Moving Ripples

Several times in literature, observations of dark waves have been reported, moving at high speed through various halo phenomena. Several theories about the causes have been proposed, but due to the limited data available, these could never be confirmed. Therefore, for several years, the Atmospheric Phenomena Working Group has been collecting observations of Moving Ripples to eventually uncover the mystery of this unusual phenomenon. Meanwhile, almost 40 partly illustrated observation reports have been collected. Additionally, there is a personal observation from July 12, 2001, where I was able to detect Moving Ripples on an Iridescent Cloud, renewing my interest in the clarification of Moving Ripples. So, it's high time to analyze the raw material. Nowadays, sound waves can be mentioned without a doubt as the cause. Currently, the sources are mainly the shock waves of supersonic aircraft. Reports often described hearing the roar of jet engines before the event. There is also an accumulation of observations near military airports. My own observation was preceded by the perception of three supersonic aircraft. G. H. Archenhold's assumption that there is a connection of Moving Ripples observations with meteor sounds from larger meteoroids or meteor shower activity could not be confirmed. This is also contradicted by the fact that the final height of meteoroids entering the Earth's atmosphere at high speed is hardly less than 60 km, and sound can only propagate downward below this height. 
However, there are known cases from the First and Second World War, where bomb detonations were assumed to be the cause of the sound waves. Two more observations from the Netherlands describe thunder as the trigger of the phenomenon. When looking at the types of halos where Moving Ripples have been observed so far, it becomes evident that they are almost exclusively halos formed on horizontal plate crystals. Most frequently, Moving Ripples have been observed on the 22° parhelia, on the parhelic circle (13 cases each), and on the 120° parhelia (5 cases). A sighting from this year describes “wave-shaped shadows” moving rapidly over the circumzenithal arc. And the circumzenithal arc, like the parhelia and parhelic circle, forms on horizontally floating ice plates. But how do the Iridescent Clouds fit into this picture? Do the shimmering colors not form on small water droplets if one trusts general literature? 
As the results of continuous observations of Atmospheric Phenomena show, 12 percent of Iridescent Clouds are observed on cirrocumulus. This type of cloud mostly consists of ice crystals and, to a smaller extent, of freezing water droplets. Especially on cirrocumulus, iridescence is often observed at a solar distance greater than 30°, which almost excludes diffraction as a cause. Therefore, the latest theories assume that the colors are either produced by interference of rays reflected at the front and back surfaces of the thinnest ice plates or by interference of rays where one part goes directly through the cloud layer while the other rays are reflected once or multiple times inside the layer. So once again, ice plates are involved. It is thus likely that sound waves preferentially set ice plates into vertical oscillations, thereby triggering Moving Ripples. This would also explain the rapid cloud dissolution  observed after the wave passed through the Iridescent Cloud. Our cloud height meter (laser ceilograph) indicated a height of 6600m for the corresponding cirrocumulus layer. As shown by the Meiningen temp (18 UTC), a humidity of 49% was recorded at 6611 m height, which was also the maximum in the height range between 6000 and 7000m. At 6005 m height, the humidity was only 26%, and at 6907 m height, 31%. Due to the vertical oscillations the ice crystals were exposed to, they simply dried out in the less humid air layers, leading to cloud dissolution within seconds. The possible cause for the moving shadow stripes could therefore be that ice plates are set into rotation and oscillation by sound waves, causing the refraction of light to partially no longer reach the observer's eye and thus create the shadow stripes. Certainly, this theory still leaves some questions open, such as why Moving Ripples often occur in several wave groups or why such stripes have not yet been observed in colorless cirrus clouds. An explanation for this could be that halos increase the observer's attention and colors enhance the contrast of the shadows. Therefore, if an unmistakable jet crosses the sky, one should definitely keep an eye out for the phenomenon of Moving Ripples. (by Claudia Hinz, 2001)

- cited in Archenhold G.H., 1984: Moving Ripples in solar haloes: are they caused by sound-waves from Meteors?- Barlow E.W., Meteorological Magazine, Vol. 78, 282-284, 1949: Halo phenomena of July 20, 1949- Gorrie I.C., Weather, Vol. 21, 392, 1972: Meteorological optical phenomena- McBeath A., 1994: Moving ripples in solar haloes - update. WGN, 134-136- Burton B.J., Journal of Meteorology, 2:233, 1977: Fast-Moving dark bands crossing the arc of contact- Archenhold G.H., Lancs Weather 34, 416, 1979: Solar halo - moving dark lines - Hasubick W. 1997: pers. communication - Rendtel J., Die Sterne 65, 58-59, 1989: Observation of moving stripes in a solar halo- Hattinga Verschure P.P., Ursa Minor, 2/89, 22- Seipelt H., Reports of the AKM 21, 33-55, 1996: USA Southwest - an atmospheric travel report - Rendtel J., Reports of the AKM 21, 181-182, 1996: Halo phenomenon and "Moving Ripples" - Molau S., METEOROS 12/98, 215-216, 1998: Observation of Moving Ripples on August 21, 1998- Gerber C., METEOROS 12/98, 219-220, 1998: Halo observation on 10/20/1998 in Munich- Seipelt H., HALO 54, May/June 1989: "Earthly" explanation for moving stripes in a solar halo?- White R., Weather, Vol. 30, 205, 1975: Rapidly moving ripples in cirrus- Jak S., Moving Halo Phenomena- Seifert W., Unexplained Observations in the Sky, Supplement to the Weather Map of the German Weather Service 12/1995- Wünsche, A. Observation of an extraordinary halo phenomenon with Moving Ripples - Hinz, C., Moving Ripples - A.Boersma Hoogeveen: pers. communication - Michael Ellestadt, Drawing - Cape Canaveral, here and here - Eruption Eyjafjallajökull, here and here - Ch. Gerber, Shadow rays in sundog, Haloblog - Peter Paul Hattinga Verschure, 06/11/1976, Moving Ripples in the Horizontal Circle (Pictures)

[1]
Moving Ripples in Solar Haloes: Are They Caused by Sound-Waves from Meteors?
G.H. Archenhold
Q. JL R. astr. Soc. 25, 122-125, 1984 SUMMARY
The normal appearances of solar haloes, which are formed by refraction or reflection of sun-rays by ice crystals floating in the Earth's atmosphere, has been disturbed occasionally by dark ripple-like bands or bars passing through them at the speed of sound. As the first observations of this kind were made in wartime it was thought that bursts of machine-gun fire or bomb explosions were the source of the sound-waves. However, this explanation is not valid in the case of later peacetime observations. The coincidence of the dates of the observed ripple phenomena, with periods of high daytime meteor activity, points to meteors as the source of the sound-waves. Reasons for supporting this hypothesis will be given. To furnish an experimental proof of the proposed hypothesis, it is suggested that sensitive sound-detectors be taken by balloon into the upper troposphere at times of great daytime meteor activity in an attempt to record the sound-waves directly. 1. THE OBSERVATIONS
Although haloes around the Sun and the Moon have attracted the attention of scientists and amateurs for centuries, no descriptions of moving dark bands of the type discussed in this paper have been given before 1944. From that year on, a number of observations made on four different dates have been published. There may have been other sightings and the author would be pleased to receive any reports concerning them. 1.1 The observational data. The first observations of dark bands moving through parts of a solar halo were made independently at Cambridge (I) and at an unspecified airfield in the south of England (2) on 1944 August 9. The bands passed either singly or in groups at irregular time intervals through a parhelic circle which was seen in cirrus clouds that had developed from contrails on a day of much military air activity. Both observers likened the phenomenon to ripples that can be seen on the surface of water that had been disturbed by a gust of wind or a stone thrown into it. Further observations of ripples in a parhelic circle were reported on 1949 July 20 (3) and on 1971 July 20 (4). On 1979 June 17 moving dark lines were seen in an upper tangential arc to the 22°-halo (5). 1.2 Common features of the observed events. The observed bands travelled at very high speed. From their angular velocity and the average height of the cirrus or cirrostratus clouds in which they appeared, it can be inferred that they travelled at the speed of sound. The phenomena occurred in types of haloes which were formed by ice crystals whose axes have a preferred position, either horizontal or vertical, as to make air resistance a maximum whilst the crystals descend through the air under the pull of gravity. Because sound-waves will disturb the equilibrium of the crystals, they can produce the observed effect, as has been suggested in (2). According to information kindly supplied by the Chief Librarian of The Times the unnamed author of the article in question was Dr A. Goldie of the Meteorological Office. The batches of waves followed each other at irregular time intervals and did not always have the same direction. W. Holt, whose observation was reported by Barlow (3), even saw waves going in opposite directions at different times. 2. THE ORIGIN OF THE SOUND-WAVES
2.1 The explosion hypothesis and its rejection. Dr. Goldie in the article quoted (2) and everyone else at the time of the 1944 observations assumed that the sound-waves which had caused the observed ripples, originated from either explosions or gun-fire. There had been many examples of fine dark lines or even ripples emanating from sites of explosions. For instance, Dr. Goldie reports an interesting observation he had made in France during the Great War. After enemy bombing had set fire to an ammunition dump, the flames from it were reflected by ice crystals so that a pillar of light was seen above the fire by observers 10 miles away. The sound-waves made by the exploding ammunition were rendered visible as dark waves sweeping upwards through the pillar of light. these observations prove that sound-waves from explosions can produce visible effects. After his 1779 June 17 observation, the author made every effort to find out whether any explosions had occurred on that day which could have been responsible for the phenomenon. Other sources that had to be considered were shock waves from supersonic flights and gun practices. The result of his inquiries was negative (6). Also, the effect of thunder had to be excluded as there were no storms in the neighborhood at the time. In consequence, the explosion hypothesis had to be rejected in this instance, and the search for another possible source of the observed sound-waves began. 2.2 The meteor hypothesis 2.2.1 The coincidence of the sound-wave observations with dates of meteor showers. All the dates on which ripples in haloes have been seen fall into periods in which meteor streams are active, in particular the daytime meteors discovered by radar methods (7). Furthermore, noctilucent clouds which, like meteor showers, are connected with the entry of cometary debris into the earth atmosphere, have appeared around June 17 and July 20 on many occasions (8). The other date, August 9, is close to the maximum of the annual Perseid shower. 2.2.2 The intensity and propagation of shock waves from meteors. As meteors usually burn out in the upper atmosphere at heights above 70 km, it may seem surprising that they should have an effect on the ice crystals composing a cloud at a height of only 7-10 km. However, one will have to consider the following facts: a) The intensity of the shock wave produced by a meteor will not diminish according to the inverse square law, but rather proportionally to distance, because the wavefront is not of a spherical shape but has the form of an extremely narrow cone, at least along most of the length of the meteor's path.
b) The progress of the wavefront is affected by changes in temperature and molecular composition of the atmospheric layers passed through, and also by winds of great speeds which vary with height.
A detailed analysis of the influence of these factors on the direction and the intensity of the sound-waves is outside the scope of this paper and must be left in this field. It may suffice here to point out that the factors mentioned in (b) play a very important part in making the sounds of explosions audible at very large distances outside the so-called zones of silence. 2.2.3 The time intervals between successive ripples. The batches of waves observed in haloes appear at irregular intervals. Their frequency matches that of meteors of a medium strong shower. For example, 60 daytime meteors per hour were counted on 1947 June 17 at the Nuffield Radio Astronomy Laboratories (9). If we attribute these meteors to the Earth's encounter with the debris of comet Schwassmann-Wachmann 1930 VI, which has a period of 54 yr, a repeat shower was due (after six revolutions) on 1979 June 17, which was the day of the latest sound-wave observation. On that day trains of waves were seen at short intervals, indicating a fairly rich meteor shower. 2.2.4 Reasons for the scarcity of the sound-wave observations. It is generally agreed that the sound-waves in haloes can be seen only when the halo producing layer of ice-crystals is relatively thin (1, 10). This condition rarely exists in normal clouds, but it will be fulfilled by clouds that have developed from contrails. In this respect, it is worth noting that the phenomena observed by the author appeared in such circumstances. This condition also explains why the phenomenon discussed in this paper has not been seen in former years when flights at great heights were uncommon. 3. CONCLUDING REMARKS
If the proposed meteor hypothesis is correct, sound-waves from meteors will reach the troposphere quite frequently. Therefore, it seems worthwhile to take sensitive sound-detectors by balloon into the high troposphere or beyond at times of pronounced meteor activity in an attempt to register the sound-waves directly. In conjunction with simultaneous meteor observations such an experiment may give conclusive proof of the suspected sound-effects produced by meteors. REFERENCES
(1) Archenhold, G.H., 1944. Nature, 154, 433.
(2) A correspondent's article, "Tracing sound waves", The Times, 1944 August 31, p. 2.
(3) Barlow, E.W., 1949. Met. Mag., 78, 282-284.
(4) Gorrie, I.C., 1972. Weather, 27, 392.
(5) Archenhold, G.H., 1979. Weather, 34, 476.
(6) Letters from Ministry of Defence and from British Aerospace, 1979.
(7) Lovell, Sir Bernard, 1954. Meteor Astronomy, Oxford University Press.
(8) Archenhold, G.H., 1935 and 1936. Beob. Zirk. astr. Nachr., 17, 37 and 18, no. 25. And Schröder, W., 1966. Beitr. Geophys., 75, 53.
(9) Lovell, Sir Bernard, 1954. Meteor Astronomy, p. 364.
(10) White, R., 1975, Weather, 30, 205.

[2]
Halo Phenomena of July 20, 1949
E.W. Barlow
Meteorological Magazine, Vol. 78, 282-284, 1949 About 1030 BST on July 20m Mr. E. V. Newnham noticed that halo phenomena were in evidence and some members of the staff of the Meteorological Office at Harrow went on to the roof to view the display, which lasted till about 1100. The phenomena seen were the halo of 22°, the two mock suns of 22°, very vividly coloured, a large part of the mock sun ring (parhelic circle) and two whote mock suns on this ring, as shown in Fig. 1. The sky was most favourable for halo production on the west side of the sun, with a very uniform veil of cirrostratus, so thin that the blue of the sky was hardly dimmed, and the bright white western part of the parhelic circle stocd out in strong contrast. Some very delicate threads of cirrus were superimposed and thesed crossed the parhelic circle almost vertically. Elsewhere, the cirrostratus was thicker or altocumulus was present. The halo complex afforded some points of special interest. Halo of 22°. - During the period of my own observation, from 1040 to 1100, the "common halo", was the least persistent and striking of all. I never saw it complete at any on time; it was rather faint and was narrower than unusual, but with more evidence of colour than it generally has. The arc of upper contact was not seen. Parhelia of 22°. - The sun's altutude being 50°, the parhelia were about 10° distant from the halo of 22°. They presented a very remarkable aspect. In all my many previous observations of muck suns I have never seen anything approaching the brilliancy and purity of colour shown on this occasion. The colours were almost of spectrum purity, a quality which the circumzenithal arc, alone of all halo phenomena, normally exhibits. The blue end of the spectrum, which is rarely seen at all in a mock sun, was very clear. Furthermore the purity of colour, implying an absence of overlapping images, resulted in each mock sun being much smaller than usual, and instead of the normal rounded form each was oblong in shape, with the lenght of the oblong inclined at about 43° to the parhelic circle, as shown in Fig. 1. It might perhaps be claimed that the linear projections of the mock sun outside the parhelic circle were the beginnings of the very rare arcs of Lowitz. For a short time the western parhelion developed the well known brilliant white tail along the parhelic circle; this soon faded, without any change in the general intensity of the parhelic circle. The eastern parhelion showed the same vivid colour is the western one, and the same shape and inclination, but was often partly obscured by cloud variation. Parhelic circle. - This was very luminous, with very sharp edges; it usually appears more or less diffuse. It passed through the western side of the halo of 22° right up to the sun: more frequently this part of this circle is absent. The part opposite the sun and most of the eastern side were not seen at all. Paranthelia of 120° (sometimes called parhelia). - The contrast between the frightly coloured oblong parhelion of 22° and the bright white round one further along the parhelic circle was very spectacular. A rough estimate of the distance between the two, compared to the known distance of the parhelion of 22° from the sun, placed the paranthelion as about 120° in azimuth from the sun, as measured round the parhelic circle. Mock suns in approximately this position, in either side of sun, have not infrequently been seen by various observers. For a short time Mr. Newnham and myself saw a short segment of the eastern side of the parhelic circle, with a paranthelion in the middle. This was relatively faint, the cloud being so thick that one would not have expected to see any halo phenomenon on it. The paranthelion was at the same distance from the sun as the western one, as nearly as cloud be judged. Mr. D. F. Bowering, at Croydon Airport, saw the halo and parhelia of 22° and the parhelic circle. Mr. W. Holt, at St. Chads Secondary Boys' School, Tilbury, Essex, saw the same phenomena as those visible at Harrow. In a letter to the Meteorological Office, he states that a rippling movement was seen to pass over the parhelic circle a number of times. At times the rippling movement passed over the whole of the circle, as shown in Fig. 2. At other times the ripples travelled round the circle itself, as shown in Fig. 3. The movement was also seen in the opposite direction. This is a very remarkable observation, of which it is difficult to find in explanation, since the only instances of the rippling of halo phenomena previously recorded occurred during the wars of 1914-18 and 1939-45, when the phenomenon was explained as being due to the waves of alternate compression and expansion of air produced by heavy gunfire or explosions.

[3]
Meteorological optical phenomena
I.C. Gorrie, Charminster, Dorset
Weather, Vol. 21, 392, 1972 I'm writing to you on behalf on my colleagues at work since on Tuesday 20 July 1971 we observed some unusual phenomena in the sky. They were first seen at 15.25 BST and lasted until 15.45. The weather was hot with a westerly wind and a large area of sky was covered by thin cirrus cloud. We saw two sun haloes; one (the smaller) had the sun at its centre and was rainbow coloured. The second halo was much larger with its centre to the north-east of the sun, the sun being on the perimeter of the larger halo. At the same time we saw what can only be described as bars or stripes, travelling across the sky and longer than the diameter of the large halo mentioned above. These bars were tapered towards each end and were slightly curved as if their centre was situated towards the east. The bars appeared to have a black centre and gleaming whitish edges. The bars came mainly from the east but were occasionally crossed by one or two from the north-east. The bars travelled very fast first of all sometimes two at a time taking only two seconds before they vanished vertically overhead. Later they took four to five seconds to travel the same distance and became more regular in their spacing and timing of following each other. They appeared to travel much faster than could an aircraft.

[4]
Moving Ripples in Solar Haloes - Update
A. McBeath
WGN, the Journal of the IMO 22:4, 1994 Three sightings of moving ripples crossing solar halo phenomena not previously widely-known are reported. This brings the total of such events observed to seven. 1. Introduction
In 1993, I issued a call for observations of moving ripples in solar haloes in WGN (1), and other publications, since if these features are the results of acoustic sound waves from meteors, enhanced activity from the Perseid shower in 1993 August might well have produced further such events. So far, no sightings have been reported as a result of that shower at least. However, three other observations of moving ripples have come to light, and several groups or individuals have expressed an interest in keeping watch for future sightings, particularly in Finland and Germany. It is to be hoped that the numbers of observed ripple phenomena will increase in the near future. 2. Observations
The first of the new sightings was made at around 13.00 UT on September 7, 1976, when fast moving ripples were seen in the anti-sun direction on a parhelic circle. This observation was made by four observers, Elaine Allchin, Tim Allchin, Bob Cripps, and Sue Haywood, who were on board a barge on the Oxford Canal near Bridge 74 (approximately 5 km south east of the town of Rugby, Northamptonshire, England, l » 1°15' W, j » 52°20' N) at the time. Figure 1 is a reproduction of the original drawing made by Haywood, which shows where the ripples were seen, and what halo phenomena were observed during the course of the day.
The written report also produced by Haywood is reprinted verbatim below (2):
While relaxing in the sunshine after lunch, Elaine saw a rainbow. We all looked up, and were rewarded by the following. (There were high fine misty clouds, drawn out by the wind). When first observed, at 12.45 GMT, the sun was the center of radius of an arc of rainbow. The Sun itself was on a large white circle. The first sun dog seen was opposite the Sun, and was white, as were the two 60° either side of it. These three, and the white circle faded and returned (not all together) more than once. The two rainbow sun dogs were more persistent, as was the rainbow itself. These latter were joined by another rainbow, tangential to the other, and appearing to join the dog. The rainbow and rainbow dogs were visible until sunset. Just before 13.00, fast moving ripples were seen across the white circle.
Without trying to explain all the phenomena seen on September 7, 1976, though it is obvious several refraction haloes (the "rainbow"-coloured features referred to above) and one reflection halo (the "large white circle") were present, the description makes it clear that the ripples were seen only in the white parhelic circle, and that the halo effects were almost certainly in high-altitude cirrus or cirro-stratus clouds (the note of "high fine misty clouds, drawn out by the wind" is an accurate description of cirrus "mare's tail" clouds). The observation tallies well with others of the ripple effect, except that this example suggests the ripples occurred in ordinary tropospheric clouds, unlike the aircraft contrails of the previous four sightings.
The second new sighting was made by Jürgen Rendtel on April 15, 1988, at around 08.34 UT from Schönefeld near Berlin, Germany (l » 13°30' E, j » 52°30' N), when moving ripples were seen for a short time in a sundog to the western side of the Sun (3). Again, this observation of the ripple effect was seen in "ordinary" cirro-stratus clouds, not in a contrail. Rendtel calls into question whether the sound from meteors could be propagated through the atmosphere as described by Archenhold (4), but Archenhold has concluded that the intensity of the sound from a meteor would decrease, not as the square of the distance from the meteor's path, but linearly. He was not able to compute the exact shape of the wavefront that would be produced, however (4, 5).
Finally, the most recent observation was made by Peter-Paul Hattinga Verschure from Arnhem, the Netherlands (l » 5°50' E, j » 52°0' N), on August 17, 1988, when moving ripples were seen in a 120° parhelia on a parhelic circle. This was to the north-north-west of the Sun. Several other refraction haloes were seen at the same time, so once more, this sighting seems to have been made in cirro-stratus clouds, not a contrail. The ripples moved from north to south, in the general direction of (although not directly towards) the Sun (6). 3. Conclusion
Although this current paper has increased the number of reported sightings of moving ripples seen in solar haloes to almost twice what already existed, more observations are badly needed, especially by instrumental techniques.
It is also important that any other previously-made but so far still unknown reports should be brought to light as soon as possible. It is worrying that Cripps reports his submission of the 1976 sighting was forwarded to several authorities in Britain soon after it was made, but that no one bothered to record or explain the phenomenon (2). Consequently, there was a good chance that but for this present appeal for data, this observation might have been permanently lost. In order to examine fully potential causes of this effect, it is vital that anyone seeing such moving ripples, or coming across other reports of them elsewhere should make them more widely-known. If anyone reading this is aware of any other outstanding observations, please contact me with details. Acknowledgments
I should particularly like to thank Bob Cripps and Jürgen Rendtel for the communication of their sightings, as well as the three other observers who reported the 1976 event, and also Teemu Hankamäki who sent a copy and translation from the Finnish of the Hattinga Verschure sighting. I'm furthermore very grateful to Gunter Archenhold for several fascinating discussions of this phenomenon since 1984. References
(1) A. McBeath, WGN 21:3, June 1993, p. 86.
(2) B. Cripps, personal communications, 1993.
(3) J. Rendtel, Die Sterne 65:1, 1989, pp. 58-59.
(4) G.H. Archenhold, Quarterly Journal of the Royal Astronomical Society 25, 1984, pp. 122-125.
(5) G.H. Archenhold, personal communications, 1994.
(6) P.-P. Hattinga Verschure, Ursa Minor, 1989, pp. 22-23.

[5]
Fast-Moving Dark Bands Crossing the Arc of contact
B.J. Burton
Journal of Meteorology (UK), 2:233, 1977. December 15, 1976. Chelmsford, Essex, England. At 1505 GMT, two groups of closely spaced grey bands were seen crossing the upper arc of contact of a 22° halo from left to right. The first group lasted 10 seconds, with a 15-second quiescent period before the second group. The second group lasted about 5 seconds. About 30 straight parallel, regularly spaced bands appeared during the first observation. Moving steadily, they took 2 seconds each to cross the arc of contact. The most likely cause of the phenomenon was thought to be changes in the orientation of the ice crystals that created the upper arc of contact. However, the author could suggest no physical mechanism for producing such unusual motion in the ice crystals.

[6]
Solar halo - moving dark lines
G.H. Archenhold, Horwich, Lancs
Weather 34, 416 (1979) On Sunday 17 June 1979 several areas of cirrus clouds had developed from aeroplane contrails in the sky over Horwich near Bolton in Lancashire. In these contrails various forms of haloes were observed. I first noticed the ordinary mocksuns of 22° at 1825 BST and later in the evening the upper tangent arc of the 22° halo and parts of the solar pillar were visible. At 2100 BST my attention was fixed on the upper tangent arc because of its straight line appearance which was probably caused by the striations of the cirrus cloud. Suddenly at 2103 narrow dark vertical lines passed quickly through this arc. The distances between the lines and their intensity were quite irregular. The whole appearance lasted for a few seconds only, but after about half a minute the same happened again. The lines moved from west to east at a speed which I estimated at roughly 2° per second. There were about four lines per degree. In over 50 years of recording haloes I have never seen anything like it. A phenomenon which compares in some respects with the one described above was seen by me and others on 9 August 1944 (Nature, 154, p. 433; and The Times of 31. August 1944). On that occasion the phenomenon appeared in the horizontal ring, the dark bands were broader and evenly spaced.

[8]
Observation of Moving Streaks in a Solar Halo
Jürgen Rendtel, Potsdam
Die Sterne 65, 58-59, 1989 On April 15, 1988, starting at 09:20 CET, I was able to observe a right sundog with a tail about 8° long in Schönefeld (near Berlin) in thin and only streaky cirrus clouds. At 09:34 CET, I noticed for approximately 20s within the bright area of the sundog, "waves" slowly moving away from the sun. The distance between the wave fronts remained constant. Approximately 6-8 waves appeared over 1° length. The intensity difference was noticeable when viewed with sunglasses. The appearance of the waves seemed weaker or interrupted at times. After 09:35 CET, further similar phenomena were no longer observable. The waves were not visible in the faint tail either. Similar observations were compiled by G. H. Archenhold (1). The apparent displacement speed is about 1°/s or slightly less. At cirrus level, this corresponds to propagation at the speed of sound. The assumption of sound waves as the cause was made even during the first such observations in 1944, since military activities (explosions) were occurring at that time. However, terrestrial sources seem unlikely. Archenhold suggests a connection with meteor sound during major meteor showers based on observational data. However, it seems very questionable to me to blame the frequent but loose and (mostly) high-speed, atmospheric-penetrating cometary meteoroids, as cometary meteors have end heights above 60 km and sound only propagates downward below this height. Therefore, larger and firmer meteoroids that penetrate deep enough into the atmosphere, such as "meteorite-suspect" fireballs, would be more likely. Sound perceptions with such objects are often described (see [2]). Deriving statistics from the few observations of moving streaks is not meaningful anyway. Archenhold's emphasized finding that such phenomena are only visible in thin halo-causing cirrus clouds can be confirmed by the observation of April 15, 1988. Finally, it should be noted that no such phenomena have been recorded in my years of halo observations and in the "Halo Observations" section of the Meteors Working Group in the DDR's Cultural Association. This, in my opinion, also indicates that there is no correlation with meteor frequency, but rather the sporadic meteoroids that penetrate deep into the atmosphere may qualify as the sound source. Literature
(1) Archenhold, G.H.: Moving ripples in solar haloes: Are they caused by sound-waves from meteors? Q.J.R. Astron. Soc. 25 (1984) 122-125.
(2) Knöfel, A.: Meteor Sound. Stars 61 (1985) 356-362.

[9]
Fig. Arnhem
Peter Paul Hattinga-Verschure
17.08.1988
Ursa Minor 2/1989 In the August play in Arnhem, rapidly moving light streaks were seen passing through the 120° parhelion. The Dutch have previous observations of this strange phenomenon, believed to possibly result from sound waves that cause plates of ice crystals to oscillate. German translation:
In August there was the spectacle of rapidly moving bright streaks in Arnhem, passing through the 120°-parhelion. The Dutchman who perceived this strange phenomenon suspects that it was caused by sound waves and the resulting oscillating plates.

[10]
USA Southwest - An Atmospheric Travel Report (Excerpts)
Holger Seipelt, Seligenstadt
Notifications of the AKM, 02/1996, pp. 33-36 On 11/23 we explored the breathtakingly beautiful Bryce Canyon National Park. The halo display began at 7:30 AM MST (Mountain Standard Time) with ordinary halos. Things got interesting at 11:00 AM MST when I noted a bow, which I initially recorded as a Parry arc. As the bow developed further, I became suspicious. I had my companion, who had little prior halo knowledge, draw what she saw in the sky and was promptly confirmed in my own observations. Unlike the Parry arc, the right and only visible end of the bow touched the 22° halo. I left it at the drawing for now and decided to consult halo literature upon returning (Note: it was later dubbed the "upper circular Lowitz arc" or MOILANEN ARC). Meanwhile, the spectacle continued in the sky. Although no phenomenon formed despite the presence of a left 120° parhelion, the 22° parhelia reached a bright intensity and were fully developed. Then the American halo producers pulled out all the stops and produced moving bands in the left parhelion just for us European tourists! As if there hadn't been enough to see in the magnificent landscape already! The bands moved with an angular speed of 3-4° per second from west to east. About 6 bands were visible inside the parhelion, most comparable to a reduced image of waves in a grain field. Their intensity fluctuated very briefly within less than a second. The parhelia were slightly tilted to the horizon, as was the inside of the parhelia. We waited for THE intensity maximum and missed it photographically again, as the show ended after a minute. I tried to calculate the real speed of the wave fronts. As a reference, I used, alongside the angular speed, the numerous contrails present, all of which were below the cirrus level. Common cruising altitudes for long-distance flights are at flight level (FL) 390 = 39000 feet standard pressure. This corresponds to about 9000 m above the Bryce Canyon level. At 30° sun altitude, this results in a displacement speed of 1074 m/s. Even at unusually low altitudes of FL 290 and relatively low cirrus level, the wave front would still be 780 m/s fast. Compared to the speed of sound at these altitudes, the moving bands would be almost four times faster (FL 390) or two and a half times faster (FL 290) than sound. To my knowledge, moving bands within the SHB were observed only once before [8]. The comparison of the observation by Jürgen Rendtel and me shows the following similarities and differences: Same:

• Number of wave crests within the parhelion
• Wave fronts perpendicular
• Bands not visible in the tail
• Visibility each in the short-term range (20 s to just under 1 min)

Different:
Displacement speed (J. Rendtel gives 10 s or smaller or about speed of sound) A little later, the moving bands were seen twice more, the third time even in a barely visible, white left parhelion, never in the tail. Although we could also see fighter jets in the mid-altitudes, thus well below the cirrus layer, as potential causes of the waves, they cannot be completely ruled out, as they do indeed fly in the more than double supersonic range. However, the cause of the moving bands can only be speculated on again. What is missing is a larger number of reliable observations. Their rarity and short duration make their perception a stroke of luck.

[11]
Halo Phenomenon and "Moving Ripples"
J. Rendtel, Potsdam
News of the AKM, 11/1996, p. 181-182 In the week after the Orionids maximum, I stayed at the Hoher List Observatory in the Eifel. Almost the entire time there were cirrus clouds of various kinds in the sky, especially in the afternoons and evenings; only at night did their extent and amount decrease, allowing astronomical observations towards morning. A large portion of the cirrus originated from contrails. Accordingly, halos were also frequently visible, but no "unusual" types. So from time to time I took a control look at the sky. On the morning of October 24, I was in the nearby town of Daun when suddenly at 09:18 CET a halo phenomenon could be observed in the relatively few cirrus clouds. All visible halos were color-intensive. Particularly striking was the combination of the 22° ring, upper tangent arc, and parry arc. The distance between the 22° ring and parry arc was exactly 8° at that moment. Of course, I hadn't taken my camera with me on this short trip... The phenomenon with the 22° ring, both sun dogs, upper tangent arc, circumzenithal arc, 46° ring, and parry arc persisted until I was back at the observatory, and much longer. Unfortunately, I didn't pay attention to whether the large arc ran "parallel" to the 22° ring - whether it was indeed the 46° ring or perhaps the supralateral arc. In the afternoon, more halos appeared, mainly the horizontal circle (sometimes complete) and - as one might already suspect - some sub-suns and other suns. However, the cirrus clouds that again resulted from numerous contrails made a clear statement difficult in most cases. Only two brightenings were clear, bright, and stable. One was the anti-sun, but also two sun dogs, symmetrically visible to the anti-sun, for a longer time. Both featured a blue excess, and despite all reservations against handheld measurements, I kept coming back to a sun distance of about 140°. (To be exact: I measured the distance from the anti-sun to about 40°). The value is relatively rough, as the corresponding area had a noticeable extent. These sun dogs - or should I better say: areas highlighted by their bluish coloration - were visibly well for quite some time. But suddenly something appeared that I had observed at a (right) sun dog some years ago (1). An area of about 5° x 7° of "waves" appeared immediately to the right of the right sun dog - thus coming from the direction of the anti-sun - and moved through/over the sun dog. Camera within reach, set up - sssst, autofocus tries to focus, which never works well on clouds, so autofocus off, manually on "¥" - seconds pass, then two shots before the waves leave the area of these sun dogs and suddenly become unrecognizable. The whole thing might have lasted a maximum of 15 seconds; during this time the wave field moved nearly 10° horizontally. The streaks (moving ripples) were slightly diagonally arranged and are visible in both photos. However, the sun dogs hardly appear - perhaps a result of the already mentioned bluish coloration? The streaks are discernible in the two images. For the reproduction shown here, the enlarged image was scanned (at a slightly darker copy already in the lab - many thanks there) and then the contrast was enhanced. As a cause for the rarely observed phenomenon of moving streaks, G.H. Archenhold suspected sound waves (2). I am not aware of any other explanation. Whether they are sound waves from meteors or from terrestrial sources is also unclear. Throughout the day, besides traffic aircraft causing the contrails, low-flying fighter jets were observed repeatedly, but not during at least five minutes before and after my observation of the moving ripples. Shortly thereafter, the cirrus largely shifted to the northeast, and the number of halo types quickly decreased. In the end, only the halos opposite the sun were visible until weaker halos around the sun appeared again later. Literature:
(1) Rendtel J., 1989: Observation of moving streaks in a solar halo. Die Sterne 65, 58-59.
(2) Archenhold G.H., 1984: Moving ripples in solar halos: are they caused by sound waves from meteors?. Ql. J. R. astr. Soc. 25, 122-125.

[12]
Observation of Moving Ripples on August 21, 1998
Sirko Molau
METEOROS 12/1998 Lucky that there are so few parking spaces in downtown Aachen, otherwise I wouldn’t have observed THIS!
Step by step: The sky was covered with rather chaotic cirrus. I can't say more precisely because I'm not a cloud expert. On the way to the cafeteria, I could show the gentlemen a halo. Both sundogs were nicely colorful and bright, and the d-segment of the 22° ring was visible. The halos changed rather quickly because the cirrus was very inhomogeneous. When I returned from the cafeteria, only the left sundog was visible. I got in my car because I had something to pick up downtown. Two lights later, I suddenly saw the 22° ring and the horizon circle reappear. Since there are houses nearby and I was in the car, I could only follow it from the sun to about 150° to the left and 30° to the right. It was visible both inside and outside the 22° ring, but there was no trace of other sundogs. The Lowitz arc (colorful) started at the left sundog, stretching downwards and right to the 22° ring. I was annoyed because I was in the car and couldn't look around properly. "I'll be there in two minutes anyway," I thought. ... think again! As everything was full, I had to drive another round. At the next traffic light, the described halo and the left sundog were discernible, no trace of the Lowitz arc anymore. It was noticeable that the halos, although not excessively bright, appeared in particularly pure colors. About 5 minutes later, I was in the student parking lot - it was 11:51 CET. I stepped out from under the trees, looked around ... and was almost struck by lightning! Through the left sundog, clearly visible, beautiful bright-dark ripples moved! They came from the direction of the sun, started at the inner edge of the sundog, and moved within seconds to the tail of the sundog, where they faded. Yet the waves started again at the inner edge, drifting outward until they disappeared with the tail about 15 degrees from the sundog. The tail was so long it almost formed the beginning of a horizontal circle. Interestingly, the waves were "only" visible in the sundog and its tail. The surrounding cirrus was not affected at all. One might think the sundog and waves were formed in a higher, invisible cirrus layer. However, the sundog looked just as 'tousled' as the previously described chaotic cirrus, so I don't believe that. I estimate the waves had a distance of 10-20 arc minutes. They moved outward at a speed of maybe 2 degrees/s. The entire spectacle lasted perhaps 10 seconds, then it was all over! Shortly after, I saw the right sundog was quite bright again. However, I can't say if the ripples were visible there as well. The described halo then glowed faintly again but in very pure colors. When I started heading back 10 minutes later, part of the horizon circle as well as the 22° ring and described halo were still visible.

[13]
Halo observation on 20.10.1998 in Munich
Christoph Gerber METEOROS 12/1998 Around 9:30 AM, when I had left the house, the low cloud cover quickly moved eastward; the sky cleared and high cirrus clouds appeared. Their delicate structure made me suspect that they could iridesce beautifully near the sun. However, this did not occur. Rather, I noticed an unusual brightening around 9:45 AM (during the tram ride) in a rather wide but sharply defined cirrus strip (initially thought to be a contrail product) in the form of a roughly vertical bar that encompassed the entire width (height!) of the cirrus (about 5°, in the NW, thus about 120°). At Sendlinger Tor (120° confirmed by rough direction estimation), it became recognizable as a clear circle about 3-4° in diameter, with the impression that the edge area shimmered slightly reddish. At the train station, I interrupted the tram ride to keep an eye on the sky (9:55 AM). And what followed was overwhelming. The 120° parhelion was unfortunately already gone, as the causer cirrus strip had already drifted further east and thus stood higher than the sun. However, the southern end at this time moved into the right parhelion area. An unusually large and bright parhelion lit up. Initially, it was bar-shaped; an area about 5° high, displaying a sharply defined reddish stripe about 1-2° wide towards the sun. On the side away from the sun, the parhelion lit up brightly over a fairly large area, tapering upwards and downwards into a bright white stripe that clung to the red bar; it later led to the horizontal circle on the right. It was easy to follow how the cloud structures moved into the parhelion area, lit up brightly, then took on a reddish hue and abruptly faded back into the colorlessness of normal clouds. The parhelion was so bright that it almost dazzled. To my great surprise, a bundle of "shadow stripes" suddenly crossed the bright parhelion area. These were narrow dark lines (perhaps a dozen or more), closely following each other, crossing the parhelion from west to east in about 1-2 seconds. They ran diagonally from the bottom left to the top right. The phenomenon reminded me vaguely of the images of the "spokes" of Saturn's rings. A few minutes later, the phenomenon even repeated, although it was now not as pronounced: the shadow stripes were not as dark, there were fewer stripes, and thus the overall appearance was also shorter (about 1 second). I cannot explain how these rapidly moving shadow stripes were formed. I have never observed anything like this before. With the visibility of the parhelion, the circumzenithal arc was also visible for a few moments, but as a narrow strip that I had never seen before (about moon's width, thus only 1/2° to 1°). It was also very faint. A few minutes later, it appeared again—in full splendor: it stretched as a brightly glowing "rainbow" below the zenith. But to my enormous surprise, it was not centered over the sun, but over the parhelion! The complete arc was visible; it began with its left end just above the sun, grew brighter and wider towards the middle which was above the parhelion, and ended about 25° to the right (thus at about the sun's distance) above the parhelion. The ZZB was so splendid and visible on such a line that the centering on the parhelion could not have been an illusion! When I looked towards the parhelion, the arc sat centrally above it; when I looked towards the sun, the arc was so shifted to the right that only its tip was above the sun. Then the ZZB swung to the east and was centered above the sun shortly thereafter, everything normal again. However, before it dissolved, the apex was already far to the left (about 15°) of the sun. The apex, although the cloud field was wide enough to constantly show the entire ZZB, migrated from west to east with the clouds! This phenomenon I have never been able to observe before. I was then again surprised at how these bright and strong phenomena suddenly disappear within a few moments (10:05 AM). Although I expected the phenomena to continue left of the sun, there was initially nothing visible. And when the halo phenomena said goodbye so suddenly, I thought it was all over. I walked to the next tram stop—and noticed there that the left parhelion began to shine (around 10:10 AM). So let the tram pass and continue watching. Besides the parhelion, a 22° ring was visible, or so I believed at least. A 15° long strip was recognizable, starting from the parhelion. But it was straight. It was a totally straight line, and I initially thought this was an optical illusion, as no such straight halo exists. The side facing the sun was, as usual, reddish, with another stripe joining it outward. The parhelion shone brightly and was round (Ø about 3°), the right half reddish, the left white (I do not remember such a "halved" parhelion either!). Then the reddish tint was faintly recognizable above and below the parhelion. It gradually became clearer, and it was clear that this was the outer left section of the 22° ring. And embedded within it was the "straight arc!" There could now be no doubt, the straight line was not part of the circle, and it was real. Over the following period, the straight line faded to the extent that the arc segment grew stronger. At the moment when both were equally strong (or rather: equally weak!), it was clear to me that I had observed a phenomenon that probably has not been documented yet. At that moment, I regretted immensely that I did not have a camera with me. This unique opportunity was over. At the end of the phenomenon (around 10:15 AM), the parhelion had already disappeared. But the adjacent approximately 15° long bright segment of the horizontal circle continued to glow brightly. And: faintly visible was now the "lower straight line." Here, too, I had the impression that the reddish line was straight and not a segment of the small ring. Moments later, all this was over—and I continued to Moosach.

[14]
"Terrestrial" explanation for moving stripes in a solar halo?
H. Seipelt
HALO On July 24, 1989, I was able to observe the following phenomenon in Lindenberg around 19 CET: A military aircraft was moving at high speed at cirrus level. According to the Huygens principle, a head wave formed. This propagated within the ice crystal cloud and therefore became clearly visible. The entire wavefront consisted of three individual waves, about 20° after the first followed an identical second cone, the Mach angle (half opening angle of the Mach cone) was about 60°, which means according to the relation sing = c/v, that the aircraft flew at about 1.2 times the speed of sound (c is the speed of sound, v the own speed of the aircraft). What is the basis of the conjecture of a connection to moving stripes in halos? In principle, there is no difference between the Mach cone of a meteorite and that of an aircraft. Only the opening angle j is a function of the own speed of a body. The speed of sound remains approximately constant, as the altitude level and thus the air density are approximately constant. Apparently, the observation was of an almost ideal cone, i.e., not everyone will be recognizable as such or at all. Therefore, in the observations of moving stripes listed in HALO 51, the sound source aircraft may not necessarily have been recognized. However, if aircraft were considered the only possible sound source, there would be no explanation for Archenhold's observation of 09.08.1944, since no aircraft routinely flew at supersonic speeds at that time. Rather, they have only become a possible cause for waves in the atmosphere, which in turn can cause moving stripes, since the second half of the forties. A complex of natural and artificial causes is probably at play for moving stripes.

[15]
Rapidly moving ripples in cirrus
R. White
Weather, Vol. 30, 205, 1975 While thumbingthrough earlier issues of Weather recently, I chanced upon the letter by I.C. Gorrie in the Sptember 1972 issue. This described a halo of 22° and what was probably a parhelic circle, though the Editor did not feel able to commit himself to such a description. Being personally more interested in optics than dynamics, I paid only passing attention to the second part of the letter. This described curious bands or stripes which swept across the sky in a matter of seconds. Some time later, while researching a completely unrelated article, I looked up E.W. Barlow's contribution on some haloes seen in 1949 I was astonished to find a description of what appeared to be the same phenomenon. I had read Barlow's article some time ago, but had not previously made the association. The conditions were very similar: a halo of 22° and a parhelic circle were visible, together with parhelia (the sun was probably too high for Gorrie to see these). Barlow described ripples sweepingacross the sky, or sometimes apparently along the parhelic circle, which are surely identical with Gorrie's bands or stripes. Barlow noted that such phenomena had been seen in the First and Second World Wars, and attributed them to shock waves from bursting bombs and shells. It is interesting to note that Gorrie's bands were curved as if their centre was situated towards the east'. The tapering towards each end, which was also noted, was probably a perspective effect. Were any detonations taking place to the east? It must seem that the connection between the haloes and the ripples is indirect, probably that the ripples are a visual manifestation, only possible in thin cirrus, og some dynamic phenomenon

[16]
Moving Halo Phenomena
Jak, S.
personal communication 13 May 1987, Wolfheze
Unstable weather, air pressure 1004 hPa, rain, hail, and thunderstorm clouds. In the upper part of a thunderstorm cloud moving southward, a moving halo phenomenon was observed. This halo 'strangely disappeared' from time to time during a lightning strike (the lightning was heard as the familiar crackling/crashing on medium wave radio, the lightning itself was not visible). Afterward, the halo disappeared. About 15 seconds later, the halo reappeared in the same form only to disappear again with a subsequent lightning strike. This happened two more times (visible), after which lower clouds hampered observation. Drawings and photos were made of the whole thing. The observation time was from 12:44 to 12:48 UTC, observer Stefan Jak (author). Analysis of the photos suggests it was a section of the described halo, visible by its typical triangular shape. It is conceivable that the electrical discharge changes the movement of the crystals through a change in charge (repolarization?) and that they return to their original movement through a general oscillation of the crystals, creating the typical flickering movement. It is also conceivable that this is not a halo but an 'electric phenomenon, like a kind of 'super' St. Elmo's fire. According to records of that day, the wind in this air mass, which was very unstable - hardly increased even at high altitudes. The upper boundary of the thunderstorm cloud where the phenomenon occurred should have been at about 8-9 km with a temperature of about -43°C at that atmospheric state. The lightning strikes, as mentioned, were not visible and probably far from the optical phenomenon. A definitive cause for this phenomenon cannot yet be specified. See also the observation of June 30, 1990, by Peter Paul Hattinga Verschure. As far as is known, these are the only two observations (and only two observers) of the whole thing. It should be noted that it is not about the precise form of the halo (they were most likely generally known halo forms), but about the movement in the neighborhood of a thunderstorm. 14. September 1987, Utrecht
Mr. de Boer saw around 14:15 UTC twice groups of waves moving at high speed (estimated 2000 km/h) through cirrus clouds with parhelia, where the parhelia disappeared. Later, aircraft were present near the clouds. 15. September 1987, Dordrecht
Mr. Dillenite saw moving waves wandering through a parhelion, as if small stripes ran diagonally from the top right to the bottom left in front of the parhelion: they shielded very small stripes of the parhelion while the stripes in between were still visible as usual. 17. August 1988, Arnhem
In the horizontal circle, Peter Paul Hattinga Verschure suddenly saw 2 to 3 waves moving through the 120° parhelia and the adjacent part of the horizontal circle at 12:07. Moving with a speed of estimated 3° per second, they traveled from north to south. They were also traceable above and below the horizontal circle. 21. February 1989, Rhoon
Observer Hein Dingemans saw a short disturbance in the horizontal circle in the form of waves in a particularly pronounced moon halo (see also WEERSPIEGEL 4/1989) after an airplane had flown through it. 30. June 1990, between Arnhem and Zutphen
A somewhat comparable phenomenon was first noted on 13 May '87 in Wolfheze. Peter Paul Hattinga Verschure observed around 20:20 motion in a part of the halo at the top of a (thunderstorm) shower cloud. A detailed report is printed in the 'Weerspiegel' (Sep. 1991). In a part of the upper tangent arc (probably), a wave moved about 10 degrees to the top left and then stood still. For several minutes PPHV could follow the phenomenon (he was traveling on a train between Arnhem and Zutphen). He observed an entire series of waves. The entire occurrence took place in an area of the sky averaging about 20 degrees, approximately 25 degrees to the top right of the sun. The phenomenon remained colorful, as one is accustomed to seeing an upper tangent arc. Later a section of the (probably) upper lateral tangent arc of the 46° ring could still be seen, which was also moving. Due to his train observation, PPHV could not determine if there were lightning discharges at this time. It is clear that the thunderstorm clouds were associated with a very active and sharply defined cold front. A convergence line had preceded. The situation led to thunderstorms almost throughout the Netherlands, which suddenly appeared in association with gust fronts, hail, and wind gusts. 98% of the WWA thunderstorm observers reported thunderstorms on this day (nearly throughout the Netherlands). 15. March 1993, Utrecht
Around 15:15, the 120° parhelia were visible. Through these, a number of waves suddenly moved from left to right for a moment (observer: AB). Translated from the Dutch: Andre Knöfel

[18] Observation of an extraordinary halo phenomenon with Moving Ripples Observation location: Graupa (near Pirna), South of Dresden
Date/Time: May 14, 2001, 12:50 CEST The day began with high and quite dense veil clouds, which decreased over the course of the morning. As in the previous days, a fairly clear, azure blue sky appeared, adorned with individual cirrus clouds. Nice weather was predicted for this day. Only in the evening and the following day were showers and thunderstorms expected to start an unstable weather phase. The wind had noticeably picked up and came from southern directions along the Elbe Valley. Around noon I noticed a cirrus cloud (feather-shaped; approx. 20° extent) standing high in the sky to the north. It slowly changed its shape and moved slowly east or southeast. Initially, I thought a particularly bright part in the center of the cloud was particularly dense because it shone conspicuously bright and white. But after a short time it became clear that a part of a halo arc or something similar had to run through the cloud, as pale color fringes could be seen at the edges. As the cloud continued to move into the arc, the visible part of the arc became larger. The arc did not appear to be sun-centered but zenith-centered.
As the arc reached its greatest extent, I noticed another phenomenon. Several times (2 or 3 times) fast wave-shaped shadows moved over the northwestern part of the arc. The waves crossed the arc from south to north or from the zenith to the northern horizon. A "wave package" consisted of about 3 to 5 dark lines, which had an extent of only about 10'. The "wave packages" followed in short intervals. The speed was astonishingly high (approx. 2° per sec). By subsequent research in literature (SuW 10/1999), Internet (satellite images) and astro software (TheSky; Halo) I can make the following additional observations:    1. the visible part of the halo was obviously part of the horizontal circle,
   2. the sun position was about 57°,
   3. the analysis of DLR satellite images from about 5:00 AM UT and 2:00 PM UT showed no major thunderclouds in the area,
   4. No military aircraft flying at supersonic speed were noticed on this day,
      the "Moving Ripples" could not be associated with any other acoustic or optical events (thunder, detonation, etc.).

[20] A.BoersmaHoogeveen( Holland ) - personal communication: On 15 - 8 - 1944, the airfield Deelen, north of Arnhem, was bombarded by English planes. During this, bombs with time fuses were also dropped. Toward evening, explosions could still be heard. Coinciding with these explosions, rapidly moving, slightly curved dark gray bands could be seen in the sky. Distance from the airfield approx. 17 kilometers, calm, cloudless, approx. 1 hour before sunset. It was the only time I saw this phenomenon.  

[21] Shadow Stripes in the Subsundog Observation by Christoph Gerber In the afternoon, a series of successive cirrus halos formed the (left) subsundog. I observed from the balcony and – as usual – took photos and photos. Mostly just for the "archive". So I was quite amazed when I suddenly noticed an extremely rare phenomenon: in a part of the subsundog, a bundle of "shadow stripes" appeared!!! I had experienced this only once before, about 20 years ago. During a stay in Munich, I saw a bundle of dark stripes pass through a subsundog. I was completely baffled – I had never seen anything like it before, nor had I heard of it. But it was not the first occurrence of this kind. There used to be a page on the AKM homepage compiling all reports of this phenomenon – where can it be found now? The case became famous when a rocket pierced a cirrus layer after launch, "destroying" a subsundog.

However, there was a significant difference from today's observation: today there were no moving stripes (as all reports have been so far), but stationary ones: they moved with the cloud. The photos show that only a relatively small area of the cirrus was affected by the phenomenon; and that the stripes were indeed "stationary" in relation to the cloud. Since I was photographing at the time, this is also very apparent in the pictures: As this section of cloud passed through the area of the subsundog, these ominous stripes appeared, outside they were gone again. The duration of the phenomenon was just over 30 seconds! That was truly a lucky shot!!! Visually they were (to me) striking, and I zoomed in because of it. So it was not the case that I only discovered the phenomenon in the pictures. Nevertheless, I'm glad that the pictures (all unedited, only cropped!) captured and reproduced the phenomenon so well. You can also clearly see that the intensity of the stripes correlates with that of the subsundog.

That was a real "cherry on top" of such 0-8-15 halos like today!! So: it can always be worthwhile, even if nothing special seems to be happening. And that compensates for "hours-long" halo photography, where usually nothing remarkable happens...

[22] Moving Ripples in the Horizontal Circle Observation by Peter Paul Hattinga Verschure, 11.06.1976

by Claudia Hinz