Abstract
Abstract. The study of long-term trends in aerosol optical properties is an important task to understand the underlying aerosol processes influencing the change of climate. The Arctic, as the place where climate change manifests most, is an especially sensitive region of the world. Within this work, we use a unique long-term data record of key aerosol optical properties from the Zeppelin Observatory, Svalbard, to ask the question of whether the environmental changes of the last 2 decades in the Arctic are reflected in the observations. We perform a trend analysis of the measured particle light scattering and backscattering coefficients and the derived scattering Ångström exponent and hemispheric backscattering fraction. In contrast to previous studies, the effect of in-cloud scavenging and of potential sampling losses at the site are taken explicitly into account in the trend analysis. The analysis is combined with a back trajectory analysis and satellite-derived sea ice data to support the interpretation of the observed trends. We find that the optical properties of aerosol particles have undergone clear and significant changes in the past 2 decades. The scattering Ångström exponent exhibits statistically significant decreasing of between −4.9 % yr−1 and −6.5 % yr−1 (using wavelengths of λ=450 and 550 nm), while the particle light scattering coefficient exhibits statistically significant increasing trends of between 2.6 % yr−1 and 2.9 % yr−1 (at a wavelength of λ=550 nm). The magnitudes of the trends vary depending on the season. These trends indicate a shift to an aerosol dominated more by coarse-mode particles, most likely the result of increases in the relative amount of sea spray aerosol. We show that changes in air mass circulation patterns, specifically an increase in air masses from the south-west, are responsible for the shift in aerosol optical properties, while the decrease of Arctic sea ice in the last 2 decades only had a marginal influence on the observed trends.
Highlights
The Arctic region is warming considerably faster than the global average, a phenomenon known as Arctic amplification
The long-term trends in σsp, σbsp, b, and α are presented in Fig. 1 based on the seasonal medians. σsp and σbsp both display increasing statistically significant trends estimated to be in the range of 0.05 and 0.01 Mm−1 yr−1 respectively. σsp and σbsp show clear seasonality with higher scattering coefficients occurring in spring and winter. b displays a nonstatistically significant decreasing trend of −0.0002 yr−1. α, shows a large and decreasing statistically significant trend of approximately −0.07 yr−1. α is largest during the spring and summer, whilst autumn experiences the smallest medians. b experiences a peak in summer and is at its lowest value in winter
We show that the increased presence of sea salt aerosol (SSA) at Zeppelin Observatory (ZEP) is the result of changes in air circulation patterns, as opposed to the retreat in Arctic sea ice
Summary
The Arctic region is warming considerably faster than the global average, a phenomenon known as Arctic amplification. The impacts of Arctic amplification can be observed in a multitude of parameters (Meredith et al, 2020), including most notably, reductions in Arctic summer sea ice (Perovich et al, 2018). Numerous other mechanisms have been studied, including changes in cloud cover (Schweiger et al, 2008), transportation of heat from the mid-latitudes (Overland and Wang, 2016), increases in the total water vapour in the Arctic atmosphere (Park et al, 2015), and sulfate aerosol reductions in Europe (Navarro et al, 2016). Arctic amplification may be linked to mid-latitude weather (Cohen et al, 2014; Pithan et al, 2018), with increased Rossby wave amplitude (Francis et al, 2017) and the appearance of atmospheric circulation anomalies (Lee et al, 2015). Changes in air circulation patterns within the Svalbard region have been
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