Particles in the great Pinatubo volcanic cloud of June 1991: The role of ice

Abstract

[1] Pinatubo's 15 June 1991 eruption was Earth's largest of the last 25 years, and it formed a substantial volcanic cloud. We present results of analysis of satellite-based infrared remote sensing using Advanced Very High Resolution Radiometer (AVHRR) and TIROS Operational Vertical Sounder/High Resolution Infrared Radiation Sounder/2 (TOVS/HIRS/2) sensors, during the first few days of atmospheric residence of the Pinatubo volcanic cloud, as it drifted from the Philippines toward Africa. An SO 2 -rich upper (25 km) portion drifted westward slightly faster than an ash-rich lower (22 km) part, though uncertainty exists due to difficulty in precisely locating the ash cloud. The Pinatubo clouds contained particles of ice, ash, and sulfate which could be sensed with infrared satellite data. Multispectral IR data from HIRS/2 were most useful for sensing the Pinatubo clouds because substantial amounts of both ice and ash were present. Ice and ash particles had peak masses of about 80 and 50 Mt, respectively, within the first day of atmospheric residence and declined very rapidly to values that were <10 Mt within 3 days. Ice and ash declined at a similar rate, and it seems likely that ice and ash formed mixed aggregates which enhanced fallout. Sulfate particles were detected in the volcanic cloud by IR satellites very soon after eruption, and their masses increased systematically at a rate consistent with their formation from SO 2 , which was slowly decreasing in mass during the same period. The initially detected sulfate mass was 4 Mt (equivalent to 3 Mt SO 2 ) and after 5 days was 12-16 Mt (equivalent to 9-12 Mt SO 2 ).Components: 12,820 words, 29 figures, 9 tables, 2 animations.

Analysis of global methane changes after the 1991 Pinatubo volcanic eruption

“…Lowe et al (1997) suggest that a large effect of enhanced stratosphere-troposphere exchange would be inconsistent with the decrease in observed δ 13 C in this period. However, other isotope data from this period do not support a strong decrease in δ 13 C between 1991(Quay et al, 1999.…”

“…Particles of ash emitted directly by the eruption would also absorb and scatter solar radiation, determining a similar effect on CH 4 lifetime. However, because of their lifetime of only a few days, they are considered to have a negligible global impact (Guo et al, 2004b;Niemeier et al, 2009) and are not included in our study.…”

Radiative and climate impacts of a large volcanic eruption during stratospheric sulfur geoengineering

“…Dust emissions are calculated online as a function of wind speed and hydrological parameters according to the Tegen et al (2002) scheme. We do not include volcanic ash emissions as it has been shown that ash sediments within a few days after the eruption from the stratosphere, and the area affected by the ash cloud is relatively small (Guo et al, 2004a). The effect of fine ash on the distribution of the volcanic cloud in the atmosphere is also relatively small .…”

Aerosol microphysics modules in the framework of the ECHAM5 climate model – intercomparison under stratospheric conditions

“…Since the flights were carried out in heights below 40 hPa the authors conclude to measure "fallout" from higher elevations. Due to the fact that these spectrometers were calibrated for sulphuric acid only and volcanic ash fallout terminates after a couple days after it was injected into the stratosphere (Guo et al, 2004), it can be assumed that these ultra large particles contain mainly sulphuric acid.…”