Meteorological environments associated with medicane development

Abstract

ABSTRACT:Medicanes are 'Mediterranean tropical-like cyclones', warm-core cyclones that occasionally put in danger the islands and coastal regions. In spite of large geographical differences between the Mediterranean Sea and the tropical oceans, their genesis mechanisms, based on the thermodynamical disequilibrium between the sea and the atmosphere, are similar.The special characteristics of the medicanes make their detection difficult: only with high resolution meteorological analysis data and dense maritime observations that task would be possible. An alternative method, using satellite data and restricted criteria about the disturbance symmetry, size and lifespan, has been successfully used to detect 12 medicanes from 1982 to 2003.To enhance the medicane prediction capability or even to assess the risk potential in future climates, it is necessary to characterize the special conditions of the synoptic-scale meteorological environments that are needed for their development and maintenance. By comparing these environments against the bulk of Mediterranean cyclonic situations, high values of mid-tropospheric relative humidity, significant diabatic contribution to the surface level equivalent potential temperature, and low values of tropospheric wind shear, are revealed as important parameters involved in medicane genesis, as in tropical cyclones. An empirical genesis index previously derived for the tropical cyclones is also tested in the study, and its behaviour is revealed as a possible discriminative parameter of the precursor environments.In the context of the growing concern about how climate change will affect the number and intensity of hurricanes, a preliminary analysis for medicanes has been done here. By projecting the previous empirical index into three different global climate model (GCM)-simulated climates, spatial distributions of the monthly index values have been evaluated. The monthly mean values and the frequency of extreme values of this index tend to decrease, showing that the number of days with a medicane risk tends to reduce at the end of the 21st century.

Detection and thermal description of medicanes from numerical simulation

“…Comparing our results with those obtained in previous studies based on a larger number of cases, three of four cyclones are developed in two preferred areas of occurrence, the Ionian Sea and the surroundings of the Balearic Islands, identified by Miglietta et al (2013) and in agreement with Tous and Romero (2013). Another cyclone developed west of Sardinia, a region where other medicanes are also located in the two aforementioned papers.…”

“…Two of them occurred in the western Mediterranean in early Fall and two have been identified in central-eastern Mediterranean in winter. Three of them have been selected from the aforementioned satellite-derived database (Tous and Romero, 2013). The ECMWF T1279L91Cy36r1 forecast model (hereafter ECT1279), which corresponds to a horizontal resolution of 15 km (detailed documentation is available at http://www.…”

Simulation of medicanes over the Mediterranean Sea in a regional climate model ensemble: impact of ocean–atmosphere coupling and increased resolution

“…The reference database shows a clear autumn maximum (September and October), while the percentage of winter medicanes is smaller than in the simulations. However, the appearance of January medicanes in the simulations is similar to that observed in other climatologies like Tous and Romero (2013) or Cavicchia et al (2013). Differently from the reference database, the latter climatologies include also the 1990s and the 1980s and thus cover all the years analyzed in the simulations.…”

“…The lowest number of medicanes is detected over the eastern Mediterranean. Other observed databases like that of Tous and Romero (2013) show similar spatial locations. The RCMs reproduce well the eastern minimum, and on average the high resolution runs improve the distribution between the western and central Mediterranean areas.…”

“…Reanalysis data are too coarse for detecting and characterizing medicanes adequately. This has led to the use of satellite data as the main way for obtaining databases of medicanes (Tous and Romero 2013). Miglietta et al (2013) combined satellite data and high resolution limited area meteorological model simulations to identify additional aspects of medicanes such as their warm core structure and high low-level wind speed.…”