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.