Transcript File
Meteorology Part 2:
Weather Variables
Earth Science
Golodolinski/Black
2009
Part II: Weather Variables
1. Temperature
2. Air Pressure
3. Relative Humidity
Weather Variables
1. Temperatures
– The measure of the
average kinetic
energy
– How fast the
molecules move
– Instrument used to
measure temperature:
Measured
in
°F
Fahrenheit
°C
Celsius
°K
Kelvin
Thermometer
– ESRT: Temperature
conversion chart on p.
13
1. Temperatures
Shown on a weather map with:
– Isotherms- Lines that connect places of equal
temperature
ESRT: Temperature conversion chart
on p. 13
& Chart Blank p. 183
ESRT: Temperature Conversion
Chart on p. 13
Chart Answers p. 183
ESRT: Temperature Conversion
Chart on p. 13
Temperature Chart Blank p. 183
ESRT: Temperature Conversion
Chart on p. 13
Temperature Chart Answers p. 183
Weather Variables
2. Air Pressure
The weight of Earth’s Atmosphere
Changes depending on the temperature
Instrument used to measure pressure:
– Barometer
Measured in inches and milibars
2. Air Pressure
Shown on a weather
map with:
– Isobars- Lines that
connect places of
equal barometric
pressures
2. Air Pressure
Mercury barometer
– As the air pressure pushes on
the surface of the mercury in
the dish, the mercury travels up
the tube.
– As pressure increases, the
mercury rises in the tube.
Cool air sinks- causes higher
pressure
– As the pressure decreases, the
mercury sinks out of the tube.
Warm air rises- causes lower
pressure
ESRT:
Pressure
Conversion
Chart p. 13
ESRT: Pressure Conversion Chart
p. 13
Blank Chart p. 184
ESRT: Pressure Conversion Chart
p. 13
Answer Chart p. 184
2. Air Pressure
State the relationship
between altitude and air
pressure.
– As the altitude increases,
the pressure decreases
Draw the relationship on
the graph.
Weather Variables
3. Relative Humidity
– A ratio between the amount of moisture is in the
atmosphere and how much moisture the
atmosphere can hold
– Measured in %
– When the air is holding as much water vapor as it can,
the air is saturated. When saturated, warm air contains
more water vapor than cold saturated air.
– When the air is saturated, the relative humidity is 100%
To summarize, when the water-vapor content of air remains
constant, lowering air temperature causes an increase in
relative humidity, and raising air temperature causes a
decrease in relative humidity.
3. Relative Humidity
Temperature & Relative
Humidity
– The warmer the temperature
is, the more moisture it can
hold
State the relationship between
temperature and relative
humidity:
– As the temperature increases,
relative humidity decreases
Draw the relationship on the
graph.
3. Relative HumidityInsturements
3. Relative Humidity
Dew Point Temperature
– The temperature in which the air is saturated
– 100% relative humidity
Determining Relative Humidity and
Dew Point Temperatures
Dry bulb
– Air temperature
Wet bulb
– Temperature an air parcel cooled by
evaporation of water (wet cloth)
When given the wet bulb and dry bulb
temperatures, you can determine the dew
point temperature and relative by follow
directions provided and using ESRT p. 12
ESRT: Dew Point Temp. p. 12
ESRT: Relative Humidity p. 12
Example 1 p. 186
Example 2 p. 186
p. 187 chart and #1-5
Practice Dew Point & Relative Humidity p. 187
Practice Dew Point & Relative Humidity p.
187 Answers
Practice Dew Point & Relative Humidity p.
187
#1-5
Condensation
– Gas to liquid
– Change of phase from
water vapor (gas) to
liquid vapor (water)
– Examples:
Water on cold glass of
water, water on mirror
after a shower, dew on
grass, fog, clouds
– Evaporation
Liquid to gas
3 Things Needed for Condensation
to Occur
1. Water vapor must be present
2. Air must be separated (relative humidity
100%)
3. Condensation nuclei (ex. dust particles)
Density of Air
Warm air rises because it is less dense
Cold air sinks because it is more dense
Formation of Clouds
Warm moist air rises
Air expands and cools due to the dew
point
Air becomes saturated
Water droplets form on dust particles
Clouds consist of water droplets and ice
crystals
Cloud Classification
Adiabatic Cooling
The cooling of a parcel of air as it rises
through the atmosphere
Dry adiabatic lapse rate
– rate of cooling or heating that applies only to
unsaturated air.
– dry air cools faster
Wet adiabatic lapse rate
– rate of adiabatic temperature change in
saturated air.
– moist air cools slower
Cloud Formation by
Adiabatic Cooling
Precipitation
Cloud particles (any form of water) too
heavy to remain suspended in the air fall
to Earth from a cloud
– Examples: rain, hail, sleet, snow, freezing
rain
– What does precipitation do for the environment?
Cleans the air
– ESRT p. 13 Present Weather
Forms of Precipitation
The type of precipitation that reaches Earth’s
surface depends on the temperature profile in the
lower few kilometers of the atmosphere.
Rain & Snow
In meteorology, the term rain means drops of water that
fall from a cloud and have a diameter of at least 0.5 mm.
At very low temperatures (when the moisture content of
air is low) light fluffy snow made up of individual sixsided ice crystals forms.
Sleet is the fall of clear-to-translucent ice.
Hail is produced in cumulonimbus clouds.
ESRT p. 13 Present Weather
Wind
The horizontal movement of air
Caused by the uneven heating of Earth’s
surface
Differences in air temperature cause
differences in air pressure
The greater the difference in air pressure,
the faster the wind
Wind
Named by the direction in which they
come from
– Ex. North wind comes from the North
Isobars
– Connect places of equal barometric
pressure on a weather map
Wind Instruments
Anemometer
– Measures wind speed
Wind vane
– Determines wind
direction
Sea Breeze
Water heats up slower
than land:
–
–
–
–
High specific heat
Cooler temperatures
Air sinks
*HIGH pressure*
Land heats up faster
than water:
–
–
–
–
Low specific heat
Warmer temperatures
Air rises
*LOW pressure*
Land Breeze
Water cools down
slower than land (stays
warmer)
– High specific heat
– Warmer temperatures
at night
– Air rises
Land cools down faster
than water
– Low specific heat
– Cooler temperatures at
night
– Air sinks
Sea and Land Breezes
Coriolis Effect
The deflection of winds and ocean currents
caused by the rotation of Earth
Deflection is to the right in the Northern
Hemisphere and to the left in the Southern
Hemisphere
Weather Factors Associated with
Different Pressure Areas
High Pressure
–
–
–
–
Cool/ cold air
Air sinks/ goes down
Air moves outward
Clockwise
– No clouds
– No precipitation
Low Pressure
–
–
–
–
Warm air
Air rises
Air moves inward
Counter clockwise
– Clouds
– Precipitation likely
ESRT: Planetary Winds p. 14
Planetary Winds
p. 191 Weather Changesadobe
Weather Changes p. 191
Weather Changes
Air Masses
Large region of the atmosphere with
uniform temperature and humidity
ESRT p. 13: Air Masses
Air Masses Table
Air Masses Map
Fronts
The boundary between 2 air masses
ESRT p. 13 Front Symbols
Cold Front
Cold air pushes the
warm, moist air upward
Cold air is located
behind the front
The greater the
differences in
temperatures, the more
likely there will be a
major storm
Usually pass quickly
Brings colder but clear
weather conditions
Warm Front
Warm air gently rolls
over the colder air
Warm air is located
behind the front
Conditions are
usually cloudy and
rainy for several
hours
Usually pass slowly
Brings warmer but
rainy weather
conditions
Occluded Front
Occurs when a cold
air mass overtakes a
warm mass and
overtakes another
cold air mass
Precipitation is
possible but not
definite
Very slight
temperature change
Stationary Front
Notice no arrows to
show direction in the
weather map symbols
Stationary means the
front is not moving
Final direction of the
movement is difficult to
predict
Winds are blowing in
opposite directions on
each side of the front
Clouds can last for days
Fronts are usually associated
with…
Clouds
Precipitation
Change in temperature
Change in wind direction
p.195 Station ModelsAdobe
Station Models
On a station model,
barometric pressure is
ALWAYS written in a
three-digit format
Converting from
millibars:
– Drop the 9 or 10 in the
front of the number and
loose the decimal point
Millibars
Station
Model
1009.3 mb
093
984.2 mb
1024.2 mb
Station Models
Converting from the station
model format to milibars
First:
– If the first number on the
station model is 0-4, place a
10 in front of the number
– If the first number on the
station model is 5-9, place a
9 in front of the number
Second:
– Place a decimal point
between the last 2 numbers
p. 195
Station
Model
Millibars
146
1014.6 mb
457
986
ESRT: Weather Map Symbols
Weather Stations
Draw a weather station using the
following information:
Need to know:
Dew Point & Air Temperature
The closer the air temperature is to the dew
point temperature, the greater the chance
for precipitation.
Determining Weather Station Values
6 stations on p. 197; Weather Map practice p. 199-203 #1-31; More
questions p. 204-207 #1-22