Dotini said:
Do such multiple vortexes feed only a single cyclonic cell, or do they each have their own? Such organization and complexity is really impressive.
Hey Steve,
I have never seen any evidence of there being more than one mesocyclone (the large, rotating updraft) inside a supercell. The mesocyclone typically has a diameter of something like 2 km, which is the diameter of a very large tornado. While there can be tornadoes anywhere in the vicinity (sometimes several km away), to my knowledge the main tornado is always associated with the mesocyclone.
DaveC426913 said:
In refuting artist's claim that dumping water into a tornado would weaken it, you pointed out that "...tornadoes form from severe rain storms and hurricanes...". While you didn't say explicitly that tornadoes get strength from moisture, it seemed to be the implication - the significance of the comment - to this reader (and thus possibly others). So I went to see if I could bolster the notion (after all that is how hurricanes get their power). But I haven't been able to find a reference either way.
Here are some rough calculations that I did, using numbers from the source that Steve quoted, as well as other sources. Tornadoes do seem to get a respectable amount of energy from the release of latent heat from the condensation of water vapor, while ohmic heating from the electric current inside the tornado appears to make a far more substantial contribution.
First the latent heat calculations. Let's assume that the ambient temperature is a sweltering 40 °C, and that the relative humidity is 100%. The lowest pressure drop ever recorded in a tornado was 100 mb below ambient. That would lower the temperature to roughly 10 °C, forcing the condensation of most of the water vapor, and the release of latent heat.
maximum water vapor content at 40 °C = 51.1 g/m3
maximum water vapor content at 10 °C = 9.4 g/m3
condensation = 51.1 − 9.4 = 41.7 g/m3
tornadic inflow (EF1) = 1,000 m3/s
total condensation = 1,000 m3/s × 41.7 g/m3 = 41,700 g/s
latent heat from condensation of water = 2,257 J/g
total latent heat = 41,700 g/s × 2,257 J/g = 94,117,000 J/s
watt = joule / second
power = 94,117,000 W
Now the ohmic heating calculations. The magnetic field generated by a tornado was measured at 1.5 × 10
−8 teslas from a distance of 9.6 km away using a magnetometer. From this we can calculate the amps.
amps = teslas × 2 π r / permeability
permeability of air = 4 π × 10−7 N/A2
amps = (1.5 × 10−8 × 2 × 3.14 × 9600) / (4 × 3.14 × 10−7) = 720 A
Guessing that the tornado was 300 m tall, and given an electric field of 5 kV/m, we can then calculate the watts.
volts = 300 m × 5,000 V/m = 1,500,000 V
watts = amps × volts = 720 × 1,500,000 = 1,080,000,000 W
More conservative estimates of the typical current densities are in the range of 100~250 amps, but even at the resultant 150~375 million watts, that's still a lot more power than the 100 million watts that could be coming from latent heating.
In addition to the ohmic and the latent heating inside the tornado, there is also, of course, the low pressure aloft inside the thunderstorm enhancing the updraft, and there is also frictional heating at the lower boundary.
Only the frictional heating at the ground level could possibly be responsible for the extreme low pressure at the base of the tornado, as it is the only energy source that is concentrated near the ground. Estimates of the (destructive) work done by the tornado on the ground are in the range of 5 million watts for an F1 tornado, to 5 billion watts for an F5. The effect on the air of the thermalized energy is, of course, to increase its buoyancy, accounting for the vigorous updraft at the base of the vortex, which cannot be explained in any other way.
Dotini said:
I was unable to locate the statement regarding "tornadoes being formed and sustained by purely thermodynamic processes" in the NOAA FAQ. Perhaps it has been deleted?
Here is the link. The quote is in a pop-up that appears if you hover over the question in the right-hand sidebar, "Are there electromagnetic or magnetohydrodynamic explanations for the development of tornadoes?"
http://www.nssl.noaa.gov/primer/tornado/tor_predicting.html"