Abstract
Solar eclipses provide a rapidly changing solar radiation environment. These changes can be studied using simple photodiode sensors, if the radiation reaching the sensors is unaffected by cloud. Transporting the sensors aloft using standard meteorological instrument packages modified to carry extra sensors, provides one promising but hitherto unexploited possibility for making solar eclipse radiation measurements. For the 20 March 2015 solar eclipse, a coordinated campaign of balloon-carried solar radiation measurements was undertaken from Reading (51.44°N, 0.94°W), Lerwick (60.15°N, 1.13°W) and Reykjavik (64.13°N, 21.90°W), straddling the path of the eclipse. The balloons reached sufficient altitude at the eclipse time for eclipse-induced variations in solar radiation and solar limb darkening to be measured above cloud. Because the sensor platforms were free to swing, techniques have been evaluated to correct the measurements for their changing orientation. In the swing-averaged technique, the mean value across a set of swings was used to approximate the radiation falling on a horizontal surface; in the swing-maximum technique, the direct beam was estimated by assuming that the maximum solar radiation during a swing occurs when the photodiode sensing surface becomes normal to the direction of the solar beam. Both approaches, essentially independent, give values that agree with theoretical expectations for the eclipse-induced radiation changes.This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.
Highlights
Solar eclipses provide an unusual opportunity to study a rapid and well-characterized change in the solar radiation entering the atmosphere
The path of the 20 March 2015 total solar eclipse across the North Atlantic and through the Faroe Islands generated an appreciable partial eclipse in the northern UK and Iceland. This presented an opportunity for a coordinated campaign of solar radiation measurements using radiometer radiosondes, launched from the University of Reading’s Atmospheric Observatory, the UK Met Office’s Lerwick site and the Icelandic Meteorological Office facilities at Reykjavik
To increase the likelihood of the sensors being above the cloud during the time of maximum eclipse, the radiosondes were launched from each site close to 0845 UT
Summary
Solar eclipses provide an unusual opportunity to study a rapid and well-characterized change in the solar radiation entering the atmosphere. Weather balloons, carrying meteorological instrument packages returning data by radio (radiosondes), potentially offer inexpensive platforms for such measurements. Some disadvantages, such as motion associated with the payload, limitations in weight, power and opportunities for instrument recovery, may, all have contributed to radiosonde platforms having been underexploited for eclipse measurements. A new data acquisition system has been developed to expand the science capabilities of standard commercial radiosonde systems in routine use internationally by meteorological services [2] This system enhancement has already been used to successfully deploy a solar radiation sensor [3]. Both items are simple and inexpensive, which, as for the radiosonde itself, removes the need for them to be recovered: the instrumentation can be regarded as disposable
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