The latest satellite-based advancements on the characterization of potential Mediterranean tropical-like cyclones

Mediterranean cyclones often exhibit phenomenological features typical of tropical (or sub-tropical) cyclones (e.g., a cloud free eye surrounded by spiraling rain bands around the center and a closed vortex associated with strong near-surface winds and heavy precipitation) causing extensive devastation over the coastal regions. More rarely (1-3 times per year) these cyclones undergo a tropical-like cyclone transition during their mature phase, exhibiting at some point during their evolution a deep warm core of diabatic origin and deep convection in proximity of the center. These cyclones are referred to as Medicanes (Mediterraean Hurricane). Generally, the term Medicane has been used for both cyclones with tropical-like characteristics, and for weaker warm seclusions present in the late stage of extra-tropical cyclones. The present work analyzes three Mediterranean cyclones (i.e., Helios, Juliette and Daniel) that occurred between February and September 2023. The analysis is mainly carried out using satellite passive microwave (PMW) measurements from different radiometers, which allow to monitor and to characterize the thermodynamic and microphysics characteristics during the cyclones’ life time, in particular the occurrence of a warm core and deep convection.  Moreover, the surface wind field is characterized by exploiting all the available scatterometers onboard LEO satellites (MetOp ASCAT and FY-3E WindRAD) highlighting the differences between the developing and the mature stage of the cyclones. Finally, a preliminary analysis about the role of dynamics and air-sea interaction processes favoring the tropical-like transition is also carried out.

The goal is to determine if the three considered cyclones exhibit tropical-like characteristics during their mature phase and can be considered as medicanes. The three cyclones show a very similar evolution during the initial phases, with stratospheric intrusion followed by the development of a warm anomaly in the low/mid-troposphere around the cyclone center, clearly driven by baroclinic processes. While for Helios, the PMW precipitation microphysics diagnostics show a near complete lack of deep convection near the cyclone center (within 100 km), during the final stage of the mature phase of Juliette and Daniel this feature is identified, indicating that diabatic heating plays a key role in the warm core development. This evolution is observed in nearly all the medicanes which have been studied, as they eventually develop a warm core driven by diabatic processes (e.g., Zorbas, Numa). Based on this analysis, it can be concluded that Helios is warm seclusion, while Juliette and Daniel can be classified as medicanes.