Monday, March 26, 2007

A spring-starter in Finland

On 25th March a relatively small high-cloud area swept over Southern Finland and produced a fine halo for observers in Helsinki, Espoo, Turku and Riihimaki. In Riihimaki the upper Lowitz arc was continuously in the sky for over three hours. In addition to Lowitz, there were also pyramidal crystal halos (9 halo/column arc?, 24 lower plate arcs, 18 plate arcs), helic arc and Wegener anthelic arc.

The photograph above is taken by Jukka Ruoskanen, and more photographs can be found here. In Helsinki the display was photographed by Marko Riikonen, in Espoo by Panu Lahtinen and Timo Kuhmonen and in Turku by Ismo Luukkonen

4 Comments:

Blogger Michael Ellestad said...

Nice catch Jukka!! I got wegener and heliac arc last year and around mid year a lower 23 degree plate arc.

29 March, 2007  
Anonymous Anonymous said...

One comment? ONE comment? I'd say it is a pretty cool display. Has anyone tried to simulate it?

Walt

31 March, 2007  
Anonymous Anonymous said...

Similar looking display by Petri Tuovinen (without odd radii) is in here:
http://www.ursa.fi/ursa/jaostot/halot/umi/1985/varit&valot685.pdf

Pages 10-11. The occurrence of upper component from Parry-Lowitz orientation and middle/circular component from plate-Lowitz orientation together is seen also in some other photographed displays. It's realy buggin me.

Marko

01 April, 2007  
Blogger Les said...

>Has anyone tried to simulate it?

Last weekend after playing with different single crystal populations for a time without success, I finally
tried two different populations.

These reproduced (1)the strong
upper Lowitz arc near the UTA and (2)the traces of the middle arc
_without_ producing (3) strong upper and lower arcs showing near the parhelia. These are absent in the image.

Sim here.

Populations:
1) Parry - Lowitz columns with (hexagonal) rhombus habit cross section 18deg sd tilts
2) Plate - Lowitz thick plates
with (hex) rhombus habit cross section 36deg sd tilts.

The strong middle Lowitz arc near the lower tangent in the simulation remains problematic - but one could argue that this was masked in the display.

OK, no one will believe it! But then other Lowitz displays give problems.

Les

01 April, 2007  

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