What causes a tornado?

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Chumisa Jackson

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What causes a tornado?
« on: 09/09/2009 10:30:03 »
Chumisa Jackson  asked the Naked Scientists:
Good day Chris
I just want to pick your brains:
According to traditional Xhosa beliefs, the tornado takes the form of a giant winged snake, known as inkanyamba. This being lives in deep water and flies through the air, looking for its mate, which lives in a deep pool or dam. We are brought up to regard the inkanyamba as an extremely dangerous, destructive presence that needed to be treated with great respect and caution at all times. As a child, he relates, they were not even allowed to use the word inkanyamba, for the inkanyamba might hear its name and come. Is this inkanyamba story true and how come can we not use our technology   to prevent it from moving around looking for its mate and prevent its mass destruction.

When it is full moon in the Southern Hemisphere ( South Africa ), I can see a picture like figure on the moon which looks like a woman carrying a baby at her back and a bucket on the head. I grew up being told this is a punishment by God to women. Apparently this woman went to fetch water from the River on Sunday which according to my grandparents they were not allowed to do that on Sunday. Has this had anything to do with moon landing? Is there any scientific reason for this? Can this be seen in other parts of the world.

Hailstones in South Africa fall in autumn and this is the time when we prepare harvesting in the fields. When the hailstones fall they cause a mass destruction in our agricultural produce in the field. We normally get out in the village and make noise with metals and shouting telling the storm to go to Embo. The hailstone normally disappears or moves to fall to other areas. What is the scientifically reason between the making of the noise and disappearance of the storm?

How could science embrace all these traditional beliefs and if they work how come the science hasn't promoted them?

Chumisa Jackson

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Offline SkepticSam

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What causes a tornado?
« Reply #1 on: 10/09/2009 17:25:07 »
Hi Chumisa, I think the lack of replies may be because people don't want to speak against your Xhosa beliefs. So I will try and give you some simplistic links that you may wish to take some time to read.
The problem with this question and similar ones on Tornadoes or other extreme weather events is that most of the research is done in and about the events in the USA. Whilst this may not seem too much of a problem it actually is. The USA has a unique landmass that is rather long and there is not much in the way of two air masses that collide over it and in an area you may have heard of, Tornado alley. The air masses are a tropical and an artic one. Believe it or not tornado alley actually extends all the way up to Canada.
So how does science say tornadoes form. Well the rather simple answer is:
"warm moist Gulf air meets cold Canadian air and dry air from the Rockies" -- is a gross oversimplification. Many thunderstorms form under those conditions (near warm fronts, cold fronts and drylines respectively), which never even come close to producing tornadoes. Even when the large-scale environment is extremely favorable for tornadic thunderstorms, as in an SPC "High Risk" outlook, not every thunderstorm spawns a tornado. The truth is that we don't fully understand. The most destructive and deadly tornadoes occur from supercells -- which are rotating thunderstorms with a well-defined radar circulation called a mesocyclone. [Supercells can also produce damaging hail, severe non-tornadic winds, unusually frequent lightning, and flash floods.] Tornado formation is believed to be dictated mainly by things which happen on the storm scale, in and around the mesocyclone. Recent theories and results from the VORTEX program suggest that once a mesocyclone is underway, tornado development is related to the temperature differences across the edge of downdraft air wrapping around the mesocyclone (the occlusion downdraft). Mathematical modeling studies of tornado formation also indicate that it can happen without such temperature patterns; and in fact, very little temperature variation was observed near some of the most destructive tornadoes in history on 3 May 1999.
http://www.spc.noaa.gov/faq/tornado/#The Basics
Although like i said, this is in the USA. In South Africa tornadoes form out of the violent thunderstorms produced by very hot afternoon and early evening air masses. As with most countries the reporting of tornadoes is said to be "underreported". They are so weak and short lived that many people just dont notice them. I dont think the South African met services actively collect tornado data, like the Met Office in the UK.
In the UK the data is collected by an organisation called TORRO http://www.torro.org.uk/site/index.php
Here are a few links that I hope will help. I can't answer for any of your cultural beliefs but just because we cant see a giant snake doesn't mean that its not there, does it?
When I get time I will see if the South African weather service have any publications about tornadic events and climatology in your area. http://dev2.weathersa.co.za/includes/weatheroption.asp