Transcript Chapter 11.2: Properties of the Atmosphere

 Students
will be able to identify three
properties of the atmosphere and how
they interact.
 Students will be able to explain why
atmospheric properties change with
changes in altitude.
 Density: The
mass per unit volume of a
material.
 Exert: To put forth.
 P. 289
 Main
Idea
 Atmospheric
properties, such as
temperature, air pressure and
humidity describe atmospheric
conditions.
•
P. 289
•
•
Temperature: A measure of
movement. The faster the particles
of a substance move, the higher is
their temperature.
3 Scales of Measurement:
1. Fahrenheit (˚F) (Most common in US)
2. Celsius (˚C)
•
These are based on the boiling and
freezing points of water.
3. Kelvin (˚K)
•
Based on Absolute Zero – where all
movement of particles stops.
Air temperature changes with changes in altitude.
 P. 290
 Air
pressure: The weight of air
exerted on a surface.
• Units: N / m² or millibars (mb.)
 100 N / m² = 1 mb.
 At sea-level atmosphere exerts pressure of
1000 mb.
 As you go higher in the atmosphere the air
pressure decreases.
Air pressure decreases with altitude (height.)
 P. 290
 Density
of Air: As you get higher in
the atmosphere, density decreases
because air molecules are more
spread out.
As with air pressure, as you get higher into the atmosphere, the density
of air also decreases.
 P. 291
 Pressure
– Temperature – Density
Relationship:
• Air pressure and Temperature:
 For air with the same density, warm air is at a
higher pressure than cool air.
• Air pressure and Density:
 For air with the same temperature high
density air is at higher pressure than low
density air.
• Temperature and Density:
 At the same pressure, warmer air is less
dense than is cooler air.
 P. 291
 Temperature
Inversion: When
warm air is on top of cooler air
(occurs in troposphere.)
• Causes: Cold clear nights, Earth does
 P. 292
not radiate heat to lower levels of
atmosphere.
• Effects: Fog, low lying clouds and
smog – smoke and fog (Haze).
• We normally expect air to become
colder as we increase in altitude in the
troposphere.
Cold air is normally above warm air.
 9.293
 Wind: Warm
air is less dense than
cool air.
• Air moves from more dense areas to
less dense areas (WIND.)
• Differences in air densities caused by
differences in heating Earth’s of
surface.
Warm air is less dense than cool air because air
molecules are more spread out.
 9.293
 Wind
and Pressure Differences:
• In atmosphere air pressure increases as
density increases.
• Result:
 Air moves from regions of high pressure
(COLD - DENSE) to regions of low pressure
(WARM – LESS DENSE.)
 9.293
 Wind
Speed and Altitude:
• Earth’s surface creates friction with
wind (slows it down.)
• Higher in the atmosphere wind blows
faster.
In the Troposphere wind speed
increases with altitude.
 9.294
 Humidity: The
amount of water
vapor in a given location of the
atmosphere.
• Expressed as relative humidity and dew
point.
• Saturation: when the amount of water
vapor in the air has reached its
maximum point.
 (The air can’t hold anymore.)
Non saturated
Saturated
 9.294
 Relative
Humidity: Amount of water
vapor in air relative to amount of
vapor needed for air to reach
saturation (expressed as a percent.)
• Example: Forecast says relative
humidity = 50%
 Means the air is holding half of the vapor it is
capable of holding.
Relative humidity is expressed as a percent.
 9.294
 Dew
Point: Temperature at which air
reaches saturation – when it will
rain.
• Cooler air has lower dew point.
• Why we have high humidity in the
summer.