1. Climate and Global Change Notes 22-1 Midlatitude Cyclones Global Circulations (Con’t) Midlatitude Cyclones Air Masses Fronts Cold Warm Occluded Lifecycle Jet Stream Structure Seasonal Variation Science Concepts The Earth System (Kump, Kastin & Crane) Chap. 4 (pp. 63-66)

2. Climate and Global Change Notes 22-2 Midlatitude Cyclones Air Masses An air mass is a large blob of air with similar temperature and moisture characteristics Two reasons for differences in these properties -Earth’s uneven heating -Earth’s surface has land and water These properties depend on the source region of the air mass Source regionsCharacteristic - A = ArcticColdest - P = Polar-- - T = Tropical-- - E = EquatorialWarmest - m = maritimeMoist - c = continentalDry

3. Climate and Global Change Notes 22-3 Midlatitude Cyclones Air Masses (Con’t) Source regions

4. Climate and Global Change Notes 22-4 Fronts Boundary between two air masses Types of fronts -Cold front - cold air advancing and replacing warmer air Blue line or -Warm front - warm air advancing and replacing colder air Red line or -Stationary front - Warm and cold air both stationary. Alternating red and blue line or Midlatitude Cyclones

5. Climate and Global Change Notes 22-5 Midlatitude Cyclones Cold Fronts Cold air advancing and replacing warmer air Warm Fronts Warm air advancing and replacing colder air

6. Climate and Global Change Notes 22-6 Mature Midlatitude Cyclone Cyclonic circulation - Low pressure system Counterclockwise circulation in the northern hemisphere Warm air mass moves north while cold air mass moves south Midlatitude Cyclones

7. Climate and Global Change Notes 22-7 Midlatitude Cyclones Occluded Fronts Boundary that separates the new cold air mass (to the west) from the older cool air mass already in place north of the warm front Cold fronts move about twice as fast as warm fronts “Got a job as a weather girl.” he said. “Channel three.” “Jenn Stone,” I said. “That’s where I’ve see her.” “That’s her with the low-pressue areas,” Jesse said, “and the occluded fronts waving at the weather charts just like she knew.” Robert B. Parker, Blue Screen, p. 198.

8. Climate and Global Change Notes 22-8 Midlatitude Cyclones Life Cycle Six Stages - a)Cyclonic shear - b)Frontal wave - c)Wave cyclone - open wave, mature cyclone - d)Shrinking warm sector - e)Occluded system - f)Dissipating stage

9. Climate and Global Change Notes 22-9 Midlatitude Cyclones Life Cycle

10. Climate and Global Change Notes 22-10 Midlatitude Cyclones Example Low-pressure system over U.S. http://visibleearth.nasa.gov/Sensors/Terra/

11. Climate and Global Change Notes 22-11 Midlatitude Cyclones Example Low-pressure system off Australia http://earthobservatory.nasa.gov/NaturalHazards/natural_hazards_v2.php3?img_id=2108

12. Climate and Global Change Notes 22-12 Midlatitude Cyclones Example Global View http://visibleearth.nasa.gov/Sensors/Terra/

13. Climate and Global Change Notes 22-13 Midlatitude Cyclones Example Surface map for 15Z 9 May ‘02 Surface data High and low pressure systems Fronts Radar http://weather.unisys.com/surface/sfc_map.html

14. Climate and Global Change Notes 22-14 Midlatitude Cyclones Example Surface map for 00Z 31 Mar ‘98 Surface data High and low pressure systems Fronts Radar

15. Climate and Global Change Notes 22-15 Jet Stream PGF - Pressure gradient force vector Geostrophic wind vector Pressure surfaces Jet stream core Structure

16. Climate and Global Change Notes 22-16 Jet Stream Seasonal Variation in the Jet Stream Summer -Weaker -Farther north Winter -Stronger -Farther south Moves with the Sun

17. Climate and Global Change Notes 22-17 Jet Stream Variation in the Jet Stream Sometimes two jet streams -Midlatitude or Polar Jet -Subtropical Jet http://rst.gsfc.nasa.gov/Sect14/Sect14_1c.html