Rare Bolivian Tonado

[TrumanBoyer]

TWC lists this video today Nov 18. It got me thinking...

http://www.weather.com/weather/vide...-tornado-caught-on-cam-22615#loc=42/203/22330

A mountain tornado in Bolivia.

Rare because its in because its in the mountains.
Rare because its in Bolivia.

Also maybe rare because it appears to rotating counter-clockwise
(as seen from above) and it is south of the equator.

It had never occurred to me before,
but I would think that at this time of year weather in tropical zones might behave more
like Northern Hemisphere systems (Clockwise Highs, Counter-clockwise Lows)
because of Cold Air (denser, higher pressure) From North pushing farther South.

Maybe winter in the Southern Hemisphere might cause the opposite tendency.

I have not studied equatorial weather in detail, but does anyone know if there is a shift
in the Intertropical Convergence Zone(s) that might cause tendencies
like what I am speculating about ??

Just Wondering....

Truman

 

[DNewman]

Wow, I didn't know that Bolivia even got tornadoes. It was probably stronger than most southern hemisphere tornadoes because of its counter clockwise rotation. Did you know that counter clockwise rotation is the strongest form of rotation on the planet, which is why the northern hemisphere, especially north America gets powerful violent tornadoes.But the southern hemisphere rotation is weak, so that's why their tornadoes are usually weaker.

 

[ahaberlie]

I'll just put this here... (Wisconsin of all places..) http://en.wikipedia.org/wiki/April_4,_1981,_West_Bend_tornado

An (E)F4 anticyclonic tornado hit the town of West Bend on April 4th, 1981. That would put this tornado in the 99th percentile based on its strength.

Anyway, Bolivia is in the tropics, more specifically southeasterly trades (Hadley Cell)

You would somewhat expect systems to behave like hurricanes in the Caribbean.. although it seems to me that storms pop up much like they do in the deep south during the summer.

So really, what feeds the spin of the thunderstorm and the low level rotation are the baroclinic boundaries and the shear in the atmosphere and how the axes of rotation line up with the inflow/updraft of the storm. What I am saying is storm positioning and orientation *IS* dependent on synoptic scale patterns (ie low pressure systems rotate counter clockwise in the mid-latitudes in the northern hemisphere) but storm relative spin is *NOT* governed by the Coriolis effect because the change in distance is too small. Therefore, either anticyclonic or cyclonic (relative to the northern hemisphere) tornadoes are possible. We just see one mode more (99.9% of the time?) because of the necessity of the lift/forcing from synoptic systems to get thunderstorms going. We see plenty of times where anticyclonic tornadoes would be possible but the orientation or lack of the synoptic system makes it hard/impossible to produce (anticyclonic) tornadoes. The case is an interesting one as it is entirely possible that the mountains had some sort of effect on the storms. Without more information it is hard to tell what was going on.

 

[scott r currens]

Rare because its in because its in the mountains.
Rare because its in Bolivia.

Also maybe rare because it appears to rotating counter-clockwise
(as seen from above) and it is south of the equator.
Truman

I agree that an intermountain tornado in the Andes of Bolivia is rare. But I disagree with the notion that tornadoes in Bolivia are rare. Argentina and Bolivia have very low population densities outside of the Major Urban areas and there is no equivlent to our storm data so very few tornadoes are documented. "If a tree falls in a forest and no one is around to hear it, does it make a sound?"

 

[Wes Carter]

Wow, I didn't know that Bolivia even got tornadoes. It was probably stronger than most southern hemisphere tornadoes because of its counter clockwise rotation. Did you know that counter clockwise rotation is the strongest form of rotation on the planet, which is why the northern hemisphere, especially north America gets powerful violent tornadoes.But the southern hemisphere rotation is weak, so that's why their tornadoes are usually weaker.

How would you physically explain this? I thought that the reason North America gets so many strong tornadoes has more to do with the orientation of the Rocky Mountains, the Appalachian Mountains, the Gulf of Mexico, and the Great Plains allowing the perfect mix to occur more frequently than other places on earth.

If you are referring to coriolis force, which does not directly influence tornado formation, why would it be stronger in the Northern Hemisphere? I could maybe fathom more land in the northern hemisphere causing sharper temperature gradients causing combined stronger winds up here, but cannot see much more than that.



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[scott r currens]

Wow, I didn't know that Bolivia even got tornadoes. It was probably stronger than most southern hemisphere tornadoes because of its counter clockwise rotation. Did you know that counter clockwise rotation is the strongest form of rotation on the planet, which is why the northern hemisphere, especially north America gets powerful violent tornadoes.But the southern hemisphere rotation is weak, so that's why their tornadoes are usually weaker.

The strongest winds measured on earth were from (clockwise) cyclonic southern hemisphere Tropical Cyclone.
"During the passage of Tropical Cyclone Olivia on 10 April 1996, an automatic weather station on Barrow Island, Australia, registered a maximum wind gust of 408 km/h (220 kn; 253 mph).[2] The wind gust was evaluated by the WMO Evaluation Panel who found that the anemometer was mechanically sound and the gust was within statistical probability and ratified the measurement in 2010. The anemometer was mounted 10 m above ground level and so 64 m above sea level.[3] During the cyclone, several extreme gusts of greater than 300 km/h (160 kt) were recorded, with a maximum 5-minute mean speed of 176 km/h (95 kt), the extreme gust factor was in the order of 2.27–2.75 times the mean wind speed. The pattern and scales of the gusts suggests that a mesovortex was embedded in the already strong eyewall of the cyclone.[3]"
http://en.wikipedia.org/wiki/Wind_speed

 

[TrumanBoyer]

GOOD POINT. But..

I think that the record wind speeds in Australia you are referring to were a freak occurrence. If I remember correctly, the measurements were made from an elevated station, and a Bernoulli effect was the likely cause.

Still, you make a very good point.

But typically storm strength in the Southern Hemisphere, at least on land, is mitigated by a number of factors.

Most of the land mass in the southern hemisphere is tropical, or subtropical.
Polar air masses don't reach land in middle latitudes nearly as often as in the Northern Hemisphere. The Southern Ocean wraps completely around the planet and creates a sort of temperature buffer around the Antarctic. Cold dry air does not move toward the equator as far or as often as it does in the N.H.

The Southern Hemisphere just doesn't get the same extreme weather setups as the northern hemisphere does. Or at least not nearly as often.

As for the rarity of Bolivian tornadoes...
I would think that there are probably many more than are reported, or recorded.
But still they are probably not a common occurrence. The setups are just not happening there. Tropical thunderstorms are an almost daily phenom, but they are pulse-type storms (air mass thunderstorms) and are far less likely to produce tornadoes.

That being said, here is another curiosity photo from Bolivia.
I Hope I can start another controversy.
Weather is boring in MD, right now, haha.

What is this picture of... ?

The caption reads "Tornadoes, reflected, Unyuni, Bolivia"
http://blog.travelpod.com/travel-photo/eadamson/everywhere/1174313520/p3140664.jpg/tpod.html

A pretty picture anyway ?
-T

 

[scott r currens]

The anemometer that recorded the record wind speed in Tropical Cyclone Olivia was mounted 10 m (33 ft) above ground level and so 64 m (209ft)above sea level.

It is true that deep troughs are less common in South America but so are death ridges and blocking patterns. Unlike North America the severe weather season doesn't end in last spring with a death ridge. Don't get me wrong, I am not saying South America gets as many tornadoes as North America but they go get a lot. There is a reason Argentina leads the world in agricultural insurance claims for hail damage.

A six year NASA satellite study also identified Argentina as having the strongest storms on earth.
http://www.nasa.gov/vision/earth/lookingatearth/intense_storms.html

 

[Josh Morgerman]

The elevation of the measuring station in Olivia (64 m) is quite high-- so those winds were not representative, necessarily, of the cyclone's actual "sea-level" intensity.

I have to say... I know the instrument was evaluated and so on, but I can't help feeling skeptical Re: values that high (220 kt). The Cuban report of 135 kt (1-min) with a gust to 184 kt in Gustav 2008 also raises eyebrows.