Download Meteorology Notes PPT

Meteorology
Atmosphere
• The layer of gases that surround the Earth.
It is a mixture of gases (such as oxygen,
nitrogen, water vapor, and carbon dioxide),
and microscopic particles (such as pollen,
dirt, and dust). The atmosphere is able to
protect us from the Sun’s harmful rays and
helps to regulate temperature
Weather
• Describes the conditions of the
atmosphere at any given location for a
short period of time. Includes factors
such as temperature, air pressure,
moisture, precipitation, wind, and cloud
cover.
Some important information:
• Weather is “driven” by the sun
• The uneven heating of the Earth’s surface
causes changes in the weather by
insolation
• Weather is described by various
atmospheric variables. . .
Atmospheric Variables
• Temperature –
– A measure of the average
kinetic energy of a
substance – NOT a
measure of how hot or
cold a substance is.
– Measured with a
thermometer.
Atmospheric Variables
Air pressure –
The weight of the overlying
atmosphere pushing
down on a given unit of
area, affected by changes
in temperature, water
vapor, and altitude.
Measured with a
barometer.
Atmospheric Variables
Humidity –
The amount of water vapor in the air.
Atmospheric Variables
Winds –
Air that moves
horizontally. They are
caused by differences
in air pressure.
Measured with an
anemometer.
The Earth’s Atmosphere
• The atmosphere is broken into several
layers based on physical
characteristics.
• Important Facts:
Almost all water vapor and weather
occurs in the Troposphere.
As altitude / elevation increases, air
pressure decreases.
There are 3 methods of energy
transfer that occur in the atmosphere:
•
•
•
Conduction – The transfer of heat through
direct molecular contact.
Convection – The circulation of a heated fluid
(liquid or gas), caused by density currents.
Radiation – The emission and transfer of
heat via electromagnetic waves. This is the
only way that energy can travel through the
emptiness of outer space.
Air has weight?
• Air pressure –
– the weight of the overlying atmosphere
pushing down on a given unit of area, affected
by changes in temperature, water vapor, and
altitude.
• High Pressure generally brings cooler,
calm weather.
•
Winds blow away from areas of high
pressure and clockwise.
•
High Pressure = Happy Weather
• Low Pressure generally brings warmer,
wet weather.
•
Winds blow toward areas of Low
pressure and counter-clockwise
•
Low Pressure = Lousy Weather
Some important facts:
• Air pressure is measured by using a
weather instrument called a barometer
– Standard air pressure is 17.7 pounds per
square inch = 29.92 inches of mercury =
1013.2 millibars = 1atm
– Winds are caused by differences in air
pressure
Factors which influence air pressure:
• Temperature –
– As the temperature of air increases, the air
expands and its density and pressure
decrease
Factors which influence air pressure:
• Altitude –
– As altitude increases, the air pressure
decreases.
Factors which influence air pressure:
• Humidity – Water vapor is less dense then air. Thus, the
more water vapor in the air, the lower the air
pressure and density
What happens to water in the
atmosphere?
• Some important facts:
Phase change – The change in the
physical state (solid, liquid, or gas) through
the addition or removal of heat.
H2O exists in all 3 phases in the
atmosphere. . .
Phase changes:
• Melting –
– when energy is added and a solid turns into a
liquid
Phase changes:
• Evaporation –
– when energy is added and a liquid turns into a
gas
Phase changes:
• Freezing –
– when energy is removed and a liquid turns
into solid
Phase changes:
• Condensation –
– when energy is removed and a gas turns into
a liquid
Phase changes:
• Sublimation –
– the process of a solid turning into a gas or a
gas turning into a solid. Energy can be added
or removed in this case.
• Much more thermal energy (heat) is
involved during evaporation,
condensation, & sublimation than freezing
and melting. . .
Some other stuff about H2O:
• Specific heat –
– The number of calories it takes to heat one
gram of a substance by 1°C.
• Calorie –
– The amount of energy it takes to heat one
gram of water by 1°C.
• H2O requires more heat to change its
temperature than most materials.
Some important facts:
• Humidity – The amount of water vapor that
is in the air.
• Warmer air can hold more H2O vapor than
cooler air. . .
• Capacity – the maximum amount of water
that the air can hold
• Saturated – When the air is filled to capacity
and holds as much water vapor as it can at a
given temperature.
• Air is not usually saturated. . .
Warmer air can hold more water vapor
To saturate a sample of air. . . either:
•
•
Add H2O vapor to the air. . .
Cool the air (“shrink it”) so condensation
occurs. . .
Dewpoint Temperature- The temperature at which the air is
saturated with water vapor. At
temperatures below the dew point,
condensation or sublimation of water
vapor occurs.
• Dewpoint temperature is measured with a
sling psychrometer. . .
Dewpoint Temperature
• Wet bulb temperatures are never higher
than dry-bulb temperatures
• H2O vapor is always present in air . . .
even in desert regions
• As air temperature approaches the
dewpoint precipitation becomes more
likely. . .
There are different ways of
examining humidity:
• Absolute humidity – The amount (mass)
of water vapor in a unit volume of air;
usually measured in grams/cubic meter.
There are different ways of
examining humidity:
• Relative humidity – The ratio of the
amount of water vapor in the air to
maximum amount it can hold; often
expressed as a percent.
How can you make a cloud?
• Cloud - a visible mass of suspended
liquid water droplets and/or ice crystals in
the atmosphere
Recipe for a cloud:
• Ingredients: Warm, moist air, condensation nuclei
• Directions:
1. Cause warm moist air to rise vertically in the
atmosphere. Heating, convection currents,
orographic lifting, or a frontal boundary can achieve
this.
2. As the warm, moist air rises, it expands and cools
3. As the moist air rises & cools to the dew point, it
becomes saturated & condensation occurs
4. Cloud formation can only occur if the H2O vapor has
something to “stick to”. Dust particles in the
atmosphere act as condensation nuclei for the H2O
vapor.
5. If these conditions are met, we have a cloud!
Types of clouds and the weather
they are associated with:
• Cumulus – clouds are the large clouds
that sometimes look like huge puffs of
cotton.
Types of clouds and the weather
they are associated with:
• Stratus – clouds are made up of low layers
of clouds that usually cover the whole sky
and blot out the sun.
Types of clouds and the weather
they are associated with:
• Cirrus – Clouds are very high, wispy
clouds made of ice. Even in the summer,
cirrus clouds are made of ice because it is
cold high above Earth.
Types of clouds and the weather
they are associated with:
• Nimbostratus – Stratus clouds which have
precipitation
Types of clouds and the weather
they are associated with:
• Cumulonimbus – Cumulus clouds that have hail
and thunder falling from them
What falls from the sky?
• Precipitation - Any form of water that
falls from the sky.
Types of precipitation
• Rain – Droplets of liquid water.
• Drizzle – Very light rain.
• Sleet – Small pellets of ice that form when
raindrops freeze as they fall to the ground.
The rain must fall through a layer of
freezing air.
Types of precipitation
• Snow – Crystalline pieces of ice
• Freezing Rain – Occurs when liquid rain
reaches the ground and freezes when it
comes in contact with objects.
Types of precipitation
• Hail –Small balls of ice that grow by
getting blown up and down in a cloud,
getting coated with water near the warmer
bottom, and freezing in the colder upper
cloud.
• Precipitation is measured with a rain
gauge
• Precipitation cleans the atmosphere by
bringing down condensation nuclei,
pollutants, and other material suspended
in the atmosphere.
• Dew – Water vapor condenses on colder
surfaces, forming a layer of liquid water.
• Frost – Solid deposition of water from
saturated air
• Fog – A cloud in contact with the ground.
Air Mass
– A large volume of air with somewhat
consistent temperature, pressure, and
water vapor content.
Air masses take on the characteristics of the
source region.
Source Region
– The region over which an air mass forms
and takes on its characteristic temperature
and moisture.
Characteristics of air masses
depend on where they form:
• Maritime air masses form over large
bodies of H2O
• Continental air masses form over land
• Polar and arctic air masses form at high
latitudes
• Tropical air masses form at low latitudes
Types of Air Masses
Air Mass
Source Location
Movement
Weather
cP
Polar regions in
Canada
South-southeast
Cold and dry
mP
Polar Atlantic, Polar
Pacific
cT
U.S. southwest
North-northeast
Warm and dry
mT
Tropical pacific,
tropical Atlantic
Northeast; northnorthwest
Warm and
humid
Southeast;
Cold and humid
southwest-south
• Some important information:
Air masses and weather generally move west to
east with a northeast “hook”
Jet stream – Fast-flowing, relatively narrow air
currents found in the atmosphere at around 11
kilometers above the surface of the Earth, just
under the tropopause.
Jet streams tend to change – these changes
influence the path air masses take.
Wind
- the horizontal movement of air in the
atmosphere
Some important facts:
• Winds are named according to the
direction from which the wind blows
• Wind is described by both speed and
direction
• A wind vane measures wind direction,
while an anemometer measures speed
Some important facts:
• Southerly winds are warmer (come from
lower latitudes)
• Northerly winds are cooler (come from
higher latitudes)
• Easterly winds are moist (come from over
the Atlantic)
• Westerly winds are dry (comes from over
the land)
Some important facts:
• Combinations of these winds bring certain
types of air. . .
• Wind is caused by differences in air
pressure
Front
- A boundary between different air masses
Cold Front
- The leading edge of a cold air mass. Cold,
dense air forces warmer, less-dense air to
rise rapidly, causing intense precipitation.
Warm Front
– The leading edge of a warm air mass. Warm
fronts possess a gentle slope to their frontal
surface. Precipitation along a warm front is
usually light but long in duration.
Occluded Front
- Cold fronts usually move faster than warm
fronts. When a cold front catches up to a warm
front, the entire warm air mass is forced to rise.
The weather is similar to a warm front
Stationary Front
- Forms when a cold front and warm front
collide but neither is strong enough to
overtake the other. The boundary is
stationary because it does not move
much. There may be light precipitation.
Some important facts:
• Warmer air can hold more water vapor than
cooler air
• Water vapor weighs less than dry air – the
higher the humidity, the less the air weighs –
resulting in lower air pressure
• So, if air cools, it contracts – holding less water
vapor – cooler air is heavier than moist air
• Convection cells “drive” the movement of air in
high and low pressure systems
• Convection cells are generated by the unequal
heating of the Earth
Cyclone
• Low-pressure systems (in the Northern
Hemisphere) that usually bring stormy
weather. Air circulates counterclockwise
and inward to the center of the cyclone.
Anticyclone
• High-pressure systems (in the Northern
Hemisphere) that often occur within an air
mass. They generally bring fair weather.
Air circulates outward in a clockwise
direction around an anticyclone.
• Winds do not blow directly in or out of
highs and lows
• Cyclones (lows) rotate counter-clockwise
in the northern hemisphere
• Cyclones (lows) bring “bad” weather
• Anticyclones (highs) rotate clockwise in
the northern hemisphere
• Anticyclones (highs) bring “good” weather
Station Model (ESRT p. 13)
1. A representation of the weather at a
location using symbols
2. Use English Units (°F, inches, miles)