JEDI-LETKF/GETLF inflation options

JEDI
1

Hello,

In the current letkf.yaml and lgetkf.yaml configuration files, three available inflation options are set as:
inflation:
rtps: 0.5
rtpp: 0.6
mult: 1.1

I suppose only one of the inflation options needs to be configured for LETKF/LGETKF, e.g., rtps=0.85, rtpp=0.0, mult=1.0 as in the operational GSI-EnKF system? Please correct me, if my understanding is wrong.

Also, I wonder how it works with all three options configured as above? Will their inflation effect be accumulated?

Thanks.
Bo

2

Hi Bo,

This is a science question. In atmosphere, RTPP and RTPS act differently in tropics vs mid-latitudes. So one might choose to use both options. However, to get stared, i would recommend to use RTPS as it seems to have better NWP scores. Multiplicative inflation is included for completeness.

So using rtps=0.85; rtpp=0.0, and mult=1.0 are good options to start from your tuning.

The three inflations factors are used sequentially so they are compounding. Multiplication is applied first to inflate the prior ensemble, then rtpp, and rtps is last.
To see how rtpp and rtps are implemented, you can look at:
https://github.com/JCSDA-internal/oops/blob/35923ceb362c9933dbdbf3d0d8f24688cf86f205/src/oops/assimilation/LETKFSolver.h#L233

Sergey

3

Sergey,

Thanks for your response. It is very helpful.

Bo