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. RT = Pg. 13

Heating of the Atmosphere The 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 RT = Pg. 14 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 = millibars or inches of mercury

Atmospheric Pressure and Density RT = Pg 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. Temperature Pressure Water molecules have a smaller mass than oxygen and nitrogen As you increase in altitude, the air pressure decreases. Water vaporAltitude 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. RT = Pg. 13 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 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 steadily falling 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.