Regional radiative impact of volcanic aerosol from the 2009 eruption of Mt. Redoubt

Abstract

Abstract. High northern latitude eruptions have the potential to release volcanic aerosol into the Arctic environment, perturbing the Arctic's climate system. We present assessments of shortwave (SW), longwave (LW) and net direct aerosol radiative forcing efficiencies and atmospheric heating/cooling rates caused by volcanic aerosol from the 2009 eruption of Mt. Redoubt by performing radiative transfer modeling constrained by NASA A-Train satellite data. The optical properties of volcanic aerosol were calculated by introducing a compositionally resolved microphysical model developed for both ash and sulfates. Two compositions of volcanic aerosol were considered in order to examine a fresh, ash rich plume and an older, ash poor plume. Optical models were incorporated into a modified version of the SBDART radiative transfer model. Our results indicate that environmental conditions, such as surface albedo and solar zenith angle (SZA), can influence the sign and the magnitude of the radiative forcing at the top of the atmosphere (TOA) and at the surface and the magnitude of the forcing in the aerosol layer. We find that a fresh, thin plume (∼2.5-7 km) at an AOD (550 nm) range of 0.18-0.58 and SZA = 55 • over snow cools the surface and warms the TOA, but the opposite effect is seen for TOA by the same layer over ocean. The layer over snow also warms by 64 W m −2 AOD −1 more than the same plume over seawater. The layer over snow at SZA = 75 • warms the TOA 96 W m −2 AOD −1 less than it would at SZA = 55 • over snow, and there is instead warming at the surface. We also find that plume aging can alter the magnitude of the radiative forcing. An aged plume over snow at SZA = 55 • would warm the TOA and layer by 146 and 143 W m −2 AOD −1 less than the fresh plume, while the aging plume cools the surface 3 W m −2 AOD −1 more. Comparing results for the thin plume to those for a thick plume (∼3-20 km), we find that the fresh, thick plume with AOD(550 nm) = 3, over seawater, and SZA = 55 • heats the upper part of the plume in the SW ∼28 K day −1 more and cools in the LW by ∼6.3 K day −1 more than a fresh, thin plume under the same environmental conditions. We compare our assessments with those reported for other aerosols typical to the Arctic environment (smoke from wildfires, Arctic haze, and dust) to demonstrate the importance of volcanic aerosols.

Porous aerosol in degassing plumes of Mt. Etna and Mt. Stromboli

“…Consequently, values of the aerosol refractive index have to be estimated with a retrieval code or specified a priori, i.e., preassigned. When values are preassigned, the refractive index of bulk matter or sulfuric acid solutions are commonly used (see, e.g., Oppenheimer, 2000, 2001;Spinetti et al, 2003;Kahn et al, 2007;Martin et al, 2009;Marenco et al, 2011;Young et al, 2012). Examples for which the refractive index was retrieved along with a size distribution can be found in the works by Toledano et al (2012), Waquet et al (2014), and references therein.…”

The impact of atmospheric mineral aerosol deposition on the albedo of snow & sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

“…Indeed, high-latitude volcanic eruptions frequently emit large quantities of ash into the Arctic (e.g. Stone et al, 1993;Zielinski et al, 1997;Young et al, 2012) disturbing the Arctic's climate system. The analysis of core samples in Arctic sea ice has exposed the presence of volcanic ash through traces of silicate shards and aged tephra (Ram and Gayley, 1991).…”

Synchronous polar winter starphotometry and lidar measurements at a High Arctic station

“…Important examples in the Arctic include the effects of transported biomass burning, forest fire and volcanic plumes (e.g. Stone et al, 2008;Engvall et al, 2009;Young et al, 2012). In addition, aerosols play a profound indirect role serving as condensation nuclei for new clouds and modifying properties of already existing clouds.…”