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 KNOTS, PLUS OTHER WIND INFORMATION

METEOROLOGIST JEFF HABY

It seems strange that a knot is so close to miles per hour. There are 1.15 miles per hour in 1.00 knots. Why is this unit needed when we already have miles per hour? Who invented knots? For what purpose were knots invented? Knots are the unit of wind measurement given on weather charts. Why then are they expressed as miles per hour to the general public? Why not just keep them as knots? Is it because the average person knows what a mile per hour is but has less of an understanding of knots? I'm contemplating the reaction a broadcast meteorologist would get if they suddenly began expressing wind speed in knots. Why are wind speeds over water expressed in knots while they are expressed in miles per hour over land? This is probably due to land vehicles giving speed in miles per hour and water going vehicles giving speeds in knots. Also, the units of knots were invented over a water surface to help with navigation. Being able to convert miles per hour to knots and vice versa is important.

The surface wind speed in knots is multiplied by 1.15 to get the speed in miles per hour. A 100 knot wind is equal to 115 miles per hour while a 10 knot wind is equal to 11.5 miles per hour. Therefore, the stronger the wind the greater the difference between the numerical value of miles per hour and knots. Here are some of the answers to the questions posed above. A knot is exactly equal to 1/60th of a degree of latitude. A 1/60th of a degree of latitude is known as a minute of latitude. Therefore a knot is equal to one minute of distance. There are 90 degrees from the equator to the pole. Therefore a knot is 1/5,400th the distance from the equator to the pole. This number is found by multiplying 90 (degrees from equator to pole) * 60 (number of minutes in a degree of latitude). The nautical mile is based on how our system of ocean navigation evolved, using a circle of 360 degrees, with each degree divided into 60 minutes and 60 seconds. At sea, one's position is always based on degrees, minutes and seconds, so therefore how fast you traverse the ocean is based on "minutes" traveled per unit time (hour); hence, the nautical mile per hour or knot. In centuries past, mariners determined the speed of their ships using a knotted "log line." The buoyant line was let out freely as the ship sailed along, and then the number of knots let out during a given time gave the shipmaster a measure of his vessel's speed.

VECTORS: Many graphical model outputs denote the wind speed at all levels in the troposphere by the use of wind vectors. The longer the winds vector, the stronger the wind. The disadvantage is that exact wind speeds are not given. It can however, give you a relative sense to which locations are experiencing strong or weak wind. Wind vectors can be used to analyze vorticity advection, divergence, convergence, confluence, and diffluence. These all have important meteorological implications.