A frontal zone seen in the satellite images and followed by fields of meteorological parameters, can sometimes deviate from the ideal
configuration of a smooth, layered cloud band. This is particularly the case within the cloud band of a
cold front, but it sometimes also
occurs within occlusions. In such cases the cloud band looks lumpy and the tops of embedded Cbs are very distinct in
all channels. The reason for this phenomenon is enhanced convection. In most cases the frontal
jet has a pronounced component normal to the
frontal zone. Convection is enhanced either by PVA in the left exit of the jet streak or, when the jet is more or less perpendicular to
the front, through a combination of potential instability and frontal convergence. There are also cases in which the jet is parallel to
the frontal cloud band, but there is also strong convection within the frontal zone.
Due to the investigetion on 50 cold fronts, 25 of the layered type and 25 of the convective type, the convective
cold fronts tends to be
more of the Kata type.
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The most distinct difference between a convective and a non convective cold
front is seen in the combination of instability index with
the thermal front parameter. In the case of a convective cold front, high values of the instability index lie within the maximum of TFP,
whilst in a layered cold front, high values of instability index are found behind the TFP, and further away from the
cold front, in the
cold air.
The physical explanation of the differences between the two front types has to be found in the differentiation between instability in
the lower parts of the troposphere and the potential instability. In the case of a convective front, the values of both are much higher
than within a layered cold front.
This is clearly shown in the cross-sections below. The convective front
(left) has a strong potential instability up to 700 hPa, over a broad zone,
while the layered front (right) only has weak potential instability up to 800
hPa.
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References