Author Topic: Solar StormWatch Resources  (Read 3976 times)


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Solar StormWatch Resources
« on: May 10, 2011, 11:24:07 am »
Want to learn something about the calibrations done to the data before we watch them? Look here.
The two STEREO spacecraft before launch:
Where is STEREO today?
Orbit Simulator for the solar system, Stereo A & B and the Kreutz group(most of the comets we see fall into this group)
STEREO website home
STEREO Artifacts
Stray light, ghosting and exploding planets
Youtube video explaining the Stereo mission.

Comet list (Up to Dec 2010)
Comets first discovered in STEREO images

STEREO SOHO SDO and STEREO again, for monthly movies with varying calibration procedures.



Realtime Data - Plots -


The SOHO Classroom

Why is the behind video flashing brightly?
There is an odd effect on the HI-1 B camera that occasionally it jumps to a different pointing direction.  If you watch the stars drifting across the background you might notice that rather than drifting smoothly across the field of view they will suddenly change position.  This then throws out the removal of the zodical light and gives rise to the flash effect, a failure to properly subtract the f-corona.

Chris Eyles
I just wanted to add to Steve's explanation of the flash effects the reason which we believe accounts for them being much more common on HI-1B than HI-1A. This is because the STEREO B spacecraft is trailing behind the Earth in its orbit around the Sun and since the HI cameras are looking towards the Earth and the region between the Sun and the Earth, this means that they are facing in the direction of travel in the orbit. Consequently, the cameras are much more likely to be "bumped" by dust particles and other debris in interplanetary space, which is what we believe causes the jumps in pointing which Steve refers to - a bit like poking your head out of a car window and facing into a snowstorm! On the other hand, because the A spacecraft is travelling ahead of the Earth, its cameras are looking back, away from the direction of travel and are much less likely to be hit by dust particles. (This is an effect we never expected before launch, otherwise we would have tried to make the camera mountings more rigid - one always gets some surprises when one launches an instrument into space!)

How fast are the videos running?
All the spot movies are 576 frames long and play at 0.1 frames/second.  This is equivalent to 16 days at 40 minutes per frame.  The videos start on the 1st, 9th, 17th and 25th of each month so the overlap is not actually a constant.  This overlap is there so that storms that cross a boundary can still be scaled.
The whats that movies are 252 frames long and again are set to play at 0.1 frames/second. This is then 7 days of data at 40 minutes per frame.  The videos start on the 1st, 8th, 15th, 22nd and 29th of each month, so except for the last there is no overlap.

What's that loop coming out of the edge of the frame?
Chris Davis
We see optical flaring (in the form of a bright loop) when a planet is near the edge of the field of view of the cameras (this can be seen in this movie when a planet exits the frames in both B and A. When there is a bright object near, or just outside the field of view, we also see secondary optical flares that appear as arcs which, as you have noted, do not move with respect to the frame (or at least move slowly).

What are these bright bars/gaps in the image?
Chris Davis
The bright bars are an artefact of data processing. The cameras don't have shutters (they made the instrument too heavy!) and so the cameras just stare into space all the time. When we come to read out an image line-by-line, the top rows are exposed for longer and contain some of the signal from the lines below them. Thus an image gets smeared as it is read out. As we know how long it takes to read out each line, we can compensate for this process and 'unsmear' the images afterwards in software. However, this all goes to pot if there are missing blocks in the image. While we can guess as to what's in these blocks we can't correct for the shutterless smearing as accurately and this leads to the kind of blocky stripes you have seen.

The background is too bright to see anything!  What is that?
Yes, this 'dirty snow' (what a great description!) is indeed the Milky Way. It appears to shimmer like it does because we have to subtract the F-corona (or Zodiacal light) from each image in order to see the solar storms (which are only around 1% of the brightness!). The F corona is sunlight scattered from dust in space and unlike the solar storms, it doesn't change very much from image to image. As the stars and storms move across the field of view, we can characterise the F corona signal by storing the minimum brightness from each pixel over a time interval. This is typically 1 day for the HI1 cameras. This we call the F-corona and subtract it. The time interval we choose is important. Too short and the stars and storms don't move across the frame and so we may subtract them too. Too long and the movement of the spacecraft makes the F-corona appear to move and so it is not subtracted properly. An interval of 1 day is best for removing the F-corona we find but for extended sources like the Milky Way, this can cause a shimmering effect. We can optimise the F-corona subtraction for the Milky Way but as our prime interest is in the solar storms for this project, we have chosen to optimise the images to see these.

Why are some particle strikes huge, and others just one faint line?
The "original" images we labelled as particle strikes were the ones with a huge number of trails across the image [I originally referred to them as Edward Scissorhands images]. These are believed to be where something hits the multi layer insulation on the spacecraft rather than the camera itself.  It seems likely that the single streaks are a near miss rather than an actual impact.  If something were to hit the camera itself then it coukd indeed be damaged, although it is quite deep inside the casing and so has some degree of protection,  There is no way to replace the optics.  Of the cameras that point directly at the sun there are filters at the front of the camera that now have pinholes in them as the result of impacts; these however can be compensated for using processing of the received data,

Why are there more particle strikes visible in STEREO A?
Chris Davis
We see more in the Ahead spacecraft because the HI is facing away from the direction of movement of the spacecraft (the ram direction) and so any impacts on the spacecraft tend to spray debris into the field of view of the HI cameras. On the Behind spacecraft, there are far fewer 'trails' because the camera is on the side of the spacecraft facing the direction of travel. In the Behind HI cameras the dust impacts wobble the whole camera (look at the wobbly stars in the HIB movies).

What's this 'giant doughnut?'
Chris Davis
Regarding this movie, the weird frames appear to be HI images have been merged with those from the sun-pointing STEREO cameras during the onboard processing. We saw this a lot when we were sorting the telemetry in the early stages of the mission (we were trying to squeeze every last drop out of the telemetry and things went a bit odd at times) but this sort of thing only happens very occasionally these days. We try to spot these odd images and remove them before making the movie files but it appears that a few have slipped through the net here. Thanks for pointing it out. Reporting such peculiar images is really useful in maintaining a healthy down-link from the spacecraft.

ChrisDavis, on things that shouldn't be marked in What's That
What we *don't* need tagging (simply because they occur almost all the time and are well-understood) are the vertical lines (bright or otherwise) that are associated with bright objects or stars in the field of view. This is just excess signal that has been allowed to 'bleed' into pixels above and below the bright object rather than saturate the whole image (see my waffle analogy elsewhere in this forum!). Equally, occurrences of the Milky Way are pretty obvious and predictable so we don't really need you to be them (although seeing anything else when the Milky Way is in the in the field of view is certainly a challenge!

ChrisDavis, on Solar Storms
One of the things that really surprised us when we first started receiving data from the Heliospheric Imagers was just how much stuff we could see. No one has ever flown a camera quite like this before and so we're on a huge learning curve too. The stuff you describe as 'smokey' (good description by the way) is probably part of the constant flow of material that is streaming off the Sun all the time (the solar wind).
The solar storms we are interested in are clouds of material that are held together in a coherent bubble by the magnetic field that they are dragging out from the Sun's surface. We can't actually image the magnetic field itself. What the cameras are seeing is sunlight scattered off the hot plasma piling up in front of and contained within the magnetic cloud. That is why these clouds fade as they travel away from the Sun. Firstly, the amount of sunlight reaching them is decreasing and secondly, the bubble is expanding and the plasma is being spread thinner and thinner until the cloud drops below the sensitivity of the cameras.
My advice would be not to let your eye be drawn by the brightest stuff nearer the Sun but watch the outer edge of the same feature as it travels across the field of view and fades. It may not be the brightest part by the time it reaches the middle but this is what we should be measuring. It is very subjective and, as Natasha has already said, this is why we need your help. The more people we have looking at each storm, the more certain we can be about what we are seeing and the more accurate our estimates of speed and direction are.

ChrisDavis, on the difference between Solar Flares and Solar Storms
May I take this opportunity to try to explain the difference between a solar flare and a coronal mass ejection (what we are calling a solar storm)?
A flare is an energetic burst of light (usually in Extreme-Ultraviolet or X-rays) that is emitted from the Sun when particles there are accelerated by magnetic field lines as they twist and contort.
A CME is a huge eruption of material and magnetic fields from the solar atmosphere that is thrown into space, usually accompanied by some reconfiguration of the magnetic field in the region of the Sun's atmosphere from where the eruption occurred.
Because both phenomena are associated with changes in the magnetic field, and the strongest, most twisted magnetic field occur in so-called active regions of the Sun, flares and CMEs can occur together but they are different things and do not necessarily happen at the same time, or at exactly the same place.
Richard Harrison describes the relationship between them as being like earthquakes and volcanoes - two related but very different phenomena that tend to occur at similar locations - in this case around continental plate boundaries on Earth.
The HI cameras image the visible light region of the Sun's spectrum where they detect CMEs travelling through the heliosphere through sunlight scattered off the cloud of material. HI would not be able to see a flare because these occur much closer to the Sun's surface and because our sensors are not capable of detecting xrays or EUV emissions. The Extreme Ultra Violet Imagers (EUVI) on STEREO are designed to do this and you will hopefully soon be able to look for flares and CMEs in these data in the new stormwatch activities :)
Very rarely a flare can be seen in visible light. This was the case for the great flare of 1859 - the so-called Carrington Event because it was observed at visible wavelengths by the UK scientist Richard Carrington. This was the most powerful storm ever recorded and is described in detail by Stuart Clarke in his excellent book The Sun Kings.
« Last Edit: May 27, 2011, 10:05:39 am by Quialiss »