Where are they? Why is there no weather?

Meteorology The study of weather Good sites for weather info: weather.com nws

Describe the weather outside right now The variables measured are: –Temperature –Humidity (Dew point and RH) –Pressure (High /Low) –Wind (speed and direction) –Precipitation (rain, sleet, snow, etc) –Cloud (percentage and type) Will these variable change over the next minute? Hour?day?week?

Air Temp Instrument: Thermometer Temp decreases as you increase in altitude

What affects our temperature? Latitude (New England vs Miami) Altitude (Lynn vs Mt Washington) Closeness to Ocean (NE vs Omaha) Cloud cover (Clear vs cloudy) Land use

Humidity Absolute Humidity – amount of water vapor in the air Relative Humidity (RH) – amount of water vapor in the air vs the amount it can hold at a specific temp. Dew Point (DP) – the temp to which air has to cool for dew to form What is the relationship between DP and RH? Instrument: Sling psychrometer

DP and RH Dew Point The closer the DP temp is the air temp more likely clouds/dew/precip will form. How does this relate to RH? Relative Humidity –Written as a percent. –The closer to 100%, the more likely clouds and precip.

Dry Bulb – AirTemp Wet Bulb - fabric Sling Psychrometer

Barometric Pressure Force or weight of air pushing on the surface of earth Pressure decreases as altitude increases (why) Moist air light (Low) Dry air heavy (High) Instrument: barometer

Barometric Pressure

Pressure High (H) Dry conditions Air circulates clockwise and outward Air is sinking from above Low (L) Wet Condition (Precipitation) Air circulates counterclockwise and inward nws-goes sat Air flows from High to Low causing wind! H L

Wind Horizontal movement of air. Caused by difference in heating of Earth (difference in air pressure [H to L]) Sun heats Earth, Earth heats atmosphere (conduction, convection, radiation) Instrument: Anemometer, Wind vane

Insolation and re-radiation

Local vs GlobalWinds Local examples Land and Sea Breezes Mountain Ranges Global winds –Move weather systems –Coriolis effect – shift in the path of fluid moving along the surface of the earth due to the rotation of the earth –Doldrums (equator) –Prevailing westerlies –Polar easterlies

Land and Sea Breeze

Mountain Ranges

Air Masses CP – Continental Polar – from the northwest Cold and dry CT – Continental tropical – from the south west Warm and dry MP – maritime polar – from the northeast Cold and wet MT – maritime tropical – from the southeast Warm and wet (hurricanes)

Air masses

Fronts Warm Front – a warm air mass overtakes a colder air mass  creates cirrus clouds Cold front – Cold air mass overtakes a warm air mass  cumulus &/or storms Stationary front – two air masses moving parallel or transformly  sluggish moving precipitation Occluded front – Fast moving cold front overtakes a warm front  high winds and heavy precipitation.

Fronts

Precipitation and Clouds Clouds form when rising air reaches the dew point temperature and there are condensation nuclei (particles of dust, pollen, ash, etc) present. Precipitation occurs when the air is saturated and water vapor becomes either a solid or a liquid. What is condensation? What are other phase changes? When is energy released? Absorbed?

This method of cloud classification was proposed by Luke Howard (1803) who named the clouds based on their form: Cirrus - curl Stratus - layer Cumulus - heap Nimbus - rain and on their height: High Middle Low Contrails fall into the category of cirrus as they are high level clouds that consist entirely of ice crystals

Reading a weather map

Sample weather map