Chapter 9 Flashcards
What are the four atmospheric scales of motion?
Microscale (meters, seconds-minutes), Mesoscale (1-100 km, minutes-hours), Synoptic Scale (100s-3000 km, days-weeks), Planetary Scale (>3000 km, weeks+).
What causes low-level turbulence?
Mechanical turbulence (obstructions like buildings, mountains) and thermal turbulence (surface heating).
How does thermal turbulence vary throughout the day?
Strongest during midday due to intense heating; weakest at night and early morning.
What is clear-air turbulence (CAT)?
Turbulence aloft not associated with clouds, caused by sudden changes in wind speed or direction (wind shear).
What is the primary cause of mountain wave turbulence (MWT)?
Oscillating air motion near and downwind of mountains.
How is wind direction reported?
Based on where it is coming from (e.g., North wind = 360°).
Define onshore and offshore winds.
Onshore wind: From water to land; Offshore wind: From land to water.
What are upslope and downslope winds?
Upslope (Valley Breeze): Air moving uphill; Downslope (Mountain Breeze): Air moving downhill.
What is a prevailing wind?
The most frequently observed wind direction over a long time period.
How can prevailing winds affect climate?
Example: Denver’s easterly winds bring clouds/precipitation, while westerly winds bring warm, dry air.
What is the highest recorded wind speed in the U.S.?
231 mph at Mt. Washington, NH, April 12, 1934.
What is the highest recorded wind speed globally?
253 mph at Barrow Island, Australia, April 10, 1996, during Cyclone Olivia.
What does an anemometer measure?
Wind speed.
What are the advantages of sonic anemometers?
No moving parts, better performance in winter (prevents icing issues), measures up to 125 knots.
What is a sea breeze?
A daytime onshore wind caused by land heating faster than water, creating a pressure gradient.
What is a land breeze?
A nighttime offshore wind caused by land cooling faster than water, reversing the pressure gradient.
How does a sea breeze front affect weather?
Can trigger thunderstorms, especially in Florida where two sea breezes converge.
What is the primary cause of lake-effect snow?
Cold air moving over a warm lake, causing air to rise, form clouds, and produce snow.
Define monsoon.
A seasonal wind pattern that changes direction, such as the Asian monsoon.
What happens during the Asian summer monsoon?
Land heats up, creating a thermal low; onshore winds bring heavy rainfall.
What happens during the Asian winter monsoon?
Land cools down, creating high pressure; offshore winds bring dry conditions.
What is the Southwest U.S. monsoon?
A mid-late summer onshore wind bringing thunderstorms to Arizona, Nevada, and New Mexico.
What causes mountain and valley breezes?
Daytime heating creates upslope winds (valley breeze); nighttime cooling causes downslope winds (mountain breeze).
What is a Chinook wind?
A warm, dry wind descending the eastern slopes of the Rockies, causing rapid temperature increases.
What are Santa Ana and Diablo winds?
Strong, dry, high-speed winds in California, often fueling wildfires.
What is a dust devil?
A small rotating updraft formed on hot, dry surfaces, typically under clear skies.
How do dust devils differ from tornadoes?
Dust devils form from the ground up; tornadoes descend from thunderstorms.
