Weather and Climate
What is the weather like today?
Is it like this EVERY day?
Why?
What is the difference between
WEATHER and CLIMATE?
Weather and Climate
 Weather – The temporary environmental
conditions in a localized area over a short
period of time.
In other words…what it’s like OUTSIDE,
right HERE, right NOW
 Climate – The long-term environmental
conditions across a large area and long time.
In other words…the AVERAGE of all the
WEATHERS
What affects weather and climate?
 There are two major factors that affect the
overall environment and climate…
-The tilt of the Earth in relation to it’s orbit
around the Sun
- The direction of that tilt that changes as
the Earth travels around the Sun
First, some basic vocabulary…
 Revolution – one ORBIT, or trip around the
Sun. This takes the Earth 365 ¼ days
Rotation – one
SPIN of the
Earth on it’s
axis. This
takes about 24
hours…one
DAY.
Earth’s TILT
 The Earth is not vertical (straight up-anddown) in relation to it’s orbital path, it’s tilted
23 ½ degrees from vertical.
 DRAW THIS ! ! !
This tilt means that
the Sun’s energy
doesn’t hit the
Earth equally.
Earth’s TILT
 This tilt results in uneven heating of the
Earth’s surface.
“Direct”
sunlight
“Indirect”
sunlight
From TILT to SEASONS
 As the Earth travels around the Sun, the tilt
changes in relation to the Sun. Sometimes
“toward” the Sun, sometimes “away”, and
sometimes neither.
 DRAW THIS !!
This creates a
predictable
cycle of
warmer and
cooler periods,
or seasons.
Seasons
 Because the direction of the tilt (“towards” or
“away”) is opposite for the Northern and
Southern hemispheres, so are the seasons.
Here is the rule to remember…
Tilted “toward” the Sun means Summer,
tilted “away” from the Sun means winter
Solstice and Equinox
 Solstice – the point at which the Earth is pointed farthest
toward / away from the Sun, creating long summer days and
short winter days . (Latin root word “sol”)
– Summer – around June 21
– Winter – around December 21
Equinox – the
point at which the
Earth is not
pointed toward OR
away from the
Sun, creating
equal day and
night. (“equi-nox”)
-Spring (“Vernal”)
around March 21
- Fall (“autumnal”)
around Sept. 21
Earth’s tilt affects length of days
 Places experiencing summer
have “longer” days
(more sunlight per 24 hrs.)
Shorter
Winter
days
Longer
Summer
days
 Places experiencing winter
have “shorter” days
(less sunlight per 24 hrs.)
 Areas above 66 ½ degrees
N or S will experience 24 hr.
extremes (light and dark)
depending on the season
24
hrs.
of
light
from
Nov.
to
Feb.
24
hrs.
of
dark
from
May
to
August
Greenhouse Effect
 RULE #1 OF NATURE – Energy can
be either absorbed or transferred
 Normally, when the Sun’s energy
penetrates the atmosphere, some of
it is absorbed, and some of it is
reflected back to space.
 Human and natural events increase
pollutants that trap the reflected
energy and send it back to the Earth
again, increasing the Earth’s heat.
Distributing the Sun’s Heat - WIND
 RULE #2 OF NATURE – Nature seeks
balance (equilibrium)
 Wind is the movement of air from High pressure to Low pressure
 Air Pressure changes with temp.
“Hot” (more active) molecules need
room to move, so they spread
apart, meaning LESS molecules
in a given space (LOW pressure)
HOT
COLD
 “Cold” (less active) molecules don’t
air
air
move as much, so they pack closer RISES SINKS
together, meaning MORE
molecules in a given space (HIGH pressure)
WIND – Sea Breeze
 When the sun shines, land (solid) heats up
faster than water (liquid) – remember RULE #1 ?
 Only the top 2-3 inches of earth get warm, then
the heat is reflected back to the air.
 The warm air rises, creating LOW PRESSURE
over the land during
the early/mid-morning
 This imbalance
(RULE #2) creates a
COOL wind blowing
in from the water,
called a SEA BREEZE
(Why do dogs dig in the dirt?)
L
H
WIND – Land Breeze
 When the sun sets, the process reverses and
land cools off faster than water (RULE #1)
 This creates COOLer air (HIGH pressure)
over the land and WARMer air (LOW
pressure) over the water at night
 The WARM wind
blowing out from the
land is called a
LAND BREEZE
L
H
WIND - Monsoons
 On a larger scale, the same factors create
monsoons - seasonal winds
 Due to the Earth’s tilt, differences in the
heating of land and ocean create long
term wind patterns that bring
seasonal rainy and dry periods.
Global Wind Patterns
 RULE # 3 OF NATURE – Nature
obeys the stronger force
 The Earth gets the most direct sunlight in the tropics,
so HOT air RISES at the Equator.
 The least sunlight hits the polar region, so the COLD
air sinks at the poles
 These two extremes force the
middle latitude winds to
flow “backwards”, rising
at 60 deg. and sinking at
30 deg., even though
that is warmer air.
Coriolis Effect
 Because the Earth spins (rotates) under the winds
as they travel N and S, they appear to curve
because of the Coriolis effect. (see it)
 The result is curved
wind patterns across
the Earth surface.
 All winds are named
for where they come
FROM.
 Areas of no major
wind pattern are
called “doldrums”
or “horse latitudes”
(Spanish explorers)
Water Currents
 Most ocean currents are affected by global
wind patterns blowing across the oceans.
Most
Most
WARM
COOL
currents
currents
flow
flow
WEST
EAST
Precipitation – Nature’s Thermostat
 There are 3 basic causes for rain. They are:
– Convection – due to evaporation and cooling
 Sun’s energy causes surface water to
evaporate and become humidity
 As the day cools off, the air cools and
condenses, causing storms and rain
 Usually in tropical environments
– Frontal – due to changes in temperature
 Starts with warm, moist air at the surface and above
 As a cold front approaches, it stays
low, forcing the moist air aloft
 This cools and condenses the air,
creating rain on the “leading edge”
of the front
 Usually in mid-latitudes where warm and cold air
systems collide
Precipitation, Part II
 Orographic – due to changes in elevation
– Moist air travels over land and approaches a steep rise in
elevation
– As the air is forced up the side of the rise, the air cools,
causing precip. on the “windward” side of the mountain
– As the (now dry) air continues over and down the
“leeward” side of the mountain, it warms up and
absorbs any available
moisture, creating a
“rain shadow desert”
– Found in areas of
mountains or other
rapid elevation change
CLIMATES
 The world is divides into three large climate
zones, based on latitude.
 DRAW THIS !!!
Low Latitude (“Tropical”)
climates – always hot
Mid Latitude (“Temperate”)
climates – hot/cold seasons
High Latitude (“Polar”) climates –
seasons either mild or extreme cold
Climate Zones
 Climate zones are divided into regions
with differences in two key characteristics:
– Amount of moisture (rain), and
– Typical temperature range through the year
 These
two characteristics are affected by
balancing the effects of four factors:




Latitude
 WRITE THESE
Altitude
DOWN !
Nearness to water
Direction of atmosphere and ocean currents
Latitude
 Due to the Earth’s tilt, the amount of sun
energy changes over the earth’s surface…
Polar (High Latitude) zone – either
mild temps. or extreme cold
Temperate (Mid-Latitude) zone –
seasonal, most varied climates
Tropical (Low Latitude) zone – yearround direct sunlight, always hot
RULE:
The HIGHER the latitude,
the COLDER the temps.
Altitude (Elevation)
 Higher elevation = thinner air, therefore
less air to hold heat makes it colder.
RULE –
The HIGHER
the elevation,
the COLDER the
temperatures.
Nearness to Water
 Land heats up and cools down QUICKLY.
 Water heats up and cools down SLOWLY.
 Therefore, water acts like a blanket… holding heat and
releasing it slowly.
 This results in smaller daily and seasonal temperature
changes near large bodies of water.
 “Coastal” areas are humid, “continental” areas are dry
30 degree change
in Houston
45 degree change
in Denver
Direction of Currents
 Global wind and ocean currents transfer heat
and moisture around the world, and help carry
moisture from the oceans to the land
– Warm water moving toward the land brings moisture (H2O)
– Warm water moving parallel to the coast brings heat, no H2O
– Cool water brings cool, dry air -> mild or desert climates
How it Works...
Tropical Wet Climate
 Latitude – in the
tropics HOT
Altitude – low land
doesn’t stop air flow
until mtns. in the west
 Nearness – flat land
“acts coastal”, allows
moisture inland
 Direction – air flow
brings in warm, moist air
from the ocean which then hits the mountain and rains
