Monday, September 18, 2006

Lowitz arcs in Czech

Martin Popek observed this display with Lowitz acrs on 16. September. Interesting feature is the lower Lowitz component extension above parhelion. In the simulation there is something like that, but it's very, very ghostly. The main body of the lower component below parhelion looks as if it were just a patch of 22° halo - the extension towards parhelion is missing. Same goes with the upper component. This is quite typical way of Lowitz arcs showing up. Circular component is seen only above parhelion.

I was given sun elevation of 39° for this display but somewhat lower elevation gave a bit better simulation results. This is for 33°. The projection in the simulation is clearly not the same as in camera and this may have caused some of the broblems. Simulation is made with Halosim by Les Cowley and Michael Schroeder.

Be the sun elevation 39° or 33°, it does not change much anything fundamentally. Several question could be raised about this display with lenghty discussions. It seems we still have a long way to understanding Lowitz arcs.

4 Comments:

Blogger Michael Ellestad said...

Marko I got a similar display like that in 2004 and all three arcs were there and circular lowitz was long and the lower lowitz arc was quite bright and so was the upper. There was also parry arc too.

19 September, 2006  
Blogger Les Cowley said...

Marko,

Was the HaloSim simulation made using the classical Lowitz orientation and regular hexagonal plates? As with other Lowitz displays, more restricted orientations and other crystal habits may be necessary.

Les

19 September, 2006  
Blogger Marko Riikonen said...

Two populations. One with classical spinning orientation and regular hexagons made upper and lower components. Other with restricted orientation and non-regular hexagons made the circular component.

This is tricky case.

19 September, 2006  
Blogger Marko Riikonen said...

Well, why not put the simulation that I made first. It's for 39° sun elevation. There are the same two populations as explained above, but this time the spinning lowitz population has 4 degs rotation, which removes the parts that extend towards parhelion.

Here

19 September, 2006  

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