The monitoring instruments at the Wageningen University weather station clearly registered the solar eclipse despite the thick cloud cover on 20 March. Around 10:36 h a strong reduction in radiation levels was discernible. For the human eye it was perceived as far less spectacular because of its adaptation capabilities.
The meteorological instruments in weather station De Veenkampen belonging to the Meteorology and Air Quality Group at Wageningen University enables researchers to study the solar radiation intensity reaching the earth’s surface. They noticed a strong reduction during the solar eclipse. Around 10:36 h, the radiation meters (pyranometers) were registering almost no radiation. At that moment the coverage of the sun was at its maximum. The solar radiation penetrating the cloud cover was reduced to around 15 Watts per square metre. Without an eclipse the intensity would normally be about 100 W/m2 and without any cloud cover, at least 450 W/m2. This measured reduction compares well with the 85% blocking of the sun by the moon. The effect of the solar eclipse was also noticeable in the air temperature close to the ground at a height of 10 cm, where the air cooled by about 2°C. The observed small delay in air temperature cooling is caused by the heat stored in the grass and soil layers.
Observations made with the naked eye are different to those made with a pyranometer instrument. The human eye would perceive the 85% drop in brightness level as 50% only. In addition, the slow change in brightness levels made it even less detectible by the human eye.