The diurnal and seasonal variability of ice nucleating particles at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

Abstract

Abstract. Cloud radiative properties, cloud lifetime, and precipitation initiation are strongly influenced by the cloud phase. Between ~ 235 and 273 K, ice nucleating particles (INPs) are responsible for the initial phase transition from the liquid to the ice phase in cloud hydrometeors. This study analyzes immersion-mode INP concentrations measured at 243 K at the High Altitude Research Station Jungfraujoch (3580 m a.s.l.) between February 2020 and January 2021, thereby presenting the longest continuous, high-resolution (20 min) data set of online INP measurements to date. The high time resolution and continuity allow to study the seasonal and the diurnal variability of INPs. After exclusion of special events, like Saharan dust events (SDEs), we found a seasonal cycle of INPs, highest in April (median in spring 3.1 INP std L−1), followed by summer (median: 1.6 INP std L−1) and lowest in fall and winter (median: 0.5 INP std L−1 and 0.7 INP std L−1, respectively). Pollen or subpollen particles were deemed unlikely to be responsible for elevated INP concentrations in spring and summer, as periods with high pollen loads from nearby measurement stations do not coincide with the periods of high INP concentrations. Furthermore, for days when the site was purely in the free troposphere (FT), no diurnal cycle in INP concentrations was observed, while days with boundary layer intrusions (BLI) showed a diurnal cycle. The seasonal and diurnal variability of INPs during periods excluding SDEs is with a factor of 7 and 3.3, respectively, significantly lower than the overall variability observed in INP concentration including SDEs of more than three orders of magnitude, when peak values result from SDEs. The median INP concentration over the analyzed 12 months was 1.2 INP std L−1 for FT periods excluding SDEs, and 1.4 INP std L−1 for both FT and BLI, and incl. SDEs, reflecting that despite SDEs showing strong but comparatively brief INP signals, they have a minor impact on the observed annual median INP concentration.

The diurnal and seasonal variability of ice-nucleating particles at the High Altitude Station Jungfraujoch (3580 m a.s.l.), Switzerland

“…Data availability. The data presented in this publication are available at the following DOI: https://doi.org/10.3929/ethz-b-000548529 (Brunner et al, 2022).…”

Measurement report: Ice-nucleating particles active ≥ −15 °C in free tropospheric air over western Europe

“…Generally, the influence of the PBL on Jungfraujoch is largest in summer and smallest in winter (Collaud Coen et al, 2011;Griffith et al, 2014). Hence, if samples are not explicitly selected for FT conditions, the majority of them will have at least some PBL influence, in particular during summer (Brunner et al, 2021b). Therefore, the concentration of INP −10 on filters not selected for FT conditions occasionally exceeded that of filters selected for FT conditions, in particular during summer (Fig.…”

“…6 in Lacher et al, 2018) as well as little seasonal variation. Later, continuous measurements by Brunner et al (2021b) found the monthly median of INP −30 in the FT background to peak in April and to be lowest in December. Brunner et al (2021a, b) found that most INP −30 at Jungfraujoch occurred during Saharan dust intrusions, by far exceeding any background concentration.…”

Measurement report: Ice nucleating particles active ≥ −15 °C in free tropospheric air over western Europe

“…Mineral dust makes by far the largest contribution to INP activated at around -30 °C at Jungfraujoch (Larcher et al, 2018(Larcher et al, , 120 2021Brunner et al, 2021aBrunner et al, , 2021b. Most INP in airborne mineral dust are probably K-feldspars, some of which are already activated at temperatures above -10 °C (Boose et al, 2016;Harrison et al, 2019).…”

“…Generally, the influence of the PBL on Jungfraujoch is largest in summer and smallest in winter (Collaud Coen et al, 2011;Griffith et al, 2014). Hence, if samples are not explicitly selected for FT conditions, the majority of them will have at least some PBL influence, in particular during summer (Brunner et al, 2021b). Therefore, concentration of INP-10 on filters not https://doi.org/10.5194/acp-2021-879 Preprint.…”