Precipitation disappears inside nested domains

[reshma_m]

Hi everyone,
I am running WRF with 3 two-way nested domains and I am experiencing an issue with precipitation fields. When plotting accumulated precipitation over the parent domain (d01), I clearly see square-shaped discontinuities corresponding exactly to the nested domains (d02 and d03). Inside the nested areas, precipitation from the parent domain is almost completely suppressed. The same effect occurs between d02 and d03. It looks like precipitation is being “overwritten” within each child domain area, creating sharp artificial boundaries.

Here is my configuration:
WRF configuration:

• max_dom = 3
• Two-way nesting (feedback = 1)
• smooth_option = 0

Horizontal resolution:

• d01: 15 km
• d02: 5 km
• d03: 1.67 km
• parent_grid_ratio = 1, 3, 3
• parent_time_step_ratio = 1, 3, 3

Microphysics:

• mp_physics = 8

Cumulus scheme:

• cu_physics = 1 (Kain-Fritsch) for d01
• cu_physics = 0 for d02 and d03

Boundary configuration:

• specified = .true., .false., .false.
• nested = .false., .true., .true.

So d02 and d03 should be receiving their lateral boundary conditions from their respective parent domains. The simulation runs without any runtime error.

My questions:

1. Is this behavior expected with two-way nesting (feedback = 1)?
2. Could feedback be suppressing parent-domain precipitation inside child-domain areas?
3. Should smooth_option be enabled? Could this be related to differences in convective parameterization between d01 (KF on) and d02/d03 (explicit convection)?

Has anyone experienced a similar issue?


Thank you very much for your help !

 

[Ming Chen]

Please see my answers below:

Hi everyone,
I am running WRF with 3 two-way nested domains and I am experiencing an issue with precipitation fields. When plotting accumulated precipitation over the parent domain (d01), I clearly see square-shaped discontinuities corresponding exactly to the nested domains (d02 and d03). Inside the nested areas, precipitation from the parent domain is almost completely suppressed. The same effect occurs between d02 and d03. It looks like precipitation is being “overwritten” within each child domain area, creating sharp artificial boundaries.

Here is my configuration:
WRF configuration:

• max_dom = 3
• Two-way nesting (feedback = 1)
• smooth_option = 0

Horizontal resolution:

• d01: 15 km
• d02: 5 km
• d03: 1.67 km
• parent_grid_ratio = 1, 3, 3
• parent_time_step_ratio = 1, 3, 3

Microphysics:

• mp_physics = 8

Cumulus scheme:

• cu_physics = 1 (Kain-Fritsch) for d01
• cu_physics = 0 for d02 and d03

Boundary configuration:

• specified = .true., .false., .false.
• nested = .false., .true., .true.

So d02 and d03 should be receiving their lateral boundary conditions from their respective parent domains. The simulation runs without any runtime error.

My questions:

1. Is this behavior expected with two-way nesting (feedback = 1)?

Yes this what is expected. With two-way nesting and feedback on, the results of child domain will feedback to its parent domain. The 'square' feature you have seen demonstrates grid-dependent precipitation feature.

1. Could feedback be suppressing parent-domain precipitation inside child-domain areas?

Precipitation in child domain is derived from pjhysics/dynamics in that domain. The feedback will make precipitation in parent-domain consistent with that in child-domain.

1. Should smooth_option be enabled? Could this be related to differences in convective parameterization between d01 (KF on) and d02/d03 (explicit convection)?

It is recommended to turn on

• smooth_option = 2

This option works to make smooth transition of all fields between parent and child domains. It is not relevant to convective parameterization.

Has anyone experienced a similar issue?

We have seen similar features. However, we usually discard results from parent domain and only focus on child domain.

Thank you very much for your help !