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Geostrophic Windspeed


Nick L

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Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    For the more in-the-know members out there...

    I'm currently doing an assignment, and on one part of the questions I have to calculate geostrophic windspeed at a given location using 500hpa geopotential height contours. From my calculations I have 319m/s - this seems too high, yet I get the same answer every time. Is this a realistic geostrophic windspeed or have I probably gone wrong in my calculations? (It is based on the the 30/10/2000 storm).

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    Posted
  • Location: Liphook
  • Location: Liphook

    Well I can't give you an answer but 319M/S is probably way too high...

    For example a category-5 hurricane has say 75-90M/S, a monster tornado probably gets upto 120-140MS range...

    319MS is something like 700mph...which seems way too fast, thats more akin to Jupiter!

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    Well I can't give you an answer but 319M/S is probably way too high...

    For example a category-5 hurricane has say 75-90M/S, a monster tornado probably gets upto 120-140MS range...

    319MS is something like 700mph...which seems way too fast, thats more akin to Jupiter!

    Thought it was a bit mad :D. Thanks, will no doubt be some very silly error that will take me several hours to find...

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    Posted
  • Location: Liphook
  • Location: Liphook

    Maybe a Decimal point went wrong somewhere?

    Because 31.9 would seem a fairly realistic outcome given it was calculated for a storm, 31.9M/S is about 70mph roughly (gotta love that my hurricane obsession help to convert all these numbers!)

    Still you'll get there in the end!

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    Maybe a Decimal point went wrong somewhere?

    Because 31.9 would seem a fairly realistic outcome given it was calculated for a storm, 31.9M/S is about 70mph roughly (gotta love that my hurricane obsession help to convert all these numbers!)

    Still you'll get there in the end!

    Most probably, wouldn't be the first time it's happened, and certainly won't be the last! Thanks, will have another go now :)

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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    Most probably, wouldn't be the first time it's happened, and certainly won't be the last! Thanks, will have another go now :)

    why not show the chart you are using, explain what you did, how, why etc, and we can then try and see where you may have gone wrong?

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    why not show the chart you are using, explain what you did, how, why etc, and we can then try and see where you may have gone wrong?

    It is a chart I've drawn myself sadly John! We have drawn several charts (surface analysis, geopotential and thicknesses) based on numerous station circles across Europe during the 30/10/2000 storm, and one of the questions is calculating the geostrophic windspeed at a station in northern Germany, based on the spacing of my geopotential height contours. I think I have just lost a power of 10 somewhere, as my friends have got in the region of 30 something.

    I am using the equation geostrophic windspeed = g/f . dz/dx, where f is the coriolis parameter. I have an annoying habit of getting orders of magnitude wrong on my answer so this is almost certainly the issue, will have a go at it again now, spent the past couple of hours doing an annoying vectors assignment!

    Edit: And what do you know? It is an order of magnitude error! I incorrectly subbed in a value of dz. It was 6dm, which for some reason I converted to 600m, rather than 60m. Problem solved, thanks for the help!

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    Ah so it was a conversion error...I suspected so once I saw the figure you had divded by 10 would roughly match something I'd have expected from a system like that!

    Yeah, as I said I have a habit of doing things like that - daft mistakes are my biggest downfall!

    Bit of a monster of an assignment though, so many sheets of paper. Two surface analysis charts drawn, two geopotential heights and one thickness chart, as well as a general sketch map of all the different factors plus answering some questions on them. The charts took absolutely hours, takes ages to get them right!! Handing it in tomorrow, won't get them marked until after the hols so hopefully I've done alright.

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    Posted
  • Location: Liphook
  • Location: Liphook

    I've always wondered just how high up the level so to speak some of the most experienced and smart self taught posters on this forum would be in relation to the Met training system...obviously the Physics/maths is the main point but I always wondered exactly what level in terms of background knowledge some people actually are at...

    Apart from John I think most people on the forum are self taught, will be nice to have someone else offically qualified in a few years!

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    I've always wondered just how high up the level so to speak some of the most experienced and smart self taught posters on this forum would be in relation to the Met training system...obviously the Physics/maths is the main point but I always wondered exactly what level in terms of background knowledge some people actually are at...

    Apart from John I think most people on the forum are self taught, will be nice to have someone else offically qualified in a few years!

    I found it quite difficult to try and teach myself, it just never seemed to go in. Although I did learn a few things from the model thread. I have learnt so much in just 1 term, although some parts are pretty damn difficult. I joked a while back saying that my aim is to understand Glacier Point's posts - I am still some way off that yet :D

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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    I found it quite difficult to try and teach myself, it just never seemed to go in. Although I did learn a few things from the model thread. I have learnt so much in just 1 term, although some parts are pretty damn difficult. I joked a while back saying that my aim is to understand Glacier Point's posts - I am still some way off that yet :D

    stick with it Nick-a proper grounding in meteorology is not easy but well worth it whether you take it up professionally or simply as a hobby.

    You mentioned thickness chart etc. Do they get you to draw a surface chart, then the 500mb chart and then what we called 'grid' the two to give you the thickness chart for 1000-500mb?

    I found that fascinating and it was before the advent of computers so the actual thickness chart used with the other two was then used to 'draw' the anticipated 1000-500mb thickness chart for T+24. Having done that one then could go on to create the Fsxx chart for T+24, much the same as the Fax chart now?

    this chart at this link would be easy for you then, putting isobars on and any fronts ?

    http://www.weatherweb.net/aviations/3huka3.gif

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    stick with it Nick-a proper grounding in meteorology is not easy but well worth it whether you take it up professionally or simply as a hobby.

    You mentioned thickness chart etc. Do they get you to draw a surface chart, then the 500mb chart and then what we called 'grid' the two to give you the thickness chart for 1000-500mb?

    I found that fascinating and it was before the advent of computers so the actual thickness chart used with the other two was then used to 'draw' the anticipated 1000-500mb thickness chart for T+24. Having done that one then could go on to create the Fsxx chart for T+24, much the same as the Fax chart now?

    this chart at this link would be easy for you then, putting isobars on and any fronts ?

    http://www.weatherwe...ions/3huka3.gif

    I don't think so. I think what we did was slightly more basic. We just drew surface charts based on station circles (so yes, like the link you posted!), then we were given another couple of charts which had values of geopotential heights and windspeed which we had to draw a chart for, as well as adding isotachs for the highest windspeeds. Then we had to do one chart on the thicknesses so we could associate the higher thicknesses with the warm sector on our surface charts - thankfully they pretty much matched!

    It's enjoyable when you finally get the general picture, but I find it quite frustrating to start with, and my rubber is rapidly wearing down :lol:. I'm sure I will get better with practice though.

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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    I don't think so. I think what we did was slightly more basic. We just drew surface charts based on station circles (so yes, like the link you posted!), then we were given another couple of charts which had values of geopotential heights and windspeed which we had to draw a chart for, as well as adding isotachs for the highest windspeeds. Then we had to do one chart on the thicknesses so we could associate the higher thicknesses with the warm sector on our surface charts - thankfully they pretty much matched!

    It's enjoyable when you finally get the general picture, but I find it quite frustrating to start with, and my rubber is rapidly wearing down :lol:. I'm sure I will get better with practice though.

    yes give it a few more charts Nick and you will get into the swing of it and really enjoy it. Its a great way to get a 3 dimensional view of the weather and how the surface and upper air interact. Like you found where the thickness pattern matched the position of the warm front.

    I almost feel jealous about it!

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    yes give it a few more charts Nick and you will get into the swing of it and really enjoy it. Its a great way to get a 3 dimensional view of the weather and how the surface and upper air interact. Like you found where the thickness pattern matched the position of the warm front.

    I almost feel jealous about it!

    It gives you a strange, satisfying feeling! We were also introduced to tephigrams the other day, took a while to get my head round them but I think I get them now. Our lecturer said that most people's first question when they first see a tephigram is "Why?!", he wasn't wrong :lol:

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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    It gives you a strange, satisfying feeling! We were also introduced to tephigrams the other day, took a while to get my head round them but I think I get them now. Our lecturer said that most people's first question when they first see a tephigram is "Why?!", he wasn't wrong :lol:

    have a read of the NW Guide on skew-t diagrams, just another version of t-phi's, might help?

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    Posted
  • Location: Liphook
  • Location: Liphook

    I found it quite difficult to try and teach myself, it just never seemed to go in. Although I did learn a few things from the model thread. I have learnt so much in just 1 term, although some parts are pretty damn difficult. I joked a while back saying that my aim is to understand Glacier Point's posts - I am still some way off that yet :D

    Yeah it is difficult to do that, esp if you don't try and look at the whole picture!

    Its actually quite funny that I could probably do a good stab at that chart John, I've funnily enough had quite alot of experience when it comes to that sort of thing, I do alot of tropical watching (Tropical storms/ hurricanes) and with very weak tropical depressions with multiple competing centers it can be really interesting to use those sorts of obs to calculate various things like where the strongest center likely is.

    As with everything there are regions of speciality, for example GP's is obviously long range, whilst some people are very good with mesoscale features and sometimes even smaller scale features then that...I sometimes wonder just what the most difficult forecasting realm is. I tend to find forecasting hurricane strength is a total nightmare, esp when sampling over the oceans aren't nearly as good and dense as overland.

    I think with something like meteorology its almost as much about experience as overall knowledge, thats esp true in fields such as tropical meteorology where recognising particular storm presentations often give a good hint of things to come...

    For example when it comes to steering of storms I've found the outflow and the angle of the storms Northern quadrant often gives a big hint of where its going. If the northern side is flat usually suggests a ridge to the north, if its quite stretched to the north/north-west then thats a big clue a upper weakness/trough is nearby to its north and the chances of it moving northwards increases greatly...its little things like that you tend to only learn from either the pros (which your on your to being Nick!) or through previous experience.

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    have a read of the NW Guide on skew-t diagrams, just another version of t-phi's, might help?

    Yeah our lecturer said that Skew-T's are similar to T-phi's, but that the Met Office prefer to use the latter. When I first saw it I thought "This looks like a Skew-T", I shall dig out your guide :)

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    Yeah it is difficult to do that, esp if you don't try and look at the whole picture!

    Its actually quite funny that I could probably do a good stab at that chart John, I've funnily enough had quite alot of experience when it comes to that sort of thing, I do alot of tropical watching (Tropical storms/ hurricanes) and with very weak tropical depressions with multiple competing centers it can be really interesting to use those sorts of obs to calculate various things like where the strongest center likely is.

    As with everything there are regions of speciality, for example GP's is obviously long range, whilst some people are very good with mesoscale features and sometimes even smaller scale features then that...I sometimes wonder just what the most difficult forecasting realm is. I tend to find forecasting hurricane strength is a total nightmare, esp when sampling over the oceans aren't nearly as good and dense as overland.

    I think with something like meteorology its almost as much about experience as overall knowledge, thats esp true in fields such as tropical meteorology where recognising particular storm presentations often give a good hint of things to come...

    For example when it comes to steering of storms I've found the outflow and the angle of the storms Northern quadrant often gives a big hint of where its going. If the northern side is flat usually suggests a ridge to the north, if its quite stretched to the north/north-west then thats a big clue a upper weakness/trough is nearby to its north and the chances of it moving northwards increases greatly...its little things like that you tend to only learn from either the pros (which your on your to being Nick!) or through previous experience.

    I think what being a member of this forum has helped do is put a few pieces of the jigsaw puzzle on the table. For example, geopotential height charts, I've seen hundreds of them so I'm familiar with, but until recently I didn't really know what it showed. Now it's been properly taught to me it makes sense. I have also learnt why the 528dam line is conducive to snow and how to calculate the likely surface temperature from a given thickness.

    There is a weekly weather and climate discussion every Friday in the Met dept, discussing some really interesting sounding topics. Sadly I have a lecture literally just before and by the time I got there I would have missed a good chunk of it. Today one of the topics was about the ECM ensembles - would have been a fascinating listen.

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    Posted
  • Location: Liphook
  • Location: Liphook

    To be honest if there was only one thing I could have other then the radar on Net weather, it'd be ECM ensemble data, however I imagine even for a basic package of the ensembles you'd be looking at huge money, on a level not really sustainable on its own even to a site this large...

    I'd certainly love to be a fly on the wall during those sorts of discussions.

    As for things such as height/thickness its only really if your taught it or if you sort of go out your way to learn it, but once you understand it you start to find out just how great a macroscale tool they actually are. I'd much rather look at the heights for example then purely depend on pressure, classic example of where they are so obviously important was things such as northerly topplers...I used to think with a pressure of say 1050mbs there'd be no chance of a 1010mb low displacing it and cutting right through so to speak but when there is no hints of a high in terms of thickness or heights then it becomes obvious what will happen.

    Tis all fun and games of course!

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    • 2 weeks later...
    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    Yeah our lecturer said that Skew-T's are similar to T-phi's, but that the Met Office prefer to use the latter. When I first saw it I thought "This looks like a Skew-T", I shall dig out your guide :)

    if you go to the Met O site and search around there is an item explaining what they are and the differences, its largely to do with how you want various lines to appear, level, straight, bent or whatever.

    Another site for explaining from an ex met man is this

    http://weatherfaqs.org.uk/node/168

    it also explains very well the theory behind thickness charts and goes into vorticity as well.

    A knowledge indeed an understanding of some of these will certainly help when you come to look at the model outputs. It will ACTUALLY mean something rather than following, understandably, what many on here do, that line means this or that.

    I'm always happy to try and answer any theory Met questions, mind you the old brain may not be able to replicate things so well these days but ask away

    jh

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    Posted
  • Location: Cheddington, Buckinghamshire
  • Weather Preferences: Winter: Cold & Snowy, Summer: Just not hot
  • Location: Cheddington, Buckinghamshire

    So, Nick, does your university offer access to ECMWF data and products? Maybe by recognizing the IP address of the university or something?

    Not that I am aware of, sadly.

    if you go to the Met O site and search around there is an item explaining what they are and the differences, its largely to do with how you want various lines to appear, level, straight, bent or whatever.

    Another site for explaining from an ex met man is this

    http://weatherfaqs.org.uk/node/168

    it also explains very well the theory behind thickness charts and goes into vorticity as well.

    A knowledge indeed an understanding of some of these will certainly help when you come to look at the model outputs. It will ACTUALLY mean something rather than following, understandably, what many on here do, that line means this or that.

    I'm always happy to try and answer any theory Met questions, mind you the old brain may not be able to replicate things so well these days but ask away

    jh

    Yes that's another difference I have noticed, studying it at degree level goes into the what, why, how etc. rather than x means y. We also go into quite extensive mathematical detail behind all the theory (I now appreciate the fact I have A Level Further Maths under my belt!). Our tephigram lecture wasn't just "this line means this, this line means that", we were told how each line was derived...I'm sure they won't mind me just posting one of the topics!

    https://www.bb.readi.../topic11_10.pdf

    I am finding that the Maths in the Meteorology modules is currently more intense than the Maths modules!

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    Posted
  • Location: just south of Doncaster, Sth Yorks
  • Location: just south of Doncaster, Sth Yorks

    Not that I am aware of, sadly.

    Yes that's another difference I have noticed, studying it at degree level goes into the what, why, how etc. rather than x means y. We also go into quite extensive mathematical detail behind all the theory (I now appreciate the fact I have A Level Further Maths under my belt!). Our tephigram lecture wasn't just "this line means this, this line means that", we were told how each line was derived...I'm sure they won't mind me just posting one of the topics!

    https://www.bb.readi.../topic11_10.pdf

    I am finding that the Maths in the Meteorology modules is currently more intense than the Maths modules!

    ah, so you are still on h easy stuff!

    have they gone into the thickness change equation and vorticity?

    wonderful-makes the hairs on the back of my neck twitch when I read my 35+years ago teory notes!

    I'll try and copy it if I can on the printer and post in here. Once you understand the various parts, the why etc, it does help explain a heck of a lot even in this model age

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