Part 3: The Shock - Arrival of the Solar Storm

The shock waves are as likely to arrive in our daytime and well goner by by nightfall. This is OK for the other half of the world in darkness! Winter time affords more hours of darkness and increases the probability of seeing the aurora. This is why some people think there are seasons for Aurora. It is thought however, the earth's axis alignment to the sun in spring and autumn enhances the aurora.

Hopefully all the signs stack up and my excitement is eventually backed up by Email reports from SPACE WATCH.

Hope and prepare for clear skies

Next task is to check the local weather and likelihood of seeing it even if it occurs at the right time of the day. The forecast charts and satellite imagery provided Metvuw.com by James McGregor of Victoria University of Wellington are excellent. See my other resources here on my Storm Chase page.

Visit the Japanese Meteorological Agency (JMA) Satellite Imagery page for updates every hour and create animations to see how the weather is flowing.

Current visible and infrared satellite images from MTSAT via NOAA updates 25 minutes past every hour. Click to enlarge.

Another good idea is to use Google Earth with its weather layer tuned on.

Invariably the maritime climate of New Zealand and our coastal position means cloud, and many a potential night is totally ruined. If need be, I can get a better understanding of the cloud cover (and possibility of 'observation holes') from the more finely detailed NOAA images by Landcare Research which update a couple of times daily.

Serious aurora watchers should be prepared to travel to clearer skies. An hour away Inland we have the Mackenzie Basin, a big open space with exceptionally clear skies. I frequently check conditions there on Tekapo Tourism's excellent webcam on Mt John, especially as it can be directed to check the weather in all directions.

It might sound ridiculous but I also use my local TImaru webcam even though it is only 1km away. It has a higher 360 degree vantage point and saves me from going outside to keep an eye on the weather.

Fortunately we have very clear skies on many winter nights. But this also means very frosty nights, and reliance on many layers of fine marino wool clothing.

Pack the Picnic

If prospects still look good I can set about making myself available in 20-70 hours time, packing up a picnic for an all night vigil and getting some extra sleep. Also I trigger off alert messages to local friends. Making an intuitive guess on the estimated time of arrival, I log my computer onto data from another spacecraft and wait for an early warning, as I go about my normal work.

Wait for the shock

Stereo (Solar TErrestrial RElations Observatory) launched in 2006, is the third mission in NASA's Solar Terrestrial Probes program (STP)

Two "Stereo" satellites, one leading the earth on its orbit around the sun and the other lagging, are able to capture side-on views of any CME as it approaches building a 3D concept of what is going on and what might happen. The red data lines below show what they have been detecting over the last few days pin pointing any shocks that might be in progress and their arrival time.

The black data lines are from NASA's Advanced Composition Explorer (ACE) launched in 1997. This sits away out with SOHO. From this far out we can get a detailed 30-60min warning of a solar impact upon earth. - ton's of time pack up the camera gear, fill the thermos, and head out into the country for some dark sky. The notebook computer comes for the ride now too.As well as giving me something productive to do while waiting, (like processing images from the digital camera) it is also fitted with mobile broadband allowing me internet access and more informed decision making in the field.

When I know an event is imminent I prefer to watch a more detailed graph on the National Weather Service's Space Environment Centre website. A full set of Ace RSTW plots available here I am mainly looking for a sharp step up in velocity and and eventual climb to of anything upwards of 800kms/sec. Finally the other major factor is the magnetic orientation of the arriving wave. This is indicated by Bt and Bz. The Bz is the most influential and i am looking for a downward (southward) level of at least -10. The best aurora seem to coincide with sharp upward (northward) Bz trends from -10.

Here was a typical set of trends for a successful Aurora on 7 November 2004. Only problem was I was in the middle of the Canterbury Plain in dense fog, which only allowed a 10 minute glimpse of the rays near Hinds.

Sometimes it will never occur at all the the whole exercise is a fizzler despite the clearest skies.

Predicting potential and results

From the ACE information the Rice Space Institute makes predictions on the solar wind conditions, which I use to check my expectations against.

Boyle Index (Asymptotic Polar Cap Potential)

Polar Cap potential and predicted Geomagnetic Activity Index (Kp)

This Wing Kp model is provided by the U.S. Air Force Weather Agency and the graphic shows the energy (Kp) output over the past 6 hours with a prediction for it in 1-4 hours timetime. Lead time depending on the speed of the solar wind, is given at the bottom. 24hr and seven day predictions are also available here.

In Canterbury NZ, the aurora should come into view low on the southern horizon, when the prediction rises above 5-6kp being overhead when 8-9kp.

A live 24 hour prediction for the auroral oval is given here by the Alaskan Geophysical Institute. The thin green line indicates from where the aurora may be seen low on the horizon. It would be overhead if the main band lies over your location. New Zealand comes into view on the right.