• Adler, R. F., and Coauthors, 2003: The Version-2 Global Precipitation Climatology Project (GPCP) Monthly Precipitation Analysis (1979–present). J. Hydrometeor., 4, 11471167, doi:10.1175/1525-7541(2003)004<1147:TVGPCP>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Beniston, M., 2003: Climatic change in mountain regions: A review of possible impacts. Climatic Change, 59, 531, doi:10.1023/A:1024458411589.

  • Beniston, M., H. F. Diaz, and R. S. Bradley, 1997: Climatic change at high elevation sites: An overview. Climatic Change, 36, 233251, doi:10.1023/A:1005380714349.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Biasutti, M., A. H. Sobel, and S. J. Camargo, 2009: The role of the Saharan low in summertime Sahel rainfall variability and change in the CMIP3 models. J. Climate, 22, 57555771, doi:10.1175/2009JCLI2969.1.

    • Crossref
    • 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, 57215739, doi:10.1175/2011JCLI4175.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bosilovich, M. G., and Coauthors, 2015: MERRA-2: Initial evaluation of the climate. NASA/TM-2015-104606, Vol. 43, 139 pp.

  • Cook, K. H., 1999: Generation of the African easterly jet and its role in determining West African precipitation. J. Climate, 12, 11651184, doi:10.1175/1520-0442(1999)012<1165:GOTAEJ>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cook, K. H., and E. K. Vizy, 2013: Projected changes in East African rainy seasons. J. Climate, 26, 59315948, doi:10.1175/JCLI-D-12-00455.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cook, K. H., and E. K. Vizy, 2015: Detection and analysis of an amplified warming of the Sahara Desert. J. Climate, 28, 65606580, doi:10.1175/JCLI-D-14-00230.1.

    • Crossref
    • 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, 553597, doi:10.1002/qj.828.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Dong, B., and R. Sutton, 2015: Dominant role of greenhouse-gas forcing in the recovery of Sahel rainfall. Nat. Climate Change, 5, 757760, doi:10.1038/nclimate2664.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Evan, A. T., C. Flamant, C. Lavaysse, C. Kocha, and A. Saci, 2015: Water vapor–forced greenhouse warming over the Sahara Desert and the recent recovery from the Sahelian drought. J. Climate, 28, 108123, doi:10.1175/JCLI-D-14-00039.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Haarsma, R. J., F. M. Selten, S. L. Weber, and M. Kliphuis, 2005: Sahel rainfall variability and response to greenhouse warming. Geophys. Res. Lett., 32, L17702, doi:10.1029/2005GL023232.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hagos, S. M., and K. H. Cook, 2008: Ocean warming and late-twentieth-century Sahel drought and recovery. J. Climate, 21, 37973814, doi:10.1175/2008JCLI2055.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Harris, I., P. D. Jones, T. J. Osborn, and D. H. Lister, 2014: Updated high-resolution grids of monthly climatic observations—The CRU TS3.10 dataset. Int. J. Climatol., 34, 623642, doi:10.1002/joc.3711.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ishii, M., A. Shouji, S. Sugimoto, and T. Matsumoto, 2005: Objective analyses of sea-surface temperature and marine meteorological variables for the 20th century using ICOADS and the Kobe collection. Int. J. Climatol., 25, 865879, doi:10.1002/joc.1169.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jiang, J. H., H. Su, C. Zhai, L. Wu, K. Minschwaner, A. M. Molod, and A. M. Tompkins, 2015: An assessment of upper troposphere and lower stratosphere water vapor in MERRA, MERRA2, and ECMWF reanalyses using Aura MLS observations. J. Geophys. Res. Atmos., 120, 11 46811 485, doi:10.1002/2015JD023752.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jones, P. D., and A. Moberg, 2003: Hemispheric and large-scale air temperature variations: An extensive revision and an update to 2001. J. Climate, 16, 206223, doi:10.1175/1520-0442(2003)016<0206:HALSSA>2.0.CO;2.

    • Crossref
    • 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, 16311643, doi:10.1175/BAMS-83-11-1631.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kobayashi, S., and Coauthors, 2015: The JRA-55 reanalysis: General specifications and basic characteristics. J. Meteor. Soc. Japan, 93, 548, doi:10.2151/jmsj.2015-001.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lavaysse, C., 2015: Warming trends: Saharan desert warming. Nat. Climate Change, 5, 807808, doi:10.1038/nclimate2773.

  • 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, 255264, doi:10.1002/asl.284.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Lebel, T., and A. Ali, 2009: Recent trends in the central and western Sahel rainfall regime (1990–2007). J. Hydrol., 375, 5264, doi:10.1016/j.jhydrol.2008.11.030.

    • Crossref
    • 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, 693712, doi:10.1002/joc.1181.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Molod, A., L. Takacs, M. Suarez, and J. Bacmeister, 2015: Development of the GEOS-5 atmospheric general circulation model: Evolution from MERRA to MERRA2. Geosci. Model Dev., 8, 13391356, doi:10.5194/gmd-8-1339-2015.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nicholson, S. E., 2005: On the question of the “recovery” of the rains in the West African Sahel. J. Arid Environ., 63, 615641, doi:10.1016/j.jaridenv.2005.03.004.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Park, J.-Y., J. Bader, and D. Matei, 2016: Anthropogenic Mediterranean warming essential driver for present and future Sahel rainfall. Nat. Climate Change, 6, 941945, doi:10.1038/nclimate3065.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Patricola, C. M., and K. H. Cook, 2007: Dynamics of the West African monsoon under mid-Holocene precessional forcing: Regional climate model simulations. J. Climate, 20, 694716, doi:10.1175/JCLI4013.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Patricola, C. M., and K. H. Cook, 2008: Atmosphere/vegetation feedbacks: A mechanism for abrupt climate change over northern Africa. J. Geophys. Res., 113, D18102, doi:10.1029/2007JD009608.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pepin, N., and Coauthors, 2015: Elevation-dependent warming in mountain regions of the world. Nat. Climate Change, 5, 424430, doi:10.1038/nclimate2563.

    • Crossref
    • 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, 28372849, doi:10.1175/1520-0477(1997)078<2837:AOOTGH>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pu, B., and K. H. Cook, 2012: Role of the West African westerly jet in Sahel rainfall variations. J. Climate, 25, 28802896, doi:10.1175/JCLI-D-11-00394.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Reynolds, R. W., T. M. Smith, C. Liu, D. B. Chelton, K. S. Casey, and M. G. Schlax, 2007: Daily high-resolution-blended analyses for sea surface temperature. J. Climate, 20, 54735496, doi:10.1175/2007JCLI1824.1.

    • Crossref
    • 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, 36243648, doi:10.1175/JCLI-D-11-00015.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Robertson, F. R., M. G. Bosilovich, J. Chen, and T. L. Miller, 2011: The effect of satellite observing system changes on MERRA water and energy fluxes. J. Climate, 24, 51975217, doi:10.1175/2011JCLI4227.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Sanogo, S., A. H. Fink, J. A. Omotosho, A. Ba, R. Redl, and V. Ermert, 2015: Spatio-temporal characteristics of the recent rainfall recovery in West Africa. Int. J. Climatol., 35, 45894605, doi:10.1002/joc.4309.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Seidel, D. J., and M. Free, 2003: Comparison of lower-tropospheric temperature climatologies and trends at low and high elevation radiosonde sites. Climatic Change, 59, 5374, doi:10.1023/A:1024459610680.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., J. T. Fasullo, and L. Smith, 2005: Trends and variability in column-integrated water vapor. Climate Dyn., 24, 741758, doi:10.1007/s00382-005-0017-4.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Trenberth, K. E., J. T. Fasullo, and J. Mackaro, 2011: Atmospheric moisture transports from ocean to land and global energy flows in reanalyses. J. Climate, 24, 49074924, doi:10.1175/2011JCLI4171.1.

    • Crossref
    • 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, 46644687, doi:10.1175/JCLI-D-12-00533.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Wang, Q., X. Fan, and M. Wang, 2014: Recent warming amplification over high elevation regions across the globe. Climate Dyn., 43, 87101, doi:10.1007/s00382-013-1889-3.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Webster, P., 1987: The elementary monsoon. Monsoons, J. S. Fein and P. L. Stephens, Eds., Wiley, 3–32.

  • Zwiers, F. W., and H. von Storch, 1995: Taking serial correlation into account in tests of the mean. J. Climate, 8, 336351, doi:10.1175/1520-0442(1995)008<0336:TSCIAI>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
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Seasonality of the Observed Amplified Sahara Warming Trend and Implications for Sahel Rainfall

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  • 1 Department of Geological Sciences, Jackson School of Geosciences, The University of Texas at Austin, Austin, Texas
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Abstract

Prior results indicate an amplified annual mean warming trend over the Sahara, with temperature trends that are 2–4 times that of the tropical mean rate. Trend analysis is conducted using five atmospheric reanalyses and three observational datasets to better understand the seasonality and physical processes of this amplified warming and the implications for Sahel precipitation. The seasonality of the amplified warming is maximum during July–October with a minimum during June. Two processes related to the amplified warming are identified. A “dry process” supports amplified warming over the Sahara when there is limited latent heating and/or evaporation to cool the surface and distribute heat to the atmosphere. In this mechanism, the warming results from changes in the upward longwave and downward longwave fluxes that are tightly coupled to each other. The second, termed a “wet process,” occurs during the summer West African monsoon season. In this mechanism there are increases in the low- and midlevel atmospheric moisture over the Sahara that add to the surface warming by increasing the longwave downward radiation. This additional atmospheric moisture is transported over the Sahara because of a strengthening of the thermal low/Saharan high circulation system. A positive feedback mechanism is discussed in which enhanced moisture transport due to the stronger Saharan warming leads to increased Sahel rainfall that further strengthens the meridional temperature and height gradients by cooling the Sahel surface, further enhancing moisture transport into the region. Both processes contribute to the amplified warming, with the amplification being greater during the summer.

© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author e-mail: Edward K. Vizy, ned@jsg.utexas.edu

Abstract

Prior results indicate an amplified annual mean warming trend over the Sahara, with temperature trends that are 2–4 times that of the tropical mean rate. Trend analysis is conducted using five atmospheric reanalyses and three observational datasets to better understand the seasonality and physical processes of this amplified warming and the implications for Sahel precipitation. The seasonality of the amplified warming is maximum during July–October with a minimum during June. Two processes related to the amplified warming are identified. A “dry process” supports amplified warming over the Sahara when there is limited latent heating and/or evaporation to cool the surface and distribute heat to the atmosphere. In this mechanism, the warming results from changes in the upward longwave and downward longwave fluxes that are tightly coupled to each other. The second, termed a “wet process,” occurs during the summer West African monsoon season. In this mechanism there are increases in the low- and midlevel atmospheric moisture over the Sahara that add to the surface warming by increasing the longwave downward radiation. This additional atmospheric moisture is transported over the Sahara because of a strengthening of the thermal low/Saharan high circulation system. A positive feedback mechanism is discussed in which enhanced moisture transport due to the stronger Saharan warming leads to increased Sahel rainfall that further strengthens the meridional temperature and height gradients by cooling the Sahel surface, further enhancing moisture transport into the region. Both processes contribute to the amplified warming, with the amplification being greater during the summer.

© 2017 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author e-mail: Edward K. Vizy, ned@jsg.utexas.edu
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