Eta coordinate Calculator

Introduction : This calculator calculates the eta coordinate for numerical weather prediction models that use this coordinate system, most notably the "Eta" model (so named because of its use of this coordinate system). The eta coordinates, or levels, create a "step" appearance to the terrain.

Mathematical equation for eta coordinate calculation

This calculator provides the tools needed to explore the relationship between pressure and the eta coordinate.

In this calculator, you have three input values:

  1. pressure at the model surface being calculated Pr. For example, in the diagram below, Pr at a height of 1000 m is 900 mb
  2. pressure at the surface (Zs=0)
  3. pressure at the top of the model (typically Pt=0)

The algorithm for the eta coordinate is:

Mathematical equation for eta coordinate calculation

Eta coordinate Calculator

Input Values:

Pressure (Pr) at the level being calculated
Pressure (Prat Zs=0
Pressure (Pt) at the top

Results:

Eta coordinate value