Ground Heat Flux Into Several Surfaces During A Partial Solar Eclipse

Abstract

Ground Heat Flux Into Several Surfaces During A Partial SolarEclipse Gregory E. Borgel* Aspects of the energy balance of the surface during a solar eclipse have been treated on a number of occasions.1 However, none of this work has been particularly concerned with the heat flux into the surfaces common in our urban environment. For this paper the ground heat fluxes (G) into three such surfaces—concrete (Gc), grass (Gg), and tarpaper roofing material (Gr)—were examined. Sample blocks of each of the three surfaces were prepared witii heat flux plates permanentìy imbedded at a depth of .5 cm. Readout was onto Rustrak strip-chart recorders and a Thornthwaite soil heat flux recorder. For purposes of correlation with G measurements, the incoming direct and diffuse solar radiation (global radiation or O + q) were recorded by a star pyranometer read into a strip-chart recorder. * Mr. Rorgel was a graduate student in geography at the University of California, Los Angeles 90024, when this paper was presented at the 1970 meeting of the Association at Santa Cruz. He is currently on leave from UCLA. He expressed thanks to the U. S. Naval Observatory, Washington, D. C, for data on the local solar eclipse, to Stella Louie for computer programming, and to Dr. W. H. Terjung for guidance and assistance. 1 W. N. Abbott, "On certain radiometric effects during the partial solar eclipse of February 25, 1952," Geofis, Pura e Applicada, Vol. 39, (1958), pp. 186-193; P. Jagannathan, O. Chacko, and S. P. Venkiteshwaran, "Insolation measurements at Poona during the solar eclipse on 14 December 1955," Indian Journal of Meteorology and Geophysics, Vol. 8, (1957), pp. 93-98; W. O. Pruitt, F. Lourence, and Todd V. Crawford, "Radiation and energy balance changes during the eclipse of 20 July 1963," Journal of Applied Meteorology, vol. 4 (1965), pp. 272-278; U. Ushiyama, F. Narita, Y. Suzuki, and T. Suzuki, "The variation of the surface meteorological elements," Geophysical Magazine, Vol.19, (1949), pp. 78-94. 171 172ASSOCIATION OF PACIFIC COAST GEOGRAPHERS The eclipse considered in this study occurred on March 7, 1970. At the observation site in the San Fernando Valley, California, the eclipse began at 8:29 a.m., achieved a maximum of 23.7% obscuration of the solar disk at 9:25 a.m., and ended at 10:25 a.m., Pacific Standard Time.2 Solar Radiation Measurements Observed Q + q during the eclipse and "expected" Q -+- q are shown in Figure 1. The latter was derived from data of another study one year earlier at a nearby site.3 A downward adjustment of the "expected" curve was made by varying the transmissivity coefficient by computer until a fit was obtained between the "expected" curve and the observed O + q on the eclipse day before and after the eclipse itself. The observed O + q plotted in Figure 1 was below the "expected " 0 + 9 throughout the eclipse. The maximum percent difference between expected and observed occurred at 9:25, which was also the time of the maximum percent obscuration of the sun. The maximum absolute difference between expected and observed Q + q occurred slightìy after the eclipse maximum because both curves were attaining higher absolute values as solar altitude increased. Table 1. Expected and Observed Q + q in Langleys per Minute "Expected" Observed TimeQ + q Q -{- q DifferenceEclipse PercentPercent 9:00 .........................325 .270 17.016.1 9:20 .........................400 .305 23.823.3 9:25 .........................410 .310 24.123.7 9:40 .........................455 .355 21.921.2 10:00 .........................505 .450 10.911.5 2 Private communication, U.S. Naval Observatory, Nautical Almanac Office, Washington, D.C, 20390. 3 Werner H. Terjung, G. E. Borgel, et al., "The effect of a cyclonic storm on the energy fluxes at the urban interface—a preliminary experiment," Archiv für Meteorologie, Geophysik und Bioklimatologie, Series B, Vol. 19, (1971), in press. YEARBOOK · VOLUME 34 · 1972 173 •5r¦4r¦2r -i--------1---------1---------T- -i------1------r Q+q *~*Exptcttd +"+Ob»»rv«d _l____I____I____1_ _1____I____' ¦____I____I____l_ Figure 1. Expected and observed direct and diffuse solar radiation . 9 IOIl1213» PST Max. Eclipse -i-------?-------1-------1-------1-------?-------1-------t- •4r I -3 Figure 2. "Normal...