Transcript Barometric Pressure

Barometric
Pressure –
The pressure
due to the
weight of the
atmosphere.
Barometric
Pressure is
also called
atmospheric
pressure or
air pressure.
Air Pressure is
measured
using a
barometer.
Differences in
air pressure
causes
wind.
WARM AIR
 Holds more water than
cold air.
 Is less dense (it will
rise)
COLD AIR
 Holds less water than
warm air.
 Is more dense (it will
sink)
Earth’s rotation
affects the
direction of wind.
Coriolis effect –
The change in
the direction of
an object’s path
due to Earth’s
rotation.
Winds in the
Northern
hemisphere curve
clockwise
Winds in the
Southern
Hemisphere curve
counterclockwise.
Global wind
patterns form
circulation
cells.
Warm and cold
fronts create
different types
of
precipitation.
Warm front
 Forms layered,
stratus-type
clouds or fog
 Produces only
drizzle or
steady rain.
Cold front
 Forms
cumulus
clouds
 Produces
showers and
thunderstorms
There are 3
stages to a
thunderstorm
1) Cumulus
2) Mature
3) Dissipating
Cumulus Stage
 First stage
 Wind
movement is
all upward
 Rain has not
yet started.
Mature Stage
 Lightning, wind,
and rain
 Hail and
tornadoes may
occur
 Wind movement
is both up and
down.
Dissipating
 Rain and wind
gusts start to
slow down/stop
 All wind
movement is
downward
Severe thunderstorms
can develop
supercells, which
have intense,
rotating updrafts.
About 10% of
thunderstorms are
severe.
Lightning – friction
between the clouds
creates regions of air
with opposite
charges.
To balance, a stepped
leader (channel of (-)
air) nears the ground
and a return stroke
(channel of (+) air)
rushes upward to
meet it.
Lightning heats the air to
about 300,000 C.
Thunder – sound made by
the rapid expansion of air
around the lightning bolt.
Hazards of
thunderstorms:
• lightning
• violent winds
• hail
• floods
• tornadoes
Hail – precipitation
in the form of
balls or lumps
of ice. Most
commonly
occurs in the
spring.
Floods – produced
when the rain falls
faster than the
ground can absorb
it or faster than
streams and rivers
can transport it out
of the area. Floods
are the main cause
of thunderstormrelated deaths each
year.
Cold air downdrafts
can produce
severe weather.
 Cold air descends
and hits the
ground
 On hitting, it bursts
outward like
spokes on a wheel.
 Wind speed can be
up to 260 km/h.
Tornadoes:
 Intense
 Short-lived
 Localized in the
mid-latitudes
 Formed when dry
air meets warm,
moist air.
Tornadoes – violent,
whirling column of
air in contact with
the ground.
Before it reaches
the ground, it is
called a funnel
cloud.
The Fujita tornado
intensity scale –
classifies tornadoes.
They usually form in the
spring in the late
afternoon. Tornado
alley – northern Texas
through Oklahoma,
Kansas, and Missouri.
Hurricanes:
 Cover a vast area
 May last for days
 The center is
called the eye.
 Get their energy
from the warm,
moist air over the
ocean.
Tropical cyclones – large,
rotating, low-pressure
storms.
• common in the summer and
fall
• thrives on energy from
warm, tropical oceans
• air pressure in the center is
low
• moves because wind
currents steer them
eye – the calm center of the
storm
eyewall – band immediately
surrounding the eye that
has the strongest winds
The Saffir-Simpson
hurricane scale
classifies
hurricanes
according to their
wind speed, air
pressure in the
center, and
potential for
property damage.
A hurricane will end
when it moves over
land and no longer has
access to the warm
ocean surface to draw
its energy, or when it
moves over colder
water.
A storm surge occurs when
hurricane-force winds drive a
mound of ocean water
toward coastal areas, where
it washes over the land.
They can reach 6m above
normal sea level. Lots of rain
and flooding also causes
enormous damage.
Climate is the
weather pattern
over a long period
of time.
Ocean and Land
influence the
climate in a
specific area.
3
Climate and Weather
• Latitude is the
primary factor that
determines climate
at a given location.
• The amount of
radiation received
from the Sun and
the prevailing
circulation features
depend on latitude.
3
Ocean and Land Influence
Continental climate –
Area with little direct
ocean influence.
Maritime climate – Area
with strong ocean
influence.
3
Ocean and Land Influence
• Wind and pressure patterns determine
precipitation.
Maritime climates are
milder:
 Summers are cooler
 Winters are warmer
 Daily temperature
varies less than a
continental climate
Mountain influence on
climate
 Act as barriers,
blocking weather
systems.
 When wind blows on
one side, a lee rain
shadow forms on the
other side.
Causes of climate
change
 Mountain building
 Continental
movement
 Ocean currents
 Changes in the tilt of
Earth’s axis of
rotation.
 Sunspot activity
 Volcanoes
 Human activity
El Nino and La Nina
 Involves the
atmosphere and
ocean.
 Opposite of El Nino
is La Nina.