Three-dimensional normal mode functions: open-access tools for their computation in isobaric coordinates (p-3DNMF.v1)

Abstract

A free software package for the computation of the three-dimensional normal modes of an hydrostatic atmosphere is presented. This software performs the computations in isobaric coordinates and was developed for two user-friendly languages: MATLAB and Python. The software can be used to expand the global atmospheric circulation onto the 3-D normal modes. This expansion allows the computation of a 3-D energetic scheme, which partitions the energy reservoirs and energy interactions between 3-D spatial scales, barotropic and baroclinic components, and balanced (rotational) and unbalanced (divergent) circulation fields. Moreover, by retaining only a subset of the expansion coefficients, the 3-D normal mode expansion can be used for spatial-scale filtering of atmospheric motion, filtering of balanced motion and mass unbalanced motions, and barotropic and baroclinic components. Fixing the meridional scale, the 3-D normal mode filtering can be used to isolate tropical components of the atmospheric circulation. All of these features are useful both in data analysis and in assessment of general circulation atmospheric models.