Local Winds

ByDiana L. Duckworth

Rustburg High SchoolCampbell County, VA

land oceanHOT 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 cloudsformed inland fromcoastline.

Clouds form whereair rises.

Evidence of seaBreeze

Photo from EOS

land oceanCOLDWARM

LOWHIGH

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

CoolHIGH

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

PressureMakes AirConvergeInto aLOW

Coriolis EffectTurns air to theRight

COUNTERCLOCKWISE AROUND A CYCLONE

Anticyclone in Northern Hemisphere – Map View

HIGH

Air DivergesFrom a HIGH

Anticyclone in Northern Hemisphere – Map View

HIGH

Air DivergesFrom 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