Oceanography | Early Online Release
the depth of greatest sound speed variability (Figure 4d). As the
number of layers increased, the mean and standard deviation of
the sound-speed profles converged, with very little diference
between the 48- and 96-layer simulations. Tese results parallel
the fndings that, for a 1 km horizontal grid spacing, a minimum
of 48 isopycnal layers is necessary to resolve displacement of iso-
pycnals by internal tides.
A DEEP LEARNING APPROACH TO INCLUDING
IGW IN OCEAN MODELS
Te fner grid spacing and the inclusion of tidal forcing in ocean
simulations improves the realism of the ocean state. However,
these improvements in a global ocean model are computationally
expensive. To reduce computational cost, we investigated using a
generative adversarial network (GAN; Goodfellow et al., 2014) to
generate a tidally forced ocean state without solving the physical
forcing equations. GANs are a deep learning technique that learn
a transformation from one statistical distribution to another
instead of learning an exact distribution. In a GAN, a “generator,”
which generates new data, is trained alongside a “discriminator,”
which is a classifer that diferentiates between actual data and
generated data. Te GAN works through iteration, with the gen-
erator learning a distribution transformation and the discrimina-
tor learning to distinguish between real data and generated data.
We trained two pairs of generators and discriminators using
Global HYCOM (1/25°) with (Exp. 19.0) and without (Exp. 19.2)
FIGURE 6. Comparison of acoustic propagation and properties between HYCOM simulations with and without tidal forcing at the Amazon Shelf, starting
at 4.1°N, 44.8°W and extending 30° (clockwise from north) as indicated in Figure 3a. (a) A snapshot from May 20, 2019, 18:00:00 of sound speed (m s–1),
vertical gradient of sound speed (s–1), and transmission loss (TL; dB) for each simulation. (b) A single sound speed profile at 100 km distance along the
radial for the tidal (red) and non-tidal simulation. (c) TL at 20 m depth, sonic layer depth (SLD) and below-layer gradient (BLG). TL is calculated from a
1,500 Hz source at 4.1°N and 44.8°W at 20 m depth.