Abstract:

In this study an attempt is made to investigate the upper-tropospheric downstream development over north-west Europe, which leads to surface cyclogenesis in the central Mediterranean. A case study is analysed to demonstrate that the upper-tropospheric downstream development could be closely related to the upper-tropospheric frontogenesis that appears upon the north-eastern flank of a blocking high. The frontogenesis is characterised by a jet streak within a strongly baroclinic zone and a tropopause folding associated with cold stratospheric air intrusion into the troposphere. According to this interpretation, the eddy ageostrophic divergence of eddy geopotential fluxes (dispersion and spreading of eddy kinetic energy), other than friction dissipation and barotropic conversion to the mean flow, is mainly responsible for the loss of kinetic energy from a decaying depression of synoptic scale that has passed the mature stage. This dispersed eddy kinetic energy accumulates in the vicinity of the aforementioned jet streak where it is transferred downstream and further triggers the generation or rejuvenation of a new disturbance.

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