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*                   T h e   M a r t i a n   C h r o n i c l e                *
* October 1990                                                         No. 5 *
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     The electronic newsletter by the International Mars Patrol (I.M.P.), 
   an observing program of the Association of Lunar and Planetary Observers   
                                   (A.L.P.O.)
                             Edited by: J.D. Beish
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                              Sand Ships of Mars

     Among one of the most exciting moments in a Mars observer's  life  is  to
catch a dust storm on Mars on the move.  It is rare indeed when one can  watch
one of these great red clouds slowly move over the Martian landscape  covering
over features that were dark and well defined just hours before.
     While no two dust clouds are  alike  they  nevertheless  exhibit  similar
characteristics. Dust clouds are frequently confused with bright white  areas,
frosts, or localized fogs, and some dense white clouds.   In  addition,  after
identification is made,  it  becomes  difficult  to  distinguish  active  dust
clouds from fresh surface dust deposits.  Such misinterpretation can make time 
studies difficult.
     A careful diagnosis of observational records of Mars  from  1877  through
the seventeen perihelic apparitions since 1907 show evidence that Martian dust 
storms have evolved in preferred  southern  locations  near  the  latitude  of
maximum insolation.  Maximum insolation occurs during Martian southern  summer
which corresponds to the terrestrial months of August, September, and  October
of perihelic apparitions (Capen and Martin, 1972). Recent studies  of  Martian
dust storms reveal three periods in the Martian year when dust  clouds  and/or
storms are most likely to occur.  These  periods  correspond  to  105  dg  Ls*
(northern summer), 255 dg Ls  (southern  spring),  and  315  dg  Ls  (southern
summer). [Beish and Parker, 1990]. * NOTE:  Ls is the Planetocentric Longitude
of the Sun.
     Since 1971, the year of the "Great Dust Storm of Mars,"   the  ALPO  Mars
Recorders have suspected that these disturbances come in pairs.   We have seen 
that in 1971 a major dust storm occurred on 213 dg Ls, followed by  a  "planet
encircling" dust storm on 260 dg Ls.  Again, in 1973 a major  storm  began  on
244 dg Ls and was followed by a "planet encircling" storm on 300  dg  Ls.  The
Viking Lander recorded two "planet encircling" storms on 204 and  268  dg  Ls.
Although the two dust storms of 1988 did not  reach  the  "planet  encircling"
stage, similar patterns emerged; during 206 dg  Ls  a  major  storm  occurred,
followed by another major storm on 313 dg Ls.
     Perhaps the statistical significance of the three periods above appear to 
mislead us when attempting to predict when these  disturbances  should  occur.
However, one should be especially alert when observing Mars during these times 
-- even though we have passed through the first sensitive period, be  watchful
in the next few weeks, alas, a major dust storm may be lurking just around the 
corner!          


                   REPORTING MARTIAN DUST CLOUDS AND STORMS 

     In analyzing the IMP data, the ALPO Mars Recorders have had  to  exercise
considerable caution in defining dust clouds. They have applied the  following
criteria:

1. The  sine  qua  non  of  Martian  dust  clouds  is  movement  with obscura-
tion of previously well-defined albedo features. Absence  of this criterion in 
the present study disqualified a candidate  from inclusion under  dust  clouds
[Beish, et al, 1990]. 

2. They are bright in red light. Repeat -- bright in red light!

3. Often, when these clouds reach heights of several kilometers, they may cast 
shadows -- that are observable from Earth.   There  are  numerous  reports  of
anomalous transient dark surface markings  appearing near  dust  clouds, espe-
cially when the solar phase angle  was reasonably large [Slipher, 1962].                          


                         A DUST CLOUD IN OCTOBER 1990

     During the first week of October 1990 the phone at  ALPO's  International
Mars Patrol headquarters began to ring. News of bright spots on Mars, "maybe a 
dust cloud or something," scoffed the cautious observers.   Their  words  were
restrained and with good reason -- past experience has taught them not to jump 
to conclusions, especially about this Martian dust storm business.  After all, 
these storms are very rare and often mislead the most experienced Martian dust 
storm watchers! 
     The genesis of the latest disturbance began on  September  25,  1990. Re-
porting from Paragould, Arkansas,  Kermit  Rhea  noted  that  Chryse  appeared
brighter than usual from the 25th. of  September  through  October  2nd.   His
observations  indicate  unusual  activity   in  the  regions  of  Chryse   and
Xanthe.
     Don Parker, fearful of awaking my family, avoided  calling  me  while  he
observed Mars at 0400 UT on October 4th  (310  dg  Ls),   suspected  that  the
bright streak bordering northern Aromatum  Promontorium in the south of Chryse 
might be the beginning of a  dust storm. The following  night  (310.5  dg  Ls)
this Mars Recorder watched with delight as the dust  cloud,  correctly identi-
fied by Parker the night before,  had  moved  southwest  onto  Eos,  partially
obscuring Aurorae Sinus with what appeared as a bright oval spot followed by a 
long streak.  The morning side of Mars had lost  its   usual  effect  of  limb
darkening and was replaced by a bright haze  extending  10  degrees  into  its
morning.  Subsequent visual reports  and photographs show that  a  dust  cloud
extended from eastern  Margaritifer Sinus (30W, 0N) to just south  of  Aurorae
Sinus.          
     October 6th. (311 dg Ls)  brought  more  meteorological  delights,  white
clouds now laced much of the morning limb  and  portions  of  Chryse,  even  a
bright white cloud was seen on the limb just to  the north of  Sabaeus  Sinus.
Morning hazes were even brighter, extending 15 to 20  degrees  away  from  the
limb.  The dust cloud of October 5th. had moved 575 miles  further  southwest,
now obscuring  the southern half of Aurorae Sinus and completely  covered  Eos
(40W, 12S).  A dull streak or "dusty trail" was observed to  extend  from  the
southeast of Aurorae Sinus over into Ophir -- one  of the brightest  areas  on
the planet Mars.
     Observers on October 7th. (311.8 dg Ls) reported an increase in meteorol-
ogy on Mars. Clouds had formed over Deucalionis Regio, Aram, and in  the crea-
tor Eros. Several discrete clouds in Chryse mixing  with  white  morning  limb
clouds and hazes. The main dust  cloud had  moved  west-southwest  anther  475
miles to 50W, 20S).   A peculiar Y-shaped dust cloud hung over  Aurorae  Sinus
extending into Ophir as if transferring dust particles  in  that  region  from
the main disturbance.
     One asks what would have  crossed Ray Bradbury's mind while viewing  such
splendor -- might  he think it was Martians on the run in their sand ships? 
     At last, the next day the small Martian dust storm appeared to  be  over.
With perfect on October 8th. (312 dg Ls), this Mars observer  saw  a  familiar
Martian landscape, with only a few alterations to the usually  dark  and  well
defined Aurorae Sinus.  Eos appeared to  have grown a little.  As expected,  a
dull dusty haze covered the  south polar  region  and  the  morning  limb  was
bright with blue and  reddish hazes  [Beish et al, 1984].
     Oh yes, all was quite again on Barzoom, lest we not  forget   Edgar  Rice
Burroughs.  


                                  CONCLUSION

     Although the October 4th. - 7th. dust disturbance  is  not  considered  a
major storm it was a significant meteorological activity.  Moving  over  1,000
miles of the Martian landscape it  did alter small portions of previously dark 
and well defined  features. A secondary dust cloud appeared in Ophir, an  area
over  650 miles west of the main dust cloud, on October 7th.  We can  theorize
that dust clouds on Mars may erupt in more than one  place if  the  conditions
are right.  Past observations of Martian  dust storms indicate  that  the  Red
Planet was very near its peak  dust storm period at 315 dg Ls. [Beish  et  al,
1990].   Remember, 315 dg Ls will fall on October 18, 1990!

                                  REFERENCES

Beish, J.D.,  and D.C. Parker,  "Meteorological  Survey of  Mars,  1968-1985,"
Journal of Geophysical Research, Vol. 95, B9,  August 20, 1990. 

Beish, J.D., Parker, D.C., and Capen, C.F., "A Major  Martian  Dust  Storm  in
1984", J.A.L.P.O., Vol. 30, Nos. 9-10, August 1984. 

Capen, C.F., and L.J. Martin,"Survey of Martian Yellow Storms."   Bull.  Amer.
Astron. Soc. 4, 374, 1972. 

Capen, C.F., "A Martian Yellow Cloud - July 1971." Icarus, 22, 345-362, 1974.

Slipher, E.C., "Mars, The Photographic Study. Northland Press, Flagstaff,  AZ,
108-109, 1962.


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