Equivalent latitude

In differential geometry, the equivalent latitude is a Lagrangian coordinate .

The calculation of equivalent latitude involves creating a monotonic mapping between the values of equivalent latitude and the tracer it is based upon: higher values of the tracer map to higher values of equivalent latitude.

A precise method is to assign a representative area to each of the tracer measurements, filling the entire globe.

Thus, for a tracer field regularly gridded in longitude and latitude, grid points closer to the pole will take up a smaller area, in proportion to the cosine of the latitude.

Now, rank all the tracer values then form the cumulative sum.