Saturday, October 29, 2016
Solar Wind Finally Observed As It Forms
Image at left shows faint solar wind before computer processing, and right after processing. To obtain the latter image a computer algorithm was used to dim the background star field.
Since the solar wind was discovered in the 1960s, solar and space physicists have yearned for way to access it visually as it first forms from the solar corona. The task hasn't been easy because of the low density of the wind and lack of luminance in relation to the corona and background stellar field, making any discriminant observation almost impossible.
Now a team led by Craig DeForest of the Southwest Research Institute in Boulder, CO has published a paper in The Astrophysical Journal describing a novel technique they've used to image it more prominently. The comparison of images above shows the differences in contrast before and after the computer processing.
For those interested the gist of the paper can be found at:
Why was this image separation so important? Well, though space and solar physicists knew the solar wind was physically connected to the corona they weren't sure how the one transitioned into the other. This is important because, as DeForest put it (quoted in Eos: Earth & Space Science News, p. 3, ):
"We're trying to understand, among other things, why the solar wind near the Earth is variable and gusty."
This "gustiness" can affect the trajectory of CMEs, coronal mass ejections which, if they strike Earth, can knock out telecommunications and damage electrical transmission lines. In effect, our ability to accurately forecast solar wind phenomena, i.e. the occurrence of magnetic substorms at Earth's magnetosphere, depends on knowing as much about it as possible.
This algorithmically enhanced imagery helps because the transition between corona and colar wind is extremely difficult to ascertain - given the faintness of the wind - against a background full of stars and interplanetary dust. Reducing the intensity of the latter therefore enhances the imagery of the solar wind. As DeForest summed up the problem: "When scientists looked at previous images seeing the corona fade it was difficult to tell whether it was fading in an absolute sense or just dropping below the stellar background".
What changed? Well, the availability of NASA's Solar Terrestrial Relations Observatory (STEREO) with its ability to render computer processed imagery. STEREO's algorithm -based processing removed all objects of "fixed" brightness, e.g. like that emanating from the dust cloud that fills the inner solar system, as well as the background stars. When these were removed it left only the moving and variable features of the solar wind itself.
Already, one major new finding revealed from the STEREO imagery is that once the solar material travels about a third of the distance from the Sun to the Earth, the magnetic fields weaken enough so that solar wind particles can disperse from the field lines. That means they can then "fan out" analogous to what an Earthly wind might do.
According to NASA, the solar wind transforms from rays to dispersed particles in a manner analogous to the way water from a water gun or hose breaks up into a spray. Closer to the nozzle, the water is one mass, but it disperses into droplets as it moves away. Similarly, the solar plasma is basically visible as one contiguous mass closer to the corona then disperses into particles further away.
Solar and space physicists are excited by this new work because it will help us to predict the arrival and strength of solar outbursts, including Earth bound CMEs.