PPUG_running_regrid

Running post processing scripts to regrid land climatology and average files

Synopsis

$PP_CASE_PATH/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 $PP_CASE_PATH/logs/lnd_regrid.log file contains the stderr and stdout from the job submission. The yellowstone submission command is:

bsub < lnd_regrid

Details

The following details were copied from the Climate and Cryosphere wiki:

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 to create the necessary regridding files.

It is necessary to run the lnd_regrid script anytime the input land model grids do not match a lat-lon grid which is required by the diagnostics packages. This is because, unlike the atmosphere model regridding operation which can reuse previously generated weights files, there are several different types of land output variables that generate different weight files. Hence, as different land variables are output for different runs of the model, it is necessary to regenerate the weights files each time.

Dependencies

The land regridding script depends on the successful generation of the climatologies and averages files produced by the lnd_averages wrapper script. There are also required input data files.