Ash and ice clouds during the Mt Kelud February 2014 eruption as interpreted from IASI and AVHRR/3 observations

Arve Kylling

doi:10.5194/amt-9-2103-2016

Abstract

Abstract. During the Mt Kelud February 2014 eruption the ash cloud was detectable on 13–14 February in the infrared with the reverse absorption technique by, for example, the Advanced Very High Resolution Radiometer (AVHRR/3). The Infrared Atmospheric Sounding Interferometer (IASI) observed the ash cloud also on 15 February when AVHRR did not detect any ash signal. The differences between ash detection with AVHRR/3 and IASI are discussed along with the reasons for the differences, supported by radiative transfer modelling. The effect of concurrent ice clouds on the ash detection and the ash signal in the IASI measurements is demonstrated. Specifically, a radiative transfer model is used to simulate IASI spectra with ash-only, with ice cloud only and with both ash and ice clouds. It is shown that modelled IASI spectra with ash and ice clouds reproduce the measured IASI spectra better than ash-only- or ice-only-modelled spectra. The ash and ice modelled spectra that best reproduce the IASI spectra contain about a factor of 12 less ash than the ash-only spectra that come closest to reproducing the measured spectra.

Highlights

During volcanic eruptions large quantities of ash may be ejected high into the atmosphere
During the Mt Kelud February 2014 eruption the ash cloud was detectable on 13–14 February in the infrared with the reverse absorption technique by, for example, the Advanced Very High Resolution Radiometer (AVHRR/3)
It was shown that modelled spectra including both ash and ice clouds better reproduced the Infrared Atmospheric Sounding Interferometer (IASI) measured spectra compared to modelled spectra including only ash

Summary

Introduction

During volcanic eruptions large quantities of ash may be ejected high into the atmosphere. The ash may be observed by both UV-visible and infrared (IR) satellite instruments. The ash make volcanic clouds rich on ice-forming nuclei. The dominant volatile in explosive volcanic eruptions is water and for eruptions reaching high and cold altitudes eruption plumes may contain ice. Durant et al (2008) showed that compared to similar meteorological clouds, enhanced ice crystal concentrations and smaller average ice size may be expected in volcanic clouds. The “specific chemical and physical properties of volcanic ash particles that could affect their ability to induce ice formation are poorly understood” (Kulkarni et al, 2015)

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