Kielder Castle Weather Station Wind data

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Dear Forest Research,

I am requesting weather information from the Kielder Castle weather
station, under the freedom of information act.

Specifically I am interested in wind data. I would like the daily
average wind speed for the weather station from the last ten years.

If this exact data is not available then I would prefer any data
you have on wind speed over the period of the last ten years.

I would prefer the information in excel format.

Kind regards,

E. Farndale

Oldham, Catherine,

1 Attachment

Edward Farndale

Our Ref: OI/194230

The data is attached as an Excel file. If you have any problems with
opening it, please contact me.

This is all the wind data we have for Kielder Castle over the period.
The following is an excerpt from the Met Office Users Guide to help
interpret the data.

5.5. Wind

Units, accuracy and precision

Horizontal wind is a 2-dimensional vector and is usually reported as an
averaged direction from which the wind is blowing and a speed. The
maximum observed speed over a specified time interval and the time of
occurrence may also be reported. The unit of speed used at UK stations
is the knot (0.515 ms-1) and the unit of direction the degree. Where
observations of wind speed from overseas stations are in ms-1, values
are converted to knots before storage. The data are reported to the
nearest knot and 10 degrees in the SYNOP and HCM messages and on Form
6910. 1-minute DALE data are recorded to the nearest 0.1 knot and 1
degree.

The accuracy requirements, which are met in most instances by the
current synoptic network, are for speed to be measured within 1 knot or
10%, direction within 5 degrees and gust speeds within 10%. There are,
however, larger errors in near calm conditions where the Munro
anemometer is used (see below).

Averaging

Speed and direction are averaged separately which introduces a slight
overestimate of the mean vector. The calculation of mean direction has
to take into account the cyclical nature of the measurement between 0
and 360 degrees. Where the sampling rate is sufficiently high, the
maximum gusts are normally calculated from 3-second averages of speed
and this is the case at most SAMOS stations today. A 1.5-second
averaging period was used in early versions of SAMOS, it is still used
at all ESAWS stations and it is the typical averaging period obtained
from an anemograph trace. Metadata describing what averaging periods
have been used at stations at a given date has been poorly recorded over
the years. Where wind speed and direction are recorded on an anemograph,
mean values and gust speeds are estimated by human analysis. Estimates
of average speed from a continuously changing dial, which are subject to
large error, are made at a few stations in the supplementary network.
This observing practice was more common in the past.

10-minute averaged winds reported in the SYNOP message are for the
period HH-20 to HH-10. Hourly mean winds in the HCM message and gusts
reported in the SYNOP message are for the period HH-70 to HH-10. Some
Ordinary Climatological Stations report run of wind from an anemometer
on a 2 m mast. This is converted to a 24-hour mean wind speed in knots
for storage in MIDAS.

Munro anemometer

The Munro cup anemometer and vane have been the basic instrumental
method for measuring wind in the UK for many years. Traditionally it has
been connected to an anemograph and/or dial, but with the advent of
automatic systems it has been attached various processing devices, e.g.
the DALE logger. The cup has a large inertia and therefore has a
relatively slow response time, but of more concern is the high start-up
speed, which in the case of the Mk4 is about 6 knots. In 1998 a project
began for the replacement of Munros by a lightweight anemometer with
better response characteristics.

Other wind measuring methods

Visual estimates of wind have been made a number of stations in the
supplementary network for many years and the observations have been
reported as 10-minute winds in the SYNOP message.

Dines pressure tube anemometers, having a better response at low wind
speeds than the Munro, were installed at a number of stations in the
early years of observing, but few of these instruments have remained in
use in recent years.

SIESAWS systems use an orthogonal arrangement of pressure tubes to
measure wind and have not proved reliable in the extreme environment in
which they are sited. Light winds were not handled well but most now
have a bias reset which the error.

Other methods of wind measurements, such as hot-wire anemometers, are
not used in operational observing.

Exposure, effective height and corrections

Correct exposure of the wind instrument is essential for accurate
measurement. The standard exposure is over level, open terrain at a
height of 10m above the ground. Open terrain is defined as an area where
the distance between the anemometer and any obstruction is at least 10
times the height of that obstruction. Measurement of wind in the direct
wake of buildings or a row of trees are of little value and this should
be borne in mind with city centre or other highly sheltered sites. If
standard exposure is unobtainable the anemometer may be installed at a
height greater than 10m. Whether or not such an adjustment is made, all
anemometers are allocated an "effective height" which is defined as the
height above open, level terrain in the vicinity at which mean wind
speeds would be the same as those actually recorded by the anemometer.
Various methods have been devised for the calculation of effective
height. At stations where the effective height differs substantially
from the actual height, corrections are applied to the 10-minute wind
speed reported in the SYNOP message. No corrections are applied to any
gusts measurements or to any hourly mean wind speeds.

Wind analysis and processing methods

Over the years many stations have provided climatological returns on
Form 6910 containing hourly mean wind, speed/direction of the maximum
gust in the hour and time of the maximum gust. The following rules have
been applied for the analysis of the anemograph record:

* Time is determined from the daily time marks made by the observer.
The observing period is defined as HH-60 to HH-0.
* Mean wind speeds are estimated to the nearest knot but a value of
1 knot is not normally reported. Where the mean speed is 0 or 1 knot and
the wind vane shows gusty, but not smooth variations, the speed is
reported as 2 knots and the gust as missing. A mean speed of 0 is only
reported if the speed trace indicates calm over the complete 1 hour
period and the vane is unmoving or records only smooth variations.
* Maximum gust speeds in each hour are analysed unless 2 knots is
reported as above. The direction of the maximum gust during the 24 hour
period is reported, but not the direction of the maximum gust in each
hour.

1-minute speeds and directions from the DALE logging system are
processed to provide mean hourly winds for the period HH-60 to HH-0. For
a number of years after its installation the processing method attempted
to mimic the Form 6910 analysis method, in particular, no instances of 1
knot mean speed were allowed. This practice was discontinued in the mid
1990s after which date simple hourly averages of the 1-minutes data were
calculated.

Sources of error

Common sources of error in the measurement of wind include:

* Poor exposure at the site. Exposure may change gradually with
time, for example as nearby trees grow, leading to slowly changing
systematic errors in the climate record.
* Poor response in low wind speeds, particularly the Mk2 and Mk4
Munro anemometers which require a speed of 6 knots to start cup
rotation.
* A scale error in measurements from DALE systems which resulted in
mean and gust speeds 5% too low. This was corrected in the early 1990s
(date unknown) in all stations except ESAWS. At ESAWS stations the error
in the gust speed is almost cancelled by the effect of using an
averaging time of 1.5 seconds rather than 3 seconds.
* Calibration errors. Depending on the calibration methods used,
systematic errors may be present in the speeds from anemographs and
consequently in the speeds reported in Metform 6910. The most likely
magnitude of the error is +5%.
* Stuck wind vane.
* Inaccurate estimation in the case of visual observations of wind.

Regards

Catherine Oldham
Librarian
Forestry Commission Library
Forest Research
Alice Holt Lodge
FARNHAM
Surrey
GU10 4LH

Tel: 01420 22255 ext 2334; Direct Line 01420 526260; Fax: 01420 23653;
email: [email address]

www.forestry.gov.uk
www.forestresearch.gov.uk

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Thank you for your help, this is very useful.

Kind regards,

E. Farndale