the White-Cloud of Alba


On the White-Cloud Activity of Alba Observed at the End of January 1995 at 051Ls

 


From CMO#179 ( 25 September 1996 )
-- 1994/1995 Mars Note
(13) --


Introduction

* The present Note deals with the phenomenon over Alba which was observed at the end of January 1995 from Japan: The white cloud at Alba was dull on 25 Jan , but was observed to burst from 26 and 27 Jan (at 051Ls) to be seen even by a 15cm reflector. On 26 January 1995 at 15:30GMT when ω=140W, Masami MURAKAMI (Mk) at Fujisawa first detected by use of a 15cm spec a white spot near Alba (when 051Ls, φ=20N, δ=13.3", ι=14). He confirmed the presence by himself on the following 27 Jan at ω=141W and 151W and also on 28 Jan from ω=110W etc (cf the news flash in p1555 of CMO #155). At the same time Tohru IWASAKI (Iw) independently pursued the phenomenon on 27 and 28 Jan and so on every 40 minutes. On the other hand, Yukio MORITA (Mo) fortunately took several pictures of the surface through filters from 27 Jan onwards, and in the present analysis his set of work plays an important role. Unfortunately the weather at Fukui was dismal those days, and though telephoned from timely from Mk, it was impossible to get the sight of Alba until 31 Jan, and hence it is rather hard or inappropriate for us to describe the phenomenon, but we try to follow the activity mostly depending on the work by Mk, Iw, Mo and others.


* The region Alba was observable from Japan up until 6 February and then it went to Europe and to the US: We are reported of the cloud activity of Alba from GROSS in Germany and from PARKER, ROBINSON and MELILLO from the US. And we of course have a data from the HST on 24 Feb.

*At the beginning of March we were again able to see the region under good seeing and the white cloud over Alba was also seen but (by comparison) looked weaker than the last time (see below).

* As everybody feels it is not easy to compare the brightness of a region in a long range of period: Even the photos and CCD images, and even other spectroscopic means, are not so stable from observers to observers, and seeing is another difficult factor. The present work is not therefore easy to be confirmed, but we tried to do as follows basically comparing carefully the series of photo-work by MORITA and reading the observing notes of the regular visual observations of MURAKAMI and IWASAKI (Their work are coded by Mo, Mk, Iw respectively). Otherwise Aa, Is, Mn and Mt are those of Hideto ASADA, Tsutomu ISHIBASHI, M MINAMI and Naoya MATSUMOTO respectively.

 

Observations of Alba in Jan/Feb in Japan

* On 25 Jan(050Ls), Iw observed Mars at
ω=134W(Iw-092D),
ω=144W(Iw-093D) etc, but Alba was not seen. Seeing was poor, but Tharsis was evident near the evening limb.

* On 26 Jan(051Ls), Mk observed, but he did not notice Alba at
ω=130W(Mk-130D) because seeing was poor (1/5), while at
ω=140W(Mk-131D) seeing somewhat improved and Alba was detected whitish bright first. Unfortunately seeing was thereafter broken down, and he was not able to catch Alba at
ω=150W(Mk-132D) and at
ω=159W(Mk-133D) as shown in the Figure.

* On 27 Jan(051Ls), Iw began to observe earlier, and at
ω=107W(Iw-094D), he detected a bright zone from Alba to Tempe: seeing being 5-6 /10, and at
ω=116W(Iw-095D), he observed that Alba was bright in a grey-whitish tint. And then at
ω=136W(Iw-097D), Iw saw the area clearly light. The Mk's first observation came at
ω=141W(Mk-134D) where Alba was definite and light zonally to Tempe. On the other hand Mt took a photo by a 44cm spec at
ω=143W(Mt-011C), but Alba is indefinite. At
ω=146W(Iw-098D), Iw saw a misty Alba in the evening, while MORITA's TP photos show definitely the bright Alba (without filter) at
ω=148W(Mo-112B): Mo confirmed the activity by his naked eye 5 minutes before at 16:15GMT. Mk's observation at
ω=151W(Mk-135D) clearly depicted Alba in the evening, separated from Tharsis. Iw saw a half-circled Alba at the evening limb at
ω=156W(Iw-099D). And then came the photos by Mo: At
ω=158W(Mo-113B), Alba was very definite (more evident in B than in R light, paired with Tharsis). At
ω=160W(Mk-136D), Mk saw a sinking Alba, but still at
ω=163W(Aa001C), Alba faintly shot (by Provia100).
* The last observation on 27 Jan was done by Mo at 3:56JST(Mo-115B) when ω=186W.

Figure: A series of the observations of the burst of Alba by Masami MURAKAMI from 26 Jan 1995

* On 28 Jan(052Ls) at
ω=108W(Iw-101D), seeing being very poor (1/10), Iw could not so vividly see Alba, while Mk met rather good seeing (4-3/ 5) at
ω=110W(Mk-138D) and saw Alba clearly (weaker than Tharsis?). Iw observed Alba to be grey-whitish at
ω=117W(Iw-102D). The following observation at
ω=120W(Mk-139D) by Mk was cited at p1560 of #155. At
ω=137W(Iw-104D), Iw saw Alba somewhat dimmer, but Mo's photo at
ω=162W(Mo-116B), Alba is quite evident near the evening limb (without filter).

* On 29 Jan(052Ls), seeing was poor for both Iw and Mk and at
ω=109W(Iw-106D) and at
ω=111W(Mk-142D) both didn't see Alba, but at
ω=129W(Mo-117B) Alba is definite both in B and without filter (Tharsis is thicker), and furthermore, at
ω=138W(Mo-118B), Alba is weaker than Tharsis in B, but still definitely light.


* On 30 Jan(053Ls) seeing recovered both for Iw and Mk and at
ω=100W(Iw-111D), the centre of Alba lighter? And at
ω=110W(Iw-112D) Alba looked weaker, while at
ω=120W(Mk-145D), Alba at meridian was certified, whitish, its west being light. On Mo's photos at
ω=120W(Mo-120B), Alba is evident through non-filter and detected also in B (weaker than Tharsis). At
ω=129W(Mk-146D), Mk felt difficult but saw Alba (Temperature: -0.5). At
ω=149W(Mk-148D), Alba still seen at the evening limb.

* On 31 Jan(053Ls), we at Fukui first saw the area and detected the phenomenon: First Iw observed at
ω=101W(Iw-116D) when Alba shows a bright- ness if seeing improves. Mk at
ω=120W(Mk-151D) did not detect Alba in particular because of bad seeing. On the other hand, at
ω=120W(Mn-370D) Mn observed that Tempe was less whitish than Alba which was also not so definite but bounded by a dark curve, and at
ω=135W(Mn-371D) Mn could not separate Alba from Tempe: less whitish than Tharsis.

* On 1 Feb(053Ls), Alba was on the morning side, and to see its evening state, we had to wait until dawn: Mk observed at
ω=100W(Mk-154D) that Alba light, and Mt's colour photo also shows Alba near the CM at
ω=100W(Mt-018C). Iw saw the centre of Alba light in a grey-whitish tinge at
ω=102W(Iw-123D), while Mk observed that at
ω=109W(Mk-155D) Alba zonally light, and at
ω=119W(MK-156D) Alba seen in the evening though not easy. Succeedingly at
ω=125W(Mo-122B), Mo detected it as an isolated light spot (without filter. conspicuous in G&B: Through B it looks as same as Tharsis).

* On 2 Feb(054Ls), Iw saw a dull Alba at
ω=093W(Iw-129D), while Aa's colour photo shows a white spot at
ω=104W(Aa-002C). Mn then saw the white cloud at Alba, the westside being bounded by a dark curve at
ω=130W(Mn-378D) which was made at 18:40GMT.

* On 3 Feb(054Ls), Mk watched three times (see the Figure), Alba was passing away from the oriental area (Tempe was seen until 6 Feb): On 3 Feb, Mk observed that Alba was connected with Tempe at
ω=104W(Mk-158D), while Mn saw a core inside Alba Patera at
ω=131W(Mn-389D). At 20:40GMT (5:40JST) the surface read ω=150W the day.

 

Discussion

* The white cloud at Alba stayed as usual at this season, but by an inspection of the series of TP photos taken by MORITA(Mo) we can safely state that a burst of the white cloud at Alba occurred around on 26 and 27 January 1995 as was observed by MURAKAMI(Mk) and IWASAKI(Iw). The scale was not so usual since it was checked by a 15cm spec (and first found by this 15cm by Mk). The long-staying white cloud may possibly undulate in its activity from time to time, while it is usually difficult to discover such a small amount of difference. Therefore we should say the occurrence just picked out must be quite an unusual one. The bursted white cloud did not so rapidly recess this time but stayed long as still observed in February. We furthermore add that the cloud was observed to be rather evident in the afternoon, and hence it followed the pattern of the usual cloud activity.

*It should be remarked in this respect that the white cloud at Alba is never to be claimed to have started from 26 Jan(051Ls). For example the CCD image by Don PARKER on 17 Jan(047Ls) at ω=107W, Alba was already whitish (see p1673).

*The burst phenomenon was also observed in 1963 near the same season, and hence this phenomenon must be quite seasonal.

 

Overseas Observations of Alba in Feb

The area of Alba then moved to face toward the western world. As we have received the reports then, the bright patch at Alba was first caught in Europe by Horst GROSS (HGr) on
9 Feb(057Ls) at ω=101W by use of a 25cm Schiefspiegler (cf.#156 p1576).
Further in the US, Donald PARKER (DPk) took the sight by CCD on
17 Feb(060Ls) at ω=133W,at ω=144W and at ω=148W Succeedingly,
Robert L ROBINSON(RRb) drew the zonal area from Alba to Tempe to be light (cf. #158 p1613) on
18 Feb(061Ls) at ω=130W
and Frank MELILLO(FMl) took a nice picture by TP through a blue filter on
18 Feb(061Ls) at ω=139W
where Alba is shown to be largely bright as well as the more limb-side Tharsis (cf. #157 p1587/88 and p1593). These all show that the white cloud at Alba remained through February, and well suggest a possibility that the cloud might have tided in and out repeatedly during the month.


* As is still fresh in our memory, at the end of February three colour photos taken by the HST on 24 Feb were published, and on one of them Alba was clearly shown to be covered by a white cloud in a complexed shape. it is difficult to say the difference of it from the image of the cloud on DPk's CCD images or on FMl's TP photo. As well FMl's Alba cloud.

 

Observations of Alba in March in Japan

* Soon after the HST time, the area came soon into sight from Japan:

* On 4 Mar(067Ls), Iw saw scarcely Alba , under poor seeing, at
ω=123W(Iw-200D), while Mn saw the area followed by a shadowy curved band at
ω=130W(Mn-503D), and observed at
ω=140W(Mn-504D) that Tharsis looked much stronger.

* As to the images on 5 Mar(067Ls), Mo's TP photos give a standard: first Iw observed Tempe light, but Alba weak at
ω=104W(Iw-202D), while Mn saw Tempe and Alba zonally light at
ω=114W(Mn-507D), and at caught Alba to be roundish light at
ω=124W(Mn-508D). Mk also saw a zonal light belt from Alba toward its east at.
ω=132W(Mk-213D). Iw saw equally the light belt under 56/10 at
ω=133W(Iw-205D). The Mn saw Alba weakly, bounded backward by a shadowy contour at
ω=134W(Mn-509D). Mo' photo then came at
ω=148W(Mo-153B) to show that Alba slightly light through G, but weaker than Tharsis (also In B) though his next one at
ω=154W(Mo-154B) still show weakly Alba in B.

* On 6 Mar(068Ls), at
ω=117W(Mn-511D), Mn saw Alba weakly light, southern border shadowy, and at
ω=125W(Iw-210D), Iw saw a light core inside Alba. Mn then at
ω=127W(Mn-512D) saw Alba zonally light. ISHIBASHI (Is) then took an interesting B390 photo at
ω=131W(Is-007B) in which Alba was definitely spot-like (also in Int). Mo's photos at
ω=134W(Mo-156B) show also Alba, while it is weaker than the Alba spot on Mo-108B on 29 Jan. In B, Alba apparently weaker than Tharsis, and as well at
ω=142W(Mo-157B), Alba still seen in the evening, but looks weaker than that Mo-112. Mn simultaneously observed at
ω=142W(Mn-513D) where Alba light but not looked so atmospheric. Mk observed at
ω=156W(Mk-217D) and noted that alba not light near the evening limb.

* On 7 Mar(068Ls), we met good seeing at Fukui (#158 p1610). Iw did no more pay attention to Alba, just at
ω=116W(Iw-215D), he noted that Alba was weak. Mk also commented at
ω=140W(Mk-140D) that it was not so light, while Mn at Fukui clearly saw Alba at
ω=140W(Mn-517D) to be compactly roundish, and at
ω=150W(Mn-518D) to be whitish. Alba was still seen clearly isolated at
ω=160W(Mn-519D), but Tharsis was much more whitish and thicker.

 

Conclusions and Outlook

Each observation in March shows that Alba was still covered locally by a whitish cloud, but the cloud even in the afternoon was thinner than before and apparently weaker than the Tharsis evening cloud. The shape looked roundish through our minor telescopes, but it must possibly be of a complexed form as was witnessed by the HST. The shape also must have been changing from day to day because the Alba area is made of a large flat patera.

* It has been a difficult problem to take account of the situation in early-Feb compared with the results at the end of Jan and also with those in February/March. In this respect, MORITA (Mo)'s continual shots played a decisive role, and by a comparative study of them together with drawings by Mk and Iw we have concluded that there occurred a burst of white-cloud around 26, 27 and 28 Jan perhaps each day in the Martian afternoon.

* The nomenclature Alba (by ANTONIADI) is after its whitish aspect due to the long-standing presence of the whitish cloud. The cloud must be caused by the water component flowed out from the north-polar region, and hence seasonally it must be maximal when the npc rapidly thaws. The water vapour abundant moves southward and may be first trapped by Alba (then by Tharsis ridges and Olympus Mons) mostly at around 050Ls. The water-vapour abundance near the season was once measured by the Viking missions (e.g. cited in CMO #108 p930 and 931), and the result is not contradictory with the present phenomenon. Over-cooled vapour must move to be warmed down to airborne ice at the summit area of the Patera, or usual vapour must be cooled down to ice particles there.

* We thus consider that this kind of burst is seasonal, and hence the same kind phenomenon must have frequently observed in the past. For example, in 1963 the Alba phenomenon was checked in Japan though the observations were not complete, and we also alluded to the possibility that similar phenomenon was recorded at the beginning of this century in Germany. These implies that a systematic study of the past records on the Alba region is needed to renew the problem.

* The upcoming apparition we are to pursue the undulation of the white region from Alba to Tharsis: even after 080Ls the observation must be necessary.

(Mn)


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