From Jeff Callaghan

>Below is an email from Peter Nielsen from the Civil Engineering Dept of the
>Uni of Qld. Peter has carried out more than 15 years study on the effects
>of storm surge and wave set up at Brunswick Heads.
>
>Attached is a time series of one year of storm surge data at Brunswick
>Heads. The data shows storm surge peaks over the year which are associated
>with known weather events, mostly east coast lows. From the spectrum
>analyses the dominant frequency is around 0ne cycle per 500 to 1000 hours (
>20 to 40 days),  As Peter notes below Cape Byron pressure (near Brunswick
>Heads)  exhibits a similar periodicity.
>
>Does anyone have an explanation for such a long period (much larger than
>the duration of the weather event which produced the surge).
>
>Jeff
>
>>From: Peter Nielsen <P.Nielsen@mailbox.uq.edu.au>
> >Subject: Re: surge
> >X-Scanned-By: MIMEDefang 2.21
> >
> >Hi Jeff,
> >
> >The autocorrelation function and the spectrum for the barometric pressure
> >at Cape Byron indicates that the main periodicity is at a period of 21days.
> >Again this seems very long compared to the apparent 2 to 5 day duration of
> >"weather events".
> >Periodicity at the same period is however also found in the tidal anomalies.
> >Do you know of any explanation for this long period?
> >Thanks
> >Peter
> >

John McBride

To me, who doesn't know anything much about storm surges, it is interesting there are quite large negative anomalies. I assume they must be associated with some sort of edge wave phenomenon because, other than the inverse baromneter effect, I can't see how else you would get a much lower than normal sea height???

Figure one is interesting in that the annual series includes a couple of real huge events. What are the dates of the huge peak and trough in the first 2000 hours of 1995 (Fig. 1)?

 Jeff Callaghan

John the large peak was assw an east coast low which affected SEQld 14-16 Feb (anals
attached) It developed off the central coast and deepened to 997 hPa early on the 15th
before making landfall on the Sunshine Coast. Winds to storm force south of the centre.
Flash floods occurred at Hervey Bay though fortunately  at low tide. The Brisbane wave
recording station recorded significant wave heights to 6.42 m on the 15th.
Jeff