Meteorology Chapter 9 Flashcards

Questions and Answers

Name the four scales of motion and give an example of each.

Microscale: eddies, downburst (microburst); Mesoscale: thunderstorms, land/sea breeze; Synoptic Scale: features on the surface weather map (low and high pressure systems, weather fronts); Global (Planetary) Scale: jet stream, long wave troughs and ridges, El Nino/La Nina, climate change.

What causes wind gusts?

Wind flows over the irregular landscape and objects, breaking into irregular, twisting eddies that influence air flow, causing fluctuations in speed and direction.

What is the height of the 'planetary boundary' or 'friction' layer?

The height is normally from the surface to 1000 m (3330 ft) AGL.

Why are winds near the surface typically stronger and more gusty in the afternoon?

Thermal turbulence increases with surface heating and instability, leading to a greater exchange of faster moving air from upper levels. Signup and view all the answers

What three factors contribute to the depth of mixing and hence, frictional influence in the planetary boundary (friction) layer?

<ol> <li>Surface heating; 2) Strong wind speeds; 3) Rough or hilly landscape.</li> </ol> Signup and view all the answers

Define 'wind shear'.

Wind shear is a sudden change in wind speed or wind direction. Signup and view all the answers

Define 'clear air turbulence'.

Clear air turbulence is turbulence that occurs in clear air due to wind shear creating eddies in a mixing zone. Signup and view all the answers

Explain how shelterbelts protect crops from wind damage.

Shelterbelts consist of trees that break wind into small eddies, minimizing damage to crops or soil erosion. Signup and view all the answers

What three factors determine the height of 'wind created waves' over a body of water?

<ol> <li>Wind speed; 2) Length of time the wind has been blowing; 3) The fetch, or distance over water the wind blows.</li> </ol> Signup and view all the answers

A wind direction is reported as 310 degrees. From what compass direction is the wind coming from?

Northwest. Signup and view all the answers

Identify a few localized winds.

Onshore wind, offshore wind, upslope wind, downslope wind. Signup and view all the answers

What is a 'prevailing wind'? What is the prevailing wind in the state of North Dakota?

The prevailing wind is the most often observed wind direction over a year; in North Dakota, it is a northwest wind. Signup and view all the answers

Explain how a 'thermal circulation' develops.

A thermal circulation is produced by unequal heating and cooling of the atmosphere near the surface, causing air movement. Signup and view all the answers

Give an example where the development of a 'thermal circulation' cell can influence the weather.

The land and sea breeze across Florida during summer influences thunderstorm activity. Signup and view all the answers

What is the difference between a 'valley' and 'mountain' breeze? When do they form?

A valley breeze is an upslope wind, while a mountain breeze is a downslope wind; the former forms during surface heating and the latter during radiational cooling. Signup and view all the answers

What is a 'monsoon'? Where is the best-known monsoon in the world?

A monsoon is a wind that changes direction seasonally; the best known is in India. Signup and view all the answers

Explain why a 'Chinook' wind is warm, dry downsloping wind.

Chinook winds warm due to latent heat of condensation on the windward side and are dry because moisture is removed as precipitation. Signup and view all the answers

How does a 'katabatic' wind differ from a 'Chinook' wind?

A katabatic wind is a cold downsloping wind, while a Chinook is warm; katabatic winds form from cold air on a plateau. Signup and view all the answers

How does the 'Santa Ana' wind differ from the 'Chinook' wind?

Santa Ana winds affect southern California and originate from an elevated plateau, heating due to compression. Signup and view all the answers

What is a 'haboob'? How do they form?

A haboob is a dust or sand storm that forms from downdrafts of thunderstorms lifting dust into a large cloud. Signup and view all the answers

What is a dust devil? How do they form?

Dust devils are spinning vortices visible due to lifted dust; they form on hot days over dry surfaces due to rising hot air. Signup and view all the answers

Study Notes

Scales of Motion

Microscale: Includes small features such as eddies and downbursts (microbursts).
Mesoscale: Comprises phenomena like thunderstorms and land/sea breezes.
Synoptic Scale: Features observable on surface weather maps, including low/high pressure systems and weather fronts.
Global (Planetary) Scale: Encompasses larger patterns such as jet streams, long wave troughs/ridges, and climatic events like El Niño/La Niña.

Causes of Wind Gusts

Wind interacts with irregular landscapes and objects, creating twisting eddies.
Eddies fluctuate wind speed and direction, leading to irregular wind motion known as wind gusts.

Planetary Boundary Layer Height

Extends from ground level to approximately 1000 m (3330 ft) above ground level.
Can be higher in rough or windy areas due to increased frictional forces.

Afternoon Wind Strength

Increased thermal turbulence due to surface heating leads to stronger winds in the afternoon.
Greater instability allows for a mix of upper-level fast moving air with slower surface air, enhancing average wind speed.

Factors Affecting Mixing Depth

Surface Heating: Creates steep lapse rates and strong thermal turbulence.
Strong Winds: Induce mechanical turbulence that increases mixing.
Rough Terrain: Generates significant mechanical turbulence.

Wind Shear

Defined as a sudden change in wind speed or direction over a short distance.
Generally, larger changes over a uniform distance mean greater wind shear.

Clear Air Turbulence (CAT)

Occurs in areas of wind shear, producing eddies in clear air.
Characterized by strong winds above and lighter winds below the mixing zone.

Shelterbelts

Composed of conifer and deciduous trees, designed to reduce wind speed.
Wind moving through breaks into smaller eddies, minimizing damage to crops and reducing soil erosion.

Wave Height Determinants

Wind Speed: Faster winds create taller waves.
Duration: The longer the wind blows, the higher the waves grow.
Fetch: The distance over water that the wind travels influences wave height.

Wind Direction

Wind reported at 310 degrees comes from the northwest, moving toward the southeast.
Winds are named based on their origin.

Localized Winds

Onshore Wind: Flows from water to land.
Offshore Wind: Flows from land to water.
Upslope Wind: Moves air uphill.
Downslope Wind: Moves air downhill.

Prevailing Wind

The most frequently observed wind direction over a year.
In North Dakota, the prevailing wind is from the northwest.

Thermal Circulation Development

Caused by unequal heating of the atmosphere, creating air movement between high and low pressure areas.
Results in the formation of pressure systems that influence local weather patterns.

Example of Thermal Circulation

Land and sea breezes in Florida lead to different wind patterns and can trigger thunderstorms during the summer due to temperature contrasts between land and water.

Valley vs. Mountain Breeze

Valley Breeze: Gentle, upslope wind formed with surface heating during the day.
Mountain Breeze: Gentle, downslope wind formed during nighttime radiational cooling.
Strongest during peak heating (afternoon) and peak cooling (sunrise).

Monsoon

Defined as seasonal wind direction changes.
Best known in India, characterized by dry winters and wet summers.
The U.S. experiences a weaker monsoon in its southwestern desert areas.

Chinook Wind

Warm, dry wind that descends mountain slopes due to latent heat from precipitation on the windward side and compression heating on the leeward side.
Commonly found along the Rocky Mountains in the U.S.

Katabatic vs. Chinook Wind

Katabatic Wind: Cold, descending wind formed from cold air on plateaus.
Differences in formation processes lead to katabatic wind being colder than the air it replaces.

Santa Ana Wind

A warm, dry wind descending from an elevated desert plateau found in southern California.
Characterized by temperature increases due to compression, unrelated to latent heat.

Haboob

A dust or sand storm formed by cold downdrafts from thunderstorms that lift debris into large, tumbling clouds.

Dust Devil

Spinning vortices visible from dust, formed on clear, hot days when surface air rises rapidly.
Distinguished from tornadoes; typically short-lived and lasts only a few minutes.

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Test your knowledge on the key concepts presented in Chapter 9 of Meteorology. These flashcards cover various scales of motion in weather patterns and other important meteorological phenomena. Perfect for students looking to reinforce their understanding of weather mechanisms.