MAUNA LOA

Trends

Direct solar irradiance has been measured at the same location at Mauna Loa since 1958. The record from Mauna Loa is unique because of its long duration and essential completeness (data are missing for only 10 months since 1958) and because of the site's clear-sky and high-altitude location. The most prominent features of the record are the dramatic decreases in atmospheric transmission after the major explosive volcanic eruptions of Agung in 1963, El Chichón in 1982, and Pinatubo in 1991. A number of other smaller eruptions (e.g., Awu in 1965 and De Fuego in 1974) have also visibly affected the record (Mendonca et al. 1978). In addition, the data show an annual cycle: a statistically significant decrease in transmission from March through June (with a minimum in May) and a second, statistically insignificant, minimum in October. The spring minimum has been attributed primarily to an influx of tropospheric aerosols that are carried over Mauna Loa from Asia by seasonal winds (Dutton 1992). Other fluctuations, potentially random, are evident in the data; however, there is no evidence of a linear trend extending over the entire period of record.

Mauna Loa
Hawaii, U.S.A.
Barren volcanic mountain slope
19° 30' N, 155° 36' W
3397 m above MSL

Solar Transmission at Mauna Loa Graph

• Monthly atmospheric solar transmission at Mauna Loa