A new classification algorithm for daughter cyclone formation with respect to the parent's frontal system – application for the Mediterranean Basin

Abstract

This article presents a semi-objective methodology to classify formation scenarios of a new 'daughter' cyclone (DC), based on the thermal field characteristics of the parent cyclone (PC). An automated algorithm assigns a DC to one of seven formation types, according to the following considerations: Whether the DC is formed on a front belonging to the parent's frontal system or to a different frontal system, and whether this frontal system is cold, warm or quasi-stationary. An additional type contains DCs formed within the warm sector of the parent. The algorithm uses measures derived from wind and temperature fields at 850-hPa: the temperature gradient, the temperature advection and the temperature Laplacian, each computed at the formation location of the DC, and also the temperature difference between the DC and the PC. The classification method was applied to 4303 Mediterranean DCs which were observed during 33 winters. Totally 85% of the DCs were identified as belonging to one of the seven predefined types, implying that the formation of the remaining 15% was not related to baroclinic or thermal factors. Among the successfully classified DCs, over half were formed on the frontal system of the parent, a third of the DCs on a separate frontal system and only 13% were formed within the warm sector. Most of the 'cold front' cyclones were formed at the major Mountain Lee locations, whereas those formed on warm fronts were generated mostly over the Adriatic, Ligurian and Aegean Seas. Inspection of composite maps of distinct formation types in various regions revealed unique formation scenarios, like DCs forming over western Morocco but belonging to third generation Genoa Lows. Other reflects discontinuous movement of cyclones, resulting from encounter with topographical obstacles, found mostly on PCs' warm fronts, or from the attraction of cyclogenetic areas left behind, mostly on PCs' cold fronts.

Mediterranean cyclones: current knowledge and open questions on dynamics, prediction, climatology and impacts

“…within their warm sector or at the warm front of the parents. Further analysis by Saaroni et al (2017) showed that over half of "daughters" formed on the frontal system of the "parent", one third on a separate frontal system and about 10 % within the warm sector of the "parent" cyclone.…”

The Connection Between North Atlantic Storm Track Regimes and Eastern Mediterranean Cyclonic Activity

“…Alternatively, some western Mediterranean cyclones are directly impacted by their North Atlantic counterparts via clustering. In this case, a secondary smaller low is formed near an existing storm (Ziv et al, 2015;Saaroni et al, 2017;Priestley et al, 2020).…”

Process-based classification of Mediterranean cyclones using potential vorticity

“…In this context, MCs have often been referred to as daughter cyclones (Romem et al, 2007;Ziv et al, 2015). Mediterranean daughter cyclones can appear in various regions relative to their parent cyclone, commonly along the parental frontal system but also in the warm sector, or can be linked to a separate synoptic system (Saaroni et al, 2017). Nevertheless, MCs differ strongly by season, location, duration, extent, and impact.…”