Exploring how a warmer Mediterranean Sea affects the origin and development of destructive Tropical-Like Cyclones

An enhanced understanding of Climate Change related implications in the maritime domain is needed in order to improve coastal infrastructure resilience and possible future operations, also in terms of climate security. Although the Mediterranean Sea is a relatively mild basin, it is however characterized by high geopolitical and economic relevance, occasionally showing intense cyclones with tropical-like characteristics known as Tropical-Like Cyclones (TLC). Many studies have highlighted that sea surface temperature (SST) distribution and anomalies play a crucial role in modulating the intense air-sea exchange, hence controlling both development and evolution of TLCs. However, given the complex interplay among ocean mixed layer, heat content and temperature, the role of the mixed layer depth (MLD) is of paramount importance. In this study we investigated the role of both SST anomaly, horizontal gradients and MLD profile on the origin and evolution of a recent record-breaking TLC (named IANOS). This cyclone originated over the southern Ionian Sea from 14 Sept 2020 to 19 Sept 2020, moving over the Central Ionian Sea from south-west to North-East, and made landfall over Greece mainland coast. It developed over a basin where a positive SST anomaly up to 4 °C was detected, which coincided with the sea area where it reached the maximum intensification and strength. We conducted a series of experiments using an atmospheric model (WRF - Weather Research and Forecasting system) driven by underlying SST (standalone configuration), either with daily update or coupled to a simple mixed-layer ocean model (SLAB ocean), with SST calculated at every time step using the SLAB ocean for a given value of the MLD. Sensitivity tests were performed increasing or decreasing MLD depth by 10 m, 30 m, 50 m, 75 m, 100 m, removing the horizontal gradients, removing the SST anomaly. Then, possible past and future climatological scenarios of MLD thickness were identified and tested. Preliminary results show that the MLD influences not only the intensity of the cyclone but also the structure of the precipitation field both in terms of magnitude and location. The fundamental role of the SST anomaly was also found to be essential to provide intense characteristics to IANOS. Results deserve further investigation in particular in the context of climate change scenarios that can provide useful insights into impact on coastal civil and military infrastructures in the whole Mediterranean region.