates. (when the atmosphere is stable for unsturated air but unstable for saturated)

Question 8

When is the atmosphere most stable?

Answer 8

During a temperature inversion.

Question 9

When does absolute instability occurs most often?

Answer 9

During the warmest months and on clear days when solar heating is intense.

Question 10

Does temperature drop more slowly with altitude?

Answer 10

Yes

Question 11

What are the differences between clouds that are associated with stable air and clouds that are associated with unstable air?

Answer 11

Stable air make very thin clouds that are widespread and vice versa.

Question 12

What enhances instability?

Answer 12

Anything that causes the surface air to heat

1. Intense solar heating warming the lowermost layer of the atmospherer.
2. The heating on an air mass from below as it passes over a warm suface
3. General upward movement of air caused by processes such as orographic lifting, frontal wedging, and convergence.
4. Radiation cooling from cloud tops

Question 13

What enhances stability?

Answer 13

Anything that causes the surface air to cool

1. Radiation cooling of the Earth’s surface after sunset
2. The cooling of an air mass from below as it traverses a cold surface
3. General subsidence within an air column.

Question 14

What is the dew point decrease rate?

Answer 14

2°C/km

Question 15

When a parcel of saturated air drop what is the rate of cooling?

Answer 15

The moment the parcel is lowered (by whatever means), it does so at the dry adiabatic rate of 10°C/km, regardless of how much water is in the parcel.

Question 16

When a parcel of air is lifted into th eair how much does it’s actual temperature and it’s dew point tempereature decrease?

Answer 16

actual temperature at 10°C/km. dew point temperature at 2°C/km. Condensation occurs when the two are equal.

Question 17

How do you find the altitude at which saturation occurs?

Answer 17

The altitude can be determined simply: divide the parcel and dew point temperatures by the rate difference

(i.e., [10 – 2]°C/km = 8°C/km).