Editorial Type:
Article
Article Type:
Research Article

Detection and Analysis of an Amplified Warming of the Sahara Desert

Kerry H. Cook Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas

Search for other papers by Kerry H. Cook in
Current site
Google Scholar
PubMed Close
and
Edward K. Vizy Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas

Search for other papers by Edward K. Vizy in
Current site
Google Scholar
PubMed Close
Print Publication:
15 Aug 2015
DOI:
https://doi.org/10.1175/JCLI-D-14-00230.1
Page(s):
6560–6580
Restricted access

Abstract

Evaluation of three reanalyses (ERA-Interim, NCEP-2, and MERRA) and two observational datasets [CRU and Global Historical Climatology Network (GHCN)] for 1979–2012 demonstrates that the surface temperature of the Sahara Desert has increased at a rate that is 2–4 times greater than that of the tropical-mean temperature over the 34-yr time period. While the response to enhanced greenhouse gas forcing over most of the globe involves the full depth of the atmosphere, with increases in longwave back radiation increasing latent heat fluxes, the dryness of the Sahara surface precludes this response. Changes in the surface heat balance over the Sahara during the analysis period are primarily in the upward and downward longwave fluxes. As a result, the warming is concentrated near the surface, and a desert amplification of the warming occurs. The desert amplification is analogous to the polar amplification of the global warming signal, which is concentrated at the surface, in part, because of the vertical stability of the Arctic atmosphere. Accompanying the amplified surface warming of the Sahara is a strengthening of both the summertime heat low and the African easterly jet and a weakening of the wintertime anticyclone and the low-level Harmattan winds. Potential implications of the desert amplification include decreases in mineral dust aerosols globally, decreases in wintertime cold air surge activity, and increases in Sahel rainfall.

Corresponding author address: Kerry H. Cook, Jackson School of Geosciences, Department of Geological Sciences, 2275 Speedway Stop C9000, The University of Texas at Austin, Austin, TX 78712. E-mail: kc@jsg.utexas.edu

Abstract

Evaluation of three reanalyses (ERA-Interim, NCEP-2, and MERRA) and two observational datasets [CRU and Global Historical Climatology Network (GHCN)] for 1979–2012 demonstrates that the surface temperature of the Sahara Desert has increased at a rate that is 2–4 times greater than that of the tropical-mean temperature over the 34-yr time period. While the response to enhanced greenhouse gas forcing over most of the globe involves the full depth of the atmosphere, with increases in longwave back radiation increasing latent heat fluxes, the dryness of the Sahara surface precludes this response. Changes in the surface heat balance over the Sahara during the analysis period are primarily in the upward and downward longwave fluxes. As a result, the warming is concentrated near the surface, and a desert amplification of the warming occurs. The desert amplification is analogous to the polar amplification of the global warming signal, which is concentrated at the surface, in part, because of the vertical stability of the Arctic atmosphere. Accompanying the amplified surface warming of the Sahara is a strengthening of both the summertime heat low and the African easterly jet and a weakening of the wintertime anticyclone and the low-level Harmattan winds. Potential implications of the desert amplification include decreases in mineral dust aerosols globally, decreases in wintertime cold air surge activity, and increases in Sahel rainfall.

Corresponding author address: Kerry H. Cook, Jackson School of Geosciences, Department of Geological Sciences, 2275 Speedway Stop C9000, The University of Texas at Austin, Austin, TX 78712. E-mail: kc@jsg.utexas.edu
Save
Cover Journal of Climate
Journal of Climate

  • Ackerley, D., B. B. B. Booth, S. H. E. Knight, E. J. Highwood, D. J. Frame, M. R. Allen, and D. P. Rowell, 2011: Sensitivity of twentieth-century Sahel rainfall to sulfate aerosol and CO2 forcing. J. Climate, 24, 4999–5014, doi:10.1175/JCLI-D-11-00019.1.

    • Search Google Scholar
    • Export Citation

  • Archer, D. E., and K. Johnson, 2000: A model of the iron cycle in the ocean. Global Biogeochem. Cycles, 14, 269–279, doi:10.1029/1999GB900053.

    • Search Google Scholar
    • Export Citation

  • Balmaseda, M. A., A. Vidard, and D. Anderson, 2008: The ECMWF ORA-S3 ocean analysis system. Mon. Wea. Rev., 136, 3018–3034, doi:10.1175/2008MWR2433.1.

    • Search Google Scholar
    • Export Citation

  • Balsamo, G., and Coauthors, 2013: ERA-Interim/Land: A global land water resources dataset. Hydrol. Earth Syst. Sci. Discuss., 10, 14 705–14 745, doi:10.5194/hessd-10-14705-2013.

    • Search Google Scholar
    • Export Citation

  • Berrisford, P., P. Kållberg, S. Kobayashi, D. Dee, S. Uppala, A. J. Simmons, P. Poli, and H. Sato, 2011: Atmospheric conservation properties in ERA-Interim. Quart. J. Roy. Meteor. Soc., 137, 1381–1399, doi:10.1002/qj.864.

    • Search Google Scholar
    • Export Citation

  • Boer, G. J., 2011: The ratio of land to ocean temperature change under global warming. Climate Dyn., 37, 2253–2270, doi:10.1007/s00382-011-1112-3.

    • Search Google Scholar
    • Export Citation

  • Bosilovich, M. G., F. R. Robertson, and J. Chen, 2011: Global energy and water budgets in MERRA. J. Climate, 24, 5721–5739, doi:10.1175/2011JCLI4175.1.

    • Search Google Scholar
    • Export Citation

  • Bristow, C. S., K. S. Hudson-Edwards, and A. Chappell, 2010: Fertilizing the Amazon and equatorial Atlantic with West African dust. Geophys. Res. Lett., 37, L14807, doi:10.1029/2010GL043486.

    • Search Google Scholar
    • Export Citation

  • Brunke, M. A., Z. Wang, X. B. Zeng, M. Bosilovich, and C. L. Shie, 2011: An assessment of the uncertainties in ocean surface turbulent fluxes in 11 reanalysis, satellite-derived, and combined global datasets. J. Climate, 24, 5469–5493, doi:10.1175/2011JCLI4223.1.

    • Search Google Scholar
    • Export Citation

  • Byrne, M. P., and P. A. O’Gorman, 2013: Link between land–ocean warming contrast and surface relative humidities in simulations with coupled climate models. Geophys. Res. Lett., 40, 5223–5227, doi:10.1002/grl.50971.

    • Search Google Scholar
    • Export Citation

  • Cook, K. H., 1999: Generation of the African easterly jet and its role in determining West African precipitation. J. Climate, 12, 1165–1184, doi:10.1175/1520-0442(1999)012<1165:GOTAEJ>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Cullather, R. I., and M. Bosilovich, 2012: The energy budget of the polar atmosphere in MERRA. J. Climate, 25, 5–24, doi:10.1175/2011JCLI4138.1.

    • Search Google Scholar
    • Export Citation

  • Dee, D. P., and Coauthors, 2011: The ERA-Interim reanalysis: Configuration and performance of the data assimilation system. Quart. J. Roy. Meteor. Soc., 137, 553–597, doi:10.1002/qj.828.

    • Search Google Scholar
    • Export Citation

  • Fiedler, S. M., K. Schepanski, B. Heinold, P. Knippertz, and I. Tegen, 2013: Climatology of nocturnal low-level jets over North Africa and implications for modeling mineral dust emission. J. Geophys. Res., 118, 6100–6121, doi:10.1002/jgrd.50394.

    • Search Google Scholar
    • Export Citation

  • Frankignoul, C., and K. Hasselmann, 1977: Stochastic climate models, Part II: Application to sea-surface temperature anomalies and thermocline variability. Tellus, 29A, 289–305, doi:10.1111/j.2153-3490.1977.tb00740.x.

    • Search Google Scholar
    • Export Citation

  • Guieu, C., M. D. Loye-Pilot, C. Ridame, and C. Thomas, 2002: Chemical characterization of the Saharan dust end-member: Some biogeochemical implications for the western Mediterranean Sea. J. Geophys. Res., 107, ACH 5-1–ACH 5-11, doi:10.1029/2001JD000582.

    • Search Google Scholar
    • Export Citation

  • Hagos, S. M., and K. H. Cook, 2008: Ocean warming and late 20th century Sahel drought and recovery. J. Climate, 21, 3797–3814, doi:10.1175/2008JCLI2055.1.

    • Search Google Scholar
    • Export Citation

  • Helmert, J., B. Heinold, I. Tegen, O. Hellmuth, and M. Wendisch, 2007: On the direct and semidirect effects of Saharan dust over Europe: A modeling study. J. Geophys. Res., 112, D13208, doi:10.1029/2006JD007444.

    • Search Google Scholar
    • Export Citation

  • Johnston, B. M., and A. J. Gabric, 2010: Long-term trends in upper ocean structure and meridional circulation of the Southern Ocean south of Australia derived from the SODA reanalysis. Tellus, 62A, 719–736, doi:10.1111/j.1600-0870.2010.00462.x.

    • Search Google Scholar
    • Export Citation

  • Jones, P. D., and A. Moberg, 2003: Hemispheric and large-scale surface air temperature variations: An extensive revision and an update to 2001. J. Climate, 16, 206–223, doi:10.1175/1520-0442(2003)016<0206:HALSSA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Joshi, M. M., and J. M. Gregory, 2008: Dependence of the land–sea contrast in surface climate response on the nature of the forcing. Geophys. Res. Lett., 35, L24802, doi:10.1029/2008GL036234.

    • Search Google Scholar
    • Export Citation

  • Joshi, M. M., J. M. Gregory, M. J. Webb, D. M. H. Sexton, and T. C. Johns, 2008: Mechanisms for the land/sea warming contrast exhibited by simulations of climate change. Climate Dyn., 30, 455–465, doi:10.1007/s00382-007-0306-1.

    • Search Google Scholar
    • Export Citation

  • Kanamitsu, M., W. Ebisuzaki, J. Woollen, S.-K. Yang, J. J. Hnilo, M. Fiorino, and G. L. Potter, 2002: NCEP–DOE AMIP-II Reanalysis (R-2). Bull. Amer. Meteor. Soc., 83, 1631–1643, doi:10.1175/BAMS-83-11-1631.

    • Search Google Scholar
    • Export Citation

  • Lavaysse, C., C. Flamant, S. Janicot, D. J. Parker, J. P. Lafore, B. Sultan, and J. Pelon, 2009: Seasonal evolution of the West African heat low: A climatological perspective. Climate Dyn., 33, 313–330, doi:10.1007/s00382-009-0553-4.

    • Search Google Scholar
    • Export Citation

  • Lavaysse, C., C. Flamant, and S. Janicot, 2010: Regional-scale convection patterns during strong and weak phases of the Saharan heat low. Atmos. Sci. Lett., 11, 255–264, doi:10.1002/asl.284.

    • Search Google Scholar
    • Export Citation

  • Loeb, N. G., L. M. Lyman, G. C. Johnson, R. P. Allan, D. R. Doelling, T. Wong, B. Soden, and G. L. Stephens, 2012: Observed changes in top-of-the-atmosphere radiation and upper-ocean heating consistent within uncertainty. Nat. Geosci., 5, 110–113, doi:10.1038/ngeo1375.

    • Search Google Scholar
    • Export Citation

  • Manabe, S., and R. J. Stouffer, 1980: Sensitivity of a global climate model to an increase of CO2 concentration in the atmosphere. J. Geophys. Res., 85, 5529–5554, doi:10.1029/JC085iC10p05529.

    • Search Google Scholar
    • Export Citation

  • Mitchell, T. D., and P. D. Jones, 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.

    • Search Google Scholar
    • Export Citation

  • Mohino, E., S. Janicot, and J. Bader, 2011: Sahel rainfall and decadal to multi-decadal sea surface temperature variability. Climate Dyn., 37, 419–440, doi:10.1007/s00382-010-0867-2.

    • Search Google Scholar
    • Export Citation

  • Ogawa, K., and T. Schmugge, 2004: Mapping surface broadband emissivity of the Sahara Desert using ASTER and MODIS data. Earth Interact., 8, doi:10.1175/1087-3562(2004)008<0001:MSBEOT>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Park, H. J., D. B. Shin, and J. M. Yoo, 2013: Atmospheric water balance over oceanic regions as estimated from satellite, merged, and reanalysis data. J. Geophys. Res., 118, 3495–3505, doi:10.1002/jgrd.50414.

    • Search Google Scholar
    • Export Citation

  • Peterson, T. C., and R. S. Vose, 1997: An overview of the Global Historical Climatology Network temperature database. Bull. Amer. Meteor. Soc., 78, 2837–2849, doi:10.1175/1520-0477(1997)078<2837:AOOTGH>2.0.CO;2.

    • Search Google Scholar
    • Export Citation

  • Prata, F., 2008: The climatological record of clear-sky longwave radiation at the Earth’s surface: Evidence for water vapour feedback? Int. J. Remote Sens., 29, 5247–5263, doi:10.1080/01431160802036508.

    • Search Google Scholar
    • Export Citation

  • Rienecker, M. N., and Coauthors, 2011: MERRA: NASA’s Modern-Era Retrospective Analysis for Research and Applications. J. Climate, 24, 3624–3648, doi:10.1175/JCLI-D-11-00015.1.

    • Search Google Scholar
    • Export Citation

  • Roberts, J. B., F. R. Robertson, C. A. Clayson, and M. G. Bosilovich, 2012: Characterization of turbulent latent and sensible heat flux exchange between the atmosphere and ocean in MERRA. J. Climate, 25, 821–838, doi:10.1175/JCLI-D-11-00029.1.

    • Search Google Scholar
    • Export Citation

  • Santer, B. D., T. M. L. Wigley, J. S. Boyle, D. J. Gaffen, J. J. Hnilo, D. Nychka, D. E. Parker, and K. E. Taylor, 2000: Statistical significance of trends and trend differences in layer-average atmospheric temperature time series. J. Geophys. Res., 105, 7337–7356, doi:10.1029/1999JD901105.

    • Search Google Scholar
    • Export Citation

  • Schroeder, M., M. Jonas, R. Lindau, J. Schultz, and K. Fennig, 2013: The CM SAF SSM/I-based total column water vapour climate data record: Methods and evaluation against re-analyses and satellite. Atmos. Meas. Tech., 6, 675–775, doi:10.5194/amt-6-765-2013.

    • Search Google Scholar
    • Export Citation

  • Serreze, M., and R. Barry, 2011: Processes and impacts of Arctic amplification: A research synthesis. Global Planet. Change, 77, 85–96, doi:10.1016/j.gloplacha.2011.03.004.

    • Search Google Scholar
    • Export Citation

  • Simmons, A. J., P. Poli, D. P. Dee, P. Berrisford, H. Hersbach, S. Kobayashi, and C. Peubey, 2014: Estimating low-frequency variability and trends in atmospheric temperature using ERA-Interim. Quart. J. Roy. Meteor. Soc., 140, 329–353, doi:10.1002/qj.2317.

    • Search Google Scholar
    • Export Citation

  • Sutton, R. T., B. Dong, and J. M. Gregory, 2007: Land/sea warming ratio in response to climate change: IPCC AR4 model results and comparison with observations. Geophys. Res. Lett., 34, L02701, doi:10.1029/2006GL028164.

    • Search Google Scholar
    • Export Citation

  • Swart, N. C., and J. C. Fyfe, 2012: Observed and simulated changes in the Southern Hemisphere surface westerly wind-stress. Geophys. Res. Lett., 39, L16711, doi:10.1029/2012GL052810.

    • Search Google Scholar
    • Export Citation

  • Tillinger, D., and A. L. Gordon, 2009: Fifty years of the Indonesian Throughflow. J. Climate, 22, 6342–6355, doi:10.1175/2009JCLI2981.1.

    • Search Google Scholar
    • Export Citation

  • Trenberth, K. E., J. Fasullo, and L. Smith, 2005: Trend and variability in column-integrated atmospheric water vapor. Climate Dyn., 24, 741–758, doi:10.1007/s00382-005-0017-4.

    • Search Google Scholar
    • Export Citation

  • Trenberth, K. E., J. Fasullo, and J. Kiehl, 2009: Earth’s global energy budget. Bull. Amer. Meteor. Soc., 90, 311–323, doi:10.1175/2008BAMS2634.1.

    • Search Google Scholar
    • Export Citation

  • Vizy, E. K., and K. H. Cook, 2009: A mechanism for African monsoon breaks: Mediterranean cold air surges. J. Geophys. Res., 114, D01104, doi:10.1029/2008JD010654.

    • Search Google Scholar
    • Export Citation

  • Vizy, E. K., and K. H. Cook, 2013: Impact of cold air surges on rainfall variability in the Sahel and wet African tropics: A multi-scale analysis. Climate Dyn., 43, 1057–1081, doi:10.1007/s00382-013-1953-z.

    • Search Google Scholar
    • Export Citation

  • Vizy, E. K., K. H. Cook, J. Crétat, and N. Neupane, 2013: Projections of a wetter Sahel in the twenty-first century from global and regional models. J. Climate, 26, 4664–4687, doi:10.1175/JCLI-D-12-00533.1.

    • Search Google Scholar
    • Export Citation

  • Vose, R. S., S. Applequist, M. J. Menne, C. N. Williams Jr., and P. Thorne, 2012: An intercomparison of temperature trends in the U.S. Historical Climatology Network and recent atmospheric reanalyses. Geophys. Res. Lett., 39, L10703, doi:10.1029/2012GL051387.

    • Search Google Scholar
    • Export Citation

  • Wang, K., and R. E. Dickinson, 2013: Global atmospheric downward longwave radiation at the surface from ground-based observations, satellite retrievals, and reanalyses. Rev. Geophys., 51, 150–185, doi:10.1002/rog.20009.

    • Search Google Scholar
    • Export Citation

  • Washington, R., and Coauthors, 2009: Dust as a tipping element: The Bodélé Depression, Chad. Proc. Natl. Acad. Sci. USA, 106, 20 564–20 571, doi:10.1073/pnas.0711850106.

    • Search Google Scholar
    • Export Citation

  • Washington, W. M., and G. A. Meehl, 1996: High-latitude climate change in a global coupled ocean–atmosphere–sea ice model with increased atmospheric CO2. J. Geophys. Res., 101, 12 795–12 801, doi:10.1029/96JD00505.

    • Search Google Scholar
    • Export Citation

  • Wilks, D. S., 1995: Statistical Methods in the Atmospheric Sciences—An Introduction. International Geophysics Series, Vol. 59, Academic Press, 467 pp.

  • Wu, L., and Coauthors, 2012: Enhanced warming over the global subtropical western boundary currents. Nat. Climate Change, 2, 161–166, doi:10.1038/nclimate1353.

    • Search Google Scholar
    • Export Citation
All Time Past Year Past 30 Days
Abstract Views 0 0 0
Full Text Views 4135 1457 359
PDF Downloads 1856 346 50