Natural Climate Variability 1 Seasonality p 126 127

Natural Climate Variability 1. Seasonality p. 126 -127 A. Tropical cyclones • hurricanes, typhoons • driven by seasonal excess heat gain during the summer B. Extra-tropical cyclones • storms outside the tropics (e. g. , “Nor’easters”) • seasonal movement of the Polar Front and Jet Stream C. Monsoons • weeks of heavy rains • seasonal reversal of the winds due to movement of the ITCZ (especially over India and southeast Asia)

Intertropical Convergence Zone (ITCZ)

Northern Hemisphere winter C. Monsoons & the movement of the ITCZ Northern Hemisphere summer

Monsoons Temperature contrasts between the land the ocean produce small-scale daily shifts in the winds (coastal sea breeze), as well as large-scale seasonal shifts in regional weather patterns p. 127 (monsoons) Summer heating causes air masses to rise over India & Asia and the ITCZ shifts north. This draws in moist air from the ocean which causes very high precipitation over the land. Winter cooling over the Himalaya & Tibetan Plateau causes air masses to sink. The ITCZ shifts south, the winds reverse and the rains end.

Seasonal Movement of the ITCZ January (N. Hemisphere winter) July (N. Hemisphere summer)

Region strongly affected by monsoon due to large seasonal movement of the ITCZ N. Hemisphere summer N. Hemisphere winter Note the reversal of the winds from one season to the next