The berg wind brain-teaser

The Herald

2 days ago

On a recent early morning broadcast, Daron Mann highlighted that he was always confused with the dynamics and principles of berg winds.
He could never understand the concept that hot air rises but descending air heats up.
Needless to say, a few minutes was not enough to explain the concept to him.
If his teacher could not help him understand this concept, he barked up the wrong tree by asking me to explain it.
Imparting knowledge to others must be one of my weakest traits. This is possibly because throughout my career I have had to learn most things for myself.
This is from the days that they shipped the first real computers to the Weather Office, through to correspondence courses at Technikon RSA and the like.
I understand concepts but often battle to explain them in a way that others understand.
Mrs Guru has realised this after leaving the cooking industry and joining me in the weather industry.
It's not easy to explain Excel to somebody that insists that a printed copy is still King. I am sitting with a dilemma of teaching an old dog new tricks.
I must say, she has excelled quickly in Excel (couldn't resist the pun) and is well past beginner's level in a very short time.
Back to Daron's dilemma and going back to basics, the biggest driver of weather is temperature, and more specifically the sun's uneven heating of the earth's surface.
Thus, his question is important in obtaining a better understanding of weather.
This is why climate change experts are most concerned about global warming as it effects all aspects of weather.
This can be seen by the effects of El Nino on weather in different parts of the globe.
Yes, it is true that hot air rises, but the statement should rather read that air that is less dense than its surroundings will rise.
This can be seen in a body of water where air bubbles rise to the surface no matter what the temperature of the air or water is. This is because air is less dense than water.
We might then ask why hot air is less dense and the simple answer is — because its molecules move faster and spread out, occupying more space. The opposite is true with cold air.
Essentially then, because of its density in comparison to its surroundings, a hot air parcel will rise to the top of a cooler air environment.
Now how does air heat when it descends? Basically, air within an area of high-pressure generally descends.
This downward motion is associated with convergence in the upper atmosphere.
In other words, the coming together of air at a height of about 5 to 10km above mean sea level.
This action forces the air below it downwards, thus causing it to warm.
Naturally, this limits the amount and depth of clouds, thus high-pressure systems are mostly associated with fair weather.
Ridging highs are another subject entirely on their own and we would not want to confuse Daron too much on this one.
Then why does it get colder the higher one goes up in the atmosphere?
The simplest answer is that you are further away from the heater, which is the surface of the earth.
Also, the higher one goes, the thinner the air and the lower the pressure.
Essentially this means that the air molecules have less energy and the overall temperature drops.
Thinner air is the reason why additional oxygen is essential when climbing Mount Everest.
I know that many will argue using the plight and flight of Icarus in Greek mythology. He was the son of Daedalus, who crafted the wings for both as a means of escape from imprisonment.
As the story goes, the wax holding the wings together melted when he flew too close to the sun.
This is a lesson of the dangers of over self-confidence and overreaching one's limits, using an analogy, rather than a solid scientific fact.
This week in history:
1981: Flood in Plettenberg Bay, just months after severe floods in Nelson Mandela Bay
Dam levels
69.79%, slightly down from previous week's 70.24%. Impofu down to 52.30%
Weather safety tips:
If you have no water to douse a fire, use sand to smother it and deprive it of oxygen.
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