Huang et al.  present a pioneering work pointing to an important problem of physical oceanography. The concept of potential spicity or spiciness which is desired to be orthogonal to the potential density in the potential temperature-salinity space has been discussed for nearly half a century. The potential density–potential spicity coordinate provides a new diagnostic tool for water mass analysis in the world’s oceans. Particularly, the orthogonality of the coordinate enables a definition of the distance between water masses and thus the radius of signal and radius of the state. The potential spicity proposed in this study is significant progress and can be widely used in oceanography.
Citation: Huang, R. X., Yu, L.‐S., & Zhou, S.‐Q. . New definition of potential spicity by the least square method. Journal of Geophysical Research: Oceans, 123. https://doi.org/10.1029/2018JC014306
—Lei Zhou, Editor, JGR: Oceans