LtE in CMO #247

From Richard McKIM


@. . . . . . I was observing Mars earlier this evening and Sinus Meridiani marked the eastern limit of the visible disk. No dust obscuration was visible at about 22h UT (27 June). But we will chase the area in the next few days.... even if by then nothing remains visible. The description sounds typical of those Hellas regional events which spread over Ausonia and across M. Tyrrhenum over a timescale of a few days. We had an example of such an event in 1988, but the dust also spread as far as Sinus Meridiani to the west, as mapped in our BAA Report. From your distribution list I think you have already alerted most UK observers who might try to follow this up. Of course, we suffer from very low altitude here during the present apparition, and seeing is often not very good.

Yours Ever      

 (28 June 2001 9:14 JST email)

 

@ . . . . . . . . . .Thank you for the images you sent, from which it is clear that this dramatic event is similar to others from the past. My research showed that regional events in Hellas could start as early as Ls = 163, and in 1986 and 1988 regional events there began around 180. The event imaged resembles the 1988 June storm in that dust expanded eastward into Ausonia and crossed Hesperia, but the interesting thing is that you remark there was a cloud right from the start over part of M. Tyrrhenum (or perhaps Hesperia). This may throw some light upon the origin of the large storm of 1894 which also began in this region (affecting mostly M. Cimmerium) but whose initial cloud was not caught.

If the Libya site becomes active again, and it was one of the most active ones up to 1958-59, we may see a return of the great Nepenthes curve! In the present instance I would ask attention to be paid to see whether the 'canal' Amenthes develops temporarily, also to the visibility of Cerberus III and Zea Lacus/Peneus.

   I do recommend your readers to get hold of a copy of my book about dust storms in which all these past events are detailed. Copies can still be obtained through the BAA.

 For the present event I will try to observe as early as possible this evening to catch the storm's westward progress on the eastern limb of the planet! Best wishes

      (28 June 2001 email)

 

@ . . . . . . . . . . .Thank you for your latest email "Storm is now global". This seems just a little premature, for I have not heard of there being any evidence that the longitudes of (for instance) Mare Erythraeum or Solis Lacus have been affected, at least not up to the time of writing this. The only thing global about the event is in terms of coverage by observers!

  Of course, it may spread further, but if it did so it would be unusual for the current Ls. One cannot compare this disturbance with the only truly global storm of 1971, or even the encircling storms of the 20th century, from 1909 to the epoch of Viking. It seems in this case that dust has propagated largely to the east, invading the southern deserts including Hellas, Ausonia and Electris, and obscuring Tyrrhenum M., Cimmerium M. and even the Syrtis Major and parts of the N. hemisphere. In this respect the progression is reminiscent of aspects of the regional storms of 1894 October, 1907 July, 1941 November, 1943 September, 1958 October, etc...., though only the 1907 event was at a reasonably similar Ls. In some of these cases dust stretched three-quarters of the way around Mars, but one would not describe any of them as being global or even encircling. Historically, the great encircling events have only broken out later in the season, and seem to require a secondary, independent focus of activity to develop to enable them to reach encircling status. Thus the seasonally earliest encircling event commenced at Ls = 204. There have been many other Hellas regional events, but in many cases dust also spread substantially to the west, and in this case there has been little of that. What is unusual in the present case is the presence of initial cloud in the Hesperia region, and the bright patch of yellow cloud observed in the Libya-Isidis area shortly afterwards. The Libya-Isidis site had produced more dust storms than any other site according to E. C. Slipher, when writing in the 1960s. But since 1958-59 the site has not been active in producing events, and became a dust-sink, witness the gradual fading of the great Nepenthes curve over the next two decades. If the site is reestablished then that feature should reappear. Wait and see!

  I was observing last night (July 1 U.T., with my 42-cm Dall-Kirkham Cassegrain) under CM = 325-335W and found a general loss of contrast, but the markings all clearly recognisable. The Syrtis Major was clearly visible though a little pale, except at the N. end. The Mare Serpentis area was well marked. Libya-Isidis and Hellas were bright and dusty on the evening side, and Hellas was brightest to the north. The SPC was seen, with a dusky boundary, but on the p. side I could not separate it from Hellas. Conditions were not good however, with Mars so low from England at present, and I hope other observers will be getting (and contributing) better views. If the present storm reaches encircling status it will be a new martian record! Let us wait and see over the next few days.

 With sincere good wishes, 

                     (2 July 2001 22:53JST email)

 

@ . . . . . . . . .Just a note to thank everyone for their work this apparition, and to ask anyone with images or drawings to send to let me have them. I am away from home from tomorrow till July 28, so will be unable to read or answer email from now until then. Some of you may wish to keep images and send them after my return, but send them in as you get them if you wish. For interest I attach a draft summary of the apparition and personnel, as submitted to the BAA Council for publication in the October number of the Journal. It is intended to update the Section's web page in due course. With best wishes 

 (4 July 2001 email)


 Richard McKIM (Peterborough, UK)

BAA Mars Secrion Director

 RMckim5374@aol.com


 Back to the LtE Home Page

 Jump to the LtE Archives