Impact of a Strong Biomass Burning Event on the Radiative Forcing in the Arctic

The aim of the presented study was to investigate the impact on the radiation budget of biomass burning smoke plume transported from Alaska to high Arctic region (Ny-Alesund, Svalbard) in early July 2015. This high aerosol load event is considered exceptional in the last 25 years with mean aerosol optical depth increased by the factor of 10 in comparison to the average summer background values. We utilised in-situ data with hygroscopic growth equations as well as remote sensing measurements as inputs to radiative transfer models with an objective to estimate biases associated with (i) hygroscopicity, (ii) variability of ω profiles and (iii) plane-parallel closure of the modelled atmosphere. A chemical weather model with satellite-derived biomass burning emissions was used to interpret the transport and transformations pathways. Provided MODTRAN simulations resulted in the mean aerosol direct radiative forcing on the level of −78.9 W m −2 and −47.0 W m −2 at the surface and the top of the atmosphere respectively for the mean value of aerosol optical depth equal to 0.64 at 550 nm. It corresponded to the average clear-sky direct radiative forcing of −43.3 W m −2 estimated by radiometers and model simulations. Furthermore, model-derived aerosol direct radiative forcing efficiency reached on average −126 W m −2  / τ 550 and −71 W m −2  / τ 550 at the surface and at the top of the atmosphere. Estimated heating rate up to 1.8 K day −1 inside the BB plume implied vertical mixing with the turbulent kinetic energy of 0.3 m 2  s −2 . Ultimately, uncertainty connected with the plane-parallel atmosphere approximation altered results by about 2 W m −2 .