Forthcoming 2007/2008 Mars
The Season of the Northern Hemisphere
CMO #327 (25 January 2007)
Masatsugu MINAMI and Masami MURAKAMI
OW, a series of the apparitions of the northern hemisphere is around the corner. It is long believed that the north polar cap (npc) and its surroundings must be much simpler than the opposite spc region, but nowadays it is well known that the northern moist atmosphere which much depends heavily on the fall and rise of the npc is as active and complex as or more than the southern hemisphere. The northern hemisphere really provides us a lot of interesting phenomena: For example there has been known an activity of the north polar hood (nph) which causes sometimes the Dawes slit, and recently the northerly originated dust storms gather interest since they sometimes come across the equator because of the pole to pole circulation. It is quite possible for the activity of the nph which gives rise to the Dawes slits to have a strong relationship with the northern moist dusts.
We so first describe something about the Dawes slits as a phenomenon that can be observed this apparition.
On the occasion of the last apparition, we alluded in CMO #305 (25 May 2005 issue) to the famous observation by William R DAWES (1799 - 1868) in 1864, and since then we called the dark segment inside the nph Dawes' slit (mostly in Japanese; In DAWES' observation on 15 Nov 1864 at 00:00GMT, he wrote it was a short and rather thick dark line). See also our Web-Site:
In the article we predicted it was possible to check in 2005, but it was also possible to do in the 2007 apparition. This was based on a theorem proposed by one of us (Mn) in 1984 (in The Heavens: the OAA Journal), and repeated several times in the CMO also (eg CMO #106 (15 June 1991) p910). In the CMO-Web, refer to:
The proposition is simple; In order to find an apparition which resembles a specific apparition, find a recurrence year which has a rational magic number akin to the irrational number 7.390. . . (the rule to find the rational magic number is in the above references). That 2005 and 2007 are similarly akin to 1864 is due to the fact that the 141 year recurrence has the magic number 7.333. . . , and the 143 year recurrence has 7.444. . . : As is clear, they closely pinch 7.390. . . (1864+141=2005, 1864+ 143=2007; we are discussing the affair of one hundred and forty three years ago!).
We also stated that the 1990 apparition gave us a chance to watch the Dawes slit: This was because the recurrence of 1990-1864=126 years has the magic number 7.375. . . which is more close to 7.390. . . ; that is 1990 apparition was quite similar to the apparition in 1864 (the year 1943 was much more akin in this respect, but we don't see there were efficient observations at that difficult times).
So in order to show how the years 2007/2008 and 2005 as well as the pair 1990/91∪1992/93 and as a third pair 1973∪1975 year apparitions were approximate each other, we depict here how the angular diameters δ and the central latitudes φ of six apparitions vary as functions of the season λ(°Ls). The φ is important because it makes us aware easily how the northern hemisphere is favourably facing to us or not. Unfortunately we lack the ephemerical data of the 1864 apparition, but we suppose its curves lie between 2005 and 2007/08 curves. In fact the maximal diameter φMax in 1864 reads 17.5" which really falls between the 2005 φMax =20.2" and the 2007 φMax=15.9" as is expected. As well φ may fall between the 2005 and the 2007/08 curve. So in respect of φ at least, 2007 looks more favourable than in 1864.
2005, we really experienced the case: The interesting intervention between the
nph and the dark marking beneath the npc in 2005 was observed for instance on 9
Oct 05 (λ=303°Ls, φ=11°S) by PELLIER (CPl) at ω=077°W, FLANAGAN (WFl) at ω=153°W, GRAFTON (EGf) at ω=162°W, and then again in Europe by KARRER (MKr)
at ω=355°W where the Dawes slit and a yellow-whitish
disturbance nearly north of Nilokeras were shot. On 11 Oct 05 (λ=304°Ls) AKUTSU (Ak) took a morning nph over M
Acidalium at ω=341°W, but unfortunately it must have been
already be at dawn at
@As shown in the Figure, δ in 2005 was rather large for λ=300°Ls ~ 310°Ls, while φ was a bit too south, and hence the situation was inferior to the conditions in 1864. On the other hand on this 2007 season φ is north but δ must be insufficient. We however consider that DAWES' case in 1864 happened around λ=337°Ls, and so we can be sure this phenomenon can be long traced, and it is expected that we may check the slit phenomenon with a favourable δ under at the best φ in 2007. In fact φ goes down to 7°N: on λ=310°Ls, φ=1°S, on λ=320°Ls, φ =3°N, on λ=330°Ls, φ=6°N, and on λ=345°Ls, φ reads 7°N.
The drawing of Mn in 1990 was made at λ=321°Ls:
where δ was inferior to the case in 2005, while φ was better than in 2005. Mn's set of drawings of the M Acidalium area was shown in:
where the area is shown four days every 40 minutes. Note that the Dawes slit was not necessarily visible every day.
In 1992, φ was further northern. But appropriate δ was not associated, as shown on the Figure.
In 1973, at the season λ=300°Ls the apparent diameter δ was the most favourable but the deep south was outside our eyes, and unfortunately or fortunately at the very season the encircling great dust storm was entrained at the Solis L area. Even if this belonged to the northern originated dust storm category, we could have not been able to search the deep north.
From the Figure, we may judge the following case of 1975 was quite akin to our 2007 case. However in 1975 we have never heard about the detection of the Dawes slit: Prof MIYAMOTO had just retired and did not stay any longer at Kwasan. The Kwasan and Hida Observatories took a total of 229 R and B images (sometimes G) by the use of TriX (non-composites), but as far as we see their report (in Contri. Kwasan and Hida Obs. Kyoto Univ No 233, 1976), some nice images show the interventions of the nph with Utopia and M Acidalium which however look normal. On 20 Nov 75 (λ=346°Ls, φ=2°S) at ω=017°W a B image shows a thin hood over M Acidalium but without the slit.
In 1975, one of us (Mn) was not productive. M Acidalium was caught frequently at λ=355°Ls ~ 360°Ls and at λ=014°Ls ~ 018°Ls (both were made by the use of a 15cm refr at the atop of the Astrophysics Dept, Kyoto Univ). In 2007 we hope everybody be more attentive.
We are now in a position to talk about the northern originated dust cases. This was also touched in CMO #305 (25 May 2005): The season around λ=350°Ls is the last of the period when pole-to-pole circulation of the northern originated dust raising (period B: λ=310°Ls ~ 350°Ls in the article in CMO #305). So, in addition to the nph watching, we should be careful about the dust raising around the area of M Acidalium and Utopia.
Letting the cross-equatorial propagation of the dusts aside, we should continue to watch the dust disturbances around the perimeter of the npc when the nph is weakened and eventually vanishes even if they do not propagate southward. The dusts around and inside the npc are also seen even after λ=360°Ls when the npc begins to thaw or sublime. The northern spring visits at the end of 2007 at the time when the angular diameter of the Martian disk is still large, and so it may be quite possible to check the peripheral dusts. Only unfortunately however the tilt φ inclines to the south at this time. The dusts near the north polar cap were not observed by Mariner 9, and so it is not certain whether the polar dust occurs every time, but they have been caught frequently by the HST and MGS, and the HST record in 1996 was press released as "Springtime Dust Storm Swirls at Martian North Pole" in
images on λ=011°Ls (
The above three have their inlets at Ω=167°W, 173°W, 159°W respectively. These dusts are considered to
be associated with fronts which passed through the surface of the npc. P B
JAMES et al in "North Polar Dust Storms in Early Spring on Mars"
Icarus 138 (1999) 64
also cites, in addition to the above three, another
case at λ=020°Ls taken on
As stated above, this kind of polar dust was not trapped by Mariner 9, but MGS frequently observed dusts near and inside the npc. One of the most famous ones is a burst from the npc observed on λ=042°Ls (29 Aug 2000), and found in
In 2002, the northern hemisphere greeted the spring equinox in mid-April, while by λ=030°Ls; the end of June 2002, the peripheral dusts near the npc occurred quite frequently and MGS accumulated the data as shown in
We now move on to other cases in the northern hemisphere: We first note that slightly far from the north circumpolar region Alba might show a white cloud activity around the end of the Baum plateau (~λ=060°Ls), and so we should be attentive though the δ must be smaller. This should be also checked in 2009/2010 more favourably. An example in 1995 can be found in
Second, the evening cloud over the higher mountains in the northern hemisphere will revive after the northern spring equinox, and so Olympus Mons and others should be attentively checked.
Last, but not the least, Novus Pons on M Acidalium (observed frequently by Elisabeth SIEGEL (ESg) in 1992/93, and named by Johan WARELL (JWr) of the NMO, and appeared in 2005 on several ccd images) should be another target to check in 2007/08. As to this we shall give another column on another occasion.
We finally note that it's a long way in 2007 to reach the opposition time (as always when the planet is at opposition after the perihelion). Until the northern winter solstice comes in mid-September, φ tilts toward south, and it is hard to observe the deep northern districts. However the northern originated dusts are to be raised from April and May, and so we should be prepared for the season of the northern hemisphere to start earlier.