Abstract
Abstract. Subsynoptic scale vortices that have been likened to tropical cyclones or polar lows (medicanes) are occasionally observed over the Mediterranean Sea. Generated over the sea, they are usually associated with strong winds and heavy precipitation and thus can be highly destructive in islands and costal areas. Only an accurate forecasting of such systems could mitigate these effects. However, at the moment, the predictability of these systems remains limited. Due to the scarcity of conventional observations, use is made of NOAA/MetOp satellite observations, for which advantage can be taken of the time coverage differences between the platforms that carry it, to give a very complete temporal description of the disturbances. A combination of AMSU-B (Advanced Microwave Sounding Unit-B)/MHS (Microwave Humidity Sounder) observations permit to investigate precipitation associated with these systems while coincident AMSU-A (Advanced Microwave Sounding Unit-A) observations give insights into the larger synoptic-scale environment in which they occur. Three different cases (in terms of intensity, location, trajectory, duration, and periods of the year – May, September and December, respectively) were investigated. Throughout these time periods, AMSU-A observations show that the persisting deep outflow of cold air over the sea together with an upper-level trough upstream constituted a favourable environment for the development of medicanes. AMSU-B/MHS based diagnostics show that convection and precipitation areas are large in the early stage of the low, but significantly reduced afterwards. Convection is maximum just after the upper-level trough, located upstream of cold mid-tropospheric air, reached its maximum intensity and acquired a cyclonic orientation.
Highlights
It has been long recognized that hurricane-like cyclones can sometimes form over the Mediterranean (Ernst and Matson, 1983; Billing et al, 1983) where they are referred to as medicanes (Mediterranean “hurricanes”)
They are of smaller size and the typical environment in which they form is different: while tropical cyclones occur in regions characterized by moist conditions, medicanes occur in much drier environment (e.g. Fita et al, 2007a)
deep convective threshold” (DCT) areas are rather marginal for this case that was rather weak, in spite of the impressive structure seen on satellite imagery (Fig. 1b)
Summary
It has been long recognized that hurricane-like cyclones can sometimes form over the Mediterranean (Ernst and Matson, 1983; Billing et al, 1983) where they are referred to as medicanes (Mediterranean “hurricanes”). The vertical profile of the atmosphere, i.e. the presence of cold air at middle and upper levels, combined with rather warm Sea Surface Temperature (SST) and boundary layer (Reed et al, 2001; Emanuel, 2005; Fita et al, 2007a), plays a crucial role in their development. This explains why these systems have been compared to polar lows (Rasmussen and Zick, 1987). Possible implication of the use of AMSU for medicanes research and forecasting are highlighted
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
