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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? Chia Chou Research Center for Environmental Changes Academia Sinica September 22, 2009 NCU
Figure 3.6 IPCC AR4
Figure 3.12 IPCC AR4
M: mass flux; q: PBL water vapor Global water vapor budget (Held and Soden 2006): thermodynamic dynamic
Thermodynamic contribution changes in moisture easy part
Figure 3.21 IPCC AR4
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
Vecchi and Soden (2007) The Walker circulation is weakened more than the Hadley circulation
In global average, P = E E ≈ LWs+SWs (assuming H is small) P ≈ LW+SW (assuming H is small) Vecchi and Soden (2007)
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)
Observed precipitation Wentz et al. 2007 7.5% per 1ºC T
Changes in convective and non-convective zones Allan and Soden 2007
Changes in zonal averages Zhang et al. 2007
enhancement of seasonal cycle in tropical precipitation Chou et al. 2007
Dynamic contribution changes in circulation hard part
The rich-get-richer mechanism (IIa) The deepening effect of convection (IIb)
>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)
shallower deeper • The deeper (shallower) convection, the more stable, -, (unstable, +) the atmosphere ascent stability Chou and Chen 2009
Mechanisms of tropical precipitation changes Chou et al. 2009
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)