Getting the Wind Up

A plant disease called “myrtle rust” has appeared in New Zealand, apparently after the spores have been blown across the Tasman sea from Australia. That’s over four thousand miles. The prevailing winds are from Australia to New Zealand and the cyclones and storms that hit New Zealand are formed in or off the coast of Australia, or further north in the Tropics, or further south in the Southern ocean.

In these areas low pressure areas form and consequently winds blow from the surrounding areas of slightly higher pressure into the lower pressure area and start to swirl clockwise. The clockwise movement is the result of the Coriolis effect, which is difficult to explain, but relates to the fact that when an object moves north or south on the rotating Earth, it moves closer to or further from the Earth’s axis of rotation.

Combination of Image:Hurricane isabel2

Combination of Image:Hurricane isabel2 2003.jpg and Image:Coriolis effect10.png to illustrate the Coriolis force better. (Photo credit: Wikipedia)

A low pressure area sucks in air and it is forced up in the centre where it cools and forms clouds and rain. As this process continues, the pressure at the centre of the low drops and the spiral of winds gets tighter and, if the low is very deep, more destructive. I’m not sure why a low deepens, when one would think that all the in-rushing air would fill the low, and the few explanations that I have read have not convinced me.

On a larger scale, bands of winds circle the Earth, with winds coming from the west in the south and the north of the two hemispheres, with prevailing easterly winds nearer the Equator in both hemispheres. The sometimes destructive cyclones and anticyclones are mere ripples in this larger flow.

English: Map of the North Pacific Subtropical ...

English: Map of the North Pacific Subtropical Convergence Zone (STCZ) within the North Pacific Gyre. Also the location of the Great Pacific Garbage Patch. (Photo credit: Wikipedia)

Even in quiet wind conditions there is usually a breeze, often stimulated by local conditions, such a large lake or sea. All that is required for a breeze is a small differential in temperature, with local heating expanding the air or local cooling causing it to contract.

The sea will absorb heat from the sun more slowly than the land, and the air over the land is therefore warmer and becomes less dense. Consequently a breeze develops flowing from the sea to the land. The reverse occurs at night, when the land cools more quickly than the sea. Such conditions are however very local and are often unnoticeable and overridden by cyclonic and anticyclonic wind conditions.

The formation of breezes. Diagram A) Sea breez...

The formation of breezes. Diagram A) Sea breeze B) Land breeze Français : Formation des brises. Diagramme A) Brise de mer B) Brise de terre (Photo credit: Wikipedia)

Within a large weather system, such as a cyclonic system, local conditions may affect the wind directions and strength. Often the wind direction and strength varies widely locally, giving rise to conditions that are described as “blustery”. While such conditions may be good for drying laundry, they making sailing a difficult pastime. Sailing races can be won or lost depending on whether or not the sailors catch the good air or fall into a pocket of stale air.

The strength of the wind obviously varies tremendously. At the one end of the scale a breeze may cause a flag to limply stir, while at the other end of the scale, a really large storm may uproot trees and destroy houses. In some parts of the world tornadoes may form when weather conditions are right and may sweep destructively over the land, ripping apart anything that stands in their way.

Large, violent tornadoes can cause catastrophi...

Large, violent tornadoes can cause catastrophic damage when striking populated areas. (Photo credit: Wikipedia)

There is energy in the wind, and efforts are being made to economically harvest this energy to reduce our reliance on fossil fuels. Such fuels are not infinite, and we will sometime or other run out of them. It may be that we have enough fossil fuels to last centuries, but getting at them involves the disruption of mining, and as they are used up, mining will become even more disruptive than it is now. Mining even small amounts will become very expensive.

It makes sense to develop machines to harvest wind power, and the signs are that this is becoming economically more competitive. At one time, before petrol engines became common, the only ways to power transport were wind and steam, and it may be that petrol and other fossil fuelled engines may only have a relatively short time span of usefulness, maybe only a century or so.

Miners digging coal

Miners digging coal (Photo credit: Wikipedia)

We also use fossil fuels for our plastics. Almost everything in our modern world has a large proportion of plastics in it, sourced almost entirely from oil. It remains to be seen if we could replace our need for fossil resources from renewable resources.

Hay fever suffers may curse the wind as it blows pollen up their noses and into their respiratory systems, but many plants rely on the wind to propagate themselves. A case in point is the myrtle rust I mentioned at the start of this post. Plant pollen can travel thousands of kilometres and fall all I know can circle the Earth. It’s an efficient way of spreading the reproductive material, but its a really inefficient way of getting the reproductive material to a member of the species of the opposite gender.

Pollen from a variety of common plants: sunflo...

Pollen from a variety of common plants: sunflower (Helianthus annuus), morning glory Ipomoea purpurea, hollyhock (Sildalcea malviflora), lily (Lilium auratum), primrose (Oenothera fruticosa) and castor bean (Ricinus communis). The image is magnified some x500, so the bean shaped grain in the bottom left corner is about 50 μm long. (Photo credit: Wikipedia)

Obviously it works best where the plants are grouped together, and it works even better if the plants are hermaphrodites, but it does work (occasionally) when the plants are far apart. This mechanism for reproduction probably arose a long time ago before plants invaded the land. plants growing in the sea, and many animals too, just broadcast their gametes into the sea and trust in at least some of them finding other gametes so that they can grow into mature individuals. (Caution: It’s complicated!)

We often hear the sound of wind. It can be caused by wind blowing through trees or other plants. It can be caused by wind blowing through gaps in our houses, mainly doors and windows. We build our houses to protect us from the wind and other aspects of the weather, as a sort of synthetic cave, I guess.

Wind chimes. {| align="center" style...

Wind chimes. {| align=”center” style=”width:80%; background-color:#f7f8ff; border:2px solid #8888aa; padding:5px;” |- | Camera and Exposure Details: Camera: Canon PowerShot S3 IS Lens: Canon 1:2.7-3.5 USM 12x Zoom Lens Exposure: mm (mm in 35mm equivalent) f/4 @ 1/125 s. |}Category:Taken with Canon PowerShot S3 IS (Photo credit: Wikipedia)

We can even make music (well, musical sounds) using the wind. Many people have “wind chimes” which are metallic objects strung on wires arranged so that the wind can bash them together, making a chiming noise. Some people like them, and others dislike them (I fall into the second camp).

Strings can be placed on a sounding board and used to produce musical sounds, and such “Aeolian Harps” were once as common as wind chimes. An accidental Aeolian harp can be heard in the sound that power and telephone lines make when a strong wind blows.

English: Aeolian harp at Tre-Ysgawen Hall This...

English: Aeolian harp at Tre-Ysgawen Hall This aeolian harp is in the grounds of Tre-Ysgawen Hall. When the wind comes from a particular direction it ‘plays’ the harp and ethereal musical sounds are produced. (Photo credit: Wikipedia)

Time for this post about wind to wind down now, if you will excuse the pun.

This picture from a NASA study on wingtip vort...

This picture from a NASA study on wingtip vortices qualitatively illustrates the wake turbulence. (Photo credit: Wikipedia)

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