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How will precipitation change under global warming?

How will precipitation change under global warming?. Chia Chou Research Center for Environmental Changes Academia Sinica September 22, 2009 NCU. Figure 3.6. IPCC AR4. IPCC AR4. Figure 3.12. IPCC AR4. IPCC AR4. M : mass flux; q : PBL water vapor. .

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How will precipitation change under global warming?

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  1. How will precipitation change under global warming? Chia Chou Research Center for Environmental Changes Academia Sinica September 22, 2009 NCU

  2. Figure 3.6 IPCC AR4

  3. IPCC AR4

  4. Figure 3.12 IPCC AR4

  5. IPCC AR4

  6. M: mass flux; q: PBL water vapor  Global water vapor budget (Held and Soden 2006): thermodynamic dynamic     

  7. Thermodynamic contribution   changes in moisture  easy part

  8. Figure 3.21 IPCC AR4

  9. 1-3% in P per 1ºC T (model simulations)   <0  slowing of tropical circulation dynamic component   7.5% in q per 1ºC T (Clausius-Clapeyron) thermodynamic component

  10. Vecchi and Soden (2007) The Walker circulation is weakened more than the Hadley circulation

  11. In global average, P = E E ≈ LWs+SWs (assuming H is small) P ≈ LW+SW (assuming H is small) Vecchi and Soden (2007)

  12. 地表長波幅射 CO2, CH4, N2O, H2O… 太陽短波幅射 增溫效應 地表吸收 less cooling by LW less latent heat release (precipitation)

  13. Observed precipitation Wentz et al. 2007 7.5% per 1ºC T

  14. Changes in convective and non-convective zones Allan and Soden 2007

  15. Changes in zonal averages Zhang et al. 2007

  16. Chou et al. 2007

  17. enhancement of seasonal cycle in tropical precipitation Chou et al. 2007

  18. Dynamic contribution   changes in circulation  hard part

  19. Classification of the Tropics

  20. Area I (P΄<0)

  21. The upped-ante mechanism

  22. Area IIa and IIb (P΄>0)

  23. The rich-get-richer mechanism (IIa) The deepening effect of convection (IIb)

  24.   >0 or <0 No constraint  7.5% in q per 1ºC T 7.5% in q per 1ºC T   <0  1-3% in P per 1ºC T (controlled by energy budget)

  25. Chou and Chen 2009

  26. shallower deeper • The deeper (shallower) convection, the more stable, -, (unstable, +) the atmosphere ascent stability Chou and Chen 2009

  27. Area III (P΄>0)

  28. Climate regime shift

  29. Mechanisms of tropical precipitation changes Chou et al. 2009

  30. Conclusion • Thermodynamic component ( )  enhance rainfall over convective regions reduce rainfall over subsidence regions rich-get-richer (poor-get-poorer) • Dynamic component ( )  reduce over convective margins (upped-ante) enhance in convective center (rich-get-richer) enhanced rainfall but weakened upward motion (deepening of convection)

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