B15 Supercycling of ocean passive tracers: Design Document
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
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 | |
| V2.0 |
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.