Multi Determination Factors

[Andrew Khan]

How can one determine or figure out if there will be lenticularis that day or perhaps halos around the sun or moon? I have heard if a cirrus layer comes through you'll likely see a sun halo, but the others I have no idea. I could use some help with this issue. There is a halo on the moon outside right now, in fact. I hace been trying to figure this out since last September....

 

[Susan Strom]

A 22 degree halo around the sun can also occur in a clear sky. In the Southwest, they are not too uncommon, but can be very subtle and hard to pick up on film particularly if they occur in a clear sky. Sometimes it helps to block the actual bright "ball" of sun a bit, perhaps with your hand or even an artistic object if one is available, showing only the halo, for a better picture.

Generally, if I were "halo hunting" I'd look for the presence of weather conditions that form ice crystals in the upper atmosphere. Cirrus formations create some great effects. High latitudes might even generate "mock" suns too (sundogs). Orientation/crystal direction influences halos and parhelia (sundogs). If I were a serious optics-hunter, I'd spend some time in polar regions.

Of course, optical effects, from irridescence to halos, vary with conditions...ice crystals aloft seem to be a common factor. If you have those anywhere...you have a chance. Parhelia would be more common at the poles. Although, here at the 34th parallel I can see 22 degree halos...simply because there is ice in the atmosphere oriented in certain directions.

Lenticular clouds are a different animal though, not dependent on ice but rather more of a temp/dewpoint process. Most of the ones I've seen while backpacking or skiing at high elevations.

A lunar diffraction corona is more common and diameter varies by water droplet size. That's why you can see small or large ones depending. The colors, if any, vary. Here's one from the desert.

Happy hunting. I like looking for those things too.

 

[Susan Strom]

Speaking of lunar coronas...a lunar corona does not necessarily require a sky/atmosphere.

It is possible to generate one, in very rare circumstances, by the mist at the base of a waterfall. My parents taught me how to find one when I was a child. It took special and rare conditions for it all to align perfectly, plus a hike to a rushing waterfall at 2 o'clock in the morning with my father while everyone else was konked out and warm in their beds, but lo and behold the darn thing was there. I remember what my dad said "That looks like a portal to another universe". It was quite a sight I have to say.

How to find a lunar rainbow (sans the sky):

Falls: Yosemite, California
Time of night: approx 2am
Time of year: May's full moon
Special conditions: Heavy spring runoff from a thick snowpack year
Falls condition: rushing, full, thunderous sound
Moon: Must be full
Sky: cloudless
Clothing needed: Rain parka; shoes with good traction
Hazards: Slippery surfaces, heavy mist, watch for loose rock
What not to do: Go off trail or near any water, rushing torrents of course, but not even near any still eddies or pools or climb on rocks.
What you'll see: A rainbow arc created at the base of the waterfall by the moon, with colors just at the ends.

How to photograph lunar rainbow: Fast film 800 ISO (transparency is preferred), B setting; bracketted exposure times and f-stops; heavy tripod, cable release, lens cloth/camera protection (cam and lens will get wet), wide angle lens. Or, you can just let that enchanting sight burn itself into your memory and let it stick with you for the rest of your life

 

[Andrew Khan]

Here was the halo from last night, as you can see, it was not nearly as big as others. In January of this year, Kurt Hulst and I witnessed a HUGE blue halo around a full moon, that lasted the entire night, but unfortunatly my camera was out of commision. Susan, did you capture that with film!

 

[Susan Strom]

Nice colors on that corona!

Yes, I shoot on transparency film...pretty much always.

 

[Greg Campbell]

Interesting question!

Predicting the conditions that favor Lenticular formation doesn't sound too hard. (Famous last words!)
You'd want a stable atmosphere - the energy released by condensation must not produce significant buoyancy, otherwise you'd get garden variety orographic cumulus. A layer of moist air, about mountain-top height, overlaid with warm dry air would be a good start. You'd also want dry air at ground level to define the cloud base. A local sounding should allow ballpark predictions. (Sure I'm missing something... :? )

The tricky part would be prediting the wind required to properly interact with a particular mountain. If the winds are too high, or too stronly sheared, I'd think that turbulence and mixing would run the clouds. Too slow, and the cloud might evaporate before forming a nice downwind cap.


Dunnow squat about high altitude ice crystal formation, so I'll leave the diffraction effects alone.

-Greg