Volcanically related secular trends in atmospheric transmission at mauna loa observatory, hawaii.

Twenty years of atmospheric transmission data from Mauna Loa Observatory show secular decreases at irregular intervals. In addition, a regular annual variation is present during unperturbed as well as perturbed periods. These variations in transmission can be measured to a few tenths of a percent from the data record. Transient decreases in transmission are strongly correlated with explosive volcanic eruptions that inject effluent into the stratosphere. Recovery from these ejections takes as much as 8 years and the recovery curve is linear. Observations in 1977 at Mauna Loa show that, for the first time since the Mount Agung eruption in 1963, the atmospheric transmission of direct-incidence solar irradiation at Mauna Loa returned to values measured in 1958 to 1962.