Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Solar Cycle Driven by More than Sunspots; Sun Also Bombards Earth with High-Speed Streams of Wind

21.09.2009
Challenging conventional wisdom, new research finds that the number of sunspots provides an incomplete measure of changes in the Sun's impact on Earth over the course of the 11-year solar cycle.

The study, led by scientists at the National Center for Atmospheric Research (NCAR) and the University of Michigan, finds that Earth was bombarded last year with high levels of solar energy at a time when the Sun was in an unusually quiet phase and sunspots had virtually disappeared.

"The Sun continues to surprise us," says lead author Sarah Gibson of NCAR's High Altitude Observatory. "The solar wind can hit Earth like a fire hose even when there are virtually no sunspots."

The study, also written by scientists at NOAA and NASA, is being published today in the Journal of Geophysical Research. It was funded by NASA and by the National Science Foundation, NCAR's sponsor.

Scientists for centuries have used sunspots, which are areas of concentrated magnetic fields that appear as dark patches on the solar surface, to determine the approximately 11-year solar cycle. At solar maximum, the number of sunspots peaks. During this time, intense solar flares occur daily and geomagnetic storms frequently buffet Earth, knocking out satellites and disrupting communications networks.

Gibson and her colleagues focused instead on another process by which the Sun discharges energy. The team analyzed high-speed streams within the solar wind that carry turbulent magnetic fields out into the solar system.

When those streams blow by Earth, they intensify the energy of the planet's outer radiation belt. This can create serious hazards for weather, navigation, and communications satellites that travel at high altitudes within the outer radiation belts, while also threatening astronauts in the International Space Station. Auroral storms light up the night sky repeatedly at high latitudes as the streams move past, driving mega-ampere electrical currents about 75 miles above Earth's surface. All that energy heats and expands the upper atmosphere. This expansion pushes denser air higher, slowing down satellites and causing them to drop to lower altitudes.

Scientists previously thought that the streams largely disappeared as the solar cycle approached minimum. But when the study team compared measurements within the current solar minimum interval, taken in 2008, with measurements of the last solar minimum in 1996, they found that Earth in 2008 was continuing to resonate with the effects of the streams. Although the current solar minimum has fewer sunspots than any minimum in 75 years, the Sun's effect on Earth's outer radiation belt, as measured by electron fluxes, was more than three times greater last year than in 1996.

Gibson said that observations this year show that the winds have finally slowed, almost two years after sunspots reached the levels of last cycle's minimum.

The authors note that more research is needed to understand the impacts of these high-speed streams on the planet. The study raises questions about how the streams might have affected Earth in the past when the Sun went through extended periods of low sunspot activity, such as a period known as the Maunder minimum that lasted from about 1645 to 1715.

"The fact that Earth can continue to ring with solar energy has implications for satellites and sensitive technological systems," Gibson says. "This will keep scientists busy bringing all the pieces together."

Buffeting Earth with streams of energy

For the new study, the scientists analyzed information gathered from an array of space- and ground-based instruments during two international scientific projects: the Whole Sun Month in the late summer of 1996 and the Whole Heliosphere Interval in the early spring of 2008. The solar cycle was at a minimal stage during both the study periods, with few sunspots in 1996 and even fewer in 2008.

The team found that strong, long, and recurring high-speed streams of charged particles buffeted Earth in 2008. In contrast, Earth encountered weaker and more sporadic streams in 1996. As a result, the planet was more affected by the Sun in 2008 than in 1996, as measured by such variables as the strength of electron fluxes in the outer radiation belt, the velocity of the solar wind in the vicinity of Earth, and the periodic behavior of auroras (the Northern and Southern Lights) as they responded to repeated high-speed streams.

The prevalence of high-speed streams during this solar minimum appears to be related to the current structure of the Sun. As sunspots became less common over the last few years, large coronal holes lingered in the surface of the Sun near its equator. The high-speed streams that blow out of those holes engulfed Earth during 55 percent of the study period in 2008, compared to 31 percent of the study period in 1996. A single stream of charged particles can last for as long as 7 to 10 days. At their peak, the accumulated impact of the streams during one year can inject as much energy into Earth's environment as massive eruptions from the Sun's surface can during a year at the peak of a solar cycle, says co-author Janet Kozyra of the University of Michigan.

The streams strike Earth periodically, spraying out in full force like water from a fire hose as the Sun revolves. When the magnetic fields in the solar winds point in a direction opposite to the magnetic lines in Earth's magnetosphere, they have their strongest effect. The strength and speed of the magnetic fields in the high-speed streams can also affect Earth's response.

The authors speculate that the high number of low-latitude coronal holes during this solar minimum may be related to a weakness in the Sun's overall magnetic field. The Sun in 2008 had smaller polar coronal holes than in 1996, but high-speed streams that escape from the Sun's poles do not travel in the direction of Earth.

"The Sun-Earth interaction is complex, and we haven't yet discovered all the consequences for the Earth's environment of the unusual solar winds this cycle," Kozyra says. "The intensity of magnetic activity at Earth in this extremely quiet solar minimum surprised us all. The new observations from last year are changing our understanding of how solar quiet intervals affect the Earth and how and why this might change from cycle to cycle."

The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under sponsorship by the National Science Foundation. Any opinions, findings and conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Scientific contacts:

Sarah Gibson, NCAR Scientist
303-497-1587
sgibson@ucar.edu
Janet Kozyra, University of Michigan Professor
734-647-3550
jukozyra@umich.edu
Note to journalists:
Correction - September 18, 2009 | The headline for this release was changed from "Solar Cycle Driven by More than Sunspots" to clarify that sunspots are not the cause of the solar cycle but rather one measure of its strength.

To request a copy of the paper, send your name, organization, and phone number to David Hosansky at hosansky@ucar.edu, Peter Weiss at pweiss@agu.org, or Maria-Jose Vinas at mjvinas@agu.org.

Title:
If the Sun is so quiet, why is the Earth ringing? A comparison of two solar minimum intervals
Authors:
Sarah Gibson, Janet Kozyra, Giuliana de Toma, Barbara Emory, Terry Onsager, and Barbara Thompson
Publication:
Journal of Geophysical Research
On the Web:
Resources for journalists:
http://www.ucar.edu/news/journalists
Read this and past releases or sign up for e-mail delivery:
http://www.ucar.edu/news/releases

David Hosansky | Newswise Science News
Further information:
http://www.ucar.edu
http://www.agu.org

More articles from Earth Sciences:

nachricht Devils Hole: Ancient Traces of Climate History
24.05.2017 | Universität Innsbruck

nachricht Supercomputing helps researchers understand Earth's interior
23.05.2017 | University of Illinois College of Liberal Arts & Sciences

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

Im Focus: Using graphene to create quantum bits

In the race to produce a quantum computer, a number of projects are seeking a way to create quantum bits -- or qubits -- that are stable, meaning they are not much affected by changes in their environment. This normally needs highly nonlinear non-dissipative elements capable of functioning at very low temperatures.

In pursuit of this goal, researchers at EPFL's Laboratory of Photonics and Quantum Measurements LPQM (STI/SB), have investigated a nonlinear graphene-based...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

Physicists discover mechanism behind granular capillary effect

24.05.2017 | Physics and Astronomy

Measured for the first time: Direction of light waves changed by quantum effect

24.05.2017 | Physics and Astronomy

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>