Directions of wrfout surface flux

[Henry18]

Hi

I’m working with WRF output files to analyze the land surface energy balance, and I’m writing to confirm the directions (signs) of the fluxes included in my analysis.

Based on the basic surface energy balance equation:

Rn = H + LE + G

I am using the following WRF variables:

• SWDNB
• SWUPB
• LWDNB
• LWUPB
• HFX
• LH
• GRDFLX

I understand the equation to be calculated as:

SWDNB − SWUPB + LWDNB − LWUPB = HFX + LH + GRDFLX

I would like to confirm that I am interpreting the sign conventions correctly:

• SWDNB and LWDNB: positive values indicate downward fluxes toward the surface.
• SWUPB and LWUPB: positive values indicate upward fluxes from the surface.
• HFX and LH: positive values indicate upward fluxes from the surface to the atmosphere, while negative values indicate downward fluxes toward the surface.
• GRDFLX: positive values indicate upward heat flux from the surface, while negative values indicate downward heat flux from the surface into the soil.

If these conventions are correct, then for analyzing the land surface energy balance, should I formulate the equation as:

SWDNB − SWUPB + LWDNB − LWUPB = HFX + LH − GRDFLX

In other words, because negative GRDFLX represents heat flux downward into the soil, should it be subtracted on the right-hand side when expressing the energy balance with the convention Rn = H + LE + G, where G is defined as positive downward into the soil?

I'm using WRF 4.7.1 with sf_urban_physics = 1. Thank you very much for your help in clarifying this.

Cheers,
Henry

 

[Ming Chen]

Hi Henry,
Please see my answers below:

Hi

I’m working with WRF output files to analyze the land surface energy balance, and I’m writing to confirm the directions (signs) of the fluxes included in my analysis.

Based on the basic surface energy balance equation:

Rn = H + LE + G

I am using the following WRF variables:

• SWDNB
• SWUPB
• LWDNB
• LWUPB
• HFX
• LH
• GRDFLX

I understand the equation to be calculated as:

SWDNB − SWUPB + LWDNB − LWUPB = HFX + LH + GRDFLX

I would like to confirm that I am interpreting the sign conventions correctly:

• SWDNB and LWDNB: positive values indicate downward fluxes toward the surface.

You are right.

• SWUPB and LWUPB: positive values indicate upward fluxes from the surface.

This is correct.

• HFX and LH: positive values indicate upward fluxes from the surface to the atmosphere, while negative values indicate downward fluxes toward the surface.

This is correct.

• GRDFLX: positive values indicate upward heat flux from the surface, while negative values indicate downward heat flux from the surface into the soil.

This is correct.

If these conventions are correct, then for analyzing the land surface energy balance, should I formulate the equation as:

SWDNB − SWUPB + LWDNB − LWUPB = HFX + LH − GRDFLX

You are right.

In other words, because negative GRDFLX represents heat flux downward into the soil, should it be subtracted on the right-hand side when expressing the energy balance with the convention Rn = H + LE + G, where G is defined as positive downward into the soil?

If G is positive downward, then Rn = H + LE + G. However, note that in WRF G (i.e., GRDFLX) is negative downward.

I'm using WRF 4.7.1 with sf_urban_physics = 1. Thank you very much for your help in clarifying this.

Cheers,
Henry

Please let me know if you have more questions. Thanks.

 

[Henry18]

Hi Henry,
Please see my answers below:

You are right.

This is correct.

This is correct.

This is correct.


You are right.

If G is positive downward, then Rn = H + LE + G. However, note that in WRF G (i.e., GRDFLX) is negative downward.

Please let me know if you have more questions. Thanks.

Hi Ming,

Thank you for the answers!

Henry