1. Class #14 Wednesday, September 30 Class #14: Wednesday, September 30 Chapters 6 and 7 Thermal Circulation, Scales of Motion, Global Winds 1

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4. 4 The thermal circulation The sea breeze is a thermal circulation. A thermal circulation has both horizontal and vertical air motions. The horizontal pressure gradient force is most important in a thermal circulation. Upward air motions occur in the warmer air column of the circulation; downward air motions occur in the cooler air column.

5. Class #14 Wednesday, September 305 More on the thermal circulation The thermal circulation begins aloft. In diagrams of the thermal circulation, “H” and “L” refer to the horizontal pressure gradient, not to the vertical pressure gradient. The thermal circulation comes about because hydrostatic balance requires that the warmer air column expands compared to the cooler air column.

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7. 7 The sea breeze Is a daytime circulation. Depends on differential heating at the surface between land and water. Has the warmer air column over the land, which absorbs more incoming solar radiation. Has the cooler air column over the water, which absorbs less radiation.

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15. Class #14 Wednesday, September 3015 The sea breeze and the land breeze As solar heating diminishes in the late afternoon, the sea breeze weakens. At night, differential cooling occurs. The cooler air column is over land, where radiational cooling is more rapid than over the water. The warmer air column is over the water. The land breeze develops at night.

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18. Class #14 Wednesday, September 3018 Scales of motion in the atmosphere Describe the size and lifetime of wind patterns in the atmosphere. Determine which forces are most important to forming the wind patterns. Are largest when the lifetimes are longest. Are smaller when the lifetime is shorter. Have a variety of names and definitions.

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20. Class #14 Wednesday, September 3020 More on scales of motion The horizontal pressure gradient force is important for all scales of motion. The Coriolis Force is important for the planetary scale, the synoptic scale, and for the larger mesoscale wind patterns. The vertical pressure gradient force is important for small mesoscale winds.

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22. Class #14 Wednesday, September 3022 The surface winds over Earth Are very complicated because of the changing seasons, differences between land and water, and differences in latitude. Can be simplified using a conceptual model. Have been described using a 3-cell model with no land and no seasons. Only temperature differences from equator to pole are included.