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The westerlies, anti-trades, [2] or prevailing westerlies, are prevailing winds from the west toward the east in the middle latitudes between 30 and 60 degrees latitude. They originate from the high-pressure areas in the horse latitudes (about 30 degrees) and trend towards the poles and steer extratropical cyclones in this general manner. [ 3 ]
A westerly wind burst is defined by Harrison and Vecchi (1997) as sustained winds of 25 km/h (16 mph) over a period of 5–20 days. [3] However, no concrete definition has been determined, with Tziperman and Yu (2007) defining them as having winds of 14 km/h (8.7 mph) and lasting "at least a few days".
The westerlies can be particularly strong, especially in the southern hemisphere, where there is less land in the middle latitudes to cause the flow pattern to amplify, which slows the winds down. The strongest westerly winds in the middle latitudes are called the Roaring Forties , between 40 and 50 degrees south latitude, within the Southern ...
It exists only in an atmosphere with horizontal temperature gradients. [5] The ageostrophic wind component is the difference between actual and geostrophic wind, which is responsible for air "filling up" cyclones over time. [6] The gradient wind is similar to the geostrophic wind but also includes centrifugal force (or centripetal acceleration ...
The term originally derives from the early fourteenth century sense of trade (in late Middle English) still often meaning "path" or "track". [2] The Portuguese recognized the importance of the trade winds (then the volta do mar, meaning in Portuguese "turn of the sea" but also "return from the sea") in navigation in both the north and south Atlantic Ocean as early as the 15th century. [3]
According to recent observations, early signs of spring have already begun in the southern United States. In the Southeast, the spring leaf-out process is 1-2 weeks later than the long-term average.
But the winds above the surface, where they are less disrupted by terrain, are essentially westerly. A low pressure zone at 60° latitude that moves toward the equator, or a high pressure zone at 30° latitude that moves poleward, will accelerate the Westerlies of the Ferrel cell. A strong high, moving polewards may bring westerly winds for days.
It might seem like a simple question. But the science behind a blue sky isn't that easy. For starters, it involves something called the Rayleigh effect, or Rayleigh scattering. But that same ...