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Atmospheric teleconnection mechanisms of extratropical North Atlantic SST influence on Sahel rainfall

Abstract

Extratropical North Atlantic cooling has been tied to droughts over the Sahel in both paleoclimate observations and modeling studies. This study, which uses an atmospheric general circulation model (GCM) coupled to a slab ocean model that simulates this connection, explores the hypothesis that the extratropical North Atlantic cooling causes the Sahel droughts via an atmospheric teleconnection mediated by tropospheric cooling. The drying is also produced in a regional climate model simulation of the Sahel when reductions in air temperature (and associated geopotential height and humidity changes) from the GCM simulation are imposed as the lateral boundary conditions. This latter simulation explicitly demonstrates the central role of tropospheric cooling in mediating the atmospheric teleconnection from extratropical North Atlantic cooling. Diagnostic analyses are applied to the GCM simulation to infer teleconnection mechanisms. An analysis of top of atmosphere radiative flux changes diagnosed with a radiative kernel technique shows that extratropical North Atlantic cooling is augmented by a positive low cloud feedback and advected downstream, cooling Europe and North Africa. The cooling over North Africa is further amplified by a reduced greenhouse effect from decreased atmospheric specific humidity. A moisture budget analysis shows that the direct moisture effect and monsoon weakening, both tied to the ambient cooling and resulting circulation changes, and feedbacks by vertical circulation and evaporation augment the rainfall reduction. Cooling over the Tropical North Atlantic in response to the prescribed extratropical cooling also augments the Sahel drying. Taken together, they suggest a thermodynamic pathway for the teleconnection. The teleconnection may also be applicable to understanding the North Atlantic influence on Sahel rainfall over the twentieth century.

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References

  1. Adler RF, Huffman GJ, Chang A et al (2003) The version-2 global precipitation climatology project (GPCP) monthly precipitation analysis (1979-present). J Hydrometeorol 4:1147–1167. doi:10.1175/1525-7541(2003)004<1147:TVGPCP>2.0.CO;2

  2. Alley RB (2007) Wally was right: predictive ability of the North Atlantic “conveyor belt” hypothesis for abrupt climate change. Annu Rev Earth Planet Sci 35:241–272

  3. 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 30:2169

  4. Biasutti M, Giannini A (2006) Robust Sahel drying in response to late 20th century forcings. Geophys Res Lett 33:L11706. doi:10.1029/2006GL026067

  5. Biasutti M, Sobel A, Camargo S (2009) The role of the Sahara low in summertime Sahel rainfall variability and change in the CMIP3 models. J Clim 22:5755–5771. doi:10.1175/2009JCLI2969.1

  6. Broecker WS, Peteet DM, Rind D (1985) Does the ocean–atmosphere system have more than one stable mode of operation? Nature 315:21–26. doi:10.1038/315021a0

  7. Chen H, Zhou T, Neale R, Wu X, Zhang G (2010) Performance of the new NCAR CAM3. 5 in East Asian summer monsoon simulations: sensitivity to modifications of the convection scheme. J Clim 23:3657–3675

  8. Cheng W, Bitz CM, Chiang JCH (2007) Adjustment of the global climate to an abrupt slowdown of the Atlantic meridional overturning circulation. Geophys Monogr 173:295

  9. Chiang JCH, Bitz CM (2005) Influence of high latitude ice cover on the marine intertropical convergence zone. Clim Dyn 25:477–496

  10. Chiang JCH, Friedman AR (2012) Extratropical cooling, interhemispheric thermal gradients, and tropical climate change. Annu Rev Earth Planet Sci 40(40):383–412

  11. 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

  12. Chou C, Neelin J, Su H (2001) Ocean–atmosphere–land feedbacks in an idealized monsoon. Q J R Meteorol Soc 127:1869–1891. doi:10.1002/qj.49712757602

  13. Chou C, Neelin JD, Chen C-A, Tu J-Y (2009) Evaluating the “Rich-Get-Richer” mechanism in tropical precipitation change under global warming. J Clim 22:1982–2005. doi:10.1175/2008JCLI2471.1

  14. Collins W, Rasch P, Boville B et al (2006) The formulation and atmospheric simulation of the Community Atmosphere Model version 3 (CAM3). J Clim 19:2144–2161

  15. Cook K (1999) Generation of the African easterly jet and its role in determining West African precipitation RID B-4998-2011. J Clim 12:1165–1184. doi:10.1175/1520-0442(1999)012<1165:GOTAEJ>2.0.CO;2

  16. Folland CK, Palmer TN, Parker DE (1986) Sahel rainfall and worldwide sea temperatures, 1901–85. Nature 320:602–607

  17. Folland CK, Owen J, Ward MN, Colman A (1991) Prediction of seasonal rainfall in the Sahel region using empirical and dynamic methods. J Forecast 10:21–56. doi:10.1002/for.3980100104

  18. 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

  19. Giannini A, Saravanan R, Chang P (2003) Oceanic forcing of Sahel rainfall on interannual to interdecadal time scales. Science 302:1027–1030

  20. Grist J, Nicholson S (2001) A study of the dynamic factors influencing the rainfall variability in the West African Sahel. J Clim 14(7):1337–1359

  21. Haarsma RJ, Selten FM, Weber SL, Kliphuis M (2005) Sahel rainfall variability and response to greenhouse warming. Geophys Res Lett 32:L17702

  22. Held IM, Delworth TL, Lu J et al (2006) Simulation of Sahel drought in the 20th and 21st centuries. Natl Acad Sci U S A 103(4):1152–1153

  23. Hoerling M, Hurrell J, Eischeid J, Phillips A (2006) Detection and attribution of twentieth-century northern and southern African rainfall change. J Clim 19(16):3989–4008

  24. Janjic Z (1994) The step-mountain Eta coordinate model—further developments of the convection, viscous sublayer, and turbulence closure schemes. Mon Weather Rev 122:927–945. doi:10.1175/1520-0493(1994)122<0927:TSMECM>2.0.CO;2

  25. Janjic Z (1996) The surface layer in the NCEP Eta model. In: Eleventh conference on numerical weather prediction, Norfolk, VA, 19–23 August. Am Meteor Soc, Boston, MA, pp 354–355

  26. Janjic ZI (2002) Nonsingular implementation of the Mellor–Yamada level 2.5 scheme in the NCEP Meso model. NCEP Office Note 437:61

  27. Kalnay E, Kanamitsu M, Kistler R et al (1996) The NCEP/NCAR 40-year reanalysis project. Bull Am Meteor Soc 77:437–471

  28. Kanamitsu M, Ebisuzaki W, Woollen J et al (2002) NCEP-DOE AMIP-II Reanalysis (R-2). Bull Am Meteorol Soc 83:1631–1644

  29. Kawase H, Abe M, Yamada Y et al (2010) Physical mechanism of long-term drying trend over tropical North Africa. Geophys Res Lett 37:L09706

  30. Lin Y, Farley R, Orville H (1983) Bulk parameterization of the snow field in a cloud model. J Clim Appl Meteorol 22:1065–1092. doi:10.1175/1520-0450(1983)022<1065:BPOTSF>2.0.CO;2

  31. Liu Y, Chiang JCH (2012) Coordinated abrupt weakening of the Eurasian and North African Monsoons in the 1960s and links to extratropical North Atlantic cooling. J Clim 25:3532–3548. doi:10.1175/JCLI-D-11-00219.1

  32. Mlawer EJ, Taubman SJ, Brown PD et al (1997) Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave. J Geophys Res Atmos 102:16663–16682. doi:10.1029/97JD00237

  33. Monin AS, Obukhov AM (1954) Basic laws of turbulent mixing in the surface layer of the atmosphere. Contrib Geophys Inst Acad Sci USSR 151:163–187

  34. Mulitza S, Prange M, Stuut JB et al (2008) Sahel mega droughts triggered by glacial slowdowns of Atlantic meridional overturning. Paleoceanography. doi:10.1029/2008PA001637

  35. Nicholson S (1979) Revised rainfall series for the West-African Subtropics. Mon Weather Rev 107:620–623. doi:10.1175/1520-0493(1979)107<0620:RRSFTW>2.0.CO;2

  36. Nicholson S (2009) On the factors modulating the intensity of the tropical rainbelt over West Africa. Int J Clim 29:673–689. doi:10.1002/joc.1702

  37. Niedermeyer EM, Prange M, Mulitza S et al (2009) Extratropical forcing of Sahel aridity during Heinrich stadials. Geophys Res Lett. doi:10.1029/2009GL039687

  38. Patricola CM, Cook KH (2008) Atmosphere/vegetation feedbacks: a mechanism for abrupt climate change over northern Africa. J Geophys Res Atmos. doi:10.1029/2007JD009608

  39. Patricola CM, Cook KH (2010) Northern African climate at the end of the twenty-first century: an integrated application of regional and global climate models. Clim Dyn 35:193–212. doi:10.1007/s00382-009-0623-7

  40. Rotstayn LD, Lohmann U (2002) Tropical rainfall trends and the indirect aerosol effect. J Clim 15(15):2103–2116

  41. 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. doi:10.1256/smsqj.52310

  42. Shanahan T, Overpeck J, Anchukaitis K et al (2009) Atlantic forcing of persistent drought in West Africa. Science 324:377–380. doi:10.1126/science.1166352

  43. Shell K, Kiehl J, Shields C (2008) Using the radiative kernel technique to calculate climate feedbacks in NCAR’s Community Atmospheric Model. J Clim 21:2269–2282. doi:10.1175/2007JCLI2044.1

  44. Skamarock WC, Klemp JB, Dudhia J et al (2008) A description of the advanced research WRF Version 3. NCAR/TN-475+STR

  45. Smirnova TG, Brown JM, Benjamin SG (1997) Performance of different soil model configurations in simulating ground surface temperature and surface fluxes. Mon Weather Rev 125:1870–1884. doi:10.1175/1520-0493(1997)125<1870:PODSMC>2.0.CO;2

  46. Soden B, Held I, Colman R et al (2008) Quantifying climate feedbacks using radiative kernels. J Clim 21:3504–3520. doi:10.1175/2007JCLI2110.1

  47. Stager J, Ryves D, Chase B, Pausata F (2011) Catastrophic drought in the Afro-Asian monsoon region during Heinrich event 1. Science 331:1299–1302. doi:10.1126/science.1198322

  48. van Kreveld S, Sarnthein M, Erlenkeuser H et al (2000) Potential links between surging ice sheets, circulation changes, and the Dansgaard–Oeschger cycles in the Irminger Sea, 60-18 kyr. Paleoceanography 15:425–442. doi:10.1029/1999PA000464

  49. Vellinga M, Wood R (2002) Global climatic impacts of a collapse of the Atlantic thermohaline circulation. Clim Change 54:251–267. doi:10.1023/A:1016168827653

  50. Wang Y, Cheng H, Edwards R et al (2001) A high-resolution absolute-dated Late Pleistocene monsoon record from Hulu Cave, China. Science 294:2345–2348

  51. Xue Y, Jagadish S (1993) The influence of land surface properties on Sahel climate. Part 1: desertification. J Clim 6(12):2232–2245

  52. Zhang R, Delworth TL (2005) Simulated tropical response to a substantial weakening of the Atlantic thermohaline circulation. J Clim 18:1853–1860

  53. Zhang G, Mcfarlane N (1995) Sensitivity of climate simulations to the parameterization of cumulus convection in the Canadian Climate Center general-circulation model. Atmos Ocean 33:407–446

  54. Zhou T, Yu R, Li H, Wang B (2008) Ocean forcing to changes in global monsoon precipitation over the recent half-century. J Clim 21:3833–3852

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Acknowledgments

This research is supported by the National Science Foundation (NSF AGS-1143329 and NSF EAR-0909195). The authors would like to thank Inez Fung, Shih-Yu Lee, Andrew Friedman and Ching-Yee Chang for useful and enlightening discussions. YL thanks Ivana Cvijanovic for helping design the GCM simulation, Alexandra Jonko for assistance with using the radiative kernel technique, Andrew Friedman and Meghan Thurlow for editing the manuscript for grammar and usage. All reanalysis data are provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, at http://www.esrl.noaa.gov/psd/.

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Correspondence to Yuwei Liu.

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Liu, Y., Chiang, J.C.H., Chou, C. et al. Atmospheric teleconnection mechanisms of extratropical North Atlantic SST influence on Sahel rainfall. Clim Dyn 43, 2797–2811 (2014). https://doi.org/10.1007/s00382-014-2094-8

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Keywords

  • North Atlantic cooling
  • Sahel rainfall
  • Atmospheric teleconnection
  • Monsoon