Quantifying the Meteorological Effects of the 2017 Great American Solar Eclipse Using Citizen Scientist Observations

Solar eclipses provide scientists an opportunity to examine the response of the atmosphere to a sudden temporary reduction in insolation at the top of the atmosphere, which produces meteorological effects unlike those from the diurnal and seasonal cycles. Observations of past events reveal a wide range of temperature depressions associated with various eclipses. Several factors have been identified in controlling the amplitude and timing of the depression, and prevailing cloud cover during the eclipse has been identified as a likely major factor.

On 21 August 2017, North America witnessed a total solar eclipse, with the path of totality passing from the United States west coast to east coast. The major public interest in the event inspired GLOBE Observer to organize a citizen science observing campaign to record the meteorological effects of the eclipse. In addition to the clouds observations routinely collected by GLOBE Observer, the observation protocol was amended to include surface air temperature observations gathered by store-purchased thermometers used by observers in the field. 18,000 observers collected 75,000 temperature observations and 20,000 cloud observations. About 8,000 of the observers positioned themselves in the path of totality, giving a nearly unbroken record of the cloud and temperature effects of the eclipse across the contiguous United States.

The collection of both temperature and cloud observations provide an opportunity to quantify the cloud-temperature relationship. The unique character of citizen science, which provides data from a large number of observations with limited quality-control, requires a methodology that leverages the large number of observers. By grouping observers along the path of totality by 1? longitude bins, the errors from individual observers are averaged out, and the meteorological effects of the eclipse can be determined robustly. The data reveal a distinct relationship between prevailing cloud cover and the eclipse-induced temperature depression, in which regions with more (fewer) clouds tended to have smaller (larger temperature depressions. Overcast regions in the eastern United States had half the temperature perturbation of the clear-sky regions along the path of totality, and the contrast is greater when including the western US.