Sunset cumulus (Jul.31)

[Roman White]

Had some of photogenic weather on the evening of July,31. Just 16 hours before this year's solar eclipse.

This one is my favourite cumulus of July (note the "tail" in the right lower part)

Play of the shadows

Jupiter in early evening twillight with cumulus in the foreground

[Steveo74]

Fantastic shots Roman!   As I said I'm still learning the formations but they are great cumulus you have captured... 

[Roman White]

Thanks Steven. I may be not correct with this, but except of cumulus I can see some patches of stratocumlus (#2,3) and little scuds below that large Cu (#1).

It would be interesting to hear from the people who know, what do they think about this? Crop from #1 photo:

[brianb]

what do they think about this?

I think it's a small patch of an accessory cloud called pileus which is created by the wind blowing past the top of the thermal in the same way that wave clouds can be formed by wind blowing past the tops of solid objects like hills.

[Roman White]

I think it's a small patch of an accessory cloud called pileus (...)

Well, I have a doubt that the structure within a green rectangle was pileus.
1) as many times as I have seen pileus, they were forming above the cumulus. And this one is extending from the side in the lower part of Cu.
2) pileus are more thin and have more gentle forms than nearby Cu.

I can see possible pileus on this photo also (red rectangle)

[martinastro]

Nice sun angle on those Mediocrus. 

There's no Pileus Cap on those clouds because the Mediocrus cloud does not have a strong enough updraught to produce one. A Cumulus Congestus is the next stage in development from the Mediocrus, these do produce the cap.

http://www.stormeyes.org/tornado/SkyPix/pileus.htm

[brianb]

Martin:

There's no Pileus Cap on those clouds because the Mediocrus cloud does not have a strong enough updraught to produce one. A Cumulus Congestus is the next stage in development from the Mediocrus, these do produce the cap.

Roman:

as many times as I have seen pileus, they were forming above the cumulus. And this one is extending from the side in the lower part of Cu.

They form above the cap but the cap can then burst through the pileus.

So what is it then? Not vellum, not extensive enough. Not incus, cloud doesn't seem to have enough vertical development to reach the freezing level.

[Roman White]

Martin, thanks for your comment. I have seen several beatiful pileus over the Cu Cong. and even simple Cu (smaller than this one on my photo). But even when I had camera near me, I was late to capture as they quickly disappeared 

They form above the cap but the cap can then burst through the pileus.

Yes, it can. But more often it cannot do that.

So what is it then? Not vellum, not extensive enough. Not incus, cloud doesn't seem to have enough vertical development to reach the freezing level.

Brian, I don't know, that's why I'm asking. 

[martinastro]

This is from wikipedia...

''Pileus (Latin for cap) is a small, horizontal cloud that can appear above a cumulus or cumulonimbus cloud, giving the parent cloud a characteristic "hoodlike" appearance. Pilei tend to change shape rapidly. They are formed by strong updrafts acting upon moist air at lower altitudes, causing the air to cool to its dewpoint. As such, they are usually indicators of severe weather, and a pileus found atop a cumulus cloud often foreshadows transformation into a cumulonimbus cloud, as it indicates a strong updraft within the cloud.

Clouds that are attached to pileus are often given the suffix "pileus" or "with pileus". For example, a cumulonimbus cloud with a pileus attached to it would be called "cumulonimbus with pileus".

From the cloud appreciation society...

Enlightened meteorologists will tell you that the ‘pileus’ is not so much a cloud as it is a cloud haircut. It is a supercooled-droplet bouffant, worn exclusively by the fashionable cumulus family. If you keep your eyes to the sky, every once in a while you’ll notice a proud cumulonimbus thunder cloud or his younger brother, the cumulus congestus, wearing this dashing haircut.

The pileus can form when a towering cumulus, like the suave model shown above, is pushing a moist layer of air upwards as he grows. If conditions are right, this elevation can be enough for the moist layer to cool and form into droplets, appearing as a smooth cloud over the cumulus congestus’ puffy summit.

But cloud fashion is more transient than most and, as the cumulus cloud continues to grow, his head soon pokes through the top of the pileus cloud. Within a few short minutes, it has slipped to his shoulders, leaving the poor fellow with all the indignity of a lopsided wig.
 
http://www.cloudappreciationsociety.org/pileus-may-%E2%80%9905/

[John9929]

I have just seen this thread about what a Pileus Cap should look like. Here is one I imaged on
September 24th 2007.

[Steveo74]

Guys! This is way off the track but since we are talking about clouds, I was going through my cloud collection and found these.  They were taken in April and it had just bucket down.





What ya think? 

[martinastro]

That's an excellent example of a Pielus Cap John. Text book actually. 

Cool cloudscapes Steven. That looks like a big sucker in the background producing the showers. What direction was it moving?

[Steveo74]

Thanks Martin, If I can remember I think it was heading SE...