PPUG_running_regrid

Running post processing scripts to regrid land climatology and average files

Synopsis

$PP_CASE_ROOT/lnd_regrid

Regrid the land climatology files (optional). This step may be necessary when the model land grid is something other than lat-lon which is required by the land diagnostics plotting routines. The regridding of the atmosphere averages is done in the atm_diagnostics scripts. Use yellowstone submission command:

bsub < lnd_regrid

Details

In order to intercompare different models, they must be interpolated from the native grid on which they were calculated to a standard grid. This procedure is known as regridding or remapping.

Fundamentally, regridding consists of two steps:

1. Creation of an interpolation matrix (weights file), which gives the amount that each point on the source grid contributes to each point on the target grid. These weights will depend on the type of interpolation desired. ISMIP6 has standardized on First-order Conservative Remapping (Jones, P.W. 1999, Monthly Weather Review, 127, 2204-2210), which does a better job preserving fluxes (or other integrals) than, eg., bilinear interpolation.

2. For each point on the target grid, sum the data values on the source grid multiplied by the corresponding weights. The same weights file may be used for more than one input variable, provided all are defined on the same source grid. Different software may do one or the other or both of these steps.

To create the weights file, you must have grid description files for your source and target grids. These files give the latitudes and longitudes of every grid point, along with the corners of the boundary of its surrounding cell. There are several ways to write these files, depending on the software you're using.

The land regridding NCL routines use the ESMF regridding library which is described here.