Saturday, June 15, 2013

Halos and contrails: Is there a connection?

The short answer is YES!

Today I received pictures from several of you regarding some wondrous halos in the sky.  Others noted an  impressive collection of contrails...and there is no accident that both apparitions appeared at the same time:  the ultimate cause is the same.

Here is a very nice picture from Brendan Fields showing both appearing at the same time!

And from Jules submitted to the Seattle Times:


 A high resolution MODIS image from today shows an extensive collection of high cirrus and cirrostratus clouds  and if you look carefully you will see lines:  those are contrails!


Halos occur when rising air in the upper tropospherc causes condensation and the formation of ice crystal clouds (cirrus and cirrostratus).   When the sun's ray's intersect the randomly oriented ice crystals, the light is bent preferentially by 22 degrees...thus producing a 22 degree halo.

Contrails occur then the air is very near or at saturation, and the addition of water vapor from the combustion in the jet engines causes the formation of a line the of clouds behind the plane.

So both halos and contrails are dependent on the upper troposphere (roughly the layer of the atmosphere from roughly 15,000 ft to 35,000 ft) become saturated or near saturated.   We can tell whether this is true of the real atmosphere by taking the observations from balloon-launched weather instrument radiosondes)  and plotting the temperature and dew point temperature on a chart (a.k.a. a sounding).

Below is the sounding from Quillayate, on the Washington coast, at 5 PM Saturday.  Note the temperature lines (red) and dew point lines (blue) are very close together from 500 hpa (around 18,000 ft) to around 350 hpa (around 25,000 ft).    The atmosphere is either at or close to saturation in this layer (saturation is evident when the temperature and dew point are the same) .

This saturated layer is associated with rising motion from an east Pacific trough/close low (see image of upper atmospheric flow at 2 PM this afternoon), the ultimate cause of both the halos and contrails seen today.





7 comments:

James said...

My wife and I were hiking in the Capitol Forest today and saw at least three different halos all at once. Two of them were in a sort of Venn diagram arrangement with a third, larger one that was offset to the left. Is the positioning of the halos affected by the geometry of the high clouds or are there other factors involved?

Chris said...

Here's a shot I took of the (double!) halo when we were driving across the 520 bridge today!

https://sphotos-a.xx.fbcdn.net/hphotos-ash3/1001331_10201252870622373_1721400281_n.jpg

Bob said...

Chris' photo appears to show a circumhorizon arc in the lower part of the image. Very cool!

http://www.atoptics.co.uk/halo/chaform.htm

Beth Niquette said...

I love these photos and the description of why we see these wonderful sun rainbows.

I was able to capture a few shots of that amazing phenomena, too. I live in Oregon--and it is summertime, so the idea of ice crystals is pretty cool. (no pun intended)

Have a lovely weekend!

Ferdi said...

I do a lot of photography here in the islands and have often wondered how I can send you interesting weather pics. I don't see a way to attach them to comments here. There was a sun dog so bright last week it was reflected dramatically off the water. I would have liked to have sent that one. Is there a way to send photos to your blog that I'm not seeing?

Seth McOmber said...

We visited Butchart Gardens this weekend and had a lovely halo above us all afternoon. Not yet knowing about the 22-degree aspect, I foolishly laid flat on my back, trying to get a photo on my phone that captured the entire halo. My wife was not pleased to have me laying on the ground among the other tourists, but the photo turned out okay: http://instagram.com/p/apkcydjKiB/

Ramanathan's Blog said...

does it mean a bad weather is approaching?