Near-surface wind field characterization of medicanes using satellite observations

Abstract

MEDIterranean hurriCANES (Medicanes) represent a subcategory of Mediterranean cyclones that typically originate as extratropical systems then acquiring characteristics similar to tropical cyclones (TCs). These include the warm core, a nearly symmetric near-surface wind circulation, and eye-like features with spiraling rainbands. This study employs satellite scatterometer data to analyse ocean near-surface wind field in order to detect the rotational center by means the newly developed Medicane Rotational Center Automated Detection (MeRCAD) algorithm. As for TCs, the radius of maximum wind (RMW) is defined as the distance between the rotational center and the area of maximum wind. Results show a significant decrease in RMW, often down to a few tens of kilometres, when the wind field is featured by a nearly symmetric circulation. This allows wind features to be used as an indicator of the possible transition to the mature stage. We also found that the maximum sustained wind associated with the medicanes' mature phase is mostly beyond 95th percentile of values observed for all Mediterranean cyclones, although they appear substantially weaker than TCs. In addition, if the tropical transition occurs, the warm core is fueled by an area of deep convection that may be located near the rotational center at distances shorter than the RMW. However, the presence of an almost symmetrical wind circulation alone is insufficient to indicate the occurrence of the mature phase, due to the possible lack of a warm core. Vice versa, the warm core may occur without the characteristic nearly-symmetric wind circulation.