Transcript Air Pressure

Weather is....
 The current state of the
atmosphere...what is happening right
now
Main points about weather:
 The sun warms the earth’s surface and all the
air above the surface
 The earth is warmed most at the equator and
least at the poles---why?(earth’s 23.5 degree tilt)
 The air over land is warmed more quickly than
air over water.
 Warm air expands and rises, creating low
pressure; cold air is dense and sinks,
creating high pressure
Weather Factors
 Weather: The state of the atmosphere at
a specific time and place
TEMPERATURE =the average Kinetic
motion of molecules
↑ TEMP= Increase movement of molecules=
feels hot
↓ TEMP= decrease movement of molecules=
feels cold
Air Pressure
 Conduction – atmosphere that touches earth’s
surface Condensation – changes a gas to a liquid
 Convection – density causes differences in air
pressure which it turn cause air to move in
convection currents
Evaporation –
changes a liquid to a gas
Winds
What causes winds?
 A wind is a
 Winds are
horizontal
measured by
movement of air
from high pressure
direction and speed
to of low pressure
 The anemometer is
 It is this difference in
the tool we use to
pressure that makes
measure this
the air move=wind
 Wind chill=↑ cooling
the wind causes
Local Winds
 The land cools and heats faster than the ocean.
Water holds heat longer than land, and takes longer
to heat or cool.
During the day, the land
SEA BREEZE
gets hotter faster than the
water. The heated air
rises, leaving behind an
area of low pressure.
Wind from the cooler sea
blows in to take the place
of that warmer air. These
happen during the day!
Land Breezes
At night the lands cools off faster than
the sea. Cool air sinks creating an area
of high pressure. Wind blows from the
land to the sea.
Weather maps
ISOBAR= connects areas of
equal pressure BAR comes
from BARometric pressure
Reading a weather map
 ISOBAR= connects areas of equal
pressure BAR comes from BARometric
pressure
Wind speed is DIRECTLY
related to the pressure
gradient
Closer the isobars
Greater the pressure gradient
Greater the wind speed
WIND MOVES
CLOCKWISE OUT
OF THE HIGH
WIND MOVES
COUNTERCLO
CKWISE INTO
THE LOW
Reading a weather map...
 Isotherm: Connects areas of equal
temperature; therm means temperature
Fronts
Air Masses
 Air masses have the same characteristics of
the surface over which it develops
Land it’s CONTINENTAL (c)
Water it’s MARITIME (m)
Warm - 25° of the equator it’s Tropical (T)
Polar of 60° north and south. Polar (P)
poles 60° to 90°, Arctic (A)
 Pressure Systems
descending (going down)=H pressure
ascending (going up)=L pressure
Types of frontal systems




Warm front
Cold front
Occluded front
Stationary Front
Fronts: the boundary
between 2 air masses
 Warm Front: warm air slides over
departing cold air- large bands of
precipitation form
This is
the
symbol
on a
map for
a warm
front
Cold Fronts
This is the symbol
for a cold front
 Cold air pushes under a warm air mass.
Warm air rises quickly=narrow bands of
violent storms form
Occluded Front
This is the
weather map
symbol for an
occluded front
 2 air masses merge and force warm air
between them to rise quickly. Strong
winds and heavy precipitation will occur
Stationary Front
This is the
weather map
symbol for a
stationary front
 Warm or cold front stops moving. Light
wind and precipitation may occur across
the front boundary
Global Patterns
Global Circulation and
Wind Systems
 Solar energy is at its
greatest around the
equator---Why?
If earth did not
rotate, we would
have 1 big
circulation cell in
each hemisphere
High
pressure
at Poles
Low
Pressure
at equator
3 convection cells due to
rotation, and unequal heating
due to tilt
WINDS AND CONVECTION CELLS
CAUSED BY DIFFERENCES IN AIR
PRESSURE
WINDS NAMED FOR THE DIRECTION FROM WHICH
THEY COME
Jet Stream
 jet streams are located near the tropopause
 The major jet streams on Earth are westerly
winds (flowing west to east).
 width typically a few hundred miles and its
thickness less than three miles.
 wind speeds vary according to the temperature
gradient, exceeding 92 kilometres per hour 398 kilometres per hour have been measured
Humidity
Water in the Atmosphere:
Humidity
 Humidity: measure of the amount of water
vapor stuck between molecules in the air.
The air’s ability to hold water depends on the air
temp
The hotter the air, the more water the air can hold
 Relative humidity: the amount of water
vapor(%) compared to the amount the air can
hold- tool used is a psychrometer.
 100%=air is saturated
Dew Point Temperature
Air Temperature = Dew Point Temperature
CONDENSATION begins
 Dew Point Temperature is a measure of how
much water vapor in the air
the temperature at which air must be
cooled in order for it to become
saturated and condenses
Ocean Currents & El
Nino/La Nina
What are El Nino and La
Nina?
 El Nino - (El Nee-nyo) is the
warming of water in the
Pacific Ocean.
Rain and flooding along the
Pacific coast
Warm water disrupts food chain
of fish, birds, and sea
mammals
Tornadoes and thunderstorms in
southern US
Fewer than normal hurricanes in
the Atlantic
 La Nina - (Lah Nee-Nyah) is
the cooling of water in the
Pacific Ocean.
Snow and rain on the west coast
Unusually cold weather in Alaska
Unusually warm weather in the
rest of the USA
Drought in the southwest
Higher than normal number of
hurricanes in the Atlantic
Ocean Currents
 A gyre is any large system of rotating ocean
currents, particularly those involved with large
wind movements or circulation patterns and
by the Coriolis Effect (spinning of the earth).
 Continental borders cause these currents to
develop an almost closed circular pattern
called a gyre.
 Deep ocean currents are caused by
differences in water temperature and
salinity.
 The Gulf Stream is a strong, fast moving,
warm ocean current that originates in the
Gulf of Mexico and flows into the Atlantic
Ocean. It makes up a portion of the North
Atlantic Subtropical Gyre.
end
Potential Climate Change Impacts
Health Impacts
Weather-related Mortality
Infectious Diseases
Air Quality-Respiratory Illnesses
Agriculture Impacts
Climate Changes
Temperature
Precipitation
Sea Level Rise
Crop yields
Irrigation demands
Forest Impacts
Change in forest composition
Shift geographic rangeof forests
Forest Health and Productivity
Water Resource Impacts
Changes in water supply
Water quality
Increased competion for water
Impacts on Coastal Areas
Erosion of beaches
Inundate coastal lands
Costs to defend coastal communities
Species and Natural Areas
Shift in ecological zones
Loss of habitat and species
The
Greenhouse Effect
Some solar radiation
is reflected by the
Earth and the
atmosphere
Solar
radiation
passes
through
the clear
atmosphere
Some of the infrared radiation
passes through the atmosphere,
and some is absorbed and
re-emitted in all
directions by
greenhouse gas
molecules. The
effect of this
is to warm
the Earth’s
surface and
the lower
atmosphere.
Infrared radiation is emitted
from the Earth’s Surface
Most radiation is absorbed by the
Earth’s surface and warms it
CONVECTION DUE TO UNEQUAL HEATING
1. Evaporation
2. Rising and
Cooling to dew
point temperature
3. Condensation
begins on
condensation
surface (aerosols,
dust)
4. Cloud forms
5. Drops get big
enough
precipitation
begins
How does moisture get
into the atmosphere?
Evaporation - liquid water
changes state into water
vapor
Transpiration – plants give
off water vapor during
their life processes
Pressure – weight of air
DIFFERENCES IN AIR PRESSURE ARE CAUSED PRIMARILY BY
UNEQUAL HEATING OF EARTH’S SURFACE
 Increase density, increase pressure
 Increase temperature, decrease pressure and
density
 Increase altitude, decrease pressure
 Increase water vapor content, decrease pressure
 Measured by a barometer
 Isobars = lines of equal pressure
Intense heat = Powerful
CONVECTION
 Warm, moist air rises and leaves behind an area
of low pressure. This is why most rain forests are
found along equatorial regions.
 That air rises until it reaches the top of the
troposphere, where it can’t rise any further.
 It spreads out towards the polar regions HOT
follows COLD wanting to share its warmth.
 As it spreads it begins to cool and sink-usually
30°N and S of the equator- sinking air produces
an area of H pressure with dry conditions= desert
regions on earth
Pressure and Density
Decrease with
ALTITUDE
The “Dry Bulb”
 Don’t let it fool you. It
is just a thermometer.
 It measures the air
temperature.
 Duh!
20°C
The “Wet Bulb”
 Has a little wet
booty tied to the
bottom.
 Gets cool when
water evaporates.
Wet Booty
12°C
A Dry Day…
 A lot of moisture
will evaporate.
20°C
 The wet bulb will
be a lot cooler than
the dry bulb.
Difference between wet bulb
& dry bulb is 12 °C.
20°C
14°C
8°C
A Humid Day…
 A little bit of
moisture will
20°C
evaporate.
 The wet bulb will
not be much cooler
than the dry bulb.
Difference between wet bulb
& dry bulb is 6 °C.
14°C
ISOBARS ARE ISOLINES OF EQUAL PRESSURE