Local Winds By Diana L. Duckworth Rustburg High School Campbell County, VA

land ocean HOT COOL LOW HIGH Ocean has high heat capacity; cooler in day than land (low heat capacity); becomes HIGH Land is warmer in day - becomes a LOW Sea Breeze in daytime from ocean to land; affects coastal areas only Sea Breeze

Note the clouds formed inland from coastline. Clouds form where air rises. Evidence of sea Breeze Photo from EOS

land ocean COLD WARM LOW HIGH Land Breeze Land is colder at night; becomes a HIGH Ocean is warmer at night; becomes a LOW Land breeze develops at night as air moves in coastal areas from high over land to low over the ocean.

Note 24 hour cycle in wind direction - Station on Oregon coast; easterly in night; northwesterly in day. Figure from National Data Buoys website

mountain valley Cool HIGH Warm LOW Valley Breeze Thin air heats & cools more rapidly than dense air –Dense air in valley remains cooler in day & becomes high pressure –Thin air in mountains warms and becomes a low pressure Air flows up from the valley in a valley breeze

Note clouds formed over the mountain ranges where air is rising. Astronaut Photo

mountain valley HIGH LOW Mountain Breeze At night, thin air cools rapidly becomes high in mountains Dense air in valleys retains heat; becomes a low Air flows down the mountain from high to low in a Mountain Breeze

Cyclones & Anticyclones Small Scale Pressure Systems

Coriolis Effect Objects moving over the surface of the earth are affected by Earth’s rotation Northern Hemisphere, path curves to object’s right Southern Hemisphere, path curves to object’s left Speed of Earth’s rotation decreases as latitude increases Effect greater at Poles than Equator

LOW Northern Hemisphere Cyclone Map View Air converges into a Low

LOW Coriolis Effect turns Wind to Right Pressure Makes Air Converge Into a LOW Coriolis Effect Turns air to the Right COUNTERCLOCKWISE AROUND A CYCLONE

Anticyclone in Northern Hemisphere – Map View HIGH Air Diverges From a HIGH

Anticyclone in Northern Hemisphere – Map View HIGH Air Diverges From a HIGH Coriolis Effect turns air to the right. WIND BLOWS CLOCKWISE AROUND A HIGH

Northern Hemisphere LOW HIGH COUNTERCLOCKWISE CLOCKWISE

Southern Hemisphere Opposite LOW HIGH CLOCKWISE COUNTERCLOCKWISE

Friction with ground slows wind down Surface winds do not blow at right angles to pressure gradient; blow more like 45° So wind spirals into a low and out from a high at ground level

In Conclusion for Northern Hemisphere There are three components of motion of air in a LOW (cyclone) –Spirals inward –Rises –Spirals counterclockwise There are three components of motion of air in a HIGH (anticyclone) –Spirals outward –Sinks –Sprials clockwise