1. introduction

This is a documentation of the research version of the National Meteorological Center (NMC) global spectral Medium Range Forecast (MRF) model developed by J. Sela (Sela 1982, 1988). The research version was developed by M. Kanamitsu and R. Kistler and differs from the MRF model in its use of extensive model diagnostics which greatly facilitate model development and experimentation. It has also been used in the Dynamical Extended Range Forecasting experiment (DERF) currently underway at NMC (Tracton et al., 1988; Kistler et al., 1988).

The MRF model has undergone many changes since it became operational in 1985, and will continue to do so (Bonner, 1988; Bonner et al., 1986). The present documentation describes changes that were introduced into the operational MRF model on August 12, 1987, including an appropriate diurnal cycle and improved computation of surface fluxes. Additional documented changes which became operational in the MRF 87 model are gravity wave drag parameterization, a new time scheme for vertical diffusion and surf ace temperature, and an increase in the horizontal resolution from rhomboidal R40 to triangular T80 truncation (Sela, 1988; Alpert et al., 1988; and Kalnay and Kanamitsu, 1988). Finally, on January 20, 1988, the number of moisture containing layers has been increased to include all the levels of the model (NWS, 1987).

At the time of this writing a number of potential model improvements are being developed or under consideration. The possible changes to the physical parameterizations include a scheme for cloud-radiation interaction (Campana and Caplan, 1988), schemes to improve surface evaporation and soil physics [Mahrt et al., 1988; Sellers et al., 1985; Shukla et al., 1988] and alternative cumulus convection parameterizations (Pan and Mahrt, 1988; Sud et al., l988; Albrecht et al., 1987); and the inclusion of cloud liquid water as a prognostic variable. We are also testing more efficient time schemes for horizontal advection, a modification of the current "silhouette" orography, a new formulation of the hydrostatic equation, a time splitting scheme for the physical parameterization, a correction of systematic errors (Saha and Alpert, 1988), a revision of the numbers and location of the vertical layers and a semi-lagrangian scheme for the moisture (Williamson and Rasch, 1988). These modifications, if adopted operationally, will be documented in forthcoming addenda to this volume. The documentation has been written in two parts. The present first volume includes a detailed description of all the components of the model (hydrodynamics, surface and atmospheric physics) as well as of the surface fields, the model structure and a model user's guide. Each chapter of this volume has been written by a different staff member. As a result different sections of the documentation are written in very different styles, but we believe that this should not detract from its usefulness.

A second volume, prepared by G. White, will contain a detailed description of the model's systematic characteristics, and a history of its evolution. We have not included the model code in the documentation because of its large volume, but it is available upon request to the Development Division of NMC.

It should be mentioned that two recently completed systems will also be documented in the near future. One of them is the "Automatic Map Launcher" created by M. Kanamitsu, which provides easy access to operational and research data sets and very flexible generation of maps. The second is the "Automatic Experiment Launcher", developed by R. Kistler, which will enhance researchers' ability to perform experiments with different parameterizations and model configurations. This work would have been impossible without the collaboration of many individuals and institutions that contributed to the development of the global spectral model at NMC. The NMC staff has contributed to model development throughout the years. Our greatest debt is to J. Sela, who developed operational MRF model and implemented most of its physics. The efforts of J. Brown and J. Gerrity, instrumental in the early phases of the development, and N. Phillips and J. Tuccillo, who provided the NGM Kuo-cumulus convection parameterization, deserve particular mention. A substantial number of the physical parameterizations were originally developed at GFDL and implemented at NMC through collaborative effort. We are particularly indebted to K. Miyakoda, S. Fels, D. Swartzkopf, J. Sirutis, and J. Mahlman for their generous support in this effort.

I would like to express my personal gratitude to Ken Campana, Jordan Alpert, and Hua-Lu Pan for editing this first edition of the documentation; to W. Bonner, for his encouragement and suggestions; to Crystal Rickett for her patient and efficient typing; and most especially to the members of the Medium Range Modeling Branch who grudgingly accepted to interrupt their more interesting and productive work in order to create this document.

References

Albrecht, B. A., V. Ramanathan, and B. A. Voville, 1987: The effects of cumulus moisture transports on the simulation of climate with a general circulation model. J. Atmos. Sci., 43, 2443-2462.

Alpert, J. C., M. Kanamitsu, P. M. Caplan, J. G. Sela, G. H. White, and E. Kalnay, 1988: Mountain induced gravity wave drag parameterization in the NMC Medium Range Forecast Model, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Bonner, W. D., G. H. White, M. S. Tracton, V. E. Kousky, and G. P. Cressman, 1986: Global analysis and prediction at NMC Washington, Second International Conference on Southern Hemisphere Meteorology, Wellington, New Zealand, December 1-5.

Bonner, W. D., 1988: Recent progress and future plans for numerical weather prediction at NMC, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Campana, K. A., and P. M. Caplan, 1988: Preliminary testing of a simple diagnostic cloud cover scheme on a medium range model, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Kalnay, E., and M. Kanamitsu, 1988: Time schemes for strongly nonlinear damping equations, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland. (Mon. Wea. Rev. accepted for publication.)

Kistler, R. E., E. Kalnay, and M. S. Tracton, 1988: Forecast agreement, persistence and forecast skill, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Mahrt, L., H.-L. Pan, P. Ruscher, C.-T. Chu, and K. Mitchell, 1988: Boundary layer parameterization for a global spectral model. Tech. Rept. No. AFGL-TR-87-0246, 210 pp. (Available from Air Force Geophysics Laboratory, Ha nscom, AFB, Massachusetts 01731.)

NWS, Technical Procedures Bulletin, #371, August 1987.

Pan, H.-L., and L. Mahrt, 1986: Interaction between soil hydrology and boundary-layer development. Bound.-Layer Meteor., 38, 185-202.

Saha, S., and J. C. Alpert, 1988: Systematic errors in an operational medium range forecast model and their correction, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Sela, J. G., 1982: The NMC Spectral Model, NOAA Tech. Rep. NWS-30, 36 pp.

Sela, J. G., 1988: The new NMC operational spectral model, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Sellers, P., Y.. Mintz, Y. C. Sud, and A. Dalcher, 1986: A simple biosphere model (SIB) for use within general circulation models., J. Atmos. Sci., 43, 505-531.

Sud, Y. C., H. M. Helfand, and M. A. Geller, 1988: A study of the influence of different cumulus parameterizations in the GLA GCM on its response to a sea surface temperature anomaly, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Tracton, M. S., and R. E. Kistler, 1988: Dynamic extended range forecasting (DERF) at NMC, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.

Williamson, D. L., and P. J. Rasch, 1988: Semi-Lagrangian moisture transport in global spectral models, Eighth Conference on Numerical Weather Prediction, February 22-26, Baltimore, Maryland.