15. POP Tools

This chapter describes various tools available for creating POP input or analyzing POP output.

15.1. Visualizing output

There is currently no standard tool for visualizing POP output. There are two freely-available software packages that can be used.

Ferret is a visualization tool developed by Steve Hankin at NOAA’s Pacific Marine Environmental Laboratory (PMEL) in Seattle. It is designed specifically for visualizing ocean model output and data. Ferret is constantly being improved and extended, and there is a very active email-based user group. For more information about Ferret, check the Ferret website

http://ferret.wrc.noaa.gov/Ferret/.

Other free visualization and analysis packages are available from the DOE-sponsored Program for Climate Model Diagnosis and Intercomparison (PCMDI) at Lawrence Livermore National Laboratory (LLNL). Although originally designed for visualizing atmospheric model output from the Atmospheric Model Intercomparison Project (AMIP), many are applicable to ocean model output and future ocean analysis tools are being added. For more information, check the website

http://www-pcmdi.llnl.gov/software/.

See the POP2 Post-Processing Utilities section on the CSEM1.0 POP2 index page.

15.2. Transformations from general grids

All POP output is on the computational grid. For general grids that are not based on latitude and longitude (e.g. the displaced-pole or tripole grids), analyzing or visualizing data leads to a distorted view of the world and colleagues may begin to question your geography. Transformation to latitude-longitude grids can be performed using the Spherical Remapping and Interpolation Package (SCRIP), available from LANL.

15.3. File format conversion

POP now supports direct netCDF output and such output is recommended unless it creates a performance bottleneck for large grids. In cases where binary output is required, conversion to netCDF can be achieved off-line through a utility called bin2nc, which is available from LANL.

POP2 supports 64-bit offset netCDF output, which allows larger file sizes than the 2Mb supported by the “classic” netCDF format. To address performance issues with large sizes, the POP2 code uses the PIO library to write netCDF output files in parallel. See the PIO library documentation for more details.

15.4. Generating grid and bottom topography files

15.4.1. Horizontal grid and topography

A graphical tool for generating horizontal grids and creating bottom topography has been developed. A working version is currently in the process of being released and will support almost-global Mercator grids, global displaced-pole grids, global tripole grids and regional grids. Some standard grids and topography used in current production runs are available from the POP website.

15.4.2. Vertical grid

There is no tool for this in the distribution. This code is essentially the same code used to generate vertical grids internally in POP, but can be used to generate a vertical grid file off-line which can be edited to suit your simulation. Note that when changing the vertical grid, you will need to re-generate the bottom topography.