Radiative impact of an extreme Arctic biomass-burning event

Abstract

Abstract. The aim of the presented study was to investigate the impact on the radiation budget of a biomass-burning plume, transported from Alaska to the High Arctic region of Ny-Ålesund, Svalbard, in early July 2015. Since the mean aerosol optical depth increased by the factor of 10 above the average summer background values, this large aerosol load event is considered particularly exceptional in the last 25 years. In situ data with hygroscopic growth equations, as well as remote sensing measurements as inputs to radiative transfer models, were used, in order to estimate biases associated with (i) hygroscopicity, (ii) variability of single-scattering albedo profiles, and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass-burning emissions was applied to interpret the transport and transformation pathways. The provided MODTRAN radiative transfer model (RTM) simulations for the smoke event (14:00 9 July–11:30 11 July) resulted in a mean aerosol direct radiative forcing at the levels of −78.9 and −47.0 W m−2 at the surface and at the top of the atmosphere, respectively, for the mean value of aerosol optical depth equal to 0.64 at 550 nm. This corresponded to the average clear-sky direct radiative forcing of −43.3 W m−2, estimated by radiometer and model simulations at the surface. Ultimately, uncertainty associated with the plane-parallel atmosphere approximation altered results by about 2 W m−2. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average −126 W m-2/τ550 and −71 W m-2/τ550 at the surface and at the top of the atmosphere, respectively. The heating rate, estimated at up to 1.8 K day−1 inside the biomass-burning plume, implied vertical mixing with turbulent kinetic energy of 0.3 m2 s−2.

Microphysical properties and radiative impact of an intense biomass burning aerosol event measured over Ny-Ålesund, Spitsbergen in July 2015

“…For our case with solar elevation >25( Arctic summer, noon) and surface albedo of 0.14 we obtained large and negative net forcing, which means a pronounced cooling of about -95 W/m 2 per unit AOD500. Recently, Lisok et al (2018) used MODTRAN simulations for this same event and came up with a direct aerosol forcing of -78.9 W/m 2 for AOD ¼0.64 at the surface, and a lower but still significant negative forcing at the top of atmosphere, in good agreement to our measurements.…”

Seasonal Variations in High Arctic Free Tropospheric Aerosols Over Ny‐Ålesund, Svalbard, Observed by Ground‐Based Lidar

“…The secondary maxima in July for and in July 2015 for , seen in Figures a and a, respectively, may have been caused by the reported smoke events in Ny‐Ålesund from biomass burning during that month (Lisok et al, ). The data from 10 and 11 July, when the smoke concentration was the highest, were not included when calculating or due to the poor signal‐to‐noise ratio at an altitude of 12–15 km caused by the high extinction of the laser light through the smoke clouds.…”

Interrelations between surface, boundary layer, and columnar aerosol properties derived in summer and early autumn over a continental urban site in Warsaw, Poland

“…Significant correlations (R > 0.5) of AOD CL and PM 2.5 were reported mainly for the eastern cities of China (Guo et al, 2009;Zheng et al, 2015;Zang et al, 2017) and the United States (Liu et al, 2007;Hutchison et al, 2008;Wang and Christopher, 2003), where the main industrial regions with extreme pollution are located. In these cases, the majority of aerosol was expected to be present within the boundary layer.…”