= PHYPRO-01_agn_OSMOSIS_science

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== Summary

||=Action       ||PHYPRO-01_agn_OSMOSIS_science                       ||
||=PI(S)        || George Nurser                                                ||
||=Digest       || Improvements to OSMOSIS OBL to improve behaviour in shelf-sea areas and under sea ice     ||
||=Dependencies || If any                                                ||
||=Branch       || source:/NEMO/branches/{YEAR}/dev_r{REV}_{ACTION_NAME} ||
||=Previewer(s) || Names                                                 ||
||=Reviewer(s)  || Names                                                 ||
||=Ticket       || #2352                                                 ||

=== Description

Improve OSMOSIS ocean boundary layer (OBL)  model in 3 areas:

1. Ensure consistent behaviour of OSMOSIS-OBL under ice. Revert to classic shear turbulence based on ice-ocean turbulent friction velocity where ice areal coverage is high; scale with ice fraction between shear turbulence and Langmuir turbulence model. Where Stokes drift unavailable, move to parametrised form.

2. Improve representation of OSMOSIS-OBL mixing in equatorial regions. Include mixing associated with shear of mean flow as in equatorial undercurrent.

3. Mixing in shelf seas. The OSMOSIS-OBL is primarily a surface boundary layer model and so is not set up for bottom-driven tidal mixing. We intend to transition to GLS in shelf seas.
􏱔􏱦􏱋􏱌􏱧􏱎
􏱺􏱢􏱟􏱺􏱢􏱞􏱢 􏱪􏱏􏱱􏱎􏱔􏱎 􏱓􏱜􏱩􏱎􏱋 􏱪􏱎􏱬􏱷􏱣􏱏􏱎􏲀 􏱣􏱜 􏱐􏱱􏱎 􏱐􏱋􏱌􏱦􏱣􏱏􏱪 􏱴􏱪􏱱􏱎􏱬􏱋 􏱾􏱣􏱐􏱱 􏱎􏲄􏱓􏱬􏱐􏱌􏱋􏱣􏱬􏱤 􏱓􏱜􏱩􏱎􏱋􏱏􏱓􏱋􏱋􏱎􏱜􏱐􏱵 􏱬􏱜􏱩 􏱣􏱜 􏱪􏱱􏱬􏱤􏱤􏱌􏱾
􏱪􏱱􏱎􏱤􏱫 􏱪􏱎􏱬􏱪 􏱴􏱣􏱜􏱐􏱎􏱋􏱬􏱏􏱐􏱣􏱌􏱜 􏱾􏱣􏱐􏱱 􏱕􏱌􏱐􏱐􏱌􏱔 􏱕􏱌􏱓􏱜􏱩􏱬􏱋􏱝 􏱤􏱬􏱝􏱎􏱋􏱵􏲂 􏱰􏱎􏱧􏱎􏱤􏱌􏱦 􏱩􏱣􏱬􏱨􏱜􏱌􏱪􏱐􏱣􏱏􏱪 􏱎􏱜􏱎􏱋􏱨􏱝 􏱕􏱓􏱩􏱨􏱎􏱐 􏱐􏱌 􏱬􏱪􏱪􏱓􏱋􏱎
􏱎􏱜􏱎􏱋􏱨􏱎􏱐􏱣􏱏 􏱏􏱌􏱜􏱪􏱣􏱪􏱐􏱎􏱜􏱏􏱝􏲂􏱞􏱔􏱦􏱋􏱌􏱧􏱎
􏱺􏱢􏱟􏱺􏱢􏱞􏱢 􏱪􏱏􏱱􏱎􏱔􏱎 􏱓􏱜􏱩􏱎􏱋 􏱪􏱎􏱬􏱷􏱣􏱏􏱎􏲀 􏱣􏱜 􏱐􏱱􏱎 􏱐􏱋􏱌􏱦􏱣􏱏􏱪 􏱴􏱪􏱱􏱎􏱬􏱋 􏱾􏱣􏱐􏱱 􏱎􏲄􏱓􏱬􏱐􏱌􏱋􏱣􏱬􏱤 􏱓􏱜􏱩􏱎􏱋􏱏􏱓􏱋􏱋􏱎􏱜􏱐􏱵 􏱬􏱜􏱩 􏱣􏱜 􏱪􏱱􏱬􏱤􏱤􏱌􏱾
􏱪􏱱􏱎􏱤􏱫 􏱪􏱎􏱬􏱪 􏱴􏱣􏱜􏱐􏱎􏱋􏱬􏱏􏱐􏱣􏱌􏱜 􏱾􏱣􏱐􏱱 􏱕􏱌􏱐􏱐􏱌􏱔 􏱕􏱌􏱓􏱜􏱩􏱬􏱋􏱝 􏱤􏱬􏱝􏱎􏱋􏱵􏲂 􏱰􏱎􏱧􏱎􏱤􏱌􏱦 􏱩􏱣􏱬􏱨􏱜􏱌􏱪􏱐􏱣􏱏􏱪 􏱎􏱜􏱎􏱋􏱨􏱝 􏱕􏱓􏱩􏱨􏱎􏱐 􏱐􏱌 􏱬􏱪􏱪􏱓􏱋􏱎
􏱎􏱜􏱎􏱋􏱨􏱎􏱐􏱣􏱏 􏱏􏱌􏱜􏱪􏱣􏱪􏱐

=== Implementation

The development branch for 2019-WP action VALID-02_GeorgeN-evalOSMOSIS has recently been synchronized with source:/NEMO/trunk@12925 (changesets [12928] and [12934])and will form the basis for the source-code "streamlining" activities of action 2020WP/ENHANCE-14_smueller_OSMOSIS_streamlining. A new branch with the new physics will be spun-off this streamlined branch 2020WP/ENHANCE-14_smueller_OSMOSIS_streamlining.


Changes for (1) and (2) will be mostly restricted to the routine zdfosm.F90. There will be a new subroutine added to handle the shear-induced mixing.

The transitioning to GLS will require setting up of the GLS routine zdfgls.F90 and code to link it with the master routine zdfosm in zdfosm.F90


=== Documentation updates

An extra paragraph or two will be added to the documentation in section 9.1.5 of the manual.

== Preview 

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[[Include(wiki:Developers/DevProcess#preview_)]]
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== Tests

1. UNDER_ICE_OSMOSIS_TEST

 Aim: to test that OSMOSIS_OBL behaves correctly under ice for a range of ice fractions \\
 Configuration: 2D model SI3 + OCE, with domain_cfg, idealised forcing (cooling/freezing phase + warming/melting phase , initial state with gradation in ice cover. \\

 Output diagnosed mixed-layer depth after specified time of cooling/mixing. Check against control run values.

 Defined but not developed.

2. EQUIATORIAL_OSMOSIS_TEST

 Aim: to test that OSMOSIS_OBL gives a  reasonable diurnal cycle of near-equatorial mixing \\
 Configuration: 2D model with ideal-age tracer TOP + OCE along meridional section across the equator 5°S--5°N  with initial state with westerly surface zonal flow and easterly zonal undercurrent, zero ideal-age tracer throughout. \\
 Idealised diurnal cycle of surface forcing.

 Output mixed-layer depth + vertical profile of age tracer after specified time of cooling/mixing. Check against control run values.

 Defined but not developed.


3. SHELF_OSMOSIS_TEST

 Aim: to test that OSMOSIS_OBL gives a smooth transition between open ocean and shelf conditioins \\
 Configuration uncertain. Might again use 2D model with gradient in tidal flow and/or bottom depth
 Output and check profile of diagnosed mixed-layer depth against control run values.

 Loosely defined and  not developed.



== Review

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[[Include(wiki:Developers/DevProcess#review)]]
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