2WHY DO WE HAVE THE WEATHER ? Just think about it!Why is there wind? Why does it blow from one direction one day and another the next?Why is it rainy one day and dry the next?How come it’s cold in the winter?How can we have hail in the summer?What causes snow and freezing rain?
3You might pick heat or sun….but another good choice would be If we were to pick one term to help explain why we have weather, what do you think would be a good word?You might pick heat or sun….but another good choice would beConvection
4Convection is the transfer of heat, usually in gases or liquids.
5After the atmosphere is warmed by radiation and conduction, the heat is transferred throughout the atmosphere by convection.Since warmed air has more space between the molecules, it’s less dense and risesCooled air is more dense and tends to sinkIn general, air near the equator tends to rise and air near the poles tends to sink
11The Weather HighwaysThe rotation of the earth creates the Coriolis effect.The Coriolis effect causes the air and water to be deflected to the West.This creates global weather highways.
12The Prevailing Westerlies Because of our latitude, most of our weather comes from the westLooking at the weather map, what type of weather might we expect?
13Combining Hadley Cells, the Coriolis Effect, and Prevailing Westerlies gives you... Tradewinds:Where do you thinkthey got their name?Who were these windsparticularly important to?
14Let’s break for a short review Transfer of heat in liquids or gases__________ air is dense and tends to sink.Cold air holds _____ moisture than warm airThe Coriolis effect causes the air and water to be deflected to the _____ of the equator
15How did you do?1. CONVECTION2. COLD3. LESS4. RIGHT
16Now What?Ok, so we know that the weather moves around on these highways and that warm air rises and cold air sinks.But why is it sunny one day, and rainy the next?
17Let’s take another look at the weather map Notice that there are H’s and L’s on the mapThere are also blue lines with spikes and red lines with half circlesLet’s take a closer look!
18High Pressure AreasWhen cooler air sinks and is warmed, the air can hold more moistureThis usually means sunny and clear skiesWinds tend to move clockwise around a high
19Low Pressure AreasWhen warm air rises and is cooled, the air can not hold as much moistureOften, these areas are associated with precipitation and stormy weatherTornadoes and hurricanes can produce very low pressure readings.
20Fronts and Air MassesAn air mass is a large body of air whose temperature and moisture are fairly similar at a given altitudeFronts are boundaries separating different air massesThere are four different air masses that affect the United States
21The Air Masses cP( continental polar) : cold, dry stable cT( continental tropical) : hot, dry, stable air aloft, unstable at the surfacemP( maritime polar) : cool, moist, unstablemT( maritime tropical) : warm, moist, unstable
22This map shows the air mass source regions and there paths