# Evaluation of the accuracy of an offline seasonally-varying matrix transport model for simulating ideal age

## Abstract

Newton-Krylov solvers for ocean tracers have the potential to greatly decrease the computational costs of spinning up deep-ocean tracers, which can take several thousand model years to reach equilibrium with surface processes. One version of the algorithm uses offline tracer transport matrices to simulate an annual cycle of tracer concentrations and applies Newton’s method to find concentrations that are periodic in time. Here we present the impact of time-averaging the transport matrices on the equilibrium values of an ideal-age tracer. We compared annually-averaged, monthly-averaged, and 5-day-averaged transport matrices to an online simulation using the ocean component of the Community Earth System Model (CESM) with a nominal horizontal resolution of 1° × 1° and 60 vertical levels. We found that increasing the time resolution of the offline transport model reduced a low age bias from 12% for the annually-averaged transport matrices, to 4% for the monthly-averaged transport matrices, and to less than 2% for the transport matrices constructed from 5-day averages. The largest differences were in areas with strong seasonal changes in the circulation, such as the Northern Indian Ocean. As a result, for many applications the relatively small bias obtained using the offline model makes the offline approach attractive becausemore »

- Authors:

- Univ. of California, Irvine, CA (United States)
- National Center for Atmospheric Research, Boulder, CO (United States)
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

- Publication Date:

- Research Org.:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

- Sponsoring Org.:
- USDOE National Nuclear Security Administration (NNSA)

- OSTI Identifier:
- 1275512

- Alternate Identifier(s):
- OSTI ID: 1398012

- Report Number(s):
- SAND-2016-6880J

Journal ID: ISSN 1463-5003; PII: S1463500316300750

- Grant/Contract Number:
- AC04-94AL85000

- Resource Type:
- Journal Article: Accepted Manuscript

- Journal Name:
- Ocean Modelling

- Additional Journal Information:
- Journal Volume: 105; Journal Issue: C; Journal ID: ISSN 1463-5003

- Publisher:
- Elsevier

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 58 GEOSCIENCES; 54 ENVIRONMENTAL SCIENCES; implicit solver; ideal age; Newton–Krylov; offline; transport matrix; global ocean modeling

### Citation Formats

```
Bardin, Ann, Primeau, Francois, Lindsay, Keith, and Bradley, Andrew.
```*Evaluation of the accuracy of an offline seasonally-varying matrix transport model for simulating ideal age*. United States: N. p., 2016.
Web. doi:10.1016/j.ocemod.2016.07.003.

```
Bardin, Ann, Primeau, Francois, Lindsay, Keith, & Bradley, Andrew.
```*Evaluation of the accuracy of an offline seasonally-varying matrix transport model for simulating ideal age*. United States. doi:10.1016/j.ocemod.2016.07.003.

```
Bardin, Ann, Primeau, Francois, Lindsay, Keith, and Bradley, Andrew. Thu .
"Evaluation of the accuracy of an offline seasonally-varying matrix transport model for simulating ideal age". United States.
doi:10.1016/j.ocemod.2016.07.003. https://www.osti.gov/servlets/purl/1275512.
```

```
@article{osti_1275512,
```

title = {Evaluation of the accuracy of an offline seasonally-varying matrix transport model for simulating ideal age},

author = {Bardin, Ann and Primeau, Francois and Lindsay, Keith and Bradley, Andrew},

abstractNote = {Newton-Krylov solvers for ocean tracers have the potential to greatly decrease the computational costs of spinning up deep-ocean tracers, which can take several thousand model years to reach equilibrium with surface processes. One version of the algorithm uses offline tracer transport matrices to simulate an annual cycle of tracer concentrations and applies Newton’s method to find concentrations that are periodic in time. Here we present the impact of time-averaging the transport matrices on the equilibrium values of an ideal-age tracer. We compared annually-averaged, monthly-averaged, and 5-day-averaged transport matrices to an online simulation using the ocean component of the Community Earth System Model (CESM) with a nominal horizontal resolution of 1° × 1° and 60 vertical levels. We found that increasing the time resolution of the offline transport model reduced a low age bias from 12% for the annually-averaged transport matrices, to 4% for the monthly-averaged transport matrices, and to less than 2% for the transport matrices constructed from 5-day averages. The largest differences were in areas with strong seasonal changes in the circulation, such as the Northern Indian Ocean. As a result, for many applications the relatively small bias obtained using the offline model makes the offline approach attractive because it uses significantly less computer resources and is simpler to set up and run.},

doi = {10.1016/j.ocemod.2016.07.003},

journal = {Ocean Modelling},

number = C,

volume = 105,

place = {United States},

year = {Thu Jul 21 00:00:00 EDT 2016},

month = {Thu Jul 21 00:00:00 EDT 2016}

}

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