An Overview of the Swell Dynamics and Their Implications over Africa: Significance to Climate Change and Forcing

Main Article Content

Modise Wiston


There is a growing interest in climate dynamics as the quantity and quality of new observational and theoretical applications are increasing. The ideas involved in understanding large-scale atmosphere-land-ocean dynamics and their interactions continue to hold special fascination because of their central importance for both theoretical and practical applications. This paper presents a theoretical assessment of the African swell dynamics imploring atmospheric formulation. Africa exhibits substantial inter-annual and inter-decadal climatic variability due to cyclone activity, storm surges and sea waves. Most of these surges and corresponding swell trains form over the tropical environment as easterly waves propagate westward across the Indian Ocean primarily between 10° and 20° S, termed source region. Localized sea surface temperatures (SSTs) and ocean upwelling play a vital role to provide moist enthalpy to power the surges. Also, multi-decadal variations in major wave activity are associated with SST changes in the Atlantic because tropical North Atlantic correlates positively with major hurricane activity. A key remote factor is temperature variability in the central and eastern equatorial Pacific associated with El Niño Southern Oscillation. The continuous erosion, perennial ocean surges, coastal swells and associated flooding due to the wave energy and its pounding effect are of great concern. Just like in most parts of the world where development of these systems is critical, they need to be closely watched particularly over southern Africa. 

Climate dynamics, swell train, source region, wave energy, ocean surge

Article Details

How to Cite
Wiston, M. (2019). An Overview of the Swell Dynamics and Their Implications over Africa: Significance to Climate Change and Forcing. International Astronomy and Astrophysics Research Journal, 1(1), 1-20. Retrieved from
Review Article


Mather A, Stretch DD. A perspective on sea level rise and coastal storm surge from southern and eastern Africa: A case study near Durban, South Africa. Water. 2012;2: 237-259.
DOI: 10.3390/w4010237

World Meteorological Organisation (WMO). The Global Climate 2001-2010: A Decade of Climate Extremes" WMO-No. 1103.

Lutjeharms JRE, Monteiro PMS, Tyson PD, Obura D. The oceans around southern Africa and regional effects of global change. South African Journal of Science. 2001;119.

Wiston M, Mphale KM. Mesoscale convective systems: A case scenario of the ‘heavy rainfall’ event of 15–20 January 2013 over Southern Africa. Climate. 2019; 7:73.
DOI: 10.3390/cli7060073

Fitchett JM, Grab SW. A 66-year tropical cyclone record for south-east Africa: Temporal trends in a global context. Int. J. Climatol. 2014;34:3604–3615
DOI: 10.1002/joc.3932

Hall R, Erdélyi R, Hanna E, Jones JM, Scaife AA. Drivers of north Atlantic polar jet stream variability. Int. J. Climatol; 2014.
DOI: 10.1002/joc.4121

Rowell S, Weather, current and routing brief. The Clipper 11/12 Round the World Race; 2011.

Quilfen Y, Yurovskaya M, Chapron B, Ardhuin F. Storm waves focusing and steepening in the Agulhus current: Satellite observations and modeling. Remote Sensing Environment. 2018;216:561–571.

Millner A, Washington R. What determines perceived value of seasonal climate forecasts? A theoretical analysis. Global Environmental Change; 2010.

Moyo EN, Nangombe S. Southern Africa’s 2012-13 Violent Storms: Role of Climate Change. 2015; Porcedia IUTAM. 2015;17: 69–78.

Woodroffe CD. Coasts: Form, process and evolution. Cambridge University Press; 2002.

Zaitchik BF, Levin NE. Understanding the dynamics of the tropical African climate. 2013; Workshop on Climate Dynamics of Tropical Africa; Baltimore, MD, 15–16 November 2012. EOS. 2013;94(23).

Bhowmick SA, Kumar R, Chaudhuri S, Sarkar A. Swell propagation over Indian Ocean Region. Int. J. Ocean Clim. Sys. 2011;2(2):87–99.

Landsea CW. A climatology of intense (or major) Atlantic hurricanes. Mon. Wea. Rev. 1993;121:1703–1713.
DOI: 10.1175/1520-0493(1993)121,1703

Rossouw M, Terblanche L, Moses J. General characteristics of long waves around the south African Coast. Stellenbosch, South Africa. CSIR; 2013.

Gray WM. Tropical cyclone genesis. Colorado State University Department of Atmospheric Science Paper No. 234. Colorado State University: Fort Collins. 1975;1–121.

Shultz JM, Shephered JM, Bagrodia R, Espinel Z. Tropical cyclone in a year of rising global temperatures and a strengthening El Nino. Disaster Health Briefing; 2014.

Holton JR, Pyle J, Curry JA. Encyclopedia of Atmospheric Sciences; 2003.

Marks FD. Hurricanes. Hurricane Research Division; 2003.

Vethamony P, Rashmi R, Aboobacker VM. Recent studies on wind seas and swells in the Indian Ocean: A review. 2013;4.

Joubert JR, van Niekerk JL. South African wave energy resources data: A case study. Center for Renewable and Sustainable Energy Studies; 2013.

Forristall GZ, Ewans K, Olagnon M, Prevosto M. The West Africa swell project (WASP). Proceedings of the 32nd International Conference on Ocean, Offshore and Arctic Engineering. OMAE2013. Nantes, France; 2013.

Thurman HV, Trujillo AP. Waves and Water Dynamics. Chapter 8. Essentials of Oceanography. 7th Ed. Prentice Hall, Indiana; 2001.

Wang Z, Montgomery MT, Fritz C. A first look at the structure of the wave pouch during the 2009 PREDICT-GRIP dry runs over the Atlantic. Mon. Wea. Rev. 2012; 140:1144–1163.

Alves JHGM. Numerical modeling of ocean swell contributions to the global wind-wave climate. Ocean Modelling; 2005.

Fan Y, Griffiths MS, Lin SJ, Hemer M. Simulated global swell and wind-sea climate and their responses to anthropogenic climate change at the end of the twenty-first century. Journal of Climate. 2014;27:3516–3536.

Freias EGG, Lorenzzetti JA, Chapron B. Swell and wind-sea distributions over the mid-latitude and tropical north Atlantic for the period 2002-2008. International Journal of Oceanography. 2012;Article ID 306723.

Carrrasco A, Semedo A, Isachsen PE, Christensen KH, Saetra Ø. Global surface wave drift climate from ERA-40: The contributions from wind-sea and swell. Ocean Dynamics. 2014;64(12):1815–1829.

Reddy-Davis CL, Vincent K. Climate risk and vulnerability: A handbook for southern Africa. (2nd Ed), CSIR, Pretoria, South Africa; 2017.
[ISBN 978-0-620-76522-0]

Lesolle D. Adaptation to global warming and resulting climatic changes. 2nd AIACC Workshop, 24–27. Dakar, Senegal; 2004.

World Meteorological Organization. Edition. Annual Summary of Global Tropical Cyclone Season. 2000; WMO/TD-No. 1082. Report No. TCP-46.

Reason CJC, Keibel A. Tropical cyclone eline and its unusual penetration and impacts over the southern african mainland. Weather Forecasting. 2004;19: 789–805.

Kadomura H. Climate anomalies and extreme Events in Africa in 2003, including heavy rains and floods that occurred during northern hemisphere summer. African Study Monographs, Suppl. 2005; 30:165–181.

Barbosa HA. The African easterly waves and their influence on hurricane activity in the tropical north Atlantic: An assessment of hurricane Bill (2009) using SERVIRI data. CWG Workshop, 17–19 April 2018, Ljubljana, Slovenia; 2018.

Trapp RJ. Formation and development of convective storms. In: Oxford Research Encyclopedia of Climate Science (Ed. H. Storch). Oxford University Press, Oxford; 2018.

Weisman MJ, Klemp JB. Characteristics of isolated convective storms. In: Ray PS. (eds) Mesoscale Meteorology and Forecasting. American Meteorological Society. Boston, MA; 1986.

Neto CPS, Barbosa HA, Beneti CAA. A method for convective storm detection using satellite data. Atmósfera. 2016;29: 343–358.

Barnes GM. Meteorological hazards in the Tropics: Severe convective storms and flash floods. In Tropical Meteorology, Encyclopedia of Life Support Systems (EOLSS). UNESCO, Paris, France. 2010;109.

Dotzek N, Groenemeijer P, Feuerstein B, Holzer AM. Overview of ESSL’s severe convective storms research using the European Severe Weather Database ESWD; 2008.

LaCasce JH. Atmosphere-ocean dynamics. E-book; 2013.

Johnson RH, Mapes BE. Chapter 3: Mesoscale processes and severe convective weather. In Severe Convective Storms by Charles A. Doswell. Meteoro-logical Monographs, E-book; 2011.

Holton JR. An Introduction to Dynamic Meteorology. Elsevier Press; 2004.

Wang Y. Hurricane dynamics. Encyclo-pedia of Atmospheric Sciences, 2nd Ed. 2016;6.

Charney JG, Eliassen A. On the growth of the hurricane depression. Journal of the Atmospheric Sciences. American Meteoro-logical Society. 1963;21(1):68–75.

Willoughby HE. Tropical cyclone eye thermodynamics. Mon. Wea. Rev. 1998; 126:3053–3067.

Gray WMCW, Landsea PW, Mielke Jr., Berry KJ. Predicting Atlantic seasonal hurricane activity 6–11 Months in Advance. Weather Forecasting. 1992;7:440–455.

Gray WMCW, Landsea PW. Mielke Jr., Berry KJ. Predicting Atlantic basin seasonal tropical storm activity by June 1. Wea. Forecasting. 1994a;9:103–115.

Gray WMCW, Landsea PW, Mielke Jr., Berry KJ. Extended range forecasting of atlantic seasonal hurricane activity for 1995, as of 30 November 1994. Department of Atmospheric Sciences, Colorado State University. Fort Collins, CO. 1994;9.

Smith RK. Lectures on dynamical meteorology. e-book. Version: June 16; 2014.

Dickinson R, Henderson-Sellers A, Kennedy P, Wilson M. Biosphere-atmosphere transfer scheme (BATS) for the NCAR community climate model. NCAR Tech Note, NCAR/TN-275+STR; 1986.

Emanuel KA. On thermally direct circulations in moist atmospheres. Journal of the Atmospheric Sciences.1995;52(15): 1529–1534.

Jury MR, Enfield DB, Mélice JL. Tropical monsoons around Africa: Stability of El Niño-Southern Oscillation associations and links with continental climate. J. Geophy. Res. 2002;107.
DOI: 10.1029/20000JC000507

Zhisheng A, et al. Global Monsoon Dynamics and Climate Change. Annu. Rev. Earth Planet. Sci. 2015;43:29–77.

Läderach A, Sodemann H. A revised picture of the atmospheric moisture residence time. Geo. Res. Lett.; 2016.
DOI: 10.1002/2015GL067449

Plumb RA, Hou AY. The response of a zonally symmetric atmosphere to subtropical thermal forcing: Threshold behavior. J. Atmos. Sci. 1992;49:1790–1799.

Wu G, Liu Y, Dong B, Liang X, Duan A, Bao Q, Yu J. Revisiting Asian monsoon formation and changes associated with Tibetan Plateau forcing: I. Formation. Clim Dyn. 2012;39:1169–1181.
DOI: 10.1007/s00382-012—1334-z

Cook KH. Large-scale atmospheric dynamics and Sahelian precipitation. Atmospheric Science Program, Cornell University, Ithaca, N. Y., Journal of Climate. 1996;1137–1152.

Van de Berg WJ. Potential vorticity: The swirling motion of geophysical fluids. Chapter 12. Vorticity in the Ocean; 2018.

Christenson CE, Martin JE, Handlos ZJ. A synoptic climatology of northern hemisphere, cold season polar subtropical jet superposition events. Journal of Climate. 2017;30:7231–7246.

Shulmeister J, Goodwin I, Renwick J, Harle K, Armand L, Mcglone MS, Cook E, Dodson J, Hesse PP, Mayewski P, Curran M. The southern hemisphere westerlies in the Australasian sector over the last cycle: A synthesis. Quaternary International Journal. 2004;118–119:23–53.

Stan C, Straus DM, Frederiksen JS, Lin H, Maloney ED, Schumacher C. Review of tropical-extratropical teleconnections on intraseasonal timescales. Reviews of Geophysis. 2017;55.

van der Wiel K, Matthews AJ, Joshi MM, Stevens DP. The influence of diabatic heating in the South Pacific convergence zone on Rossby wave propagation and the meanflow. Quarterly Journal of the Royal Meteorological Society. 2016;142:901–910.


Lin YL, Liu L, Tang G, Spinks J, Jones W. Origins of the pre-tropical storm Debby 2006 African easterly wave-mesoscale convective system. Meteorol Atmos Phys; 2013.
DOI: 10.1007/s00703-013-0248-6

Ferreira RN, Rickenbach T, Williams E, Guy N. African easterly waves and Atlantic hurricanes; 2009.

Bannon PR. On the dynamics of the east african jet I. Simulation of the Mean Conditions for July. Journal of Atmospheric Sciences. 1979;36(II):2139–2152.

American Meteorological Society.

Grist JP, Nicholson SH. Easterly waves over Africa. Part II: Observed and Modeled Contrasts between Wet and Dry Years. Mon. Wea. Rev. 2001;130:212–225.

Hagos SM, Cook KH. Dynamics of the West African monsoon jump. J. Clim. 2007;20:5264–5284.
DOI: 10.1175/2007JCLI1533.1

Cornforth RJ, Hoskins BJ, Thorncroft CD. The impact of moist processes on the African easterly jet–African easterly wave system. QJR Meteorol Soc. 2009;135: 894–913.

Klein C, Heinzeller D, Bliefernicht J, Klunstmann H. Variability of West African monsoon patterns generated by a WRF multi-physics ensemble. Clim Dyn. 2015; 45:2733–2755.
DOI: 10.1007/s00382-015-2505-5

Thorncroft CD, Hodges K. African easterly wave variability and its relationship to Atlantic tropical cyclone activity. J. Climate. 2001;14:1166–1179.

Burpee RW. Characteristics of African Easterly Waves. In: Johnson RH, Houze RA. (eds) A half century of progress in meteorology: A tribute to Richard reed. Meteorological Monographs. American Meteorological Society. Boston, MA; 2003.

Skinner CB, Diffenbaugh NS. Projected changes in African easterly wave intensity and track in response to greenhouse forcing. Proc. Natl Acad. Sci. USA. 2014; 111:6882–6887.

Dieng AL, Sall SM, Eymard L, Leduc-Leballeur M, Lazar A. Trains of African easterly waves and their relationship to tropical cyclone genesis in the eastern Atlantic. Mon. Wea. Rev., 2017;145:599– 616.

Bain CL, Parker DJ, Dixon N, Fink AH, Taylor CM, Brooks B, Milton SF. Anatomy of an observed African easterly wave in July 2006. Q. J. R. Meteorol. Soc. 2011;137:923–933.
DOI: 10.1002/qj.812

Burpee RW. Characteristics of North African easterly waves during the summers of 1968 and 1969. J. Atmos. Sci. 1974;31: 1556–1570.

Pasch RJ, Avila LA, Jiing JG. Atlantic tropical systems of 1994 and 1995: A comparison of a quiet season to a near-record-breaking one. Mon. Wea. Rev., 1998;126:1106–1123.
DOI: 10.1175/1520-0493(1998)126,1106

White JD. Mechanisms of African easterly wave genesis; 2018.

Kruger AC, Golinger AM, Retief JV, Sekele S. Strong wind climatic zones in South Africa. Wind and Structures. 2010;13(1).

Ghil M, Chekroun MD, Simonnet E. Climate dynamics and fluid mechanics: Natural variability and related uncerta-inities. Physica D: Nonlinear phenomena, Special Issue on the Euler Equations: 250 Years; 2010.
DOI: 10.1016/j.physd.2008.03.036

Lucarini V, Blender R, Herbert C, Ragone F, Pascale S, Wouters J. Mathematical and physical ideas for climate science. Reviews of Geophysics; 2014.
DOI: 10.1002/2013RG000446.