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<p class="MsoNormal"><span style="font-family:"Calibri",sans-serif"></span><span style="font-size:11.0pt">Hi Emma,</span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"> </span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">It is correct that in the Release 4 adjoint, seaice_model_ad and seaice_fake_ad are entirely skipped.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Since sensitivities to atmospheric forcings are not directly altered by the presence of sea ice, I agree with your interpretation that adxx_taux and adxx_tauy represent sensitivities to ocean TAUX/Y, the stress
beneath the sea ice.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Best,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:11.0pt">Ou <o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt"><b><span style="font-size:12.0pt;color:black">From:
</span></b><span style="font-size:12.0pt;color:black">ecco-support <ecco-support-bounces@mit.edu> on behalf of Emma Boland <emmomp@bas.ac.uk><br>
<b>Date: </b>Wednesday, November 6, 2024 at 5:53</span><span style="font-size:12.0pt;font-family:"Arial",sans-serif;color:black"> </span><span style="font-size:12.0pt;color:black">AM<br>
<b>To: </b>ecco-support@mit.edu <ecco-support@mit.edu><br>
<b>Subject: </b>[EXTERNAL] [ecco-support] How to interpret adjoint sensitivities under sea ice in ECCOv4r4</span></p>
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<p>Hi ECCO team,</p>
<p>I'm looking for some guidance in how to interpret what release 4 is doing with the adjoint under sea ice, especially the wind stress sensitivities.</p>
<p>As far as I can tell, the behaviour is controlled by useSEAICEinAdMode (set to false in data.autodiff) and SEAICEapproxLevInAd (appears to be left at default value of 0).</p>
<p>autodiff_params.h says:</p>
<p>" SEAICEapproxLevInAd :: level of approximation in seaice adjoint<br>
C -1 (and .NOT.useSEAICEinAdMode) : use seaice_fake adjoint<br>
C 0 (and .NOT.useSEAICEinAdMode) : omit all of seaice thermo adjoint <br>
C 0 (and useSEAICEinAdMode) : use all of seaice thermo adjoint<br>
C >= 1 (and useSEAICEinAdMode) : omit pieces of seaice thermo adjoint "</p>
<p>So release 4 falls in the second category, "omit all of seaice thermo adjoint". In the adjoint, in do_oceanic_phys_ad, this skips entirely seaice_model_ad
<b>and</b> skips seaice_fake_ad. </p>
<p>Is this correct? I.e. surface sensitivities are not directly altered by the presence of sea ice (although indirectly influenced by the ocean-ice state)? 'omit all of thermo adjoint' seems to imply there is some 'seaice<i> dynamic
</i>adjoint' applied, but I can't obviously see where this is. I'd appreciate any guidance, especially as to whether adxx_taux/y should be therefore interpreted as sensitivities to oceTAUX/Y under ice, rather than EXFtaux/y.</p>
<p>Thanks,</p>
<p>Emma</p>
<p>-- </p>
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<p class="MsoNormal"><span style="font-size:12.0pt">Dr Emma Boland | Physical Oceanographer | British Antarctic Survey
<br>
High Cross, Madingley Road, Cambridge CB3 0ET<br>
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