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Originally Posted by simonrp84
(Post 18770328)
To go back to the air mass talk from the previous page I thought that this might be of interest:
http://farm8.staticflickr.com/7102/7...67cf399c_c.jpg A larger image is here: http://farm8.staticflickr.com/7102/7...7d5ef47e_o.png It's a satellite-derived map of air mass that we produce, this image is from yesterday afternoon. The air mass types are the same as BotB mentioned and also included is an indicator of whether the air is stable or unstable. Because it's from satellite data the image isn't a direct measurement of air mass type - we can't get that information directly - but instead it uses some clever tests on the data we do have in order to derive an indirect 'guess' or the air mass type. In most conditions it does a pretty good job but occasionally it gets confused - a few times I've seen it conclude that air over the Sahara is polar, for instance. I'll link to it in the previous post on air masses and include the additional types of air mass info... (Equatorial temperature and stable/unstable info) As everyone can see, there is a lot more of the mP type of air mass around, both in the Northern Hemisphere and Southern...also this image really shows the scale of the air masses, although there would be many smaller mP air masses that are separate in that big sea of green as well...just varying in the temperature and humidity levels of the mP mass... Interesting that over Africa you can see such large areas of very hot, very dry air that then also would be stable (as it has little moisture)... All very good tools to see where the moisture and convective regions can develop when forecasting and extremely useful when there are no other data points available such as over the oceans and uninhabited regions... I obviously need to go and check out EUMETSAT pages more! ;) |
Originally Posted by HIDDY
(Post 18772079)
A question BotB...I took a look at the Met offices satellite images for my area. It does show some cloud over the province but how do you tell if it's rain cloud or not? It's been constant moderate rain all day here yet the cloud shown looks quite thin.
So, first pressure, to see if the clouds are associated with a front or are just developments from the air mass...then the satellite pic...to see if the cloud is expansive or smaller individual type clouds, finally if precip is coming from that cloud now and together with the knowledge of time of day and direction the cloud is heading you can decide if it will continue to rain/start to rain, etc... Might be best to use some examples...I'm not sure I will have time tonight but maybe later this coming week I'll try to post some images of what i mean and see if that makes more sense? ;) |
Originally Posted by BotB
(Post 18772181)
Might be best to use some examples...I'm not sure I will have time tonight but maybe later this coming week I'll try to post some images of what i mean and see if that makes more sense? ;)
By the way they did forecast some rain here today but not as much as there has been. |
Really good to see the developments and what can be derived from satellite info now...thanks for sharing this I obviously need to go and check out EUMETSAT pages more! A question BotB...I took a look at the Met offices satellite images for my area. It does show some cloud over the province but how do you tell if it's rain cloud or not? It's been constant moderate rain all day here yet the cloud shown looks quite thin. The satellite is picking up rain over Buenos Aires today, though, but for copyright reasons there's a 24 hour delay until I can post a pic - I'll put it up here tomorrow. |
Originally Posted by simonrp84
(Post 18772476)
The satellite is picking up rain over Buenos Aires today, though, but for copyright reasons there's a 24 hour delay until I can post a pic - I'll put it up here tomorrow.
I'm sure BotB will be glad of the extra help. Just been out with the dogs and it's still raining here. |
After a slight delay caused by my forgetfulness here you go:
http://farm6.staticflickr.com/5451/7...daf72e4a95.jpg And in a bigger size also. That's from 1030 UTC on Sunday and the colors denote the probability that it's raining. Purple is highest, then red, then green, then brown. Around Buenos Aires the average probability was 40-50% but there's occasional patches of 60-70%. I have just noticed that it says there's a 90% probability of rain over my house at that time and I remember it was quite sunny - so like I said this is not completely accurate :D |
Originally Posted by simonrp84
(Post 18780899)
That's from 1030 UTC on Sunday and the colors denote the probability that it's raining. Purple is highest, then red, then green, then brown. Around Buenos Aires the average probability was 40-50% but there's occasional patches of 60-70%.
I have just noticed that it says there's a 90% probability of rain over my house at that time and I remember it was quite sunny - so like I said this is not completely accurate :D It's been dry since....bit gloomy this morning though. |
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Originally Posted by BotB
(Post 18770147)
Hope the new job goes well, congrats! Make sure to take lots of cloud pics when travelling around and back to the UK ;)
Kind of you to ask about making this a sticky but I don't imagine it appeals to enough of the FT'ers to be that useful! ^ I'm hopeful that enough pics and posts will keep it in the first 7 pages in any case! To your cloud photo and comments... Actually, this highlights an interesting point about how people describe weather... From the pictures, and if I had no background info...I would say that this second photo especially is indeed quite threatening...and a convective type cloud coming from daytime heating (convection) or a cold frontal passage...however, when you said that it had been raining for two days straight...this would, on the face of it, indicate a warm front and stable cloud (as unless there were breaks in the rain, a convective cloud cannot rain that long)...so difficult to call this one. There are cases where two fronts meet (called an occluded front) which can indeed have prolonged rain and stable cloud but with some 'embedded' convective clouds such as towering Cumulus or Cumulonimbus...I'll try to have a look and see if I can get some satellite pics or weather data from then and come back to this but I do suspect the cloud you show here is a CB and the quite strange 'scoop' we see here is an 'outflow with some precipitation forming cloud as it is funnelled downwards...I can believe you that there may have been a funnel' cloud which is the start of a Tornado and occurs more than people realise...as long as it didn't touch down no worries...but not a good thing to fly through...regardless of size of aircraft! This was why I asked about the second picture as it is a great photo and indicative of very serious downdrafts...I expect there were microbursts in that cloud...to have it embedded in a warm front would make it that much more dangerous as unless pilots know about this development they may not realise there is a CB hidden in there...Although the satellite and other data would show this at some stage. ^^ I have asked matthandy on his new TR about which camera he has because I have an exciting itinerary SYD - LDH - SYD - LHR... the exciting bit being LDH and I will be equipped then with weather knowledge then! looking at stock photos on the internet I am very excited by some interesting activity (like this one) which only you, the tsar, will be able to analyse! And it should be stickied because it is weather information which is very useful in the aviation industry ;) ;) I have heard of microbursts before and have associated them with certain death (I recall watching air crash investigations when a Boeing 737 lost lift and simply fell out of the sky due to this little isolated pockets). Interesting observations about the funnel cloud... it did start spinning in the view but then it lost momentum (and thank god it did). I have never seen such whether activity in my life so far so living here in Sydney has been an eye opener... in London its constant dampness / drizzle and non-stop rain but when I was younger living in the Philippines, weather was more polarised in a sense that if it rains, it does so heavily in a typhoon-type fashion (which we seem to get a lot of). Whilst typing this something has triggered on my brain. Philippines usually has a thing called an ITCZ or an Inter-Tropical Convergence Zone which I believe is a precursor to a typhoon? I have never really researched much into ITCZ as we would have gotten a few of those each year and for me it seemed just a very scary version of rain and winds but not enough to be typhoon strength! /AE |
/AE |
Originally Posted by angeloedades
(Post 18805850)
I have asked matthandy on his new TR about which camera he has because I have an exciting itinerary SYD - LDH - SYD - LHR... the
Originally Posted by matthandy
(Post 18760800)
I’ve often been asked what camera equipment I use for my reports. Well, I’ve been lucky enough to get my hands on a shiny new Nikon D800 36mp DSLR, which arrived only a few weeks before I started this trip. I used two lenses for this report, the Nikon 24-70mm f2.8 and the Nikon 70-200mm f2.8 VRII. I’ve also used my iPhone 4, as sometimes it’s not appropriate to wield my DSLR around. All of the photos have been processed in Adobe’s Lightroom 4 to my own style (which you may or may not like ).
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Originally Posted by Stez
(Post 18805882)
Ahem, it is in his TR: ;)
/AE |
I'll have to do a lesson on lenticular clouds to show how this happens and illustrate the way they form these interesting shapes...another thing for the to do list! ;)
Originally Posted by angeloedades
(Post 18805850)
I have asked matthandy on his new TR about which camera he has because I have an exciting itinerary SYD - LDH - SYD - LHR... the exciting bit being LDH and I will be equipped then with weather knowledge then! looking at stock photos on the internet I am very excited by some interesting activity
And it should be stickied because it is weather information which is very useful in the aviation industry ;) ;) I have never seen such whether activity in my life so far so living here in Sydney has been an eye opener... in London its constant dampness / drizzle and non-stop rain but when I was younger living in the Philippines, weather was more polarised in a sense that if it rains, it does so heavily in a typhoon-type fashion (which we seem to get a lot of). Whilst typing this something has triggered on my brain. Philippines usually has a thing called an ITCZ or an Inter-Tropical Convergence Zone which I believe is a precursor to a typhoon? I have never really researched much into ITCZ as we would have gotten a few of those each year and for me it seemed just a very scary version of rain and winds but not enough to be typhoon strength! Your comment above really highlights what a difference the air masses make where you are living or travelling. As mentioned, over the UK it is very moderate with little extremes due to the moderate maritime (moderately moist) Polar (moderate temperatures of 5 C to 20 C) air masses which bring the moderate cloud and rain on a continuous basis to our island...(not including the extremes of flooding lately which are due to the larger scale weather patterns changing with time)...whereas in Australia you have far more temperature differences possible due to the strong heating from the Sun over that nice 'hob' of a Country as well as the never ending source of warm moisture from the Oceans...allowing some truly staggering weather to occur. Like the Country...nothing moderate about Australia! :) The ITCZ (or Inter Tropical Convergence Zone) is an excellent example of air masses at their most provocative...this thin band of latitude is where the air masses are very unstable, are very hot and have no end of moisture available so they always provide the 'clockwork' thunderstorms and there is a 'ring' of them continuously occurring around the world...like a necklace with some charms on it...(the charms in this case being the Cumulonimbus clouds!)... I'll have a look for a satellite photo of the ITCZ and post that a bit later... In any case, thanks for the continued interest in the weather and clouds everyone...keep those cloud photos coming and remember to look up or out the window instead of down or hiding away from the weather!^ |
ITCZ images:
So, as we mentioned above, the ITCZ is where the thunderstorms form continuously and are aided by the very hot (Sunlight is strongest here), very moist (provided by the surrounding Oceans) air masses and the global wind patterns that provide the upward lift (the hot air rises at the Equator) so the conditions are unstable and form convective cloud...these usually turn into Thunderstorms and are Cumulonimbus clouds... You can see them quite clearly from the satellite images below...one is an excellent example from the Wiki page on ITCZ and I have placed an oval around the middle of the globe where you can see the small, circular, strong white 'blobs' (which are CB clouds) and are in the ITCZ. You can also see a Hurricane... http://farm6.staticflickr.com/5199/7...3deab2b2_b.jpg ITCZ picture from Wikipedia by BA_pics, on Flickr the above image is in the public domain so I believe it is free from copyright but it comes from NASA and I hope I have credited it enough by saying that! The next image below is from EUMETSAT and is the latest publicly available satellite image showing the same thunderstorm clouds around the Equator that make up the ITCZ but this time over Africa and Europe rather than the North and South American image above. The ITCZ is not as easily identified as above but you can see some similar small white circles effectively in a line around the Equator that are the thunderstorms and are the ITCZ. http://farm6.staticflickr.com/5193/7...1745ac95_b.jpg Latest satellite image 23 June by copyright EUMETSAT 2012, on Flickr Hope these are of interest...especially if you have a long haul flight that passes through the Equator and are awake to look out the window at that time...some of henkybaby's pics show the cloud development from that region...as well as others...:) Let me know if there are any questions! (I'm hoping simonrp84 will have some new surprise for me on this as well! :D ) |
That is freaking awesome! ^ :D
With the second picture its not as obvious but you can almost see the banding in the equator. When I first came to SYD via TPE we flew over MNL / ZAM (where I come from) and it was scary and certainly bumpy... not sure if it was due to an ITCZ but it was definitely bumpy until we reached the Northern Territory in Australia. I will definitely have my eyes peeled on this one next time especially on my SYD to SIN sector! :D See weather stuff can be cool :cool: (or kewl if you prefer) /AE |
Forecasting rain from weather data...how?
So HIDDY, you asked how we can tell where it is going to rain and where it won't…@:-)
Using your EZE BA destination as an example :) As mentioned, it is best to look at the pressure map that someone has produced, which shows the weather fronts and pressure systems based on lines of equal pressure (isobars)… From the UK Met Office website: http://farm8.staticflickr.com/7276/7...366ccc4a_z.jpg Pressure map for South America from UK Met Office by BA_pics, on Flickr This shows that there is a very tight gradient between the tip of the continent and the border of Brazil (as the pressure goes from 984 hPa up to 1020 hPa or more…these tightly packed lines over BA indicate that the wind would be fairly strong and that the mountains are breaking up the weather front that is stretched from West to East just South of you… The cloud West of the continent is some mid level cloud (Stratocumulus or Altocumulus) that is fuelled by the Ocean water…as it hits land and is forced up over the mountains it does cool and help cloud growth on the one hand but it also loses its main source of moisture so this balances out and if the cloud is not particularly thick or the system not particularly strong it will dissipate the cloud…and this also means it will lose any rain or moisture as it goes over the mountains. As it comes down over the Eastern side it descends and warms up so can hold more moisture but still does not form cloud and the source of moisture is still missing… Then as the air continues moving Eastwards it goes over the warmer water again and gains its source of moisture back…so the conditions allow it to develop into thicker cloud and some precipitation again…as you can see from the low pressure system to the East of BA. This 'line' of low pressure and cloud / rain come and go depending on the factors that affect the pressure at this time of year and the winds, temperature, etc… The associated satellite picture of the same region shows the thicker cloud (or colder cloud in some cases…not this time…I will explain that another time when talking about the images of clouds we see in satellite images)…where the precipitation is possible…it still may not be raining under this thicker cloud but this is the area where it would rain…the thinner cloud is not thick enough or moisture laden enough to produce the cycles needed to give rain… http://farm9.staticflickr.com/8159/7...8d9d2b5e_z.jpg Satellite Image from US government agency by BA_pics, on Flickr in this satellite photo, the green / blue 'blobs' are the thicker mid level cloud that could precipitate…there are some thinner clouds that are not 'coloured' here (they are white) but they would not cause any rain… So now we know where the current cloud is thick enough to rain…and where it is not thick enough… The next thing you would do is to look at surface observations from areas that are West of the mountains and see if they show rain as the cloud hits land and moves over the mountains…then you would look at the area in Argentina that is East of the mountains and see if the cloud remained strong enough after that ascent / descent to continue to rain…and finally follow an Easterly station route to see if it continues to your location…This only works when you have this West to East storm track…for a system coming from South to North or some other track you would obviously need to follow that progress…you would see how the pressure systems and clouds are moving over the last 24 hours and then follow that cloud and that precipitation…then follow those stations you can get ground weather from to see if there is rain/snow, etc…and if it is strengthening or weakening, etc.. So knowing what has happened in the immediate past helps to understand what will happen in the next 12 hours…further out than this is hard as any small change to the influence of the system will have a big effect on the future of that system the farther forward you look…hence why the forecasts are always changing…we try to forecast on what we know…but we only know so much…if we get that slightly wrong or something big changes…we are going to be changing the forecast significantly to adjust to this change… This is why it is also very hard to tell someone what the weather will be like when they ask you on the tube or such…unless you have been watching the charts and following what is causing the current situation (which takes about 2-4 hours to really get to grips with) then you can't possibly forecast what will happen in a days time…:( Just looking at the clouds in the immediate area will only give you about 1-2 hours of certainty… Hope this is of use and interest and helps to answer your question HIDDY? |
We have set a trend. Some nice ones here:
http://science.nationalgeographic.co...photos/clouds/ and although 3 yr old a very nice article on a (then) new cloud type. http://news.nationalgeographic.com/n...loud-pictures/ Can we really still find new types? |
So cloudman, the other day, while flying, beautiful blue skies with just gorgeous fluffy white clouds, and then a small sliver of a reddish cloud as if it was sitting in top of white feathers... Why was it the only red one, and no, no sun around.
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AMS was very windy today, mostly at ground level. There was actually more turbulence when the plane was still parked than after we took off. The poor F70 was really shaking.
Lots of layers of clouds when we broke the lower cloud ceiling. http://pic40.picturetrail.com/VOL359.../403164276.jpg http://pic40.picturetrail.com/VOL359.../403164332.jpg Does that explain the high winds? On arrival in Bristol there was a very long (miles and miles) cloud that look like but wasn't a roll cloud. I tried to make a panoramic shot. Will upload it later. |
Originally Posted by henkybaby
(Post 18810185)
We have set a trend. Some nice ones here:
http://science.nationalgeographic.co...photos/clouds/ and although 3 yr old a very nice article on a (then) new cloud type. http://news.nationalgeographic.com/n...loud-pictures/ Can we really still find new types? The 'new' cloud type I must I admit I am sceptical as I feel it is a cloud phase between a smooth based Stratocumulus/Cumulus that is developing some Mammatus features and shows the exact same downward flows in the cloud which extend the cloud base in pockets... As to discovering new clouds...I think that may very well be possible with time as the man made influences and gases start to affect cloud growth and types...we may find that releasing all of the particles of CO, SO4, etc...may allow cloud growth in places we would normally not get cloud as there would be no CCN (small particles for the moisture to 'wrap' around...time will tell.
Originally Posted by Yahillwe
(Post 18812236)
So cloudman, the other day, while flying, beautiful blue skies with just gorgeous fluffy white clouds, and then a small sliver of a reddish cloud as if it was sitting in top of white feathers... Why was it the only red one, and no, no sun around.
What I expect you saw (but without a picture it is hard to be certain ;) )...were Cumulus clouds (as the fluffy white clouds) while the red small sliver cloud was likely a very high Cirrus cloud...things can be deceiving at altitude...so even though there was no Sun around that you could see in a direct line (it would be below the horizon compared to where you were)...with the high cloud (probably based at around 32,000 feet or higher the Sun wouldn't need to be visible but the Sun's rays may still have been shining in a 'straight line' from behind the Earth (relative to your position) and only were noticeable when it 'hit' something...like this high thin Cirrus cloud...so it reflected the 'red' longer wavelengths of the Sun's light and you were seeing this... Hope that answers your question? Looking forward to more and some nice photos of clouds with all the travelling you do! ;)
Originally Posted by henkybaby
(Post 18812264)
AMS was very windy today, mostly at ground level. There was actually more turbulence when the plane was still parked than after we took off. The poor F70 was really shaking.
Lots of layers of clouds when we broke the lower cloud ceiling. http://pic40.picturetrail.com/VOL359.../403164276.jpg http://pic40.picturetrail.com/VOL359.../403164332.jpg Does that explain the high winds? On arrival in Bristol there was a very long (miles and miles) cloud that look like but wasn't a roll cloud. I tried to make a panoramic shot. Will upload it later. The clouds in the pictures do not explain the high winds...I'll look into that and come back with (hopefully!) an explanation... Some nice Cumulus floccus there henkybaby in the first picture! ^ Above that there is some scattered Stratus and the quit a bit higher up the last layer which is Altocumulus. Interesting to see such well defined Cumulus and then the higher based Stratus...not that common...Stratus usually forms below other cloud when the air becomes saturated from precipitation and makes 'new' cloud...or when moisture from lots of rain starts to get burned off by the Sun and lift up to form saturated air and makes Stratus...so to see it above the Cumulus and no higher thick cloud that is precipitating to form this is unusual...interesting...can't explain that one. :confused: ^ (I love a challenge!)...this Stratus above the Cumulus can be clearly seen in the second photo just behind the end of the tip of the wing...you can see a 'grey' diffuse long thin cloud and behind it the lower Cumulus 'much more brilliant coloured white' cloud... Thanks everyone...keep the pictures and questions / links / weather items coming ^ |
The Bristol cloud...
http://pic40.picturetrail.com/VOL359.../403165280.jpg Not the clearest picture in the world... It is the one just above the wingtip and it stretches for as far as the eye can see to the left and right. It was clearly only a couple of hundred feet wide but not compact enough to be a roll cloud. EDIT: maybe this picture is better http://pic40.picturetrail.com/VOL359.../403165465.jpg |
Originally Posted by henkybaby
(Post 18812264)
AMS was very windy today, mostly at ground level. There was actually more turbulence when the plane was still parked than after we took off. The poor F70 was really shaking.
<snip> Does that explain the high winds? Glad that you had a decent flight once up in the air though! ^ |
Originally Posted by henkybaby
(Post 18812542)
The Bristol cloud...
http://pic40.picturetrail.com/VOL359.../403165280.jpg Not the clearest picture in the world... It is the one just above the wingtip and it stretches for as far as the eye can see to the left and right. It was clearly only a couple of hundred feet wide but not compact enough to be a roll cloud. The same formation process is involved for this occurrence as for roll clouds to start (but additional factors keep the roll cloud developing whereas here they stop)...so well spotted! This is a classic example of orographic lift...or physics in motion. The atmosphere is near saturation and just needs that extra little 'something' to cause some lift and then condenses to form cloud...in this case the local 'hills' which are only 30-50 m high are enough to cause the saturated air to condense into some Cumulus cloud and form that line of cloud (which I imagine you would see a small line of hills there as well (and obviously as the air is forced up and over these hills it is 'channelled' into a stronger lifting flow. So the Cumulus forms from nothing when the air moves over this hill range and then the Cumulus carries on until another 'local' effect changes the cloud development (either positively or negatively)...after this line of Cumulus moves away a bit the Cumulus will again start to form at the same location say 20 to 30 minutes later...so forming 'bands' of Cumulus as long as the wind stays from that direction and the Sun is up and helping with the convective cycle (and the air mass is the same!) Hope that helps explain this line of Cumulus forming from local lifting of saturated air and local geography which if the right conditions existed (in Australia for example) could then further develop into roll cloud...but Bristol is moderate in this one regard! :D Thanks for the picture, nice one. ^ |
Originally Posted by BotB
(Post 18807465)
Hope this is of use and interest and helps to answer your question HIDDY? The weather has been beautiful here over the last few days no doubt caused by the high pressure. It touched 20c this afternoon which isn't bad for a winters day. Windier today than it was yesterday so I guess the isobars are being pushed together. |
Originally Posted by HIDDY
(Post 18812681)
The weather has been beautiful here over the last few days no doubt caused by the high pressure. It touched 20c this afternoon which isn't bad for a winters day. Windier today than it was yesterday so I guess the isobars are being pushed together.
Hope that the high pressure stays strong enough for you over the next few days but they seem to want to forecast the lows each side of the land mass building a low pressure bridge and bringing more cloud and precip to you... Will depend on how strong the temperature differences are over the next few days... |
Originally Posted by BotB
(Post 18812719)
Hope that the high pressure stays strong enough for you over the next few days but they seem to want to forecast the lows each side of the land mass building a low pressure bridge and bringing more cloud and precip to you... Will depend on how strong the temperature differences are over the next few days... |
What a great thread.^ As BotB said at the beginning the height of some of CB clouds that you fly around during the summer thunderstorm season across Canada and the American midwest are really amazing to see considering you are already at 35000 feet. I'll try and take some pictures this summer even though they are non BA related.
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Apologies for linking to the DM :eek:, but these remarkable pics are worth a look. http://www.dailymail.co.uk/news/arti...fog-night.html
From a meteorological POV, the conditions to create this phenomenon only occur twice a year, I wonder why ? |
Lesson 4: Fog
http://farm9.staticflickr.com/8012/7...3251c55d_c.jpg Precipitation Fog by BA_pics, on Flickr As dunk asked about why the fog only formed twice a year in Dubai I thought I would talk a bit about fog and how it forms which will hopefully help those thinking about it when trying to fly from an airport that is experiencing fog or trying to figure out when it will dissipate (which you can really only tell if you know how it formed in the first place)… So, to start…Fog is the same as cloud but it is ground based rather than in the air. It is a stable type of cloud and is related to Stratus…so generally does not form in convective or turbulent conditions…I was taught that there are essentially 7 types or ways fog can form (this may be taught differently now….); Radiation Fog: basically the strong diurnal change of temperature between daytime and nightime mean that during the day the air is warm and can hold a lot of moisture and when it is clear skies and the season is right (Autumn or Winter) then the temperature very quickly drops to the dew point and the air saturates causing fog until the Sun comes up again to 'burn' off the moisture. This fog is typically only a few meters deep vertically and quickly burns off when the Sun comes up…it only forms over night and is always in calm wind conditions. If some wind comes along it will disperse the fog once turbulence starts. (so wind or Sun will get rid of it). Advection (also called Frontal) Fog: Warm moist air passes over colder ground (regardless of where)…as the warm moist air moves over the cold ground it drops the temperature of the air to that of the ground and the extra moisture cannot go anywhere so forms fog (cloud) as the air is saturated for that temperature. The combinations are usually warm Ocean water air is blown over colder (for example snow packed land) and as long as that directional flow remains the same the fog will remain. A change in direction of the wind, a change of air mass over that surface, or strong heating of the surface will stop the fog formation…this fog can occur in very strong wind conditions if the main conditions are right (warm moist air passing over cold ground). The warm moist air can be from a warm air front passing over cold ground as well…so not always at edges of water/land Sea Smoke: This is the opposite of the above…cold dry air passing over moist warm surfaces (so usually very local cold air passing over warm Ocean areas or warm lakes)…the colder air cannot hold much moisture so it becomes quickly saturated from the warm (and therefore very moist) water below it…and through this transference the air becomes saturated and forms fog. Again, a change in wind direction (so the air is not so cold), or warmer air mass changes will break up the fog…strong winds can again occur with this type of fog…if the direction and the air mass characteristics are the same. This is usually very local form of fog…can be a few meters deep and only a few meters wide / long. There is a special version of this called Arctic sea smoke which just denotes that the air is extremely cold (-35 C or colder) and when it is passed over such warm ocean currents it sublimates (passes through two changes of state) directly to ice crystals instead of water droplets... Precipitation Fog: This forms when it is precipitating! So, as it rains, the air below the cloud becomes saturated and then supersaturated and forms cloud as well…this usually then joins the cloud base and effectively lowers the cloud base as time goes on…This fog is usually short lived and is associated with warm frontal passages so is quite temporary. I happen to have a photo set of how precipitation fog forms so will post this here; First…you need a good strong storm…for example: CB clouds over the Rockies in Colorado in Summer (and yes, BA did fly me there…actually managed to sit in NF on a CW ticket!)… http://farm8.staticflickr.com/7110/7...fc274d33_c.jpg CBs coming to town by BA_pics, on Flickr Then you see the storm and heavy rain showers coming in the distance: http://farm6.staticflickr.com/5116/7...bc98349f_c.jpg visibility lowering in rain by BA_pics, on Flickr and finally you have the fog being formed in the precipitation: http://farm9.staticflickr.com/8012/7...3251c55d_c.jpg Precipitation Fog by BA_pics, on Flickr and later you can see some examples of the cloud lowering from the precipitation saturating the air below the cloud: http://farm8.staticflickr.com/7279/7...af0ea421_c.jpg Cloud forming from precipitation by BA_pics, on Flickr but back to types of fog... Upslope Fog: or effectively the same way cloud forms…air is forced up a hill or mountain and then cools, the air becomes saturated and condenses, forming fog or cloud…this will continue until the conditions change…the wind direction reverses to flow downhill or the air is not so moist (air mass change)... Valley Fog: Radiation fog that is trapped in a valley and capped by an inversion (warm air is trapped above cold air in winter…usually in valleys between two mountains with strong diurnal temperature swings…many airports are built into such valleys! This can be quite hard to dissipate…the inversion needs to break down (mixing of the air to great heights by a change in weather systems) to get rid of this type of fog…. Freezing Fog: effectively upslope fog but at cold air temperatures in winter…the small drops of fog freeze to surfaces causing rime icing (also known as hoar frost) when they are lifted up a slope and effectively become freezing drizzle but are not falling out of a cloud but rather being pushed up a mountain…this can occur in strong winds…Wind direction change or air mass change will stop the process but very heavy accumulation can occur if this continues for a day or so… So, now we know the various formation methods and types of fog…what does Dubai get that causes the strange conditions mentioned in the DM article... At least in the Autumn, the fog formation is advection fog. Background: Around the world…The Oceans heat up slower than land but hold the heat longer than land…so it is quite normal that land masses are warmer than surrounding oceans for the early summer months but the oceans are warmer than land in Autumn… (they have been storing that Sunshine and heat all Summer long and only very slowly release the heat back into the atmosphere…in Dubai in Sept. the very hot ocean (say 34 C temperature…obviously very moist) air is blown over the Dubai coast which can in Sept. only be around 20 C ….so the warm moist air that is advected over the colder land (this is relative here) then cools and saturates causing cloud…until the wind direction changes or the air mass over the land changes…so the fog can last for a few days. In the Spring: If I am honest I am not sure…I have not been to Dubai and don't have the experience first hand…however from the Dubai Airport Met Office site…they say that the weather is very changeable due to the large scale weather systems in force at that time of year…so I assume that the fog is then Radiation fog if it is only a nightly occurrence, or Sea smoke (as the land would heat up more than the surrounding water at this time of year so the opposite to the above Autumnal formation of the fog…or it could simply be precipitation fog but this is unlikely given the photos show clear air above a certain height and the formation process seems to be sea smoke if I had to pick one… Hope this is of use and interest and explains the fog in Dubai as well as anywhere you may travel with BA! Now…to make this UK and BA related… What types of fog does BA have to deal with at LHR/LGW/EDI/NCL etc… Well, we are surrounded by large water masses so we definitely can be affected by the advection fog on coastal areas, or sea smoke as well depending on the time of year…we also get some limited periods of precipitation fog, but mostly we get radiation fog… BTW, Fog is the one thing that Satellite photos have a really hard time to show as it is usually very warm compared to most clouds temperatures (as the fog is based on the ground and is therefore not a -20 C or colder temperature) such that the fog is not too different to the ground temperatures so doesn't come up in the imagery very well (yet!) Questions? |
Crazy .......s!
I can't resist posting this...
During one of my visits to Boulder, CO to NCAR (National Center for Atmospheric Research) I ran across these Tornado chasers making their way to Kansas... http://farm6.staticflickr.com/5199/7...d2788ea7_b.jpg tornado chaser 2 by BA_pics, on Flickr You should have felt the ground vibrate when that thing drove off...MPG that this thing gets...OMFG!!! http://farm9.staticflickr.com/8143/7...cbac53a7_b.jpg Tornado chasers by BA_pics, on Flickr Yes, someone actually sits in this thing in the middle of the Tornados path (when they get lucky :)) and hopes that the sheet metal is heavy enough to stay put and not get picked up and tossed about! :eek: |
Oh, dear … the things young people do!! :D :D
I note, dear BotB, you have not specifically mentioned one of my favourite terms [although you have alluded to it obliquely]. The adiabatic lapse rates – which refer to the change in temperature of a parcel of air as it moves upwards (or downwards) without exchanging heat with its surroundings. The temperature change that occurs within the air parcel reflects the adjusting balance between potential energy and kinetic energy of the molecules of gas that comprise the moving air mass. There are two adiabatic rates:[6] * Dry adiabatic lapse rate * Moist (or saturated) adiabatic lapse rate http://en.wikipedia.org/wiki/Lapse_rate |
Some from me.
CYYC/YYC-EGLL/LHR, over N. Canada. http://i20.photobucket.com/albums/b2...9/_DSC1564.jpg EDDF/FRA-EGLL/LHR, coming over the Channel from the cockpit. http://i20.photobucket.com/albums/b2...9/_DSC2931.jpg |
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^^^ Heathrow Tower!
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Originally Posted by BotB
(Post 18818001)
As dunk asked about why the fog only formed twice a year in Dubai I thought I would talk a bit about fog and how it forms which will hopefully help those thinking about it when trying to fly from an airport that is experiencing fog or trying to figure out when it will dissipate (which you can really only tell if you know how it formed in the first place)…
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Originally Posted by T8191
(Post 18818447)
I note, dear BotB, you have not specifically mentioned one of my favourite terms [although you have alluded to it obliquely].
(BotB note: the term was adiabatic lapse rate...) I just love the terminology, but for the life of me [even though I've done calculations based on it] I can't remember ever hearing it expressed in English!! :D I just hope we don't put off anyone with descriptions of technical terms...so for the advanced class today: Lapse rates: as you point out there are two…a dry and a saturated adiabatic lapse rate.. so what are they and why are they of interest? The adiabatic lapse rates (besides being a brilliant term to use in the pub)…is a way to follow the path any parcel of air would take as it rises in the atmosphere and follow how the physics would apply to that parcel of air. What? I hear you say… When you lift a parcel of air up in the atmosphere…it needs to be warmer than the surrounding air or it would not continue to rise @:-) … So, that particular parcel of air has a known temperature (when it started out), pressure (where we lifted it from) and dew point (moisture content of that parcel of air)…. When we lift this parcel of air (which is warmer than the surrounding air as mentioned) it rises…and because the pressure decreases as it rises the parcel expands…this requires energy…so we use up the energy in the parcel of air and this causes the temperature in the parcel to drop…but the temperature is still higher than the dew point (which remains constant as the amount of moisture in the parcel is still the same and the temperature has not dropped to that dew point level so the air is not saturated yet) so the rate that the parcel rises at is known as the 'dry' adiabatic lapse rate…or according to ICAO we lose about 9.8 degrees C / 1000 meters of ascent in a nice straight forward manner :) Obviously, if the air in the parcel is still warmer than the surrounding air, it will continue to rise…once the temperature drops to the dew point, the air becomes saturated…this level where the air becomes saturated is called the convective condensation level (or CCL) and the rate that the parcel then continues to rise is different as the air is saturated and the energy needed to expand and cool now creates heat as well which warms up that parcel a bit at the same time it is cooling so it cools slower as it ascends further…so the rate of temperature lose with height is not as much as when it was dry…this is the saturated adiabatic lapse rate…. We use them to find out where cloud could develop and how thick that convective type cloud could be and what layers of cloud there could be… This is all a fancy way of knowing how an air parcel will rise in the atmosphere…if it is saturated it rises and loses temperature at a different rate (slower) than when it is not saturated… The lines of a tephigram show the rates of rise for any given starting temperature / dew point and pressure. What is a tephigram? http://en.wikipedia.org/wiki/Tephigram A great bunch of lines on paper to help decide what is happening in the world according to the laws of physics! A tephigram is a snap shot of the atmosphere looked at in cross section. (so you see the atmosphere from the ground up to the tropopause in a vertical line and can see where cloud will develop, what the winds are like, if there will be thunderstorms… This is one of THE most useful tools a meteorologist has to understand what the atmosphere is doing right now…and then looking upstream to understand what is coming towards that location. I'll have a go at explaining the relevant bits another time but these pages should keep you busy for some time T8191… Tephigram plots for quite a few locations around the world updated several times a day… Tephigrams provided by weatheronline And this page tells you how to read a tephigram…so you can start to disect the atmosphere at any location in the world you choose and know what will happen to that parcel of air you raise up… How to use a tephigram Better than any video game I tell you…Here you can create your own world of clouds and thunderstorms, lightning, rain, etc…^ :cool: Back in the day...you had to send this weather balloon up and then plot the data by hand and then analyse the chart...nowadays...I tell ya...they have it easy...the bloomin' computer does all this whiz bang stuff... :) :) |
Originally Posted by Heathrow Tower
(Post 18818630)
Some from me.
CYYC/YYC-EGLL/LHR, over N. Canada. http://i20.photobucket.com/albums/b2...9/_DSC1564.jpg EDDF/FRA-EGLL/LHR, coming over the Channel from the cockpit. http://i20.photobucket.com/albums/b2...9/_DSC2931.jpg The first picture shows some Stratocumulus I believe and the long line of cloud is a weak weather front showing the boundary between two air masses! ;) I am guessing but it looks like the front is moving from right to left in the picture and if this is a warm front then the colder air mass is the clear air to the left of that wall of cloud...and the air behind the wall of cloud is warmer in nature. (might only be a few degrees)...No idea of the moisture content of the two air masses but I would again guess the air in front is moist as there is some convective cloud around...but not a lot given that the temperature is not that warm and there is not that much topographical areas to cause lift here...Also the tops of the clouds are cut off very evenly...so to go back to the adiabatic lapse rates...these cloud tops are exactly where the surrounding air is at the same temperature as the parcels of air that have been lifted to create this cloud and why the cloud does not extend any higher! The second photo (again a brilliant photo ^) shows some great Altostratus that is being highlighted by longer wavelength red spectrum light from the Sun...as you are higher up in the atmosphere while flying you see more red long wavelength radiation (or to use a friendlier term...sunshine) that is not being scattered out by the usually much more prevalent shorter wavelength blue spectrum light...that we see at the ground...this is further strengthened by the fact that the Sun is not high in the atmosphere here (its rising or setting) so there is more of the blue light being scattered in the air and allowing the red spectrum to reach your eye...:cool: |
Originally Posted by Heathrow Tower
(Post 18818733)
Some land-based photos...
http://i20.photobucket.com/albums/b2...921024x683.jpg http://i20.photobucket.com/albums/b2...06683x1024.jpg http://i20.photobucket.com/albums/b2...233800x531.jpg The first one is showing some very low based ACC (Altocumulus Castellanus forming that incredibly is also turbulent in the downward flow as well...so the cloud is developing in both directions...this can be seen in the Mammatus that are formed / forming on the bottom...Not seen this before at mid levels so a new lesson for me...thank you! Not particularly good to fly through that air at that time (especially in smaller aircraft...):eek: The next photo shows some great Cumulus and Virga (precipitation that does not reach the ground)...the air is hot and moist at elevation but is dry as a popcorn f@rt at lower levels...so the precipitation and energy get soaked up by the atmosphere as it falls downward...until the air is moist enough to allow the precipitation to reach the ground. ^ And finally the third photo...simply brilliant. I have no idea how this formed like this...but very, very nice to look at and try to analyse...^^ You've set the bar mighty high Heathrow Tower... ^ Thanks for the great pics, a real pleasure to view. |
Lots of different things going on in the sky over where I am tonight. I took this about 10 minutes ago - the iPhone doesn't really do it justice:
http://farm9.staticflickr.com/8023/7...2e285452d9.jpg Sadly not taken from a BA (or any) plane, but on the plus side that is the view from my living room! |
Thank you BotB.
Some more! http://i20.photobucket.com/albums/b2...089800x531.jpg The following one was taken 10 minutes or so after the one in my post above. http://i20.photobucket.com/albums/b2...9/DSC_8229.jpg |
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