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ATS 553

Why is the Winter Hemisphere Hadley Circulation stronger than the Summer Hemisphere Hadley Circulation?. ATS 553. Based on:. “Role of Continents in Driving the Hadley Cells”, by Kerry H. Cook, Journal of the Atmospheric Sciences , 1 April 2003, 957-976. In Intro, you learned….

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ATS 553

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  1. Why is the Winter Hemisphere Hadley Circulation stronger than the Summer Hemisphere Hadley Circulation? ATS 553

  2. Based on: • “Role of Continents in Driving the Hadley Cells”, by Kerry H. Cook, Journal of the Atmospheric Sciences, 1 April 2003, 957-976.

  3. In Intro, you learned…

  4. Maybe you even learned… • Northern Hemisphere Summer

  5. Maybe you even learned… • Southern Hemisphere Summer

  6. However, Ramage shows… • Northern Hemisphere Summer

  7. However, Ramage shows… • Southern Hemisphere Summer

  8. So the question is… • Why is the Hadley Circulation so strong in the WINTER Hemisphere?

  9. But a better question is… • Why is the Hadley Circulation so WEAK in the SUMMER Hemisphere?

  10. Strength of the Hadley Circ. • Described by the low level meridional winds

  11. But first, let’s talk about trade winds.

  12. H H H H H H L L L L L L H H H H H H

  13. H H H H H H L L L L L L H H H H H H

  14. H H H H H H L L L L L L H H H H H H

  15. H L H H L L Summer L L L L L L H H H H H H

  16. H L H H L L Summer L L L L L L H H H H H H

  17. Maintaining trade winds

  18. What determines friction?

  19. What determines friction? Summer hemisphere has weaker trade winds, so friction is less.

  20. What determines friction? If friction is smaller, what happens to f times v?

  21. What determines friction? Therefore, the v component has to be smaller!

  22. What determines friction? Therefore, the Hadley Circulation has to be smaller in the Summer Hemisphere!

  23. Temptation: • To say that it must just be the opposite in the Winter Hemisphere: • “In the summer hemisphere, heat lows over continents result in a weak meridional pressure gradient force, weak trade winds, and a weak Hadley Circulation.”

  24. Temptation: • To say that it must just be the opposite in the Winter Hemisphere: • “In the summer hemisphere, heat lows over continents result in a weak meridional pressure gradient force, weak trade winds, and a weak Hadley Circulation.”

  25. Temptation: • To say that it must just be the opposite in the Winter Hemisphere: • “In the winter hemisphere, polar highs over continents result in a strong meridional pressure gradient force, strong trade winds, and a strong Hadley Circulation.”

  26. However… • That’s not how it works in the Winter Hemisphere. • Polar highs are VERY VERY shallow features, with almost no impact on the meridional pressure gradient force.

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