Download 2.0 Global Weather Patterns

Global Weather Patterns
AZ State Standards
• Concept 2: Energy in the Earth System (Both Internal
and External)
• Understand the relationships between the Earth’s land
masses, oceans, and atmosphere.
• PO 2. Explain the mechanisms of heat transfer
(convection, conduction, radiation) among the
atmosphere, land masses, and oceans.
• PO 11. Describe the origin, life cycle, and behavior of
weather systems (i.e., air mass, front, high and low
systems, pressure gradients).
• PO 15. List the factors that determine climate (e.g.,
altitude, latitude, water bodies, precipitation,
prevailing winds, topography).
Content Objectives
• SWBAT to describe the mechanisms by which
water condenses to form clouds and how that
affects precipitation patterns worldwide.
• SWBAT explain the rainshadow effect and predict
locations on a map of where it would occur
based on prevailing winds.
• SWBAT explain how monsoons function and
describe the locations on Earth where they occur.
Convection of Water Vapor
• Warm air can hold more H2O vapor than cold air.
• Warm moist air rises and then cools.
Convective plume
Water droplets collide, grow larger, and eventually become
too heavy to be lifted by the convective flow any longer
Convection of Water Vapor
• Warm air holds more water vapor than cold air
• Warm moist air rises and then cools.
• The water vapor begins to condense into clouds.
• Rain occurs when the drops become too heavy to
be held aloft by the convective currents.
Rule of Thumb
• High Pressure Means Dry Weather
• Low Pressure Means Wet Weather
Dry
Wet
World Precipitation Map
The Four Ways of Lifting
Convection
Warm air mass
Topographical (Orographic) Lifting
Cold air mass
Frontal Lifting
Convergence
All clouds and storms are caused by the rising and cooling of air
and the condensation of water vapor into clouds.
Primarily a phenomenon of hot seasons and locations
Convection
Occurs year-round in mountainous regions
Topographical Lifting
Primarily a spring/fall event when air of different temperatures meet
Warm air mass
Cold air mass
Frontal Lifting
Convergence
At 60° N or S or in specific locations
The Rainshadow Effect;
A Special Case of Orographic Lifting
Rainshadow Effect
1) When warm moist air arrives from the ocean and begins to rise over land
features, it will cool and the water vapor will condense.
This is topographic lifting.
2) This forms clouds and eventually rain on the windward side of the
mountains. The windward sides of the mountains often have lush forests.
Temperate Rainforests in the PNW average 100-200” of rain per year!
Ocean
Rainshadow Effect
1) When warm moist air arrives from the ocean and begins to rise over
land features, it will cool and the water vapor will condense.
This is topographic lifting.
2) As air descends into the inter-mountain trough, temperatures warm
and the air gets drier. Rainfall in Seattle is only 40” per year or less
3) That is actually less than any city east of the Mississippi River!
Ocean
Drier
inter-mountain trough
Rainshadow Effect
1) As the air rises again on the next range, topographic lifting causes
air to cool, condensation into clouds, and rain to fall again on the
windward side.
2) At high enough elevations it falls as snow. Up to 600-800” can fall
in the Cascade Mountains per winter.
Ocean
Drier
inter-mountain trough
Rainshadow Effect
1) As the clouds descend down the leeward slopes, the air warms again
and the water droplets evaporate into the air.
2) The air warming and drying as it sinks is called Adiabatic Heating
3) This results in less precipitation and cloud cover.
4) That creates a Rainshadow Desert.
Rainshadow Desert
Ocean
Drier
inter-mountain trough
Rainshadow Effect
Rainshadow Effect
Ocean
Drier
intermountain trough
Rainshadow
Desert
Precipitation Map of Washington
Rainshadow Effect in Hawaii
300”
20”
150” of rain and 15” of rain,
only 15 miles apart!
Do We Have A Rainshadow Here?
5,000 feet elevation south of Flagstaff
• Ever notice that it is much greener driving south
to Phoenix and than driving north to Page?
Do We Have A Rainshadow Here?
• Ever notice that it is much greener driving south
to Phoenix and than driving north to Page?
5,000 feet elevation north of Flagstaff
Monsoons come up from the south
Continental Versus Marine Climates
• Land heats up faster and hotter than water does.
That is because rock has a lower specific heat
capacity than water.
• Large land masses are hotter in summer and
colder in winter than those near the coast.
Monsoon Seasons
• Monsoons are typically associated with summer rains.
• But, technically it refers to a seasonal changing of the
wind direction associated with heating of the
continental land masses.
Monsoon Flow
• Cold air sinks and then spreads out when it hits
the ground. This high pressure prevents moisture
from the ocean from coming onto land.
Winter is typically dry for continental climates
Monsoon Flow
• Warm air rises. This creates low pressure which
sucks moisture in from the ocean.
Summers are typically wet for continental climates
Monsoon Seasons
• Winters on continents tend to be dry and cold
• Summers on continents tend to be hot and wet
Let’s Examine the Normal Climate
Patterns of North America
• First important distinction:
• Weather and Climate are different terms
• Weather refers to what is happening locally on
a daily basis
• Climate refers to the normal patterns of
temperature and precipitation over a large
area on a seasonal basis over many years.
For Instance
• The average high is 86F in June in Flagstaff and
June is the driest month of the year on average.
• Today it was only 74F and it rained 1”.
• Does this disprove June is typically dry in this
region?
Another Example
• Death Valley is the hottest
and driest location on the
continent.
• Yet, during my first two
visits, I was rained on both
times…
• Your personal experience
does not always jive with
reality!
winter
summer
World Precipitation Map
World Vegetation Pattern
What Triggers the Monsoons?
When heat in Sonoran Desert is strong enough to overcome downdrafts
from 30N to suck moisture in from Gulf of Mexico
World Precipitation Map
World Photosynthesis Patterns
Content Objectives
• SWBAT to describe the mechanisms by which
water condenses to form clouds and how that
affects precipitation patterns worldwide.
• SWBAT explain the rainshadow effect and predict
locations on a map of where it would occur
based on prevailing winds.
• SWBAT explain how monsoons function and
describe the locations on Earth where they occur.