Featured Research

from universities, journals, and other organizations

Spring Is Aurora Season

Date:
March 10, 2008
Source:
NASA/Goddard Space Flight Center
Summary:
What are the signs of spring? They are as familiar as a blooming daffodil, a songbird at dawn, a surprising shaft of warmth from the afternoon sun. And, oh yes, don't forget the aurora borealis. Spring is aurora season. For reasons not fully understood by scientists, the weeks around the vernal equinox are prone to Northern Lights. Canadians walking their dogs after dinner, Scandinavians popping out to the sauna, Alaskan Huskies on the Iditarod trail -- all they have to do is look up and behold, green curtains of light dancing across the night sky. Spring has arrived! This is a bit of a puzzle. Auroras are caused by solar activity, but the sun doesn't know what season it is on Earth. So how could one season yield more auroras than another?

This photograph of an aurora was taken in Alaska.
Credit: Jan Curtis of the Geophysical Institute at the University of Alaska

What are the signs of spring? They are as familiar as a blooming daffodil, a songbird at dawn, a surprising shaft of warmth from the afternoon sun. And, oh yes, don’t forget the aurora borealis. Spring is aurora season. For reasons not fully understood by scientists, the weeks around the vernal equinox are prone to Northern Lights. Canadians walking their dogs after dinner, Scandinavians popping out to the sauna, Alaskan Huskies on the Iditarod trail -- all they have to do is look up and behold, green curtains of light dancing across the night sky. Spring has arrived!

This is a bit of a puzzle. Auroras are caused by solar activity, but the sun doesn’t know what season it is on Earth. So how could one season yield more auroras than another?

“There’s a great deal we don’t understand about auroras,” says UCLA space physicist Vassilis Angelopoulos. For instance, “Auroras sometimes erupt with little warning and surprising intensity. We call these events ‘sub-storms,' and they are a big mystery.” What triggers the eruptions? Where is sub-storm energy stored? (It has to gather somewhere waiting to power the outburst.)

And, of course, why springtime?

To answer these questions and others, NASA has deployed a fleet of five spacecraft named THEMIS (short for “Time History of Events and Macroscale Interactions during Substorms”) specially instrumented to study auroras. Angelopoulos is the mission’s principal investigator.

Launched in February 2007, THEMIS has already observed one geomagnetic storm with a total energy of five hundred thousand billion (5 x 10^14) Joules. “That's approximately equivalent to the energy of a magnitude 5.5 earthquake,” says Angelopoulos. “This storm moved twice as fast as anyone thought possible,” crossing an entire polar time zone in 60 seconds flat!

THEMIS may have found the storm’s power supply: "The satellites have detected magnetic ‘ropes’ connecting Earth's upper atmosphere directly to the sun," says Dave Sibeck, project scientist for the mission at the Goddard Space Flight Center. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras." Sibeck likens them to ropes because the magnetic fields in question are organized much like the twisted hemp of a mariner’s rope. Solar wind particles flow along the ropes in whirligig trajectories leading from the sun to Earth.

It turns out that magnetic connections between the sun and Earth are favored in springtime. It’s a matter of geometry: As Earth goes around in its orbit, Earth’s magnetic poles wobble back and forth. (The poles don’t really wobble, but the combination of Earth’s 23-degree polar tilt plus orbital motion makes the poles seem wobble from the solar point of view.) Around the time of the equinox, Earth’s magnetic field is best oriented for “connecting-up” with the sun, opening the door for solar wind energy to flow in and spark Northern Lights.

But wait, there are two equinoxes, spring and fall, with similar magnetic geometry. Indeed, autumn is aurora season, too. Geomagnetic disturbances are almost twice as likely in spring-fall versus winter-summer, according to historical records.

THEMIS is just getting started. The five spacecraft are on a two-year mission to explore Earth’s magnetic field and they are only now settling into their optimum science orbits. “With five satellites, we can map the complex ebb and flow of energy during geomagnetic storms better than any single satellite ever could,” points out Angelopolous. “There’s no telling what we might learn.”


Story Source:

The above story is based on materials provided by NASA/Goddard Space Flight Center. Note: Materials may be edited for content and length.


Cite This Page:

NASA/Goddard Space Flight Center. "Spring Is Aurora Season." ScienceDaily. ScienceDaily, 10 March 2008. <www.sciencedaily.com/releases/2008/03/080306161746.htm>.
NASA/Goddard Space Flight Center. (2008, March 10). Spring Is Aurora Season. ScienceDaily. Retrieved October 1, 2014 from www.sciencedaily.com/releases/2008/03/080306161746.htm
NASA/Goddard Space Flight Center. "Spring Is Aurora Season." ScienceDaily. www.sciencedaily.com/releases/2008/03/080306161746.htm (accessed October 1, 2014).

Share This



More Earth & Climate News

Wednesday, October 1, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Raw: 12 More Bodies Found on Japan Volcano

Raw: 12 More Bodies Found on Japan Volcano

AP (Oct. 1, 2014) — A dozen more bodies were found Wednesday as Japanese rescuers resumed efforts to find survivors and retrieve bodies of those trapped by Mount Ontake's eruption. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Cultural Learning In Wild Chimps Observed For The First Time

Cultural Learning In Wild Chimps Observed For The First Time

Newsy (Oct. 1, 2014) — Cultural transmission — the passing of knowledge from one animal to another — has been caught on camera with chimps teaching other chimps. Video provided by Newsy
Powered by NewsLook.com
Raw: Trapped Scientist Rescued from Cave in Peru

Raw: Trapped Scientist Rescued from Cave in Peru

AP (Oct. 1, 2014) — A Spanish scientist, who spent 12 days trapped about 1300 feet underground in a cave in Peru's remote Amazon region, was rescued on Tuesday. (Oct. 1) Video provided by AP
Powered by NewsLook.com
Media, Industry Groups React To Calif. Plastic Bag Ban

Media, Industry Groups React To Calif. Plastic Bag Ban

Newsy (Sep. 30, 2014) — California is the first state in the country to ban single-use plastic bags in grocery, liquor and convenience stores. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins