Transcript Low pressure - Sonoma Valley High School

19.2 Pressure Centers & Wind
Highs and Lows
• Cyclones-Low pressure regions where
pressure decreases to the center
• Anticyclones- High pressure regions
where pressure increases to the center
Cyclonic and Anti-cyclonic Winds:
Effects of the Pressure Gradient
and the Coriolis Effect
• Northern Hemisphere: Winds blow counter
clockwise around a low (cyclone) and
clockwise around a high (anticyclone)
• Friction causes a net flow of air inward
toward a low and outward away from a high
Weather and Air Pressure
• Rising Air (rises over a low pressure zone
and raises relative humidity) = Cloud
formation & Precipitation
• Sinking Air (sinks over a high pressure zone
and lowers relative humidity) = Clear Skies
Pair share: What happens to the rising
air that increases relative humidity?
Global Winds
• Unequal heating of the Earth’s surface
causes wind
• The atmosphere balances this
unequal heating by moving warm air
toward the poles and cool air toward
the equator
AND ……
Effects of a Rotating Earth on
Winds: Coriolis Effect
• The space between the
Equator and Pole now
divides into 3 wind “cells”
instead of one, with wind
directions alternating
• This creates the
“Westerlies” (global winds
that travel from the west
(for the US this is the
prevailing wind direction,
carrying our weather) and
the Trade winds which
travel from the east across
Central America
Effects of Land and Water
• Land adds further differences: heats up
and cools down faster than water
19.3 Regional Wind Systems
Local Winds
• Caused by topographical effects or the
surface being either water or land
• Land and Sea Breezes - Land heats up and
hot air rises, moving air in from the ocean
during the day (sea breeze) and moving air out
to the ocean at night (land breeze)
Valley and Mountain Breezes
• Valley Breeze : daytime heating causes less
dense, hot air to rise from the valley floor
• Mountain Breeze : nighttime cooling causes
more dense, cold air to sink from the
mountain toward the valley floor
El Nino
• Every 3 to 7 years normal cold offshore South
American eastern Pacific ocean currents yield to
warm currents from the equator, causing poor fishing
and above average rainfall in other regions.
Normal year
•
Pair share: Compare
the water off the
cost of South
America in the top
picture to the
bottom. How are
they different?
El Nino year
La Nina
Atmospheric conditions that occur when
surface temperatures of the eastern
Pacific are colder than normal, resulting in
colder than normal air over the northern
US states and warmer than normal air in
the middle and southern states
Global Precipitation Pattern
• Pair share: What 4 regions of the
Earth get the most rain?
White Board Review
1. What type of weather is rising air
associated with?
2. How does the atmosphere balance
unequal heating of the Earth’s surface?
3. What type of local winds can form in the
Grand Canyon at night?
4. From which direction does a SE wind
blow?