2015/16, Report no.2: New methane-dark waves on the NEB
Jupiter in 2015/16, Report no.2:
New methane-dark waves on the NEB
As the NEB expansion event develops, images in methane absorption bands are showing a large-scale wave pattern on and around the expanded sector – as suggested in the previous bulletin. This is an important phenomenon that has not been observed since 2000-01, except for a limited sector during the NEB expansion in 2009.
The present wave pattern is best seen in images at 2.16 microns from Dr Glenn Orton at the NASA Infrared Telescope Pacility (IRTF) on Mauna Kea, as posted on the JunoCam web pages [Ref.1]. But it can also be seen, partially, in images at 0.89 microns from several amateur observers – especially Phil Miles in Queensland who is getting good results thanks to a 20-inch telescope. Attached are compilations of images in these and other wavebands.
The wave pattern is obvious in the 2.16 micron images, all across the sector where the NEB has broadened, and some way east and west as well; but is absent on the other side of the planet. The spacing of the patches is not uniform, and pairs of images taken one week apart show some changes. Near the f. end of the expanded sector (where there are visible waves coincident with the methane-dark waves), one of the methane-dark patches moved rapidly (Nov.22-29). Near the p. end of the expanded sector (now p. white spot Z), two new methane-dark patches developed (Nov.21-28), and a new visibly-dark anticyclonic spot also developed nearby. All this suggests that the methane pattern is associated with dynamic disturbance as the expansion propagates.
The well-observed wave pattern in 2000-01 was important because it showed that thermal waves (observed by Cassini, and previously from infrared observatories) were the same as the
the methane-dark waves (observed by Tomio Akutsu, Dr Glenn Orton, and Cassini) and were linked to visible circulation patterns flanking the NEBn retrograde jet (observed by amateurs) [Ref.2]. Over the coming months, we have the opportunity to find out whether the present wave pattern behaves in the same way, using images in the methane bands to track the waves, and in visible light to track the underlying disturbances.
I suspect that one reason the waves are only weakly visible in images at 0.89 microns is that all observers so far are using filters with 18 nm width, whereas when Akutsu recorded them well in 2000, his filter had 6.5 nm width. Broader filters view deeper levels than narrower filters, so some contribution from the main cloud-tops may dilute the signal from the overlying haze. If any observers have access to narrower filters, please try them, in spite of the long exposures that they require.
–John Rogers (BAA Jupiter Section Director), 2015 Dec.8.
 NASA: JunoCam:
 Rogers JH, Akutsu T, & Orton GS, JBAA 114 (no.6), 313-330 (2004). ‘Jupiter in 2000/2001: Part II: Infrared and ultraviolet wavelengths: A review of multispectral imaging of the jovian atmosphere’
FIGURES (on separate page – follow link below):
Sets of images, 2015 Nov., at 0.89 microns (Nov.25-Dec.5), at visible wavelengths, at 1.6 and 2.16 microns, and at 5.1 microns. The images at 1.6, 2.16, and 5.1 microns were all taken by Dr Glenn Orton & colleagues with the SpeX instrument at the NASA IRTF, and were posted on the JunoCam web pages [Ref.1], and are reproduced by permission.