Volcanic eruptions affect cyclones

The number and intensity of hurricanes and typhoons will change for up to four years

Large volcanic eruptions in the tropics affect the number and intensity of tropical cyclones. Because they change the conditions in the birth of hurricanes and typhoons. © NOAA
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Hidden side effect: A violent volcanic eruption in the tropics significantly changes the cyclone activity worldwide. Hurricanes and typhoons can become rarer or more frequent for up to four years, depending on the earth hemisphere in which the eruption took place. The reason for this effect lies in the cooling climate effect of the eruption clouds and in a consequent shift of atmospheric currents, as the researchers report.

Volcanic eruptions not only have consequences for their immediate environment, they can also have a decisive influence on the global climate. Ash and sulfur aerosols of the eruption cloud spread in the upper atmosphere and act as a sun filter. Throughout history, volcanic eruptions have often caused cold spells, resulting in crop failures, starvation, epidemics and even the collapse of entire empires.

How do eruptions affect the storm?

But can tropical volcanic eruptions also influence specific weather events such as hurricanes and typhoons? After all, previous studies have shown that large eruptions can also affect precipitation patterns and even climatic phenomena like the El Nino. For hurricanes, however, the effect has remained unclear: "So far, only a handful of studies have studied the effects of volcanic eruptions on tropical cyclones - and these have yielded conflicting results, " report Francesco Pausataa from the University of Quebec in Montreal and his team.

To clarify the question, the researchers simulated the effects of a large tropical volcanic eruption in the southern or northern hemisphere of the earth using a current Earth-climate model. The model used was the eruption of the Tambora in 1815. In addition to control simulations without outbreak, the scientists also ran additional passages in which they examined the interaction with the El Nino phenomenon.

The number and intensity of the eddy currents is changing

The result: A tropical volcanic eruption has measurable effects on cyclone frequency for up to four years. Especially in Southeast Asia and Australia, the number of typhoons and their intensity decreases, regardless of which hemisphere the eruption occurred in. At the same time, the eddy currents' educational regions continue to move south, as the researchers report. display

"In other regions, however, eruptions in the south or north have opposite effects, " explain Pausataa and his colleagues. Thus, when a tropical volcano erupts south of the equator, the number and intensity of hurricanes in the North Atlantic increases. By contrast, if the eruption lies in the tropical belt of the northern hemisphere, the Atlantic cyclones will decrease.

Shifting of the tropical weather band

But what is the cause of this effect? "So far it has been suggested that the cooling effect on sea temperatures could be responsible for this, " the researchers explain. "Others assumed an indirect consequence of changing El Nino patterns." However, the current simulations show that the effect of volcanoes on eddy currents is much stronger than El Nino alone explains rbar.

Instead, the volcanic eruptions affect the Intertropical Convergence Zone (ITCZ). This low pressure trough, which spans the globe in the equator, is prone to precipitation, temperatures and winds in the low latitudes. "The eruptions cause an asymmetric cooling of the hemispheres, which shifts the intra-tropical convergence zone, " report Pausataa and his colleagues.

A tropical eruption just north of the equator shifts the ITCZ ​​to the south, an eruption south of the equator shifts the convergence zone to the north. Because this also changes precipitation, winds and temperatures in the birth regions of tropical storms, this influences the number and frequency of such storms, according to the researchers.

Important for risk forecasts

In the opinion of the scientists, this finding is not only important for meteorologists and climatologists, it could also help in estimating the current hurricane and typhoon risk. "These results will be of great value to society, " emphasize Pausataa and his colleagues. "Because they allow one to better prepare for the changes in hurricane activity following large volcanic eruptions." (Proceedings of the National Academy of Sciences, 2019; 10.1073 / pnas.1900777116)

Source: PNAS

- Nadja Podbregar