How to measure the? the wind? Sunshine? The answer here.
Measurement of atmospheric pressure and barometers
Atmospheric pressure is the pressure exerted by the column ofabove a surface. It depends on weather conditions and decreases with altitude. It is commonly measured in hectopascals (hPa, hundreds of Pascal) and is worth an average of 1,013 hPa at sea level.
The pressure is measured using barometers. Thecolumn barometer is the best known. Developed by Torricelli in 1643, it includes a glass tube about 80 cm long, closed at one end. In his experience, Torricelli filled it with mercury and returned it. The mercury then dropped without flowing. This phenomenon is a direct consequence of the atmospheric pressure and the lowering is all the stronger as the pressure is low.
Current barometers still use this method. The only difference is that the open part is now bent upwards. Some Torricelli barometers also have a constriction that locally increases the amplitude of mercury displacement and allows a more precise measurement (of the order of one-tenth of a millimeter of mercury). Finally, the measured value is to correct the altitude (to reduce the pressure at sea level, ten hPa for 80 altitudes) and temperature (the mercury has a large coefficient of).
It should be noted that the indications “Rain – Variable – Beautiful” placed on some barometers do not make much sense because the evolution of the pressure matters more than its strict value: a rising pressure is a sign of good weather, even if the pressure is low in absolute value. Likewise, a high but declining pressure is a sign of deterioration of the weather situation.
Another type of barometer, the barometer recorder, consists of a metal container in which one has evacuated and reacted to variations in pressure. Its wall is then subjected towhich, communicated to a stylet applied to a rotating cylinder, make it possible to trace the evolution of the pressure. Some barometers use the principle of the empty container but are not recorders.
The average pressure is of the order of 10 5 N () per square meter, which was formerly called the (its thousandth is the millibar) and which is worth 10 5 Pa (Pascal) or 1000 hPa (hectopascal).
Wind measurement: wind vane (direction) and speed (anemometer)
The wind is a horizontal movement of air on the surface of the Earth. It arises from a difference in pressure, and propagates perpendicularly to the isobars, from high pressures to low, to reduce pressure differences. The wind can be defined by its direction (most often its origin) and by its(in Beaufort, kilometer per hour, meter per second …).
A wind vane is used to measure wind direction and anfor speed.
The wind vane is a plate of variable shape, movable about a vertical axis and placed at the top of aor mast. Under the effect of the wind, the wind vane is placed in the direction of the wind (the plate on the opposite side to the origin of the wind). Reading the angular position of the wind vane, in the or electronically, gives the direction of the wind.
The anemometer is an instrument that serves, in general, to measure the flow velocity of a gaseous fluid. It can consist of a simple propeller equipped with a speed(which must then be oriented in the direction of the wind) or a rotor supporting three half-spheres placed at 120 ° from each other and equipped with a sensor.
Measurement of sunshine and heliograph
The density of cloud cover is important for the localand its evolution. It is also called “cloudiness” and is measured in bytes: an 8/8 sky is completely overcast and a 4/8 sky is half covered.
The instrument used to measure the cloudiness is theinstrument that indicates the of sunshine from sunrise to sunset sun. It consists of a glass ball which, by acting as a magnifying glass, concentrates the sun’s rays on a strip of paper where they burn the surface locally. This strip of paper is graduated in an hour is its study allows us to know, at every moment of the day if the solar rays crossed or not the cloud cover.
It is also possible to useto measure the intensity of solar radiation.
Electronic stations are integrated instruments that include all or part of the meteorological instruments mentioned on this page and the previous one. Some are sometimes even doubled, like the thermometer, the… This allows knowing the “climate” in the place where the station is, often indoors. Wires or radio waves connect the other instruments to the station.
The interest of the electronic stations is great:
- Remote measurement: without leaving home.
- A quick reading of all measured parameters.
- Frequent reading of values: every 10 seconds for example!
- Instant weather forecasts.
- Ability to communicate with a and perform, via software, analyzes, statistics and forecasts.
- The possibility of programming alarms: frost, strong wind, depression …
Electronic stations cost, depending on their complexity, from $100 to $600.