Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 15. huhtikuuta 2010 klo 14:11 (GMT)
The Eyjafjallajökull volcano on Iceland erupted Wednesday, sending a towering cloud of volcanic ash 6 - 11 km (20,000 - 36,000') high in the air from its 1666 meter (5500') high peak. The ash cloud has caused a dramatic interruption of air traffic over much of northern Europe today, and this disruption will spread southwards and eastwards over the next day as the ash cloud gradually spreads and disperses (Figure 2.)
Figure 1. Ash plume from Eyjafjallajokull Volcano over the North Atlantic at 11:35 UTC April 15, 2010. Image credit: NASA.
Figure 2. Forecast extent of the ash cloud from the Eyjafjallajökull volcano on Iceland at 12 UTC (8 am EDT) and 00 UTC tonight (8 pm EDT.) The red colors show the extent between the surface and 20,000', the green colors between 20,000 - 35,000', and the blue line between 35,000 - 55,000'. Commercial jetliners typically cruise at 35,000'. Image credit: UKMET Office.
Iceland volcano not likely to significantly affect the climate or weather
Volcanic eruptions are capable of significantly cooling the climate for 1 - 2 years after a major eruption spews sulfur dioxide gas forcefully enough so that it reaches the stratosphere. Once in the stratosphere, the gas reacts to form highly reflective sulfuric acid droplets mixed with water (sulfate aerosol particles). Our volcanoes and climate page covers the topic in more detail. 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. 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. 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.
There have been at least two exceptions to the tropics-only rule. Realclimate.org discusses the eruption of the Laki volcano in Iceland, between 1783-1784. The eruption was probably not able to inject much sulfur into the stratosphere. However, since the eruption was sustained for so long, significantly elevated sulfur concentrations were seen in the lower atmosphere over much of the Atlantic and European regions, which had a pronounced cooling effect on the region.
scienceblog.com has an interesting article about the largest volcanic eruption of the 20th century--the 1912 eruption of Alaska's Mt. Novarupta, located in the same chain of volcanoes as Mt. Redoubt. According to a NASA computer model, Novarupta's climate-cooling aerosols stayed north of 30°N latitude, and did not cause global cooling. However, the model indicates that the eruption may have indirectly weakened India's summer monsoon, producing an abnormally warm and dry summer over northern India.
It does not appear that the current eruption of the Eyjafjallajökull volcano on Iceland was large enough to alter the atmospheric circulation of the Northern Hemisphere and cause a change in the late spring/early summer weather patterns. A series of several major eruptions over the next few weeks would be required for that to happen. The volcano is also too far north for the cooling effect of its ash cloud to affect the sea surface temperatures in the tropical Atlantic for the coming hurricane season. However, the ash could should bring spectacular sunsets to Europe over the next week, and to North America by sometime next week, as the jet stream wraps the ash cloud eastwards across the Northern Hemisphere.
Portlight aid ship nears Haiti
Portlight.org continues to work hard to get food and medical supplies into the earthquake zone in Haiti. Their latest effort is a shipment of 30,000 pounds of rice and 20,000 pounds of other supplies, mostly medical equipment, that has been loaded onto the schooner Halie and Mathew. The schooner is expected to land in Haiti today to deliver the supplies. Please visit the Portlight.org web site or the Portlight blog to learn more and to donate to this worthy cause.
Figure 2. Relief supplies for Haiti earthquake victims being loaded onto the schooner Halie and Mathew.
Paul Timmons (Presslord) and Pat Pearson (Patrap) of Portlight will on the Internet radio show, the Daily Downpour Link. The hosts are wunderground meteorologists Shaun Tanner and Tim Roche. The show airs today, Thursday, April 15, at 4pm Eastern.
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