Controls on surface aerosol particle number concentrations and aerosol-limited cloud regimes over the central Greenland Ice Sheet

Heather Guy,Claire Pettersen,David D Turner,Von P Walden,Ralf Bennartz,Benjamin J Murray,Ian M Brooks,Matthew D Shupe,Christopher J Cox,Ryan R Neely Iii,Ken S Carslaw,William D Neff

doi:10.5194/acp-21-15351-2021

Abstract

Abstract. This study presents the first full annual cycle (2019–2020) of ambient surface aerosol particle number concentration measurements (condensation nuclei > 20 nm, N20) collected at Summit Station (Summit), in the centre of the Greenland Ice Sheet (72.58∘ N, −38.45∘ E; 3250 ma.s.l.). The mean surface concentration in 2019 was 129 cm−3, with the 6 h mean ranging between 1 and 1441 cm−3. The highest monthly mean concentrations occurred during the late spring and summer, with the minimum concentrations occurring in February (mean: 18 cm−3). High-N20 events are linked to anomalous anticyclonic circulation over Greenland and the descent of free-tropospheric aerosol down to the surface, whereas low-N20 events are linked to anomalous cyclonic circulation over south-east Greenland that drives upslope flow and enhances precipitation en route to Summit. Fog strongly affects particle number concentrations, on average reducing N20 by 20 % during the first 3 h of fog formation. Extremely-low-N20 events (< 10 cm−3) occur in all seasons, and we suggest that fog, and potentially cloud formation, can be limited by low aerosol particle concentrations over central Greenland.

Highlights

To investigate the effect of near-surface local processes that have the potential to modify surface aerosol particle concentrations, we look at four event types: fog, precipitation, blowing snow (BLSN), and strong surface-based temperature inversions (SBIs)
Hirdman et al (2009) used FLEXPART back trajectory simulations to show that surface aerosol particle concentrations at Summit are an order of magnitude less sensitive to surface emissions from within the Arctic compared to loweraltitude Arctic sites, which is a possible explanation for why Summit does not experience Arctic haze build-up during the winter
Despite the potential for SBIs to act as a barrier for turbulent mixing and reduce the rate that aerosol particles are transported down to the surface (Dibb et al, 1992; Li et al, 2019; Thomas et al, 2019), we found no consistent change in N20 during the first 3 h of SBI events and no relationship between the change in N20 and the mean intensity of the SBI, which ranges between 0.23 and 0.92 ◦C m−1

Summary

Introduction

The Greenland Ice Sheet (GrIS) has been losing mass at an unprecedented and accelerating rate since the early 21st century (Rignot et al, 2008, 2011; van den Broeke et al, 2016; Fettweis et al, 2017; Trusel et al, 2018; The IMBIE Team, 2020) and, as a result, has become the largest single contributor to global sea level rise (van den Broeke et al, 2016; Bamber et al, 2018; Slater et al, 2020) The majority of this mass loss is due to changes in the ice sheet surface mass balance (Slater et al, 2020) and, in particular, increased surface melt and run-off (Enderlin et al, 2014; van den Broeke et al, 2016; The IMBIE Team, 2020). Improving our understanding of aerosols and their relationship with cloud properties over the GrIS is key to reducing the uncertainty in future projections of GrIS melt and global sea level rise

Methods

Results

Discussion

Conclusion