Where does front collide?

In meteorology a front is the sloping boundary between two air masses of different temperature and density, such as the leading edge of a cold air mass undercutting warmer air. J. Bjerknes and the Bergen school named these boundaries in his 1919 On the structure of moving cyclones, borrowing the word from the battle fronts of the First World War, and showed how a travelling cyclone is organised around a warm front and a cold front that can occlude as one overtakes the other. The referent is a physical discontinuity in the atmosphere, marked on a chart and tracked as it moves, and it is unrelated to a line of soldiers, a concealed coalition, or a surface of constant phase. What it names is where two air masses meet, not who faces whom or what a wave is doing.[1]

Unit

A boundary surface between two air masses, tracked on a weather chart

Recovery means

Not applicable

Measured by

Located from temperature, pressure, wind, and humidity gradients and drawn on synoptic charts

In physics a wavefront is a surface on which the phase of a wave is the same at a given instant, so that every point on it is oscillating in step. Born and Wolf's Principles of Optics gives the standard account, in which light spreads as a family of such surfaces, plane or spherical, advancing along the rays at right angles to them. The referent is a geometrical surface defined by constant phase, located in space and measured in the units of the wave itself, and it is not a line of troops, a weather boundary, or a political coalition. It names where a wave is momentarily in phase, a purely physical surface, and a method built for it says nothing about the human meanings of the word.[2]

Unit

A surface of constant phase, advancing at right angles to the rays

Recovery means

Not applicable

Measured by

Constructed from the phase of the wave, as the locus of points reached at the same instant