An amazing triple jet

Science nugget: July 11, 1998

Phenomenon

The eagle-eyed Sam Freeland has spotted (again) one of the most remarkable solar phenomena Yohkoh SXT has seen. It consists of three simultaneous and extremely similar X-ray jets. As you will see in Sam's movie
 
 
 

The movie shows two frames of the standard SXT movie, which reveal that at about 12:57 UT on July 7, three curved jets appeared. The lightcurves peak simultaneously within the sampling, a few minutes. Jet "A" would be the one at (S21,E45); "B" at (N12,E31), and "C" at about (N17,W13) in the leading part of NOAA AR 8264, which had been producing many jets. The full-Sun image shows the geometry. Please ignore the vertical spike extending N from jet source "C", because this is a saturation artifact.

The jets are different

Yes, these jets are simultaneous; yes, they are curved in curiously similar and symmetrical ways; yes, they have about the same lengths, but... one of them seems to have excited a long-lived loop:
 
 
 

These are sequential differences of three images, as noted, and the second difference shows the jets dark (because they've faded) but jet "B" shows a bright and fuzzy aftermath, linking the jet bright point to an active region. There is no obvious remnant from the other two jets.

How probable is this?

Well-developed jets of this quality do not happen too often. If we guess one per week, and claim that the simultaneity is within five minutes, there would be a probability of about .0004 for two such events to occur together. Thus in seven years (350 weeks) of Yohkoh data, we actually would have a fairly high probability - 15% - of seeing a pair of events. But the probability drops to 6 x 10^(-5) for three at once. The probability is a lot smaller for such a beautiful match in properties, of course. Of course this is a posteriori and one will never know until more examples are found, but it seems just too extraordinary to be a coincidence.

What does it all mean?

It seems, on the basis of this one observation, that it would be highly unlikely for emerging flux to arrive simultaneously at positions so far removed. The limit imposed on the exciter (trigger) speed would be >1000 km/s for a five-minute time difference. This could only be coronal in origin, not sub-photospheric. This seems to rule out one of the most popular jet models. But what bizarre MHD effect in the global corona could suddenly make up its mind to pluck three beautiful jets out of the photosphere at once? And another question - how do the well-defined curvatures of the jet structures fit into the quadrupolar structure of the global corona so well defined by the late lamented LASCO?

H. Hudson (hudson@isass0.solar.isas.ac.jp)