A hypercane is a hypothetical class of extreme
tropical cyclone that could form if sea surface temperatures reached approximately , which is warmer than the warmest ocean temperature ever recorded. Such an increase could be caused by a large
asteroid or
comet impact, a large
supervolcanic eruption, a large submarine
flood basalt, or extensive
global warming. There is some speculation that a series of hypercanes resulting from the
impact of a large
asteroid or comet contributed to the
demise of the non-avian
dinosaurs.
The hypothesis was created by
Kerry Emanuel of
MIT, who also coined the term.
Additionally, it is also speculated that many planets that could orbit red dwarf stars, if they have liquid water, would permanently experience hypercanes on their sunlit faces due to the effects of tidal locking. This could potentially challenge any life forms that were to live there.
Description

In order to form a hypercane, according to Emanuel's hypothetical model, the ocean temperature would have to be at least 49 °C (120 °F). A critical difference between a hypercane and present-day hurricanes is that a hypercane would extend into the upper
stratosphere, whereas present-day hurricanes extend into only the lower stratosphere.
Hypercanes would have wind speeds of over , potentially gusting to ,
and would also have a central pressure of less than , giving them an enormous lifespan of at least several weeks.
This extreme low pressure could also support massive storm systems roughly the size of North America.
For comparison, the largest and most intense storm on record was 1979's
Typhoon Tip, with a 1-minute sustained wind speed of and a minimum central pressure of . Such a storm would be nearly eight times more powerful than
Hurricane Patricia, the storm with the highest sustained wind speed recorded, which had 1-minute sustained winds of 345 km/h (215 mph). However, hypercanes may be as small as in size, and they would lose strength quickly after venturing into colder waters.
The waters after a hypercane could remain hot enough for weeks, allowing more hypercanes to form. A hypercane's clouds would reach into the
stratosphere. Such an intense storm would also damage the Earth's
ozone layer, potentially having devastating consequences for life on Earth.
Water molecules in the stratosphere would react with
ozone to accelerate decay into O
2 and reduce absorption of
ultraviolet light.
Mechanism
A hurricane functions as a
Carnot heat engine powered by the temperature difference between the sea and the uppermost layer of the troposphere. As air is drawn in towards the eye it acquires
latent heat from evaporating sea-water, which is then released as
sensible heat during the rise inside the eyewall and radiated away at the top of the storm system. The energy input is balanced by energy dissipation in a turbulent
boundary layer close to the surface, which leads to an energy balance equilibrium.
However, in Emanuel's model, if the temperature difference between the sea and the top of the troposphere is too large, there is no solution to the equilibrium equation. As more air is drawn in, the released heat reduces the central pressure further, drawing in more heat in a runaway positive feedback. The actual limit to hypercane intensity depends on other energy dissipation factors that are uncertain: whether inflow ceases to be
isothermal, whether
shock waves would form in the outflow around the
eye, or whether turbulent breakdown of the vortex happens.
See also
*
Global catastrophic risk
*
Saffir–Simpson scale
*
Tornado
*
Extraterrestrial cyclone
*
Great Red Spot
*
Great Dark Spot
References
{{Cyclones
External links
Hypercanes: The Next Big Disaster Movie?– YouTube
Category:Tropical cyclone meteorology
Category:Weather hazards
Category:Doomsday scenarios
Category:Geological hazards
Category:Future problems
Category:Meteorological hypotheses