The Design Document page provides a description of the algorithms, implementation and planned testing including unit, verification, validation and performance testing. Please read Step 1.3 Performance Expectations that explains feature documentation requirements from the performance group point of view.

Design Document

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The first table in Design Document gives overview of this document, from this info the Design Documents Overview page is automatically created.

In the overview table below 4.Equ means Equations and Algorithms, 5.Ver means Verification, 6.Perf - Performance, 7. Val - Validation

Equations: Document the equations that are being solved and describe algorithms
Verification Plans: Define tests that will be run to show that implementation is correct and robust. Involve unit tests to cover range of inputs as well as benchmarks.
Performance expectations: Explain the expected performance impact from this development
Validation Plans: Document what process-based, stand-alone component, and coupled model runs will be performed, and with what metrics will be used to assess validity

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In the table below 4.Equ means Equations and Algorithms, 5.Ver means Verification, 6.Perf - Performance, 7. Val - Validation, - competed, - in progress, - not done

Overview table for the owner and an approver of this feature

1.Description	Implement supercycling advection of ocean passive tracers
2.Owner	Katherine Smith Andrew Bradley Mathew Maltrud
3.Created	Aug 13, 2021
4.Equ
5.Ver
6.Perf
7.Val
8.Approver	Katherine Calvin (Unlicensed)
9.Approved Date	20 Aug 2021
V2.0

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Table of Contents

Title: Ocean Passive Tracer Supercycling

Requirements and Design

E3SM CBGC Group

Date: 08/13/2021

Summary

Transport of ocean BGC tracers is ~70% of the cost of MPAS-O (when BGC tracers are turned on). We hypothesize that the advection step of the BGC tracer transport can be increased to 2-3 times that of the baroclinic time step with little loss in accuracy, thereby decreasing the overall cost of transport for BGC tracers in the ocean. We propose to implement a tracer-consistent, mass-conserving supercycling of the advection of all passive tracers in MPAS-O. If possible, options to (i) supercycle the tracer advection at time-steps larger than the sea-ice coupling interval (referred to as supercycling-over-coupling [SOC]) and (ii) subcycle the BGC reactions will be included. We propose to validate the scheme in MPAS by testing in a G-case configuration (ocean + ice), comparing mass conservation of carbon within the ocean, and comparing monthly averages of BGC tracer outputs.

Requirements

Requirement: Implement supercycling up to ocean-ice coupling time interval

Date last modified: 08/16/2021
Contributors: Andrew Bradley

Requirement: Implement supercycling of tracer over the ocean-ice coupling time interval (for use in spin-up of low-res)

Date last modified: 08/16/2021
Contributors: Andrew Bradley

Requirement: Implement nightly test in E3SM

Date last modified: 08/16/2021
Contributors: Katherine Smith

Algorithmic Formulations

Date last modified: 08/13/2021

Contributors: Andrew Bradley

Design and Implementation

Supercycling is implemented by accumulating the total mass flux when integrating the total density rho, using the b coefficients in the RK4 table combined with averaging over multiple steps. This mass flux is then used as the total mass flux when integrating mixing ratios q.

Date last modified: 08/13/2021

Contributors: Andrew Bradley

Planned Verification and Unit Testing

Verification and Unit Testing: Test tracer-consistency

Date last modified: 08/13/2021

Contributors: Andrew Bradley

Tracer consistency is tested by setting one debugTracer to a constant value and measuring its departure from that value in each cell in each time step.

Verification and Unit Testing: Test mass-conservation

Date last modified: 08/13/2021

Contributors: Andrew Bradley

Mass conservation is tested by measuring global mass at each time step and comparing with the first time step.

Planned Validation Testing

Validation Testing: Validating oceanic carbon mass-conservation

Date last modified: 08/13/2021

Contributors: Katherine Smith

Global simulations will be performed and comparisons of oceanic carbon mass-conservation will be compared between non-supercycled, suercycled, and supercycled over the ocean-ice coupling time interval will be compared. We expect mass-conservation to be comparable between all three.

Validation Testing: Validate against satellite products for ocean surface Chl-a/NPP

Date last modified: 08/13/2021

Contributors: Katherine Smith

Global simulations will be performed and comparisons of ocean surface CHl-a will be compared between non-supercycled, suercycled, and supercycled over the ocean-ice coupling time interval will be compared. We expect minimal changes to occur when switching on supercycling (both under and over the ocean-ice coupling time interval).

Planned Performance Testing

Performance Testing: Determine performance by running MPAS-O with Supercycling turned on and off.

Date last modified: 08/13/2021

Contributors: Andrew Bradley and Katherine Smith

We will test the performance of the supercycling feature by running a global simulation with and without supercycling turned on and compare timers of overall run time between the two. We expect a speed up of the run time with supercycling turned on.

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