• Afiesimama, E. A., 2007: Annual cycle of the mid-tropospheric easterly jet over West Africa. Theor. Appl. Climatol., 90, 103111, doi:10.1007/s00704-006-0284-y.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Bender, C. M., and S. A. Orszag, 1978: Advanced Mathematical Methods for Scientists and Engineers. McGraw Hill, 593 pp.

  • Carlson, T. N., and C. B. Benjamin, 1980: Radiative heating rates for Saharan dust. J. Atmos. Sci., 37, 193213, doi:10.1175/1520-0469(1980)037<0193:RHRFSD>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Charney, J. G., and M. E. Stern, 1962: On the stability of internal baroclinic jets in a rotating atmosphere. J. Atmos. Sci., 19, 159172, doi:10.1175/1520-0469(1962)019<0159:OTSOIB>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, S.-H., J. Dudhia, J. S. Kain, T. Kindap, and E. Tan, 2008: Development of the online MM5 tracer model and its applications to air pollution episodes in Instanbul, Turkey, and Sahara dust transport. J. Geophys. Res., 113, D11203, doi:1029/2007JD009244.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, S.-H., S.-H. Wang, and M. Waylonis, 2010: Modification of Saharan air layer and environmental shear over the eastern Atlantic Ocean by dust-radiation effects. J. Geophys. Res., 115, D21202, doi:10.1029/2010JD014158.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chen, S.-H., Y.-C. Liu, T. R. Nathan, C. Davis, R. Torn, N. Sowa, C.-T. Cheng, and J.-P. Chen, 2015: Modeling the effects of dust-radiative forcing on the movement of Hurricane Helene (2006). Quart. J. Roy. Meteor. Soc., 141, 25632570, doi:10.1002/qj.2542.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Cho, H.-R., and M. A. Jenkins, 1987: The thermal structure of tropical easterly waves. J. Atmos. Sci., 44, 25312539, doi:10.1175/1520-0469(1987)044<2531:TTSOTE>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Chou, M. D., and M. J. Suarez, 1999: A solar radiation parameterization for atmospheric studies. Vol. 15, Technical Report Series on Global Modeling and Data Assimilation, NASA Tech. Memo. NASA/TM-1999-104606, 51 pp. [Available online at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990060930.pdf.]

  • Chou, M. D., M. J. Suarez, X. Z. Liang, and M. M. H. Yan, 2001: A thermal infrared radiation parameterization for Atmospheric Studies. Vol. 15, Technical Report Series on Global Modeling and Data Assimilation, NASA Tech. Memo. NASA/TM-1999-104606, 68 pp. [Available online at https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20010072848.pdf.]

  • Cuesta, J., J. H. Marsham, D. J. Parker, and C. Flamant, 2009: Dynamical mechanisms controlling the vertical redistribution of dust and the thermodynamic structure of the West Saharan atmospheric boundary layer during summer. Atmos. Sci. Lett., 10, 3442, doi:10.1002/asl.207.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Echols, R. S., and T. R. Nathan, 1996: Effect of ozone heating on forced equatorial waves. J. Atmos. Sci., 53, 263275, doi:10.1175/1520-0469(1996)053<0263:EOOHOF>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Edmon, H. J., B. J. Hoskins, and M. E. McIntyre, 1980: Eliassen–Palm cross sections for the troposphere. J. Atmos. Sci., 37, 26002616, doi:10.1175/1520-0469(1980)037<2600:EPCSFT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Engelstaedter, S., and R. Washington, 2007: Atmospheric controls on the annual cycle of North African dust. J. Geophys. Res., 112, D03103, doi:10.1029/2006JD007195.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ghan, S. J., 1989a: Unstable radiative dynamical interactions. Part I: Basic theory. J. Atmos. Sci., 46, 25282543, doi:10.1175/1520-0469(1989)046<2528:URIPIB>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Ghan, S. J., 1989b: Unstable radiative dynamical interactions. Part II: Expanded theory. J. Atmos. Sci., 46, 25442561, doi:10.1175/1520-0469(1989)046<2544:URDIPI>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Grogan, D. F. P., T. R. Nathan, R. S. Echols, and E. C. Cordero, 2012: A parameterization for the effects of ozone on the wave driving exerted by equatorial waves in the stratosphere. J. Atmos. Sci., 69, 37153731, doi:10.1175/JAS-D-11-0343.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Grogan, D. F. P., T. R. Nathan, and S.-H. Chen, 2016: Effect of Saharan dust on the linear dynamics of African easterly waves. J. Atmos. Sci., 73, 891911, doi:10.1175/JAS-D-15-0143.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Grogan, D. F. P., T. R. Nathan, and S.-H. Chen, 2017: Saharan dust and the nonlinear evolution of the African easterly jet–African easterly wave system. J. Atmos. Sci., 74, 2747, doi:10.1175/JAS-D-16-0118.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hall, N. M. J., G. N. Kiladis, and C. D. Thorncroft, 2006: Three-dimensional structure and dynamics of African easterly waves. Part II: Dynamical modes. J. Atmos. Sci., 63, 22312245, doi:10.1175/JAS3742.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Hess, M., P. Koepke, and I. Shult, 1998: Optical properties of aerosols and clouds: The software package OPAC. Bull. Amer. Meteor. Soc., 79, 831844, doi:10.1175/1520-0477(1998)079<0831:OPOAAC>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jones, C., N. Mahowald, and C. Luo, 2003: The role of easterly waves on African desert dust transport. J. Climate, 16, 36173628, doi:10.1175/1520-0442(2003)016<3617:TROEWO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jones, C., N. Mahowald, and C. Luo, 2004: Observational evidence of African desert dust intensification of easterly waves. Geophys. Res. Lett., 31, L17208, doi:10.1029/2004GL020107.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Jury, M. R., and M. J. Santiago, 2010: Composite analysis of dust impacts on African easterly waves in the Moderate Resolution Imaging Spectrometer era. Geophys. Res. Lett., 115, D16213, doi:10.1029/2009JD013612.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Karyampudi, V. M., and T. N. Carlson, 1988: Analysis and numerical simulations of the Saharan air layer and its effect on easterly wave disturbances. J. Atmos. Sci., 45, 31023136, doi:10.1175/1520-0469(1988)045<3102:AANSOT>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kaufman, Y. J., I. Koren, L. A. Remer, D. Tanré, P. Ginoux, and S. Fan, 2005: Dust transport and deposition observed from Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) spacecraft over the Atlantic Ocean. J. Geophys. Res., 110, D10S12, doi:10.1029/2003JD004436.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kiladis, G. N., C. D. Thorncroft, and N. M. J. Hall, 2006: Three-dimensional structure and dynamics of African easterly waves. Part I: Observations. J. Atmos. Sci., 63, 22122230, doi:10.1175/JAS3741.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Knippertz, P., and M. C. Todd, 2010: The central west Saharan dust hot spot and its relation to African easterly waves and extratropical disturbances. J. Geophys. Res., 115, D12117, doi:10.1029/2009JD012819.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Kok, J. F., 2011: A scaling theory for the size distribution of emitted dust aerosols suggests climate models underestimate the size of the global dust cycle. Proc. Natl. Acad. Sci. USA, 108, 10161021, doi:10.1073/pnas.1014798108.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Leroux, S., and N. M. J. Hall, 2009: On the relationship between African easterly waves and the African easterly jet. J. Atmos. Sci., 66, 23032316, doi:10.1175/2009JAS2988.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Leroux, S., N. M. J. Hall, and G. N. Kiladis, 2011: Intermittent African easterly wave activity in a dry atmospheric model: Influence of the extratropics. J. Climate, 24, 53785396, doi:10.1175/JCLI-D-11-00049.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Liou, K. N., 2002: An Introduction to Atmospheric Radiation, Academic Press, 583 pp.

  • Ma, P.-L., K. Zhang, J. J. Shi, T. Matsui, and A. Arking, 2012: Direct radiative effect of mineral dust on the development of African easterly waves. J. Appl. Meteor. Climatol., 51, 20902104, doi:10.1175/JAMC-D-11-0215.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Miller, R. L., and I. Tegen, 1998: Climate response to soil dust aerosols. J. Climate, 11, 32473267, doi:10.1175/1520-0442(1998)011<3247:CRTSDA>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Miller, R. L., P. Knippertz, C. P. García-Pando, J. P. Perlwitz, and I. Tegan, 2014: Impact of dust-radiative forcing upon climate. Mineral Dust: A Key Player in the Earth System, P. Knippertz and J.-B. W. Stuut, Eds., Springer Science, 327–357, doi:10.11007/978-94-017-8978-3_13.

    • Crossref
    • Export Citation
  • Nathan, T. R., 1989: On the role of ozone in the stability of Rossby normal modes. J. Atmos. Sci., 46, 20942100, doi:10.1175/1520-0469(1989)046<2094:OTROOI>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nathan, T. R., and L. Li, 1991: Linear stability of free planetary waves in the presence of radiative–photochemical feedbacks. J. Atmos. Sci., 48, 18371855, doi:10.1175/1520-0469(1991)048<1837:LSOFPW>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Nathan, T. R., and D. Hodyss, 2010: Troposphere–stratosphere communication through local vertical waveguides. Quart. J. Roy. Meteor. Soc., 136, 1219, doi:10.1002/qj.532.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pedlosky, J., 1987: Geophysical Fluid Dynamics. Springer, 710 pp.

    • Crossref
    • Export Citation
  • Prospero, J. M., 1999: Long-range transport of mineral dust in the global atmosphere: Impact of African dust on the environment of the southeastern United States. Proc. Natl. Acad. Sci. USA, 96, 33963403, doi:10.1073/pnas.96.7.3396.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Prospero, J. M., and T. N. Carlson, 1972: Vertical and areal distributions of Saharan dust over the western equatorial North Atlantic Ocean. J. Geophys. Res., 77, 52555265, doi:10.1029/JC077i027p05255.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Pytharoulis, I., and C. Thorncroft, 1999: The low-level structure of African easterly waves in 1995. J. Atmos. Sci., 127, 22662280, doi:10.1175/1520-0493(1999)127<2266:TLLSOA>2.0.CO;2.

    • Search Google Scholar
    • Export Citation
  • Reed, R. J., A. Hollingsworth, W. A. Heckley, and F. Delsol, 1988: An evaluation of the performance of the ECMWF Operational System in analyzing and forecasting easterly wave disturbances over Africa and the tropical Atlantic. Mon. Wea. Rev., 116, 824865, doi:10.1175/1520-0493(1988)116<0824:AEOTPO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Rennick, M. A., 1976: The generation of African waves. J. Atmos. Sci., 33, 19551969, doi:10.1175/1520-0469(1976)033<1955:TGOAW>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Simmons, A. J., 1977: A note on the instability of the African easterly jet. J. Atmos. Sci., 34, 16701674, doi:10.1175/1520-0469(1977)034<1670:ANOTIO>2.0.CO;2.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thorncroft, C. D., 1995: An idealised study of African easterly waves. III: More realistic basic states. Quart. J. Roy. Meteor. Soc., 121, 15891614, doi:10.1002/qj.49712152706.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thorncroft, C. D., and B. J. Hoskins, 1994: An idealized study of African easterly waves. I: Linear theory. Quart. J. Roy. Meteor. Soc., 120, 953982, doi:10.1002/qj.49712051809.

    • Crossref
    • Search Google Scholar
    • Export Citation
  • Thorncroft, C. D., N. M. J. Hall, and G. N. Kiladis, 2008: Three-dimensional structure and dynamics of African easterly waves. Part III: Genesis. J. Atmos. Sci., 65, 35963607, doi:10.1175/2008JAS2575.1.

    • Crossref
    • Search Google Scholar
    • Export Citation
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Subcritical Destabilization of African Easterly Waves by Saharan Mineral Dust

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  • 1 Atmospheric Science Program, Department of Land, Air, and Water Resources, University of California, Davis, Davis, California
  • | 2 Department of Atmospheric and Environmental Sciences, University at Albany, State University of New York, Albany, New York
  • | 3 Atmospheric Science Program, Department of Land, Air, and Water Resources, University of California, Davis, Davis, California
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Abstract

A theoretical framework is presented that exposes the radiative–dynamical relationships that govern the subcritical destabilization of African easterly waves (AEWs) by Saharan mineral dust (SMD) aerosols. The framework is built on coupled equations for quasigeostrophic potential vorticity (PV), temperature, and SMD mixing ratio. A perturbation analysis yields, for a subcritical, but otherwise arbitrary, zonal-mean background state, analytical expressions for the growth rate and frequency of the AEWs. The expressions are functions of the domain-averaged wave activity, which is generated by the direct radiative effects of the SMD. The wave activity is primarily modulated by the Doppler-shifted phase speed and the background gradients in PV and SMD.

Using an idealized version of the Weather Research and Forecasting (WRF) Model coupled to an interactive dust model, a linear analysis shows that, for a subcritical African easterly jet (AEJ) and a background SMD distribution that are consistent with observations, the SMD destabilizes the AEWs and slows their westward propagation, in agreement with the theoretical prediction. The SMD-induced growth rates are commensurate with, and can sometimes exceed, those obtained in previous dust-free studies in which the AEWs grow on AEJs that are supercritical with respect to the threshold for barotropic–baroclinic instability. The clarity of the theoretical framework can serve as a tool for understanding and predicting the effects of SMD aerosols on the linear instability of AEWs in subcritical, zonal-mean AEJs.

© 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: Terrence R. Nathan, trnathan@ucdavis.edu

Abstract

A theoretical framework is presented that exposes the radiative–dynamical relationships that govern the subcritical destabilization of African easterly waves (AEWs) by Saharan mineral dust (SMD) aerosols. The framework is built on coupled equations for quasigeostrophic potential vorticity (PV), temperature, and SMD mixing ratio. A perturbation analysis yields, for a subcritical, but otherwise arbitrary, zonal-mean background state, analytical expressions for the growth rate and frequency of the AEWs. The expressions are functions of the domain-averaged wave activity, which is generated by the direct radiative effects of the SMD. The wave activity is primarily modulated by the Doppler-shifted phase speed and the background gradients in PV and SMD.

Using an idealized version of the Weather Research and Forecasting (WRF) Model coupled to an interactive dust model, a linear analysis shows that, for a subcritical African easterly jet (AEJ) and a background SMD distribution that are consistent with observations, the SMD destabilizes the AEWs and slows their westward propagation, in agreement with the theoretical prediction. The SMD-induced growth rates are commensurate with, and can sometimes exceed, those obtained in previous dust-free studies in which the AEWs grow on AEJs that are supercritical with respect to the threshold for barotropic–baroclinic instability. The clarity of the theoretical framework can serve as a tool for understanding and predicting the effects of SMD aerosols on the linear instability of AEWs in subcritical, zonal-mean AEJs.

© 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: Terrence R. Nathan, trnathan@ucdavis.edu
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