The precision of JEDI

JEDI
1

In the JEDI tutorial, it stated that “Note that the tutorial test cases are designed with single-precision MPAS model test dataset. Therefore, we pre-compiled mpas-bundle code with single-precision mode“.

How to compile the MPAS-JEDI bundle with a single-precision mode?

When I have an already compiled MPAS-JEDI, how to tell whether it is compiled in a single-precision mode or a double-precision mode?

2

I found out that there is a line in the CMakeLists.txt to control the precision:

set(MPAS_DOUBLE_PRECISION “ON” CACHE STRING “MPAS-Model: Use double precision 64-bit Floating point.”)

On a relative but separate note, does the precision affect the data assimilation impacts?

3

Hi @JiaWANG ,

On a relative but separate note, does the precision affect the data assimilation impacts?

I don’t expect that the use of single precision MPAS model will affect the DA result very much.
The data structure of mpas-jedi fields inherit from MPAS-Model’s pool data structure. So the precision of MPAS-Model build will also determine the precision of mpas-jedi fields data structure. This leads to the less memory requirement for mpas-jedi application and smaller mpas/mpas-jedi NetCDF file size.

Thank you,
BJ

4

Thanks BJ. Understand that the precision needs to be consistent between MPAS and JEDI.

May I ask that in your group’s research work, which precision do you use?

5

The precision of MPAS Model and MPAS-JEDI does not need to be the same. It is not a requirement. Also note that the (most) DA procedures, which happen in the generic JEDI components, is still done with a double precision.

In MMM, we are mostly using the single precision build of MPAS-Model for our experiment.

Thank you,
BJ

6

Then a double precision MPAS can generate a single precision DA input file, which will be read by a single precision JEDI?

Thanks for the clarification about the double-precision internal procedures.

Have you done internal comparisons of DA performance between the single versus double precision?

7

Then a double precision MPAS can generate a single precision DA input file, which will be read by a single precision JEDI?

Yes, you can find the related information from Configuring Model Input and Output — MPAS Atmosphere documentation

Have you done internal comparisons of DA performance between the single versus double precision?

I don’t remember if we’ve done this before.

Thank you,
BJ