Description of the Incremental Interpolation Method

The incremental interpolation method gives fine scale details to a spatially and temporally coarse data (see Figure 1 below). For a downscaling simulation with pressure-level base field data, it is highly recommended to use this method. For detail, please refer a paper below:
Yoshimura, K. and M. Kanamitsu, Specification of external forcing fields for regional model integrations, Monthly Weather Review, in print.

gsm_inc script

gsm_inc script is a sample script of the incremental interpolation method. This script creates global full sigma level files in high time frequency from only daily and 5 vertical level data.

How to use

  1. install T62 gsm, choose "gsm_inc" script
  2. $ cd gruns/runscr ; tar xvf sigtool.tar ; ./
  3. $ ./gsm_inc
The sigtool.tar contains tools for adding and subtracting sigma files. You might need to specify FC/FFLAGS in for your computer.

What does it do?

What gsm_inc script does are followings:
  • Prepare daily ERA40 data in 1000, 850, 700, 500, and 200 hPa.
  • Make a 24-hr guess by GSM.
  • Incremental interpolation in vertical for 24Z (see Figure 2 below).
  • Incremental interpolation in time for 6Z, 12Z, and 18Z (see Figure 3 below).

How to apply the sigma data to RSM

Just specify the sig.ftXX files as BASE files of a rsm/rsim simulations.


Figure 1: Schematic of the incremental interpolation.


Figure 2: Schematic of vertical incremental interpolation


Figure 3: Schematic of the incremental interpolation in time.