finnish halo observing network: search for rare halo phenomena

Finnish Halo Observing Network: search for rare halo

phenomena

Marko Pekkola

The Finnish Halo Observing Network obtains information about rare halos through literature study and

amateur network observations. Recent photographs and historical drawings of some yet unexplained halo

effects are presented.

Observations of the Finnish Halo Observing Network

During the first half of this century there was littlesystematic research on rare halo phenomena. In par-ticular, the lists and theoretical views of Bravais,'Pernter and Exner,2 Minnaert,3 and Visser4 5 about therarest known halos did not have much in common.The adoption of computer simulation techniques hasimproved the situation remarkably.6 7 But still manyquestions remain. The old literature of atmosphericoptics is filled with strange observations and claimedrarities. Which of these exist in nature and which arethe result of faulty observations and drawings? Howrare are the rare halos? Which halos have been suc-cessfully photographed and which have not? Also theera of computer simulations has introduced new ques-tions. Many theoretical effects that appear in com-puter simulations have not yet been observed, or havethey?

To answer these questions, organized networks ofamateurs watch the skies with cameras and recordobserved halo phenomena. During its existence, theFinnish Halo Observing Network has made hundredsof observations and taken thousands of photographs ofcomplex halo displays and rare halos. At the presenttime the network has approximately 30 members mak-ing observations on a regular basis. Another similarorganization is the Dutch Weather Observing Networkwith about ten active members.

The author is with Astronomical Association Ursa, Rautalammin-tie 5 D 40, 00550 Helsinki, Suomi-Finland.

Received 3 October 1990.0003-6935/91/243542-03$05.00/0.

© 1991 Optical Society of America.

In 1985 the author started a literature search totrack down old records of interesting single sightingsand major displays of halo phenomena. This has en-abled us to compare centuries-old observations withnew ones and to make critical analyses of both of them.One of the most interesting results thus far has been aseries of observations made of vertically elliptical ha-los. In the old literature of atmospheric optics thereare some single reports of vertically elliptical halos,usually seen surrounding the moon but occasionallyaround the sun. Perhaps because of the lack of photo-graphs, these phenomena are no longer mentioned inthe major modern works on halos. These ellipses haverecently been described only by Corliss, 8 who placesthem in his list of rare and unexplained "anomalies."At least two different-sized vertically elliptical haloshave now been photographed in Finland.9 Examplesof these are shown in Plates 39 and 40.

Traces of some new theoretically predicted haloshave also been observed and photographed includingtangential arcs of concentric rings,10 various types ofLowitz arcs,1 and possibly also diffuse anthelic arcs.'2

Of the old and famous rare halo phenomena such asScheiner's and Hevel's halos, the latter has possiblybeen photographed. In some all-sky photographs tak-en by Pekka Parviainen of the halo complex of Turkuon 23 Apr. 1987, a faint arc is seen at an azimuthalangle of 900 from the sun. The only complex displayconsisting of multiple-scattering halos13 was observedby a group of nonmembers in 1976, but no photographsare available of this uncertain sighting. There are stillmany phenomena described in the literature that havenot been observed by members of European amateurhalo networks. In most cases there are no knownphotographs of these phenomena, and no theoreticalmodels for them. It is possible that many of theseeffects are in fact the result of faulty observations ordrawings. However, some observations were madecarefully by professionals and appear to be reliable.Two of the most interesting of these elusive phenome-na are shown in Figs. 1 and 2.

3542 APPLIED OPTICS / Vol. 30, No. 24 / 20 August 1991

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Fig. 1. White faint line parallel to the parhelic circle (and 9 below it) observed in Maudheim, Antarctica, on 14 Sept. 1950 by Liljequist. 14

In the literature there are perhaps only three observations of this kind of rare halo candidate. The first of these reports was made in Indonesiain 1933 byVisser and the third in The Netherlands in 1950 byJ. C. Ruiter. Tothe bestof our knowledge, there isyet no theoryfor this halo, norare there any photographs that would confirm its existence.

Summary

The extensive observations of the Finnish Halo Ob-serving Network provide information about the fre-quency and degree of rarity of different halos. Manyphenomena often stated in the literature as being rarehave been found to be more common, at least in Fin-land. Lowitz arcs, infralateral and supralateral arcs of

/ N 46°, Parry arcs, 120° parhelia, 9 and 18° rings, andanthelic arcs of Wegener are observed regularly severaltimes a year. On the other hand, phenomena such asthe heliac arc, subheliac arc, 350 ring, Kern's arc, andthe anthelic arcs of Tricker have so far been observedat the most only a few times a decade.

Throughout the world many active networks of ama-teur astronomers exist who search for new comets,supernovas, etc., thereby providing a service to theworldwide astronomy community. There are manyreasons for also establishing networks of atmosphericphenomena observers. The study of rare halo phe-nomena is but one of these reasons. To the best of ourknowledge, this challenge has been answered in Eu-

\ + k A -- ' >^ /rope perhaps only by Finnish amateur astronomersand Dutch weather amateurs, since as of yet, only a fewpeople are aware of how exciting it is to observe andstudy these phenomena.

Fig. 2. Great halo display of Dorpat, Estonia, on 5 June 1849.15When compared with modern computer simulations, it seems that Referencesall the normal halo components of this display have been drawn 1. A. Bravais, "M6moire sur les halos et les ph6nomenes optiquesexceptionally well. Only the white arcs marked with the letters 0 qui les accompagnent," J. E. Roy. Polytech. 18,164 (1847).and P do not appear in the simulations. In the old literature there 2. J. M. Pernter and F. M. Exner, Meteorologische Optik, 2nd ed.are about ten observations of this kind of white faint curving arc. (Braumfiller, Vienna, 1922).These effects are often referred to as Arctowski arcs. As far as we 3. M. Minnaert, The Nature of Light and Colour in the Open Airknow no photographs and no theory are known for them. (Dover, New York, 1954).

20 August 1991 / Vol. 30, No. 24 / APPLIED OPTICS 3543

4. S. W. Visser, Optische Verschijnselen aan de Hemel, Vers-

preide Opstellen (Koninklijk Nederlands Meteorologisch Insti-tuut 3, s'Gravenhage, 1957).

5. S. W. Visser, "Die haloerscheinungen," in Handbuch der Geo-

physik (Borntrager, Berlin, 1960), Vol. 8, pp. 1054-1055.

6. R. G. Greenler, Rainbows, Halos and Glories (Cambridge U.

Press, Cambridge, England, 1980).

7. F. Pattloch and E. Trinkle, "Monte Carlo simulation and analy-

sis of halo phenomena, " J. Opt. Soc. Am. A 1, 520-526 (1984).

8. W. R. Corliss, "Rare halos, mirages, anomalous rainbows," in

Sourcebook Project (Sourcebook Project, Glen Arm, Md., 1984).

9. J. Hakumdki and M. Pekkola, "Rare vertically elliptical halos,"Weather 44, 466-473 (1989).

10. R. A. R.Tricker, "Arcs associated with halos of unusual radii," J.

Opt. Soc. Am. 69, 1093-1100 (1979).11. J. R. Moller, R. G. Greenler, and A. J. Mallmann, "Arcs of

Lowitz," J. Opt. Soc. Am. 69, 1103-1106 (1979).

12. R. G. Greenler and E. Trdnkle, "Anthelic arcs from airborne ice

crystals," Nature (London) 311, 339-343 (1984).

13. E. Trinkle and R. G. Greenler, "Multiple-scattering effects in

halo phenomena," J. Opt. Soc. Am. A 4, 591-599 (1987).

14. G. H. Liljequist, Halo-Phenomena and Ice-Crystals, Norwe-gian-British-Swedish Antarctic Expedition 1949-1952, Scien-tific Results (Norsk Polar Institut, Oslo, Norway, 1956), Vol. II.

15. R. Meyer, Die Haloerscheinungen (Verlag von Henri Grand,

Hamburg, Germany, 1929).


Plate 1. Pastel primary rainbow photographed near Marion Cen-ter, PA.

Plate 5. The I.-polarized component of a rainbow seen in Boulder,CO. Photograph courtesy of A. B. Fraser.

Plate 2. Portion of a primary rainbow photographed in State Col-lege, PA.

Plate 6. The CIE 1976 UCS diagram as photographed from acomputer's red-green-blue color monitor.

Plate 3. Vivid primary rainbow photographed in Seattle, WA.Photograph courtesy of A. B. Fraser.

Plate 7. The l-polarized counterpart of Fig. 5. Photograph cour-tesy of A. B. Fraser.

Plate 4. The 1.-polarized component of a rainbow seen in Seattle,WA. Photograph courtesy of A. B. Fraser.


Plate 8. Corona with three red rings photo-graphed by one of the authors (J. A. Lock) on22 Aug. 1989. The photo also shows someiridescence near the edges of the cloud farfrom the location of the corona.

Plate 9. Fogbow on Mauna Kea Summit(13,760 f).

Plate 10. Fogbow on Mauna Kea flank(10,500 ft).

Plate 11. Fogbow in marine stratus.

(a)

(c) (d)

Plate 12. Color photographs of solar corona displays from cirrus ice crystal clouds obtainedat (a) 2229 on 6 Apr. 1989, (b) 2306 on 6 Apr. 1990, and (c) 2100 and (d) 2233 on 3 June 1990.All the photographs were taken with a 55-mm lens using a polarizing filter.


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Plate 13. Photograph of the rainbow region of an oblate water drop Plate 14. Photograph of scattering from a drop as in Plate x butilluminated by white light from a xenon lamp. The arc on the left is with the oblateness increased so that the Airy caustic and cusp areassociated with the usual Airy caustic while near the center is a closer. Diameter D of the drop was 1.8 mm.transverse cusp caustic. The horizontal scattering angle 0 increasesfrom left to right where 0 1520 on the right edge of the patternrecorded. Diameter D of the drop was 1.9 mm.

Plate 15. Photograph of scattering from a drop for a shape at orclose to that giving a HUFS. The cusp and Airy caustics havemerged. Diameter D of the drop was 2.1 mm and the scattering wasvertically polarized.

Plate 16. Photograph of an unidentified caustic produced in therainbow region of a highly oblate drop of water. The horizontalscattering angle 0 increases from left to right. The colored arc on theright crosses the midplane near the angular location of the usual Airycaustic for the primary rainbow. The lack of symmetry about themidplane for this particular photograph may be a consequence ofeither imperfect symmetry of the drop or imperfect alignment of theincident beam with the equatorial plane of the drop.


Plate 17. The multicolored pattern in this photograph takenthrough a polarizing filter results from transformations of partiallypolarized skylight on transmission by the stress-induced birefrin-gent airplane window. Not all colors are seen with equal probabilityor have equal maximum purity. Pure oranges and reds are conspic-

uous by their absence. The purest colors are purples and yellowish-

greens.

Plate 18. Skylight is neither uniform in color nor in brightness,

varying from bright white near the horizon to dark blue overhead.

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Plate 19. This polarizing filter enclosed within a birefringent plas-tic case was photographed under tungsten illumination with a polar-izing filter on the camera. The colors are purer and span a wider

gamut than those shown in Plate 17 because tungsten light is redderthan skylight and the degree of polarization of the light incident onthe case is higher than that of skylight.


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Plate 20. Photograph of colored bands associated with the transition to total reflection from bubbles in a cloud. The most pronounced bandis a red-yellow band located just above an imaginary horizontal line drawn half-way up the picture. A second fainter band is present above itnear the left side. Reflections from the window are visible near the right side. The focal length of the camera lens was 50 mm.

Plate 21. Successive mountain ridges # 1. Plate 22. Successive mountain ridges # 2.


Plate 23. Gradation of sky color

from the horizon up over CliffsidePark, N.J.

Plate 24. Gradation of sky color from hori-zon up after sunset over Egypt.

Plate 25. Twilight scene after sunset nearWhite Plains, N.Y., resembling FredericChurch's Twilight in the Wilderness.

Plate 26. Transparency. Wilson Hurley,Towering Cumulus. Oil on Canvas, 1977.

Plate 27. Color gradation just before sun-set in two small cumulonimbus over NewYork City.

Plate 28. Color difference between strato-cumulus and cirrus near sunset at San Die-go, CA.

Plate 29. Brightness differencebetween cumulus and cirrocumu-lus, Haines Falls, N.Y. Cumulusis illuminated by reflected sun-light, optically thinner cirrocu-mulus by transmitted sunlight.

Plate 30. Dark fractostratus beneath an al-tostratus deck over Cliffside Park, NJ.Compare with Plate 31.

Plate 31. Lighter fractostratus beneath adark stratus deck over Cliffside Park, NJ.Compare with Plate 30.


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Plate 32. Skywithstrangeorangehuedur- Plate 33. Crepuscular rays passing Plate 34. Rainbow over Niagara Falls buting intense shower (no thunder) looking through a break in a stratocumulus deck late beneath nonprecipitating stratocumulus ofsouth over New York City. afternoon over Cliffside Park, NJ. Some late afternoon, showing the shadow of late

rays are broad, while others are pencil thin. afternoon crossing the bow at 90°.

Plate 35. Pair of seated, crowned, and flute-playing figures be- Plate 36. Classic Fremont rock art panel, both pecked and painted,neath red-white-red (10-cm) rainbow pictographs, below a large located high above Feron Creek in the western San Rafael Swellbird figure from Ceremonial Cave, Canyon de Chelly, Ariz. region of Utah. The main -2-m-diameter rainbow shelters a triad

of large ceremonial figures, along with numerous concentric circlesand other figures. To the right of this panel are a red-white-redrainbow and a single-arced rainbow that spreads from the out-stretched hands of a horned Fremont anthropomorph.


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Plate 37. Multicolored (40-cm) rainbow from a small shelter in Plate 38. Pictograph of a decorated Jornada froglike creature from

Red Hole Wash in the western San Rafael Swell region of Utah, also a small rock shelter near Chloride, N.M. The rainbow arc that

containing red Fremont anthropomorphs. This figure depicts the spreads from the fingertips of this zoomorph is -25 cm in diameter.

proper colorization for the primary rainbow and also encloses con-

centric circles that could represent the approximate antisolar point.

Plate 39. Hissink's ellipticalhalo in Kuopio, Finland, on 18Feb. 1988 at 10:36 GMT. Thevertical diameter of this phenom-enon is 10-11°. Photograph byJuhana Hakumdki.

Plate 40. Schlesinger's elliptical halo (ver-tical diameter -7°) in Kuopio, Finland, on13 May 1989. Photograph by Juhana Ha-kumaki at 10:13 GMT with a 28-mm lens.Hissink's and Schlesinger's elliptical halosare as of yet theoretically unexplained phe-nomena to the best of our knowledge.


finnish halo observing network: search for rare halo phenomena

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