Cyclonic Niño
Tropical cyclones are dangerous and destructive weather phenomena that are responsible for nearly $10,000,000,000 damage every year in the United States alone.
[7] The effects have usually been described as a temporary cooling of the water surface[8] by up to 6 °C (11 °F)[9] that tends to weaken the storm[7] but is dissipated by the sea and the atmosphere in one-two months.
[d][22] Estimates of ocean heat content through satellite imaging support that tropical cyclone activity increases the heat content of the oceans, although there are some caveats[23] and the effect on global heat fluxes is not particularly large under present-day tropical cyclone activity;[2] however, according to one study the effect might be large enough to explain discrepancies between the steady state ocean mixing observed in the tropics and the amount required by planetary energetics, as the former is insufficient otherwise.
[31] Tropical cyclones induce mixing of the sea surface waters;[28] with a tenfold increase in ocean mixing within two bands 8–40° north and south of the equator – especially mixing occurring in the Central Pacific where tropical cyclone activity is low under present-day climate – heat would be introduced into these sea currents and eventually lead to a warming of the central and eastern Pacific Ocean similar to El Niño and a warming of the upwelling regions,[31] with a warming of about 2–3 °C (3.6–5.4 °F) in the zone of the East Pacific cold tongue.
It is also subject to positive feedback, as the warming of the eastern Pacific in turn increases tropical cyclone activity; eventually a climate state featuring a permanent El Niño and a weaker El Niño Southern Oscillation can arise.
[38] Later researchers have suggested that the increased winds may actually strengthen the El Niño Southern Oscillation[39] and that Eocene and Pliocene warm climates still featured an ENSO cycle.
[37] A 2019 study concluded that tropical cyclone activity in the Western Pacific is correlated to El Niño-associated temperature anomalies months later.
[44] A 2010 climate simulation indicated that increasing the average winds of tropical cyclones induced warming in the Eastern Pacific and cooling in the Western Pacific,[45] consistent with an El Niño like response; there is also strengthening of the Hadley cell of the atmospheric circulation[46] and some heat is transported out of the tropics by the western boundary currents.
Similar effects but of much smaller magnitude are seen in the North Atlantic and other oceans[48] and there are also changes to the Indonesian Throughflow.
[54] A 2014 study showed a total increase in ocean heat content caused by the typhoons and hurricanes active between 2004 and late 2005.
This was the case for example during the late Cretaceous, during the Paleocene-Eocene thermal maximum during which temperatures in the Arctic exceeded 20 °C (68 °F) at times,[67] during the Eocene[5] and during the Pliocene between 3 and 5 million years ago.
