Sarah Grawe

Ice-nucleating particles (INPs) play a crucial role in Earth's weather and climate by influencing cloud properties and precipitation. However, their abundance in the free troposphere, vertical distribution, and transport mechanisms are not well-characterized. This study presents immersion INP measurements from filter samples collected aboard the High Altitude and LOng range research aircraft (HALO) in the troposphere and the lower stratosphere (up to 14.5 km) over Europe during the CIRRUS-HL (Cirrus in High Latitudes) campaign in summer 2021. By sampling cloud particle residuals and aerosol particles in the inflow and outflow of deep convective clouds (DCCs), and performing offline INP analysis, we shed light on the vertical transport and segregation of INPs in DCCs. INP-temperature spectra of convective inflow included both INPs active at high ( T > −15 °C) and low temperatures ( T < −20 °C). In contrast the outflow spectra only featured INPs active at low temperatures. We explain the observed INP segregation in the updraft with precipitation scavenging of INPs active at high temperatures. INPs active at lower temperatures ( T < −20 °C), however, are efficiently transported upwards into the free troposphere. There, ambient temperatures are below −40 °C, i.e., temperatures far below the temperatures at which these INPs initiate immersion freezing. In the DCC outflow, INP concentrations exceed the upper tropospheric background concentration by at least two orders of magnitude. These INPs are then available for ice formation in mid and upper tropospheric clouds.

Ice-nucleating particles (INPs) play a crucial role in Earth’s weather and climate by influencing cloud properties and precipitation. However, their abundance in the free troposphere, vertical distribution, and transport mechanisms are not well-characterized. This study presents immersion INP measurements from filter samples collected aboard the HALO research aircraft in the troposphere and the lower stratosphere (up to 14.5 km) over Europe during the CIRRUS-HL (Cirrus in High Latitudes) campaign in summer 2021. By sampling cloud particle residuals and aerosol particles in the inflow and outflow of deep convective clouds (DCCs) and performing offline INP analysis, we shed light on the vertical transport and segregation of INPs in DCCs. While INP-temperature spectra of convective inflow included both INPs active at high (T > -15 °C) and low temperatures (T < -20 °C), the in-cloud and outflow spectra only featured INPs active at low temperatures. We explain the observed INP segregation in the updraft with precipitation scavenging of INPs active at high temperatures. In contrast, INPs active at lower temperatures (T < -20 °C) are efficiently transported upwards into the free troposphere with ambient temperatures below -40 °C, i.e., temperatures far below the temperatures at which these INPs initiate immersion freezing. In the DCC outflow, INP concentrations exceed the upper tropospheric background concentration by at least two orders of magnitude. These INPs are then available for ice formation in mid and upper tropospheric clouds.

Ice-nucleating particles (INPs) play a crucial role in Earth’s weather and climate by influencing cloud properties and precipitation. However, their abundance in the free troposphere, vertical distribution, and transport mechanisms are not well-characterized. This study presents immersion INP measurements from filter samples collected aboard the HALO research aircraft in the troposphere and the lower stratosphere (up to 14.5 km) over Europe during the CIRRUS-HL (Cirrus in High Latitudes) campaign in summer 2021. By sampling cloud particle residuals and aerosol particles in the inflow and outflow of deep convective clouds (DCCs) and performing offline INP analysis, we shed light on the vertical transport and segregation of INPs in DCCs. While INP-temperature spectra of convective inflow included both INPs active at high (T > -15 °C) and low temperatures (T < -20 °C), the in-cloud and outflow spectra only featured INPs active at low temperatures. We explain the observed INP segregation in the updraft with precipitation scavenging of INPs active at high temperatures. In contrast, INPs active at lower temperatures (T < -20 °C) are efficiently transported upwards into the free troposphere with ambient temperatures below -40 °C, i.e., temperatures far below the temperatures at which these INPs initiate immersion freezing. In the DCC outflow, INP concentrations exceed the upper tropospheric background concentration by at least two orders of magnitude. These INPs are then available for ice formation in mid and upper tropospheric clouds.

Ice-nucleating particles (INPs) play a crucial role in Earth’s weather and climate by influencing cloud properties and precipitation. However, their abundance in the free troposphere, vertical distribution, and transport mechanisms are not well-characterized. This study presents immersion INP measurements from filter samples collected aboard the HALO research aircraft in the troposphere and the lower stratosphere (up to 14.5 km) over Europe during the CIRRUS-HL (Cirrus in High Latitudes) campaign in summer 2021. By sampling cloud particle residuals and aerosol particles in the inflow and outflow of deep convective clouds (DCCs) and performing offline INP analysis, we shed light on the vertical transport and segregation of INPs in DCCs. While INP-temperature spectra of convective inflow included both INPs active at high (T > -15 °C) and low temperatures (T < -20 °C), the in-cloud and outflow spectra only featured INPs active at low temperatures. We explain the observed INP segregation in the updraft with precipitation scavenging of INPs active at high temperatures. In contrast, INPs active at lower temperatures (T < -20 °C) are efficiently transported upwards into the free troposphere with ambient temperatures below -40 °C, i.e., temperatures far below the temperatures at which these INPs initiate immersion freezing. In the DCC outflow, INP concentrations exceed the upper tropospheric background concentration by at least two orders of magnitude. These INPs are then available for ice formation in mid and upper tropospheric clouds.

Ice-nucleating particles (INPs) play a crucial role in Earth’s weather and climate by influencing cloud properties and precipitation. However, their abundance in the free troposphere, vertical distribution, and transport mechanisms are not well-characterized. This study presents immersion INP measurements from filter samples collected aboard the HALO research aircraft in the troposphere and the lower stratosphere (up to 14.5 km) over Europe during the CIRRUS-HL (Cirrus in High Latitudes) campaign in summer 2021. By sampling cloud particle residuals and aerosol particles in the inflow and outflow of deep convective clouds (DCCs) and performing offline INP analysis, we shed light on the vertical transport and segregation of INPs in DCCs. While INP-temperature spectra of convective inflow included both INPs active at high (T > -15 °C) and low temperatures (T < -20 °C), the in-cloud and outflow spectra only featured INPs active at low temperatures. We explain the observed INP segregation in the updraft with precipitation scavenging of INPs active at high temperatures. In contrast, INPs active at lower temperatures (T < -20 °C) are efficiently transported upwards into the free troposphere with ambient temperatures below -40 °C, i.e., temperatures far below the temperatures at which these INPs initiate immersion freezing. In the DCC outflow, INP concentrations exceed the upper tropospheric background concentration by at least two orders of magnitude. These INPs are then available for ice formation in mid and upper tropospheric clouds.

This study introduces the T-Bird, a novel aircraft-towed platform developed to measure aerosol and turbulence properties close to the surface, particularly over sea ice and open water in the polar regions. The T-Bird, towed by the Alfred Wegener Institute's Polar aircraft, offers a unique capability to capture data from altitudes as low as 10 m while the aircraft operates at its lowest allowed operation altitude. This measurement platform allows for simultaneous data collection of aerosol, turbulence, and meteorological parameters across multiple vertical layers. The T-Bird is equipped with specialized aerosol instrumentation to assess particle number concentration, number size distribution, and absorption coefficient and to collect filter samples. It has been tested under Arctic conditions during the BACSAM (Boundary layer and Aerosol and Cloud Study in the Arctic, based on aircraft and T-Bird Measurements) campaign in October 2022. This paper provides technical details on the T-Bird's design, with special focus on the aerosol instrumentation and its performance during Arctic flights addressing measurement challenges in the lowermost atmosphere. The first measurements demonstrate its potential to enhance our understanding of aerosol dynamics and atmospheric boundary layer processes in remote environments.

This study introduces the T-Bird, a novel aircraft-towed platform developed to measure turbulence and aerosol properties close to the surface, particularly over sea ice and open water in the polar regions. The T-Bird system, towed by the Alfred Wegener Institute's Polar aircraft, offers a unique capability to capture data from altitudes as low as ~10 m while the aircraft operates at its lowest allowed operation altitude. This measurement platform allows for simultaneous data collection of turbulence, aerosol, and other atmospheric parameters across multiple vertical layers. The T-Bird is equipped with specialized aerosol instrumentation to assess particle number concentration, number size distribution and absorption coefficient and to collect filter samples. It has been tested under Arctic conditions during the BACSAM (Boundary layer and Aerosol and Cloud Study in the Arctic, based on aircraft and T-Bird Measurements) campaign in October 2022. This paper provides technical details on the T-Bird's design, with special focus on the aerosol instrumentation, and its performance during Arctic flights addressing measurement challenges in the lowermost atmosphere. The first measurements demonstrate its potential to enhance understanding of aerosol dynamics and boundary layer processes in remote environments.

This study introduces the T-Bird, a novel aircraft-towed platform developed to measure turbulence and aerosol properties close to the surface, particularly over sea ice and open water in the polar regions. The T-Bird system, towed by the Alfred Wegener Institute's Polar aircraft, offers a unique capability to capture data from altitudes as low as ~10 m while the aircraft operates at its lowest allowed operation altitude. This measurement platform allows for simultaneous data collection of turbulence, aerosol, and other atmospheric parameters across multiple vertical layers. The T-Bird is equipped with specialized aerosol instrumentation to assess particle number concentration, number size distribution and absorption coefficient and to collect filter samples. It has been tested under Arctic conditions during the BACSAM (Boundary layer and Aerosol and Cloud Study in the Arctic, based on aircraft and T-Bird Measurements) campaign in October 2022. This paper provides technical details on the T-Bird's design, with special focus on the aerosol instrumentation, and its performance during Arctic flights addressing measurement challenges in the lowermost atmosphere. The first measurements demonstrate its potential to enhance understanding of aerosol dynamics and boundary layer processes in remote environments.

The HALO–(𝒜𝒞)³ aircraft campaign was carried out in March and April 2022 over the Norwegian and Greenland seas, the Fram Strait, and the central Arctic Ocean. Three research aircraft – the High Altitude and Long Range Research Aircraft (HALO), Polar 5, and Polar 6 – performed 54 partly coordinated research flights on 23 flight days over areas of open ocean, the marginal sea ice zone (MIZ), and the central Arctic sea ice. The general objective of the research flights was to quantify the evolution of air mass properties during moist and warm-air intrusions (WAIs) and cold-air outbreaks (CAOs). To obtain a comprehensive data set, the three aircraft operated following different strategies. HALO was equipped with active and passive remote sensing instruments and dropsondes to cover the regional evolution of cloud and thermodynamic processes. Polar 5 carried a similar remote sensing payload to HALO, and Polar 6 was instrumented with in situ cloud, aerosol, and trace gas instruments focusing on the initial air mass transformation close to the MIZ. The processed, calibrated, and validated data are published in the World Data Center PANGAEA as instrument-separated data subsets and listed in aircraft-separated collections for HALO ( Ehrlich et al., 2024 a , https://doi.org/10.1594/PANGAEA.968885), Polar 5 ( Mech et al., 2024 a , https://doi.org/10.1594/PANGAEA.968883), and Polar 6 ( Herber et al., 2024 , https://doi.org/10.1594/PANGAEA.968884). A detailed overview of the available data sets is provided here. Furthermore, the campaign-specific instrument setup, the data processing, and quality are summarized. Based on measurements conducted during a specific CAO, it is shown that the scientific analysis of the HALO–(𝒜𝒞)³ data benefits from the coordinated operation of the three aircraft.