Recent surveys, including our Martian meteorology study, have shown that dust events can occur during virtually any season [Martin and Zurek, 1993. Beish and Parker, 1990]. Classically, the storms occurring during southern summer (270° – 359° Ls) are larger and more dramatic, and can even grow rapidly to enshroud the whole planet.  Planetary researchers refer to these massive dust storms as "planet-encircling" storms that usually occur around 315° Ls.  It should be remembered, however, that these global dust storms are quite rare – only ten have been reported since 1873, and all but two have occurred since 1956.

While predicting these events is nearly impossible to do, our studies show that the Martian dusty season indicates that the number of dust clouds is more often observed from mid-southern summer, between 241° and 270° Ls, with a peak period at 255° Ls. In the past, many of the major dust events occurred during the same seasonal period and led some researchers to refer to these major dust storms as "precursor storms prior to planet-encircling events." When a major dust event does occur during this period then we find that the highest probability of predicting planet-encircling dust storms occurs during mid-southern summer at or near 315° Ls [Beish, 1999].

A recent survey by professional researchers shows that dust events can occur during virtually any season [Martin and Zurek, 1993]. Their paper reinforces our study for a main peak period for dust events is 285° Ls (just after southern summer solstice) and a secondary peak has been observed in early northern summer, around 105° Ls. Their paper articulates our hypnosis that dust storms occurring during southern summer are larger and more dramatic. Local dust storms can even grow rapidly to enshroud the whole planet. A secondary peak at around 105° Ls has also been observed in early northern summer (90 – 179° Ls).

We have sense dismissed the notion that Mars has a dust storm season; however, it is clear from all the evidence over the past 32 years, 1971 through mid-2003, that observers expected to see some dust activity when Mars is near perihelion.  Major dust obstructions have been recorded on Mars within +/- 65 degrees of perihelion time and we must all be aware of this possibility in the next three months.
The Martian dusty period usually begins around 241° Ls and ends around 270° Ls. During that period observers have the highest probability of seeing a dust cloud or maybe a major dust storm by 255° Ls. An exception to this was the 2001 planet-encircling storm that occurred at around 185 degrees Ls or 65 degrees before perihelion.  This was the earliest major storm on record, and it surprised us because is started nearly two Martian "months" before the observed dusty "season" and four "months" before the high probability period of 285° Ls or when the highest number of dust clouds have been recorded at 315° Ls.

Much more common is the "localized" dust event, often starting in desert regions near Serpentis-Noachis, Solis Lacus, Chryse, or Hellas. During the 1997 apparition, CCD and HST observations revealed localized dust clouds over the north polar cap early in northern spring [Troiani, et al, 1997], [Parker, et al, 1999]. The MGS MOC recorded two large dust clouds over Acidalium Mare and a smaller dust cloud over Syria-Claritas region just west of Solis Lacus. This dust system moved over parts of Thaumasia and Solis Lacus.

Dust streaks have been seen in northwest of the Hellas Basin across Serpentis-Noachis (320° W, 30° S), or in the "Eye of Mars" (the Solis Lacus region; 90° W, 30° S), or perhaps in 1988 within the Chryse Basin (40° W, 10° N), the last because dust clouds were reported in Chryse during the two apparitions prior to 1986, in 1982 and 1984. The discovery of new dust cloud sensitive areographic locations is most important to future Martian exploration missions. To detect dust clouds, use red, yellow, and magenta filters.

There are numerous reports of anomalous transient albedo features appearing near dust clouds, especially when the solar phase angle was reasonably large. When these clouds reach heights of several kilometers, they may cast shadows that are observable from Earth. Dr. Richard McKim (BAA) has written an excellent review of Martian dust storms [McKim, 1996].

The 2007 apparition of Mars has just barely started when a major dust storm has been imaged by several expert Mars observers as Mars is far away from Earth with an apparent diameter of only 6.2 seconds of arc.  Some may say "oh no, not again; another dusty Mars to hide its surface from our cameras!"  Another exciting dust event apparently has started in the late weeks of June 2007 and continues a month later with the latest images posted on July 27.  What will Barsoom do next!!!!

This article is under construction and more dusty Mars reports will no doubt be forth coming. Please stand by because if this storm encircles the entire north and south of Mars we may see it subside in the next week or so.  We have seen his before and coined the phrase, "precursor dust event" to the “big one” that usually follows the first storm around 75 degrees Ls or a terrestrial month later.  So, by mid-September 2007 we should expect to see the “big one”  -- if Mars follows our rules.

Images of dust storm during the early 2007 apparition of Mars.  First images of dust storm during the early 2007 apparition of Mars. Bright dust cloud in Noachis-Pandorae on 2007-06-24 by David Moore (USA).  Following the next day, 2007-06-25, Jim Melka (USA) imaged the dust cloud appears to have moved a little westward and south.  Then on 2007-06-26 the dust cloud grows and expands west and south as imaged by E. Lomeli (USA).

Following the next day, 2007-06-27, Larry Owens (USA) and Jim Melka imaged the dust cloud that appears to have expanded westward and to the southeast.

* Revision:  Also, several interesting dust events that may correlate with ground-based observations are recorded on the Malin Space Science Systems Home Page in a “Series of Storms Shrouds Mars in Dust,” Captioned Image Release No. MSSS-3 — 19 & 20 July 2007 (http://www.msss.com/msss_images/2007/07/19/index.html).
 

It's triplets!  All there Tharsis volcanoes peak out from the dust layer.  LEFT: Dave Tyler’s 11 August image taken at the same UT as CENTER: Ed Grafton’s images that reveals Tharsis Montes. RIGHT: Larry Owen’s image on august 22.

When this dust storm ended is as always hard to determine; apparently major dust clouds were not seen past the first week of August 2007.   The dusty atmosphere continues to reduce surface during the first week of September, but appears to be clearing.   The Tharsis volcanoes peeked out from the dust around August 11 (293° Ls) and the dark hollows of the huge mountains could still be seen on August 22.

* Revision:  On August 5 and August 09, two storms were observed west of Elysium Mons. One large storm developed in the same area on August 9. These dust storms dissipated after only one day.
(See:  http://www.msss.com/msss_images/2008/08/13/)
 
 

Short lived dust storms west of Elysium Mons on August 5 and August 09, 2008, image from Malin Space Science Systems Home Page.

Beish, J.D., and D.C. Parker (1990). "Meteorological Survey of Mars, 1968-1985," Journal of Geophysical Research, Vol. 95, B9, pp. 14567-14675. August 20.

Beish, J.D. (1999), "Meteorological Survey of Mars For Opposition Years 1965 - 1995," The ALPO Computing section, November. http://www.tnni.net/~dustymars/MOM.htm

Martin, L. J. and R. W. Zurek (1993). “An Analysis of the History of Dust Activity on Mars.” Journal of Geophysical Research, Vol. 98, no. E2, pp. 3221-3246.

McKim, R. (1996). “The dust storms of Mars.” Journal of the British Astronomical Association, Vol. 106, no. 4, pp. 185-200.

Parker, D.C., J.D. Beish, D. M. Troiani, D. P. Joyce, and C. E. Hernandez (1999), "Telescopic Observations of Mars, 1996-1997: Results of the Marswatch Program," ICARUS, Vol. 138, No. 1, March, P.3.

Troiani, D.M., D.P. Joyce, D. C. Parker, C. E. Hernandez, and J.D. Beish (1997), "Telescopic Observations of Mars, 1996-1997: Results of the MarsWatch Program I: Surface and Dust," Second Mars Telescopic Observations Workshop, Tucson, AZ, October 2-3.
 

or go back to the Sand Ships of Mars.