Anticipating bursts of activity (sub-storms) during weaker aurora in Southern New Zealand, especially 6:00pm-12:pm.
(kindly dubbed by the Aurora Australis Facebook friends as the "Cloake Effect")
For years now, in hope, I have watched a stupid blue line wondering when it might snap up suddenly. For minimal aurora, (say less than 5-6KP for mid NZ) this has become my best guide for seeing scores of auroras without having to sit out all night in vane hope. As we are experiencing weaker conditions for aurora, we need to look harder, and to my surprise, there are many brief opportunities to see decent aurora, as a result.
Please keep in mind there are great complications in making predictions and this is a work in progress. I am just trying to pick out a few reliable patterns to improve our chances of seeing a decent show. Aurora can be seen outside these patterns.
GOES satellites
If we think of the earth's magnetic field having a domed head, facing the sun and solar wind, and a long tail, streaming from our night side, away from the sun, GOES 13 & 15 weather satellites circle around with the earth daily, rotating and and out of the head and tail. The tail wags in the solar wind, changing in size, yo-yoing in and out from the earth. At times it is able to flick quick bursts of energy back to earth, powering into the aurora. NOAA give a more technical explanation under their details tab under their graph
Coincidentally GOES15 (the blue line) is in the tail region during early NZ night time measuring it's strength, indicating what it might be doing. GOES13 (red) does the same earlier, in the late afternoon.
By fathoming what the GOES are doing and telling us, we can get a good idea of the status of the aurora. A study of the incoming solar wind driving the tail can help us anticipate what it might do. We get this data from the ACE satellite, which is another story.
Daily cycle
GOES15 is most sensitive in graphing the tail's contribution around 9:00pmNZ, and we will see the blue line moves up and down a lot more than at other times of the day. At 9:00am GOES15 is in the head where the Earth's magnetic field is compressed and therefore much stronger. It barely indicates anything from the tail. Any variations are direct effects from the incoming solar wind.
Therefore, we need to ignore the daily wave pattern (the effect of the satellites circling around) and rather study the movements more by the hour.
See here for the GOES Magnetometer graph
Green aurora arc
Southern glow is most likely when readings are much lower than average. The green arc is likely to approach (rise and grow wider) at bottom of major downswings < 50nt.
Red aurora rays
I find the formation of red rays coincide with many of the upswings but to differing degree. The lower the upswing series starts (eg <30 nT) the greater the effect. Subsequent cycles may also have lesser or greater effect.
During minor events, rays usually appear in short bursts (5-15+ mins) during sharp upswings, far longer (eg 30-60+ mins) if the upswing increases in drawn-out steps, especially when the blue line starts to level off at peak. They can continue for hours if the line levels off with small rises and falls.
Predictions
Ha! but when, how fast, and how much at a time????. I have seen rays appear before, during, and at the end of a major upswings (or small series), and I think they are most likely stronger towards, and over the top of the swing especially if the solar wind settles down and eases back.
The trick is anticipating what this blue line might do. Obviously the more faster and lower it goes, the more and quicker it might go back up - at some stage, but not always, as I have seen it linger low for many hours. These trends can be influenced by incoming solar wind fluctuations and I am now studying what these might be, with some early success, observing how its magnetic (Bz), speed and density trends may trigger the rays. Recent predictions are becoming accurate within the minute.
Brendan Davies in Tasmania, has developed charting of many of the incoming factors that may help us understand the resulting GOES. I am interested in studying here: aurora.brendandaveyphotography.com.
Local NZ Data?
I have had a very simple magnetometer made for me and currently testing it. It this proves useful, I plan to graph it's data on this website along with GOES and lead-adjusted ACE data. Hopefully this combination of data will improve our knowledge of pending events. We expect another to be in operation from Dunedin.
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