1. Insolation and Monsoonal Circulation GEOL 3100 Earth’s Climate and Environment: Past, Present, and Future

2. Monsoonal circulation What is the primary reason for monsoonal circulation? –Land and sea have very different capacities to store heat What are the two main monsoonal systems on Earth? –African and Asian monsoons –We will concentrate on the African monsoon

4. Important orbital factors Where does the sun beat down the strongest throughout the year? –Where it is most directly overhead Where and when is the maximum northward extent of maximum solar heating? –23.5N, June 21 What is the current tilt of the Earth’s axis? –23.5 degrees

5. What is the ITCZ and what does it correlate with? The Inter tropical convergence zone is where there is the most vertical convection driving Hadley cell circulation The latitudinal shift of the ITCZ in Africa produces a gradient of decreasing moisture northward of the equator

6. This produces the full range in wet to dry biomes in the tropics to subtropics

7. Activity Which orbital cycle should have the biggest effect on monsoonal strength? –Precession Why? –The Earth-sun distance changes the strength of the sun at its summer solstice maximum Which orbital cycle has the biggest effect on the lower latitudes? –Precession

8. The stronger the summer insolation forcing, the bigger the temperature gradient and the stronger the summer monsoonal winds AND The weaker the winter insolation forcing, the stronger the gradient and the stronger the winter monsoonal winds

9. Activity: Draw summer subtropical insolation for the last 60 ka and estimate when maxima in African monsoons would have occurred.

10. Evidence for past monsoon strength Mediterranean “stinky muds” Freshwater diatoms in Atlantic off coast of N. Africa Change in species of plankton in Equatorial Atlantic off coast of Africa

11. Sapropels in the Mediterranean are created when top-to- bottom circulation is prevented by strong Nile runoff

14. What is necessary for freshwater diatoms coming from Northern Africa? Lakes How often should there be lakes in N. Africa? every 23,000 yrs How often do we expect to see pulses of freshwater diatoms in the sediment downwind from N. Africa? every 23,000 yrs

16. The monsoon winds weaken trade winds in the equatorial Atlantic Activity: Which will produce stronger upwelling, stronger or weaker trade winds? Why?

17. The stronger the trade winds, the more upwelling occurs in the Equatorial Atlantic and visa versa Different species of plankton grow in these two cases

19. Do times of low summer insolation show up in lake level records?