[Kryptid (OP)]

I had come across the concept of a "hypercane" some time ago: http://www.dailygalaxy.com/my_weblog/2009/04/is-a-mega-katri.html

The idea is that an oceanic impact from a large asteroid could cause great heating of the waters for an extended period of time. These especially warm waters rise and spawn very tall, very powerful tropical cyclones (sometimes known as "hypercanes") with winds up to 500 miles per hour.

This led me to wonder if a similar scenario could result in the genesis of extremely powerful tornadoes. I admit that my learning about tornado development is a bit rusty. If memory serves me well, tornado-producing thunderstorms tend to develop in the Midwestern United States due to a mixing of warm, moist air from the Gulf of Mexico and cool, dry air from Canada. The temperature differences create atmospheric instability, resulting in powerful storms.

Can we conceive of a scenario that magnifies this temperature difference? My thought is that this might occur if a Chicxulub-like meteor impact event occurred in the Gulf of Mexico during an Ice Age. This would create temperatures in the Gulf much higher than usual with temperatures in Canada being much lower than normal. Could this conceivably result in the production of very strong tornadoes, or would it instead create a very large number of ordinary-strength tornadoes?

As an alternative scenario, would tornadoes in the distant past (hundreds of millions or billions of years ago) have been much stronger than those in the present day due to the increased rotational rate of the Earth back then (stronger Coriolis effect)?

[evan_au]

A hurricane like Katrina can devastate a stretch of coast. It makes a bigger mess if it hits a populated city like New York. But the damage is mostly damaged houses, flooded tunnels, shut down electricity and traffic, and washed-away foreshores.

However, a large meteorite impact in the mid-Atlantic would produce a tsunami that would wash away any large city facing the Atlantic. Think of the Fukushima tsunami striking the entire Atlantic coast of Europe and North America.

A worse problem could occur with a meteorite which is large enough to leave a vacuum in its wake as it struck the ground. The vaporized rock from the impact would get blown into space, and fall back over the whole earth over the succeeding hours to a day. This rain of micrometeorites could bake entire continents of the Earth.

Fortunately, large meteorites are much rarer than hurricanes.

[puppypower]

The sun and water are the two modern engines of tornadoes. When surface water evaporates, via the sun, to become a vapor, the water vapor will exert a partial pressure in the atmosphere. When gases dissolve into each other, each will exert a partial pressure. When clouds and rain form, the water vapor condenses out of the atmosphere, removing its partial pressure contribution. This is why clouds and rain is associated with low pressure systems. 

This affect is similar to canning; preserving. You heat the jars in boiling water to increase the partial pressure of the water above the veggies. The jars are then covered, hot. As the jars cool, the water condenses and a vacuum is pulled. The hot vapor rains out onto the veggies and now the top of the veggies is under low pressure.

In the USA in the spring, we have the cold air coming eastward out of the snow covered Rocky Mountains. This cold air meets the hot moist air from the south coming from the Gulf of Mexico. The cold air is denser and the hot air is less dense, so when the two meet the hot air will rise and cool. 

This can create an interesting scenario. As the warm air rises into the cooler upper atmosphere and condenses, a dynamic vacuum is being pulled vertically which can cause a suction that speeds up the flow of warm air upward. The thundercloud is lowering local pressure due to the bulk condensation of water, which pulls air in from all sides; hot and cold air. The hot air will rise with the vertical condensation suction accelerating vertical air flow, this leads to even more condensation. The vertical vacuum acceleration can lift clouds 50,000-75,00 feet. It is this compounding suction, with factors that cause shear and spin, will result in tornadoes.

If you needed to make a bigger and better tornado, you would need a source of not just warm moist air, but hot moist air. This could be supplied by a huge  steam plume from a crustal or volcanic event. If the partial pressure of the steam in local air is really high; steam plume pushed away all the surrounding air away, so the local air becomes almost pure water vapor,  when the vertical condensation vacuum begins to accelerate the pressure can fall so low, we might get an F-7.

The current theory of the earth is the oxygen in our atmosphere came from life. This exerts a partial pressure of about 20% to the modern atmosphere. If we subtracted out the oxygen; before life, the air pressure would be lower. With the hot earth boiling water and the oceans streamy, the water partial pressure could be naturally huge. Vertical lift to condense in the upper atmosphere would make huge tornadoes and lightning. Life by adding O2, added more background pressure to the atmosphere, so storms mellowed.

[evan_au]

The current theory of the earth is the oxygen in our atmosphere came from life....
If we subtracted out the oxygen; before life, the air pressure would be lower.

This does not follow.

Life did not just create oxygen out of nothing, and add it to the atmosphere.

It is thought that the early atmosphere had a high level of carbon dioxide CO₂ (like Venus). Through photosynthesis, living algae & plants converted atmospheric carbon dioxide CO₂ into oxygen O₂, using the carbon for building their own biomass.

This process does not increase the pressure of the atmosphere - in fact, iron minerals would have reacted with the atmospheric oxygen, taking it out of atmospheric circulation, and resulting in a net reduction of atmospheric pressure (not an increase, as suggested).

See: http://en.wikipedia.org/wiki/Great_Oxygenation_Event

[puppypower]

The current theory of the earth is the oxygen in our atmosphere came from life....
If we subtracted out the oxygen; before life, the air pressure would be lower.

This does not follow.

Life did not just create oxygen out of nothing, and add it to the atmosphere.

It is thought that the early atmosphere had a high level of carbon dioxide CO₂ (like Venus). Through photosynthesis, living algae & plants converted atmospheric carbon dioxide CO₂ into oxygen O₂, using the carbon for building their own biomass.

This process does not increase the pressure of the atmosphere - in fact, iron minerals would have reacted with the atmospheric oxygen, taking it out of atmospheric circulation, and resulting in a net reduction of atmospheric pressure (not an increase, as suggested).

See: http://en.wikipedia.org/wiki/Great_Oxygenation_Event

You are correct in terms of photosynthesis. The photosynthesis equation is 6CO2 + 6H2O ------> C6H12O6 + 6O2. The moles of CO2 lost and the moles of O2 gained offset so there is very little partial pressure change in terms of these two atmospheric gases. Water is a wild card since it can be gas, liquid and solid with ocean of water to replenish the atmosphere.

The water will add partial pressure based on the surface temperature and the evaporation rate with plenty of water in the oceans to meet almost any evaporation scenario. If we assume CO2 is a green house gas, then the original high ratio of CO2 to O2 partial pressure will keep the earth hotter and allow more H2O in the atmosphere; bigger storms.

If we go earlier than photosynthesis; abiogenesis and pre-life, the Miller style Experiments suggest something different was occurring before life and photosynthesis appears. The larger storms in the early hot atmosphere, full of CO2, are generating lots of lightning.

The Miller Experiment:

The experiment used water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2). The chemicals were all sealed inside a sterile 5-liter glass flask connected to a 500 ml flask half-full of liquid water. The liquid water in the smaller flask was heated to induce evaporation, and the water vapour was allowed to enter the larger flask. Continuous electrical sparks were fired between the electrodes to simulate lightning in the water vapor and gaseous mixture, and then the simulated atmosphere was cooled again so that the water condensed and trickled into a U-shaped trap at the bottom of the apparatus.

Professor Jeffrey Bada, himself Miller's student, inherited the original equipment from the experiment when Miller died in 2007. Based on sealed vials from the original experiment, scientists have been able to show that although successful, Miller was never able to find out, with the equipment available to him, the full extent of the experiment's success. Later researchers have been able to isolate even more different amino acids, 25 altogether. Professor Bada has estimated that more accurate measurements could easily bring out 30 or 40 more amino acids in very low concentrations, but the researchers have since discontinued the testing. Miller's experiment was therefore a remarkable success at synthesizing complex organic molecules from simpler chemicals, considering that all life uses just 20 different amino acids.[7]

Originally it was thought that the primitive secondary atmosphere contained mostly ammonia and methane. However, it is likely that most of the atmospheric carbon was CO2 with perhaps some CO and the nitrogen mostly N2. In practice gas mixtures containing CO, CO2, N2, etc. give much the same products as those containing CH4 and NH3 so long as there is no O2. The hydrogen atoms come mostly from water vapor. In fact, in order to generate aromatic amino acids under primitive earth conditions it is necessary to use less hydrogen-rich gaseous mixtures. Most of the natural amino acids, hydroxyacids, purines, pyrimidines, and sugars have been made in variants of the Miller experiment.[9][25]

The  Miller experiment and the modified Miller Experiments both sequestered gases from the atmosphere, to form a large range of chemicals, without generating the offset O2 of photosynthesis. Before life, the atmospheric pressure was lowering. Once O2 begins to form, via photosynthesis,  Miller style sequestering becomes disrupted, since O2 tends to reverse these reactions. A balance begins to form connected to life.