• Betts, A. K., F. Chen, K. E. Mitchell, and Z. I. Janjic, 1997: Assessment of the land surface and boundary layer models in two operational versions of the NCEP Eta Model using FIFE data. Mon. Wea. Rev., 125 , 28962916.

    • Search Google Scholar
    • Export Citation
  • Black, T. L., 1994: The new NMC mesoscale model: Description and forecast examples. Wea. Forecasting, 9 , 265278.

  • Black, T. L., and Coauthors. 1997: Changes to the Eta forecast systems. NWS Tech. Proc. Bull. 441, 16 pp. [Available from Office of Meteorology, National Weather Service, 1325 East–West Highway, Silver Spring, MD 20910.].

    • Search Google Scholar
    • Export Citation
  • Bruyère, C. L., W. Jordaan, E. R. Poolman, and H. A. Riphagen, 2000: The influence of Eta model terrain representation on precipitation predictions. Part 2: Detailed investigation of a light rainfall event over the interior of South Africa. Directorate Research RES/64, 53 pp. [Available from South African Weather Bureau, Private Bag X097, Pretoria 0001, South Africa.].

    • Search Google Scholar
    • Export Citation
  • Chen, F., K. Mitchell, J. Schaake, Y. Xue, H. L. Pan, V. Koren, Q. Y. Duan, K. Ek, and A. Betts, 1996: Modelling of land-surface evaporation by four schemes and comparison with FIFE observations. J. Geophys. Res., 101 , 72517268.

    • Search Google Scholar
    • Export Citation
  • Colle, B. A., K. J. Westrick, and C. F. Mass, 1999: Evaluation of MM5 and Eta-10 precipitation forecasts over the Pacific Northwest during the cool season. Wea. Forecasting, 14 , 137154.

    • Search Google Scholar
    • Export Citation
  • Fritsch, J. M., and Coauthors. 1998: Quantitative precipitation forecasting: Report on the Eighth Prospectus Development Team, U.S. Weather Research Program. Bull. Amer. Meteor. Soc., 79 , 285299.

    • Search Google Scholar
    • Export Citation
  • Gallus, W. A., 1999: Eta simulations of three extreme precipitation events: Sensitivity to resolution and convective parameterization. Wea. Forecasting, 14 , 405426.

    • Search Google Scholar
    • Export Citation
  • Gollvik, S., 1999: On the effects of horizontal diffusion, resolution and orography on precipitation forecasting in a limited area model. Meteor. Appl., 6 , 4958.

    • Search Google Scholar
    • Export Citation
  • Janjić, Z. I., 1996a: The surface layer parameterization in the NCEP Eta model. Research Activities in Atmospheric and Oceanic Modelling, CAS/JSC Working Group on Numerical Experimentation, WMO/TD-No. 734, Rep. 23, 4.16–4.17. [Available from World Meteorological Organization, Case Postale 2300, CH-1211, Geneva 2, Switzerland.].

    • Search Google Scholar
    • Export Citation
  • Janjić, Z. I., . 1996b: The Mellor–Yamada level 2.5 scheme in the NCEP Eta model. Preprints, 11th Conf. on Numerical Weather Prediction, Norfolk, VA, Amer. Meteor. Soc., 333–334.

    • Search Google Scholar
    • Export Citation
  • McDonald, B. E., and J. D. Horel, 1998: Evaluation of precipitation forecasts from the NCEP's 10 km mesoscale Eta model. Preprints, 12th Conf. on Numerical Weather Prediction, Phoenix, AZ, Amer. Meteor. Soc., J27–J30.

    • Search Google Scholar
    • Export Citation
  • Mesinger, F., 1996: Improvements in quantitative precipitation forecasts with the Eta regional model at the National Centers for Environmental Prediction: The 48-km upgrade. Bull. Amer. Meteor. Soc., 77 , 26372649.

    • Search Google Scholar
    • Export Citation
  • Mesinger, F., Z. I. Janjić, S. Nickovic, D. Gavrilov, and D. G. Deaven, 1988: The step-mountain coordinate: Model description and performance for cases of Alpine lee cyclogenesis and for a case of an Appalachian redevelopment. Mon. Wea. Rev., 116 , 14931518.

    • Search Google Scholar
    • Export Citation
  • Nutter, P. A., and J. Manobianco, 1999: Evaluation of the 29-km Eta Model. Part I: Objective verification at three selected stations. Wea. Forecasting, 14 , 517.

    • Search Google Scholar
    • Export Citation
  • Paccagnella, T., S. Tibaldi, R. Buizza, and S. Scoccianti, 1992: High-resolution numerical modelling of convective precipitation over northern Italy. Meteor. Atmos. Phys., 50 , 143163.

    • Search Google Scholar
    • Export Citation
  • Poolman, E. R., H. A. Riphagen, R. D. Sewell, W. A. Krige, and N. de Villiers, 1994: Regional prediction at the South African Weather Bureau with NMC's step-mountain eta coordinate model. Preprints, 10th Conf. on Numerical Weather Prediction, Portland, OR, Amer. Meteor. Soc., 555–557.

    • Search Google Scholar
    • Export Citation
  • Riphagen, H. A., E. de Coning, L. R. van Hemert, W. J. Tennant, J. D. Gertenbach, and I. T. Hunter, 1996: Experience with an upgraded Eta assimilation and prediction system at the South African Weather Bureau. Preprints, 11th Conf. on Numerical Weather Prediction, Norfolk, VA, Amer. Meteor. Soc., 88–90.

    • Search Google Scholar
    • Export Citation
  • Riphagen, H. A., J. D. Gertenbach, C. L. Bruyère, and W. Jordaan, 1999: The 1998 upgrade of the Eta model at the South African Weather Bureau. Directorate Research RES/59, 50 pp. [Available from South African Weather Bureau, Private Bag X097, Pretoria 0001, South Africa.].

    • Search Google Scholar
    • Export Citation
  • Rogers, E., D. G. Deaven, and G. J. DiMego, 1995: The regional analysis system for the operational eta model: Original 80-km configuration and recent changes. Wea. Forecasting, 10 , 810825.

    • Search Google Scholar
    • Export Citation
  • Rogers, E., T. L. Black, D. G. Deaven, and G. J. DiMego, 1996: Changes to the operational “early” Eta analysis/forecast system at the National Centers for Environmental Prediction. Wea. Forecasting, 11 , 391413.

    • Search Google Scholar
    • Export Citation
  • Rogers, E., and Coauthors cited. 1998: Changes to the NCEP operational “early” Eta analysis/forecast system. [Available online at http://www.nws.noaa.gov/om/447/body.htm.].

    • Search Google Scholar
    • Export Citation
  • Staniforth, A., 1997: Regional modeling: A theoretical discussion. Meteor. Atmos. Phys., 63 , 1529.

  • Warner, T. T., R. A. Petersen, and R. E. Treadon, 1997: A tutorial on lateral boundary conditions as a basic and potentially serious limitation to regional numerical weather prediction. Bull. Amer. Meteor. Soc., 78 , 25992617.

    • Search Google Scholar
    • Export Citation
  • Yucel, I., W. J. Shuttleworth, and J. Washburne, 1998: Evaluating NCEP Eta Model–derived data against observations. Mon. Wea. Rev., 126 , 19771991.

    • Search Google Scholar
    • Export Citation
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Experiments with the NCEP Regional Eta Model at the South African Weather Bureau, with Emphasis on Terrain Representation and Its Effect on Precipitation Predictions

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  • 1 South African Weather Bureau, Pretoria, South Africa
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Abstract

This paper describes experiments with the National Centers for Environmental Prediction (NCEP) regional Eta Model, which runs operationally at the South African Weather Bureau. Experiments were designed to assess manual methods of improving the model representation of the surface topography at low resolutions where this might be feasible. The manual terrain modifications, applied in the then-operational 80-km Eta Model, involved either indirect alteration of the terrain through judicious rearrangement of the model coordinate surfaces, or the direct modification of the model terrain to accommodate meteorologically important features of the actual topography not well represented in the model. Also studied was the effect on the model terrain of changes in the horizontal grid configuration, with a potential for exploitation at higher model resolutions. Trials at higher resolutions also became available as part of a stepwise implementation of an upgrade to the 80-km system. This upgrade contained the important model enhancements installed at NCEP in January 1996 (new soil hydrology, land surface and viscous sublayer parameterization, and revised turbulence scheme) and February 1997 (notably changes to the radiation package and land surface model). A case of light nocturnal rainfall over Gauteng, linked to a topographical trigger and poorly forecast on the day, was the focus of a study to demonstrate the viability of the methods. Specifically, the link between changes in model topography and in precipitation forecasts from the model was investigated.

As expected, the model enhancement contained in the upgrade package provided the greatest impact on the precipitation predictions, and higher horizontal resolutions generally led to better representations of the terrain and more realistic forecasts. Nevertheless, the possibility exists of improving the high-resolution model topography yet further through modifications to the grid structure. If, however, higher horizontal resolutions are not affordable, it seems from this prototype study that slight grid shifts or manual modification of the model terrain could be useful and viable options. There is some potential in the judicious choice of the vertical coordinate structure, although what is good for one region might prove bad for another. There seems to be more potential in the manual correction of meteorologically significant deficiencies in the model terrain. These approaches are likely to be beneficial also in the presence of higher vertical resolution, which in itself may not be sufficient to improve the topography. Altering the terrain by hand, even at low resolutions, is a laborious task and only feasible at low resolutions but with the Eta Model being run on smaller machines, in centers with limited resources, this option seems to deserve consideration.

Corresponding author address: H. A. Riphagen, South African Weather Service, Room 5089, Forum Bldg., 159 Struben St., Pretoria 0002, South Africa. Email: hilarie@weathersa.co.za

Abstract

This paper describes experiments with the National Centers for Environmental Prediction (NCEP) regional Eta Model, which runs operationally at the South African Weather Bureau. Experiments were designed to assess manual methods of improving the model representation of the surface topography at low resolutions where this might be feasible. The manual terrain modifications, applied in the then-operational 80-km Eta Model, involved either indirect alteration of the terrain through judicious rearrangement of the model coordinate surfaces, or the direct modification of the model terrain to accommodate meteorologically important features of the actual topography not well represented in the model. Also studied was the effect on the model terrain of changes in the horizontal grid configuration, with a potential for exploitation at higher model resolutions. Trials at higher resolutions also became available as part of a stepwise implementation of an upgrade to the 80-km system. This upgrade contained the important model enhancements installed at NCEP in January 1996 (new soil hydrology, land surface and viscous sublayer parameterization, and revised turbulence scheme) and February 1997 (notably changes to the radiation package and land surface model). A case of light nocturnal rainfall over Gauteng, linked to a topographical trigger and poorly forecast on the day, was the focus of a study to demonstrate the viability of the methods. Specifically, the link between changes in model topography and in precipitation forecasts from the model was investigated.

As expected, the model enhancement contained in the upgrade package provided the greatest impact on the precipitation predictions, and higher horizontal resolutions generally led to better representations of the terrain and more realistic forecasts. Nevertheless, the possibility exists of improving the high-resolution model topography yet further through modifications to the grid structure. If, however, higher horizontal resolutions are not affordable, it seems from this prototype study that slight grid shifts or manual modification of the model terrain could be useful and viable options. There is some potential in the judicious choice of the vertical coordinate structure, although what is good for one region might prove bad for another. There seems to be more potential in the manual correction of meteorologically significant deficiencies in the model terrain. These approaches are likely to be beneficial also in the presence of higher vertical resolution, which in itself may not be sufficient to improve the topography. Altering the terrain by hand, even at low resolutions, is a laborious task and only feasible at low resolutions but with the Eta Model being run on smaller machines, in centers with limited resources, this option seems to deserve consideration.

Corresponding author address: H. A. Riphagen, South African Weather Service, Room 5089, Forum Bldg., 159 Struben St., Pretoria 0002, South Africa. Email: hilarie@weathersa.co.za

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