Applying The Deep Atmospheric Concept to The NCEP Mesoscale Spectrum Model: First Part - Implementation of a Generalized Coordinate

Less approximation is the trend for numerical weather prediction development. During the past decade, the deep atmospheric system has been developed in several operational weather prediction centers, for example, NICAM in Japan and ENDGame in Met Office, UK. In this study, we are applying the deep atmospheric concept to the NCEP Mesoscale Spectral Model (MSM)(Juang, 2000) in an attempt to understand the impacts of different dynamic codes on weather forecast.

The MSM used to be an operational model for weather forecast in the United States until 2011 and now it is an open-source model for worldwide community research and academic uses. The MSM can be used for numerical weather and climate predictions both. The current MSM is a nonhydrostatic system in sigma (terrain-following) coordinates. To meet the purposes of this research, the MSM dynamic code is in the development to be switchable between multiple options: a hydrostatic and a nonhydrostatic formulations, and also deep-atmospheric and shallow-atmospheric formulations. This model can be utilized for more studies of investigating the sensitivities of different dynamic codes.

The first part of this research will demonstrate the transformations of the model coordinate from the terrain-following coordinate to the generalized coordinates. The following is to implement the system into the model. The generalized hybrid coordinates are the combination of sigma and pressure coordinates, which use sigma surfaces near the ground surface and transit to the pressure surfaces near the top. The benefit to use the generalized vertical coordinate is that we can generate the deep-atmospheric equations from the shallow-atmospheric equations by modifying the existing terrain-following vertical coordinate, without the need to change substantially the scientific and computing infrastructure in the model. This presentation is to present some of the preliminary results of the implementation, and to discuss the future work.