Role of moist and dry air advection in the development of Mediterranean tropical‐like cyclones (medicanes)

Abstract

Two tropical‐like cyclones in the Mediterranean Sea, aka medicanes, are analysed herein by means of numerical simulations. The cyclones, which were recently investigated in Miglietta and Rotunno, Quarterly Journal of the Royal Meteorological Society, 2019, 145, are reconsidered in the present study, in which we focus on their respective preconditioning phases. In particular, here we analyse how local evaporation and/or long‐range transport of air masses may precondition the environment where the Mediterranean cyclones form. Numerical simulations indicate a rather different behaviour for the two cyclones. The first medicane (December 13–15, 2005) developed over the southern Mediterranean Sea, in a region of high low‐level humidity content, which existed before the cyclone formation; the air, originally dry over the eastern Balkans and the African mainland, gained humidity during its transit over the sea surface. In contrast, the second medicane (October 6–10, 1996) strongly intensified while benefitting from the intense sea‐surface fluxes due to the outbreak of Tramontane and Cierzo winds near the Balearic Islands, where the cyclone developed. Although limited to just two case studies, these results identify two different mechanisms conducive to an environment favourable for the intensification of medicanes in the western or southern Mediterranean. In addition, the role of dry air near the cyclone core, associated with upper‐tropospheric dry intrusions, is analysed. Sensitivity experiments were performed, constraining the relative humidity in the initial and boundary conditions to values above 50%. The advantage of this strategy is the ability to change the humidity content in the dry regions without modifying the associated strong potential vorticity anomalies. For both cases, we find that the humidity increase had the effect of inducing an earlier onset of cyclone development and of producing stronger, longer‐lasting vortices.

Mediterranean cyclones: current knowledge and open questions on dynamics, prediction, climatology and impacts

“…The latter includes the investigation of DI's implication in warm seclusion (e.g. Miglietta et al, 2021), the role of frontal structures and the possible role of convection in sustaining the cyclonic circulation alone (Dafis et al, 2020).…”

Mediterranean cyclones: Current knowledge and open questions on dynamics, prediction, climatology and impacts

“…Indeed, open questions on processes still concern the role of vertical wind shear (especially under the presence of superposed jets) and the potential of tropical transition taking place in the region. The latter includes the investigation of DI's implication to warm seclusion (e.g., Miglietta et al, 2021), the role of frontal structures, and the possible role of convection in sustaining alone the cyclonic circulation (Dafis et al, 2020). In addition to open questions on atmospheric processes, other subjects range from the criteria for the reliable definition of medicanes to their classification, both as a particular category and as a member of the broad category of subtropical cyclones, with the possibility of acquiring a tropical cyclone structure in a few cases.…”

Impact of Lightning Data Assimilation on the Short-Term Precipitation Forecast over the Central Mediterranean Sea

“…The role of the Mediterranean Sea in heavy-precipitation storms has been also considered in the literature [56][57][58][59]. Because the Mediterranean Sea is a warm sea, it feeds the cyclones with large amounts of water vapor, reinforcing the cyclones and increasing their lifetime [60]. Often, storms form over the Mediterranean Sea [61][62][63], or spend most of their lifetime over the sea, as in the case of Medicanes [64][65][66], and are then advected toward land, causing floods, windstorm, and surges.…”