Issues with forcing.kpar and forcing.chl.[ab]

[Luana F. Bueno]

Hi Alan,

I am preparing a simulation with NPZD in HYCOM and I have some doubts about it:

1- Regarding the version which still uses the forcing.kpar.[ab], my question is why did you limit the extremes values for it (minimum of 0.04 and maximum of 0.2)?
I download the SEAWIFS KD490 (forcing_kPAR_NPZD_LSE36_KD490_08_Ago.png) product and when limiting the extremes (Aforcing_kPAR_NPZD_LSE36_limites_08_.png) like you guys I loose the monthly variation. That was not what I saw in this document that I found online (https://apps.dtic.mil/sti/pdfs/ADA593093.pdf) that, despite being annual, it seems that the limits were only imposed in the high-latitude regions and not in the middle of South Atlantic, for example.

I also have an old file that I believe that come from  you guys (seawifs_mon_kpar.d) and when plotting it after applying hycom's pre-processing code, I get the map below (forcing_kPAR_NPZD_LSE36_2015_08_.png) which does not make much sense for me. Is it right?

Overall I'm not sure which kpar is the right one to use, is it the kd490? From my research, yes, it is, even because the other  SEAWIFS PAR product (SeaWiFS_Mapped_MonthlyClimatology9km) does not have distinction in the

continental shelf like de kd490 has. Besides that, should I limit the extremes like it seem that you used to do even thought it is killing my monthly variation?

and

2- Why do you guys change the estimation of kpar from chl when entering with forcing.chl instead? Does it give a better estimation of the light attenuation?

I am about to estimate kpar via the product of seawifs from chl using what it is done by the subroutine swfrac_ij in order to see what form this kpar will take.

Hope you can clear this up for me and thank you in advance for that.

Best regards,

  

Luana Ferraz Bueno

[Alan Wallcraft]

Our Kpar scheme uses a single exponential profile and  is described in:

A. B. Kara, A. B., A. J. Wallcraft and H. E. Hurlburt, 2005:
A New Solar Radiation Penetration Scheme for Use in Ocean Mixed Layer Studies: An Application to the Black Sea Using a Fine-Resolution Hybrid Coordinate Ocean Model (HYCOM)
Journal of Physical Oceanography vol 35, 13-32

The range 0.04 to 0.2 (m^-1) covers the classic Jerlov range and 2.0 is "mud".

The chl scheme uses two exponentials and surface chlorophyll-a (mg m-3) is a more natural quantity than Kpar.  I don't think there is a HYCOM publication that described the scheme, but from thermf.F90:

! ---   shortwave attneuation scheme from:
! ---    Lee, Z., K. Du, R. Arnone, S. Liew, and B. Penta (2005),
! ---     Penetration of solar radiation in the upper ocean:
! ---     A numerical model for oceanic and coastal waters,
! ---     J. Geophys. Res., 110, C09019, doi:10.1029/2004JC002780.
! ---   This is a 2-band scheme with "frac_r" fixed. However,
! ---    "beta_b" and "beta_r" are now depth dependent.
! ---   Required input to the scheme is the total absorption coefficient
! ---    at the surface for 490 nm waveband (a490, m-1) and the
! ---    total backscattering coefficient at the surface at the same
! ---    waveband (bb490, m-1).
! ---   However, here simple "CASE 1" relationships between these surface
! ---    optical properties and surface chlorophyll-a (mg m-3) are assumed.
! ---   These assumptions are considered valid for global, basin-scale
! ---    oceanography. However, coastal and regional applications tend
! ---    to be more complex, and a490 and bb490 should be determined
! ---    directly from the satellite data.
! ---   Authored by Jason Jolliff, NRL; week of 14 November 2011

Alan.

[Luana F. Bueno]

Alright Alan,

Thank you so much for replying back to me.

I wish to all you guys HYCOM a Merry Christmas and a Happy New Year!