This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: 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.
Forecasting tropical cyclone intensity is currently more difficult than forecasting where the storm will go. This is mostly because tropical cyclone intensity is affected by many conditions in the atmosphere and ocean. Scientists know that these storms draw their power from warm ocean water.
But the storm's winds can churn colder water up from layers below, cooling the sea surface. This normally results in a reduction in the storm's intensity. Previous research also found that deep warm water can limit storm-driven cooling and enable rapid intensification and that winds blowing along ocean fronts can increase upper-ocean mixing.
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. Yet these processes may be important for helping scientists predict storm intensity.
To see how sea surface temperature gradients (SSTGs) affect tropical cyclone intensity, the team combined global tropical-cyclone track records from 2003–2022 with high-resolution satellite sea surface temperature maps. They measured small-scale temperature gradients days before storms arrived, then compared these gradients with storm-driven cooling and later changes in cyclone wind speed. 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. The study authors write, "Considering more extreme cases, tropical cyclones (TCs) with rapid intensification (RI) reach much greater strength within a short time, posing a major challenge for operational forecasting.
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