Initial Conditions

[Yichen Yang]

Hello!

I'm not sure I understand the term 'Initial conditions' in WRF modeling and would like some help. If I simulate in nested domains, I need observational (model) data such as GFS to set up the initial and the boundary conditions. Such data are time-dependent so I understand that the model will be forced to align with the data on the boundary of the child domain for every couple of hours. But how is the model initialized to postulate the conditions (like soil moisture) inside the domain?

Are the data interpolated to get initial values for each grid inside? If I have the data for a few days with 6-hour interval, are the initial conditions only provided by the data at the first timestep?

A more specific question is, if I run simulations for two small areas with exactly the same land cover type but in different background climate (mainly different in soil moisture). How does the model work to reflect the background impacts on local climate? Does the climate control only rely on the initial conditions from observational data?

Thank you very much!

 

[Ming Chen]

Hi,
Please see my answers below:
I'm not sure I understand the term 'Initial conditions' in WRF modeling and would like some help. If I simulate in nested domains, I need observational (model) data such as GFS to set up the initial and the boundary conditions. Such data are time-dependent so I understand that the model will be forced to align with the data on the boundary of the child domain for every couple of hours. But how is the model initialized to postulate the conditions (like soil moisture) inside the domain?

GFS data at the initial time of your WRF simulation will be interpolated to WRF grids. The data in WRF grids is initial condition for WRF.
Note that initial condition includes data in the atmosphere and also the data in soil levels

Are the data interpolated to get initial values for each grid inside? If I have the data for a few days with 6-hour interval, are the initial conditions only provided by the data at the first timestep?

It is correct that the forcing data is interpolated to each grid in WRF domain. The initial condition is only needed at the beginning of WRF integration

A more specific question is, if I run simulations for two small areas with exactly the same land cover type but in different background climate (mainly different in soil moisture). How does the model work to reflect the background impacts on local climate? Does the climate control only rely on the initial conditions from observational data?

No. The model run is under constraint of both initial condition and lateral boundary forcing, Differences in background climate state should be reflected in initial and lateral boundary forcing.

 

[Yichen Yang]

Hi,
Please see my answers below:
I'm not sure I understand the term 'Initial conditions' in WRF modeling and would like some help. If I simulate in nested domains, I need observational (model) data such as GFS to set up the initial and the boundary conditions. Such data are time-dependent so I understand that the model will be forced to align with the data on the boundary of the child domain for every couple of hours. But how is the model initialized to postulate the conditions (like soil moisture) inside the domain?

GFS data at the initial time of your WRF simulation will be interpolated to WRF grids. The data in WRF grids is initial condition for WRF.
Note that initial condition includes data in the atmosphere and also the data in soil levels

Are the data interpolated to get initial values for each grid inside? If I have the data for a few days with 6-hour interval, are the initial conditions only provided by the data at the first timestep?

It is correct that the forcing data is interpolated to each grid in WRF domain. The initial condition is only needed at the beginning of WRF integration

A more specific question is, if I run simulations for two small areas with exactly the same land cover type but in different background climate (mainly different in soil moisture). How does the model work to reflect the background impacts on local climate? Does the climate control only rely on the initial conditions from observational data?

No. The model run is under constraint of both initial condition and lateral boundary forcing, Differences in background climate state should be reflected in initial and lateral boundary forcing.

This is a perfect answer to me. Thank you very much.

 

[Yichen Yang]

Hi,
Please see my answers below:
I'm not sure I understand the term 'Initial conditions' in WRF modeling and would like some help. If I simulate in nested domains, I need observational (model) data such as GFS to set up the initial and the boundary conditions. Such data are time-dependent so I understand that the model will be forced to align with the data on the boundary of the child domain for every couple of hours. But how is the model initialized to postulate the conditions (like soil moisture) inside the domain?

GFS data at the initial time of your WRF simulation will be interpolated to WRF grids. The data in WRF grids is initial condition for WRF.
Note that initial condition includes data in the atmosphere and also the data in soil levels

Are the data interpolated to get initial values for each grid inside? If I have the data for a few days with 6-hour interval, are the initial conditions only provided by the data at the first timestep?

It is correct that the forcing data is interpolated to each grid in WRF domain. The initial condition is only needed at the beginning of WRF integration

A more specific question is, if I run simulations for two small areas with exactly the same land cover type but in different background climate (mainly different in soil moisture). How does the model work to reflect the background impacts on local climate? Does the climate control only rely on the initial conditions from observational data?

No. The model run is under constraint of both initial condition and lateral boundary forcing, Differences in background climate state should be reflected in initial and lateral boundary forcing.

Hi,

Sorry I have a quick question. I have understood that the initial and boundary conditions from the reanalysis data will show the differences in background climate. The impacts will be not only on the soil moisture but also on other atmospheric variables. However, I found a variable named 'SLMO' in LANDUSE.TBL which indicates 'Soil Moisture Availability'. It shows that the SLMO values are prescribed for all the land use types, regardless what's provided by the reanalysis data. Does the 'Soil Moisture Availability' only represent the saturation state of the grids (like a consistent surface property), so the soil moisture from the reanalysis data still plays their own roles?

 

[Ming Chen]

Hi,
This parameter is used to describe the moisture characteristics of soil, and it only depends on soil type. So you are right that it doesn't change under different climate scenarios, and it only changes with soil type.
The analysis/forecast products used to drive the WRF model provide soil moisture and soil temperature, and these two variables are different under different climate scenarios.