Will the eruption of Redoubt in Alaska affect the tropics?

[cycloneye]

This has to be a good question to ask as MT Redoubt in Alaska has made a significant eruption of ash close to 50,000 feet.The question is if this eruption may affect the tropical areas of the world (Atlantic,EPAC,WPAC) in terms of activity of storms.

Details of the eruption can be seen at Geology subforum at Global Weather forum
viewforum.php?f=67

Link to Mt Redoubt thread:
viewtopic.php?f=67&t=104544&start=0

[Chacor]

It's not a super eruption. Don't think impact - if any - will be major.

[KWT]

Yeah from what I've heard you need a bigger eruption to have a major impact, esp when this volcano is also as far north as it is.

[cycloneye]

I found a pretty comparable situation from Mt Redoubt to a 1912 eruption of Novarupta in terms of changes in weather patterns in the world and the tropics on that year.

In June 1912, Novarupta—one of a chain of volcanoes on the Alaska Peninsula—erupted in what turned out to be the largest blast of the twentieth century. It was so powerful that it drained magma from under another volcano, Mount Katmai, six miles east, causing the summit of Katmai to collapse to form a caldera half a mile deep. Novarupta also expelled three cubic miles of magma and ash into the air, which fell to cover an area of 3,000 square miles more than a foot deep.

Despite the fact that the eruption was comparable to that of the far more famous eruption of Krakatau in Indonesia in 1883 and so near the continental United States, it was hardly known at the time because the area was so remote from English-speaking people.

Almost a hundred years later, researchers are paying attention. Novarupta is near the Arctic Circle and its impact on climate appears to be quite different from that of "ordinary" tropical volcanoes, according to recent research by climatologists using a NASA computer model.

When a volcano anywhere erupts, it does more than spew clouds of ash, which can shadow a region from sunlight and cool it for a few days. It also blows sulfur dioxide—a gas irritating to the lungs and smelling like rotten eggs. If the eruption is strongly vertical, it shoots that sulfur dioxide high into the stratosphere more than 10 miles above Earth.

Up in the stratosphere, sulfur dioxide reacts with water vapor to form sulfate aerosols. Because these aerosols float above the altitude of rain, they don't get washed out. They linger, reflecting sunlight and cooling Earth's surface.

This can create a kind of nuclear winter (a.k.a. "volcanic winter") for a year or more after an eruption. In April 1815, for instance, the Tambora volcano in Indonesia erupted. The following year, 1816, was called "the year without a summer," with snow falling across the United States in July. Even the smaller June 1991 eruption of Pinatubo in the Philippines cooled the average temperature of the northern hemisphere summer of 1992 to well below average.

But both those volcanoes as well as Krakatau were in the tropics.

Novarupta is just south of the Arctic Circle.

Using a NASA computer model at the the Goddard Institute for Space Studies (GISS), Prof. Alan Robock of Rutgers University and colleagues found that Novarupta's effects on the world's climate would have been different. (Their research was funded by the National Science Foundation.)

Robock explains: "The stratosphere's average circulation is from the equator to the poles, so aerosols from tropical volcanoes tend to spread across all latitudes both north and south of the Equator." Aerosols would quickly circulate to all parts of the globe.

But the NASA GISS climate model showed that aerosols from an arctic eruption such as Novarupta tend to stay north of 30ºN—that is, no further south than the continental United States or Europe. Indeed, they would mix with the rest of Earth's atmosphere only very slowly.

This bottling up of Novarupta's aerosols in the north would make itself felt, strangely enough, in India. According to the computer model, the Novarupta blast would have weakened India's summer monsoon, producing "an abnormally warm and dry summer over northern India," says Robock.

Why India? Cooling of the northern hemisphere by Novarupta would set in motion a chain of events involving land and sea surface temperatures, the flow of air over the Himalayan mountains and, finally, clouds and rain over India. It's devilishly complex, which is why supercomputers are needed to do the calculations.

To check the results, Robock and colleagues are examining weather and river flow data from Asia, India, and Africa in 1913, the year after Novarupta. They are also investigating the consequences of other high-latitude eruptions in the last few centuries.

http://www.scienceblog.com/cms/huge-vol ... 11657.html

[wxman57]

Eruptions at high latitudes generally disperse much more quickly. Probably no effect. Now the better question is how the underwater volcano erupting near Tonga may affect SSTs in Nino 3.4 region just to its north. Could it lead to additional warming and perhaps an El Nino this fall?

[cycloneye]

Dr Jeff Masters says effects around the world should be minimal.

Many historic volcanic eruptions have had a major cooling impact on Earth's climate. However, Redoubt is very unlikely to be one of them. To see why this is, let's examine recent volcanic eruptions that have had a significant cooling effect on the climate. In the past 200 years, Mt. Pinatubo in the Philippines (June 1991), El Chichon (Mexico, 1982), Mt. Agung (Indonesia, 1963), Santa Maria (Guatemala, 1902) Krakatoa (Indonesia, 1883), and Tambora (1815) all created noticeable cooling. As one can see from a plot of the solar radiation reaching Mauna Loa in Hawaii (Figure 2), the Mt. Pinatubo and El Chichon eruptions caused a greater than 10% drop in sunlight reaching the surface. The eruption of Tambora in 1815 had an even greater impact, triggering the famed Year Without a Summer in 1816. Killing frosts and snow storms in May and June 1816 in Eastern Canada and New England caused widespread crop failures, and lake and river ice were observed as far south as Pennsylvania in July and August. Volcanic eruptions cause this kind of climate cooling by throwing large amounts of sulfur dioxide gas into the stratosphere. This gas reacts with water to form sulphuric acid droplets (aerosol particles), which are highly reflective, and reduce the amount of incoming sunlight.

You'll notice from the list of eruptions above that all of these climate-cooling events were from volcanoes in the tropics. Above the tropics, the stratosphere's circulation features rising air, which pulls the sulfur-containing volcanic aerosols high into the stratosphere. Upper-level winds in the stratosphere tend to flow from the Equator to the poles, so sulfur aerosols from equatorial eruptions get spread out over both hemispheres. These aerosol particles take a year or two to settle back down to earth, since there is no rain in the stratosphere to help remove them. However, if a major volcanic eruption occurs in the mid-latitudes or polar regions, the circulation of the stratosphere in those regions generally features pole-ward-flowing, sinking air, and the volcanic aerosol particles are not able to penetrate high in the stratosphere or get spread out around the entire globe. Redoubt is located near 59° north latitude, far from the tropics, and thus is unlikely to be able to inject significant amounts of sulfur aerosols into the stratosphere. Furthermore, the previous 1989 - 1990 eruption of Redoubt (Figure 3) put only about 1/100 of the amount of sulfur into the air that the 1991 eruption of Mt. Pinatubo did, according to the TOMS Volcanic Emissions Group. We can expect the current eruption of Redoubt to be similar in sulfur emissions to the 1989 - 1990 eruption, and have an insignificant impact on global climate.

http://www.wunderground.com/blog/JeffMa ... rynum=1203

[xironman]

Now the better question is how the underwater volcano erupting near Tonga may affect SSTs in Nino 3.4 region just to its north. Could it lead to additional warming and perhaps an El Nino this fall?

From what I understand a volcano does not put out nearly enough energy to significantly effect the temperature of a body of water as large as the central pacific.

[tolakram]

I've been following Redoubt on the radar, if you get lucky you can see an eruption before it's reported.

http://www.wunderground.com/radar/radbl ... 9&smooth=0

Setting the angle up to 1.45 you can see Redoubt as the west southwest of Anchorage, shading the echos behind it. If you watch closely every time Redoubt belches steam or ash it shows up as yellow echos. Big eruptions or explosions are red, looking like a super cell, and you'll be able to follow the ash cloud as it blows away from the volcano.

Closeup:

http://www.wunderground.com/radar/radbl ... rainsnow=0

Here is the observatory site:

http://www.avo.alaska.edu/activity/Redoubt.php

Not exactly tropical.