Modal view of atmospheric circulation
MODES performs decomposition of global circulation in terms of three-dimensionally orthogonal eigensolutions (Hough harmonics) of the linearized primitive equations. In this way, spatial and temporal variability associated with the two main circulation regimes, the Rossby and inertia-gravity regime, can be quantified across scales. 3D linear wave theory is most useful in the tropics where two special wave solutions, the Kelvin wave and the mixed Rossby-gravity wave, accounting for a significant part of tropical variability, obliterate the distinction between fast and slow dynamics in the midlatitudes.
A book on the applications of normal-mode functions in weather and climate dynamics and numerical weather prediction research: https://www.springer.com/gp/book/9783030609627