"Graeme Smith" wrote in message
. uk...
Tudor Hughes wrote:
Graeme Smith wrote:
Hi,

If I take 5 minute readings from a barometer what is the preferred/usual
method for calculating the rate of change over an hour.

Thanks,

Graeme

It would be very unsound to extrapolate a 5-minute change to
one hour because the barometer may only change by 0.1 or 0.2 mb in that
time. Can you read it that accurately, and is it that accurate anyway?
The only proper way to do it is to measure the pressure at the
beginning and end of the hour in question.

Tudor Hughes, Warlingham, Surrey.


Sorry, I should have been clearer. I have continuous readings at 12 per
hour.

If I have a set of data like this (in 15 minute intervals rather than
the 5 I have for the sake of clarity):

Time Pressure
1000 1000
1015 1005
1030 1005
1045 1005
1100 1005
1115 1005
1130 1010

At 1100 if I take the 1000 and 1100 I can say that the pressure changed
5mb in one hour. At 1115 doing the same, except with 1015 and 1115, I
would have to say that the pressure is steady. But at 1130 I am back to
a change of 5mb.

So what I would like to know is given this sort of situation, how is the
rate of change normally calculated?

You should take your sensor back to the manufacturer. A change
of 5mbar in 15 minutes is well outside the bounds of experience,
at least in non-artificial conditions, at a fixed site in the UK ...
save, perhaps, for a tornado passing overhead. Although gravity
waves may, exceedingly rarely, approach it.

Pressure changes are normally smooth enough for an hourly value,
recorded on the hour, to provide more than enough information
about them. Shorter fluctuations associated with mesoscale
phenomena (e.g. thunderstorms) often merit closer inspection,
but then an hourly rate-of-change would not be relevant for them.

Philip