One hundred and fifty years ago, the science of weather took a wrong turning.
The barometer took over as forecaster's tool and older astrological methods that employed weather cycles died with their practitioners.
Hence today, as in 1860, meteorologists can still only confidently predict one day ahead.
That the barometer has lasted unchanged until this day is remarkable, considering its limited accuracy.
Those who remember school science will recall The Ideal Gas Law which states that pressure, volume and temperature of an enclosed gas are dependent on each other.
We can think of the atmosphere as a gas in a fixed container, kept intact and bound to the earth by gravity and rotation.
Scientists and barometer salesmen will try to convince you that the air-pressure change of the barometer indicates weather change. But volume and temperature fail to get much mention.
Pressure, as when we put our finger against the tabletop, is when something is pushed. But the moon and its gravitational force cannot push anything. You can liken it to sea-tides. If you are in a boat out at sea, shut your eyes and put your hand in the water.
The pressure of waves against your palm will not tell you whether you are on a high or low tide. But a look at the volume of water in a bay will. Volume can exert pressure given other conditions.
The barometer measures weight of air brought about by pressure, but what we need better to establish atmospherically-speaking, is volume.
We want to know how much height there is to the air over a particular place because more or less air stretched or compacted means more of earth's protection against the two nasties - the searing heat of the sun and the freezing cold of space.
The barometer measures the weight of a pretend thin high column of air above and pressing down on, a square inch of ocean, about the size of a postage stamp.
The instrument is a mini-scales, and measures weight of air at that spot, called "atmospheric pressure." Colder air is heavier. Two barometers at two different sea-level locations will show which has the heavier air (higher pressure).
But air is elastic; it can be stretched like a rubber band, and the barometer has no way of recording height of the atmosphere.
Because a rubber band will weigh the same if it is stretched or at rest, a barometric needle may stay still while weather changes or the needle may move whilst weather stays constant.
Heavier air due to higher pressure is associated with clearer skies and calmer winds. Descending heavier cold air causes higher pressures and rising warmer air can lower pressure bringing winds and rain.
One would think more rising warm air must occur around the equator, but most depressions and low pressure areas begin in colder latitudes.
Also there can be no descending cold air without simultaneous rising warm air, meaning pressure in the atmosphere should always remain constant.
We know that it does not. Temperature changes must also be included. At any time temperatures are influenced by cloud cover, height of air or changes in air density, angle of the sun and direction of wind.
Wind direction depends on whether morning or afternoon, whether coastal or inland, elevated or flat, whether the moon is at or near the horizon or high or gone from the sky and the moon's monthly proximity to its equinox.
Clouds are formed by temperature drop and the height of the air during the day is controlled by the position of the moon.
The angle of the sun depends on the month of the year. Temperatures and volume can combine to produce pressure and if one factor increases whilst the other decreases, pressure can remain constant.
There a way to use the barometer to 'read' weather changes and that is in conjunction with a thermometer.
If the barometer stays the same but temperature drops, there may be chances of rain.
If the barometer stays the same but thermometer rises, expect a clearing. If the barometer goes up but the thermometer remains steady, rain could ensue again.
If the barometer rises or falls while the thermometer plunges, a thunderstorm could be close by.
Barometer falling with thermometer rising indicates heavy rain. When both rise, either the wind is about to change or the weather is to improve; but when both fall, weather is probably deteriorating quickly.
The mercury level seldom falls for snow. A first rise after a low or a rapid rise can indicate unsettled weather.
A rapid rise or fall associated with a kingtide can be a warning of earthquakes. If the barometer is constant, it may mean rain or rain may be clearing. If it drops; rain, frost, or thaw, and if it rises; wind change, gale, rain, frost or clearing.
By itself the instrument is too flawed to base important decisions around, and forecasters may proudly proclaim the weather is fickle, as if it is trying to be elusive.
This justifies their claims that the weather cannot be predicted. Reliance on the barometer is a bit like using an accident as an indicator that one was driving too fast.For more writing from Ken Ring, visit www.predictweather.com
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