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