Stratospheric dust measurements, 1970–1977

Stratospheric aerosol measurements have been made by laser radar at São José dos Campos (23°S, 46°W) since July 1970. From 1970 to 1974 the measured scattering ratios for the 20‐km layer were similar to those reported for other locations. A large increase was observed in April 1975, 6 months after the eruption of Volcán de Fuego in Guatemala. This delay in the transport of the Fuego dust to our latitude is interpreted as being due to the inhibition of southward eddy transport during the southern summer by the mean meridional circulation. A maximum monthly average scattering ratio of 1.28 measured at a wavelength of 5890 Å was observed at 20 km in August 1975. Since early 1976 the 20‐km scattering ratio has oscillated around a value of about 1.15, but the integrated columnar backscattering coefficient above 17 km, indicative of the total stratospheric dust loading, has increased by about 40%. Scattering from the upper stratosphere, at heights above 30 km, was observed in the southern springs of 1971, 1972, and 1973. There appears to be some evidence that the dust responsible for this scattering was of extraterrestrial origin.