Download presentation
Presentation is loading. Please wait.
1
Sahel Rainfall change in the future? Papers review
2
References Giannini et al., 2008: A climate model-based review of drought in the Sahel: Desertification, the re-greening and climate change Cook, 2008: The mysteries of Sahel droughts Biasutti et al., 2009: The role of Sahara low in summertime rainfall variability and change in CMIP3 models Nicholson, 2009: A revised picture of the structure of the ”monsoon” and land ITCZ over West Africa
3
“ Sahel drought “ Phenomenon: drying from 1960 recovery from 1980 (disputable) Different projections between GCM models under GHGs forcing
4
Current motivation of the study A Open Question: What will the future precipitation be in the climate change? What contributes to the different simulations of the model? → required more understanding of potential mechanisms involved to drive Sahel rainfall (and its variability)
5
Early studies Human land-use practice (Charney, 1975) Global SSTs : (1) Atlantic interhemespheric gradient (atmosphere-ocean feedback to shift ITCZ) (2) Tropical Pacific (ENSO warming whole tropics) (3) Tropical Indian (deep convections shift, Chou) → Ocean forcing intensified by land-atmosphere feedbacks
6
Ocean forcing ? SST and rainfall relationship hold for past/present but not future by statistics study → future change may control by (1) nonlinearity and details of SST pattern (2) other mechanisms
7
Other mechanisms ? (1) Biasutti: (Models) “West African Monsoon“ → land-sea thermal contrast Sahara heat low (3D structure) (2) Nicholson (Obs.& Reanalysis) “Local up-level circulation” → African Westerly Jet
10
Biasutti et al., 2009 but what causes variability of SHL?
11
Nicholson 2009, 2007 Decouple the land ITCZ and rainbelt Features in the upper-level circulation override the surface factors
13
Nicholson 2009, 2007 Moisture source: locally recycled rather than come from Atlantic
14
Nicholson 2009, 2007 Identified 4 rainfall patterns Mechanism controlling the location of AEJ?
15
Nicholson 2009, 2007 Bimodal state of WAM: strengthen of AWJ
16
Nicholson 2009, 2007 Development of AWJ Strong cross-equatorial pressure gradient Inertial instability
17
Nicholson 2009, 2007 Strong cross-equatorial pressure gradient caused by surface temperature gradient → what causes the variability of AWJ?
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.