Question about srflx

General scientific issues regarding ROMS

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kate
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Question about srflx

#1 Post by kate » Tue Jul 08, 2008 7:42 pm

Say, I was wondering something. srflx is used to heat up the water column in pre_step3d when SOLAR_SOURCE is defined. It is also used in lmd_skpp/lmd_bkpp to add to the buoyancy. Isn't that a form of double-dipping? Also, it isn't protected by SOLAR_SOURCE in lmd (nor in get_data).

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wilkin
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Re: Question about srflx

#2 Post by wilkin » Wed Jul 09, 2008 3:29 am

srflx is used in lmd_skpp to compute the mixed layer depth because of the role of shortwave penetration as a buoyancy flux. However, lmd_skpp doesn't go beyond computing the mixed layer depth, i.e. the shortwave radiation does not get absorbed there. That happens in pre_step3d. Without defining LMD_MIXING (i.e. KPP - very confusing mix of TLA's - three letter abbreviations), pre_step does the job in the case SOLAR_SOURCE is activated (in MY25_MIXING and GLS_MIXING). In these cases the vertical profile of solar penetration is governed by the Jerlov water type option in ocean.in.

We're working on coupling the ECOSIM and BIO_FASHAM shortwave radiation absorption (dependent on bio-optics) back to the solar source heating. Stand-by for an update on this.
John Wilkin: DMCS Rutgers University
71 Dudley Rd, New Brunswick, NJ 08901-8521, USA. ph: 609-630-0559 jwilkin@rutgers.edu

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susonic
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Re: Question about srflx

#3 Post by susonic » Fri Dec 18, 2009 12:50 pm

Hi,

Would you give me more information of the Jerlov water type. The water type 1 is representing the clearest water and
5 corresponding to the shortest penetration of solar radiation. This is all I know. Am I understanding right?
Then, what is the criteria determining the water type?
Any information would be great.

Thanks in advance.

-Peter

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wilkin
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Re: Question about srflx

#4 Post by wilkin » Fri Dec 18, 2009 3:19 pm

The implementation is described in the ROMS wiki:
https://www.myroms.org/wiki/index.php/Jwtype

The wiki entry includes the reference to the Simpson and Paulson paper. It is:
Paulson, C. A., and J. J. Simpson, 1977: Irradiance measurements in the upper ocean. J. Phys. Oceanogr., 7, 952–956
The paper summarizes Jerlov's classification quite well, so this reference is probably all you need for an explanation.

If you wish to modify these parameters for your particular application you could directly edit the entries in mod_scalars.F. But I recommend a more safe approach that would not change the default behavior of ROMS, which is to add another entry of your own by increasing the dimension of lmd_mu1, lmd_mu2 and lmd_r1 (in mod_scalars.F) to 6, adding your new values to the table, and activating them by choosing WTYPE=6 in your ocean.in
John Wilkin: DMCS Rutgers University
71 Dudley Rd, New Brunswick, NJ 08901-8521, USA. ph: 609-630-0559 jwilkin@rutgers.edu

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susonic
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Re: Question about srflx

#5 Post by susonic » Fri Dec 18, 2009 5:23 pm

Thank you prof. Wilkin. You're very kind.

Here is another question. The explanation which you linked to me is related with lmd mixing and Jerlov water type. Then, what if I want to use the other vertical mixing. Say, GLS vertical mixing scheme.
My model result is telling me that different water type result in different mixed layer depth when I use the
GLS mixing scheme. But I can't find how the water type affect with the vertical mixing scheme in the ROMS code.
Would you give me a keyword or suggestion?

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wilkin
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Re: Question about srflx

#6 Post by wilkin » Sat Dec 19, 2009 1:01 am

Joonho,

Do not be mis-led by the subroutine name. You need to look at what the ROMS code is doing - this is a good exercise for novice users.

The file lmd_swfrac.F begins with the CPP test:

Code: Select all

#if defined NONLINEAR && (defined LMD_SKPP || defined SOLAR_SOURCE) ...
Thus, if the LMD scheme OR solar_source option is defined (regardless of whether LMD is defined or not), then ROMS activates the vertical penetration of solar radiation according to the "Jerlov" scheme (as interpreted by Simpson and Paulson 1991). The default if GLS is activated is to also activate the SOLAR_SOURCE option.

Something I often recommend to new users is to view the contents of the "Build" directory. In your case with GLS active you will see that pre_step.f90 calls lmd_swfrac.f90 and lmd_swfrac applies the Jerlov exponential light penetration. lmd_swfrac is written the way it is because of the peculiar requirements of the LMD/KPP scheme.
John Wilkin: DMCS Rutgers University
71 Dudley Rd, New Brunswick, NJ 08901-8521, USA. ph: 609-630-0559 jwilkin@rutgers.edu

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susonic
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Re: Question about srflx

#7 Post by susonic » Sat Dec 19, 2009 3:33 am

Ah... I should have looked at the code carefully.
Thank you for the advices, prof. Wilkin. :)

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