Chapters 5 Motion in the Atmosphere Motion is called Wind or Air Currents

1. Chapters 5 Motion in the Atmosphere Motion is called Wind or Air Currents depending on direction of motion and scale Influenced by global, regional and local factors Air motion is both an effect of air pressure differences and a cause of pressure changes Air circulation patterns are responsible for many of the climatic zones on earth related to movement of moisture

2. Air pressure Defined as the force exerted over an area in essence the force of the weight of the air Pressure is variable- even without air motion Why? Amount of air varies from one location to another due to changes in elevation, thickness of the atmosphere, and concentration of gases

4. Tropics Poles Elevation differences

5. Air pressure is measured in units that express the force Variable depending on what we want to try to do with it Newton = Force to accelerate 1 kg x 1meter second Dyne = force to accelerate 1 gram x 1 cm second Pressure terms Pascal = 1N/m2 Bar = 106 dynes/ cm2 millibar = 1/1000 x 1 Bar inches or mm of mercury are used to measure the pressure as air displaces the weight of Hg

6. Air always corrects for force imbalances in the system Air moves from high pressure toward low pressure Air parcels moving from opposing directions are said to be converging this will create a pressure imbalance if left alone Air parcels moving away from a central location are said to be diverging this too will create an imbalance if left unchecked Air moves differently depending on a number of forces acting on it Pressure gradient = the pressure imbalance between 2 points Frictional force = the force slowing the motion of the air as it drags across a surface Coriolis force = the force exerted on objects in motion over long distances- created by earth’s rotation

7. Must look at pressure at the surface and aloft This map is at the surface

8. Coriolis force

11. No frictional force to interfere with other forces at higher elevations in the atmosphere e.g., coriolis effect (Ce), centripetal force (Cf) and pressure head (PH)

12. deflection by coriolis force direction air wants to move direction air actually moves At the surface frictional force interferes to cause crossing of isobars

16. Periodic (localized) winds daily or annual variations in temperature and pressure cause the development of periodic or localized wind fields Several are common, and they vary in duration and scale Small scale winds Land breeze vs Sea breeze Fohn, Santa Ana, or Chinook winds Valley vs Mountain breezes

17. Sea breeze vs land breeze Develops due to differential heating of land vs water - during the day, land heats up fast; water slowly creates convectional lifting over land wind from the ocean rushes in to fill the void - during the night, land cools off quickly; water remains warm creates a a convection current over the water air from land rushes in to fill the void

18. Sea breeze vs Land breeze

19. Valley vs Mountain breeze similar to sea vs land breeze mountain tops heated by sunlight trigger updrafts in the mountains that draw air up the slopes from the valley floor below Valley-breeze at night, cool air aloft tries to sink, and slides down the slopes to the lower valley floor, forcing warmer air to rise Mountain-breeze

21. Katabatic winds • includes Santa Ana, Chinook and Fohn winds • cooler drier air from high elevations is rapidly warmed as it descends to lower elevations • the reverse of the adiabatic process • +7.7°F/1000 ft • Since the air was dry to start, as it warms it becomes really moisture starved • Absorbs as much water from wherever it can • When funneled through narrow mountain passes can cause really high velocity winds

22. Santa Ana Wind A katabatic wind

23. Global circulation is set up by radiation imbalances related to latitude and land vs ocean mass distribution

24. Radiation imbalance sets up a south to north heat flow-> and a corresponding North to south wind to compensate for the pressure imbalance

27. Tropical waves generally track along the easterly trade winds move from east to west Brings tropical moisture to areas that don’t always have it Can assist in development of tropical storms hurricanes, typhoons, cyclones

28. ITCZ- Intertropical Convergence Zone along the equator air converging to fill void left as heated air rises creates unstable conditions and perpetual rainy zone Migrates with the seasonal shift in solar radiation changes toward the north in summer toward the south in winter in the middle for fall and spring

29. Trade winds called the southeasterlies (S) or the northeasterlies (N) depending upon which hemisphere you are in remember it is based on the direction the wind comes from

32. Westerlies Common in the mid-latitudes (30-60°N-S) Create and move storm centers form west to east Interaction with tropical and polar air occurs in this zone creates mid latitude cyclonic circulations low pressure cells that are associated with frontal boundaries

34. Monsoonal circulation 180° reversal of wind direction often associated with seasonal changes often associated with rainy vs dry seasons caused by position of H vs L pressure

37. Ocean thermohaline conveyor belt