On Monday, the LI-COR campus was in the path of totality for the August 21, 2017 solar eclipse. Here are data collected during the eclipse at our campus in Lincoln, Nebraska, USA. Even though cloud cover obscured our direct view of the eclipse, there were observable differences in light intensity, photosynthesis measurements, and environmental flux during totality.
The partial eclipse began around 11:37 AM CST, with totality happening from 1:02 PM to 1:04 PM. The eclipse was over by 2:37 PM. Check out our live broadcast of the solar eclipse on Facebook.
Of course, we had to measure light intensity during a solar eclipse. Four recently-calibrated LI-190R quantum sensors measured photosynthetic photon flux density (PPFD in µmol m-2 s-1) and five LI-200R pyranometers measured global irradiance (W m-2) every five seconds. The cloud cover before the event kept light intensity lower than usual. During totality, all sensors dropped to near zero, and then the sensors quickly recovered to readings typical of mostly sunny conditions.
Figure 1. Average PPFD during the eclipse.
Figure 2. Average global irradiance during the eclipse.
Leaf-level photosynthesis was monitored during the solar eclipse outside a greenhouse on the LI-COR campus, using two LI-6800 Portable Photosynthesis Systems on a sunflower leaf and a rose leaf. There was significant cloud cover throughout the event, but the impacts of the eclipse can still be seen. PPFD values (in μmol m-2 s-1) dropped to near zero during the totality, and assimilation rates dropped to a minimum of -1.5 μmol m-2 s-1 (Figure 3). Stomatal conductance also dropped to a minimum of ~0.5 mol m-2 s-1, lagging the minimum light level by a few minutes. By about 2 PM, PPFD returned to typical levels, with minimal cloud cover and an increase in assimilation, as well.
Figure 3. PPFD, Leaf Temperature, Assimilation and Stomatal Conductance on a sunflower leaf and a rose leaf during the solar eclipse. The vertical red line indicates the time of totality. The horizontal green line in the middle plot is an assimilation rate of zero (i.e. assimilation and respiration are equal, thus no net carbon exchange is occurring). This occurred at a light intensity of ~ 30 umol m-2 s-1.
Figure 4. Assimilation rate during the eclipse as a function of PPFD values. Higher PPFD values measured in the instrument on the rose leaf are likely due to an angle more normal to the sun.
We also looked at environmental flux data from our LI-COR Experimental Research Station (LERS). Typically, we process eddy covariance data in 30 minute intervals. For the eclipse, we processed the flux data in 15 minute intervals to get a more detailed look at what went on in the ecosystem. The CO2, H2O, and air temperature data were processed in 1 minute intervals.
The eclipse brought down the available energy for a brief period of time. This is reflected in the scalar concentrations and fluxes which are directly or indirectly driven by available energy. The CO2 mixing ratio increased and attained a peak value of about 452.6 ppm about 45 minutes after the eclipse totality. The water vapor mixing ratio also showed a decreasing trend, but recovered much faster than CO2 after the totality. Air temperature also showed a similar pattern as the CO2 concentration.
During the eclipse, the ecosystem shifted from being a sink for CO2 to a source of CO2 (see Figure 8). CO2 fluxes recovered slowly almost 45 minutes after totality. Sensible heat and latent heat fluxes showed similar trends.
Figure 5. CO2 mixing ratio as a function of time during the eclipse.
Figure 6. H2O mixing ratio as a function of time during the eclipse.
Figure 7. Air temperature during the eclipse.
Figure 8. CO2 flux during the eclipse.
Figure 9. Sensible heat flux during the eclipse.
Figure 10. Latent heat flux during the eclipse.
There you have it: light intensity, photosynthesis, and environmental flux data from the 2017 Great American Eclipse. While our scientists were running these experiments, other LI-COR employees gathered around to enjoy the show. Many had never seen a total solar eclipse before. Even with the clouds, we had a great time observing this incredible phenomenon.