Frontogenesis is a term describing the formation of a weather front or the regeneration and intensification of existing, decaying, fronts. The necessary conditions for frontogenesis are:

  • Temperature Gradient - There must be a temperature difference between two air masses. No frontogenesis takes place around the Equator where air Masses are of similar temperature.
  • Convergence of air masses - Air masses must be converging, attempting to occupy the same space.

Convergence of air masses

As an area of low pressure forms in the northern hemisphere, air flows towards the Low and rises. Because of the rotation of the Earth, the winds will flow in an anticlockwise direction around and into the Low. Warm air from the south, and cool air from the north, will be pulled towards the Low. The boundary between the two air masses is a front.

The sharpening of the front

The effect of convergence towards a front is generally to narrow the transitional zone between the adjacent air masses. In other words to sharpen the front. Ageostrophic wind components directed towards the front on both sides, brings the isotherms closer together. The intervening air is squeezed upwards and the transitional zone becomes narrower and the front sharper. The sharpness of the front is maintained against the natural tendency towards a diffuse mixing of the air from each airmass.

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