Radiation and Energy Balance Changes During the Eclipse of 20 July 1963

Abstract

Several radiation components, the energy balance of a vegetative surface, and the latent heat flux from a shallow water surface were measured at Davis, Calif.,ay of the 20 July 1963 eclipse and on the following day. Both days were clear and very similar temperature, humidity and wind conditions were experienced. The eclipse period lasted from 1135 to 1359 Pacific Standard Time. Maximum obscuration was at 1249 with 24.5 per cent of the sun's area affected (0.371 units of solar diameter). At time of maximum eclipse at Davis the total incoming shortwave, and normal incidence radiation was 24 per cent lower than at the same time on 21 July. Net radiation above a 12-cm tall perennial cover was reduced 27-28 per cent. Net radiation Just above a 2.5-cm layer of water underlain by a black polyethylene sheet was reduced 29 per cent. Changes in weight of a very sensitive 6.1-meter diameter lysimeter indicated that evapotranspiration followed the changing pattern of net radiation quite closely during the eclipse. The percentage reduction both at 1249 and for the total eclipse period was almost the same as for net radiation. The same was true for reduction of total convective and soil heat transfer for the overall eclipse period. A lag in response of evaporation to changing net radiation for the water surface was noted, although for the total eclipse period the per cent change of evaporation and net radiation was nearly identical.