Description of a flexible and extendable

physical-biogeochemical model system

for the water column

Hans Burchard 1, Karsten Bolding 2, Wilfried Kuhn 3,

Andreas Meister 4, Thomas Neumann 1, Lars Umlauf 1,

hans.burchard@io-warnemuende.de

1. Baltic Sea Research Institute Warnemunde, Germany; 2. B olding & Burchard

Hydrodynamics, Asperup, Denmark; 3. Institute of Oceanogr aphy, University of Hamburg,

Germany; 4. Faculty of Mathematics and Informatics, Univer sity of Kassel, Germany

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 1/??

Motivation for GOTM-BIO

Major aim:

Building a framework for coupledphysical-biogeochemical model simulations

Starting from the existing GOTM (see below) model, weintend to

extend the physics towards the needs ofbiogeochemical modelling: wrt. mixing, air-seainteraction, light

set up example biogeochemical models properly linkedto physics

provide documentation and support for use andextention of model

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 2/??

Cooperation, funding

IOW staff involved: Lars Umlauf, Thomas Neumann,Hans Burchard

External scientists involved: 200 registered GOTMusers, plus unknown number of unregistered people

No direct funding. Planned as integrating model forSOPRAN (German SOLAS, FS 1). Used in 3D modelGETM (QuantAS-OFF funding, Küste & Gesellschaft)

Current status: house project, part of IOW modelenvironment, maybe BMBF funding requested

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 3/??

GOTM, http://www.gotm.net

Challenge

Aim

The Idea

Key features

Software

Fortran code

Test cases

Forcing

How to run?

Information

What's

Publications

E-mail list

FAQ

User Group

Hot Links

Who's Who?

Guestbook

PPM:

10/26/00 20:48:54

New

GOTM is a one-dimensional numerical modeldeveloped and supported by a core team ofocean modellers. GOTM aims at simulatingaccurately vertical exchange processes in themarine environment where mixing is known toplay a key role. GOTM is freely available underthe GPL (Gnu Public License).

The interested user can download the sourcecode , a set of test cases (Papa, November, Flex,...) and a comprehensive report .

You are warmly invited to join the GOTM mailinglist and send any comments/questions to theGOTM team or become a GOTM contributor . TheGOTM developers are grateful to their sponsors .

Page "www.gotm.net" maintained by webmaster. Last update: 10/28/00 18:10:02

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 4/??

GOTM

GOTM is a physical model for the water column withstate-of-the-art turbulence parameterisations

GOTM has conventional light and air-sea flux modelsincorporated

GOTM is Public Domain since 1999 (25.000 loginssince then)

Under Google, GOTM turbulence gives 554 hits

Many extentions to GOTM exist. E.g. both ERSEM(European Regional Seas Ecosystem Model) versionsare implemented into GOTM, see e.g. Allen et al. 2004.

GOTM is popular because of its quality turbulencemodels which perform numerically sufficiently stable.

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 5/??

What is it good for ?

Any kind of ecosystem modelling in the water columncan be investigated. Advantage: fast execution, highresolution; disadvantage: neglect or parameterisation oflateral processes

The user has to properly describe the processes ! Oncethis is done, model modification should be easy.

Focus on fast processes such as photochemistry ispossible, see SOPRAN proposal.

In the following, we will show some example results.

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 6/??

Stiff versus explicit solvers

Surface nutrient content in Northern North Sea seen withnumerical different solvers:

-35

-30

-25

-20

-15

-10

-5

0

5

10

0 50 100 150 200 250 300 350

RK4, ∆t = 20 s

nut(z

=0)

[mm

olN

m−

3]

4th-order Runge-Kutta

RK4, ∆t = 2 hRK4, ∆t = 1/2 h

Julian Day 1998

0

2

4

6

8

10

0 50 100 150 200 250 300 350

RK4, ∆t = 20 s

nut(z

=0)

[mm

olN

m−

3]

Julian Day 1998

Modified Patankar-Runge-Kutta

MPRK2, ∆t = 2 hMPRK2, ∆t = 1/2 h

Explicit solver at long time steps (left) does not obey nutrient limitation. Stiff solver (right,

Burchard et al. [2003]) is stable and accurate. Note the different scales.

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 7/??

Neumann et al. 2002 model

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 8/??

Gotland Basin simulations

Basic experiment: model simulations for 1983-1991 atstation 271 in Central Gotland Sea. Forcing by output ofatmospheric model, initialisation by physicalobservations.

Sensitivity studiesExperiment with increased diapycnal mixing(kmin = 4 · 10−6 J kg−1 instead kmin = 1 · 10−6 J kg−1)Experiment with increased wind forcing in Februaryand March (factor 2 applied to wind speed inFebruary and March)

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 9/??

Base run: temperature

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 10/??

Base run: Chl-a

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 11/??

Base run: DIN

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 12/??

Base run: DIP

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 13/??

Base run – Dia run: O2

solid: Base run; dashed: increased diapycnal mixing

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 14/??

Base run – Wind run: Cyanos

solid: Base run; dashed: increased winter storms

FS2 Workshop, Baltic Sea Research Institute Warnemunde, Germany, Mar. 13, 2005. – p. 15/??