Global evolution of the Mt. Pinatubo volcanic aerosols observed by the infrared limb‐sounding instruments CLAES and ISAMS on the Upper Atmosphere Research Satellite

Abstract

The cryogenic limb array etalon spectrometer (GLAES) and the improved stratospheric and mesospheric sounder (ISAMS) instruments on board the Upper Atmosphere Research Satellite (UARS) have been used to produce global information on the Mt. Pinatubo volcanic aerosol for the period from October 1991 to April 1993. The satellite infrared extinction measurements near 12 μm are converted into the aerosol‐related parameters necessary for modelling the effects of the volcanic aerosol on the aeronomy of the stratosphere and are presented as zonal mean distributions for 80°S to 80°N averaged over ∼35‐day periods. The aerosol composition is derived from the GLAES and ISAMS temperature measurements and the water vapour abundances are obtained from the microwave limb sounder (MLS). The aerosol volume density is obtained from the extinction measurements from which the surface area density and the effective particle radius are estimated. The maximum aerosol surface area density has a value of about 50 μm2 cm−3 at a height of 24 km at the equator in October 1991, before decaying exponentially with a time constant of 443±10 days. The surface area density remained well above preemption values in April 1993. The effective particle radius in the tropics decays monotonically from 0.65 μm in October 1991 to 0.4 μm in April 1993. The global aerosol sulphate mass loading is 19.5 Mt in October 1991 and decays exponentially with a time constant of 342±8 days to a value of 4.3 Mt by April 1993. Four months after the eruption the calculated optical thickness at 1.02 μm was ∼0.25 in the tropics. Rate constants are derived for the heterogeneous reactions of N2O5 and ClONO2 on the sulphate aerosols. The application of the aerosol parameters to the investigation of tracer transport, heterogeneous chemistry, and radiative transfer is discussed.