Abstract
Studies have shown that hurricanes and typhoons, apart from being extreme weather phenomena, cause increases in marine chlorophyll-a concentrations and even phytoplankton blooms. Medicanes are the tropical-like Mediterranean cyclones that induce hazardous weather conditions as well. In this study, a couple of medicanes, over the central and eastern parts of the Sea, are examined for the first time in respect to their possible influence on chlorophyll concentrations. The affected area was delineated with the use of numerical model data, while the sea surface temperature and chlorophyll variations were assessed based on satellite-derived data. The results showed that medicanes trigger surface chlorophyll increases; after the cyclones’ passage, the concentrations were higher compared both with those before and with the climatological monthly values over a large part of the affected area. The mechanisms proposed to explain hurricanes’ favorable influence on chlorophyll concentration seem to be valid for medicanes as well. Area averaged chlorophyll concentrations presented analogous increases to the ones reported for hurricanes, though on a smaller scale. Despite the much lower intensity of medicanes compared with hurricanes, the observed increase in surface chlorophyll after their passage points to their favorable influence.
Highlights
The Mediterranean Sea is characterized by a very high rate of cyclone formation and is ranked as one of the world’s main regions for cyclogenesis [1,2,3]
The affected area was delineated with the use of numerical model data, while the sea surface temperature and chlorophyll variations were assessed based on satellite-derived data
The results showed that medicanes trigger surface chlorophyll increases; after the cyclones’ passage, the concentrations were higher compared both with those before and with the climatological monthly values over a large part of the affected area
Summary
The Mediterranean Sea is characterized by a very high rate of cyclone formation and is ranked as one of the world’s main regions for cyclogenesis [1,2,3]. The Mediterranean cyclones gain features of tropical cyclones: “eye”, axisymmetry with spiral cloud bands, very strong surface winds and warm core [4,5]. Due to their similarities with hurricanes, these cyclones are called Mediterranean hurricanes or medicanes [4]. Climatological approaches have estimated the medicanes’ frequency to ~1.5 per year for the whole basin [6,15,16]; they have indicated the most common regions for medicane formation: the western Mediterranean (around the Balearic islands) and the Ionian Sea (often extended southward to the North African coast) [6,14,16,17]. A frequency decrease along with an intensity increase is predicted for medicanes in the following years [15,18,19,20]
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