As if they don't already have enough on their plate, astronauts aboard the International Space Station (ISS) are turning storm chasers. On April 13, a 16-m (52-ft) remote controlled robotic arm installed the 314-kg (692-lb) Space Storm Hunter instrument package on Europe's Columbus laboratory module, where it will make an extensive survey of terrestrial thunderstorms.
Thunderstorms are among nature's most spectacular phenomena. If their dramatic displays of lightning and booming thunder weren't impressive enough, their capacity for dealing death and destruction certainly drives the point home. Yet despite over 250 years of research since Benjamin Franklin's reckless kite experiment in 1752, our understanding of these storms remains incomplete.
According to NASA, the problem is that thunderstorms are very uncooperative beasts that often form in inaccessible regions. Worse, some of the most interesting and important characteristics of the storms occur in the upper atmosphere far beyond the reach of balloons or aircraft, yet too low for most satellites to observe. Many of these also occur in the visible spectrum and it's obvious that ground optical observations in a thunderstorm is an exercise in frustration.
To overcome this, ESA's Space Storm Hunter was recently transported to the ISS aboard an unmanned SpaceX Dragon cargo ship. More prosaically known as the Atmosphere-Space Interactions Monitor (ASIM), it consists of infrared and ultraviolet cameras, photomultiplers, and X-ray and gamma-ray detectors.
The job of the instruments is to look straight from the space station's altitude of 254 mi (408 km), where it will make a two-year study of thunderstorm-generated electrical discharges in the upper atmosphere, from the stratosphere and mesosphere to the ionosphere on the edge of space. These transient luminous events will provide scientists with new insights into the inner workings of thunderstorms and similar phenomena.
Sprites, elves, and giants
At one time, thunderstorms were thought to be gigantic static electricity generators, but for over a century it's been recognized that they are much more complex. In fact, they are natural particle accelerators that can boost electrons to relativistic energies, creating high-energy effects, including X-rays or even gamma-rays as the electrons collide with nitrogen atoms in the upper atmosphere.
For something involving millions of volts of electricity, many of these phenomena have names that seem more appropriate for the nursery than the laboratory. Flashes from electrical breakdowns in the mesosphere are "sprites." Lightning discharges shooting up into the stratosphere are "blue jets." An electromagnetic pulse forming a ring in the lower ionosphere is an "elf." And a "giant" is a large electrical discharge from the top of a thunderstorm to the bottom ionosphere. Added to this are the flashes of X-rays and gamma-rays.
The hope is that the low altitude of the ISS, combined with its complete coverage of tropical and subtropical regions where thunderstorms are most common, will allow the advanced instruments to make an unprecedented study of the upper atmosphere. Gaining a better understanding of thunderstorm physics may also shed light on how they affect weather and climate.
Currently, the Space Storm Hunter is undergoing testing and calibration as each of its sensors are brought on line over the next six weeks. This includes tasks like adjusting the cameras so they bring in neither too little or too much light, as well as checking the communication link from the ground station at White Sands, New Mexico, to the operations and control center in Brussels via transatlantic cable and the Columbus Control Centre outside Munich.
"High-altitude observation allows us to study these events without the obscuring clouds," says principal investigator Torsten Neubert of the National Space institute of the Technical University of Denmark. "With ASIM we will better understand the complex processes of upper-atmospheric lightning, which are also elements of ordinary lightning, although they take on different forms. This understanding can improve technology for detecting ordinary lightning."
The video below shows a thunderstorm as seen from the ISS.
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