Weather Systems
Anticipation Guide #2 Density differences in the atmosphere are responsible for redistributing earth s heat When air is heated it rises, cools and expands releasing energy mt air masses are warm and dry air masses Air masses exchange heat and moisture with the surface over which it travels Air masses can never modify and will always be associated with their source regions
Focus Question How can the weather conditions in Canada affect our weekend?
VA SOL SOL 3 The student will investigate and understand how to read and interpret maps, globes, models, charts, and imagery. Key concepts include a. maps (..weather) and SOL 13 The student will investigate and understand that energy transfer between the sun and the Earth and its atmosphere drives weather and climate on Earth. Key concepts include b. prediction of weather patterns
Enduring Understanding Energy transfer between the Earth s surface and the atmosphere creates the weather. The atmosphere remains in balance until acted on by an outside force.
As air rises, it expands and cools.
Weather Systems Heat energy on Earth is in constant motion as it flows from areas of higher temperature to areas of lower temperature. This heat flow creates our global wind systems that transport colder air to warmer areas and vice versa in a constant balancing act of heat energy
Coriolis effect If Earth did not spin predicting weather would be much easier. Cold air at the poles would flow towards the equator and displace the warm air which would rise and flow back towards the poles as it cools in the upper atmosphere, but since it does spin and since air is a fluid material the prediction is far more difficult
Coriolis effect The Coriolis Effect on Earth causes moving particles (air molecules ) to deflect to the right in the northern hemisphere and to the left in the southern hemisphere
Coriolis Effect
Global Wind Patterns For thousands of years mariners have utilized predictable wind patterns to navigate the globe. There are three basic zones per hemisphere. Meteorology now provides an understanding of the reasons for these reliable winds
Global Wind Patterns Trade Winds occur at where the warm, rising air from the equator begins to cool and sink. They occur below 30 degrees latitude and blow in an east to west direction
Question How do you think this wind pattern got its name?
Horse Latitudes Along the 30 degree line the sinking air causes a belt of high pressure with very little horizontal movement. Sailors used to refer to these as the horse latitudes because they would sometimes become stranded in the calm seas and have to throw their horses overboard because they couldn t feed them
Global Wind Patterns Prevailing Westerlies flow between 30 and 60 degrees latitude and blow from west to east. This pattern is responsible for much of the weather in North America
Global Wind Patterns Winds are named for the direction they blow from
Global Wind Patterns Polar Easterlies blow from east to west between 60 deg and the poles and are characterized by very cold air
Global Wind Patterns
Jet Streams Often the weather report will state that the jet stream is affecting today s forecast in some way. Earth weather is strongly influenced by atmospheric conditions and events between the wind zones
Jet Streams Jet Streams are narrow bands of fast, highaltitude, westerly winds and flow at speeds of 185 km/hr Their position varies and drives large-scale weather systems
Fronts Since air masses of different characteristics are constantly in motion some of them are bound to eventually collide
Fronts Front is the narrow region separating two air masses of different densities Density differences are caused by differences in temperature, pressure, and humidity
Fronts There are four main types of fronts and the interaction of colliding air masses often causes dramatic changes in weather
Fronts Cold Fronts occur where cold, dense air displaces warm air and we see clouds, showers, and thunderstorms
Fronts-Cold Front Generally, with the passage of a cold front, the temperature and humidity decrease, the pressure rises. http://www.classzon e.com/books/earth_ science/terc/conten t/visualizations/es2 002/es2002page01. cfm?chapter_no=vi sualization
Cold Front-crossing NYS - October 2008 (metars and satellite)
Fronts Warm Fronts are where advancing warm air displaces cold air and we see extensive cloudiness and precipitation
Fronts-Warm Generally, with the passage of a warm front, the temperature and humidity increase, the pressure decreases. http://www.cla sszone.com/b ooks/earth_sci ence/terc/cont ent/visualizatio ns/es2002/es2 002page01.cf m?chapter_no =visualization
Fronts Stationary Fronts are where the two air masses meet but neither advances. Little cloudiness and precipitation is seen
Fronts Occluded Fronts occur where a cold air mass overtakes a warm front and wedges it upward. It then collides with another cold front and causes precipitation on both sides
Fronts-Occluded Occluded front is formed when a cold front overtakes a warm front.
Pressure Systems The vertical movement of air combined with the coriolis effect results in the formation of rotating low and high pressure systems
High Pressure System High Pressure Systems are formed by dense, sinking air and move in a clockwise direction (in the northern hemisphere) High pressure is associated with fair weather
Low Pressure Systems Low Pressure Systems form by low density rising air moving in a counterclockwise direction Low pressure is associated with stormy weather