2001 Mars CMO Note
- 02 -

 The dust cloud is macroscopically form-preserving:
  The first statement that I want to cite is one sentence from S EBISAWA & A DOLLFUS, Martian Dust Storms at the Early Stage of Their Evolution, Icarus 66 (1986) 75. They wrote concerning the dust lobate observed in July 1971 (at 214°Ls) as follows: "Conversely, our visual observations of the same night (10 - 11 July) indicated that the yellow component of this cloud did not appear to expand but maintained nearly the same sharp boundary throughout the Martian day." Why conversely? It's because there was already published a paper by Chick F CAPEN (The Martian Yellow Cloud of July 1971, Icarus 22 (1974) 345) in which CAPEN, based on the hourly photos taken at the Republic Observatory in South Africa, stated as follows: the cloud was first seen as an irregularity on the morning limb, but as it rotated onto the visible disk it expanded to east-west and had the same appearance and location as the initial clouds of the dust storms observed in August 1956, May 1969, and September 1971.
  On the contrary the first citation implies that EBISAWA and DOLLFUS, originally based on their experience in 1956, have confirmed their different view-point when they were confronted with this dust cloud presence in July 1971 at Meudon. We should recall the photographic images show the periphery of the Martian disk in lower contrast, and the noon line or the CM line appears too brighter. For example, Leonard J MARTIN, in 1973 Dust Storm on Mars: Maps from Hourly Photographs, Icarus 29 (1976) 363, described the variations on the 11th day of both 1971 and 1973 dust storms at 2 hour intervals (on 3 Oct 1971 and 23 October 1973 respectively), but the ingredients of the dust clouds near the noon line or the CM are shown to be much brighter. Since the disk rotates, the ingredients look like moving from the area of Hellas to Noachis and then gradually to the far west Solis L area. Though Day 11 does not belong to the initial stage, but in a mature phase, it is even hard to believe in general that any condensed part moves with the rotation speed, and so it is natural to consider that such a chase of the brightest component does not produce the movement or motion.

  The 1971 Great Dust Cloud Was Arisen at Dawn:
  The other statement that I want to cite here was given by William A BAUM in his note entitled Results of Current Mars Studies at the IAU Planetary Research Center (in "Exploration of the Planetary System" (edited by Woszczyk and Iwaniszewska, IAU 1974), p241): It is concerned with the great dust cloud secondly arisen in 1971, and BAUM wrote "In September 1971, for example, there was no visible evidence of any unusual activity on September 21st, but early the following morning as Noachis emerged from the morning terminator, it was brighter and whiter than any features of the storm during the days that followed. What would trigger such a vigorous onset? And why so early in the day, possibly even before dawn." I suppose any Lowellian believed in the condensed ingredient near noon, and hence this fact must have never been anticipated. The allusion to the association of the white condensate with the morning dust cloud must also be seriously treated to be important.

  To Sum Up Preliminarily:
  If any dust cloud in the initial stage does not show any particular change in shape and brightness from afternoon to evening, it must be natural to imagine that the dust cloud has preserved its shape and brightness from the early morning throughout the day until the sunset. If it already showed a different configuration in the preceding Martian day, there may be nothing to do but to consider that the dust outbreak must have been created at the rear side of the disk. Is it possible however for such a change to occur at night? How can we imagine such a drastic change to occur at night whilst it receives no serious variation in the daytime when the solar insolation is strong? We are then led to the supposition that the localised dust cloud just tends to be created or changed when the area moved from the day to the night zone, and/or when it comes across the dawn line. The night air could however bring a stabilisation rather than the further disturbance to any germ, and so we may say it is finally natural to suppose that the localised dust cloud is to be entrained at dawn or early in the morning. If a patch of localised dust cloud existed for several days, it must imply the dust core repeated a process of dissipating immediately after nightfall and of being rebuilt freshly again at dawn, whatsoever shape it may take same as or differently from the preceding day's.
  The idea that the dust cloud emergence is associated with the water vapour was insisted by Shotaro MIYAMOTO throughout his Mars observer career. It is highly possible for the water vapour to contribute really to the morning state of the dust cloud especially in the initial phase. The problem of water condensate in relation to the early stage of the 2001 major dust storm will be treated in another Note, and we are just going here to put forward a point of view that the emergence phenomenon witnessed in 1971 early in the morning with an association with the white mist is no special one, but a very common phenomenon to hold for every early stage of the major dust clouds. We here point out that the dust whirlwinds or the dust devils observed in 2001 well suggest and support the above view.

  28 June (Day 4):
  From Asia there was observed on 28 June a bright resonant dust devil occurring at the area now called Isidis Planitia (let us regard its centre was around (275°W, 30°N) and denote the point as C). It was not known the day before. I received a phone call from HIGA (Hg) at Okinawa near at midnight, and he assured me a bright spot was there clearly seen on the Video monitor: It was already outside of the thick morning mist, but he said it was not visible in B (Sony is very sensitive to B). Concerning this affirmation, I emailed world widely from Kyoto on 29 June at 01:19 JST (16:19 GMT on 28 June). Cf #248 p3089. Responding to this email, TAN Weileong (WTn) in Singapore immediately replied to me at 2:49 JST as "I've got some images from abt 12:00 to 14:00 Japan time, will be processing them after this. Not much images just 4 sets of images," and at 9:21 JST in the morning I received his set of excellent images at LCM=274°W (15:32 GMT=24:32 JST), and on 30 June all other images reached us at 5:02 JST. These gave us a local situation of the dust devil, and sharing these news, Don PARKER (DPk) also referred to the dust devil on WTn's image in a reply to me on 29 June at 14:41 JST (#247 p3053).

  The C point was already near the CM at Singapore, but fortunately AKUTSU (Ak), who just flew to Okinawa on the day, started earlier from 10:47 GMT (LCM=205°W) by shooting the C-point by the use of WAKUGAWA's telescope having a 40cm speculum equipped with a Nikon digital camera (Nikon Cool Pix 990). Ak's images compose thus an important set. A failing is however a lack of data coverage between LCM=213°W and LCM=232°W: At the former moment, the C point is obscure under the morning mist, while in the later the dust devil is already evident. Since the phase angle is 13°, the C point is at 7h LMT in the former, while the LMT already proceeded to 10h in the latter. We cannot thus pin down no narrower than to say the devil occurred around from 8h to 10h. Fortunately, Hg started taking pictures by Sony Video around from LCM=216°W, and the Tape at hand shows the surfaces to fill in the gap at LCM=218°W, 226°W, 230°W. These show still the morning mist thickly but the bright dust devil is apparent at LCM=226°W, and also we can catch a glimpse of the bright emergence of the dust devil at LCM=218°W (TSUNEMACHI (Ts) also checked these points on the monitor). And so, we can conclude the bright dust devil popped out around 7:30 LMT. Ak continued to shoot at LCM=239°W, 258°W & 271°W, and Hg's Video shows us the surfaces at LCM= 235°W, 245°W, 251°W, 262°W, 267°W, 272°W, 279°W, 284°W & 290°W (this was counted by Ts). WTn at Singapore shot at LCM=274°W, 277°W, 283°W & 285°W.

  29 June (Day 5):
  Similar example of the resonant local dust disturbance was witnessed on 29 June at M Cimmerium. This took a strange shape of an arched slug, as it were, and hence the form-preserving of the dust during the observation time was more conspicuous. The ingredient stayed from Hesperia to Eridania and its eastern end went down to cut the preceding part of M Cimmerium: Let the EN end of the dust be denoted D, its position being (210°W, 30°S).

The Ground Dust Devil Does Not Propagate Macroscopically:
  The observations on 28 and 29 June suggest us that what we have to admit includes the early morning rise of the dust devil as well as the form-preserving of the dust cloud during the day. Furthermore the above discussion suggests us give up the point of view that the localised dust core propagates horizontally just like a Typhoon. Let us try to accept a stupid view that the dust core at C on 28 June propagated to D on 29 June. As we discussed, it must move or expand from C to D semi-diurnally (at night), and so it must move 65°during 12 hrs; implying that it must have moved 10°within 2 hrs. It is too rapid. Even if we admit a diurnal motion, it must propagate 5°per 2 hrs. We traced both on 28 June and on 29 June for 5 hrs, and hence how can we miss the horizontal movement even based on the Earth-based observations? The sharp bright spot on 28 June was quite localised and did never move eastward even on WTn's final image at LCM=284°W (after 5 hrs).

  We don't say the core will never deform nor move microscopically: In fact the Viking blue channel detected a local dust cloud in a tongue or lobate shape at 227.7°Ls near the crater named Oudemans at (092°W, 10°S) when the first global dust storm in 1977 did not yet completely dissipate. Its size was about 3x10⁵km² and at the altitude of 10km. The IR thermal mapper (below) fortunately repeated measurements of the area four times on the preceding day during the time from 11.8 hrs LMT to 17.0 hrs LMT, and detected a movement along the latitude by 6°, and longitudinally by 3° (Alan R PETERFREUND & Hugh H KIEFFER, Thermal Infrared Properties of the Martian Atmosphere 3. Local Dust Clouds, J Geophys Res 84 (1979) 2853). Hence such a deformation should always occur. (It is slightly not understandable for such a bit large movement to allow an identification with the visual dust lobate on the following day at the same site).

  On the other hand, the vast numbers of the airborne dust particles injected high up by the ascending air current onto the upper atmosphere should more rapidly expand at high speeds. A classical model of Y MINTZ allows the winter jet to travel at 60~70m/s. Our season was spring, but a speed at 35m/s at higher altitude may be enough to cover globally the planet surface within one week. Without this kind of eastward spread, the resonant series of dust devils could have never occurred one after another. The amount of suspended dust thus must have been renewed and augmented day after day in the initial phase, and thus the major yellow dust cloud was evolved.

  Numerical experiments show that the growth of the dust cloud is quite negligible toward the horizontal direction, while it makes a dust column vertically upto the upper troposphere or to stratosphere. For example, Robert M HABERLE, Conway B LEOVY & James B POLLACK, Some Effect of Global Dust Storms on the Atmospheric Circulation, Icarus 50 (1982) 322. The airborne dust, if it reaches the height of 40 km, then gets onto the circulation current. The upper circulation air is cause by the westerly having a speed of 70 m/s ~ 30m/s from winter to spring in the low-latitude zone. Another older literature is also suggestive: Peter J WEBSTER, The Low-Latitude Circulation of Mars, Icarus 30 (1977) 626.

 Tc vs Ts:
  The Viking spacecraft carried an instrument called the InfraRed Thermal Mapper (IRTM) and observed the Martian surface through the channels centred at 7, 9, 11, 15, 20micron , and sent back a wealth of information on the thermal and reflective behaviours of the Martian surface and atmosphere. Terry Z MARTIN, Alan R PETERFREUND, Ellis D MINER, Hugh H KIEFFER & Garry E HUNT, Thermal Infrared Properties of the Martian Atmosphere 1. Global Behavior at 7, 9, 11, and 20micron , J Geophys Res 84 (1979) 2830, G E HUNT, Infrared Properties of the Martian Atmosphere 4. Predictions of the Presence of Dust and Ice Clouds From Viking IRTM Spectral Measurements, J Geophys Res 84 (1979) 2865. The IRTM also gave several surface images through the temperature brightness. Otherwise the Viking did not have a wider camera and it just provided mosaics made from several tiny images through 3micron (300nm) or shorter (ultraviolet).

  Out of such IR bands, the 7micron one is thought of as representing the surface temperature, not so much affected by the dust content of the atmosphere. On the other hand, the 9micron band temperature is affected by airborne dust. If the dust cloud is too thick, we cannot say the 7micron channel shows the surface, but even then it tells us about the lower layer than the 9micron band does. Let T7 and T9 denote the brightness temperatures through the 7micron and 9micron channels respectively, and then we can consider that deltaT=T7-T9 is close to Ts-Tc. In fact, T7-T9 is minus at night but reverses the sign in the daytime. The change of sign occurs around at 8:00 LMT and at 18:00 LMT. Around from 18:00 LMT the heat radiation from the airborne dust affects T9 which becomes higher than the cooling down Ts.   IRTM observations show that the thermal contrast deltaT remains low diurnally if the atmosphere is clean. However, once it becomes dusty, deltaT much decreases at night, and becomes large in the daytime. Furthermore the situation in the lower latitude zone is different from that at the higher latitudes: If the atmosphere becomes much dusty, deltaT quite decreases at night at the more southerly latitudes, while at the lower latitudes deltaT does not turn minus until late at night. The remnant heat still continues to survive even after nightfall nearly until midnight: The heated-dust laden atmosphere radiates downward and warms the surface at night, or it becomes a thermal blanket to prevent the surface from cooling down.

  The above picture is rather typical, and in reality it was reported when the 1977 dust storms prevailed, even the southernmost latitude areas or the south polar region suffered from a strong insolation, and deltaT varied largely because the night was scarce in summer: Garry E HUNT, On the Opacity of Martian Dust Storms Derived by Viking IRTM Spectral Measurements, J Geophys Res 84 (1979) 8301. Also the night behaviour of deltaT at the tropical zone looked not simple: Terry Z MARTIN, Mean Thermal and Albedo Behavior of the Mars Surface and Atmosphere over Martian Year, Icarus 45 (1981) 424. The measurements of T7 and T9 are not easy when the temperature is low, and so the results at the polar region and the area where the night ground fog prevails are complex. In that case T7 may scarcely be equal to Ts.

  Our case in 2001 is however different in season from the 1977 cases, and the sub-solar point lingered near the equator, and so the situation should be more standard than the 1977 cases. We can thus consider the case to hold in the initial phase that deltaT is quite negative even when it is dusty at the more southerly latitudes. This implies meteorologically any of local dust disturbance at the southern Hellas or at the perimeter of the subliming/thawing spc seen before the vernal equinox must have subsided each night. Furthermore it is supposed physically that the sand dust lying there consist of coarser particles. Conversely speaking, the dust devils near at Hesperia worked more effectively (than the Hellas dust bowl) to make a dust plume made of fine-grained particles reaching the upper troposphere from the meteorological and physical standpoints.

  As far as we checked, from the end of June to the beginning of July the water vapour played a certain role at the morning side, but gradually the work of water condensate ceased as the atmosphere temperature extraordinarily rose because of the formation of thick yellow cloud.

To Sum Up Finally:
  The consequences driven from the observations of the dust devils observed on 28 June and 29 June lead us to the following summary:

1. To give rise to non-local dust cloud, an appropriate amount of airborne dust and the water vapour are needed: The former keeps a temperature at night to raise a thermal tide, and the latter governs a drastic change at dawn.
2. If at the low latitudes there are aroused a cold front and a convergence from the dawn to the morning, a violent whirlwind may possibly be caused to raise a rapid ascending current which sends up a vast amount of the fine-grained dust particles, depending on some physical and topographical conditions.
3. The dust devil thus generated remains localised macroscopically at the same site, and does not move horizontally from the morning to the nightfall.
4. The ascending of airborne dust to the troposphere works still during the day and makes a vast yellow cloud circulation at the higher altitudes.
5. The yellow cloud thus generated in the initial stage feeds back to create other dust devils next morning.
6. The re-natal dust devils may be entrained again at the same site, but as well may occur at the preceding (eastward) sites if the threshold conditions are gradually preceded.
7. In the initial stage of the yellow cloud, the water vapour still tends to make condensate at the morning side.
8. Finally the activity of the water condensate at the morning side subsides as the yellow cloud becomes thick enough.