Wildfire smoke over the North Pole during the winter period 2019-2020 and impact on cirrus evolution.

Abstract:

Massive bush fires fuelled by high, record-breaking temperatures raged in the Arctic in summer 2019. The enormous fire activity triggered strong pyrocumulonimbus (pyro-Cb) convection across the Arctic circle (e.g. Canada, Siberia). The ash spread over the whole upper troposphere and lower stratosphere in the Arctic circle in winter 2019/2020. There, this reservoir of aerosols might have influenced the characteristics of cirrus clouds. These additional smoke aerosols may act as ice nucleating particles (INP) at low temperatures (<-30°C). Usually, Arctic cirrus clouds form due to the homogeneous freezing process, or heterogeneous freezing processes triggered by background aerosol. However, in winter 2019/2020 the smoke aerosol concentration was at least one order of magnitude larger than in a climatological mean. Therefore, the smoke aerosols must be accounted for in terms of being an additional significant contributor to additional heterogeneous freezing processes in cirrus clouds.

In concrete, the influence of smoke from big fire smoke released through pyro-Cb convection across the Arctic circle in summer 2019 on cirrus clouds is investigated using ground-based remote sensing lidar and cloud radar data obtained from the German research vessel Polarstern drift from September 2019 to September 2020 in the central Arctic in the frame of the MOSAiC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) campaign.

Case studies will be presented, showing the influence of the smoke aerosols (measured by lidar) acting as INP on the ice crystal number concentration (measured by cloud radar).