Weak sea-surface temperature gradients may fuel stronger tropical cyclones
The fact that the ocean gets colder as you go deeper is fairly intuitive, but a similar gradient exists along the surface of the ocean, even at scales of 1 kilometer to tens of kilometers. A new study, published in the Proceedings of the National Academy of Sciences, suggests that this horizontal gradient significantly contributes to the intensity of tropical cyclones, providing a potential tool for better storm warning systems.
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Recent improvements in the resolution of ocean observations and numerical models have indicated that a significant horizontal temperature gradient exists at the sea surface across relatively short distances of 1 kilometer to tens of kilometers. The team involved in the new study says that in situ observations of the upper ocean under extreme cyclone conditions are also rare, making it difficult to study submesoscale processes until now.
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They found that cyclones crossing weak prestorm SSTGs tend to cause less ocean cooling and, thus, more intense storms. Conversely, stronger SSTGs meant more mixing and cooling, resulting in weaker storms. At a global scale, they found that storms over the weakest gradients became about 40% stronger than those over the strongest gradients.
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The study authors write, "Current coupled TC–ocean models generally cannot explicitly resolve these small-scale turbulent processes, highlighting the need for scale-aware parameterizations . Future advances in high-resolution observations, process-resolving simulations, and submesoscale theory are essential for translating the mechanism identified here into improved representations of ocean feedbacks in TC intensity prediction models."