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Wind Terms: Wind Windvane / Anemometer Beaufort Douglas Wind The wind blows because air has weight. Cold air weights more than warm air, so the pressure of cold air is greater. When the sun warms the air, the air expands, gets lighter, and rises. Cooler, heavier air blows to where the warmer and lighter air was, or in other words, wind usually blows from areas of high air pressure to areas of low pressure. If the high pressure area is very close to the low pressure area, or if the pressure difference (or temperature difference) is very great, the wind can blow very fast. Although wind blows from areas of high pressure to areas of low pressure, it doesn't blow in a straight line. That's because the earth is rotating. In the northern hemisphere, the spin of the earth causes winds to curve to the right. (To the left in the southern hemisphere) This is called the coriolis force. So in the northern hemisphere, winds blow clockwise around an area of high pressure and counter-clockwise around low pressure. You can mesure wind with a Anemometer Windvane / Anemometer The use of simple instruments to indicate the direction of wind is very old practice. However, the measurement of its force and speed is a much more recent accomplishment. The first record of the wind vane was first done about 300 years ago, but the first practical use of this instrument took place in the last half of the 1800s. Anemometer (Greek anemos, “wind”; metron, “measure”), an instrument that measures wind speed. The most common kind of anemometer consists of three or four cups attached to short rods that are connected at right angles to a vertical shaft. As the wind blows, it pushes the cups, which turn the shaft. The number of turns per minute is translated into wind speed by a system of gears similar to the speedometer of an automobile. Wind velocity is also measured by the pressure of the air blowing into a Pitot tube (an L-shaped tube, one end open toward the flow of air and the other end connected to a pressure-measuring device), and electrically by the cooling effect of the wind on a heated wire, which causes the electric resistance of the wire to change. An anemometer in which surface is held normal, or nearly normal, to the wind is theoretically simple but more difficult in practice. Beaufort Scale: Scale: Name English: Name Spanish: Average wind speed in Knots: 0 Calm Calma 0 1 Light Air Ventolina 2 2 Light Breeze Flojito 5 3 Gentle Breeze Flojo 10 4 Moderate Breeze Bonancible 16 5 Fresh Breeze Fresquito 20 6 Strong Breeze Fresco 25 7 Moderate Gale Frescachón 30 8 Fresh Gale Temporal 35 9 Strong Gale Temporal Fuerte 45 10 Whole Gale Temporal Duro 50 11 Storm Temporal Muy Duro 60 12 Hurricane Temporal Huracanado 70 Douglas Scale: Scale: Name English: Name Spanish: Average wave height in Metres: 0 Calm Calma 0 1 Rippled Rizada 0 - 0.25 2 Smooth Marejadilla 0.25 - 0.50 3 Slight Marejada 0.50 - 1.25 4 Moderate Fuerte Marejada 1.25 - 2.50 5 Rough Gruesa 2.50 - 4.00 6 Very Rough Muy Gruesa 4.00 - 6.00 7 High Arbolada 6.00 - 9.00 8 Very High Montañosa 9.00 - 14.00 9 Phenomenal Enorme More then 14 metres

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