Research and Development of SWOT Measurements in the Canadian Oceans: Part II 1Guoqi Han, 1Will Perrie, 1Jim Gower, 1Josef Cherniawsky, 2Nicolas Grisouard, 3Francis Poulin

1Fisheries and Oceans Canada, 2University of Toronto, 3University of Waterloo

Objectives •To improve knowledge of coastal and

submesoscale processes off the Canadian coasts

• To improve coastal tide models for more

accurate tide correction in the Canadian coastal

ocean.

•To understand wave-current interactions in the

Gulf Stream front zone

• To develop a model for correcting infragravity

wave effects

•To diagnose the SWOT signature of interactions

between geostrophic flows and

•Invisible near-inertial waves

•High-mode internal tides

Infragravity Waves

Interactions between

Geostrophic flows and

high-mode internal tides

High-resolution

Modelling

Acknowledgement: The project is supported by the SWOT Canada (SWOT-C) Program, Canadian Space

Agency.

References

Chen, C. R. H. Liu and R. C. Beardsley, 2003. An unstructured grid, finite volume primitive equation coastal ocean model: Application to coastal

ocean and estuaries. J. Atmos. Oceanic Technol., 20, 159-186.

Chen, C., R. Beardsley, and G. Cowles, 2006. An unstructured grid, finite-volume coastal ocean model. FVCOM user manual, second edition,

315pp.

Ardhuin, F., A. Rawat Arshad, and J. Aucan, 2014. A numerical model for free infragravity waves: Definition and validation at regional and global

scales. Ocean Modelling, 77, 20-32. http://dx.doi.org/10.1016/j.ocemod.2014.02.006.

Figure 10. Internal tides do possess an altimetric signature, which in the

submesoscale range will be difficult to distinguish from that of

geostrophically balanced motions. Using pre-existing numerical datasets and

with the help of idealized numerical experiments, we will develop a

methodology to disentangle the two types of signatures without relying on

temporal information

In numerical studies, ultra high-resolution two-way dynamically coupled

models for wave-current interactions in frontal regions of the Gulf Stream

show evidence for the impact of strong submesoscale currents on ocean

surface features, particularly ocean surface waves and sea surface heights.

We will also improve coupled wave-current models for wave-current

interaction features.

Initial high-resolution coastal models have been established and are being

refined off Eastern Canada. This is based on COAWST – coupled ROMS,

SWAN and WRF models for ocean, waves and atmosphere, respectively.

•Zhimin Ma (Postdoc)

•Guoqiang Liu (Research Associate)

Oceanic infragravity waves are surface gravity waves with periods of several

minutes and corresponding wavelengths of 1-10 kilometers. When propagating

freely in the deep ocean, these waves cause an additional several centimeters

variations in the sea surface level; but in the coastal regions, they can cause

large sea level variations up to 10 centimeters. In the context of future wide-

swath SWOT altimetry mission, these waves need to be better quantified as

they have wavelengths that will be resolved by such measurements. Moreover,

the energies of these infragravity waves are expected to be a significant

contribution to the error budget for possible measurements of the sea level

height associated with submesoscale currents, at horizontal scales of around

1~10 km. Therefore, global numerical models of infragravity waves will likely be

very necessary for the analysis of the planned SWOT mission. Preliminary

versions of these models are presently emerging in the literature (Ardhuin et al.,

2014). Thus, it will be possible to determine the noise level induced by the

infragravity waves in the SWOT data, which will help to get the more accurate

estimates of submesoscale currents in the open ocean and in coastal Canadian

waters.

Wave-Current Interactions

Figure 6. A high-resolution coastal and embayment model

off Eastern Newfoundland is being established.

Other Contributors

Figure 9. In this example, we initiate an unstable sub-inertial internal

wave embedded in a submesoscale front. We let it break and explore the

consequences on the energy budget of the front.

Interactions between

Geostrophic flows and near-

inertial waves Near-inertial waves are horizontal fluid oscillations with a very weak altimetric

signature. However, they can strongly interact with fronts and eddies. What is

their “shadow” influence on submesoscale geostrophic flows, and can it be

diagnosed from space? We will conduct numerical and theoretical experiments

to expand our knowledge on inertial wave-submesoscale interactions.

☜ Near-

inertial wave,

trapped in a

submesoscale

front, breaking

• High-mode internal tides interacting with submesoscale flows ⇒ decoherence.

• How to de-tide (or de-geostrophize…)?

☜ Mode-1

Internal tide

scattered by

geostrophic

eddies

We will improve high-resolution three-dimensional

circulation models for selected regions in the Canadian

Atlantic, Pacific, and Arctic based on existing DFO

modeling work. These circulation models will resolve

submesoscale features such as coastal upwelling and

shelf-edge fronts that meet the requirement to fulfill

SWOT objectives. We will use the Finite Volume Coastal

Ocean Model (FVCOM), an unstructured grid, three-

dimensional, primitive equation, finite-volume coastal

ocean model (Chen et al., 2003; 2006), to simulate coastal

tides and shelf circulation.

We will generate simulated SWOT data in Canadian

waters based on existing regional model output and a

SWOT simulator provided by the Jet Propulsion

Laboratory (JPL). Various error sources from orbit,

instrument, and geophysical corrections will be

considered in generating simulated SWOT data. The

simulated SWOT data will be analyzed to extract

mesoscale and submesoscale features.

The SWOT ocean simulator will also be applied to

generate simulated coastal sea level data from tide-gauge

observations and from model outputs. The simulated data

will be analyzed to examine capability of capturing storm

surges during the cal/val mission with a 1-d repeat cycle.

Figure 8. Global simulation of wave heights from infra-gravity waves (m), which

has same order as SWOT signal noise level: May 6 2012 at 12:00 UTC.

Figure 7. Difference of Significant Wave Height between SWAN and

ROMS-SWAN coupled model: 2012 Oct 01- 2012 Oct 14.