Mediterranean hurricanes: large-scale environment and convective and precipitating areas from satellite microwave observations

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 midtropospheric air, reached its maximum intensity and acquired a cyclonic orientation.

Tropical transition of a Mediterranean storm by jet crossing

“…Documented from both the observational (Moscatello et al, 2008b;Claud et al, 2010;Conte et al, 2011) and numerical (Moscatello et al, 2008a;Davolio et al, 2009;Miglietta et al, 2011) points of view, the role of the upper-level trough on the intensification of the storm has been evaluated for the first time.…”

“…This unique dataset combined with the strong intensity of the medicane motivated a number of studies using numerical experiments (Moscatello et al, 2008a;Davolio et al, 2009;Miglietta et al, 2011;Laviola et al, 2011) and satellite observations (Claud et al, 2010;Conte et al, 2011). The overview of the case given below is based on these previous studies.…”

“…Among the Mediterranean cyclones accompanied by upper-level anomalies and deep convection, about 15 mesocyclones have been observed over the last 20 years, preferentially in autumn (Fita et al, 2007). They share some similarities with tropical cyclones and a number of case studies have been made on these hurricanelike cyclones or medicanes (Mediterranean 'hurricanes'; Lagouvardos et al, 1999;Pytharoulis et al, 2000;Reale and Copyright c 2011 Royal Meteorological Society Atlas, 2001;Homar et al, 2003;Fita et al, 2007;Moscatello et al, 2008aMoscatello et al, , 2008bDavolio et al, 2009;Claud et al, 2010;McTaggart-Cowan et al, 2010;among others). A medicane exhibits a clearly defined eye, quasi-circular cloud patterns, strong surface winds sometimes reaching the intensity of a tropical storm, deep convection and the presence of a warm core.…”

A high resolution climatology of precipitation and deep convection over the Mediterranean region from operational satellite microwave data: development and application to the evaluation of model uncertainties

“…According to Kleespies and Watts (2007), based on radiative transfer simulations for diverse atmospheric profiles, the brightness temperature bias between AMSU-B and MHS for channel 5 would be approximately 0.1 K, with a standard deviation of also approximately 0.1 K. A further evaluation, based on a larger sample, indicates that the differences between AMSU-B and MHS depend on the amount of water vapour in the atmosphere and range from −1 to 3 K (in the latter case when the atmosphere is very dry) (John et al, 2012). It has also been suggested that MHS could be more sensitive to convection than AMSU-B (Mo, 2006;Claud et al, 2010).…”

“…Claud et al, 2010). The forecast of the medicane was performed with the nonhydrostatic model Meso-NH (Lafore et al, 1998) using the two-way interactive gridnesting method with triply nested grids, with a horizontal grid spacing of 32, 8 and 2 km.…”