# Increasing the horizontal resolution

The relationship between the spectral truncation, T, the number of grid points used to represent the shortest wave (i.e. linear, quadratic or cubic) and the grid point resolution, N, allows for three possible approaches for increasing the horizontal resolution:

1. increase the number of wave numbers in the spectral representation but keep the same Gaussian grid by reducing the number of grid points used to represent the shortest wave (i.e., increase T with TQ →TL keeping N constant);
2. increase the number of wave numbers in the spectral representation and the Gaussian grid resolution but keep the number of grid points used to represent the shortest wave constant (i.e. increase T and increase N).
3. keep the number of wave numbers in the spectral representation constant and increase the Gaussian grid resolution by increasing the number of grid points used to represent the shortest wave (i.e., TL →TC, and increase N).

The planned horizontal resolution upgrade is achieved by:

• increasing the Gaussian grid resolution by keeping the spectral truncation constant but representing the shortest wave by four grid points (use the cubic representation);
• introducing a new form of the reduced Gaussian grid - the octahedral grid.

The notation TCO (CO - Cubic Octahedral) is used to indicate the corresponding spectral truncation.