Abstract
Abstract. On 16–17 September 2013 strong surface winds over tephra deposits in southern Iceland led to the resuspension and subsequent advection of significant quantities of volcanic ash. The resulting resuspended ash cloud was transported to the south-east over the North Atlantic Ocean and, due to clear skies at the time, was exceptionally well observed in satellite imagery. We use satellite-based measurements in combination with radiative transfer and dispersion modelling to quantify the total mass of ash resuspended during this event. Typically ash clouds from explosive eruptions are identified in satellite measurements from a negative brightness temperature difference (BTD) signal; however this technique assumes that the ash resides at high levels in the atmosphere. Due to a temperature inversion in the troposphere over southern Iceland during 16 September 2013, the resuspended ash cloud was constrained to altitudes of < 2 km a.s.l. We show that a positive BTD signal can instead be used to identify ash-containing pixels from satellite measurements. The timing and location of the ash cloud identified using this technique from measurements made by the Visible Infrared Imaging Radiometer Suite (VIIRS) on board the Suomi National Polar-orbiting Partnership (NPP) satellite agree well with model predictions using the dispersion model NAME (Numerical Atmospheric-dispersion Modelling Environment). Total column mass loadings are determined from the VIIRS data using an optimal estimation technique which accounts for the low altitude of the resuspended ash cloud and are used to calibrate the emission rate in the resuspended ash scheme in NAME. Considering the tephra deposits from the recent eruptions of Eyjafjallajökull and Grímsvötn as the potential source area for resuspension for this event, we estimate that ∼ 0.2 Tg of ash was remobilized during 16–17 September 2013.
Highlights
Iceland is one of the most active volcanic regions on Earth, with ≥ 20 eruptions per century (Thordarson and Höskuldsson, 2008), and explosive eruptions can leave behind widespread ash deposits (e.g. Larsen et al, 2001; Carey et al, 2010; Jude-Eton et al, 2012)
The flow rate sampled by the optical particle counter (OPC) is 1 L min−1, and particle concentrations are calculated from the count data by assuming that particles are spherical and have a density of 2300 kg m−3
The Visible Infrared Imaging Radiometer Suite (VIIRS) satellite imagery of the resuspended ash cloud during 16–17 September 2013 clearly indicates that the source of the remobilized ash cloud is over southern Iceland, and the two distinct plumes observed in the visible imagery (Fig. 4) suggest that both the Eyjafjallajökull and Grímsvötn deposits are the primary sources of the remobilized ash
Summary
Iceland is one of the most active volcanic regions on Earth, with ≥ 20 eruptions per century (Thordarson and Höskuldsson, 2008), and explosive eruptions can leave behind widespread ash deposits (e.g. Larsen et al, 2001; Carey et al, 2010; Jude-Eton et al, 2012). Larsen et al, 2001; Carey et al, 2010; Jude-Eton et al, 2012) These deposits are subject to intense aeolian processes: Iceland is windy, and the lack of vegetation inhibits soil formation and particle binding, resulting in significant remobilization events in the years following a volcanic eruption (Arnalds et al, 2016). In the following year the eruption of Grímsvötn resulted in further widespread tephra deposits (Hreinsdöttir et al, 2014), providing an additional source of remobilized ash which is not accounted for in the calibration presented in Leadbetter et al (2012). We use satellite-based measurements in combination with radiative transfer modelling to quantify the total column mass loadings of the resuspended ash cloud These are used to calibrate the emission rate applied in the resuspension scheme in NAME.
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