[wxqc] Pressure Frequency Analysis

[Mark Wyman]

Hmm, that makes sense. 

Myself being in Northern Latitudes don't get much of a solar effect,
especially in the winter when I ran my programs in school. However the
temperature varied greatly and I was able to replicate the change in
temperature correlating to change in pressure since I could select the
coefficients from the FFT in the area of interest, and re-plot the
re-generated data over the weather data to see the timing and how it
related. It was correlated directly with daily temperature swings at the
sensor, not necessarily outside. Then again, back 14 years ago, my pressure
sensor wasn't all that good so it may have had a significantly larger error
than yours does.

Down where you are, there may be a lot more stability to air pressure than
up north, so you may be able to pick the data out much better than I could.
Our pressure swings in spring and autumn are huge. Sort of like last week,
we went from 30.6 down to 29.5? or so in less than 24 hours, (I have the
exact data at home) then it bounced around on its way back up over the next
three days with some brutal winds and snow.

-Mark

-----Original Message-----
From: wxqc-bounces at lists.gladstonefamily.net
[mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Steve Dimse
Sent: Thursday, December 06, 2007 11:08 AM
To: Discussion of weather data quality issues
Subject: Re: [wxqc] Pressure Frequency Analysis


On Dec 6, 2007, at 8:56 AM, Mark Wyman wrote:

> Having a little background in this myself, just about everything but  
> weather
> systems is "buried in the noise". What I mean by that is there is so  
> much
> going on in the normal atmosphere that it is quite difficult to  
> extract
> anything with real meaning.

This is exactly what Fourier analysis is for. It detects the frequency  
components of what appears to be an irregular wave, in other words  
finding things buried in the noise!

> Your 12 and 24 hour peaks are likely due to
> heating of the sensor during the day causing some error. You need a  
> very
> good sensor set to compensate for this.

No, the diurnal variation in atmospheric pressure is well documented,  
it truly is a tidal phenomenon. It is not even buried in the noise, it  
is clearly discernible in any plot of pressure in areas with  
significant insolation:

http://www.findu.com/cgi-bin/wxpage.cgi?call=CW0925&last=480

The barometric variation due to weather is obviously of greater  
magnitude, but the effect is clear to the eye even without Fourier  
analysis. The effect is greater in tropical regions than the poles,  
and in higher latitudes greater in summer than winter, because these  
areas receive more solar heating.

Steve K4HG
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