Spring halos in Eastern Germany: 46°/supralateral splittings, tangent/Parry arc twins, a great pyramidal show, and biting cold

During the past months the sun was only rarely seen in Eastern Germany, and the number of observed halos was correspondingly low. Moreover, when everybody was hoping for the onset of spring, the winter regained its strength after March 10^th, and people were confronted with masses of snow and untypically cold days and nights for this time of year. But embedded in this belated winter period was a row of days (March 23^rd-28^th) with a remarkable outbreak of halo activity. This report will concentrate mainly on my own observations, though there is also more and complementary material available at the Meteoros message board (in German language).

Saturday, March 23^rd

In Hörlitz, Lower Lusatia (51° 31’ N, 13° 57’ E), the 22° ring and upper tangent arc (or upper part of the circumscribed halo, respectively) were visible from noon on, later to be joined with a suncave Parry arc for some minutes around 15:00 CET (15:01, unsharp masked) as well as a parhelion with a notable blue hue (15:08). From 16.00 to 16.45 the circumzenithal arc was also present. In the evening, the 22° ring, circumscribed halo, both paraselenae and the paraselenic circle appeared at the moon (19:34, USM). The further development is nicely illustrated by a time lapse video I took from 19:54 to 21:54. A weak 9° ring was also present, as visible in the filtered version of the frame from 21:04.

Sunday, March 24^th

Solar halos were again visible from noon on, but quickly changing as the cirrus clouds moved across the sky. I took a second time lapse video (13:23 to 14:40) from the same position as in the night before, showing the 22° ring and the upper part of the circumscribed halo. Note the increase in the wind velocity compared to the night before. This really “fresh” breeze from the East in combination with temperatures below 0 °C even at high noon was challenging for both the observer an the technical equipment. Though the video may suggest that the halo activity decreased during the afternoon, there were occasionally some colourful surprises embedded in the flow of cirrus patches (16:00).

Monday, March 25^th and Tuesday, 26^th (after midnight)

I continued my observations in the afternoon of March 25^th from the town of Dresden, Saxonia (51° 3’ N, 13° 46’ E). However, as I was later told, I already missed a parhelic circle segment that had been visible around noon. When I had the opportunity to look at the sky, all the halos seemed to reassemble slowly out of nothing (15:58, USM). This pattern of standard halos remained stable throughout the afternoon, and was joined by a photographically detectable supralateral arc at around 17:15. Its left wing became visible to the naked eye at around 17:35. Remarkably, a photo from 17:27 shows both the supralateral arc and the real circular 46° halo in the unsharp masked version, with the former touching the circumzenithal arc and the latter missing it; and both arcs merging at the left side at the spot where I later could see the “supralateral” arc by eye. Very likely this bright region was indeed not a pure supralateral arc, but a mixture with the 46° ring. An alternative way for halo image processing is the subtraction of the blue image channel from the red, which also yielded a convincing result here. Throughout the last months I had the opportunity to record this 46°/supralateral merging (or splitting) effect several times, though it never was clearly visible to the naked eye and could only be revealed by image processing.

At 18:10 (2° solar elevation) all halos had vanished for the naked eye, except for a bright upper tangent arc sitting on a weak 22° ring. Once more, unsharp masking revealed a surprise, namely a weak upper sunvex Parry arc looking like a shifted twin of the tangent arc (USM, R-B). This Parry arc had not been present in photos taken 8 minutes earlier.

Up to this point, the halo activity had already been much higher than what we get in average, but the definite climax was yet to come during the night. A weak 22° ring with a right paraselene (the view to left was obscured) was present around 21:00. At around 21:50 a weak 9° halo could be traced from the photos. At 23:30 the 9° ring was plainly visible, having a brighter spot at its bottom (i.e. the lower 9° plate arc). Due to this encouraging observation, I placed my camera on a cherry pit pillow at the balcony balustrade, and started an automatic time lapse series over almost 4 hours. Occasionally, I entered the balcony from inside to take a glimpse at the sky, but I did not want to disturb the fisheye photo recording by my presence. Hence my visual inspections were not carried out with full adaption to darkness. The 9° ring was very prominent until approx. 03:00, with a bright bottom and from time to time quite bright sides. The 22° halo was rather diffuse, which I took as a sign that further pyramidals might be hidden there. On its top something like a diffuse combination of  an upper tangent arc and a 23° plate or Parry arc was seen. Since the unusual quality and rareness of such an observation was immediately clear to me,  I was very excited what the time lapse video from 23:49 to 03:42 would reveal. The results did even exceed my expectations, especially in the unsharp masked version. In the following pictures (composites of each two neighbouring frames from the time lapse series for the sake of noise reduction) I labelled the halo species I could identify.

00.32.45, lunar elevation 35° 8’:
The distinction between the 23° plate arc and the Parry arc is difficult, but the presence of the other plate arc justifies the interpretation as the former effect. However, there is not enough detail in the bright region at the bottom of 22° ring to decide if more than an ordinary lower tangent arc, e.g. a  20° plate arc, is present. The circular 23° halo is either missing or masked by the outer intensity gradient of the 22° ring. It is however the only smaller halo that requires the prismatic top faces (or bottom faces, as being equivalent for random orientations) of the crystals, and hence it represents a special case. Against this view stands the presence of the 46° halo (at least 1 h later, see below), which requires such crystal faces as well, so the problem remains open.

A version of this photo without the labels is displayed as the title image of this report.

01.29.45, lunar elevation 29° 39’:
At this stage of the display, the bright regions at the sides of the 9° ring appear very prominent, corresponding to the visual impression. They can be associated with column arcs, however, I did not find traces of column arcs of the other halo families in the photos (yet).

01.36.45, lunar elevation 28° 52’:
A very strong unsharp masking reveals the additional presence of the 35° and 46° halos. The clear intersection with the paraselenic circle demonstrates that indeed the circular 46° ring and not an infralateral/supralateral combination is dominant. Note that this situation changes towards the final frames of the video, in which a clear supralateral arc without a 46° ring can be seen.

All radii have been checked by calculating the angular distance of several stars from the moon.

Tuesday, March 26^th and Wednesday, March 27^th (after midnight)

During the afternoon the halo activity rose again, until at around 14:00 both a complete 22° ring and 9° ring were visible again in rather structured cirrostratus clouds. Over the next hour, the clouds became more uniform, but also more dense (15:12). Unsharp masking and subsequent Red-Blue subtraction revealed also a weak 35° halo and 46° halo, both not being visible to the naked eye (USM, R-B). In the R-B picture, an additional ring-like feature is visible at about 12° distance from the sun, likely an artefact of this processing mode in connection with the camera and lens. It could be traced in later photographs (15:22, USM, R-B, composite of two images), maybe together with faint traces of the pyramidals near the 22° halo. As in the night before, the pyramidals faded over time, until a pattern of prismatic halos remained (16:35, USM).

Moon halos seemed at first unlikely due to the increasingly dense clouds, but after midnight once more the 22°/9° ring combination stood in the sky, however rather diffuse and less colourful than before (00:38, USM, composite of two images). A supralateral arc (or 46° halo) additionally appeared around 02:00 (02:12, USM, composite of two images).

Wednesday, March 27^th and Thursday, March 28^th (after midnight)

Around noon, a complete parhelic circle together with the 22° ring, circumscribed halo and both parhelia could be seen in the region of Dresden, though I personally missed this observation. When I began to look at the sky in the early afternoon (I was somehow a little afraid that this flood of halos would never end), the parhelic circle had lost most of its brightness, but was still detectable at the sunward side of the sky. No pyramidal halos showed up anymore, so maybe the most exotic halo species at this point was a small Lowitz arc reaching from the right parhelion to the 22° halo. However, the detection is difficult due to the presence of contrails and lower clouds, that produce artefacts in the image processing (13:34, USM). R-B subtraction also revealed a weak 46° halo.

Again, the clouds did thicken towards the evening, but this day before midnight a light snowfall set in. The series of halos seemed to have come to definite end. Nonetheless, during the night the upper part of the 22° halo appeared on the moon, just as to wave goodbye after an astonishing week full of surprises and challenges (02:11) and certainly one of the most remarkable periods in my 18 years of skywatching.

All images and videos from this report can be found here in chronological order. Any details concerning camera and lens type, focal length, precise time stamps etc. will be provided on request.

Author: Alexander Haußmann, Dresden, Germany

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