Preprints
https://doi.org/10.5194/gmd-2021-51
https://doi.org/10.5194/gmd-2021-51

Submitted as: model evaluation paper 14 Apr 2021

Submitted as: model evaluation paper | 14 Apr 2021

Review status: this preprint is currently under review for the journal GMD.

Australian tidal currents – assessment of a barotropic model (COMPAS v1.3.0 rev6631) with an unstructured grid

David Anthony Griffin1, Mike Herzfeld1, Mark Hemer1, and Darren Engwirda2,3 David Anthony Griffin et al.
  • 1Oceans and Atmosphere, CSIRO, Hobart, TAS 7000, Australia
  • 2Center for Climate Systems Research, Columbia University, New York City, NY, USA
  • 3NASA Goddard Institute for Space Studies, New York City, NY, USA

Abstract. While the variations of tidal range are large and fairly well known across Australia (less than 1 m near Perth but more than 14 m in King Sound), the properties of the tidal currents are not. We describe a new regional model of Australian tides and assess it against a validation dataset comprising tidal height and velocity constituents at 615 tide gauge sites and 95 current meter sites. The model is a barotropic implementation of COMPAS, an unstructured-grid primitive-equation model that is forced at the open boundaries by TPXO9v1. The Mean Absolute value of the Error (MAE) of the modelled M2 height amplitude is 8.8 cm, or 12 % of the 73 cm mean observed amplitude. The MAE of phase (10°), however, is significant, so the M2 Mean Magnitude of Vector Error (MMVE, 18.2 cm) is significantly greater. The Root Sum Square over the 8 major constituents is 26 % of the observed amplitude. We conclude that while the model has skill at height in all regions, there is definitely room for improvement (especially at some specific locations). For the M2 major-axis velocity amplitude, the MAE across the 95 current meter sites, where the observed amplitude ranges from 0.1 cm s−1 to 156 cm s−1, is 6.9 cm s−1, or 22 % of the 31.7 cm s−1 observed mean. This nationwide average result is encouraging, but it conceals a very large regional variation. Relative errors of the tidal current amplitudes on the narrow shelves of NSW and Western Australia exceed 100 %, but tidal currents are weak and negligible there compared to non-tidal currents, so the tidal errors are of little practical significance. Looking nation-wide, we show that the model has predictive value for much of the 79 % of Australia’s shelf seas where tides are a major component of the total velocity variability. In descending order this includes the Bass Strait, Kimberley to Arnhem Land and Southern Great Barrier Reef regions. There is limited observational evidence to confirm that the model is also valuable for currents in other regions across northern Australia. We plan to commence publishing ‘unofficial’ tidal current predictions for chosen regions in the near future, based on both our COMPAS model and the validation data set we have assembled.

David Anthony Griffin et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on gmd-2021-51', Anonymous Referee #1, 25 May 2021
    • AC1: 'Reply on RC1', David Griffin, 01 Jul 2021
  • RC2: 'Comment on gmd-2021-51', Anonymous Referee #2, 08 Jun 2021
    • AC1: 'Reply on RC1', David Griffin, 01 Jul 2021
  • CC1: 'Comment on gmd-2021-51', roger proctor, 09 Jun 2021
    • AC1: 'Reply on RC1', David Griffin, 01 Jul 2021

David Anthony Griffin et al.

David Anthony Griffin et al.

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Short summary
In support of the developing ocean renewable energy sector, and indeed all mariners, we have developed a new tidal model for Australian waters and thoroughly evaluated it using a new compilation of tide gauge and current meter data. We show that while there is certainly room for improvement, the model provides useful predictions of tidal currents for about 80 % (by area) of Australian shelf waters. So we intend to commence publishing tidal current predictions for those regions soon.