The Phenomenon of Mist and Haze

[mazzy1026]

These types of weather have haunted me the most in trying to gain my PPL. I have read the MET books and found that they only give a general idea as to the origin and dissipation of said. It seems that Fog is different, in saying that there are two types (convection and radiation) and that it generally follows a pattern, I.e. it appears, usually early morning and then disappears, in late morning - Haze seems different though.

So is it that this time of the year brings the most? It seems that here (North West) we have had mist and haze every day for about a month now, and it just wont go away. Is this an Autumnal characteristic, and do you find that it limit's you a lot as well in your flying. Obviously, the weather as an entirety is a mystery and will never be fully understood (disclaimer) :cool:

Regards,

Maz :ok:

[nick14]

Well to start with fog and mist are the same thing but separated noly by a definition. Mist become fog when the visibility drops below 1000m and vice versa.

Mist and fog is characterstic of the winter months. The amazingly clear winter skies cause sudden drops in temperature,
(u may have noticd when ure nads suddenly drop of)
The moisture in the air just above the ground is then cooled below its dewpoint and condenses forming radiation fog/mist.

Advection fog/mist is when a moist air mass moves onto an area of the surface that is colder than the last and cools the air mass below dewpoint etc.

Mist and fog become frequent in the Autumnal months and especially in the winter due to the cold cloudless nights and moist air.

Help?

Nick
:ok:

[maggioneato]

We seem to get the consistent haze when the winds are light and south easterly, even in the summer. The winds pick up westerly out of comfortable crosswind limits so we are still grounded, at least where I fly from. That's aviation for you. Did get to fly yesterday in spite of the viz. I found when I used to fly from LPL, often it was fogged in, localized around the airfield, but once clear of the area it was so different. Very frustrating, but you will get there in the end Maz. I don't think I will ever understand the weather fully.

[mazzy1026]

Advection fog/mist is when a moist air mass moves onto an area of the surface that is colder than the last and cools the air mass below dewpoint etc.
I found when I used to fly from LPL, often it was fogged in, localized around the airfield, but once clear of the area it was so different.

Yes, half of liverpool is coastal, so I assume the Mersey and Irish Sea will contribute to what was said above :=

It's frustrating when you tell someone (on a nice sunny day) that you can't fly cos of the weather, to which they reply "But it's a gorgeous day" - when in fact the vis is awful :{

[IO540]

Sunny but hazy days are actually great for flying (use a GPS, etc) - it's just that the instructor can't send you off on a solo because there is a min viz requirement, and you are flying on HIS insurance ;)

Once you have a PPL, haze becomes a non-issue (usually).

[Farmer 1]

Haze is when the visibility is reduced due to solid particles suspended in the air. It happens at times of light winds, and favourite spots are industrial areas in valleys. You just have to wait for another weather system to come, increase the wind and blow the haze away.

Advection fog can be identified from radiation fog by the temperature. If it feels warm, then it's the former, and you will probably be stuck with it for days.

[mazzy1026]

Yeah, there's been times in the past when I've gone out with an instructor and he's agreed that we'll 'climb above it' - sometimes without success. You can usually see what's directly beneath you, but not ahead.

As you say, he won't sign me solo (rightly so) so getting this QXC done is proving difficult!

[High Wing Drifter]

Fog/Mist = Visible moisture. Generally, you need clear skyies (can there be more than one?) so the land cools rapidly. As mentioned you get it when winds are light. If there is no wind you tend to see a very heavy dew. If the wind is stronger then you tend to see low stratus. Assuming light winds and a suitably clear sky, the coldest time of the day is about 5am, so the air near the ground can condense and you get morning fog. In the evening, the ground is likely to cool rapidly (more quicly that the air), so the air temp drops below the dewpoint and condenses causing evening fog. It is epecially so Spring and Autumn because the temperature range between night and day is highest.

Advection fog I am a little hazey on (pun intended). I see it as simply warm wet air getting shoved over something cold. Because the air needs to be moist this usually involved warm and cold sea currents rather than warm sea and cold land mass, because in the latter case the surface wind would blow out to sea. But I suppose the land could be a tad warmer encouraging the air in, but not warm enought to disperse the fog. Therefore it is usually seen at coastal areas or out to sea. I didn't think we get much of that round these parts, apart from a bit of Sea Haar and Fret along the North Sea coasts oop North I didn't think we see much of its ilk.

Haze = Solid particulates in the air reducing viz. The usual suspects are high pressure systems and/or inversions preventing the particulates from convecting away from the lower levels. Sometimes, I have noticed, it takes a day or two to build up. The conditions usually go hand in hand with light winds. When the wind picks up it is because of the onset of a front or the system moving away, thus releasing the crud, so the view that the wind blows it away is a little inaccurate (methinks).

[Farmer 1]

HWD,

Methinks you're about right. I was trying not to be too technical, so avoided terms like particulate and inversion. However, a front will bring some wind with it, and somehow or other the haze will eventually be dispersed. Visibility in haze can be very much reduced indeed, and it is definitely unpleasant for flying in, particularly into sun.

Radiation fog requires clear skies, to allow the earth's heat to radiate at night, but I believe a cloudy sky actually helps to extend the life of advection fog.

Advection fog is caused by a warm moist airmass flowing over a cold surface, which lowers the temperature of the air in contact with it to below the dew point. ("Warm" and "cold" are relative terms, of course, and the surface can be sea or land.) Whereas the maximum windspeed for radiation fog to form is, as I remember, eight knots, I was taught advection fog can form in winds of up to 20 knots. However, I personally think that upper figure can be much higher.

Advection fog is also known as sea fog, because it is more commonly found at sea. But not always; in a small country like the UK, it is not too improbable for such an airmass to work its way a fair distance inland. And when it does, you'll have plenty of opportunity to get the manuals out.

[mazzy1026]

Thanks for the detailed responses people - appreciated :ok:

[Aussie Andy]

Hi there Mazzy, excellent question! I think haze can be one of the insidious Met phenomena, especially for low hrs pilots. You get days when it's like flying inside the proverbial milk-bottle!

I didn't strike too many hazy days during my training (just lucky!?) but about 4mths post-PPL in that first Autumn I did - it just wasn't on my list of things to be concerned about, and as long as it was above 5k I would go off and fly... one day though, in ~6k vis and with family aboard, I found my nav was up the spout and it was a struggle to get back... managed OK, used VORs etc - and then when as I approached the field from the north, the sun made the whole thing much worse!

That experience made me very afraid of low vis and so for the next 6mths I was reluctant to fly with vis anywhere less than say 8k! This was fixed when a mate (thanks Alex!) flew with me to Blackpool from Wycombe on a ~6k vis day, and I got my confidence back...

Like many others before me, I realised that there is much more to learn once you have the license!! One of the best solutions I'd recommend for post-PPL learning Irv Lee's excellent Seminars (http://www.higherplane.flyer.co.uk/seminars.htm) - he covers lots of practical stuff, including a Met refresher. I think it's really good to do this within say 6~12mths of getting your license so you will have had experiences / challenges which you can raise in Q&A in the seminar. Irv also writes on Met phenomena in one of the mags, and I think he did do a column on Mist and Haze at some stage (reprints?)...

Just to finish up, last Sunday was a typical poor vis / haze day - high pressure, light winds, and a major inversion layer holding down all the crud and particulate matter. I have my IMC rating now so this doesn't phase me (much!) these days and so I decided to get up and have a look... climbing out of Benson to the north-west we had about 7k flight visibility, but on turning back into sun towards the base, it was about 2k! Found the base again OK with GPS and was able to fly a visual circuit just fine once not directly into sun....

Hope this helps!

Andy :ok:

[Irv]

Thanks for the vote, A-A!
The worst thing about haze is usually flying NE in the morning and thinking "well its hazy, but ok", and then having to fly SW in the afternoon to get back. Then of course, the wind is often WSW in the UK, so many of our runways are 24 - 26, so the runway in use is directly into a lowering sun in haze - good news for noseleg manufacturers and the mechanics who fit them!
Two main types of hazy situations:

1- The ones when haze builds up day by day under high pressure - maybe ok for 3 or 4 days, then starts to get worse and worse day by day. Annoyingly, all non-pilot friends make a point of telling you it must have been a great flying day as the sun was shining and the sky was blue. (they only look up, not noticing its white near the horizon) - and your lesson or flight was cancelled or curtailed.
The haze (as stated earlier) in this case is pollution, so each days industrial and motor car output is added to the previous days, as high pressure clamps it down. (I seem to remember Easter 2003 had 10 - 14 days of 'great sunny weather' but by day 8 it was getting dangerous!)

2- the days when there is a definite temperature inversion or minor lapse rate which has the same effect, trapping in the pollution below, but offering the prospect of escaping above the inversion layer into super visibility if you CAN get above it. How do you know the inverson tops to decide if you can escape above? You might be able to spot it from the lapse rates on Metform 214. In practice, many pilots either keep climbing as it looks like the top is just above, in which case it never is, or they accept flying in the murk, perhaps later finding from another pilot that the clear air was only about 500' above them. ALTERNATIVE, and much simpler, look at the BALLOONING section of the metoffice aviation site, where it will tell you the expected inversion top in various parts of the country. (yes, i have asked them to copy it to somewhere more obvious!). Beware two things when flying above the inversion - (a) winds usually stronger, which may be good or bad for your fuel consuption and navigation, and (b) expect vibrations when re-entering the haze layer in the descent - can be worrying if you don't realise its 'normal'.

[IO540]

Irv

Why would one get vibration when re-entering the haze layer from above?

[Irv]

Remeber these days are often blue sky, so you get morning heating on the surface, causing thermal turbulence in air, which builds up and rises, but when insufficient to break through a strong inversion, it gives a layer of disturbed air just under the inversion top.

This can be quite worrying to get vibrations after a long perfect flight above the inversion just after you start the descent. If you're not expecting it, you relate it to the thing you last 'touched' - and that was the throttle reduction to start the descent - conclusion - something wrong with engine!

(Of course you have to remember how S### Law out-trumps anything - now you know this, on the day you knowledgeably put the vibration down to inversion turbulence, it will be the day you don't have carb heat selected before descent, and it will be the engine)

[skydriller]

I was taught advection fog can form in winds of up to 20 knots
You were indeed taught correctly, as I have been stuck on a North Sea Rig that was completely closed in with sea fog where it was indeed very blustery ~ stronger than 20Kts.

Sea Fog, or Haar?!? is indeed wierd stuff. One minute you are in bright clear warm sunshine, the next its like winter! The stuff moves around in odd patterns too, I actually enjoy watching it sometimes as the banks of fog change so quickly, spooky stuff....

Regards, SD.

[Farmer 1]

Bin there, dun that.

My crew-change day, 0500, foghorn starts transmitting .._
Guaranteed.

"Forty-knot fog", was a frequently-coined phrase.

[Aussie Andy]

ALTERNATIVE, and much simpler, look at the BALLOONING section of the metoffice aviation site, where it will tell you the expected inversion top in various parts of the country. Who knew!!! Just looked it up: http://secure.metoffice.com/aviation/aviationProductList.do?action=balloonfc

[mazzy1026]

Some really interesting stuff here - cheers :ok:

[foghorn]

foghorn starts transmitting .._

You rang?

(I'll get me coat...:} )

[skydriller]

....When working offshore sometimes I kind of lose track of what day it is...:zzz:

...then I wake up one morning to hear BAAARRRRP,... BAAARRRRP...

......Oh, It must be Crew Change day, today...:hmm: :suspect::mad: :{ ... are the emotions that generally follow....

Regards, SD..

[Irv]

A_A wrote:
Who knew!!! Just looked it up: http://secure.metoffice.com/aviation/aviationProductList.do?action=balloonfc
but if you don't already have a (free) Met Office 'logon', you'll need to get one via the Met Office Aviation Register Page (http://secure.metoffice.com/register.do?subid=3) first before using that previously quoted link.

[mazzy1026]

Like it ............. :D

[Tinstaafl]

Saw the Haar a lot when I was working in Shetland. Often rather more than a mere 20kts. 20kts was barely a light breeze there. Our limit was 50kts due to door opening limits (although higher windspeeds could be handled if we got the fire truck to park across the nose as a wind break).

It's really weird seeing the fog whip by while expending effort to stand against the wind.

[Helli-Gurl]

You guys should talk to my EX re this, he is an expert at throwing up mist and haze to hide the truth!!!! ;)

x

[mazzy1026]

You guys should talk to my EX re this, he is an expert at throwing up mist and haze to hide the truth
I think that's one of the male genes :D ;)

[david viewing]

What about the 'Warm Sector'? This seems to fit better with the description of persistent haze than mist/fog explanations which surely should vary during the day.

The reduced viz in the warm sector (between warm and cold fronts) can persist for a day or two and make cross country VFR flying impractical despite otherwise stable conditions.

It seems to involve clean maritime (SW) air so I'm not convinced about particulates. But if it is trapped humidity, why doesn't it burn off in the afternoon?

Can someone please explain what causes this reduced viz and where it goes after the passage of the cold front? The idea that the wind just blows it away doesn't quite work for me.

I realise I'm probably displaying cataclysmic ignorance here!

[mazzy1026]

But if it is trapped humidity, why doesn't it burn off in the afternoon?
Exactly my thoughts - I have always wondered this myself. Perhaps it is too thick (base to top) or too dense?

[JustaFew]

Liverpool airport suffers from haze when the wind is from the east round to the south-east; blown from the interior of the country I guess. No idea why the top of the haze-layer varies though; particle size, wind velocity perhaps?

[ProfChrisReed]

mazzy1026 asks why on some murky/hazy warm days the haze (non-technical sense) doesn't burn off in the afternoon.

The answer is the temperature inversion with height. At some point (say 3k ft), the rate at which the air becomes colder with height is lower than the rate at which a parcel of air, heated by the ground, loses heat as it rises.

This means that the warm air rising (or thermal, as we glider pilots say), stops at the inversion. So all the haze remains trapped under the inversion and just recirculates.

If the ground temperature rises high enough, the thermals "break down" the inversion which then disappears. Heated air rises above it to the next inversion, or until it forms cumulus and thereafter runs out of energy at the cloud tops.

If this happens the hazy air below the inversion mixes with the clean air above, and the haze " burns off".

If it never gets hot enough for this to happen (and of course, the haze cuts down solar heating to the ground), the haze remains all day.

A helpful introduction to temperature soundings and forecasting is at:

http://www.itadvice.co.uk/weatherjack/tut-soundings/tut-snds-01.html

[Gertrude the Wombat]

Unusual (to me) conditions this lunchtime.

In the past I have encountered either a haze layer or low cloud. Today we had both - low cloud at around 1700', in places, top of haze layer at 3500'. So where there wasn't cloud I could fly above the haze layer in my usual fashion, but where there was cloud I was crawling along at 1500' in horrible visibility.

Still, it's a wasted trip in which you don't learn anything. Today was my first opportunity to refuse an instruction from ATC on the grounds that it would be illegal:

"Expect an overhead join"

"You're joking, I'm not going up to 2000', the cloud is lower than that."

"Er, OK, try a right base join then."

(By which time whilst I wasn't high enough for the overhead join I'd ended up too fast and too high to land from right base, so had to go around. With a first-time-in-light-aircraft passenger, and whilst I'd remembered to stock up on sick bags I'd forgotten to include the "we might have to go around" bit in the pax briefing. Ho hum.)

[mazzy1026]

I can imagine it's something the weather man may miss out on occasion, due to it's nature - and also, the fact that it can catch you out if your not too careful in the air.......