Greetings and Introductory Post

[Rich West]

Hi everyone

I am a Brit who has become interested in meteorology over the past six months. I started off wanting to learn some cloud progressions to be able to make a short term prediction for the purposes of prioritising tasks in a bushcraft and/or survival situation. However, I started noticing little things like transitional clouds to bigger things like clouds in the sky under an anticyclone which raised questions not clearly answered in my accumulating meteorology library. I am sure they may be answered somewhere but at this precise moment I need to find things out with enough details but not too much. I wanted to do a meteorology course online but our Open University here does a short course which seems to cover the things I have access to but doesn't do anything further and there seem to be no opportunities for an online degree. In lieu of this I wanted to join a community of enthusiastic folks with whom I can discuss these issuss with and also in the long run as I learn more to help out those with less knowledge.

My introductory question relates to the anticyclone I have been observing. When I first saw stratocumulus clouds in a firmly established anticyclone I was surprised. Subsiding air will be lowering and warming layers not maintaining them I reasoned. My next thought was that the divergence zone must be at an altitude just above the cloud layer and indeed after much hunting I found one diagram on a site showing this. However, it begged the question that if the air is diverging above the Sc then the layer between the ground and the top of the sc is either stationary or rising air to keep the Sc layer formed and if this is true then why is the ground pressure still reading high when air is not subsiding here?

As always I am very grateful for help given.

Cheers and all the best

Rich

 

[Dave Gallaher]

I will leave your question to the better brains and educations here, but welcome to the board. Hope you will enjoy and contribute.

 

[Rich West]

Hi Dave

Thanks for the welcome (and the only reply!). I do hope someone will be willing to help because I have question constipation ....my next one was about the recent frontal systems extending right through the anticyclones we have had.

All the best

Rich

 

[Keith Wilson]

Welcome to Stormtrack Rich!

 

[Shawn Gossman]

Welcome to ST, you picked a great forum to join

Sent from my DROID3 using Tapatalk

 

[Greg Blumberg]

Hi Rich, I can take a shot at answering your question.

What I think you are dealing with is the breaking of a conceptual model. The conceptual model you have is that the anticyclone will always have warming and subsiding motions, but it's not fitting with your observations. I think this is great because you're starting to revise the model you know of to make it fit your observations. That's a big part of what meteorology is about. Let me give you a push in what I think is the right direction.

One primary reason this clouds could exist is that you are dealing with very different scales of vertical motion. The warming and subsiding motions we speak of with an anticyclone is associated with synoptic scale vertical motion, in which you have large scale warming and subsiding motions (I'm talking about this downward motion over a horizontal distance of 1000 km of very slow descent of air (about 1 cm/s.) There are many other speeds and horizontal scales of vertical motion that could be going on to produce the stratocumulus you speak of. So just because you have an anticyclone, doesn't mean that every place has downward motion and thus you don't get any clouds or any rain. This is just a rule of thumb. There are many different scales of motion in the atmosphere, and the processes that govern those we sometimes can see and sometimes can't. This is part of the reason why it's hard to answer your question, is because it's hard to pin down the why with just a single visual observation!

 

[Rich West]

Thanks for the welcome Keith and Shawn.

Many thanks, Greg, for engaging with me. Yes, luckily I had some good physics training many, many years ago and enjoy both observation and model checking

Yes, the model I found showed the air wasn't subsiding below the top of the Sc layer in that anticyclone, at least. You are now pointing me into the direction of other pressure systems having areas of differently moving vertical columns I see. This is very interesting as I have some questions for later- on the cyclonic conveyors.

If the pressure is diverging at the Sc top then could the ground pressure still show a high barometric reading?

Cheers and all the best

Rich

 

[Rich West]

Continued: My guess is that it wouldn't and therefore there is something else going on in a system where the diverging air is above a Sc layer. It would be logical for an extensive Sc layer- as I had on the day of my observations (and would be present in anticyclonic gloom conditions) - to indicate a wide area cut off from the descending air reaching the ground. However, my barometer was showing high pressure on the day. Which point of my reasoning is incorrect or is there another thing I am missing?

The variation in local vertical air columns I am guessing will explain how the cold conveyor in an extra tropical cyclone can be descending. I haven't noticed a specific pressure change just after the observed cold front passed, that would indicate this subsiding air..just a gradual rise as the ridge afterwards was moving in. However, I think there should have been. I may have missed it- what order of change could this conveyor bring?

Also one thing from the last week. The MET office issues daily surface charts. These have shown a number of frontal systems lately but there has been no sharp temperature changes (the temperature has remained high for February) and the rain has been very mild and short, although we have had extensive alto stratus at points, extending into nimbostratus on one occasion at least, BUT no other frontal changes being observed. Not only am I confused by frontal systems extending into high pressure areas (we are under anticyclonic curvature from the top of the Azores High) but I am confused about the following: My obs show the air temp to be stable and varying (I propose) only by diurnal and cloud cover events. The air coming up from the south is Atlantic mT air, which explains the warmth. However, the METs fronts will only agree with this in the warm sector according to basic theory. Either side of that the air should be cold, but if it is all coming in on SWesterly winds following the general anticyclonic isobars then there is a problem. Can you help with this too, please, Greg?

I know this is an awful lot of stuff but I think it boils down to only a few basic principles (I hope). Until there is a distance learning/online degree course I am left with no option but to pick you good folks' brains

Thanks in advance to Greg and anyone else that will jump into the fray. Cheers.

All the best

Rich

 

[Greg Blumberg]

Hi Rich,

Do you live in the UK? I'm needing some perspective of what you're noticing. Also, could you post the maps you're looking at? I have an idea of what's going on, but I need to know more about your location.

Greg

 

[Rich West]

Hi Greg

NE Scotland. The original impetus for this post occurred a few months back so dont have the pressure maps anymore, sorry. However, I was thinking that the issue must be generic as anticcylonic gloom caused by Sc covering the whole sky is a common phenomena I am guessing, judging by it being given a name.

Best

Rich

 

[Rich West]

Re: frontal part of question: http://www.metoffice.gov.uk/weather/uk/surface_pressure.html 12 UTC 28th Feb 2012 is a reasonable (not the best) example of the fronts impinging into an HP system. The warm front is shown reaching down to 1024mb and close to the High centre. I have seen cold fronts on previous charts that extend right through larger HP systems too.

 

[Rich West]

OK as no-one has answered my question I will take a stab myself now that my tears have dried.

The air below Cirrus and above Stratocumulus is descending as it should. The air from ground up to the top of Sc is stationary, however, I think the subsiding atmosphere might be compressing the stationary layer and thus causing it to be high pressure too. Obviously I can't say for sure as the experts are silent but that's my newbie guess.

The patch of Ac that came through the HP system the other day is a result I am guessing of orthographic lift by the local mountains.

All the best

Rich

 

[J Tyler]

Hi Rich, and welcome.

I would suggest you start a new thread and give it a title that includes your question. Reason being, when I saw your title, I didn't bother to read it for several weeks because I assumed it was just a new member introducing themselves and saying hello. I'm willing to bet that when others see the very interesting topic you are discussing, they will jump in. I would love to help, but this is way above my pay grade (ie, I'm not smart enough!). Enjoy your time here!

 

[Tim Supinie]

Hello and welcome, Rich! Though you've apparently been here for a month already.

I agree with what Greg said about the conceptual model breaking down. On the synoptic scale vertical motions are usually about 1 cm/s, so they might be easily disrupted by things that aren't on the synoptic scale (like orographic forcing you mentioned). The same general idea goes for fronts through high pressure areas. Perhaps the front was drawn along a coastline, so the air on one side was influenced by the land (warmer during the day, colder at night) and the other was influenced by the water (less diurnal fluctuation).

I'm not sure what sort of data the UK Met Office uses to draw those maps, so I can't say as to the thought process behind placing their fronts.

 

[Rich West]

Hi Jeff and Tim.

Many thanks for the welcome and posts.

I will take your advice Jeff and repost. Cheers

Tim, I agree that local effects can overcome the overall downward motion- we both emntion orographic lift in regards to this. However, I proposed the compressed air hypothesis as it is common for stratocumulus clouds in HP systems to be widespread and not local, plus they do not seem (from my limited experience) to necessarily have anything to do with any surface features or boundary conditions. What do you think?
With regards to fronts, your idea sounds very interesting and I will see if the maps over the next few weeks or months provide any supporting evidence that I can see. Cheers.

All the best to you both

Rich