98/99 Mars CMO Note (12)

1998/99 Mars CMO Note
- 12 -

from CMO #233

Clouds over Elysium Mons

  The trend of the activity of the orographic cloud over Elysium during the season from 060°Ls to 160°Ls is well known, and already compiled by S A SMITH and B A SMITH in 1972 based on a survey of the past archives of the Blue-light Martian photos as was introduced in CMO #134 (25 June 1993) p1251. The summit of Elysium Mons (longitude=213°W) is followed by a cotton-ball-like orographic cloud on the afternoon side, and it becomes Very Active from around 090°Ls; this is similar to the activity of Olympus Mons but the very-active state of Elysium Mons remains slightly longer up until about 145°Ls. To discuss the orographic cloud we should always discriminate the morning and the afternoon side of the disc by determining the noon line referring to the phase angle.

  The observational results of Elysium in 1997, especially around 090°Ls were reported in 1997 Note (7) filed in CMO #205 p2295. For example, we cited the observations of Elysium by ISHADOH (Id) on 10 Mar 1997 (089°Ls) at LCM=231°W~LCM=302°W.
  Another important observations were made by HIGA (Hg) and others concerning a thick doubled cloud covering the morning Elysium at 107°Ls as reported in CMO #197 p2179.

  In 1997 the planet was closest to the Earth at the season 093°Ls, while in 1999 it was at 132°Ls. This implies we were to observe the later stage of the cloud activity of Elysium.

  We first show the images by Hg made on 26 Feb 1999 (102°Ls, the apparent diameter=10.0") and 3 Mar 1999 (105°Ls): The former was made at LCM=232°W, while Elysium Mons was at about 15:30 LMT. These on 3 Mar 1999 (105°Ls) are the sequels to those shown at the upper low of the file at page 2752 in the preceding issue (#232). Elysium showed up already at LCM=138°W (Elysium Mons at 9:00 LMT) and passed the noon already at LCM=187°W (12:20 LMT). Characteristically Elysium at around this season is considerably bright in the morning accompanied by a diffused large morning cloud.

  The Sun faces to the northern hemisphere of Mars during the seasons from 000°Ls to 180°Ls. We once elucidated an atmospheric global circulation in the northern summer in 1997 Note (2) in CMO #200 p2232:
  In short, the northern polar district is more warmed up than the lower latitude region during the northern summer because the Martian atmosphere is thinner and the polar region has no night, and thus the air mass ascends with water vapour from the north polar cap and flows toward the equatorial band as an upper air-current. This current receives the Coriolis force to be more retained upper near at the middle latitudes. Note that the atmospheric pressure of the air mass near the noon line is lower to induce the morning air to come near the noon line. This air mass at the same time goes to the afternoon side to be cooled down to make water-vapour condensed cloud near the summits of the high mountains, and further descends during the night. The night air with much of water vapour is invited in the morning to blow as a lower westerly to the noon line because of the ascending air mass near the noon line. This gives rise to the morning mist/cloud near the middle latitudes at this season. The mist/cloud disperses however near the noon line, and again we see the orographic cloud in the afternoon.
  The water vapour is abundant on the northern hemisphere from 080°Ls to 150°Ls, and its peak occurs near at the season 120°Ls (cf the results made by the Vikings presented in CMO #108 p0931). So we may say we can observe evidently before and after 120°Ls typical cloudy phenomena different in the morning and in the afternoon. The doubled morning mist observed in 1997 by Hg and others at 107°Ls was also a typical morning Elysium lower cloud.

  At the season 120°Ls in 1999, the morning Elysium appearing from the morning cloud became to be caught from 4 Apr (119°Ls) (before opposition) in Japan. The seeing was rather stable. Here we show images made by AKUTSU (Ak) on 4 Apr at LCM=183°W in which Elysium at 11:00 LMT is shown well.

  We also make a list here to show how we observed Elysium on 5 Apr (120°Ls):

5 Apr 1999 (120°Ls, the central latitude=16°N, the phase angle=16°,  the apparent diameter=14.4")
    Mk-086D  13:50 GMT LCM=150°W    09:00 LMT
    Ak- CCD  13:59 GMT LCM=152°W
    Mk-087D  14:30 GMT LCM=160°W
    Ak- CCD  14:45 GMT LCM=163°W
    Mn-389D  14:50 GMT LCM=165°W
    Mk-088D  15:10 GMT LCM=170°W
    Mn-390D  15:30 GMT LCM=175°W    10:30 LMT
    Mk-089D  15:50 GMT LCM=180°W
    Mn-391D  16:10 GMT LCM=184°W
    Mn-392D  16:50 GMT LCM=194°W
    Id-034D  17:00 GMT LCM=196°W    12:00 LMT
    Mn-393D  17:30 GMT LCM=204°W
    Id-035D  17:40 GMT LCM=206°W
    Mn-394D  18:10 GMT LCM=214°W
    Nj-201D  18:50 GMT LCM=223°W
    Mn-395D  19:10 GMT LCM=228°W
    Nj-202D  19:30 GMT LCM=233°W
    Mn-396D  19:50 GMT LCM=238°W
    Nj-203D  20:10 GMT LCM=243°W    15:00 LMT
  The morning mist was rather thick and covered Elysium up until around LCM=190°W. Going to the afternoon side, Elysium was bright around Elysium Mons and made a Y-shaped bright area with Cebrenia. Olympus Mons was brilliant near the evening limb. We here show ISHADOH (Id)'s drawing Id-035D (12:30 LMT).

  Here also the images by Hg on the following 6 Apr (120°Ls): these are the sequels to the second low of the file in #232 : The Elysium Mons at LCM=196°W is just before the noon line, and the last image 13:00 LMT.

  The characteristic cloud on Elysium Mons is an orographic cloud and becomes more evident and brilliant as it goes from the noon to the evening side. This apparition, Elysium faced to the American continents when Mars was at opposition and so it was revealed there how Elysium Mons started to be covered by the cotton-ball like cloud and how it became brighter at this season.

  Don PARKER (DPk) succeeded in catching this phenomenon on 24 Apr (129°Ls) 1999 by shooting every forty minutes. The excellent sequence here of the B light images shows well how the orographic cloud of Elysium Mons becomes independently condensed. The time was from 10:20 LMT to 13:00 LMT, and so these are good photos to show the phenomenon before and after the noon. The aspect of the phenomenon at noon suggests a possible mutual interaction of the low morning mist and the high afternoon cloud.

  As May came in, we in Japan observed the region from the beginning to 17 May (140°Ls): On 6 May (135°Ls) we watched at Fukui the brighter Elysium Mons inside Elysium from LCM=216°W (11:30 LMT) to LCM=236°W (12:50 LMT); this remained as a roundish compact bright area up until LCM=265°W (14:50 LMT). And it was quite near the evening limb at LCM=285°W (16:00 LMT). We cited our drawing on the day at LCM=245°W (13:30 LMT) at p2698 of #229. HST's image was also cited at p2697 (of #229) the local time of Elysium of which is just before the noon.

  Here we cite two images made by Ak on 7 May (135°Ls); in the former images Elysium Mons (longitude=213°W) is at meridian but its time was 11:25 LMT. The later one at LCM=249°W shows the summit at 13:50 LMT. We should note that these prove an existence of a mist flow from the inside of Elysium to the east-southern direction across Cerberus. We regard that this is also faintly shown in HST's image.
  The images on 8 May (136°Ls) by Hg are found at p2700 (at LCM=232°W, 241°W, 251°W; all afternoon: see below).
  We can also find an image on 9 May (136°Ls) at LCM=253°W made by TAN Wei-Leong (WTn) in CMO #227 p2665. The Elysium cloud was still alive.
  Even on 17 May (140°Ls) Elysium appeared from under the morning mist.

  A list of our observations done during the period from 5 May (134°Ls) to 13 May (138°Ls) is found at pages #229 p2702~2704 in #229 though they were chosen for the Utopia phenomenon, but mostly available for the present case. For example, the data on 8 May (136°Ls,the phase angle=11°) is recited as follows; here the LMT is for Elysium Mons (8:10 LMT~14:40 LMT):

8 May 1999 (136°Ls,  the central latitude=21°N,  the phase angle=11°,  the apparent diameter=16.1")
   Mn-517D 10:10GMT LCM=167°W    8:10 LMT
   Mn-518D          LCM=177°W  morning mist 
   Nj-289D 11:00GMT LCM=182°W           
   Mn-519D          LCM=186°W           
   Nj-290D          LCM=191°W    9:50 LMT
   Mn-520D          LCM=196°W           
   Mo-   B          LCM=197°W           
   Nj-291D 12:30GMT LCM=201°W           
   Mo-   B          LCM=204°W           
   Mn-521D 12:50GMT LCM=206°W   E Mons shines
   Nj-292D          LCM=211°W    11:10 LMT 
   Mk-134D          LCM=213°W           
   Mo-   B          LCM=204°W           
   Mn-522D          LCM=216°W           
   Ak- CCD          LCM=219°W            
   Nj-293D          LCM=221°W           
   Mk-135D          LCM=223°W   12:00 LMT
   Mn-523D 14:10GMT LCM=225°W            
   Mo-   B          LCM=226°W           
   Nj-294D          LCM=230°W           
   Hg- VTR          LCM=232°W    p2700 
   Mk-136D          LCM=233°W           
   Mn-524D 14:50GMT LCM=235°W   12:45 LMT 
   Ak- CCD          LCM=237°W            
   Mo-   B          LCM=239°W           
   Nj-295D          LCM=240°W   13:00 LMT  
   Hg- VTR          LCM=241°W    p2700 
   Mk-137D          LCM=243°W           
   Mn-525D 15:30GMT LCM=245°W            
   Mo-   B          LCM=246°W           
   Nj-296D 15:50GMT LCM=250°W   13:45 LMT 
   Hg- VTR          LCM=251°W    p2700   
   Mk-138D          LCM=252°W           
   Mn-526D          LCM=255°W           
   Ak- CCD          LCM=263°W            
   Mn-527D 16:50GMT LCM=264°W   14:40 LMT
  Next we refer to the observations by DPk on 24 May and 25 May (144°Ls): the former is at LCM=271°W (at 14:20 LMT) and the latter LCM=263°W (at 13:40 LMT): Both show clearly still prevailing cloud over Elysium Mons (both in B and G). We so here show a file made of DPk's photos from 095°Ls through 144°Ls in 1999 ranging only at 14:00 LMT~15:00 LMT. The orographic cloud still stays alive.

  In June, the Japanese observers came to observe Elysium from 9 June (152°Ls, the phase angle=32°). We cite here the observations concerned by the present writer (Mn):

  Mn-664D LCM=259°W 12:50LMT  not whitish  
  Mn-665D LCM=269°W 13:30LMT  still reddish  
  Mn-666D LCM=279°W 14:10LMT  not so whitish  
  Mn-667D LCM=288°W 15:50LMT  limb light  
  These show that the orographic cloud of Elysium Mons has been weaker. Elysium and Cebrenia made a Y-shaped light distribution: the area may be dusty, but the water vapour looks to have lacked though the morning mist was still faintly seen.

  As to the morning mist, it was already weak over the morning Elysium on DPk's images on 4 June (149°Ls) at LCM=186°W (weak in B). We here show a drawing by Id on 12 June (153°Ls) and CCD images by Ak on 14 June (155°Ls). Id's was at LCM=223°W implying 10:45 LMT, and Ak's were at LCM=208°W and LCM=222°W: Elysium Mons on the former was at 9:30 LMT. Already the apparent diameter has shrunk to 13". Note the morning mist was visible to the naked eyes until 22 June (159°Ls) in Japan.

  We have thus reviewed the latter stage of the white cloud activity of Elysium observed in 1999. The VA state of Elysium Mons rapidly decreased from 145°Ls to 150°Ls. As to the observations after the season, the present apparition has not been so appropriate because of the large phase angle in quite a latter stage. Hence we should expect the next apparition to provide the final data.