Energy tracked from solar wind to Earth
In July 2012, scientists took advantage of a rare eight satellite conjunction across the magnetotail to gain more details of the substorm process. Below is a depiction of of the satellites involved:
“One of the unique features of our research field is that microscopic things can sometimes run the whole show,” says David Sibeck, the project scientist for ARTEMIS and THEMIS at NASA’s Goddard Space Flight Center in Greenbelt, Md. “The tiniest causes may have global consequences."Indeed, small events that happen for a millisecond can drive energy flows lasting up to 30 minutes and cover an area 10 times larger than Earth.
To cover such a vast region, multiple spacecraft are needed, situated at different points throughout the magnetosphere, the protective bubble created by the Earth's magnetic field within the flow of the solar wind.
Have a look at the video to get an idea of the scale we're talking about:
While much of these details have been known and modeled for some time, this is the first multi-scale in-situ measurement, and paid off with some new information about the process.
The energy that this represents is equivalent to a 7.1 magnitude earthquake. For more details, check out the paper that was produced from the mission results:
Electromagnetic Energy Conversion at Reconnection Fronts
V. Angelopoulos, A. Runov, X.-Z. Zhou, D. L. Turner, S. A. Kiehas, S.-S. Li, and I. Shinohara
Science 27 September 2013: 341 (6153), 1478-1482. [DOI:10.1126/science.1236992]
Earth’s magnetotail contains magnetic energy derived from the kinetic energy of the solar wind. Conversion of that energy back to particle energy ultimately powers Earth’s auroras, heats the magnetospheric plasma, and energizes the Van Allen radiation belts. Where and how such electromagnetic energy conversion occurs has been unclear. Using a conjunction between eight spacecraft, we show that this conversion takes place within fronts of recently reconnected magnetic flux, predominantly at 1- to 10-electron inertial length scale, intense electrical current sheets (tens to hundreds of nanoamperes per square meter). Launched continually during intervals of geomagnetic activity, these reconnection outflow flux fronts convert ~10 to 100 gigawatts per square Earth radius of power, consistent with local magnetic flux transport, and a few times 1015 joules of magnetic energy, consistent with global magnetotail flux reduction.
Late next year, NASA is scheduled to launch the Magnetospheric Multiscale (MMS) mission which will add one more important elelment of the reconnection process - getting a simultaneous measurement of the front side reconnection that preceeds the process shown above.
More information can be found at this NASA page: Several NASA Spacecraft Track Energy Through Space