Properties of the Atmosphere Section 11.2

Temperature Measured using one of two common scales (Fahrenheit or Celsius); based on the freezing and boiling points of water The SI unit for temperature is Kelvin; the zero point is absolute zero (the lowest temperature any substance can have) We discussed the changes in temperature throughout the atmosphere

Air Pressure The pressure exerted on a surface by the weight of the atmosphere above Earth Pressure = force / area Units are N/m2 Often measured in millibars (mb) Air pressure decreases with altitude as the mass of air above you decreases

Air Pressure The density of air decreases with altitude Pressure, temperature, and density are all related in the atmosphere At the same density warmer air is at a higher pressure than cooler air At the same temp., air with higher density exerts more pressure than low density air At the same pressure, warm air is less dense than cool air

Temperature Inversion Temperature inversion – is an increase in temperature with height in an atmospheric layer In the troposphere occurs with a rapid cooling of land on a cold, clear, calm winter night Fog or low level clouds; increase pollutants in the air; Smog

Wind In the lower atmosphere, air moves from high density regions to low density regions Density differences are caused by unequal heating at Earth’s surface Air moves from a region of high pressure to an area of low pressure Wind speed is measured in (mph), (km/h), or knots. 1 knot = 1.85 km/h

Humidity The amount of water vapor in the atmosphere at a given location on Earth’s surface Relative humidity is the amount of water vapor in the air compared to the total amount it can hold; expressed as % Saturation occurs when the water vapor in a volume of air has reached its maximum amount

Humidity Dew point is the temperature at which air must be cooled at constant pressure to become saturated Latent heat is the extra thermal energy contained in water vapor compared to liquid water Adiabatic heating – air is compressed Adiabatic cooling – air expands

Humidity Dry adiabatic lapse rate – 10 oC / 1000 m Moist Adiabatic lapse rate – 4 oC / 1000 m Complete Problem Solving Lab on page 283 for a daily grade. Answer #’ 1-5.