E. Wind Speed and Direction
What Causes Wind?
For example, picture what happens when you take a bucket of water out of a bathtub. There isn't less water in just that one spot. The remaining water distributes over the area of the tub with an even surface at the top. There is a lower level of water overall, but the water that remains is evenly distributed.
When air warms, it rises. The air above land heats faster than the air above water because land absorbs more heat than water (water reflects more of the sun's rays). As a result, the air from the cooler area above water moves into the low-pressure area created by the rising warm air to equalize the pressure of the air. This movement of air to the area of lower pressure causes a breeze from the ocean, especially on a warm day.
In the evening, the water is slow to lose the heat it stored up during the day (slower than the heat loss on land), so the opposite effect occurs. Air from above the land quickly loses its heat as the sun sets, and it is now cooler than the air from above the water. So, as the air above the water is warmed by the heat released from the water, it rises, creating an area of lower pressure than that of the air above the land. The land air moves in from the area of higher pressure to the lower pressure area causing an outgoing breeze from the land.
On a larger level, differences in air pressure are caused by
differences in air temperatures, which causes air to move in patterns,
which cause winds of various intensities. Breezes and winds do not
only occur in places that are close to the water, but the basic
principles are the same in terms of cold and warm air fronts rising,
falling and moving. Cold and warm air fronts play a major role in
temperatures and precipitation around the world. These world systems
are in constant motion causing winds of various strengths and
directions ranging from a very mild breeze to a dangerous hurricane.
Measuring Wind Speed - Beaufort Scale
You can tell that he was British by the wording of the descriptions in the scale. We still use this scale to describe the wind, but we also more accurately measure the speed of the wind now, providing more detailed and useful information for scientists.
An instrument called an anemeter is the instrument used by weather scientists to measure wind speed. These are usually electronic now and computers convert electronic signals from instruments into digital displays.
Measuring Wind Direction
To determine the direction of the wind, you can use a weather vane or a windsock. When describing the direction of the weather, you determine the direction that the wind is coming from and NOT the direction that it is blowing towards. So, if your weather vane's arrow is pointing north, the wind is a southerly wind (comes from the south and is blowing towards the north). If your windsock is pointing to the south east, then you are experiencing a north west wind.
Davies, Kay. (1992). The Super Science Book of Weather. England: Wayland Publishers Ltd.
Dickinson, Terence. (1988). Exploring the Sky by Day. Ontario: Camden House Publishing.
Ward, Alan. (1992). Project Science: Sky and Weather. New York: Franklin Watts Inc.
Mezger, Gabi. (1995). Weather Instruments: Teacher's Guide. New Hampshire: Delta Education Inc.
Kary, Diana. (1996). Ready, Set, Science: Weather Activity Guide. Calgary: Science Alberta Foundation.