IOP: Man-made aurora to help predict space weather

[bystander]

Man-made aurora to help predict space weather
Institute of Physics - 08 June 2010

For more than twenty five years our understanding of terrestrial space weather has been partly based on incorrect assumptions about how nitrogen, the most abundant gas in our atmosphere, reacts when it collides with electrons produced by energetic ultraviolet sunlight and ‘solar wind’.

New research published today, Tuesday 8 June, in IOP Publishing’s Journal of Physics B: Atomic, Molecular and Optical Physics describes how scientists from NASA’s Jet Propulsion Laboratory (JPL) at the California Institute of Technology have fired electrons of differing energies through a cloud of nitrogen gas to measure the ultraviolet light emitted by this collision.

The researchers have found that well-trusted measurements published in a 1985 journal paper by researchers Ajello and Shemansky contain a significant experimental error, putting decades of space weather findings dependent on this work on unstable ground.

The difference between these contemporary findings and the 1985 researchers’ work stems from the 2010 team’s improved ability to create and control the collisions and avoid the analytical pitfalls that plagued the 1985 findings.

The new results from the team at JPL suggest that the intensity of a broad band of ultraviolet light emitted from the collision changes significantly less with bombarding electron energies than previously thought.

As the ultraviolet light within the so called ‘Lyman-Birge-Hopfield’ (LBH) band is used by the likes of NASA and the European Space Agency to better understand the physical and chemical processes occurring in our upper atmosphere and in near-Earth space, the results will give some immediate cause to reflect.

Lyman–Birge–Hopfield emissions from electron-impact excited N₂

• Journal of Physics B: Atomic, Molecular and Optical Physics, Volume 43,
  Number 13, (08 June 2010), DOI: 10.1088/0953-4075/43/13/135201

[bystander]

New Experiments Rattle Space Weather Research
Science NOW - 09 June 2010

Scientists trying to confirm a long-standing model of atmospheric physics have inadvertently shaken one of the foundations of the field. New tests show that the model, used to interpret energy emissions in Earth's upper atmosphere, is seriously flawed. The findings should help researchers build a better picture of how our planet interacts with solar radiation and the particle stream called the solar wind, and they may give a similar boost to studies of the atmosphere on Saturn's big moon Titan.

For decades, scientists have been studying what happens when Earth's magnetic field grabs high-energy particles from the sun and steers them toward the North and South poles. En route, some of them strike nitrogen molecules in the upper atmosphere, freeing electrons and generating both ultraviolet and visible light. Understanding this process is necessary to unravel what causes auroras (the Northern and Southern Lights), how much solar energy hits Earth's upper atmosphere at any given time, and how the solar wind creates electromagnetic interference with telecommunications.

Researchers can't measure directly how much solar energy is hitting the atmosphere. Instead, they calculate it by measuring how much light the excited nitrogen molecules give off—a bit like determining the horsepower of a car engine by measuring the gases spewing from its exhaust. (Earth's upper atmosphere is about 80% nitrogen.) For 25 years, their estimates have relied heavily on a set of data generated partly by electron-collision experiments and mostly by mathematical models. The data are based on particular wavelengths of ultraviolet light, called the Lyman-Birge-Hopfield (LBH) band, generated when freed electrons strike atmospheric nitrogen. The numbers are critical for building models of Earth's upper atmosphere. But there was a problem: The baseline LBH data in the model covered less than 20% of the observable LBH-band emissions.

So 2 years ago, a team at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, set out to expand the data set. The researchers began by duplicating the original experiments. They fired a beam of electrons at nitrogen gas in a chamber—essentially creating a miniature aurora in the lab—and then analyzed the resulting LBH emissions. The results startled them. The team reported online yesterday in the Journal of Physics B: Atomic, Molecular and Optical Physics that the new data differ from the original by almost a factor of 2. Roughly speaking, it means that estimates of incoming solar energy based on the 1985 model have been way off.