Frontogenesis

Frontogenesis is the synoptic-scale process by which a horizontal temperature gradient on a chosen pressure or isentropic surface is intensified, forming or sharpening a meteorological front. A front is the boundary between air masses with contrasting temperatures and humidities. Frontogenesis occurs when air of different temperatures is advected toward each other by the flow, especially where deformation or convergence acts on an existing gradient. Upper-level dynamics, such as jet streaks, can generate ageostrophic circulations that enhance low-level convergence and vertical motion, reinforcing surface frontogenesis.

Frontogenesis is opposed by frontolysis, the decay or weakening of a front, which can result from diffluence, divergence, entrainment, or turbulent mixing that erodes the gradient.

Forecasting uses diagnostic fields of frontogenesis and frontolysis derived from wind, temperature, and geopotential data to identify where fronts will intensify and lift air to produce precipitation. The rate of change of the temperature gradient normal to the front is a key diagnostic, and is considered with the gradient’s orientation and the surrounding flow.

Frontogenesis is a central concept in midlatitude meteorology, underpinning the evolution of fronts associated with extratropical cyclones, drylines, and warm and cold fronts. It is closely linked to processes such as isentropic ascent, deformation, and ageostrophic circulations that shape weather along fronts.

See also: frontolysis, weather front, mid-latitude cyclone, isentropic analysis.