The midlatitude Ferrel westerlies

These are the winds of the mid-latitudes emanating from the poleward sides of the subtropical high-pressure cell (see Figure 7.12). They are far more variable than the trades in both direction and intensity, for in these regions the path of air movement is frequently affected by cells of low and high pressure, which travel generally eastward within the basic flow. In addition, in the northern hemisphere the preponderance of land areas with their irregular relief and changing seasonal pressure patterns tend to obscure the generally westerly airflow. The Isles of Scilly, off southwest England, lying in the south-westerlies, record 46 per cent of winds from between south-west and north-west, but fully 29 per cent from the opposite sector, between north-east and south-east.

The westerlies of the southern hemisphere are stronger and more constant in direction than those of the northern hemisphere because the broad expanses of ocean rule out the development of stationary pressure systems (Figure 7.15). Kerguelen Island (49°S, 70°E) has an annual frequency of 81 per cent of winds from between south-west and north-west, and the comparable figure of 75 per cent for Macquarie Island (54°S, 159°E) shows that this predominance is widespread over the southern oceans. However, the apparent zonality of the southern circumpolar vortex (see Figure 7.10) conceals considerable synoptic variability of wind velocity.

Continue reading here: The General Circulation

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  • tomba greenhand
    How is weather affected by the westerlies in the midlatitudes?
    2 years ago