SUBJECT: THE MARTIAN CHRONICLE FILE: UFO3333
PART 6
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T h e M a r t i a n C h r o n i c l e
November 1990 No. 6
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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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A DUST CLOUD IN NOVEMBER 1990
While using the University of Hawaii's 24-inch at Mauna Kea Observatory,
Beish received a call from Don Parker with an alert of yet another dust storm.
Beish was there during 30 October through 7 November 1990 photographing Mars
for Lowell Observatory's International Planetary Patrol. On 4 and 5
November he recorded in color three dust clouds moving across the Aurorae
Sinus-Solis Lacus regions.
METEOROLOGY OF MARS IN 1990
The ALPO/IMP has over 20,000 observations of Mars and many of the late
Chick Capen's scientific papers covering his meteorological studies of the
Red Planet. Results of Capen's work and more recent studies by the IMP, Beish
and Parker published "Meteorological Survey of Mars, 1968-1984" in the Journal
of Geophysical Research, (95, B9, August 20, 1990) that can be used to predict
the times when clouds, hazes, and other atmospheric phenomena are most likely
to occur on Mars.
As we draw nearer to closest approach (20 NOV 04UT) and opposition (27
NOV 21UT) the orbit of Mars will pass through 336 degrees and 340 degrees
Planetocentric Longitude of the Sun (Ls), respectively. These periods corre-
spond to late Martian southern summer and observers should begin to see an
increase in cloudiness on Mars. Already clouds have been seen forming in the
evening in Libya, an area just east of Syrtis Major.
Approaching local Martian noon, discrete white orographic clouds, identi-
fied as water clouds by the Mariner 9 spacecraft, are seen in Martian spring
and summer forming on the upper slopes of the large volcanoes (Olympus Mons
[113W, 18N], Ascraeus Mons [104W, 11N], Pavonis Mons [112W, 00], Arsia Mons
[120W, 09S], and Elysium Mons [212W, 25N]), and between Tharsis Tholus and
Valles Marineris (80-100, 04N). These seasonal clouds ("W-clouds") were well
observed during northern Summer (120 - 160 Ls) in 1984 and in 1986 after rapid
thawing of the North Polar Cap (NPC) began (204-209 Ls). In the future, it
will be interesting to learn if these orographic clouds occur twice each
Martian year, because they originate in the equatorial region of the planet.
Look for them after the large southern basins, Hellas and Argyre, have lost
their whiteness and have returned to a dark-ocher hue, and during the rapid
retreat of the South Polar Cap (SPC) from southern mid-Spring until Summer
(235- 270 Ls). Because of the observed appearance and seasonal behavior of the
great southern basins, the authors suspect that they act as "cold traps"
during Mars' southern Autumn and Winter, thus controlling the water vapor in
that hemisphere. Because orographic clouds are best seen through blue and
violet filters, they are well-elevated and are probably generated by mechani-
cal uplift, and growing by convection.
A faint veil of wispy white clouds with variable shapes and levels of
opacity, known as the equatorial cloud band (ECB), is occasionally seen ex-
tending across Mars' disk. Because the ECB is detected best in ultraviolet
and violet light, it resides at a chilly high altitude, and is probably com-
posed of Carbon Dioxide ice crystals. Because the ECB is equatorial, it too
may occur twice each Martian year, appearing with the sublimation of each cap.
Limb haze appears as a bright misty arc of light on the sunrise or sunset
limb of Mars, and is caused by the observer's oblique view through the equiva-
lent of several Martian atmospheres of aerosols, which may consist of Carbon
Dioxide ice crystals, fine dust, cirrus-type water clouds, or a mixture of
these. Consequently, the observation of the global location, color, and densi-
ty of limb haze is a very sensitive method of diagnosing the global system of
Martian weather and unusual polar phenomena. Sometimes, the color and density
of the hazes help to detect dust storms that have begun on the other side of
the planet.
Limb haze may be seasonal or nonseasonal and, since it does not rotate
with the planet, disappears around local 8 or 9 A.M., Mars time. It is best
seen in violet light if at high altitudes, or in blue light if at mid-alti-
tudes.
A most delicate and challenging feat of observation is the detection of
volatiles at the boundary between the Martian atmosphere and its surface. In
this volatile regime, ice-fogs and frosts, often called bright patches, can be
distinguished from elevated clouds by means of comparing their relative
brightnesses and boundary definitions as seen with the aid of blue, blue
green, green, and yellow filters. If the suspect bright feature appears
brighter in blue light than it does in green or yellow light, it is an atmos-
pheric cloud. If it is brighter and better defined in blue-green light than
in blue or yellow light, it is probably ice-fog contiguous to the surface. If
the patch appears brighter with sharp boundary in green and yellow light and
is not well seen in blue light, it can be identified as surface frost. A
boundary-layer volatile's diurnal behavior and location also helps to distin-
guish it from clouds and limb haze. Fogs and frosts form in the chill of the
Martian night, rotate with the planet, dissipate in the morning sunlight, and
usually disappear by local noon. Fogs normally form in valleys, in fossae
(linear depressions), basins, and on upper slopes. Frosts are usually noted
on cool, light albedo features, plana (plateaus), montes (mountains), and
floors of large craters. Because these volatiles are topographically con-
trolled the discovery of their locations and seasonal occurrence is most
important to the study of Martian weather patterns and areography.
************************** MARS OBSERVER'S HANDBOOK **************************
* *
* Now available from the Astronomical League is the Mars Observer's Handbook *
* by Jeffrey D. Beish and Charles F. Capen at a new low price of $8.00. This *
* very important and informative book is in second printing due to popular *
* demand. Formerly published for The Planetary Society's Mars Watch '88, the *
* book was sold out and has been out of print for the past two years. Send *
* $8.00, check or money order to: Astronomical League Sales, Four Klopfer *
* Street, Pittsburgh, PA 15209. *
* *
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******** Introduction to Observing and Photographing the Solar System ********
* *
* Picked as one of the top twelve non-technical astronomy books of 1989 by *
* the ASP, Introduction to Observing and Photographing the Solar System, *
* by T.A. Dobbins, D.C. Parker, and C.F. Capen contains both theoretical and *
* observational information on Solar System objects. Very detailed chapters *
* on Mars, astrophotography, micrometry, etc. Forward by A.L.P.O. founder *
* Walter H. Haas. Hardcover, $19.95 from Willmann-Bell, Inc., P.O. Box 35025 *
* Richmond, VA 23235, (804) 320-7016. *
* *
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http://www.ufobbs.com/ufo <<<------- *
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