Vertical resolution increase of the Japan Meteorological Agency Global Spectral Model
Various modifications are applied to current operational model described in JMA (2013). The changes contain an introduction of two-stream approximation for long wave radiation scheme, changing the application criteria of energy correction term in convective parameterization, an upgrade of monthly ozone climatology in the mesosphere, adding 2nd-order linear horizontal diffusion in the divergence equation and adjusting 4th-order linear diffusion as a sponge layer around the model top region, and modification of the Rayleigh friction. The forecast score statistics shows the overall improvements in the northern hemisphere and the stratosphere but slight degradation for some elements in the southern hemisphere and the tropics. Model forecast characteristics change significantly due to the modification of energy correction term in convective parameterization, especially in the tropics. In the stratosphere and mesosphere, improvements result from two-stream approximation long wave radiation scheme, an upgrade of ozone climatology, and modification of horizontal diffusion.
To achieve better forecast performance in the middle atmosphere, a non-orographic gravity wave drag scheme based on Scinocca (2003) is under development and testing for the new GSM. The revised model successfully reproduces QBO in the tropical stratosphere although its period is shorter and amplitude is weaker than observed. The model climatology of the middle atmosphere is also improved compared to the results with Rayleigh friction.