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Last edited [[Timestamp]]

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'''Author''' : Karen Edwards 

'''ticket''' : #855

'''Branch''' : [https://forge.ipsl.jussieu.fr/nemo/browser/branches/2011/dev_r2802_TOP_substepping] 
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=== Description ===
Update the substepping option (using nn_dttrc) to work in the new TOP routines in VN3.3.1. This includes reintroducing the variable nittrc000 throughout the code and including the provision for averaging physics variables over the substep period. 

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=== Testing ===
Testing could consider (where appropriate) other configurations in addition to NVTK].

||NVTK Tested||!''NO!''||
||Other model configurations||!''AMM7, MED12!''||
||Processor configurations tested||[1x1, 1x2 and 4x8]||
||If adding new functionality please confirm that the [[BR]]New code doesn't change results when it is switched off [[BR]]and !''works!'' when switched on||!''YES!''||

(Answering UNSURE is likely to generate further questions from reviewers.)

'Please add further summary details here'

 * Processor configurations tested
 * etc----

=== Bit Comparability ===
||Does this change preserve answers in your tested standard configurations (to the last bit) ?||!''YES - for physics !'''||
||Does this change bit compare across various processor configurations. (1xM, Nx1 and MxN are recommended)||!''NO!''||
||Is this change expected to preserve answers in all possible model configurations?||!'''YES - for physics/ NO - for TOP models'''||
||Is this change expected to preserve all diagnostics? [[BR]]!,,!''Preserving answers in model runs does not necessarily imply preserved diagnostics. !''||!''YES!''||

If you answered !'''NO!''' to any of the above, please provide further details:

 * Which routine(s) are causing the difference?
 * Why the changes are not protected by a logical switch or new section-version
 * What is needed to achieve regression with the previous model release (e.g. a regression branch, hand-edits etc). If this is not possible, explain why not.
 * What do you expect to see occur in the test harness jobs?
 * Which diagnostics have you altered and why have they changed?Please add details here........

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=== System Changes ===
||Does your change alter namelists?||!'''NO !'''||
||Does your change require a change in compiler options?||!'''NO !'''||

If any of these apply, please document the changes required here.......

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=== Resources ===

If substepping is used (nn_dttrc >1 in namelist_top), a set of time mean arrays are allocated to average a number of the physics variables over the 
tracer step. This will also decrease run time needed as the main TOP_SRC routines are not called every model time step.

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=== IPR issues ===
||Has the code been wholly (100%) produced by NEMO developers staff working exclusively on NEMO?||!'''YES/ NO !'''||

If No:

 * Identify the collaboration agreement details
 * Ensure the code routine header is in accordance with the agreement, (Copyright/Redistribution etc).Add further details here if required..........