Midterm Colloquium by Pernille Kirstein Hansen – Niels Bohr Institutet - Københavns Universitet

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Midterm Colloquium by Pernille Kirstein Hansen

Cold Wake of Tropical Cyclones in the Atlantic Ocean with Special Focus on Hurricane Nadine.

Tropical cyclones have long been known to leave a trace of cold water in their wake. This study focuses on the ocean's response to long-lasting tropical cyclone Nadine (10 September to 4 October) and is carried out using data from the National Ocean and Atmospheric Administration's High-resolution Blended Analysis of Daily SST and Ice and best track data from the National Hurricane Center.

Nadine became the fourth longest-lived tropical cyclone in the Atlantic basin with its 23,5 days during which it achieved hurricane status twice 13 days apart. It moved around in a loop in the north eastern tropical Atlantic Ocean crossing its own track several times causing a distinctive area of cold surface water. The passage showed an SST decrease of about 3 C primarily due to vertical mixing and upwelling in response to the storm's strong surface winds. When re-encountering its self-induced cold wake, a negative feedback was created, reducing the energy transport from the ocean to the atmosphere decreasing the storm intensity.

Nadine is compared with 5 other tropical cyclones from the same 2012 Atlantic hurricane season which clearly shows a greater area of SST cooling during Nadine. Hurricane Leslie also left a clear trace with an estimated 4 C SST decrease, but not all of the storms showed this tendency. Comparison indicate that slow-moving storms tend to create greater SST anomalies than fast-moving storms. Heavy precipitation also contributes to the cooling of the sea surface. The temperature of the precipitation can be linked to the temperature of the atmosphere, which is colder than the ocean, but the total e ffect is small compared to the resulting vertical mixing.