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Original Research Papers

Numerical simulations of a severe rainfall event over the Eastern Cape coast of South Africa: sensitivity to sea surface temperature and topography

Authors:

A. T. Singleton,

Oceanography Department, University of Cape Town, ZA
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C. J. C. Reason

Oceanography Department, University of Cape Town, ZA
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Abstract

The intense precipitation event over East London, South Africa, on 15–16 August 2002 is investigated using a mesoscale model (MM5) and its sensitivity to sea surface temperature (SST) and topography tested. Over 300 mm of rain fell in 24 h over East London as compared to the August average of 78 mm. The intense precipitation resulted from a cut-off low system aloft and the formation of a low-level jet (LLJ) near the surface.

The MM5 control simulation indicated that the intense precipitation was due to the ascent of moist air at the leading edge of the LLJ, which advected warm moist air at low levels onto the coastal mountains and was enhanced by the formation of a meso-beta scale low-pressure system just off the coast. The ascent at the leading edge of the LLJ formed the ascending arm of a convective circulation cell.

Sensitivity experiments with MM5 indicated that the warm core of the Agulhas Current contributed to the formation of the meso-beta scale low, while the mesoscale structure of the SST field was important in determining its location and that of the LLJ, and therefore the precipitation in the model. Most of the moisture originated from the Agulhas Current region. The South African topography was found to influence the location of the LLJ via trapping a near-surface warm trough on the eastern side of the Drakensberg mountains. We suggest that deficiencies in the control experiment may have been due to inaccuracies in using a weekly mean SST field to force the model at the lower boundary.

How to Cite: Singleton, A.T. and Reason, C.J.C., 2006. Numerical simulations of a severe rainfall event over the Eastern Cape coast of South Africa: sensitivity to sea surface temperature and topography. Tellus A: Dynamic Meteorology and Oceanography, 58(3), pp.355–367. DOI: http://doi.org/10.1111/j.1600-0870.2006.00180.x
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  Published on 01 Jan 2006
 Accepted on 9 Jan 2006            Submitted on 2 Mar 2005

References

  1. Barry , R. G. and Chorley , R. J. 1992 . Atmosphere, Weather and Climate, 6th Edition . Routledge , New York , 392 pp .  

  2. Chen , F. and Dudhia , J. 2001a . Coupling an advanced land-surface/hydrology model with the Penn State/NCAR MM5 modeling system. Part I: Model implementation and sensitivity. Mon. Wea. Re v . 129 , 569 – 585 .  

  3. Chen , F. and J. Dudhia , 2001b. Coupling an advanced land-surface/hydrology model with the Penn State/NCAR MM5 modeling system. Part II: Preliminary model validation. Mon. Wea. Rev . 129 , 587 – 604 .  

  4. Colle , B. A. and Mass , A. F. 2000 . The 5-9 February 1996 flooding event over the Pacific Northwest: Sensitivity studies and evaluation of the MM5 precipitation forecast. Mon. Wea. Re v . 128 , 593 – 617 .  

  5. Cressman , G. 1959 . An operational analysis system. Mon. Wea. Re v . 87 , 367 – 374 .  

  6. Crimp , S. J. and Mason , S. J. 1999 . The extreme precipitation event of 11-16 February 1996 over South Africa . Met. Atmos. Phys . 70 , 29 – 42 .  

  7. Estie , K. E. 1981 . The Laingsburg flood disaster of January 1981 . South African Weather Bureau Newsletter 383 , 19 – 32 .  

  8. Grell , G. A. 1993 . Prognostic evaluation of assumptions used by cumulus parameterizations. Mon. Wea. Re v . 121 , 764 – 787 .  

  9. Grell , G. A. , Dudhia , J. and Stauffer , D. R. 1994 . A description of the fifth generation Penn State/NCAR mesoscale model (MM5). NCAR Tech. Note NCAR/TN-398 STR , 122 pp .  

  10. Haywood , L. Q. and Van den Berg , H. 1968 . Die Port Elizabeth storeëns van 1 September 1968 . SouthAfrican WeatherBureau News/etter 234 , 157 – 169 .  

  11. Haywood , L. Q. and Van den Berg , H. 1970 . The Eastern Cape floods of 24-28 August 1970 . South African Weather Bureau Newsletter 257 , 129 – 141 .  

  12. Hong , S.-Y. and Pan , H.-L. 1996 . Nonlocal boundary layer vertical dif-fusion in a medium-range forecast model. Mon. Wea. Re v . 124 , 2322 – 2339 .  

  13. Hoskins , B. J. , McIntyre , M. E. and Robertson , A. W. 1985 . On the use and significance of isentropic potential voracity maps . Quart. J. Roy. Met. Soc . 111 , 877 – 946 .  

  14. Jury , M. R. , Valentine , H. R. and Lutjeharms , J. R. E. 1993 . Influence of the Agulhas Current on summer rainfall along the southeast coast of South Africa . J. AppL Meteor 32 , 1282 – 1287 .  

  15. Kleinschmidt , E. 1950a . Uber aufbau und entstehung von zyklonen I . Teil. Meteor Rundschau . 3 , 1 – 7 .  

  16. Kleinschmidt , E. 1950b . Uber aufbau und entstehung von zyklonen II . Teil. Meteor. Rundschau . 3 , 54 – 61 .  

  17. Mason , S. J. 1995 . Sea surface temperature-South African rainfall as-sociations, 1910-1989 . Int. J. Climatol . 15 , 119 – 135 .  

  18. Morgan , M. C. and Neilsen-Gammon , J. W. 1998 . Using tropopause maps to diagnose midlatitude weather systems. Mon. Wea. Re v . 126 , 2555 – 2579 .  

  19. Palmén , E. and Newton , C. 1969 . Atmospheric circulation systems . Aca-demic Press , New York , 603 pp .  

  20. Reason , C. J. C. 2001 . Evidence for the influence of the Agulhas Current on regional atmospheric circulation patterns . J. Clim . 14 , 2769 – 2778 .  

  21. Reason , C. J. C. and Mulenga , H. M. 1999 . Relationships between South African rainfall and SST anomalies in the South West Indian Ocean . Int. J. Climatol . 19 , 1651 – 1673 .  

  22. Romero , R. , Doswell DI, C. A. and Ramis , C. 2000 . Mesoscale numerical study of two cases of long-lived quasi-stationary convective systems over eastern Spain. Mon. Wea. Rev . 128 , 3731 – 3751 .  

  23. Rouault , M. , White , S. A. , Reason , C. J. C. , Lutjeharms , J. R. E. and Jobard , I. 2002 . Ocean-atmosphere interaction in the Agulhas Current region and a South African extreme weather event . Wea. Forecasting 17 , 655 – 669 .  

  24. Taljaard , J. J. 1985 . Cut-off lows in the South African region . South African Weather Bureau Tech. Paper 14 , 153 .  

  25. Triegaardt , D. O. , Terreblanche , D. E., van Heerden , J. and Laing , M. V. 1988 . The Natal floods of September 1987. South African Weather Bureau Tech. Paper 19 , 62.  

  26. Walker , N. D. 1990 . Links between South African summer rainfall and temperature variability of the Agulhas and Benguela Current systems . J. Geophys. Res . 95 , 3297 – 3319 .  

  27. Yeh , H.-C. and Chen , Y.-L. 2002 . The role of offshore convergence on coastal rainfall during TAMEX IOP 3. Mon. Wea. Re v . 130 , 2709 – 2730 .  

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