Beyond cold and warm: an objective classification for maritime midlatitude fronts

Abstract

This study introduces a detailed and objective classification for midlatitude maritime fronts. The classification is based on a principal component analysis (PCA) to determine the dominant patterns of variability between fronts. Here, fronts are defined as three‐dimensional frontal volumes, which are detected in the ERA‐Interim dataset for a large number of locations in the Atlantic, Pacific and Indian oceans during both winter and summer. In addition to the well‐established distinction between warm and cold fronts, the PCA exposes several new dimensions of variability: (i) front intensity, (ii) surface fluxes and (iii) along‐front transports, linked to the intensity of the associated conveyor belts. These new dimensions of variability are regionally and seasonally robust and a lagged composite analysis demonstrates that each of the new front types evolves in a dynamically characteristic way. Further, the new front types can be related to established ones like katafronts and anafronts. The new front types are finally redefined based on simple parameter thresholds to simplify their application in future studies.