The North American Solar Eclipse of 2017: Observations on the Surface Biosphere, Time Responses and Persistence
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The North American Solar Eclipse of 2017: Observations on the Surface Biosphere, Time Responses and Persistence Bruce B. Hicks1 Neal S. Eash3
· William R. Pendergrass III2 · Joel N. Oetting3 · Deb. L. O’Dell3 ·
Received: 21 February 2020 / Accepted: 23 October 2020 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract Observations of the near-surface components of the vegetated terrestrial air–surface system during and around the complete solar eclipse of 21 August 2017 were made in the U.S.A. at three sites of intensive measurement in Tennessee and at a number of locations in Idaho. Data obtained relate to a variety of surfaces, from barren to forest. Results reveal details of how the atmospheric, vegetative, and soil components of the ecosystem respond to a short-term change in incoming radiation. In particular, the role of vegetation as it contributes to thermal storage is demonstrated. The observations enable examination of the lags involved as the influence of the reduction in incoming radiation propagates through the environment. The variety of sites reveals the following: (a) the change in the surface temperature as measured using infrared thermometry followed quickly after the change in incoming solar radiation; (b) the sensible heat flux became negative for about 30 min around the time of the total eclipse; (c) CO2 fluxes reversed in sign; (d) latent heat fluxes continued after the sensible heat flux reversed in sign (these last two observations indicate the role of soil efflux of CO2 and water vapour); (e) changes in air temperature lagged, dependent upon surface vegetation and the observation height; (f) the lull in wind speed commonly associated with an eclipse was observed to be shallow, extending vertically to a few tens of metres; and (g) the magnitude of the air-temperature response to the eclipse depended on site-specific factors, but a few tens of metres above the surface the site-specificity disappeared. Keywords Heat storage · Solar eclipse · Thermal inertia · Time lags
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Bruce B. Hicks [email protected]
1
Metcorps, P.O. Box 1510, Norris, TN 37828, USA
2
NOAA ARL Atmospheric Turbulence and Diffusion Division, P.O. Box 2456, Oak Ridge, TN 37833, USA
3
Department of Biosystems Engineering and Soil Science, University of Tennessee, Knoxville, TN 37991, USA
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B. B. Hicks et al.
1 Introduction In the early afternoon of 21 August 2017, a solar eclipse was observed at several research sites in east Tennessee. These sites carried instrumentation permitting an examination of the way in which the different vegetated surfaces reacted. The first location (35.654° N; 84.405° W, in Sweetwater, Tennessee) was a field of grazing pasture, carrying a suite of radiation sensors, as well as sonic anemometry. About 5 km north-north-east of the first location, a second site (35.696° N; 84.387° W, in Loudon, Tennessee) was of mature maize, instrumented with both sub-surface and in-air systems, also including sonic ane
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