Sailors and landlubbers alike tend to plan their lives around the wind, writes Matt Vance, but attempting to explain its whimsical behaviour is elusive to all but the most dedicated scholars.
In the cabin of Whitney Rose, there is a haunting din of the wind in the rigging. In the black of night and at anchor the boat has become a musical instrument with taut strings of wire plucked by the wind and amplified into the curved soundbox of the hull.
If the wind can be said to have a voice, this is it. At its most benign it is a lullaby, but tonight it is a chorus of demonic moans. From my warm bunk, I listen to the eerie music from the rigging; each time it climbs a note I can feel an involuntary clenching somewhere deep inside me.
Given the wind’s ability to have a voice and behave like an unseen force, it is not surprising that throughout many cultures the wind has been given god-like qualities. In the Old Testament, the wind seems to be at the command of a jealous and vengeful God. He unleashes it at his will to punish everything from genocide to overdue library fines.
In aboriginal culture, the wind is said to be the restless souls of the dead. Storms and tornados are the unhappy dead – the gentle breeze that of the content. In New Zealand, it is said the demigod Maui can ride the winds and imprison them in caves, corking their entrances with large rocks. Despite Maui’s power he cannot catch the west wind, nor find a cave large enough to store its might and therefore it prevails in what we now call the roaring forties.
Around 340BC Aristotle had a crack at explaining the mystery of wind declaring it a “dry exhalation arising from the earth.” At first glance, this looks like an attempt to explain wind as caused by an upward drift of warm air, which is not far from the mark. Unfortunately, Aristotle goes past the mark when he expanded on his theory to include some magic from the sun and the effects of subterranean winds erupt from the earth’s core, creating a form of meteorological flatulence.
This view of wind remained unchallenged until the 17th century when Galileo’s student, Evangelista Torricelli, invented the barometer and created the first instrument for measuring atmospheric air pressure. This phenomenon is at the heart of modern meteorological theory and Torricelli’s work eventually led to a network of observatories around Europe, which compared weather data including air pressure readings.
Linking these differences in air pressure together and coming up with the modern version of our understanding of wind fell to astronomer Edmund Halley. In between naming famous comets, Halley presented a ground-breaking paper to Britain’s Royal Society, which suggested that differences in atmospheric pressure stir the air and bump it into motion. As an example, he correctly deduced that the trade winds were caused by the intense heat and rising air of the equatorial regions.
As is often the case with good ideas, Halley’s theory was not widely accepted for decades due in part to another member of the Royal Society (Dr Martin Lister) who had put forward a well-received case that the wind was caused by the exhalations of large patches of Sargasso weed found near the centre of the North Atlantic gyre. It was Aristotle’s flatulence theory re-configured and as every five-year-old knows, fart jokes trump the truth hands down.
With Edmund Halley’s theory not only was the concept of wind explained, but also the underlying basis for global atmospheric circulation. When he stated that the trade winds were caused by the heating and rising air of the Equator he identified the first of three heating and cooling loops in the atmosphere called Hadley cells.
Reaching the troposphere somewhere in the vicinity of 6-10km from the earth’s surface all this hot equatorial air identified by Halley is deflected and begins to flow towards the poles. Surface winds caught in the vacuum created by this rising air rush toward the equator from the north and south and are turned westward by the earth’s spin, also known as the Coriolis effect.
In the Southern Hemisphere, these are the southeast trade winds and are known to be some of the steadiest and most consistent breezes on the planet. The air that has risen at the Equator reaches south to around 30° of latitude where it begins to cool and descend. This creates high pressure and dry, sunny conditions and is one of the reasons that Australia is an island with vast sections of its hinterland devoted to arid desert.
This high pressure is one half of another loop, or Hadley cell, that links the rising air of the Sub-Antarctic lows to the south of New Zealand. The final southern Hadley cell is based on the large area of high pressure and descending cold air above Antarctica. All this cold air originates as relatively warmer moist air rising off the Southern Ocean forming low pressure.
When viewed from the perspective of the South Pole, this appears as a large polar high surrounded by a pack of marauding lows that seem to circle the Antarctic continent in an endless succession across the Southern Ocean. In the Northern Hemisphere, there is an equivalent, but because it is covered mostly by landmass, it does not have the sting or the momentum that the Southern Ocean does.
In a perfect theoretical globe, these high and low-pressure Hadley cells would be the end of it, but as any New Zealander knows, we live in a much more complex, perverse and chaotic world of wind. As luck and geography would have it New Zealand straddles the zone between the Sub-Antarctic lows and the Sub-Tropical highs which battle it out over the top of us making for some rambunctious weather.
The top end of these Sub-Antarctic lows bring wind from a consistently westerly direction and that makes us, by world standards, a windy country and gives us a reputation that means most international cruising yachts visiting our shores only ever go about as deep south as Ponsonby.
No sooner had scientists worked out the origins of the wind than they had to contain it and measure it. In 1805 Royal Navy Commander Francis Beaufort devised a wind force scale based on the stress exerted on a fully-rigged man-of-war. His scale had 12 stages ranging from flat calm to a hurricane.
Initially, Beaufort’s scale did not refer to wind speed or sea state, as there was no standardised way to measure these. While the scale was adopted by the 1874 International Meteorological Committee it took until the following century to develop a way of measuring wind with the invention of the modern anemometer.
While the Beaufort scale is still used in the UK, the colonies have never been big on it and for that reason, most New Zealand sailors refer to wind speed in knots and occasionally in bastards i.e. “It’s blowing 40 bastards.”
For sailors, understanding wind is a vital skill, which determines our experience and safety on the water. Landlubbers mostly ignore it, yet throughout human history, it has been the shifting of winds and their attendant areas of high and low pressure that have wiped out entire ecosystems and scattered civilisations like dust.
The wind has steered history with a much stronger hand than religion or military might; it has determined everything from what civilisation rose to power to influencing which global trading paths those civilisations used to expand their empires.
Ironically, while the future of humanity will be determined by global warming it is not the heat that will be the problem. It will be the effect of more energy in the global circulation system we experience as the wind that will determine, along with sealevel rise, who wins and who loses in a world dominated by the movement of air.
