Toms and Avhrr Observations of Drifting Volcanic Clouds from the August 1991 Eruptions of Cerro Hudson

Clouds of fine volcanic ash (1-15 μm) and sulfur dioxide gas from Cerro Hudson 5 three August 1991 eruptions were measured with the infrared advanced very high resolution radiometer (AVHRR) and the ultraviolet total ozone mapping spectrometer (TOMS). TOMS data show that the first eruption released 700 kT SO 2 on August 8, a second eruption on August 12 produced about 600 kT, and the third on August 15 released about 2700 kT SO 2 . Following the third eruption, the SO 2 and ash appear to have separated, with the ash residing at lower levels near the tropopause and losing 90% of its mass within a few days, while the SO 2 was stratospheric, losing only two-thirds of its mass over the first week. A fragment of the volcanic cloud drifted across Australia on August 19-20 where it was characterized by both TOMS and AVHRR; because this cloud was a significant concern to aviation, it offers a successful test of long-term cloud detection by satellites.