Total Solar Eclipse 11 August 1999
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UK total solar eclipse - 11 August, 1999
John Harris, Head of Geography, Radley College, Abingdon UK.
mjh@radley.org.uk and www.rmplc.co.uk/eduweb/sites/radgeog/
"The coming eclipse will be a lifetime memory for those who are caught
up in it. No television or photograph can do it justice; it must be experienced.
Plan to be there." How could the Harris family resist, having read
Jay Anderson's of Environment Canada, "The enchantment of eclipses"
in the July 1999 edition of Weather, published by the Royal Meteorological
Society? Furthermore there was an urgent appeal for eclipse weather data
from Edward Hanna at the Department of Meteorology, University of Reading,
UK.
We packed a tent, recording equipment and emergency provisions and joined
the million or so UK eclipse watchers who travelled south west to Devon
and Cornwall to the narrow zone of totality which stretched from Newfoundland
in the west across Europe, Turkey, Iraq , Iran, Pakistan to India. We camped
at Yelverton on the edge of Dartmoor with its fascinating granite tors,
wild horses and moorland walks. The preceding few days were mainly clear
and sunny and conditions seemed hopeful for good viewing conditions. We
walked, cycled, explored and waited......
The morning of 11th August dawned bright and cloudless but by 7 am ominous
cloud was building from the west and the radio reported rain in Cornwall.
Meanwhile the general UK forecast suggested that most of central, eastern
and northern UK in the partial eclipse zone would benefit from a ridge of
high pressure with clear skies and good viewing conditions.
Having heard the pessimistic local forecast we jumped into the car and rushed
through narrow country lanes to the Dart Valley at Dartington (latitude
50.26N, longitude 3.41W), 12 km inland, west of Torbay in South Devon. This
proved to be a good choice. We arrived at 09.30 GMT and set up equipment
to record temperature, wind and pressure recordings at 5 minute intervals.
Readings were taken at 1 metre and 5 cm above ground level (in a shaded
location above a gravel surface, 4 metres from the main A385 road). Excitement
mounted as we watched the moon encroach. We continued to have frequent glimpses
despite a thin covering of cloud. Cloud obscured our final views during
the short period of totality and so we were not able to observe the diamond
ring, Baily's Beads, corona or other special effects. Fortunately we were
subsequently able to see pictures filmed from planes flying above cloud
level.
The temperature dropped, though not consistently (see data table and graph),
during the period leading up to and following totality. In the last 15 minutes
prior to totality the air felt damp and chilly. An overall drop of 1.9 deg
C was recorded at 1 metre and 2.3 deg C at 5 cm. The overall lowest temperature
of 15.7 deg C was recorded at ground level a few minutes after totality,
thus creating a minor temperature inversion effect. Temperatures then began
to slowly rise.
Fig 2: Temperature variations at Dartington, Devon, UK
Observations by John Harris, Geography Dept Radley College, UK
Fig 2: Temperature variations on the Isle of Purbeck
Observations by Mr J M Walker, Education Officer, Royal Meteorological Society
Location: Isle of Purbeck, 1.5 km WSW of Kingston, Dorset, UK
Grid ref of site: 943792
Height above sea level: 150 metres
Point where observations made: on a bridle-path, beside a field of maize,
the plants mostly 1 to 1.5 metres high.
Very slight slope upwards to the south, beyond which the land falls away
quickly to the English Channel.
Distance from the site to the sea: 1.7 km
Fairly steep slope to the north, down a field to a tarmacked country lane
(leading to a private estate) and, on the other side of the lane, a narrow
belt of woodland.
Maximum eclipse: 99.8% at 11:17 British Summer Time (10:17 GMT)
There was a slow and steady reduction in light level during the 45 minutes
preceding totality. Cows clustered and birds nested as "twilight"
descended. An eerie hush descended. The most rapid light reduction was in
the final few seconds before totality as the moon's shadow rushed overhead.
During totality an orange glow remained along much of the horizon. House
and car lights shone brightly and the skies rapidly filled with celebratory
fireworks. Thin cloud obscured our view of any stars or planets. Within
a minute the sky rapidly lightened.
A slight westerly wind (1 kph) continued intermittently during the observation
period, possibly as a result of our location in the west-east trending Dart
valley. There was no increased "eclipse wind" at the time of totality
as had been predicted by some researchers. Pressure remained constant at
1022 mb and there was no apparent change in cloud type or density.
Totality passed all too quickly in a frenzy of flash bulbs, fireworks and
clapping. We felt elated and were thrilled to have been part of this great
event. We spent the rest of the day blissfully unaware of the 38 mile long
traffic jams as eclipse watchers flooded out of south west England. This
was quite literally the experience of a lifetime since the next UK eclipse
will not be until 2090.
Table 1: Temperature changes at Dartington, Devon UK, 11 August, 1999
Shade readings were taken at 1 metre and 5 cm above ground level.
Times are GMT. Totality was at 10.11 GMT
Time 1 m 5 cm
09.40 17.9 18.0
09.45 17.4 17.1
09.50 17.6 17.5
09.55 17.2 17.2
10.00 17.3 17.3
10.05 16.8 16.9
10.10 16.5 16.4
10.15 16.4 16.6
10.20 16.0 15.7
10.25 16.1 15.8
10.30 16.6 15.8
10.35 16.6 16.5
10.40 16.8 16.4
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