Transcript Local Winds - Smyth County Schools

Local Winds
By
Diana L. Duckworth
Rustburg High School
Campbell County, VA
LOW
land
HOT
HIGH
Sea Breeze
COOL ocean
• 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
Note the clouds
formed inland from
coastline.
Clouds form where
air rises.
Evidence of sea
Breeze
Photo from EOS
Land Breeze
HIGH
land
COLD
LOW
WARM ocean
• 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
Warm LOW
Valley Breeze
mountain
Cool
HIGH
valley
• 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
HIGH
Mountain
Breeze
mountain
LOW
valley
• 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
Northern Hemisphere Cyclone Map View
LOW
Air converges into a Low
Coriolis Effect turns Wind to Right
Pressure
Makes Air
Converge
Into a
LOW
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
COUNTERCLOCKWISE
HIGH
CLOCKWISE
Southern Hemisphere Opposite
LOW
CLOCKWISE
HIGH
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