Spring-time international aerosol campaign at AWIPEV
The role of aerosol remains an important source of insecurity within the Arctic Climate system. While normally the Arctic is well isolated from some major aerosol sources as deserts, volcanoes, anthropogenic activities or pollen, elevated concentrations can occur, especially in spring. The increase of aerosol in this season is called “Arctic Haze”. In the still dry and cold atmosphere aerosol particles can be advected for long distance without significant rain out and appear even at remote sites in the high Arctic. However, the Arctic is especially climatologic sensitive in spring; the amount of solar radiation determines the onset of the melting season and the vertical exchange of energy in the atmosphere. Aerosols interact in many ways with the climate system: they can scatter sun light, which is called “dimming” or sediment down to the snow covered ground, reducing its albedo “darkening”. Moreover aerosols are indispensable for cloud formation as they provide the surface on which rain drops or ice crystals can form.
Currently researchers from Poland (Institute of Oceanology, Sopot, Univ. Warsaw), Norway (Alomar, Rocket range) and Germany (Univ. Karlsruhe, AWI-Potsdam) use the facilities of the AWIPEV base as well as installations at Gruvebadet for a common effort to study aerosols, both by in-situ and remote sensing instruments. In-situ instruments are directed into the atmospheric layer which contains the aerosol. In our case a tethered balloon is used to carry for example an impactor on which aerosol deposits and can later be analysed with microscopes to derive the chemical composition, size and shape of each individual particle (Fig.1). From this information the refractive index can be estimated, which links this experiment to the remote sensing instruments as for example a lidar (Fig 2). In a lidar short pulses of a laser are sent into the atmosphere and a part of this light is backscattered by aerosol and recorded by a telescope. Hence, these remote sensing instruments directly measure some of the scattering properties of the particles. As each measurement gives a different information, it is important to combine them as closely as possible. Such an attempt to determine precise aerosol properties from different well combined experiments are called “closure studies”.
Another attempt to combine the different aerosol measurements is seen in Fig.3: A Ceilometer , which is a small lidar, from the Polish colleagues aims from the roof of the AWIPEV observatory towards Gruvebadet. In this building instruments that measure the size distribution of aerosol have been installed – next to the long-term measurements which are regularly performed by the University of Florence. By this set-up possible spatial inhomogeneities in the aerosol load which might result by channeling of the wind through the mountains in the surrounding shall be detected.
The aerosol load during the „Arctic Haze“ season varies from year to year. Nevertheless this campaign shall contribute to the following questions:
- Give a case study for a precise determination of the radiative forcing of Arctic Haze
- Outline a strategy for more regular aerosol closure studies in Ny-Ålesund