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Wind direction and speed

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Wind direction and speed

A cup anemometer and windvane. Image by Noaa.gov.

A cup anemometer and windvane. Image by Noaa.gov.

ZIMSEC O Level Geography Notes: Wind direction and speed.

Wind is the movement of air across the earth’s surface due to differences in pressure between two regions. Air moves from high pressure regions to low pressure regions. The differences in pressure can be caused by differential heating of the earth’s surface or by earth and sea breezes.

Two aspects of wind are measured at weather stations:

  1. Wind direction- this is done using a wind wane-the red-tailed instrument in the picture and the information is plotted given in terms of the cardinal points of a compass.
  2. Wind speed- this is done using an cup anemometer and the speed is given in knots or as is increasingly becoming the case in km/hr.

Points of a compass

The points of a compass. Image by MediaWiki.

The points of a compass. Image by MediaWiki.

  • The four points N,S,E and W are referred to as the cardinal points.
  • The additional four points SW,SE,NE and NW are referred to as the inter-cardinal or ordinal points.
  • The additional points e.g. SSW are called the secondary-inter-cardinal points.
  • Wind direction is typically given in using either the cardinal points or sometimes in terms of the ordinal points.

Knots

  • A note is a speed equal to 1.852 Km/hr.
  • It used to be the most popular unit to measure air speed and ZIMSEC examinations and textbooks still use it.
  • It has largely been superseded in most reports by the more familiar metric unit km/hr.

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By | 2017-01-17T11:22:54+00:00 May 19th, 2015|O Level Geography, Weather and Climate|2 Comments

About the Author:

He holds an Honours in Accountancy degree from the University of Zimbabwe. He is passionate about technology and its practical application in today's world.

2 Comments

  1. pretty March 20, 2016 at 8:51 pm - Reply

    Thank you for the notes but we need past examination papers for geography we like people like to our country

    • Garikai Dzoma March 21, 2016 at 6:59 am - Reply

      Hi, we will post question papers eventually but at the moment we have chosen instead to concentrate on adding notes as we are short staffed and do have full time jobs. This is an exhausting venture that continually takes a toll on our personal lives so we try to juggle everything. As I write this I am late for my other job so I have to go.

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