Potential vorticity patterns in Mediterranean “hurricanes”

Abstract

The potential vorticity (PV) anomalies due to the intrusion of dry stratospheric air and those generated by the tropospheric diabatic latent heating are qualitatively analyzed for five Mediterranean tropical‐like cyclones (also known as Medicanes). Model simulations show the presence of an upper level PV streamer in the early stages of the cyclone, located on the left exit of a jet stream, and a middle‐low level PV anomaly generated by the convection developing around the low‐level vortex. In the mature stage, the upper level PV anomaly around the cyclone evolves differently for each case and appears somehow dependent on the lifetime. Only for the 2006 Medicane, the PV anomalies form an intense PV tower extending continuously from the lower troposphere to the lower stratosphere.

Development mechanisms for Mediterranean tropical‐like cyclones (medicanes)

“…For example, it would be interesting to explore how the different nature of the cyclones discussed here is connected with the location of cyclogenesis, that is, if western Mediterranean cyclones, which can take advantage of more intense sea fluxes associated with mesoscale winds, can more easily reach a fully tropical‐like structure. The analysis presented here and that of the intense cyclone occurring in November 2011 (Miglietta et al, ) in the western Mediterranean seem to support this hypothesis.…”

“…As in Fita and Flaounas (2018), the Kain-Fritsch (Kain, 2004) convection scheme is employed, since it provides a more realistic track compared to the simulation using the Betts-Miller scheme for this case (which produces an erroneous landfall over northern Libya). Following the conclusions in Miglietta et al (2017) and considering that convection is explicitly resolved in the inner grid, we expect the cyclone properties to be robust and independent of the different choice of the parametrizations adopted in the two control runs. We checked that this is the case for both events; the simulations showed only relatively minor sensitivity to the physical schemes, both in terms of position and intensity of the cyclone.…”

“…A similar evolution was observed in idealized numerical experiments using an axisymmetric non-hydrostatic model to reproduce the evolution of a polar low (Emanuel and Rotunno, 1989) and in the simulations of the intense TLC that developed in the western Mediterranean in November 2011 (see fig. 2a,b in Miglietta et al, 2017), where a maximum in "wet" PV developed in its mature stage. In contrast, for the second cyclone the weaker sea-surface fluxes do not allow any further development, and the vortex remains connected with the large-scale PV structure in which it formed (Figure 14d).…”

“…In that case, a tropical transition and a dramatic intensification occurs after a short but intense interaction of the cyclone with an upper‐level PV streamer associated with a different, large‐scale cyclone (fig. c,d in Miglietta et al, ), undergoing a strong intensification as it moved close to the left exit of a jet stream (Chaboureau et al, ).…”

Sensitivity of a Mediterranean Tropical-Like Cyclone to Different Model Configurations and Coupling Strategies

“…In particular, [9] showed how the use of more resolved and realistic SST fields (as in our case WRF10) with respect to the adoption of remotely sensed SST satellite fields with low spatial and temporal resolution (as our case WRF5) can play an important role to achieve better results in terms of trajectory and intensity of the cyclone. Other studies have focused on the identification of the physical factors that led to the formation and maintenance of this TLC [60]. In this study, we evaluate the sensitivity to initial conditions, resolution of the SST and to different levels of coupling, starting with a standalone WRF setup (with different initialization times), then employing a coupled atmospheric-ocean (AO) approach and finally a fully coupled implementation including waves (AOW).…”