ZONAL INDEX The measure of the strength of the westerly winds of the middle latitudes. It is expressed as the horizontal pressure difference between 35 degrees and 55 degrees latitude, or as the corresponding geostrophic wind.
One method is to use a measure of the 500 mbar strength between defined latitudes: By taking the difference between mean 500 mbar contour heights between latitude 35 and 60 North, this simple method yields high numbers ( a high zonal index ), ...
index - 1. The indicating part of an instrument; for example, the hand of a watch or the meniscus of a mercury column. 2. See circulation index. 3. See zonal index.
zonal westerlies"The average west-to-east component of wind over the continuous 20- degree belt of latitude in which this average is a maximum. It is usually found, in the winter season, in the vicinity of 40-60°N latitude. See zonal index.
 See also: Zonal, Air, Pressure, Meteor, Surface
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