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Frontology

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The front #

A front is a region of the troposphere constituting a dynamic and thermal transition zone between two air masses with different characteristics (Source: Météo-France).

A front is a surface of discontinuity (transition zone) where two air masses with different properties confront each other. There are different types of fronts:

  • warm fronts,
  • cold fronts,
  • occluded fronts,
  • stationary fronts.
Cold front

Cold front

Cold air, which by its dynamics, meets warmer air.
Warm front

Warm front

Warm air, which by its dynamics, meets colder air.
Occluded front

Occluded front

A blanket of warm air that overhangs colder air.
Stationary fronts form when two air masses with different characteristics meet but have no flow toward each other.

Going further

Creating a disturbance #

Creating a disruption

Creating a disruption

Step 1 and 2: warm air from the south and cold air from the north meet. The air masses do not mix, the system begins to roll up: this is the birth of the warm and cold fronts.

Stage 3: the system begins to turn counterclockwise. The warm air is trapped by the cold air.

Step 4: Trapped between the two cold air masses, the warm air is rejected at altitude: this is the beginning of the occlusion. The fact of turning will create a depression associated with the disturbance. At the end of the life of a disturbance, the air masses amalgamate and/or no longer become sufficiently different to maintain the fronts: this is frontolysis.

Disturbance seen from above #

Perturbation seen from above

Perturbation seen from above

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