The SI Weather

2:45 PM | The Iceland volcano erupts, but a far bigger explosion occurs on the other side of the world

[Ash plume from Rabaul volcano in Papua New Guinea]


The Bardarbunga volcano in Iceland that we have been tracking in recent days has finally erupted, but it was not a big explosive event. Meanwhile, there has actually been a far bigger eruption in Papua New Guinea at the Rabaul volcano on Mount Tavurvur and this has the potential to do more damage to nearby population centers.

The Iceland volcano which sits beneath a glacier has been receiving most of the attention lately and last night it finally started erupting as lava emerged from a fissure. A fissure eruption is one in which lava essentially flows up through vents in the ground spread out over a larger area. The eruption lasted about four hours and came after weeks of earthquakes in the region. The eruption did not spew ash into the atmosphere and has had minimal effects on flights and it is in a relatively remote area of Iceland. Even though the eruption has stopped for the time being, earthquakes continue to rumble indicating magma is still on the move, and this volcano will continue to be closely monitored. By the way, in an odd twist of fate by Mother Nature, the remains of Hurricane Cristobal raced from off the US east coast into the North Atlantic during the past couple of days and actually dumped some serious snow on Iceland as well as on eastern sections of Greenland.

Papua New Guinea
Meanwhile, on the other side of the world, the large Rabaul volcano began erupting earlier today and it has spewed out plenty of ash into the atmosphere. The ash plume has apparently reached about 11 miles into the air and has indeed disrupted air travel in that part of the world. This was the first major eruption of this volcano – one of the most active in Papua New Guinea - in about twenty years. In 1994, an eruption there nearly destroyed Rabaul altogether, forcing residents to flee.

Volcanic eruptions along with oceanic and solar cycles play crucial roles in our global climate. The most substantive climatic effect from volcanoes results from the production of atmospheric haze. Large eruption columns inject ash particles and sulfur-rich gases into the troposphere and stratosphere and these clouds can circle the globe within weeks of the volcanic activity. The small ash particles decrease the amount of sunlight reaching the surface of the earth and lower average global temperatures. The sulfurous gases combine with water in the atmosphere to form acidic aerosols that also absorb incoming solar radiation and scatter it back out into space. In fact, the formation of atmospheric sulfur aerosols has a more substantial effect on global temperatures than simply the volume of ash produced during an eruption.

Not only does the type and amount of ash from volcanic eruptions play a critical role in its potential effect on global temperatures, but the location of the eruption is also very important. Volcanic eruptions in the tropics, for example, can be much more important than those in the mid-latitudes for a couple of reasons. First, the sun heats equatorial regions more than in mid-latitude or polar regions; therefore, any disruption to solar radiation in the tropics can have more serious effects on global temperatures. Second, upper level winds - which act to spread and disperse ash plumes – are typically weak over tropical regions as compared with the mid-latitudes, for example, and this could impact the longevity of any ash cloud in a particular region.

The atmospheric effects of volcanic eruptions were confirmed by the 1991 eruption of Mount Pinatubo, in the Philippines. Pinatubo’s eruption cloud reached over 40 kilometers into the atmosphere and ejected about 17 million tons of SO2, just over two times that of the El Chichon, Mexico volcano in 1982. The sulfur-rich aerosols circled the globe within three weeks and produced a global cooling effect approximately twice that of El Chichon. The Northern Hemisphere cooled by up to 0.6 degrees C during 1992 and 1993.

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3:00 PM | The first half of September looks quite warm in the Mid-Atlantic region

[Euro computer model forecast at 500 millibars for September 7th]


August has brought a continuation of below normal temperatures to the Mid-Atlantic region following a slightly cooler-than-normal month of July, but it looks like at least the first half of September will be on the warmer-than-normal side. The persistent upper air pattern of recent months featuring numerous troughs of low pressure centered over the Midwest and Great Lakes will change over the next several days to one with strong high pressure ridging centered in the Southeast US. Indeed, the 500 millibar forecast map from the latest European computer forecast model run (above) depicts high pressure in the Southeast US about 10 days from now. From this position, high pressure over the Southeast US will pump in warm, humid air from the Gulf of Mexico region to the Mid-Atlantic which until now this summer has not been sustainable by the atmosphere for more than a couple of days at a time. Supporting evidence for this warm outlook during the first half of September comes from NOAA’s Climate Forecast System (CFS version 2) forecast model which shows warmer-than-normal conditions during the first 10 days of September in much of the eastern half of the nation (orange/red areas in two maps below). Looking even farther ahead, I believe it is possible that the warmer-than-normal weather pattern that develops next week may end up continuing into October, but there is likely to be a transition back to colder-than-normal conditions before the winter locks in.

[NOAA/Climate Forecast System forecast maps for temperature departures from normal for the next two weeks]

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1:00 PM | Northern lights, an update on the Iceland volcano, and mysterious lights from the Napa earthquake


Northern Lights
[Northern lights earlier today as seen in Devil's Tower, Wyoming; courtesy]

A coronal mass ejection (CME) reached the Earth’s upper atmosphere early today sparking bright auroras around the North and South Poles and in high latitudes. In fact, reports of northern lights have poured in today from across the northern US including such states as Maine, Michigan, Wisconsin, Idaho, North Dakota and Washington. The CME that instigated today’s display was launched toward Earth on August 22nd. According to “”, the solar wind speed did not change much when the slow-moving CME arrived. However, the storm cloud was still “effective” because it contained a south-pointing magnetic field that opened a crack in Earth’s magnetosphere. Solar wind is pouring in to fuel the on-going display. High latitude sky watchers should remain on alert tonight for auroras as solar wind conditions continue to favor geomagnetic activity.

[NOAA POES satellite data shows the extent of this morning’s "statistical aurora oval" well down into the mid-latitudes; courtesy NOAA Space Prediction Center].

Iceland Volcano
Earthquakes are rocking Iceland’s Bardarbungo volcano, adding to concerns that magna movements may trigger an eruption that could hinder air traffic. Two earthquakes measuring over 5.0 shook the volcano under the vast Vatnajokull glacier earlier today and over 500 quakes have hit the area since midnight. Scientists say that 50 million cubic meters of molten rock has moved in a 24 hour period. If it continues to head north, it could link up with the Askja system and trigger a large eruption. In 2010, Iceland's Eyjafjallajokul volcano erupted and sparked a week of international aviation chaos. Some 100,000 flights were cancelled after aviation officials closed Europe's air space for five days out of fears that volcanic ash could harm jet engines.

[The ash cloud from the Eyjafjallajokull eruption in 2010 created a major disruption for air travel]

Mysterious Lights
Mysterious flashes of light in the sky were reported by several people during last Sunday’s magnitude 6.0 earthquake in the Napa region of northern California. Witnesses said the strange phenomenon looked like lightning and similar flashes of light have been reported in earthquakes around the world from Japan to Peru. One scientist called this phenomenon “earthquake lights” and suggested they are a consequence of the stresses building up deep below the earth that cause an electric current to flow to the surface and burst through the earth. This typically happens before or during an earthquake. Most reports said there were one to two seconds between the light flashes. Research continues in this area - many seismologists do not believe such things are real.

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12:30 PM | 75th Anniversary of “The Wizard of Oz” and the incredible tornado scene



Last Friday was the 75th anniversary of the release of "The Wizard of Oz" which was the first movie to depict an authentic looking tornado using improbable “1930’s style” special effects. Through the decades, this all-time classic has inspired movie-goers and “weather weenies” alike with the scene of a twister lifting Dorothy’s home into the sky over rural Kansas farm land.

The movie was based on a novel called "The Wonderful Wizard of Oz" written by L. Frank Baum in the year 1900. The setting of the movie in rural Kansas and the name of its main character, Dorothy Gale, were not just random choices. Baum had been a newspaper editor in the "Dakota Territory” (now South Dakota) and recalled the story of twin tornadoes that destroyed the rural town of Irving, Kansas in May of 1879. The name of one of the victims of this tornado outbreak was found in a mud puddle - and her name was Dorothy Gale.

The tornado scene
As far as the tornado scene is concerned, it is still regarded as incredibly realistic – even in today’s era of computer-generated special effects. The first attempt at a tornado by the movie’s special effects director, Arnold Gillespie, was to use a 35-foot tall rubber cone, but this turned out to be too rigid and simply wouldn’t move. Next, the special effects director recalled from his experience as a pilot (even had his own airplane) that wind socks at airports had the classic funnel-shape of a tornado. He decided to make a tornado out of muslin (plane woven cloth) which would allow it to twist, bend and move from side-to-side. He built a 35-foot long tapered muslin sock and connected the top of it to a steel gantry suspended at the top of the stage. The gantry alone cost more than $12,000 (in 1938 dollars) and was specifically built for the tornado by Bethlehem Steel. It was a mobile structure similar to those used in warehouses to lift heavy objects and could travel the entire length of the stage. The bottom of the sock disappeared into a slot on the stage floor where it connected to a rod which came up through the base of the tornado to pull it from side-to-side. By moving the gantry and rod in different directions, the tornado appeared to "snake" across the stage.

To produce the dust and debris that makes a real tornado visible, they used compressed air hoses to spray a powdery brown dust known as “Fullers Earth” from both the top and bottom of the funnel. The muslin sock was sufficiently porous that some of the dust sifted through giving a blur or softness to the material and a fuzziness to the edges so that it didn’t look like a hard surface.

Four or five feet in front of the cameras were two panels of glass on which gray balls of cotton (great for mammatus clouds) had been pasted. The two panels moved in opposite directions adding to the boiling sensation and, at the same time, they obscured the steel gantry and top portion of the tornado. Dense clouds of yellow-black smoke made from sulfur and carbon were injected onto the set from a catwalk above the gantry. The stage hands had no respirators and stayed up there breathing the stuff until they couldn't stand it. Many of them became ill and some coughed up black-yellow mucous even days after the tornado was photographed.

Once the tornado had been filmed, there was still plenty of work to be done. Rear- projection was used to transfer the previously shot tornado image onto a translucent screen while actors such as Dorothy were placed in front of it. Wind machines provided the big blow while stage hands threw dried leaves and other debris in the air. When the tornado came real close to the house at the end of the scene, more debris and dirt were added in the foreground to obscure the fake tornado while providing more realism. The tornado scene in "The Wizard of Oz" ended up costing more money than any other special effect in the movie. So essentially, "The Wizard of Oz" tornado was nothing more than a large tapered cloth sock with lots of wind and dirt thrown at it.

"The Wizard of Oz" was nominated for six Academy Awards and won two including “Best Original Song” (Over The Rainbow), but it did not win an Oscar for its amazing special effects and it did not win the Oscar for “Best Picture”. That honor went to another famous movie from 1939 with coincidentally a “weather-related” name - "Gone with the Wind". For additional information, check out the Penn State Department of Meteorology “Weather World” video presentation by Dr. Jon Nese (

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