Lidar observations of Kasatochi volcano aerosols in the troposphere and stratosphere

L. Bitar, T. J. Duck, N. I. Kristiansen, A. Stohl, and S. Beauchamp, Journal of Geophysical Research, 115, D00L13, doi: 10.1029/2009JD013650, 2010.

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Abstract. The eruption of Kasatochi volcano on 7-8 August 2008 injected material into the troposphere and lower stratosphere of the northern mid-latitudes during a period of low stratospheric aerosol background concentrations. Aerosols from the volcanic plume were detected with a lidar in Halifax, Nova Scotia (44.64N, 63.59W) one week after the eruption and for the next four months thereafter. The volcanic origin of the plume is established using the FLEXPART Lagrangian particle transport model for both the stratosphere and troposphere. The stratospheric plume descended 47.1 +/- 2.8 m/day on average as it dispersed, corresponding to a cooling rate of 0.60 +/- 0.07 K/day. The descent rate was the same for the tropopause (within statistical uncertainties). The top of the plume remained steady at about 18 km altitude, and was likely sustained by vertical eddy diffusion from large-scale horizontal mixing. The lower boundary of the plume descended with the tropopause. The optical depth between 15-19 km altitude was relatively constant at 0.003 for 532 nm wavelength. Observations and modeling of Kasatochi aerosols in the middle and lower troposphere indicate they reached the ground. The volcanic contribution to surface PM2.5 did not exceed 5 ug/m^3 at the measurement site.



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