The contribution of Saharan dust to the ice-nucleating particle concentrations at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

Abstract

Abstract. The ice phase in mixed-phase clouds has a pivotal role in global precipitation formation as well as for Earth's radiative budget. Above 235 K, sparse particles with the special ability to initiate ice formation, ice-nucleating particles (INPs), are responsible for primary ice formation within these clouds. Mineral dust has been found to be one of the most abundant INPs in the atmosphere at temperatures colder than 258 K. However, the extent of the abundance and distribution of INPs remains largely unknown. To better constrain and quantify the impact of mineral dust on ice nucleation, we investigate the frequency of Saharan dust events (SDEs) and their contribution to the INP number concentration at 243 K and at a saturation ratio with respect to liquid water (Sw) of 1.04 at the High Altitude Research Station Jungfraujoch (JFJ; 3580 m a.s.l.) from February to December 2020. Using the single-scattering albedo Ångström exponent retrieved from a nephelometer and an Aethalometer, satellite-retrieved dust mass concentrations, simulated tropospheric residence times, and the attenuated backscatter signal from a ceilometer as proxies, we detected 26 SDEs, which in total contributed to 17 % of the time span analyzed. We found every SDE to show an increase in median INP concentrations compared to those of all non-SDE periods; however, they were not always statistically significant. Median INP concentrations of individual SDEs spread between 1.7 and 161 INP std L−1 and thus 2 orders of magnitude. In the entire period analyzed, 74.7 ± 0.2 % of all INPs were measured during SDEs. Based on satellite-retrieved dust mass concentrations, we argue that mineral dust is also present at JFJ outside of SDEs but at much lower concentrations, thus still contributing to the INP population. We estimate that 97 % of all INPs active in the immersion mode at 243 K and Sw=1.04 at JFJ are dust particles. Overall, we found INP number concentrations to follow a leptokurtic lognormal frequency distribution. We found the INP number concentrations during SDEs to correlate with the ceilometer backscatter signals from a ceilometer located 4.5 km north of JFJ and 1510 m lower in altitude, thus scanning the air masses at the same altitude as JFJ. Using the European ceilometer network allows us to study the atmospheric pathway of mineral dust plumes over a large domain, which we demonstrate in two case studies. These studies showed that mineral dust plumes form ice crystals at cirrus altitudes, which then sediment to lower altitudes. Upon sublimation in dryer air layers, the residual particles are left potentially pre-activated. Future improvements to the sampling lines of INP counters are required to study whether these particles are indeed pre-activated, leading to larger INP number concentrations than reported here.

Measurement report: The Urmia playa as a source of airborne dust and ice-nucleating particles – Part 1: Correlation between soils and airborne samples

“…Studies have shown that soil wind erodibility is also affected by soil texture and organic matter (Motaghi et al, 2020). Soil organic matter and clay can improve soil aggregation by gathering soil particles together and binding them, leading to larger aggregates, which are more resilient against wind erosion (Charman and Murphy, 2000;Ghaderi and Ghodoosi, 2005;Colazo and Buschiazzo, 2010;Mahmoodabadi and Ahmadbeigi, 2013;Sirjani et al, 2019). The high EF of Sa sheets (Fig.…”

“…Mineral dust particles have been found to be the dominant INP type at temperatures below 258 K (Hoose and Möhler, 2012;Murray et al, 2012). Indeed, Brunner et al (2021) estimated that 97 % of all INPs active at 243 K at the high-altitude station at Jungfraujoch, Switzerland, are dust particles. At higher temperatures, biological particles are considered more relevant (Conen et al, 2011;Kanji et al, 2017;Testa et al, 2021).…”

Retrieving ice-nucleating particle concentration and ice multiplication factors using active remote sensing validated by in situ observations

“…Nonetheless, the Jungfraujoch Research Station (approximately 140 km WSW of Weissfluhjoch) released a Saharan dust event warning only at 13:37 UTC. Brunner et al (2021) reported that the determination of a Saharan dust event varies based on the underlying parameter used as proxy. The three samples with higher INP concentrations (orange crosses on 18 and 19 February in Fig.…”

Ice nucleation by smectites: The role of the edges

“…Mineral dust has been found to be the prevailing INP type at temperatures below 258 K (Kanji et al, 2017;O'Sullivan et al, 2018;Brunner et al, 2021), while biological particles such as bacteria, pollen, fungi, and proteins are considered to dominate ice nucleation at higher temperatures (DeMott and Prenni, 2010;Després et al, 2012;Kanji et al, 2017). Feldspar, quartz, and clay minerals have proven to be relevant mineral INPs in immersion freezing mode (Atkinson et al, 2013;Pinti et al, 2012;Kanji et al, 2017;Kaufmann et al, 2016;Boose et al, 2016;Kumar et al, 2018;2019a;2019b).…”