Quantification of volcanic cloud top heights and thicknesses using A‐train observations for the 2008 Chaitén eruption

Abstract

New evidence of vertically thin (< 400 m), low‐level (< 10 km) volcanic ash clouds, as well as confirmation of previously reported high‐level (>10 km) ash clouds, from the May 2008 Chaitén eruption in southern Chile is presented. A‐train remote sensors were used to measure high‐resolution volcanic cloud top heights (VCTHs) during the explosive phase (2–10 May 2008) of the eruption. Ash clouds were identified using a reverse absorption technique applied to hyperspectral measurements taken by the Atmospheric Infrared Sounder. Once identified, heights and thicknesses were derived from the Cloud‐Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument. As these two instruments are part of the same constellation of satellites, coincident retrievals are routinely possible. Collocation of the data allowed for detection of volcanic ash within CALIOP profiles. Using a simple thresholding algorithm, VCTH and thickness were derived from the CALIOP profiles. A total of 12 VCTH measurements, ranging from 3.7 to 16.6 km, have been derived. Back trajectories from the Hybrid Single Particle Lagrangian Integrated Trajectory dispersion model were used as a check on volcanic origin of the detected ash clouds. Ensemble forward trajectories were generated to demonstrate how the new data could be used to improve Volcanic Ash Advisory Center operations. The findings reported here demonstrate several cases where low‐level ash was not recorded previously and include observations of thin ash clouds at large distances (∼4000 km) from the volcano.

Lidar ratios of stratospheric volcanic ash and sulfate aerosols retrieved from CALIOP measurements

“…The AIRS spectrometer disperses upwelling radiation across highly sensitive detector arrays, which results in 2378 spectral samples (nominal spectral resolution of λ/∆λ = 1200). These high-spectral resolution measurements cover three infrared wavebands (3.74-4.61 µm, 6.20-8.22 µm and 8.8-15.4 µm;Aumann et al, 2003) and can be used to detect volcanic ash (Prata et al, 2015) and SO 2 (Hoffmann et al, 2014). An individual AIRS granule comprises 90…”

“…We present CALIOP-derived lidar ratios for the ash layers produced by the 2011 Puyehue-Cordón Caulle (hereafter Puyehue) eruption and the sulfate layers produced by the Kasatochi and Sarychev Peak (hereafter Sarychev) eruptions in 2008 and 2009, respectively. We use independent, passive infrared detection from the Atmospheric Infrared Sounder (AIRS) to identify volcanic ash in CALIOP profiles following the method presented by Prata et al (2015). We also extend this method to sulfates using SO 2 as a proxy for SO 4 2− .…”

Volcanic ash in bare ice south of Sør Rondane Mountains, Antarctica: geochemistry, rock magnetism and nondestructive magnetic detection with SQUID gradiometer

“…Terminal fall velocity of particles with mean diameter of 50 μm is calculated as ~0.1 m/s. Height of the volcanic cloud is controlled by the magma discharge rate and wind conditions (e.g., Suzuki and Koyaguchi 2013), which could reach up to 16 km (e.g., Prata et al 2015). Assuming that volcanic cloud with column height of 12 km was formed by an explosive phreatomagmatic or magmatic eruption, ash particles with diameter of 50 μm would have taken ~28 h to settle down onto the surface of sampling sites (altitude ~2 km).…”

Cloud Photogrammetry from Space

“…Pros / Cons Lidar and radar (Carn et al, 2009;Karagulian et al, 2010;Prata et al, 2015;Stohl et al, 2011) + very high vertical resolution and accuracy -too long revisit time (16 days) and only nadir observations from currently operational instruments (lidar CALIOP, radar CPR)…”