Atmospheric solar transmission at Mauna Loa

E.G. Dutton

National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Climate Monitoring and Diagnostics Laboratory, 325 Broadway, Mail Stop R/E/CG1, Boulder, Colorado 80303, U.S.A.

Period of Record

1958-92

Methods

The atmospheric transmission of solar irradiation at Mauna Loa, Hawaii, U.S.A., was measured over a broad spectral band by means of a normal-incidence pyrheliometer having a quartz window transmitting over the range 300-3000 nm. In order to ensure that measurements were independent of instrument changes (including differences among the several pyrheliometers used over the period of record, instrument errors and drift, and variations in the transmittance of the quartz window due to temperature changes) and the effects of Sun-Earth geometry (i.e., seasonal and time of day changes in solar irradiance), a ratioing method was used whereby daily values of atmospheric transmission [known as atmospheric transmission factor (ATF)] were calculated by using the equation

ATF = 1/3 (I5/I4 + I4/I3 + I3/I2) ,

where I is the measured direct-incidence solar irradiation and the subscripts of I are the secants of the zenith angle at the time of measurement (see Ellis and Pueschel 1971; also Mendonca et al. 1978; Dutton 1992). Variations in ATF can be interpreted as instrumentally and temporally stable equivalents of changes in the vertical transmission of the direct solar beam. Thus, they are measures of the relative changes in total optical depth. The data base presented here in Trends consists of monthly averages of ATF for cloud-free mornings at the Mauna Loa Observatory in Hawaii. At Mauna Loa, a month typically has from 5 to 20 cloud-free mornings, with an average of 15.



Mauna Loa, Hawaii, U.S.A.
Barren lava field of an active volcano
19°32' N, 155°35' W
3397 m above MSL

Solar Transmission at Mauna Loa Trends

Solar Transmission References

CITE AS: Dutton, E.G. 1994. Atmospheric solar transmission at Mauna Loa. In Trends: A Compendium of Data on Global Change. ORNL/CDIAC-65. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

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Date created 12/06/96 (jaw)