Question about tornadoes

[HurricaneBill]

Look! A post NOT about global warming!

Anyway, I have a question regarding tornadoes. Can tornadoes form at or close to the equator?

[Aslkahuna]

How close is close since they been reported south of 10N in the Philippines.

Steve

[SunBoy2121]

well the word "close" in that sentence is very vague, you'd have to be more specific. But as far as at the equator, no, because there's not differential in temperature there. Of course this is a main ingredient.

[Aslkahuna]

Tropical tornadoes tend to form in a region of horizontal shear in a convergence zone or in conjunction with Tropical cyclones. However, the tornado I refer in the Philippines formed in northern Mindanao in a baroclinic zone associated with a Tropical Low interacting with an unusually deep penetration of the Polar Front. Tornadoes in Central Luzon tended to occur wit Trade Air regimes with good veritcal shear overlying the dry air over very moist air Trade airmass triggered by sea breeze front convergence-or during strong shear patterns late in the Summer Monsoon.

Steve

[HurricaneBill]

Well, I guess they can. This one formed in Singapore.

[youtube]http://www.youtube.com/watch?v=oOjo7tSL0GE[/youtube]

[wjs3]

I think the question behind your question is really "like tropical cyclones that usually require distance from the equator, so coriolis can impart "spin" to them..." are tornadoes the same way, and a rarity in equatorial regions?

The answer is no...as others have posted, spin in tornadoes comes from vertical wind shear, which does not require coriolis, so can happen near/on the equator.

[Aslkahuna]

As Vamei proved even typhoons can form close to the equator though they are rare. In those cases horizontal shear tends to trigger the spin in absence of Coriolis (In WPAC Tropical Cyclones formed below 10 N quite frequently).

Steve

[wjs3]

See, I knew someone was going to call me on that...thanks for the reminder, Steve.

Yes, tropical cyclones can form near the equator. But for most, the conceptual model of coriolis playing a role in TC formation is a good one. And, I think (I might be mistaken) that the question behind the question here is "what gives tornadoes their rotation?"...hence my answer...It's something different than what gives TCs their rotation.

...please don't shoot me if I'm wrong!

WJS3

[Aslkahuna]

No shooting-shear is the driver for the devlopment of tornadoes. In the case of the mesocyclone tornadoes the shear is largely vertical and in the range of of 25 m/s or more (velocity shear which means both directional and speed shear) whereas landspouts and gustnadoes tend to occur in regions of horizontal shear in conjunction with convergence such as might be found along a gust front or a flanking line (such is also the method of formation of waterspouts and deep tropical tornadoes). Cold air funnel type tornadoes form as a result of the strong instability and vorticity associated with a cold core ULL. This is the most common type of tornado in coastal SoCA (which is why tornadoes occur in Winter there) and they often start as waterspouts which come ashore. On rare occasions cold air funnel tornaode can reach EF2 intensity.

Steve