THE ATMOSPHERIC CIRCULATION SYSTEM

1. THE ATMOSPHERIC CIRCULATION SYSTEM

2. GOALS • Describe the major characteristics of the atmospheric circulation • Explain why they occur • Illustrate the way in which they affect the transport of energy and materials around the globe

3. OBJECTIVES • Explain why weather and climate vary across the globe • Emphasize that the responses to global-scale processes and changes may not be uniform across the globe

4. Why does air move? • Latitudinal energy distribution uneven • Tropics – surplus • Poles – deficit • Temperature gradient causes density & pressure differences • Cause global-scale pattern of wind-belts • NET EFFECT • Restore latitudinal energy balance by moving surplus energy away from the tropics to cancel deficit at poles • Earth’s atmospheric circulation has a direct impact on the global distribution of temperature & precipitation

5. THE GLOBAL CIRCULATORY SUBSYSTEMS • Circulation of energy and matter throughout the Earth system is ordered • Subsystems work to maintain the planet in thermal and chemical equilibrium • All subsystems act to help regulate the global temperature

6. CIRCULATION PUMPS • Short time scale (years to decades) • Tropical ocean circulation pump • Moves air and water over globe • Energy source is the sun • Atmospheric Circulation • Longer time scales (1000s of years) • Deep-ocean circulation pump • Moves water • Energy source is the sun • Thermohaline Circulation • Longest time scale (millions of years) • Interior circulation pump • Moves continents & Earth’s interior • Energy source is radioactive decay and heat from Earth’s interior • Convection Currents

7. THE ATMOSPHERIC CIRCULATION

8. The Movement of Air • SYSTEM – Movement of Air • PRODUCT – Vertical Movement of Air • PROCESS – • Change in buoyancy • Mechanical forcing

9. Buoyancy • Due to density differences • T↑ : D↓ (air expands) – positive buoyancy – air rises • T↓ : D↑ (air condenses) – negative buoyancy – air subsides

13. The Movement of Air • SYSTEM – Movement of Air • PRODUCT – Horizontal Movement of Air • PROCESS – Difference in Pressure

14. Horizontal Movement • Air moves from high-pressure (cool, dry air) to low-pressure (warm, moist air) • Air moves down the pressure gradient • Air moves form high pressure regions to low pressure regions

16. Uneven Heating of the Atmosphere

18. Distribution of Insolation • Gradient in absorbed energy single most important control on temperature • Most weather/climate is the response of atmosphere to the unequal distribution of energy by latitude

19. GLOBAL SCALE ATMOSPHERIC CIRCULAITON • Represent negative feedback loop • Atmosphere responds to temperature gradient by latitudinal transfer of energy to reduce gradient and restore energy balance • Sun continually adds energy, so balance never attained

20. Rising air hits stratospheric barrier and is forced to diverge (Divergence – movement of air outward from a high pressure region) ITCZ = Intertropical Convergence Zone (Convergence – movement of air inward toward a low pressure region

21. As air rises, it cools and condenses, forms clouds ITCZ = extensive cloud cover and precipitation

23. WORLD DESERTS AT 30° N and 30° S LATITUDES

24. HADLEY CIRCULATION • Air movement pattern – • Convergence at tropics • Divergence • Subsidence at 30° N & S latitudes • Dominant tropical circulation

25. HADLEY CIRCULATION

26. Hadley Cells and ITCZ • Globally noncontinuous • Most obvious in Atlantic and Pacific Oceans • Large scale circulation in Southeast Asia & Indian Ocean dominated by monsoon • Release of latent heat in ITCZ convective towers drive Hadley Circulation Pump • Radiation, evaporation, transportation, condensation

27. MID &HIGH LATITUDE CIRCULATION • Cold polar air moves toward equator • Warm tropical air moves toward pole • Create Polar Front Zone (steep Temperature Gradients)

28. MERIDIONAL CIRCULATION Alternating N & S moving air at surface

29. EXPECTED

30. OBSERVED

31. Coriolis Effect • The apparent tendency for a fluid moving across Earth’s surface to be deflected from a straight path • Results from observers frame of reference • Coriolis Effect

32. Northern Hemisphere – deflected right

33. Southern Hemisphere – deflected left

34. RESULT

35. ACTUAL

36. MID LATITUDE FLOW PATTERNS • Cyclonic Flow – air flowing into a low pressure region • Hurricane Sandy • Extratropical cyclones – cyclones formed outside of the tropics • Anticyclone – air flowing out of a high pressure region • Circulation patterns flow along polar front

37. UPPER-LEVEL FLOW

38. UPPER-LEVEL FLOW • Air will flow down the pressure gradient • Wind speed greatest where pressure gradient greatest • upper troposphere at mid latitudes • Jet Stream

39. UPPER-LEVEL FLOW • Due to balancing of pressure gradient force and Coriolis force air flow is nearly geostrophic (air flow at right angles to the gradient) • But flows in wavelike patterns around globe

40. ROSSBY WAVES Steer high and low pressure systems that produce weather

41. SEASONAL VARIABILITY • Distribution of solar energy varies with the seasons

44. SEASONAL VARIABILITY • Tropics receive large input of solar radiation at all times • Seasonal variability of where sun is overhead affects circulation patterns

45. SEASONAL VARIABILITY

46. TEMPERATURE & RAINFALL DISTRIBUTION • Atmospheric circulation affects global temperature & rainfall distributions • Atmosphere important part of thermoregulatory system • Evaporation/precipitation influenced by temperature/energy • Transport of water modifies temperature distribution by modifying radiation budget & feeds back and affects circulation • TEMPERATURE, PRECIPITATION & CIRCULATION LINKED CLOSELY BY FEEDBACKS

47. OCEAN LAND COMPARISONS OCEAN LAND High albedo Absorb less solar energy Slow downward transfer of heat Low Thermal Conductivity Low Heat Capacity Changes temperature rapidly Solar radiation reflected or absorbed at surface • Low albedo • Absorb more solar energy • Rapid downward transfer of heat (turbulent mixing) • High Thermal Conductivity • High Heat Capacity • Changes temperature slowly • Solar radiation absorbed below surface

48. SEA BREEZE

49. CONTINENTALITY • More extreme climate variability and temperature changes over land compared to water • Winter – land surfaces much colder • Summer – land surfaces much warmer • Greatest seasonable variability – interior of continents • Least seasonal variability – tropical oceans

50. CONTINENTALITY EFFECTS