3. Stability

Changing Stability » Advection Frontal Inversions

Idealized soundings through an anafront and a katafront

Fronts mark a boundary between two air masses, which sometimes may be seen in soundings, most often as a frontal inversion.

Observational studies of cyclones and frontal zones have determined that there are two primary types of cold frontal zones: katafronts and anafronts. With a katafront the component of flow perpendicular to the frontal zone is downward toward the surface of the earth, while with an anafront air flows up the face of the frontal surface. A cold anafront is akin to a warm front in reverse and reveals a similar sounding pattern.

This plot shows two idealized soundings for an anafront and a katafront. The anafront sounding, on the left, shows a weak frontal inversion and a small dewpoint depression, indicating a deep layer of high relative humidity. The katafront sounding, on the right, shows a rather strong inversion aloft, which has been enhanced by subsidence along the frontal zone. This subsidence also creates a substantial layer of dry air, shown by the large dewpoint depression above the inversion.

Typically, passage of an anafront is marked by a sharp drop in temperature at the surface, but not humidity, while passage of a katafront is marked by a sharp drop in humidity, but not temperature.