What is a Front? What are the different types of Fronts?

It’s a term introduced by Bjerkness school in Norway(1918) to describe a sloping boundary plane

or surface of separating 2 air masses that exhibit different meteorological properties or characteristics.

the interface of which may be narrow & on a small scale when it is termed as a -frontal surface(eg.-warm

front associated with depression) & may be broad & on scale of a frontal zone(eg.-Atlantic Polar Front).

The different types of front are as follows:-

1)The Arctic Front:-this is a distinctive baroclinic zone separating the ice & snow of the high Arctic regions from the more moderate polar/tundra environments to the Pacific portion does move further south into N.W.North America in winter as the high Arctic freeze is acentuated by polar night.

2)Polar Front:-It's well known active zone of frontogenesis in Atlantic & pacific oceans. It’s quite variable depending on the seasonal distribution & extent of polar & tropical air masses. In the winter, it shifts equatorwards when the Atlantic front may extend into Gulf of Mexico to represent the juxtaposition of cold north American air mass & warmer Tm air mass. A secondary zone evolvs at this time in the central Pacific whenever the sub-tropical high there is split into 2 cells with converging air currents between them.

                      In summer,it contracts polewards 2 principle zones of polar front activity occur over the mid-latitudes of North America & western Asia/Japan in relation to the general weak meridional temperature gradient. The frontal activity is rather slight at this time of year,compared to the more vigorous winter activity.

3)Medditerranean Front:-This is the only a winter feature when, at intervals, air streams from Europe(Pm/Pc) & N.Africa(Tc) converge Mediterranean sea bringing together air masses of markedly different temperature conditions.

This convergence initiates & sustains frontogenesis, which can lead to cyclogenesis & distributed cyclonic activity with clouds, rain, gales. In summer the sub-tropical westerly Jet stream & sub-tropical anticyclone & the resultant dynamic divergence means that the frontogenesis can't occur, so hot, dry weather preavails.

4)Ocluded front:-a type of front developed in id-latitude depression which results in more than rapidly advancing cold front; the effect is to raise the tropical maritime air mass of the warm sector well above the Earth's surface. The formation of an occlude front thus marks the onset of the decay phase of a depression. Eventually the 2 limbs of the cold front become united &,is fuly occluded latent heat of condensation, the depression, the warm air is found only aloft. With the diminishing supply of latent heat of condensation there are 2 types of occlusion:-

a)Warm occlusion:-It's formed where the advancing cold air is warmer than the cold air ahead of the warm front,it will ride above the leading cold air in manner of a warm front.

b)Cold occlusion:-Where the advancing cold air is cooler than the cold air ahead of the warm front,it will undercut the leading cold air in the manner of a cold front.

       Any cyclone within which there has developed an occluded front is called occluded cyclone. Eg.-Temperate cyclone.

5)Ana Front:-It's  active all the time ,since unstable conditions promote a pronounced uplift of warmer air (analogous to Anabatic wind) & extensive cumuliform clouds develop at cold fronts, often to the tropopause, accompanied by torrential rain/hail showers. when coupled with Jet stream scavenging, Ana cold Fronts can produce violent tornadoes, but these are common in western Europe(compared with more frequent Ana Warm Front).

6)Kata Front:-It's generally inactive since stable conditions are conducive to descending air (analogous to katabatic winds).Air steam convergence occurs in the lowest few kilometers & warm air ascent(& flattened cloud development) is confined to this layer. Above this narrow zone of uplift, divergent or frontolytic conditions exit, with a strong subsidence inversion accentuating stability. Kata warm fronts are rare in Western Europe, although Kata cold fronts are more common in this region but are not conducive to tornado development.