I'm trying to calculate the monthly rainfall duration (hours) using data
from my
Tipping Bucket Gauge - this is connected to a data logger (Casella Rainfall
Logging System) and the Gauge tips every 0.2mm
Using the gauge software I can look at minute data. Now this is where I'm
not quite sure of things
For example a month gives a total figure of 585 minutes (585 / 60 = 9.7hrs)
Is this method of calculation correct - its seems very low for the entire
month ?
How should rainfall duration be calculated using a TBR ?

Regards

Richard

Maybe there's an official answer, but unofficially I would have
thought that rainfall duration is difficult to define in any exact
terms for an AWS. Presumably you have to specify some minimum interval
between tips which you would interpret as one period of rain having
ended and before the next is deemed to have started.

If you have rainfall at eg 3mm/hr which is still pretty steady rain,
this corresponds to no more than 0.05mm/min or in other words 4
minutes between tips of a 0.2mm gauge. And it wouldn't perhaps be
uncommon to have a prolonged period of lighter drizzle at eg 1mm/hr,
which would cause a tip no more than every 12-15mins. So you might
want to set an interval of at least one hour between tips to denote
the boundary between periods of rain and even this would be inadequate
in some situations.

JGD
www.weatherstations.co.uk

In message , Richard Griffith
writes
I'm trying to calculate the monthly rainfall duration (hours) using data
from my
Tipping Bucket Gauge - this is connected to a data logger (Casella Rainfall
Logging System) and the Gauge tips every 0.2mm
Using the gauge software I can look at minute data. Now this is where I'm
not quite sure of things
For example a month gives a total figure of 585 minutes (585 / 60 = 9.7hrs)
Is this method of calculation correct - its seems very low for the entire
month ?
How should rainfall duration be calculated using a TBR ?


It can't really be done. If the rain is slight it can rain for quite
some time before the first tip of the bucket. "Moderate" rain starts at
only 0.5mm/hour. If it rains continuously at a rate of 0.2mm/hour you
will get one tip every hour. On the other hand if there is a brief
shower every hour with each shower giving 0.2mm there will also be one
tip of the bucket every hour.

Norman.
(delete "thisbit" twice to e-mail)
--
Norman Lynagh Weather Consultancy
Chalfont St Giles 85m a.s.l.
England

In the dim and distant days of full time weather observing, we used to
record the time of onset and cessation of precipitation from a visual
observation. As has been said, it could be well over an hour before the
tipping bucket registered, and maybe 4 or 5 hours with a fine drizzle.
In fact during lengthy spells of coastal drizzle my personal definition
of when it had changed from light to moderate, was prompted by the
tipping bucket measuring 0.2mm. It is not unusual for there to be many
hours of drizzle but to only register a 'trace'.

"Richard Griffith" wrote in message
...
I'm trying to calculate the monthly rainfall duration (hours) using data
from my
Tipping Bucket Gauge - this is connected to a data logger (Casella
Rainfall Logging System) and the Gauge tips every 0.2mm
Using the gauge software I can look at minute data. Now this is where I'm
not quite sure of things
For example a month gives a total figure of 585 minutes (585 / 60 =
9.7hrs)
Is this method of calculation correct - its seems very low for the entire
month ?
How should rainfall duration be calculated using a TBR ?

As others have explained, it can't really be done. Last year I did
a fairly detailed comparison at Hampstead of the AWS's tipping
bucket gauge and the Dines Tilting Syphon Rain-Gauge (if
you're not familiar with it, this is a mechanical device which was
standard until recently which provides a continuous record of
rainfall duration, amount, and intensity), and I couldn't devise
any simple rule which would allow the tipping-bucket to emulate
the Dines TSR in respect of duration.

I did come up with one rule of thumb, though, which you may find
useful. Defining a wet hour (Hw) as one with rain recorded by
the tipping bucket, monthly rainfall duration approximately
equalled 0.75*Hw. The figure varied somewhat between very
dry months and very wet months, though during the short
period of my comparison this variation didn't appear to be
systematic enough to build into the equation.

I dare say the figure (that is, the 0.75 above) would vary slightly
according to what part of the country you're in ... i.e. what sort
of rainfall regime you have.

Hope this helps a little
Philip Eden

As others have already pointed out, it is not really possible to derive
duration of rainfall from a TBR. Using a TSR, the duration of 'measurable'
rain is defined as rain faling with an intensity of at least 0.1 mm/hr.
Again, as others have stated, it is possible to have continuous drizzle
giving about this rate, so that it will be possible to have 2 hours worth of
measurable rain before the TBR records a tip. To emulate the definition
obtainable with a TSR, an automatic device would have to be able to resolve
rates of 0.1 mm/hr to better than 0.1 hours, or amounts of 0.01mm in this
period. So, duration of rainfall, and rainfall rates except in heavy
precipitation, are not suitable parameters to attempt with a TBR.

--
Bernard Burton
Wokingham, Berkshire, UK.

Satellite images at:
www.btinternet.com/~wokingham.weather/wwp.html
"Richard Griffith" wrote in message
...
I'm trying to calculate the monthly rainfall duration (hours) using data
from my
Tipping Bucket Gauge - this is connected to a data logger (Casella
Rainfall
Logging System) and the Gauge tips every 0.2mm
Using the gauge software I can look at minute data. Now this is where I'm
not quite sure of things
For example a month gives a total figure of 585 minutes (585 / 60 =
9.7hrs)
Is this method of calculation correct - its seems very low for the entire
month ?
How should rainfall duration be calculated using a TBR ?

Regards

Richard