STATE OF THE ATMOSPHERE Advanced Earth Science

Temperature vs. Heat  NOT THE SAME THING!!  Temperature measures how fast or slow molecules move around  More molecules or fast molecules = high temp  Less molecules or slow molecules = low temp  Heat is a transfer of energy that occurs because of a difference in temperatures between substances  What kinds of energy transfers have we talked about??

Measuring Temperature  Let’s review...  Temperature can be measured in three ways  Fahrenheit  Celsius  Kelvin  Measured with a thermometer

Dew Point  The temperature to which air must be cooled at a constant pressure to reach saturation  Saturation: the point at which the air holds as much water vapor as it possibly can

Why is dew point important?  Until the air is saturated, condensation cannot occur  Condensation: occurs when matter changes state from a gas to a liquid  Water vapor changes into liquid water  This eventually falls as… RAIN

Vertical Temperature Changes  How does atmospheric temperature in the troposphere change with relation to altitude?  Temperature decreases as altitude increases  Individual air masses change as well  How fast or slow they change temperature depends on whether or not the air mass is saturated

Adiabatic Lapse Rates  Dry adiabatic lapse rate: rate at which unsaturated air (no heat is being added or removed) will cool  About 10°C per 1000m  If the air continues to rise it will eventually cool to its condensation temperature  Lifted Condensation Level (LCL): the height at which condensation occurs

Adiabatic Lapse Rates (cont’d)  Clouds form when water vapor condenses to water droplets, so LCL’s usually correspond to the base of a cloud  Above the LCL air becomes saturated and cools more slowly  Moist Adiabatic Lapse Rate: rate at which saturated air cools  4-9°C per 1000m

Air Pressure-Temperature-Density Relationships  Does air have mass?  Does air exert pressure?  Why don’t we feel it?  Does pressure increase or decrease with height?  How does density relate to air?  Where would the more dense air be? High or low?  Does temperature affect density? How?

 Pressure is measured in millibars or millimeters of Mercury  Pressure is measured with a barometer

Temperature Inversions  Exception to the rule.  Temperature Inversion: an increase in temperature with height in an atmosphere layer  In what layers of the atmosphere do we see temperature inversions?  Can worsen air pollution problems  Act like a lid to trap pollution under the inversion layer

Wind  Air moves in response to density imbalances created by unequal heating and cooling of the Earth’s surface.  Imbalances create areas of high and low pressure (think weather channel!)  In simple terms, wind is air moving from areas of high pressure to areas of low pressure

Wind (cont’d)  Cool air is high pressure  Warm air is low pressure  Measured in knots, mph, km/h  Measured by anemometer

Relative Humidity  Humidity: the amount of water vapor in air  Relative Humidity: the amount of water vapor in air relative to how much water vapor that air is capable of holding  Expressed as a percentage  What would 100% relative humidity mean?  If the air is completely saturated what percent relative humidity would there be?

Relative Humidity (cont’d)  Measured with a hygrometer  The most simple type of hygrometer is a sling psychrometer  Sling Psychrometers have a “wet” bulb that measures how much water can evaporate, giving you a dew point value  A dry bulb takes the air temperature