MCSs frequently develop at the leading edge of frontal cloud bands.
A specific distribution is necessary: a warm conveyor belt at low levels
ahead of the front and a dry intrusion in the layers above.
Such a situation develops when a jet streak crosses the front; dry air on the cyclonic side of the jet axis overruns the frontal cloud band and reaches its leading edge. Whilst the relative streams of the dry intrusion are sinking behind the frontal cloud band, they change to rising
when they cross the front.
Under such conditions the troposphere is characterized by :
- frontal conditions indicated by TFP, a zone of high thickness gradients, a downward inclined gradient of isentropes, a frontal circulation created through convergence and upward vertical motion
- a wave developing on the front
- a rising warm conveyor belt in low to middle layers along the leading edge of the frontal cloud band
- a rising dry intrusion in middle to high layers along the same leading edge of the frontal cloud band
- the effect of both conveyor belts lying on top of each other leads to the unstable stratification of the troposphere
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MCSs develop in connection with warm air, therefore they can be found in front of or within the leading parts of cold fronts. Cbs develop in an entirely different synoptic environment, at the rear parts of cold fronts or in the cold air.
References