Transcript Weather

Weather
Weather is the state or condition of the
atmosphere at a particular location for a
short period of time. Different weather is
created by changes in the amount of heat
energy in the atmosphere due to incoming
solar radiation.
Weather can be measured and observed with
many variables, such as:
Atmospheric Energy
•
The Sun is the main source of energy on
Earth for the weather. The energy from
the sun travels to earth in electromagnetic
waves, some of which we can see and
some of which we cannot see.
• Incoming solar radiation has a specific
wave length (ESRT p.14)
• Wave energy can do 2 things once it hits a
surface:
1. Be absorbed
2. Be reflected
Weather
• Most of the energy from the sun is reflected
off of the earth.
• This energy does not go back into space, it
is trapped by the atmosphere.
• This process keeps our planet warm and
how energy is stored for the creation of
weather.
Energy Transfer in the Atmosphere
Review: What are the 2 methods of energy transfer?
1. Radiation
2. Convection
Radiation – is the transfer of electromagnetic energy
through space in the form of electromagnetic
waves. (no medium needed)
• Energy radiated from the sun reaches the earth
• Energy from the Sun in the form of
electromagnetic waves is reflected from the
earth and radiated back into the atmosphere.
Energy Transfer in the Atmosphere
Convection – is the transfer of heat energy by
movements of liquids and gases, caused by
differences in density.
• Convection causes warm air to rise and cold
air to sink and will be a major principle in
the formation of many weather events
(wind, rain, thunderstorms)
Energy Principles
Conservation of Energy – energy cannot be
created or destroyed.
Kinetic Energy – the energy of motion. (Ex.
A ball rolling down a hill)
Potential Energy – stored energy, that has the
ability to do work in the future.(Ex. A ball
resting at the top of a hill)
Heat as Energy
Specific Heat – the quantity of heat required to raise
the temperature of 1 gram of a substance by one
degree Celsius. Every substance has its own specific
heat. (ESRT p. 1)
Calorie – the quantity of heat required to raise the
temperature of one gram of water one degree
Celsius.
• If heat is lost at one source another substance will
grain that heat, due the principle of conservation of
energy.
Heat Energy and Phase Changes
If we heat a cup of water what do we expect to
happen?
• During a phase change, when heat is added
the temperature will stay the same, because
all the heat energy is being used for the
phase change.
• When heat is used to change the phase of a
substance and the temperature doesn’t
increase, we call this latent heat.
What type of energy is this?
Heat Energy and Phase Changes
What phase changes require the addition of
heat? (Latent heat gained)
What phase changes require the removal of
heat? (Latent heat lost)
Atmospheric Variables (ESRT p.13)
Station Model Practice
Temp: 27°F
Temp: 87°F
Weather: snow
Weather: haze
Visibility: ¼ mile
Visibility: 4 miles
Dewpoint: 25°F
Dewpoint: 67°F
Wind speed: 25 knots
Wind speed: 5 knots
Wind direction: northeast
Wind direction: southeast
Cloud cover: 100%
Cloud cover: 25%
Barometric pressure: 925 mb
Barometric pressure: 1018.5 mb
Pressure trend: -18
Pressure trend: +10
Precipitation: .68 inches
Precipitation: .08 inches
Identify the temperature, barometric pressure,
cloud cover, pressure trend, precipitation
(amount and type), wind (speed and direction),
dewpoint, and visibility.
30
1/8 *
27
96
-34
1.2
A note on barometric pressure…
• Pressure in millibars is usually between 950.0
and 1050.0.
• On a station model to save space the “9” or “10”
is dropped and decimal point is omitted.
• To correctly read the station model we need to
add back in the “9” or “10” and decimal.
• If the number is above 500, place a “9” before it.
• If number is below 500, place a “10” before it.
• Then always add back in the decimal before the
last number.
Temperature – What are some factors that
affect air temperature?
• Altitude
• Insolation (intensity, duration, latitude)
• Proximity to Water (specific heat)
Dew point (ESRT 12)
3 steps to find dew point using a psychrometer.
1. Using a psychrometer find wet bulb and dry
bulb temperatures.
2. Calculate difference between wet and dry
bulb temperatures. (wet bulb depression)
3. Using dry bulb temp. and difference, find
dewpoint on ESRT p. 12 (top chart)
Steve LaPoint explains...
Relative Humidity (ESRT p.12)
3 steps to find relative humidity using a
psychrometer
1. Using a psychrometer find wet bulb and dry
bulb temperatures.
2. Calculate difference between wet and dry
bulb temperatures. (wet bulb depression)
3. Using dry bulb temp. and difference, find
relative humidity on ESRT p. 12 (bottom
chart)
Atmospheric Pressure – the force or the
weight of the air pushing down on a surface.
“A column of air above the surface.”
Isobars – lines connecting points of equal
atmospheric pressure.
How does altitude affect atmospheric
pressure?
“As altitude increases, atmospheric pressure
decreases.”
Winds
• Winds occur because of a pressure
difference between air masses.
• Pressure differences occur because of
differences in temperatures.
Warm air = low density = low pressure
Cold air = high density = high pressure
Winds
• Sea breeze (onshore breeze) – occurs
during the day.
• Land breeze (offshore breeze) – occurs
during the night.
Winds
Jet Stream – winds at high altitudes and
speeds which are part of the planetary
convection cells. The jet stream moves in
eastward in a wavelike pattern about 7 to 8
miles above the surface. Many storms are
moved by the jet stream.
Speed in winter = 75 mph
Speed in summer = 35 mph
Polar and Sub-Tropical Jet Stream
How the Jet Steam forms…
Rising and sinking air due to pressure
differences creates these upper air wind
belts (Jet Stream). ESRT p.14
Clouds and Rain (Condensation)
How does condensation form clouds? What
else helps?
• Water vapor in the air cools when it rises,
condenses into liquid water droplets that
make up clouds.
• Dust particles in the air help to form
droplets, they act as a nucleus around which
water can condense.
Clouds and Rain (Condensation)
Orographic lifting – mountains act as
barriers to the flow of air, forcing the air to
rise. As the air rises it cools and condenses,
forming clouds and precipitation.
Clouds and Rain (Condensation)
Precipitation types
• Rain
• Drizzle
• Sleet
• Snow
• Freezing rain
• Hail
Air Masses
Air-mass – huge body of air in the
troposphere having similar pressure,
moisture, wind, and temperature. (ESRT
p.13)
• Maritime – air-mass that develops over
water (moist)
• Continental – air-mass that develops over
land (dry)
Air Masses Continued…
• Polar – air-masses that develop in higher
latitudes (cool)
• Tropical – air-masses that develop in lower
latitudes (warm)
Air Mass Symbols (ESRT p.13)
Cyclones and Anticyclones
Cyclone (Low pressure area) – storms
L
Winds move counterclockwise and inward.
Cyclones and Anticyclones
Anticyclone (High pressure area) – nice weather
H
Winds move clockwise and outward.
Fronts – the boundary between 2 air masses.
Warm front – warm air meets and rises over cold air on the
ground.
Cold front – cold air meets and pushes out warm air.
Occluded front – faster moving cold front overtakes slower
moving warm front.
Stationary front – warm air mass and cold air mass are side
by side, neither air mass is moving.
Warm Front
Warm air meets and rises over cold air on the ground.
Extended periods of precipitation occurs ahead of the
front and will last until the front passes.
Cold Front
Cold air meets and pushes out warm air. Short but heavy
period of precipitation. Wind shift and rapid change in
weather conditions once the front has passed. Violent
thunderstorms can occur at the front.
Occluded front
Faster moving cold front overtakes slower moving
warm front (cooler air). Overcast and light
precipitation may occur.
Stationary Front
Warm air mass and cold air mass are side by side,
neither air mass is moving.
Weather Maps
Placing fronts on a map can show movement of
weather.
Winter Storms in NYS