> From jhr11@hermes.cam.ac.uk Thu Feb 12 05:25 MST 2004 Date: Thu, 12 Feb 2004 12:24:11 +0000 (GMT) From: "J.H. Rogers" X-X-Sender: jhr11@orange.csi.cam.ac.uk Subject: Re: Jupiter EZ: UV-IR mismatch Dear Mr. Akutsu (& others), Indeed, Voyager images shed light on the UV mismatch puzzle in the EZ(N). Attached is a set of Voyager 1 images from 1979 Jan.26 (a randomly selected date, with a complete rotation of the planet), both in UV and in visible light. Active plumes (marked P) indeed coincide in UV and visible, and are very bright in UV. However, the more diffuse bright areas are differently distributed in UV; in four cases (marked *), the UV bright area is largely centred further f.than the visibly bright area - just as in Tomio Akutsu's images this year. If both sets of images were at the same resolution, the appearance would be very similar. There is one difference between 1979 and 2004: In 1979, there was intense yellow-orange colour (UV-dark) over EZ(S) and more weakly over parts of EZ(N). In 2004, there is much less colour; however, the EZ(N) is again weakly yellowish (UV-dark) in images, so the role of UV albedo may be the same. It is generally thought that the visibly bright patches are circulation cells that lie between the dark NEBs projections, and that both UV and methane bands view the higher haze layer over the EZ. So as a working hypothesis, I suggest that the effect is due to UV albedo of the haze layer: UV-dark ('yellowish') in the p. (rising?) parts of the circulation cells, but UV-bright ('white') in the f. parts, which may overlie the adjacent festoons. (Perhaps the haze particles become whiter with time at high altitude?) The methane images look different because the haze layer is always bright in methane bands, but it is partly transparent in the near-IR, at least at some times and places, so the cloud-free dark projections can be seen through it. (At least, this year they can!) Any comments? Best wishes, John _________________________________ John H. Rogers, Ph.D. Jupiter Section Director, British Astronomical Association. > From jhr11@hermes.cam.ac.uk Thu Feb 12 15:26 MST 2004 Date: Thu, 12 Feb 2004 22:25:28 +0000 (GMT) From: "J.H. Rogers" Subject: Re: Jupiter EZ: UV-IR mismatch MIME-Version: 1.0 Hi Antonio, Many thanks for your comments. Replies: 1) In that Voyager 1 sequence, the blue images look quite like the green and orange images in EZ(N). Voyager's blue filter was not very 'deep', and the violet filter was not used in that particular sequence; I will look for a good Voyager 2 sequence. On Tomio Akutsu's images, the blue channel (from RGB) looks intermediate between UV and longer wavelengths. I suspect that the appearance in blue may be variable, as 'yellowish/reddish' colour on Jupiter consists of absorption that is always present to some extent in UV but spreads to a variable extent thru violet and blue. 2) Looking at Akutsu's images over the past 4 apparitions, the yellowish colour and UV darkness in EZ(N) may be slightly stronger this apparition than last apparition: as strong as in 2001/02. This contrasts with 2000/01 when the EZ was white and not UV-dark (although Akutsu then used a U-360 filter, whereas he used a 340 nm filter in later apparitions). It will be worth looking more carefully for UV-Visible misalignments in past apparitions. I agree, it is possible that major misalignments only appear when there is yellowish colour, as in 1979 and in 2004. 3) In UV images, as in deep blue images, the dark (bluish) NEBs projections are of course pale or invisible, so it is not difficult for overlying haze to mask them. 4) See my book p.141-3, inc. notes on Voyager images with the 'white/orange fronts'. Fig.9.12 shows visible and UV images of the EZ during the expansion of one such white (and UV-bright) area which erupted from an active plume, expanding rapidly in the f. direction. That was slightly different from the cases we are considering where there is not an active plume. For more on circulations of those EZ(N) cells, see Galileo analysis of NEBs features, and the Showman & Dowling model [reviewd in JBAA 111, 245]. Good night! John On Thu, 12 Feb 2004, António José Cidadão wrote: > Hi John (all), > > Very interesting and demonstrative indeed! > > There is always something that I "actively" force myself to recall > (frequently a posteriori, I'm affraid) when dealing with UV filters. One > thing is a 225nm UV filter like that of Cassini, beyond the sensitivity > range of our CCD detectors, that produces a "negative" effect of methane > images (e.g. see http://ciclops.lpl.arizona.edu/PR/2000J23/bluvmt.jpg). > Regions with a "cloud-free" upper atmosphere, i.e. methane negative, would > allow intense UV scattering and a bright UV image. The other thing is a > 345nm UV filter like that of Voyager, a wavelenght compatible with our > detectors, and that, as you John have very well put it several times in the > past, mostly gives us a "deep-violet" or "deep-blue" panorama where the > albedo differences already present with those filters are emphasiesed. Thus, > in the first case (225nm filter) we mostly probe the scattering effects of a > cloud-free high atmosphere, while in the second (345nm filter) we may better > detect features/albedo differences (e.g. due to blue absorbing haze or thin > cloud layer in the atmosphere) that may well already be visible in the blue > or violet channels. So..., these questions appear in my mind: > > a) are Voyager's UV images different from the violet or blue images that > probe took? b) is the same effect already present in Tomio's (or other > observer's) B channel images? > > Perhaps the answer is yes to both questions, and then we could immagine a EZ > plume, forming at the NEBs following the IR hot spots and expanding > equatorially and drifting f. to its origin. During this process, it would be > readily visible at its origin with IR filters but not yet at wavelengths > highly sensitive to the blue absorbing haze (e.g. our's and Voyager's UV > filters). More equatorially and f. of its origin, plumes could rise higher > in the atmosphere, getting above the blue absorbing haze (specially if it > is an important issue at the time - yellowish EZ; starting to become bright > with UV filters and continuing to be bright in IR) and, perhaps, > transitorially disturbing the high altitude haze detected by methane filters > (originating a difuse and slightly darker EZ at those places, and not > producing a carbon copy of IR hot spots). This is just rephrasing your > working hypothesis John, and nothing else... > > Best wishes > > Antonio > > p.s. yesterday it was not good to grab a decent UV image due to high > turbulence.... >