Atmospheric Temperature, Pressure and Density

What is Weather?Weather is the

condition of the variables

of the atmosphere for

any given location for a

specific period of time.

Weather Variables include: temperature, air pressure, wind, moisture conditions, cloud cover,

precipitation and storms.

Atmospheric Temperature Atmospheric Temperature is measured in degrees Celsius, Fahrenheit or

Kelvin scales. Air temperature is measured

with a thermometer.

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Heating of the AtmosphereThe sun is the source of almost all heat in the atmosphere. If the intensity and duration of insolation is high, then the heat

energy within the atmosphere and at earth’s surface will increase. Ways by which the atmosphere can be heated include

the following:

Conduction

Heat energy from the sand moves into the atmosphere at the interface between atmosphere and

lithosphere

Conduction of heat from sand to air above sand.

Direct Absorption of Insolation

Heating of the Atmosphere

Absorption of Long-wave Terrestrial Radiation

Insolation absorbed by aerosols (ie: dust, volcanic ash, etc…) in the atmosphere lead to atmospheric heating.

Radiation from the Earth’s surface (ie: infrared radiation) is absorbed in the atmosphere with water vapor, CO2 and other gases. This will lead to atmospheric heating.

Heating of the Atmosphere

Condensation Coriolis Effect

The condensation of water (phase change

from gas to liquid) releases stored heat into

the atmosphere.

The rotation of the Earth creates friction with the atmosphere – producing a small amount of heat

in the atmosphere.

Transfer of Heat in the Atmosphere

Heat Energy within the atmosphere is

transferred by convection.

Air that is heated becomes less dense, will rise and lead to

a drop in air pressure.

Once in the upper atmosphere, air will cool, descend back to Earth and lead to

an increase in air pressure

Changes in Air Density and Air Pressure lead to the creation of

convection cells – circular patterns of heat transfer within the

atmosphere.

Transfer of Heat in the Atmosphere

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What happens to air

temperature and air

pressure as a parcel of air rises in the

troposphere?

As a parcel of air rises in the

troposphere, its temperature and pressure

decrease.

Atmospheric Pressure and Density

Atmospheric Pressure – or Barometric Pressure and Air pressure – is the pressure

exerted on a parcel of air due to weight of the overlying atmosphere pushing down

upon it.

Atmospheric Pressure is measured in millibars and/or inches of

mercury using an instrument known as a barometer.

Standard atmospheric Pressure at sea level is known as 1 atmosphere.

1 Atmosphere = 1013.2 millibars or 29.92 inches of mercury

Atmospheric Pressure and

Density

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999.0 millibars

Luis noticed a drop in air pressure for a parcel of

air moving over binghamton, ny. The barometer he is using

measured the air pressure of the parcel of

air as 29.5 inches of mercury.

What is this measurement in

millibars?

Comparison of Atmospheric Pressure with other variables

As air temperature increases, air

pressure decreases.

As the amount of water vapor

in the atmosphere

increases, the air pressure decreases.

Tem

pera

ture

Pressure Pressure

Water molecules have a smaller mass

than oxygen and nitrogen

As you increase in altitude, the

air pressure decreases.

Wat

er v

apor

Altit

ude

Pressure

Weather Station Model

A weather station model is a series of symbols referencing weather data collected for a particular

location at a specific time of day.

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TEMPERATURE

The air temperature is recorded in (˚F)

The location has an air temperature of 28˚F.

Weather Station Model

Barometric (Air) Pressure

The Barometric Pressure is recorded in millibars.

**If the number is above 500, place a “9” in front of the first number and place a decimal

before the last number.**

**If the number below 500, place a “10” in front of the first

number and place a decimal before he last number.**

The location has a barometric pressure of

1019.6 millibars.

Weather Station Model

Barometric Trend

The barometric trend is recorded in millibars. Place a

decimal between the two numbers to determine the

barometric trend

+ = pressure higher than 3 hrs. ago.

- = pressure lower than 3 hrs. ago.

/ = pressure that is steadily rising

\ = pressure that is steadilyfalling

The barometric trend for the location is as follows: There has been a steady rise in barometric pressure over the last three hours by 1.9 millibars.