[wxqc] High Frequency Updates verses Noise (or when the seagull, butterfly, and flea have their day)

[Gerry Creager]

Dave,

I don't think you're making a mountain out of a molehill.  I personally 
think 5 minute (or maybe 6 minute) intervals are a good starting point. 
  We've not established the Nyquist frequency of the atmosphere at the 
surface, so until we do, and start seriously oversampling, more is better.

The only potential problem I could see would be if we chanced upon a 
harmonic component.  Having done this in looking for optimal GPS 
geodetic observation durations, I can't tell you how hard it is to 
determine the nature of the problem until you get the correct index of 
suspicion.

I think where we're going, though, is good.  I'd love to see 1-min 
intervals but I agree that our processing capacity is likely to limit 
that utility.

I'd forgotten the Swift quote: You are the literary dilitante!  I don't 
think I'll forget Lorenz' papers on chaos and the implications for weather.

Regards,
Gerry

Dave Helms wrote:
> Hey Sam,
> 
> You got me thinking about the importance, or lack of importance, of high 
> frequency observations. Chaos theory explains how it is possible for 
> small differences in the initial conditions to cause large differences 
> in future predictions. The atmospheric physicist Edward Lorenz 
> discovered this by making what he thought were statistically 
> insignificant approximations in his numerical weather models which he 
> observed caused disproportionately large changes to the forecast output.
> 
> Its true that most wiggles on your time series will never influence 
> future weather events in any tangible way. However, there are several 
> cases that show how gravity waves, detectable by small pressure changes, 
> can travel hundreds of miles to trigger thunderstorm formation.
> 
> More from Edward Lorenz and Johnathan Swift on the importance of small 
> differences in initial conditions -
> 
> In a paper in 1963 given to the New York Academy of Sciences, Lorenz 
> remarked: /
> One meteorologist remarked that if the theory were correct, one flap of 
> a seagull's wings would be enough to alter the course of the weather 
> forever./
> 
> At the December 1972 meeting of the American Association for the 
> Advancement of Science in Washington, D.C., the sea gull had evolved 
> into the more poetic butterfly - the title of his talk was:
> /Predictability: Does the Flap of a Butterfly’s Wings in Brazil set off 
> a Tornado in Texas?/
> 
> In an 1733 quatrain by Jonathan Swift:
> "So, naturalists observe, a flea will bite its dog most readily. The 
> dog, surprised, will bite its master, who changes course with actions 
> rasher."
> 
> One more plug for the magic of 5 minute updates... It is always better 
> to have time synchronized data updates. ASOS is currently delivering 
> only hourly updates, but there is interest from both the government and 
> private sector in collecting ASOS data every minute (AWOS stations 
> typically send updates every 20 minutes). However, every other major 
> observing system in NOAA updates every 5 minutes including GOES Rapid 
> Scan, NexRad storm mode, and the NOAA Profiler Network.
> 
> 
> Sorry about my fixation on this issue as I'm making a mountain out of a 
> mole hill, me thinks :),
> 
> Dave
> CW0351
> 
> ***********************************************************
> More on butterflies, power outages, and ensemble model prediction:
> http://www.uh.edu/engines/epi652.htm
> http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2003/08/15/MN191082.DTL
> http://www.windows.ucar.edu/physical_science/physics/thermal/Butterfly.html
> http://www.its.caltech.edu/~mcc/chaos_new/Lorenz.html
> http://www.kporterfield.com/writes/Creative_Writes_13.html
> http://boinc-doc.net/boinc-wiki/index.php?title=Why_doesn't_the_exact_same_model_work_out_the_same%3F 
> 
> 
> An Ensemble Forecasting Primer: 
> http://ams.allenpress.com/amsonline/?request=get-document&doi=10.1175%2F1520-0434(1997)012%3C0809:AEFP%3E2.0.CO%3B2 
> 
> To describe the flow of information from small to large scales, the 
> authors offer an inversion of the 1733 quatrain by Jonathan Swift that 
> inspired Richardson2 
> <http://ams.allenpress.com/amsonline/?request=get-document&doi=10.1175%2F1520-0434%281997%29012%3C0809:AEFP%3E2.0.CO%3B2#n2> 
> :
> 
> 
> 
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> 
> The contents of this message are the responsibility of the author.

-- 
Gerry Creager -- gerry.creager at tamu.edu
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