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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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On Feb 11, 9:16*am, "Andy M." wrote:
On Feb 10, 9:07*am, Sir Loin Steak wrote: On Feb 10, 7:47*am, "Andy M." wrote: On Feb 9, 11:34*pm, Liam Steele wrote: On 09/02/12 21:42, Andy M. wrote: On Feb 9, 9:28 pm, Liam *wrote: I know this forum is populated by various people with meteorology backgrounds, so thought I'd ask here first... For my PhD I am assimilating data into a general circulation model. Now what I want to do is compare the assimilation result (a simple lat-lon plot of whatever) with a lat-lon plot of the observations. I can simply subtract one from the other to get a difference plot, but I was wondering if there was a statistical way to compare the 'fit' between two 2D plots? The model calculates the average rms error over all lat-lon points, but this isn't very helpful, as one particularly bad gridpoint can skew the whole result. If you can give any helpful advice I shall endeavor to mention you in the acknowledgements of my thesis. ![]() Many thanks, -- Liam (Milton Keynes)http://physics.open.ac.uk/~lsteele/ Why not treat the assimilated version as a forecast? *You can construct various forecast scores averaged over spatial zones. *We often use ROCs but it depends what you want to test. *Anything you might do with a time series i.e. *sequence of forecasts you can use for a single event over space. You could use this to test the improvement between different assimilation methods and different assimilation starting points. *I have no direct experience of working in assimilation schemes but we look for skill in much that we do. There is a good page on verification here. http://www.cawcr.gov.au/projects/verification/ Andy Further reading of the web page has brought up the CRA verification method, which compares spatial details as well as magnitudes. And, it even has some IDL code supplied! Looking good... http://www.cawcr.gov.au/projects/ver...ification.html -- Liam (Milton Keynes)http://physics.open.ac.uk/~lsteele/ Yes it is a good site .., I have not used those scores but having some *idea of the spatial coherence and the departure from the target is good ... might look myself. You should also think about getting hold of a copy of Jolliffe and Stephensonhttp://books.google.co.uk/books/about/Forecast_verification..html?id=Q... I am told by Dave that a new edition is on its way. What model are you building the assimilation system for? Good Luck, Andy I am working on a model of the martian atmosphere, and we are currently using the 'Analysis Correction' assimilation scheme that they used at the Met Office in the early 90s. There are more modern assimilation schemes, but apparently they have difficulty when only assimilating a few observations (and for Mars we only have one sounder that gives us observations). I'm looking in particular at water vapour and ice data, and trying to get the model's cloud prediction as accurate as possible so we can work out what role they play in Mars' climate. As an example, I've put three plots up on my website:http://www.physics..open.ac.uk/~lste...similation.png. The top panel is observation data, the middle panel is an assimilation and the bottom panel is a standard model run. To my eye the assimilation resembles the observations more than the standard model, but it actually has a larger rms error. Hence I was looking for something that weights things spatially as well as simply by magnitude. Liam Thanks for this If you ever get chance I would love to see a surface energy budget (for somewhere) from the simulation for summer time. I am currently teaching this with my second years for the earth of course. *I once set an exam question based around a radiation budget for the Martian surface with quite a few hints and values given. No one tried it so I did not put it on ever again. *I must have had data from one of the landers in the late 1990s If you have the 4 way radiation streams (simulated) at the surface (or near surface) that would be great if you have the heat fluxes as well even better. Thanks, Andy google Andy Morse Liverpool if you want to contact me at work. I should of added for one martian sol or three sols in a row. |
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