Abstract
Given the pronounced warming in the Indian Ocean sea surface temperature (SST) during the second half of the twentieth century and the empirical relationship between the Indian Ocean SST and Sahel summer precipitation, we investigate the mechanisms underlying this relationship using the GFDL atmospheric model AM2.0 to simulate the equilibrium and transient response to the warming of the Indian Ocean. Equatorial wave dynamics, in particular the westward propagating equatorial Rossby waves, communicates the signal of tropospheric warming and stabilization from the Indian Ocean to the African continent. The stabilization associated with the Rossby wave front acts to suppress the convection. Feedbacks with local precipitation and depletion of moisture amplify the dynamically induced subsidence. While this stabilization mechanism is expected to operate in climate change response, the future prospects for the Sahelian climate under global warming are complicated by the intricate sensitivities to the SSTs from different ocean basins and to the direct radiative forcing of greenhouse gases.
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References
Bader J, Latif M (2003) The impact of decadal-scale Indian Ocean sea surface temperature anomalies on Sahelian rainfall and the North Atlantic Oscillation. Geophys Res Lett 30(22):2169. doi:10.1029/2003GL018426
Biasutti MB, Held IM, Sobel AH, Giannini A (2008) SST forcings and Sahel rainfall variability in simulations of the 20th and 21st centuries. J Clim 21:3471–3486. doi:10.1175/2007JCL11896.1
Chou C, Neelin JD (2004) Mechanisms of global warming impacts on regional tropical precipitation. J Clim 17:2688–2701. doi:10.1175/1520-0442(2004)017<2688:MOGWIO>2.0.CO;2
Cook KH, Vizy EK (2006) Coupled model simulations of the West African Monsoon system: 20th and 21st century simulations. J Clim 19:3681–3703. doi:10.1175/JCLI3814.1
Copsey D, Sutton R, Knight JR (2006) Recent trends in sea level pressure in the Indian Ocean region. Geophys Res Lett 33:L19712. doi:10.1029/2006GL027175
Delworth TL et al (2006) GFDL’s CM2 global coupled climate models. Part I: formulation and simulation characteristics. J Clim 19:643–674. doi:10.1175/JCLI3629.1
Douville H (2005) Limitations of time-slice experiments for predicting regional climate change over South Asia. Clim Dyn 24:373–391. doi:10.1007/s00382-004-0509-7
Du Y, Xie S-P (2008) Role of atmospheric adjustments in the tropical Indian Ocean warming during the 20th century in climate models. Geophys Res Lett 35:L08712. doi:10.1029/2008GL033631
Easterling DR, Peterson TC, Karl TR (1996) On the development and use of homogenized climate data sets. J Clim 9:1429–1434. doi:10.1175/1520-0442(1996)009<1429:OTDAUO>2.0.CO;2
Emaneul KA, Neelin DJ, Bretherton CS (1994) On large-scale circulations in convecting atmospheres. Q J R Meteorol Soc 120:1111–1143. doi:10.1002/qj.49712051902
Folland CK, Palmer TN, Parker DE (1986) Sahel rainfall variability and worldwide sea temperature, 1901–85. Nature 320:602–606. doi:10.1038/320602a0
Folland CK, Owen J, Ward MN, Colman A (1991) Prediction of seasonal rainfall in the Sahel region using empirical and dynamical methods. J Forecast 10:21–56. doi:10.1002/for.3980100104
Fontaine B, Trzaska S, Janicot S (1998) Evolution of the relationship between near global and Atlantic SST modes and the rainy season in West Africa: statistical analyses and sensitivity experiments. Clim Dyn 14:353–368. doi:10.1007/s003820050228
GFDL’s GAMDT Global Atmospheric Model Development (2004) The new GFDL global atmospheric and land model AM2/LM2: evaluation with prescribed SST simulations. J Clim 17:4641–4673. doi:10.1175/JCLI-3223.1
Giannini A, Saravanan R, Chang P (2003) Oceanic forcing of Sahel rainfall on interannual and to interdecadal time scales. Science 302:1027–1030. doi:10.1126/science.1089357
Giannini A, Saravanan R, Chang P (2005) Dynamics of the boreal summer African monsoon in the NSIPP1 atmospheric model. Clim Dyn 25:517–535. doi:10.1007/s00382-005-0056-x
Giannini A, Biasutti M, Held IM, Sobel AH (2008) A global perspective on Afircan climate. Climatic Change 90:359–383. doi:10.1007/s10584-008-9396-y
Gill AE (1980) Some simple solutions for heat-induced tropical circulation. Q J R Meteorol Soc 106:447–462. doi:10.1002/qj.49710644905
Gleckler PJ, Taylor KE, Doutriauz C (2008) Performance metrics for climate models. J Geophys Res 113:D06104. doi:10.1029/2007JD008972
Grist JP, Nicholson SE (2001) A study of dynamics factors influencing the rainfall variability in the west African Sahel. J Clim 14:1337–1359. doi:10.1175/1520-0442(2001)014<1337:ASOTDF>2.0.CO;2
Hagos SM, Cook KH (2008) Ocean warming and the late-twentieth-century Sahel drought and recovery. J Clim 21:3797–3814. doi:10.1175/2008JCLI2055.1
Hastenrath S (1990) Decadal-scale changes of the circulation in the tropical Atlantic sector associated with Sahel drought. Int J Climatol 10:459–472. doi:10.1002/joc.3370100504
Hastenrath S, Wolter K (1992) Large-scale patterns and long term trends of circulatioin variability associated with Sahel rainfall anomalies. J Meteorol Soc Jpn 70:1045–1055
Heckley WA, Gill AE (1984) Some simple analytical solutions to the problem of forced equatorial long waves. Q J R Meteorol Soc 110:203–217. doi:10.1002/qj.49711046314
Held IM, Suarez MJ (1994) A proposal for the intercomparison of the dynamical cores of atmospheric general circulation models. Bull Am Meteorol Soc 75(10):1825–1830. doi:10.1175/1520-0477(1994)075<1825:APFTIO>2.0.CO;2
Held IM, Delworth TL, Lu J, Knutson T, Findell K (2005) Simulations of Sahel drought in the 20th and 21st centuries. Proc Natl Acad Sci USA 102(50):17891–17896. doi:10.1073/pnas.0509057102
Hoerling MP, Hurrell JW, Eischeid J, Phillips AS (2006) Detection and attribution of 20th century Northern and Southern African monsoon change. J Clim 19:3989–4008. doi:10.1175/JCLI3842.1
Hurrell JW, Hoerling MP, Phillips AS, Xu T (2004) Twentieth century north Atlantic climate change. Part I: assessing determinism. Clim Dyn 23:371–389. doi:10.1007/s00382-004-0432-y
Janicot S, Moron V, Fontaine B (1996) Sahel drought and ENSO dynamics. Geophys Res Lett 23(5):515–518. doi:10.1029/96GL00246
Janicot S, Trzaska S, Poccard I (2001) Summer Sahel-ENSO teleconnection and decadal time scale SST variations. Clim Dyn 18:303–320. doi:10.1007/s003820100172
Kang SM, Held IM, Frierson DWM, Zhao M (2008) The response of the ITCZ to extratropical thermal forcing: Idealized slab-ocean experiments with a GCM. J Clim 21:3521–3532. doi:10.1175/2007JCLI2146.1
Kirtman BP, Shukla J (2002) Interactive coupled ensemble: a new coupling strategy for CGCMs. Geophys Res Lett 29(10). doi:10.1029/2002GL014834
Knutson TR, Delworth TL, Dixon KW, Stouffer RJ (1999) Model assessment of regional surface temperature trends (1949–1997). J Geophys Res 104(24):30981–30996. doi:10.1029/1999JD900965
Knutson TR, Delworth TL, Dixon KW, Held IM, Lu J, Ramaswamy V, Schwarzkopf MD, Stenchikov G, Stouffer RJ (2006) Assessment of twenty-century regional surface temperature trends using the GFDL CM2 coupled models. J Clim 19:1624–1651. doi:10.1175/JCLI3709.1
Koster RD, Suarez MJ, Heiser M (2000) Variance and predictability of precipitation at seasonal-to-interannual timescales. J Hydrometeorol 1:26–46. doi:10.1175/1525-7541(2000)001<0026:VAPOPA>2.0.CO;2
Lamb PJ (1978) Case studies of tropical Atlantic surface circulation patterns during recent sub-Saharan weather anomalies: 1967 and 1968. Mon Wea Rev 106:482–491
Levitus S, Antonov JI, Boyer TP, Stephens C (2000) Warming of global ocean. Science 287:2225–2229. doi:10.1126/science.287.5461.2225
Lintner BR, Chiang JCH (2006) Adjustment of the remote tropical climate system to El Nino conditions. J Clim 20:2544–2557. doi:10.1175/JCLI4138.1
Lu J, Delworth TL (2005) Oceanic forcing of the late 20th century Sahel drought. Geophys Res Lett 32:22706. doi:10.1029/2005GL023316
Milly PCD, Shmakin AB (2002) Global modeling of land water and energy balances. Part I: the land dynamics (LaD) model. J Hydrometeorol 3:283–299. doi:10.1175/1525-7541(2002)003<0283:GMOLWA>2.0.CO;2
Mitchell TD, Jones PD (2005) An improved method of constructing a database of monthly climate observations and associated high-resolution grids. Int J Climatol 25:693–712. doi:10.1002/joc.1181
Neelin JD, Su H (2005) Moist teleconnection mechanisms for the tropical South American and Atlantic sector. J Clim 18:3928–3950. doi:10.1175/JCLI3517.1
Neelin JD, Yu J (1994) Modes of tropical variability under convective adjustment and the Madden-Julian oscillation. Part I: analytical results. J Atmos Sci 51:1876–1894. doi:10.1175/1520-0469(1994)051<1876:MOTVUC>2.0.CO;2
Neelin JD, Chou C, Su H (2003) Tropical drought regions in global warming and El Nino teleconnections. Geophys Res Lett 30:2275. doi:10.1029/2003GL018625
Nicholson SE, Grist JP (2001) A conceptual model for understanding rainfall variability in the West African Sahel on interannual and interdecadal timescales. Int J Climatol 21:1733–1757. doi:10.1002/joc.648
Nicholson SE, Kim J (1997) The relationship of the El Nino-Southern Oscillation to African rainfall. Int J Climatol 17:117–135. doi:10.1002/(SICI)1097-0088(199702)17:2<117::AID-JOC84>3.0.CO;2-O
Nicholson SE, Palao IM (1993) A re-evaluation of rainfall variability in the Sahel. Part I: characteristics of rainfall fluctuations. Int J Climatol 13:371–389. doi:10.1002/joc.3370130403
Palmer TN (1986) Influence of the Atlantic, Pacific and Indian Oceans on Sahel rainfall. Nature 320:251–253. doi:10.1038/322251a0
Rao KG, Goswami BN (1988) Interannual variations of sea surface temperature over the Arabian Sea and Indian monsoon: a new perspective. Mon Weather Rev 116(3):558–568. doi:10.1175/1520-0493(1988)116<0558:IVOSST>2.0.CO;2
Rayner NA, Parker DE, Horton EB, Folland CK, Alexander LV, Rowell DP, Kent EC, Kaplan A (2003) Global analyses of SST, sea ice, and night marine air temperature since the late nineteenth century. J Geophys Res 108(D14):4407. doi:10.1029/2002JD002670
Reed R, Hollingsworth A, Heckley W, Delsol F (1988) An evaluation of the performance of the ECMWF operational system in analyzing and forecasting easterly wave disturbances over Africa and tropical Atlantic. Mon Weather Rev 116:824–865. doi:10.1175/1520-0493(1988)116<0824:AEOTPO>2.0.CO;2
Rodwell MJ, Hoskins BJ (1996) Monsoons and the dynamics of deserts. Q J R Meteorol Soc 122:1385–1404. doi:10.1002/qj.49712253408
Rotstayn L, Lohmann U (2002) Tropical rainfall trends and the indirect aerosol effect. J Climate 15:2103–2116
Rowell DP (2001) Teleconnection between the tropical Pacific and the Sahel. Q J R Meteorol Soc 127:1683–1706. doi:10.1002/qj.49712757512
Rowell DP (2003) The impact of Mediterranean SSTs on the Sahelian rainfall season. J Clim 16:849–862. doi:10.1175/1520-0442(2003)016<0849:TIOMSO>2.0.CO;2
Rowell DP, Folland CK, Maskell K, Ward MN (1995) Variability of summer rainfall over tropical north Africa (1906–92): Observations and modeling. Q J R Meteorol Soc 121:669–704
Shinoda M, Kawamura R (1994) Tropical rainbelt, circulation, and sea surface temperatures associated with the Sahelian rainfall trend. J Metab Soc Jpn 72:341–357
Thorncroft CD, Hoskins BJ (1994) An idealized study of African easterly waves. I: a linear view. Q J R Meteorol Soc 120:953–982. doi:10.1002/qj.49712051809
Tippett MK (2006) Filtering of GCM simulated Sahel precipitation. Geophys Res Lett 33:01804. doi:10.1029/2005GL024923
Vecchi GA, Soden BJ (2007) Global warming and the weakening of the tropical circulation. J Clim 20:4316–4340. doi:10.1175/JCLI4258.1
Vizy EK, Cook KH (2001) Mechanisms by which Gulf of Guinea and eastern North Atlantic Sea surface temperature anomalies can influence African rainfall. J Clim 14:795–821. doi:10.1175/1520-0442(2001)014<0795:MBWGOG>2.0.CO;2
Vizy EK, Cook KH (2002) Development and application of a mesoscale climate model for the tropics: influence of sea surface temperature anomalies on the West African monsoon. J Geophys Res 107(D3):4023. doi:10.1029/2001JD000686
von Storch H, Zwiers FW (1999) Statistical analysis in climate research. Cambridge University Press, p 484
Wang B, Ding Q, Fu X, I-S K, Jin K, Shukla J, Doblas-Reyes F (2005) Fundamental challenge in simulation and prediction of summer monsoon rainfall. Geophys Res Lett 32:15711. doi:10.1029/2005GL022734
Ward MN (1998) Diagnosis and short-lead time prediction of summer rainfall in tropical North Africa at interannual and interdecadal timescales. J Clim 11:3167–3191. doi:10.1175/1520-0442(1998)011<3167:DASLTP>2.0.CO;2
Xie P, Arkin PA (1997) Global precipitation: a 17-year monthly analysis based on gauge observations, satellite estimates and numerical model outputs. Bull Am Meteorol Soc 78:2539–2558. doi:10.1175/1520-0477(1997)078<2539:GPAYMA>2.0.CO;2
Yoshioka M, Mahowald NM, Conley AJ, Collins WD, Fillmore DW, Zender CS, Coleman DB (2007) Impact of desert dust radiative forcing on Sahel precipitation: relative importance of dust compared to sea surface temperature variations, vegetation changes and greenhouse gas warming. J Clim (submitted)
Zeng N, Neelin JD, Lau KM, Tucker CJ (1999) Enhancement of interdecadal climate variability in the Sahel by vegetation interaction. Science 286:1537–1540. doi:10.1126/science.286.5444.1537
Zhang R, Delworth TL (2006) Impact of Atlantic multidecadal oscillations on India/Sahel rainfall and Atlantic hurricanes. Geophys Res Lett 33:17712. doi:10.1029/2006GL026267
Acknowledgements
I like to first acknowledge Drs. I. M. Held and T. L. Delworth for their mentorship during my visit at GFDL when the reported work was carried out. I am indebted to A. Giannini and M. Biasutti for providing the station based Sahel rainfall index and data from the NSSIP1 simulations and their helpful comments during the formative stage of the paper. I would like to express my appreciation to M. Hoerling and another anonymous reviewer for their perceptive review, which helps improve substantially the manuscript. I also thank G. Meehl and A. Sealy for their encouragement and conducting the NCAR internal review. I acknowledge the Climate Research Unit at University of East Anglia for providing the gridded land precipitation data set. X. Jiang provided the linearized dry GCM for the experiments on the dry response to a prescribed equatorial heating. J. Lu is supported by the Advance Study Program (ASP) at NCAR.
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Lu, J. The dynamics of the Indian Ocean sea surface temperature forcing of Sahel drought. Clim Dyn 33, 445–460 (2009). https://doi.org/10.1007/s00382-009-0596-6
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DOI: https://doi.org/10.1007/s00382-009-0596-6