Frontal Movement

About a hundred cold fronts track along the southern coasts of South Africa and Australia annually, i.e. about two a week on average. Most derive from low pressures at about 60°S, extending into the troughs between subtropical highs (Figure 12.1 and Figure 12.7), as in Figure 13.1 for a particular day. They are typically oriented north-west—south-east and tend to

Figure 13.5 The correspondence of cloud seen from a satellite and the position of a front, both at noon GMT on 8 November 1995. The dashed line indicates the position of a prefrontal trough (Figure 13.2).

Figure 13.6 The position of the front of the Southerly Change that traversed the south island of New Zealand on 2 February 1988. The lines are isochrones showing the boundary of the cold air at the given times of day.

behind the southern end. The northern end may extend well towards the equator, especially in winter. For instance, there is a cold front through Mt Isa (at 20°S in Queensland) several times a year in the form of a shallow wedge of cooler air, travelling as a density current (Note8.C ) through the PBL. Ripples form at night as the front ploughs through the stable air, and they can run ahead on top of the PBL to create a Morning Glory in the Gulf of Carpentaria (Note 8.L).

Cold fronts in South America can travel as far as 5°S in the lee of the Andes (Figure 13.8). Such an incursion of polar air, known as a friagem, can greatly harm Brazil's coffee crop (Section 3.6).

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  • Virginio
    What is frontal movement?
    8 years ago

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