NRL Marks Achievements of Extreme-ultraviolet Imaging Spectrometer

4/13/2011 - 42-11r
Contact: Donna McKinney, (202) 767-2541

Scientists from the Naval Research Laboratory's Space Science Division recently celebrated more than four years of scientific operation of the Extreme-ultraviolet Imaging Spectrometer (EIS) on the joint Japanese, UK, US Hinode satellite by hosting a science and technical meeting at George Mason University. At the meeting considerable discussion centered on recent EIS observations of strong solar flares that mark the rapid rise of the new solar cycle.

This meeting brought together key members of the EIS science team from the US, Japan, the United Kingdom, and Norway. Participants at the meeting reviewed important science findings from the mission to date and planned approaches to future operations.

The Hinode spacecraft carrying the EIS was launched in September 2006. The EIS provides measurements of properties of the solar corona such as its temperature, density, and dynamics (flows and turbulence). These measurements are critical for understanding the physical origins of solar activity, which are the basis for space weather and adverse effects on the near-Earth environment.

From the NRL perspective, one of the most important science findings to date is the discovery of outflows of plasma from the edges of solar active regions, explains Dr. George Doschek, the NRL EIS team principal investigator. This plasma may be accelerated at greater altitude in the corona and is a potential source of the slow component of the solar wind. Understanding this component is important for space weather because higher speed solar wind disturbances that could impact Navy space systems must propagate through it to reach the near-Earth environment.

Of more immediate interest at the meeting were presentations describing the first observations of the strong solar flares that mark the rapid rise of the new solar cycle. At last the long solar minimum appears to be over and the EIS team is working to make the observations that satisfy its high-energy science objectives. Solar flares are one of the principal causes of space weather disturbances due to their intense UV and X-ray radiation that alters the properties of the ionosphere. In addition to a practical interest, they are fundamentally important in attempts to see how magnetic energy in the solar atmosphere is stored and released in the form of multimillion degree gas, producing in some cases the vast coronal mass ejections that can be the most catastrophic to Navy assets in space. A key physical process being studied and believed to be the cause of energy release in flares is called magnetic reconnection, which involves restructuring the magnetic field locally in the atmosphere and transferring magnetic energy into intense heating and kinetic energy of the gas trapped by the fields.

Data from a major solar flare that occurred near Sun center on 18 February 2011. Left: An image of gas at a temperature of about 15 million degrees trapped by magnetic fields in the form of a loop. The hottest plasma is near the top of the loop and adjacent to one of the loop footpoints. Right: A plot of a portion of an extreme-ultraviolet spectrum from the EIS instrument that can be read as a remote sensing thermometer. Reading spectra like the one shown allows the temperatures, densities, abundances, and plasma motions to be measured anywhere in the solar atmosphere. In this case, the strong signal at 192.0 Å shows that the temperature in the flare has reached 15 million degrees.

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