THE AIR AROUND YOU
CHAPTER 2; SECTION 1 WEATHER
Weather – the state of the atmosphere at a specific time and place
4 WEATHER FACTORS
1. temperature
2. moisture
3. wind
4. air pressure
The SUN has a strong influence on the weather.
Temperature- a measure of molecule movement
- when molecules move faster the temperature is warmer
- when molecules move slower the temperature is cooler
WIND
Wind – when air moves from high pressure areas (cold) to low pressure
areas (warm)
Wind vane- an instrument used to show the direction the wind comes from
Wind sock- blows in the direction of the wind
Anemometer- an instrument used to measure the wind speed
HUMIDITY
Humidity- the amount of water vapor in the air
**warm air can hold more water vapor than cold air
Relative humidity- the amount of water vapor in the air compared to the
amount of water vapor the air can hold
Dew point- the temperature at which air is saturated and condensation form
CLOUDS
Formation of clouds- Warm, moist air rises and cools and the air can no
longer hold as much water vapor, so some of the water vapor turns into tiny
droplets of liquid (which are clouds).
Condensation nuclei- small particles that water droplets form on
Luke Howard developed the first system of classifying clouds by shape and
height.
WAYS TO CLASSIFY CLOUDS
1. SHAPE
a. stratus clouds- sheets or layers of clouds located close to the earth
b. cumulus clouds- big, white, fluffy clouds (look like cotton) with a flat
base
c. cirrus- thin, feathery clouds made of ice crystals found high in the
atmosphere
2. HEIGHT
a. cirro – refers to clouds found high up in the atmosphere
b. alto- refers to clouds found in the middle of the atmosphere
c. strato- refers to clouds found low in the atmosphere
3. PRODUCES RAIN OR SNOW
a. nimbus- a dark cloud that does not let light through and produces rain
or snow
example: cumulonimbus cloud is a big, dark rain cloud
PRECIPITATION
Precipitation- water that falls from a cloud
- the type of precipitation depends on the air
temperature
Rain- occurs anytime water falls from clouds and the temperature
is above freezing
Snow- when the temperature near the cloud and near the ground is
below freezing
Sleet- the temperature near the cloud is warm, but the temperature
near the ground is cold. Sleet occurs when water droplets fall from
a cloud and freeze when they get closer to the ground.
Hail- The top of the cloud is cold while the bottom of the cloud is
warmer. Ice crystals fall from higher in the atmosphere, then begin
to melt as they fall. Wind (an updraft) pushes the melted ice
crystal back up causing it to freeze again. As the ice crystal is
tossed up and down it grows larger.
THE AIR AROUND YOU
Chapter 2; Section 2
AIR MASSES
Air mass- a large body of air that has properties like the earth’s surface that
is formed above
-When looking at air masses we look for temperature and moisture
-There are 6 major air masses in the United States.
1. Low pressure system
L
-winds move counterclockwise
-brings stormy weather
-move northeast across U.S.
2. High pressure system
H
-winds move clockwise
-brings fair weather
-move southeast across U.S.
FRONTS
Front - A boundary between two different air masses
-clouds and precipitation usually form at a front
Cold Front- occurs when colder air advances pushing up warmer air up
Warm front- occurs when warm air advances and goes over cold air
Occluded front- involves 3 different air masses; when two colder masses of
air force the warm air up
Stationary front- occurs when warm air and cold air masses collide but
neither air mass moves
THE AIR AROUND YOU
CHAPTER 2; Section 3
FORCASTING WEATHER
Meteorologist- a person who studies and predicts the weather
To predict weather, the atmosphere and earth’s surface are looked at.
Station model- a point on a map that shows the weather conditions for a
specific area
STATION MODEL
Cloud cover
Temperature
barometric pressure
(air pressure)
Dew point
change in air pressure
Wind direction (SE)
Isotherm- a line drawn on a map that connects areas with the same
temperature
Isobar- a line drawn to connect points of equal atmospheric pressure; when
isobars are close together the air pressure changes rapidly, which makes
stronger winds
2 instruments used to measure humidity (water vapor)
1. hygrometer
2. psychromoter