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Source Analysis of Greenland Air

Dr Jim McQuaid (SEE), Dr Ryan Neely (NCAS/SEE), Prof Ben Murray (SEE), Dr Daniel Grosvenor (NCAS)

Project partner(s): Prof Lian Benning, GFZ, Potsdam, Germany (CASE)

Contact email: j.b.mcquaid@leeds.ac.uk

Summary

The poles are said to be the barometer of the planet and it is critical we understand the processes which are impacting them at this time. The melting of the Greenland icesheet is estimates to have contributed to 16% of planetary sea level change since the early 1990s. 

The warming/cooling effect of arctic clouds are in a very fine balance, optically thin clouds can impose a measured warming as was observed in summer 2012 when an optically thin layer persisted over the Greenland icesheet for a period, the layer was sufficiently insulating that the surface layer warmed causing an unprecedented melt across the entire icesheet, estimated at close to 100% of the icesheet was above 0 °C for several days.

There are many hypotheses as to the range of and sources of the atmospheric aerososl which contribute to the budget of so called cloud condensation nuclei (CCN) which for the ‘seed’ for cloud formation.

Airborne material being deposited to the surface can persist and in turn modify the surface albedo which leads to further modification of melt rates during summer months. A major NERC project; Black and Bloom, is currently investigate the different components which contribute to the surface albedo in south west Greenland, this project has already gathered a wealth of compositional data from field samples. Analyses have shown that a significant fraction is very local, having recirculated onto the icesheet against the surface katabatic winds, further evidence of the complexity of atmosphere above the icesheet, both close to the surface as well as in the free troposphere above.

In early 2019 a major NERC/NSF initiative; Greenland Aerosol Cloud Experiment (GrACE) will begin to make some of the most comprehensive coupled observations of aerosols and clouds on the icesheet. Coupled to GrACE, this project will undertake a comprehensive study of the airmasses which impact on the icesheet identifying case studies for closer inspection. We will use back trajectory analysis to develop an airmass history profile. From this we can develop climatologies to understand the influences of different airmass profiles, we know that “local” air impacts the icesheet and that complex circulation patterns exist, coupled to the barrier to downward mixing effected by the boundary layer clouds that are often found over the icesheet.

Case study selection will be through remote events entraining cloud active material (CCN) into airmasses upwind of the icesheet as well as typical and atypical meteorological conditions at the Summit site. In addition to understanding processes above, within and below the clouds we would use the long standing snowfall/icesheet accumulation dataset in conjunction with the airmass indexing to investigate the relationship between accumulation rates and the source, type and concentration of the CCN in the region. Such details will enhance our understanding of the potential growth rates of the icesheet under a changing climate, this is a key metric to our estimation of the surface mass balance (SMB) of the icesheet

During the field observational phases in 2019 and 2020 aerosol samples will be collected at the surface as well as deploying the Leeds SHARK sampler and remotely piloted drones to collect samples both within the boundary layer and in the free troposphere above. These will be used to allow us to understand the transport regime between the FT/BL and the surface. Alongside the aerosol measurements, surface samples will be collected during the 2019 fieldseason for isotopic analysis at the CASE partner (Prof Liane Benning, GFZ, Potsdam), these will provide further evidence to the aerosol sampling. There will be the opportunity to participate in fieldwork during summer 2020 based at the NOAA/NSF research base at Summit in Greenland

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