Local & Regional Circulations
Thermal Circulations: thermal highs & lows
Atmosphere warm or cools locally.
Shallow system (few km above ground).
Weaken with height.
Sea (Lake) & Land Breezes: a type of thermal circulation, due to uneven heating rates of land and water.
Sea breeze is usually stronger than land breeze, due to greater contrasts in temp during daytime.
Begins at approximately mid-morning.
By late afternoon, cool ocean air may reach a depth of 1000 feet and extend inland more than 12 mi.
Sea Breeze Front: leading edge of the sea breeze as it moves inland ... temp drop of approx. 10 F in one hour is common.
Sea Breeze Convergence Zone: common on Pacific coast, where air flow around hills rather than over them; also, common over Florida's interior, where thunderstorms often form in summer; can happen over the Great Lakes too.
Mountain & Valley Breezes: develop along mountain slopes.
Mountain heats up before valley and wind blows up mountain slope.
Reverse is true at night, as mountain top cools faster.
Winds are usually in the 5-10 mph range.
Katabatic
Winds: technically any downsloping wind, but is stronger than
typical mountain breeze.
Elevated plateau provides cold source, PGF causes air to spill down the mountain slope; Columbia Gorge and Cascades in US.
Can reach hurricane force wind speeds, but is usually 10-15 mph or less.
Can exceed 100 mph in Greenland and Antarctica.
Also known as Bora (Russia), Mistral (Rhone Valley of France).
Chinook Winds: a warm, dry wind descending a mountain range.
Through adiabatic compression, air warms and dries out; can cause a temp rise of over 35 F in one hour on the eastern slopes of the Rockies; relative humidity can drop to less than 5%.
Usually found with strong westerly winds blowing over a north-south mountain range (i.e., Rockies)
Can reach speeds of 50-100 mph.
Also known as Foehn (Germany), Zonda (Argentina).
Santa Ana Winds: a warm, dry wind that blows from the east or northeast over southern California.
Warms and dries out through adiabatic compression;
High pressure usually centered over Great Basin; wind funnels through mountain canyons; can reach speeds of 50-100 mph.
Creates dust storms; can aggravate brush fires due to dried out vegetation; can "fan" existing fires.
Dust Devil: a swirling column of air common to the hot, dry desert
Created by a strong updraft during the heat of the day, usually under a clear sky.
The spinning vortex sucks dust and sand upwards.
The diameter can range from 10 feet to as much as 100 feet and the vortex can reach from less than 1000 feet to several thousand feet high.
Unlike a tornado, the dust devils winds increase with height.
Are generally weak and do little damage.
Can also occur between buildings or other objects, that create a swirling motion due to forced wind flow.
Also known as Willy-Willy (Australia)
Haboob: a desert wind that creates blinding sandstorms.
Cold downdrafts along leading edge of thunderstorms lifts dust & sand into a huge, tumbling dark cloud that may extend horizontally over 150 km and rise vertically to the base of the thunderstorm.
Dust devils and tornadoes are possible along the turbulent cold-air boundary.
Most common in African Sudan and the Southwest U.S. (southern Arizona).
Other Desert Winds: can be exceedingly hot and can raise the temp to 120+ F, while lowering the relative humidity to under 10%.
Leste (Morocco)
Leveche (Spain): a Leste that crosses the Mediterranean Sea
Sirocco (Sahara Desert - North Africa)
Khamsin (Egypt, Red Sea & Saudi Arabia)
Sharav (Israel)
The above tend to be most common in Spring and Fall, due to the dry Mediterranean Summers.