Saturday, 29 December 2007

halo search engine

Google has created a new service, "Custom Search Engine". I used this service to create a "Halo search" - search on all good sites dedicated to halo phenomena. This service can be used on any webpage (simple script), or on the home search page.

For example, when I try to search Minnaert's cigar in Halo Seach - I get 3 links, then try to search in a google "Minnaert's cigar" - 4 link, then in google, but Minnaert's cigar (without "") - 341.

You are welcome to use and improve it.

Monday, 24 December 2007

Crystal Swarm Effects

Divergent light halos can exhibit peculiar effects that are attributable to a homogenous or nonhomogenous crystal swarm. Here we present two such effects, where different parts of the "Minnaert cigar" are present in halos.

Image 1 displays a strong upper tangent arc (the whole frame and a crop is provided). It consists of two distinct parts: the upper part formed in bright separate glints and the lower more diffuse part. The diffuse part of the arc is formed in crystals further away from the camera, narrowing along the Minnaert cigar towards the lamp. The upper part is formed in crystals closer to the camera.

It is perhaps worth pointing out that the Moilanen arc is visible only in separate glints. This suggests that in this display it only formed in crystals closer to the camera, hit by relatively non-divergent rays.

The crystal swarm was homogenous as it had already travelled few kilometres from the snow guns. Total exposure time for the image 1 is 630 seconds.

Image 2 presents two photos of different stages of a display. During stage 1 the halos look familiar: 22° halo, upper tangent arc and Parry arc among others are present. During stage 2, however, some curious changes have occurred. It looks like the tangent arc has shifted towards the lamp. Also, less clearly, there is a section of an additional circular halo on the left, apparently having the same radius as the shifted tangent arc.

The effects observed during stage 2 must be caused by inhomogeneity of the crystal cloud between the observer and the lamp (the snow guns were right next to the point of observation). The crystal swarm was more concentrated close to the lamp causing the shift of the tangent arc and 22° halo along the Minnaert cigar. This is supported also by the weakening of these halos at their normal radii, formed in close by separate crystals (compare to stage 1). An animated gif is provided for an easy comparison.

These shifted halos represent a vertical cross section of the Minnaert cigar close to the lamp. Horizontal cross section of 22° halo has been documented on snow surface, as shown by these photographs: surface halo 1, surface halo 2.

Marko Riikonen & Jari Luomanen

Sunday, 16 December 2007

Diamond dust shocks in Hyvinkää, Finland

On the evening of 13th December the temperature was dropping fast and moisture level was above 95%. It was time to go. And what an evening it turned out to be! Very good crystal material created amazing halos in the beam of a portable light or car headlight. A crystal swarm lasted typically less than 15-30 minutes at a given location and then the search for another good spot started. Later in the night I was able to enjoy a display for maybe an hour at a completely dark field. During that time I had time to lay on my back (while the camera exposure was ongoing) and absorb the amazing sight.

There are several interesting features in the photos (blue spot, the "dark loop" on top of diffuse arcs etc.). On the attached photo there is a rough draft simulation illustrating the different intensity effects. Obviously fine tuning has to be done. More photos and some text can be found here. A more detailed description will follow after I have had time to concentrate on the photos and simulations.

Saturday, 15 December 2007

Home Made Halo

During the past year and a half I have tried to figure out how to build a Snowgun. Or, rather, an ice crystal gun since snow is not needed for creating halos. Hence, the objective has been to construct a "halo gun".

After some unsuccesful experimenting I came up with an idea of mixing small amounts of kaoline with water and spraying the solution into air. Kaoline is low cost material mainly used in ceramic industry. The halo gun itself is a simple device: all is needed is an air compressor and a paint spray gun.

On 28 November the weather finally allowed for testing the device. When sprayed into air the solution immediately transformed into ice crystals. I followed the crystal swarm to a nearby road to see whether it created any halos. It certainly did. After the second spraying the halos got even better. I observed both 22 and 46 degree halo, CZA, UTA, M-arc, parhelia, and parhelic circle. The above photograph was captured during the peak of one halo gun generated display.

The halo gun even worked with hot water which prevented the nozzle from freezing. Without Kaoline I was not able to produce ice crystals, regardless of the temperature of the water. Clearly, kaoline plays a huge part in the nucleation process.

Thus far the highest temperature where I have successfully created haloes using this method has been as high as -2 degrees celsius. This ice nucleation temperature is significantly higher than what is cited for Kaolin in various sources in literature. Similar high-temperature ice nucleation characteristic is known for Pseudomonas syringae bacterial protein, which is commonly used to intensify snow production in snow guns.

In January we will go with a small group of people to Kilpisjarvi biological station in the northhernmost Finland to experiment more thoroughly with halo making.

Monday, 10 December 2007

Divergent light effect around power cables

This divergent light effect was observed around power cables that reflected light from a bright lamp. The lamp was positioned behind and above the cables. The bulb of the floodlight can be seen through the dark filter.

The photographs were shot between 1 and 2 am, 29 November 2007 in Tampere, Finland. At the time of the observation the ambient temperature was -4 - -3 degrees Celsius.

The cables’ surface appears to reflect light very well. The effect was visible from a rather narrow sector only. As the observer moved sideways, the effect disappeared. At the peak of its intensity, when the telephoto shot was taken, it was very bright. The effect was clearly defined as is shown in the photographs.

Divergent light parhelia as well as upper and lower tangent arcs were also observed. The divergent light upper tangent arc can be distinguished as the diffuse glow above the lamp. In the telephoto shot it manifests itself in the individual crystal trails between the camera and the cables. In this sense, the image shows two halos on top of each other. Strong pillars and UTAs were observed above light sources further away (see image 2).

The effect around the cables had a 3D appearance, like a vortex or a funnel, but it did not extend towards the observer. Rather, it seemed to encapsule the cable. The other halos that formed in the light of this lamp had a strong 3D character. Both tangent arcs as well as the parhelia arched along the Minnaert’s cigar from the eye of the observer towards the lamp. Unfortunately, this 3D effect cannot be satisfactorily captured in a still photograph.

Earlier that night it had proved difficult to photograph crystal samples due to high temperature. Towards the end of the display the temperature had risen to -3 degrees Celsius. Hence, no crystals were photographed during the observation. However, the known halos observed suggest that singly oriented columns and plates were prominent in the crystal population.

At the time of the writing (10 December 2007), the cause of the effect remains unknown. Hypothesises concerning the nature of the effect are most welcome as are previous observations in case there are any.

For larger images, see here.

Saturday, 8 December 2007

New home for Halo Reports

Because users are increasingly unhappy about the terms of use for the Blogger, we have decided to move the Halo Reports to another server. The new home is at the Ursa Astronomical Association server. Veikko Mäkelä made all the ground work. No more postings can be done to Halo Reports here, at the Blogger. With time, we try to move the old postings to new home so that the Halo Reports here at Blogger could be permanently removed.

The panorama is from Rovaniemi in the end of November.

By Marko Riikonen

Wednesday, 5 December 2007

Sky Haloes in Southern Germany

Although this year only few haloes appeared over Germany, I could observe the second complex halo display on Mt. Wendelstein. In the morning I saw my first subsun in this year, which appeared in freezing fog. Later a veil of cirrostratus from a low pressure area over the Mediterranean Sea crossed the Alps from the south. Under those weather conditions, large halo displays can be seen very often. In my own statistics, 80% of all larger halo displays appeared when there was a southerly stream of air over the Alps, or under foehn conditions. And also this time there was a large choice of haloes in the southern part of the sky, which lasted for about two hours and a half. Between 10.10 and 12.45 CET the 22°-halo, a bright upper tangent arc and a faint Parry arc, both sundogs with Lowitz arcs, the parhelic circle, an almost complete supralateral arc, a faint infralateral arc on the right side, and a complete sun pillar were visible. Unfortunately, the haloes appeared only over a small area on the northern rim of the Alps. So except of me, only my husband who was down in the valley at that time, could enjoy similar haloes.

By Claudia Hinz

Tuesday, 4 December 2007

More photos from three weeks ago in Rovaniemi

It seems putting the photos of the recent displays to my web page will delay. So, in a meanwhile here are two more photos of the display three weeks back.

When light source is at 0° elevation, some difficulties arises in identifying certain halos. Tricker arc and subanthelic arc merge together, as do helic and subhelic arcs. However, the subanthelic arc is formed by Parry-oriented crystals, while Tricker arc is from singly oriented columns. Because in this display the 46° supralateral arc is rather strong, and there are only weak indications of 46° Parry or Tape arcs, probably singly oriented columns were in command. The even brightness of the Tricker/subanthelic loop is also typical for Tricker arc. Subanthelic arc has strong brightenings on the sides - at least in the simulations - and that is actually what seems to be present in the the display of last weekend.

The reason why halos are seen so strongly in the halogen light is probably the relatively dark background sky as compared to sun or moon situation. Yet all the halogen lamp displays that I have photographed so far have been hampered by city lights. Once the crystal cloud drifts to the dark outskirts of the city, more intense appearances should be expected.

By Marko Riikonen

Monday, 3 December 2007

More results from the latest display in Rovaniemi

Here is some more material from the diamond dust in Rovaniemi three nights ago. After the heaviest Parry-crystal bombarding was over, Moilanen arc appeared, as shown in the photo on the left. Moon gives the beauty spot.

I have crystal photos from this stage, but as usual, they give no clue to Moilanen arc. In the earlier Parry-stage there was no indication of Moilanen arc whatsoever, but I did not manage to get the crystals. This bugs, because comparing the samples might have pushed us forward in solving the mystery.

The upper left image shows parhelia from streetlamp - the stripes that are parallel to the electric lines. Then there are also arcs extending slightly obliquely downwards. While visually parhelia curved towards me, these other arcs curved away and around me. As far as I understand from looking at divergent light simulations by Lars Gislen et. al, this effect is a 120° parhelion. In the photo only the brightest part of 120° parhelia is seen, visually the crystal glitter extented much further. Also a full parhelic circle was seen visually.

The lower left photo shows what was seen around the half moon at its best. For long time there was hardly no moon halo, although in the beam of the halogen torch a great display was present. Some indication of Lowitz arcs is present in the moon photo. The crystal sample may be representative of this stage, but I am not sure. Crystal photos of Lowitz displays are also very welcome

By Marko Riikonen

Saturday, 1 December 2007

Another halogen lamp display from Rovaniemi

A bright halogen spotlight and diamond dust is a magic combination.

Spot yourself exactly in the middle of the beam and breathtaking halo views may rewards you. An outsider will see just somebody bathing in the light and may wonder what is going on. There might be a Moon in the sky at the same time - like in the case shown here - but it shows hardly no halos at all. The lamp creates its own universe of halos.

The Ounasvaara snow guns created this display last night in Rovaniemi in the beam of a Cyclops Thor Platinum X-15 halogen lamp. Because of the lack of 46° lateral arcs, this display must have been dominated by Parry crystals. Indeed, in the lower right image there are both upper and lower Tape arcs as an indication of Parry orientation.

An interesting feature is seen in the images on left (the lower image is an unsharp masked from the upper). There seems to be a loop inside the helic arc. Much like the loop formed by the subanthelic arc.

On the upper right is a simulation that shows a quite similar loop (arrow). The crystals in simulation are Parry oriented and they are semitriangular, a half way between a triangle and regular hexagon. The thing in the photo looks to me like a halo and it might be the one shown in the simulation. I have not raytraced it, so I don't know what it might be called. There are some differences in the loop sizes between the simulation and the photos, but then again the projections are not exatly the same.

A bit more could be said about the results of the last night, but this must do for now. The simulation was made with a program by Jukka Ruoskanen.

By Marko Riikonen