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About this plot:
Solar radiation (downward, short-wave radiation) affects the activity of honey bees. Bees flying in the direct sunlight have higher thorax temperatures, which slows them down. Burrill and Dietz (1981) showed that the number of foraging flights increased up to a level of 450 W/m^2, and then decreased as the radiative flux increased above 450 W/m^2.
Solar radiation also warms the bee hive, which raises the temperature in the hive. During foraging higher temperatures around 90-95F accelerate the curing of honey. In the winter it keeps the hive warmer.
When the maximum daily solar radiation drops below 100 W/m^2 and the cloud cover exceeds 75 - 90% it is assumed there is not enough polarized light for the bees to navigate long distances,. Consequently we assume the bees cannot forage even if the temperature and wind speeds are favorable.
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