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Global Spectrum Model


Leader of the Project: Dr. Ming-Dean Cheng

Current Model :( Jan 2004)

  * Data assimilation

  Scheme: 3-dimensional variational method (derived from NCEP  Spectral Statistical   Interpolation scheme)

  Update cycle: 6-hourly

* Dynamics

   Horizontal resolution: Triangle truncation 179 waves

    Vertical resolution: 30 sigma levels

    Time step: 480 sec

    Diffussion: 4th order horizontal diffusion

    Prognostic variables: vertical vorticity, horizontal divergence, surface pressure, specific humidity, virtual potential temperature

* Physics

Radiation: Harshvardhan et al.(1987)

Cumulus: relax Arakawa-Schubert scheme(Moothi and Suarez 1992)

Large scale precipitation

Shallow convection: Li(1994)

Vertical turbulence mixing: TKE-e scheme(Detering and Etling 1985)

Surface flux: similarity theory(Businger 1971)

Soil model: one layer model with restoring force nudging to climate

Gravity wave drag: Palmer et al.(1986)

 

 

Operational Procedure:

Now the global model is running four times a day.

For the 00Z run, model performs a 120 hours forecast.

For the 12Z run, model performs a 192 hours forecast.

For the 06Z and 18Z, model performs a 6 hours forecast.

Future task:

Enhance the use of new radiance data of new satellites.

Upgrade soil model from one layer to multi-layer.

Improve moist physical process by TRMM information.

Increase the resolution from T179L30 to T239L40.

Develop cloud scheme to resolve grid-scale precipitation.

 

Reference:

Businger, J. A., J. C. Wyngaard, Y. Izumi, and E. F. Bradley, 1971: Flux-profile relationships in the atmospheric surface layer, J. Atmos. Sci, 28, 181-189.

Detering, H. W., and D. Etling, 1985: Application of the E- turbulence model to the atmostheric boundary layer. Bound –Layer Meteor., 33, 113-133.

Harshvardhon, R. Davies, D. A. Randall, and T. G.. Corsetti, 1987: A fast radiation parameterization for atmospheric circulation models, J. Geophys. Res. 92, 1009-1016.

Li, J.-L., 1994: On shallow cumulus parameterization scheme for large-scale planetary boundary layers, Ph.D. thesis, University of Wisconsin-Madison, pp203.

Liou, Chi-Sann, Jen-Her Chen, Chuen-Teyr Terng, Feng-Ju Wang, Chin-Tzu Fong, Thomas E. Rosmond, Hong-Chi Kuo, Chih-Hui Shiao, and Ming-Dean Cheng, 1997: The second-generation global forecast system at the central weather bureau in Taiwan. Weather and Forecasting, 3, 653-663.

Moothi, S., and M. J. Suarez, 1992: Relaxed Arakawa-Schubert: A parameterization of moist convection for general circulation models. Mon. Wea. Rev., 120, 978-1002.

Palmer, T. N., G. Shutts, and R. Swinbank, 1986: Alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parameterization. Quart. J. Roy. Meteor. Soc., 112, 1001-1039.