shortwave solar radiation in ROMS surface forcing

[jiangtao]

Hi,

I have a question about the shortwave radiation in the surface forcing. For long wave radiation, you can either input downwelling long wave radiation or net long wave radiation. But for shortwave radiation, it is not so clear. When I looked into the bulk_flux.F, it seemed to me that net shortwave radiation is assumed because I didn't see any adjustment to the input for the reflection of shortwave radiation at the surface. And the reflection could be up to 25% of the incoming solar radiation. As a matter of fact, the reflection of the longwave radiation is not taken into account either, I think. However, the reflection of longwave radiation is only about 3% (the emmiss coefficient is equal to 0.97 but isn't applied to the downwelling long wave radiation). Could anyone please clarify this for me?

Thanks a lot,

Jiangtao

[jacopo]

ROMS expects you to provide the NET shortwave radiation.

Looking in bulk_flux.F...

Code: Select all

    # elif defined LONGWAVE_OUT
!
!  Treat input longwave data as downwelling radiation only and add
!  outgoing IR from model sea surface temperature.
!
          LRad(i,j)=lrflx(i,j)*Hscale-                                  &
     &              emmiss*StefBo*TseaK(i)*TseaK(i)*TseaK(i)*TseaK(i)
 

The term
emmiss*StefBo*TseaK(i)*TseaK(i)*TseaK(i)*TseaK(i)
is only the emitted, so the downwelling longwave is supposed to be already provided to the net of reflection, i.e., the full term

IRdown * (1-reflectivity)

[jiangtao]

Thanks for the reply.
I have another question about other properties in the surface forcing: should I use wind, air temperature, relative humidity and air pressure at 10-meter-height or at surface? In mod_scalars.F, it's said that the height of atmospheric boundary layer is set to 10m and the wind, temperature and humidity measurements are at 10m. What about pressure?

-Jiangtao

[wilkin]

The BULK_FLUX option for surface heat and momentum flux boundary conditions uses the COARE algorithms described in:

Fairall, C., E. Bradley, D. Rogers, J. Edson, and G. Young, 1996: Bulk parameterization of air-sea fluxes for TOGA COARE. Journal of Geophysical Research, 101, 3747-3764.

Fairall, C. W., E. F. Bradley, J. E. Hare, A. A. Grachev, and J. Edson, 2003: Bulk Parameterization of Air–Sea Fluxes: Updates and Verification for the COARE Algorithm. Journal of Climate, 16, 571-591.

Following meteorological conventions, the input data are wind velocity at 10 m height, air temperature at 2 m height, relative humidity at 2 m height, and air pressure at sea surface.

For example, if you were using the NCEP NAM forecast data available from the NOMADS Opendap server at
http://nomad3.ncep.noaa.gov/ncep_data/index.html

you would want the following variables described at, e.g. http://nomad3.ncep.noaa.gov:9090/dods/n ... r_00z.info

ugrd10m ** 10 m u wind [m/s]
vgrd10m ** 10 m v wind [m/s]
pressfc ** surface pressure [pa]
tmp2m ** 2 m temp. [k]
rh2m ** 2 m relative humidity [%]

[jacopo]

the heights of measurements are, by default (from mod_scalars.F)

Code: Select all

#ifdef BULK_FLUXES
!
!-----------------------------------------------------------------------
! Constants used in surface fluxes bulk parameterization.
!-----------------------------------------------------------------------
!
!    blk_Cpa       Specific heat capacity for dry air (J/kg/K).
!    blk_Cpw       Specific heat capacity for seawater (J/kg/K).
!    blk_Rgas      Gas constant for dry air (J/kg/K).
!    blk_Zabl      Height (m) of atmospheric boundary layer.
!    blk_ZQ        Height (m) of surface air humidity meassurement.
!    blk_ZT        Height (m) of surface air temperature meassurement.
!    blk_ZW        Height (m) of surface winds meassurement.
!    blk_beta      Beta parameter evaluated from Fairall low windspeed
!                    turbulence data.
!    blk_dter      Temperature change.
!    blk_tcw       Thermal conductivity of water (W/m/K).
!    blk_visw      Kinematic viscosity water (m2/s).
!
        real(r8) :: blk_Cpa = 1004.67_r8      ! (J/kg/K), Businger 1982
        real(r8) :: blk_Cpw = 4000.0_r8       ! (J/kg/K)
        real(r8) :: blk_Rgas = 287.1_r8       ! (J/kg/K)
        real(r8) :: blk_Zabl = 600.0_r8       ! (m)
        real(r8) :: blk_ZQ = 10.0_r8          ! (m)
        real(r8) :: blk_ZT = 10.0_r8          ! (m)
        real(r8) :: blk_ZW = 10.0_r8          ! (m)
        real(r8) :: blk_beta = 1.2_r8         ! non-dimensional
        real(r8) :: blk_dter = 0.3_r8         ! (K)
        real(r8) :: blk_tcw = 0.6_r8          ! (W/m/K)
        real(r8) :: blk_visw = 0.000001_r8    ! (m2/s)
#endif

so I suppose you should set blk_ZW, blk_ZT and blk_ZQ according to the height of your input data.
Any confirmation on that?

Jacopo

[rsignell]

When BULK_FLUXES is defined, the default "measurement" height for temperature, humidity and wind are all set to 10 m, as Jacopo mentioned.

Yet it seems likely that most people using BULK_FLUXES are using met model output, which typically outputs temperature and humidity at 2 m, and wind at 10 m, as John Wilkin has mentioned.

Perhaps the default heights for temperature and humidity (currently both 10 m) in mod_scalars.F should be changed to 2 m.

Code: Select all

#ifdef BULK_FLUXES
!
!-----------------------------------------------------------------------
! Constants used in surface fluxes bulk parameterization.
!-----------------------------------------------------------------------
!
!    blk_Cpa       Specific heat capacity for dry air (J/kg/K).
!    blk_Cpw       Specific heat capacity for seawater (J/kg/K).
!    blk_Rgas      Gas constant for dry air (J/kg/K).
!    blk_Zabl      Height (m) of atmospheric boundary layer.
!    blk_ZQ        Height (m) of surface air humidity meassurement.
!    blk_ZT        Height (m) of surface air temperature meassurement.
!    blk_ZW        Height (m) of surface winds meassurement.
!    blk_beta      Beta parameter evaluated from Fairall low windspeed
!                    turbulence data.
!    blk_dter      Temperature change.
!    blk_tcw       Thermal conductivity of water (W/m/K).
!    blk_visw      Kinematic viscosity water (m2/s).
!
        real(r8) :: blk_Cpa = 1004.67_r8      ! (J/kg/K), Businger 1982
        real(r8) :: blk_Cpw = 4000.0_r8       ! (J/kg/K)
        real(r8) :: blk_Rgas = 287.1_r8       ! (J/kg/K)
        real(r8) :: blk_Zabl = 600.0_r8       ! (m)
        real(r8) :: blk_ZQ = 2.0_r8           ! (m)
        real(r8) :: blk_ZT = 2.0_r8           ! (m)
        real(r8) :: blk_ZW = 10.0_r8          ! (m)
        real(r8) :: blk_beta = 1.2_r8         ! non-dimensional
        real(r8) :: blk_dter = 0.3_r8         ! (K)
        real(r8) :: blk_tcw = 0.6_r8          ! (W/m/K)
        real(r8) :: blk_visw = 0.000001_r8    ! (m2/s)
#endif       

-Rich

[kate]

Perhaps this just needs to be documented. I checked the atmospheric forcing I'm using and it is at ten meters, consistent with my ROMS.

[duckweed]

ROMS expects you to provide the NET shortwave radiation.

However,for the Jerlov water type
https://www.myroms.org/wiki/index.php/Jwtype
Qsw is the downward shortwave radiation at the sea surface.

So, i have a little confused about the srflux.

[wilkin]

Qsw is the same as srflux and is the downward shortwave radiation at the sea surface that enters the ocean.

The remark that it is net shortwave is to emphasize that on the atmosphere side the reflected upward shortwave (due to ocean surface albedo) needs to be subtracted from the downward shortwave to get the flux that crosses the air-sea interface.