2010. december 26., vasárnap

Faint halo

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Now anyone can photograph bright halos, but what about the faint halos? The pillar in light clear sky snowfall is prominent here, but the parhelia in the other photo is less so. Not faintest possible, sure, I gave it even some contrast with slight usming. Also shown is factory exhaust plume. This is still rather minor, it was not that cold. The photos are from 22 December 2010.

2010. december 25., szombat

Reflected Lowitz arcs on 14 December 2010

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I spent whole day out on Pyhäjärvi ice to look for this display. In the beginning had to do some running to get inside the diamond dust which was at the far end of the lake. Reflected Lowitz arcs are seen in stacked images. A reminder of Moilanen arc and helic arc are also present.  Yet another helic arc without Parry arc.  Sometime after midday the the diamond dust vanished and I started to pack up to walk back about 4 km to car. But this was a very short lived moment and the diamond dust enshrouded the place again and I stayed untill sunset. At the end there was only sun pillar. Tempereture was below -20 C.

2010. december 24., péntek

Light pillars 15/16 December

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Some pillars in Tampere and Ylöjärvi. This was the last night the snowguns were running in Tampere.  Temperature was around -25 C.

2010. december 21., kedd

Sun pillar and moon corona 21 December 2010 in Joensuu

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Some elementary stuff. Although there is high cloud, light snowfall made the sun pillar. In the evening there was moon corona. Took a hdr set and worked it with FDR-tools, which is good for coronas.

Floodlight helic arc on 15/16 December 2010 in Tampere

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This one was seen from automatic gas station lights. The helic arc is rises diagonally from the lamp. I was desperately looking for a place for the spotlight, but the surroundings were totally light polluted. Just 300-400 meters away it was totally dark wilderness, though, but the diamond dust never reached there.  So I just photographed the halos in this light. I walked closer to see if I could see 3D structure in helic arc, but as expected, it disappeared.  The tangent arc had no seagull shape at the appropriate lamp elevation, indicating presence of Parry arc, which certainly was there.  The helic arc is doubled because there are two lights.

2010. december 20., hétfő

Spotlight display 15/16 December 2010 in Tampere

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This one came as an almost complete surprise. I had seen moment before parhelia from streetlight when driving, but they were weak. The pillars were almost non existent, so when I parked at the hospital area and turned on the long lights, I was surprised to see the crystals glitter in the beam in a very much all sky display manner. This was confirmed as I walked the beam.

Taking on the spotlight took some time and I did not get much photos. There was also serious light pollution. Just a bit further away towards the lake it would have been darker, but you have to take the first photos where ever the display is, or you risk not getting photos at all (this wisdom Luomanen told me recently).

Simulations of the display are made with Jukka Ruoskanen's HaloPoint 2.0. The most interesting point to me is the 5 degree rotational Parry population that had to be used to get the intensity of the diffuse B arc right. Nothing new here, of course, this kind of effect is pretty common in the spotlight displays. Lessen the rotation and they turn into subanthelic arcs. The Parry population makes also right kind of brightenings at Tape arc locations. Should they be called Tape arcs or 46° supralateral arc, is probably a matter of taste.

In simulation the subhelic /helic arc (they overlap at 0° light elevation)  is too intense as always. Perhaps the Lefadeux hollowed crystal simulations could fix it.  I have included also simulations showing the diffuse anthelic arc A and B components (well, actually they are independent halos), which are clearly discerned in the photo. In sun displays these are less easy to distinguish, which is why we normally talk only about the diffuse arcs.

Temperature was around -22° C. It is rather unusual to get column (or Parry) stuff at these temps.

2010. december 19., vasárnap

Spotlight Moilanen arc and windshield subparhelia

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Some stuff from the night of 11/12. December 2010 with Luomanen. We took replicas of the Moilanen arc display, but they failed. Could have been an enlightening case.  On the windshieldd there was also parhelic circle, cza, cha - the usual stuff. Luomanen is holding the lamp.

2010. december 18., szombat

Halos from Mustavuori snowguns 12 December 2010

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Mustavuori snowguns made this display. Some driving around and quick stops were involved as the diamond dust changed its location. Moilanen arc occurred on two stages, better second time. The photos of it above are 101 and 120 seconds stacks with 43 and 52 frames respectively. Crystal sample was taken, but too late, the display started soon vanish as I got the dish out. There were not much crystals in the sample and nothing special shows up in the two photos.

There is faint helic arc but no Parry arc (not even with heavy usm). Helic arc occurs pretty much in any diamond dust halo display. It has been seen even with sun pillar only. The question is what kind of helic arcs these non-Parry occurrences are? Do they arise from the same angle as Parry helic arc? If not, how many different helic arcs there are? Should probably compare this one with simulations, it comes out pretty strong with heavy usm (checked that, it has the same angle as normal helic arc).

The photos with sun in it has a pretty strong overexposed area. I have had Nikon D70 for about 5 years and this has always been the problem. Only now I realized that blocking the sun is the cure for it. So, in the future photos there will always be blocker. Actually, it is good to stack even the smooth diamond dust displays. Earlier I did not think it would help much, but it does.

2010. december 16., csütörtök

Hole punch cloud 14 December 2010 in Tampere

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I went to check the diamond dust even though it was cloudy. There was nothing, as expected. I was reporting in the phone to Luomanen the situation when hole punch cloud caught my attention. The Ac was probably the slowest moving I have ever seen and there was plenty of time to photograph this. Much different from the other hole puch a few days earlier in Hervanta, which moved and changed really fast. I have never seen hole punch clouds before and now two cases in the row!

2010. december 9., csütörtök

Column crystals halos on 8/9 December 2010

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Halos from column orientation were the main feature of this night in Tampere. In the beginning I was looking at the display with Luomanen but we did not have cameras. The display sort of took us off guard, it was thickly overcast and temperature at -5 C.  Anyway, Y-pillars were visible in Hervanta and we got crystal replicas at least.  Closer to the streelights beautiful circumscribed halos appreared, but it looked like there was some tilt involved. Columns with hollow ends in the replicas.

Later I continued on my own and took photos under streelight near Mustavuori.  Took also crystal photos - the crystals have become more equidimensional (the temp also had dropped to -7 C). Plenty of triangles (the photos above are all from this live sample) which probably have been falling in Parry orientation but Parry was impossible to distinquish under the lamp. Certainly triangular thick plates do not take plate orientations because there was no sign of plate halos in this display. Kern from triangular plates is only theoretical consideration.

For the last I went back to Hervanta where I photographed the Y-halo from the police training area floodlight. Also helic arc is visible. At some place there was also parhelia. The display lasted several hours and who knows how long it had been going on before we entered the scene.

2010. december 4., szombat

Diamond dust halos from Kontiolahti snowguns on 1 December 2010

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It was cold morning, at lowest the car showed -31 C. I drove to Mustavaara but guns were not on. But at the distance about 10 km away I saw there was swarm at Kontiolahti biathlon stadium so I drove there and got this little display from lake Höytiäinen ice. The ice fog was a bit too thick and Ac was taking over the sky. Temperature at the location was around -25 C.

Light pillars and submoon from Mustavaara snowguns on 29/30 November 2010

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There are two rules for success in seeing diamond dust halos. First you have to go where the diamond dust is. Second, when you think it is time to go home, you don't. On many nights I am actually going back to home two three times, but turn back and get results. There should be a rule for example for the cases when the sky turns overcast: don't go home until after you have waited minimum 1½ hours. Often ehough I have noticed how the sky has gotten soon clear again on the way home.  And you never go home when the diamond dust is on the treshold.  Treshold conditions may last hours but eventually the diamond dust develops. It may not be untill the early morning hours, but it develops.  And even if the diamond dust is not that good, you don't go home. Change in wind direction can make dramatic changes in halos.

This night I did not have to wait for the condition to develop. The swarm was on as I arrived to the scene soon after darkfall, temperatures around -25 C.  But it was not that good, only weak pillars were seen. But I waited and eventually in the morning hours got some photos in Heinävaara, where the swarm headed from Mustavaara. Nothing spectacular but the half moon submoon was really worth the wait. It was an eerie apparition, following by your side like a messenger from beyond.

2010. december 3., péntek

Diamond dust parhelia on 29 November 2010 from Kontiolahti snowguns

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I screwed up this one. The condidionts were on and I was waiting in Mustavaara for three hours for them to start the snowguns while there was actually diamond dust from Kontiolahti biathlon stadium snow gunning not far from Mustavaara. Eventuallly I saw the Kontiolahti swarm in the distance as I walked up the Mustavaara flank. After three km of driving I entered the diamond dust and got a couple of photos from parhelia against pine forest. The ice fog extended at least 12 km from the source, but I was still deep within. Who knows how far it reached.

Spotlight halos from Mustavaara snowguns 23/24 November 2010

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The moon halos disappeared as the cloud got thicker and I headed back to Joensuu. The wind was even stronger now, with snowdrift and snowdevils on the road and snow dropping off the trees. On the way at the quarry, however, there was a swarm and I took there some photos with positive and negative lamp elevation. Nothing special, but the photos show nicely the effect of varying crystal tilts on halos. Eventually the swarm died off and moon was shining again surrounded by 22° halo in high clouds.

Moon halos from Mustavaara snowguns 23/24 November 2010

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When it is windy you don't get diamond dust halos in Finland. For some reason (could it be that in still weather radiative cooling is stronger and thus relative humidity can rise to reach ice saturation?) there is not enought moisture in the air for ice crystal growth in windy weather. This night is was windy but I nevertheless drove 25 km to Mustavaara to check the situation. As expected there was no diamond dust and I was thinking of going back to Joensuu. Still it looked like it was on the treshold so I decided to wait. This paid off as eventually the ice fog from the snow guns starting spreading and 22° halo was seen in it. Further away the display was a bit better, with also parhelia visible (there was also high cloud in the background, which may have partly contributed to the display, in the second photo the 22° halo on the left is in high clouds). I tracked the cloud extent to 10 km from the source but at that time it was already receding, so probably it was wider at its best.

So this display broke the "no wind" curse for me in Finland. At polar areas where it is hardly ever calm, diamond dust halo displays seem to occur at any wind speeds.

2010. december 2., csütörtök

Spotlight halos from Mustavaara snowguns 17/18 November 2010

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The moon halo display vanished as it got eventually overcast. It was still low stratus with occasional fog on the ground, but apparently the moisture just became too much for the snow guns' ice dust to nucleate a hole. Diamond dust nevertheless continued under cloudy skies and I turned on the spotlight. It was rather good, plate crystals still in charge and with negative elevation lamp (about 11° below horizon) there appeared several "super"-halos (equal to "sub"-halos when light is above the horizon). All were visible to the naked eye, the superparhelic circle at the superanthelic region was bright. At its best the superparhelic circle extended all the way to the superparhelia but I did not get that stage photographed. At the same time was also normal parhelic circle visible.  I though of seeing a ghost of super-120° parhelion, but decided it was just white snow on the far hill. In the photos, however, super-120° parhelia are visible in a similar ghostly manner, so probably that was what I saw.

Getting these photos was mostly waiting. Mainly it was water fog, but then, for maximum few minutes at a time good crystal swarms swept by. In one exposure both water fog and diamond dust stage was captured so that there is also fogbow visible. In reality halos and fogbow were not much visible at the same time. Water fog and diamond dust don't just occur simultaneously. Eventually it got worse and I headed back to Joensuu. But on the way there was diamond dust at the quarry, 7 km as the crow flies from Mustavaara. So I took some photos there as well, climbing up a gravel mountain, leaving the lamp at the bottom and thus obtaining about 35° negative light source elevation.

Moon halos from Mustavaara snow guns 17/18 November 2010

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This display was a result of low Stratus turning into ice crystals. It was right on when I arrived with car to the scene, which made me regret my idling in the comfort of indoors. The nucleating agent was the ice dust from Mustavaara snowguns. Essentially this created a punch hole in the cloud layer. All around this few kilometers wide opening it was overcast. Moon was three days short of full and an all sky plate crystal display was seen. The best of the crystal swarm moved back and forth and I tried to follow it with car.