Thanks decimon.
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Posted on 06/14/2011 3:47:19 PM PDT by decimon
Since 1611, humans have recorded the comings and goings of black spots on the sun. The number of these sunspots wax and wane over approximately an 11-year cycle -- more sunspots generally mean more activity and eruptions on the sun and vice versa. The number of sunspots can change from cycle to cycle and 2008 saw the longest and weakest solar minimum since scientists have been monitoring the sun with space-based instruments.
Observations have shown, however, that magnetic effects on Earth due to the sun, effects that cause the aurora to appear, did not go down in synch with the cycle of low magnetism on the sun. Now, a paper in Annales Geophysicae that appeared on May 16, 2011 reports that these effects on Earth did in fact reach a minimum -- indeed they attained their lowest levels of the century -- but some eight months later. The scientists believe that factors in the speed of the solar wind, and the strength and direction of the magnetic fields embedded within it, helped produce this anomalous low.
"Historically, the solar minimum is defined by sunspot number," says space weather scientist Bruce Tsurutani at NASA's Jet Propulsion Lab in Pasadena, Calif., who is first author on the paper. "Based on that, 2008 was identified as the period of solar minimum. But the geomagnetic effects on Earth reached their minimum quite some time later in 2009. So we decided to look at what caused the geomagnetic minimum."
Geomagnetic effects basically amount to any magnetic changes on Earth due to the sun, and they're measured by magnetometer readings on the surface of the Earth. Such effects are usually harmless, the only obvious sign of their presence being the appearance of auroras near the poles. However, in extreme cases, they can cause power grid failures on Earth or induce dangerous currents in long pipelines, so it is valuable to know how the geomagnetic effects vary with the sun.
Three things help determine how much energy from the sun is transferred to Earth's magnetosphere from the solar wind: the speed of the solar wind, the strength of the magnetic field outside Earth's bounds (known as the interplanetary magnetic field) and which direction it is pointing, since a large southward component is necessary to connect successfully to Earth's magnetosphere and transfer energy. The team -- which also included Walter Gonzalez and Ezequiel Echer of the Brazilian National Institute for Space Research in São José dos Campos, Brazil -- examined each component in turn.
First, the researchers noted that in 2008 and 2009, the interplanetary magnetic field was the lowest it had been in the history of the space age. This was an obvious contribution to the geomagnetic minimum. But since the geomagnetic effects didn't drop in 2008, it could not be the only factor.
To examine the speed of the solar wind, they turned to NASA's Advanced Composition Explorer (ACE), which is in interplanetary space outside the Earth's magnetosphere, approximately 1 million miles toward the sun. The ACE data showed that the speed of the solar wind stayed high during the sunspot minimum. Only later did it begin a steady decline, correlating to the timing of the decline in geomagnetic effects.
The next step was to understand what caused this decrease. The team found a culprit in something called coronal holes. Coronal holes are darker, colder areas within the sun's outer atmosphere. Fast solar wind shoots out the center of coronal holes at speeds up to 500 miles per second, but wind flowing out of the sides slows down as it expands into space.
"Usually, at solar minimum, the coronal holes are at the sun's poles," says Giuliana de Toma, a solar scientist at the National Center for Atmospheric Research whose research on this topic helped provide insight for this paper. "Therefore, Earth receives wind from only the edges of these holes and it's not very fast. But in 2007 and 2008, the coronal holes were not confined to the poles as normal."
Those coronal holes lingered at low-latitudes to the end of 2008. Consequently, the center of the holes stayed firmly pointed towards wind at Earth begin to slow down. And, of course, the geomagnetic effects and sightings of the aurora along with it.
Coronal holes seem to be responsible for minimizing the southward direction of the interplanetary magnetic field as well. The solar wind's magnetic fields oscillate on the journey from the sun to Earth. These fluctuations are known as Alfvén waves. The wind coming out of the centers of the coronal holes have large fluctuations, meaning that the southward magnetic component – like that in all the directions -- is fairly large. The wind that comes from the edges, however, has smaller fluctuations, and comparably smaller southward components. So, once again, coronal holes at lower latitudes would have a better chance of connecting with Earth's magnetosphere and causing geomagnetic effects, while mid-latitude holes would be less effective.
Working together, these three factors -- low interplanetary magnetic field strength combined with slower solar wind speed and smaller magnetic fluctuations due to coronal hole placement -- create the perfect environment for a geomagnetic minimum.
Knowing what situations cause and suppress intense geomagnetic activity on Earth is a step toward better predicting when such events might happen. To do so well, Tsurutani points out, requires focusing on the tight connection between such effects and the complex physics of the sun. "It's important to understand all of these features better," he says. "To understand what causes low interplanetary magnetic fields and what causes coronal holes in general. This is all part of the solar cycle. And all part of what causes effects on Earth."
Sun and wind ping.
Whatever it means, it’s Bush’s fault.
Jokes aside.. the “anomalous low” did correspond to Nov. ‘08, and the magnetic consequence to the solar wind arrived eight months later. Never mind, I’m putting my tinfoil hat back in the drawer.
Another cool post.
Thanks. This looks like another piece of the puzzle.
Of course. I was a combat engineer.
Yeah, forced labor. ;-)
Here is a link about the newest active volcano, the one in Eritria. There is some question as to whether it is from Dubbi, a volcano with some activity in the past 200 years, or from Nabro, with no activity in historical times. It was preceeded by several 5+ earthquakes. This seems to be a really good private volcano site. Perhaps you would want to post this as a separate Catastrophism ping.
Thanks g.
I checked Google today. It is confirmed that it is Nabro, with no known historical eruption. However, at another site I saw something about an 8 km caldera, and superimposed/or nearby? a 5 km caldera, so they had some really severe eruptions in the past. Today the output seems to be diminishing, but also moving toward Saudi air space.
Been doing a little more reading. There’s a historical correspondence of decreased solar activity with increased volcanic activity. Which also may cause more immediate trends toward colder weather (downward temp spikes of a couple years or so).
I think that's been an argument in a thread or two. But then, every contention becomes...contentious.
Agreed, and thanks. For those who see an opportunity for contention, fire away for our learning pleasure. But I wasn’t saying that there’s any direct causal relationship between increased solar and volcanic activity, of course. ...only coinciding occurrences in history.
There is a causal relationship between major eruptions or more eruptions and colder weather, though (sulfur particle reflections).
Oops. Correction. But I wasn’t saying that there’s any direct causal relationship between decreased solar and increased volcanic activity, of course.
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