Form page for development work

A wiki page associated with a give action should be created in wiki/${YEAR}WP/${WORKING_GROUP|INSTITUTE}-${ACTION_NUMBER}_${PI} using this template.
From that, you can customize it while editing within the TracForm container {{{#!TracForm ... }}}. If necessary, you can copy the entire form (add a number _[0-9] to wiki page name) or the respective area in order to match the number of the (P)Reviewer(s). The best solution is not to extend significantly the length of the page.

This is the color code for the fulfilment of this form:

PI(S)

Previewer(s)

Reviewer(s)

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The PI is responsible to closely follow the progress of the action, and especially to contact NEMO project manager if the delay on preview (or review) are longer than the 2 weeks expected.

Abstract

A Wetting and Drying (W/D) Method for NEMO-shelf Based on Flux Limiter

Hedong Liu and Jason Holt (NOC, UK)

NEMO discretize its computational domain with the structured C-grid, hence its W/D algorithm needs to deal with two types of grid cells: velocity grid cells and tracer grid cells. The essences of current method are to keep the positivity of watermass and avoid unphysical overshooting of velocity.At the same time, this method must respect the properties of local and global mass conservation. There are quite many existing methods for W/D,(see Balzano,A, 1998 and Medeiros,S.C. and Hagen,S.C, 2013). But there are still some robustness issues, such as model stability, computational efficiency. In the current method, a flux limiter has been developed to take care of the mass positivity while a new barotropic pressure gradient filter is developed to prevent the velocity overshooting at the wetting and drying cells on a steep slope.

In the following parts of this note, we will first derive the flux limiter and demonstrate its applications to the continuity equation, tracer equations. As the momentum equations is also linked with the W/D processes, we then detail the design of the gravity forcing filter which aims to remove the errors generated by the normal pressure gradient calculations in the W/D area. The implementation of the method in NEMO v3.6_STABLE source code will be illustrated at the last.

Flux limiter

In NEMO, the water column can be considered as a control volume V. The horizontal advection is the main process causing the wetting and drying on the grid cells (with the evaporation and precipitation as the other two reasons which will be dealt separately). For such a control volume V, we can define a flux limiter as follows:

This section should be completed before starting to develop the code, in order to find agreement on the method beforehand.

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Once the PI has completed this section, he should send a mail to the previewer(s) asking them to preview the work within two weeks.

Preview

Since the preview step must be completed before the PI starts the coding, the previewer(s) answers are expected to be completed within the two weeks after the PI has sent his request.
For each question, an iterative process should take place between PI and previewer(s) in order to reach a "YES" answer for each of the following questions.

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Once all "YES" have been reached, the PI can start the development into his development branch.

Tests

Once the development is done, the PI should complete this section below and ask the reviewers to start their review in the lower section.

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Review

A successful review is needed to schedule the merge of this development into the future NEMO release during next Merge Party (usually in November).

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Once review is successful, the development must be scheduled for merge during next Merge Party Meeting.