MYNN (Improved Mellor-Yamada) Level-3 Model

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• Fortran code (latest version, Feb. 2009): MYNNmodel.f [Footnote]
• Fortran code (version 1.1, Dec. 2005): MYmodel.f
• Fortran code (version 1.0, Aug. 2005): MYver10.f
• Note: Whenever you use this code, please quote some of the references below.

References

• Nakanishi, M. and H. Niino, 2009: Development of an improved turbulence closure model for the atmospheric boundary layer. J. Meteor. Soc. Japan, 87, 895-912.
• Nakanishi, M. and H. Niino, 2006: An improved Mellor-Yamada Level-3 model: Its numerical stability and application to a regional prediction of advection fog. Boundary-Layer Meteor., 119, 397-407.
• Nakanishi, M. and H. Niino, 2004: An improved Mellor-Yamada Level-3 model with condensation physics: Its design and verification. Boundary-Layer Meteor., 112, 1-31.
• Nakanishi, M., 2001: Improvement of the Mellor-Yamada turbulence closure model based on large-eddy simulation data. Boundary-Layer Meteor., 99, 349-378.

ChangeLog

• 2009-02-12 * Added tcd(nz+1)=0.0 and qcd(nz+1)=0.0 to avoid unexpected heating due to the countergradient terms.
• 2009-01-13 * Added a restriction of elf (correspondent to a length scale in the free atmosphere), changed the Crank-Nicholson scheme to the full-implicit scheme and then provided a sample program of the time-integration scheme, and changed pdt(1)=pdt1-pdt(2) etc to pdt(1)=pdt(2) etc and thus deleted sgm(1)=sgm(2) for the level-2.5 model in sub mym_condensation. [diff MY->MYNN]
• 2005-12-22 * Modified two closure constants (C_2=0.75 and C_3=0.352) and stability functions for turbulent kinetic energy and scalar variances (S_q=3*S_M and S_tl=S_qw=S_tq=S_M), and simplified the scheme for ensuring the realizability.
• 2005-09-25 * Announced release of MYmodel.

Acknowledgements

• This work was supported by Research Revolution 2002 (RR2002) of Project for Sustainable Coexistence of Human, Nature and the Earth of the MEXT of the Japanese Government.
• The authors thank Drs. Kazuo Saito and Tabito Hara, Japan Meteorological Agency, and Drs. Minoru Chikira and Akira Noda, Frontier Research Center for Global Change, for evaluating the MYNN model and promptly incorporating it into their models.
• The authors also thank Dr. Mariusz Pagowski, National Oceanic and Atmospheric Administration, for incorporating the MYNN model into the Weather Research and Forecasting (WRF) model.

Footnotes

For 3rd level simulation with a coarse grid of a few tens of kilometers, numerical instability often occurs. The cause of this instability has not been clarified yet, but mostly it can be avoided through the following changes:

<       enum = qdiv*e6c*( t3sq-t2sq )
---
>       if ( t2sq .ge. 0.0 ) then
>         enum = max( qdiv*e6c*( t3sq-t2sq ), 0.0 )
>       else
>         enum = min( qdiv*e6c*( t3sq-t2sq ), 0.0 )
>       end if

<       enum = qdiv*e6c*( c3sq-c2sq )
---
>       enum = max( qdiv*e6c*( c3sq-c2sq ), 0.0 )

where c2sq is nonnegative and a change for r2sq is the same as that for t2sq.