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I am posting an algorithm (more of a procedure description) and I request a review of the correctness of the algorithm.

Goal - To bring in scalar field values such as temperature, geopotential height, surface pressure, specific humidity found in a NOAA reanalysis file(typically Gaussian grid) into a rotated lat lon grid.This algorithm does NOT apply to vector field values such as zonal and meridional velocities.

Given the following inputs-

  1. latitude of the rotated north pole
  2. longitude of the rotated north pole
  3. latitude of the geographical north pole
  4. longitude of the geographical north pole

Step 1 - Given the four input values use the following public routines available to transform coordinates in global Gaussian grid to rotated lat lon grid phi2phirot and rla2rlarot

Step 2 - Since these are scalar field values there are no transformation equations for Temperature, Surface Pressure, Geopotential height and Specific Humidity. They remain unchanged to a change of coordinate systems( Scalar Fields unchanged. However the positions of the scalar field values would now be different(change of origin).

NOTE

I am aware that there is a similar question on GIS SE - Transforming from regular lat lon to rotated lat lon they use a different approach by transforming first to Cartesian and then transforming back into lat lon. The public routines that I cite do not require a transformation to Cartesian first.

Reference

Lauritzen, P. H., C. Jablonowski, M. A. Taylor, and R. D. Nair (2010), Rotated Versions of the Jablonowski Steady-State and Baroclinic Wave Test Cases: A Dynamical Core Intercomparison, J. Adv. Model. Earth Syst., 2, 15, doi:10.3894/JAMES.2010.2.15

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