AS4.2 | As spring arrives: Processes leading up to annual Arctic sea-ice melt
EDI
As spring arrives: Processes leading up to annual Arctic sea-ice melt
Co-organized by CL4/CR3/OS1
Convener: Michael Tjernström | Co-conveners: Paul Zieger, Penny Vlahos, Jessie Creamean, Cort ZangECSECS
Orals
| Wed, 17 Apr, 14:00–15:45 (CEST)
 
Room 1.85/86
Posters on site
| Attendance Thu, 18 Apr, 10:45–12:30 (CEST) | Display Thu, 18 Apr, 08:30–12:30
 
Hall X5
Orals |
Wed, 14:00
Thu, 10:45
While observed volume, concentration and extent of Arctic sea ice have decreased dramatically over the last decades, climate model simulations of the recent past feature a slower sea-ice decline than observed. These same models are then used to project future sea ice changes, raising the question if even the most optimistic future emission scenarios will be enough to preserve the summer sea ice in the future.

Although the sea-ice decrease is the most pronounced in late summer, understanding coupled key processes of ocean/sea-ice/atmosphere-system during the so-called shoulder seasons, the onsets of the melt in spring and freeze up in autumn, is important since the timing of these set the boundaries for the length of the melt season and therefore strongly influence the total melt in any given year.

While the autumn freeze onset has received some attention, substantially less is known about the spring melt onset, partly because of a lack of observations to characterize and understand the processes controlling or leading up to it, on different scales. An improved understanding of this season is important, to inform model development crucial for simulations and assessments of future changes in the Arctic climate system.

This session focuses on the late winter and early spring in the Arctic and especially the onset of the summer sea-ice melt. We invite presentations broadly on ocean, sea-ice and atmospheric processes over a large spectrum of scales governing or being strongly affected by this transition, from long-term observations and reanalysis, process and climate modeling and especially from observations from new field campaigns covering this time period, such as MOSAiC and ARTofMELT.

Orals: Wed, 17 Apr | Room 1.85/86

14:00–14:05
14:05–14:15
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EGU24-6663
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On-site presentation
Christopher Cox, Amy Solomon, Ola Persson, Matthew Shupe, Michael Gallagher, Von Walden, Michael Town, Donald Perovich, Sarah Webster, and Jacob Anderson

Onset of surface melt over sea ice is a factor in the duration of the melt season. Onset is often triggered by advection of warm, moist air from lower latitudes. This is especially characteristic of early dates of onset, but such events have also been hypothesized to precondition the ice for an earlier onset even when they don’t act as the trigger. The importance of atmospheric advection to the melt season is well-recognized by the community. Less attention has been given to the potential limitations of these events and to what alternate mechanisms may also be important for initiation, which is the subject of this presentation. We discuss two case studies.

In the first case, atmospheric advection from the North Atlantic in late May 2020 caused onset to occur over a wide area of the sea ice north of Greenland, including the floe being measured by the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Approximately 6 weeks prior, in April, an anomalously warm advection event also impacted the MOSAiC floe and was responsible for ~40% of the total warming the ice underwent that spring. Using a diffusion model for the ice forced by surface temperatures that both include (observationally) and exclude (synthetically) the April event, we show that its influence relative to its absence was reduced by ~80% within 10 days. The result is explained by a negative feedback that suppresses conduction within the ice when warming events occur. Consequently, despite the apparent influential nature of the April event suggested by the observations, the ice temperatures would likely have been similar several weeks before onset if the April event had not occurred. This implies there are limitations to such events in preconditioning the sea ice for early onset.

Our second case examines data collected from a buoy in the Beaufort Sea during a regional onset event observed in June 2022. In this case, the air that caused melt at the buoy came from the north during a period of generally zonal flow of the polar jet (and lack of poleward moisture transport). Analysis of back trajectories indicates that the air had a residence time in the Arctic of 7-10 days prior to causing melt. The air began at mid-tropospheric levels near the pole then circulated around persistent, large-scale high pressure over the East Siberian Sea, descending along its track. Reanalysis data suggests the adiabatic contribution to the subsidence was sufficient to warm the air to the freezing point when it reached the surface, moving southward across the Beaufort Sea. This case indicates that subsidence is a mechanism internal to the Arctic that is capable of causing melt onset, though its climatological significance remains an open question.

How to cite: Cox, C., Solomon, A., Persson, O., Shupe, M., Gallagher, M., Walden, V., Town, M., Perovich, D., Webster, S., and Anderson, J.: Perspectives on limitations and mechanisms for atmospheric initiation of onset of the summer melt season over sea ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6663, https://doi.org/10.5194/egusphere-egu24-6663, 2024.

14:15–14:25
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EGU24-15627
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Highlight
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On-site presentation
Michael Tjernström, Paul Zieger, and Sonja Murto and the ARTofMELT Science Team

The spring season in the Arctic Ocean has gained relatively little attention with detailed observations from expeditions, due to difficulties to navigate in the ice at this time of the year. This paper reviews experiences from the ARTofMELT (Atmospheric rivers and the onset of sea-ice melt) expedition in spring of 2023.

ARTofMELT had two objectives: To study processes leading up to the onset of the sea-ice melt and to explore links to so-called atmospheric rivers (ARs). ARs are spatially and temporally distinct inflows of warm and moist air from farther south. To fulfill these goals, we instrumented the Swedish research icebreaker Oden and planned to locate her in the Atlantic sector of the Arctic Ocean north of Svalbard from early May to mid-June. Oden was equipped with advanced meteorological instrumentation including standard meteorology and 6-horly radiosoundings, radar and lidars for cloud and wind measurements, and a surface flux tower with eddy-covariance. An advanced suite of atmospheric chemistry and aerosol observations were also deployed along with water isotope measurements, and also sampled and profiled the upper ocean structure. To identify upcoming ARs, we used ensemble forecasts from the European Centre for Medium-Range Weather Forecasts (ECMWF) at lead time up to seven days, to allow time to navigate the icebreaker to optimal positions and establish ice camps. While carrying out most of the observations on board, in-situ observations on the ice provide valuable details on the impact of ARs on the ice. On ice camps we therefore deployed a surface energy budget station and an ROV surveying the ice from below and also flew a tethered balloon HELIKITE system from the aft of the ship. Additionally, we also used the helicopter to deploy scientists on the ice (sampling snow, ice and water) and deploying buoys, and for flying the HELIPOD instrument package.

ARTofMELT left Svalbard on 8 May and returned on 15 June. Starting with quite cold later winter conditions there was a brief warming period around mid-May, with an AR that brought air temperatures above the melting point twice (19 and 20 May). This was interrupted by a major storm, followed by a cooler period. From the end of May the surface started to gain heat, culminating in the onset of the melt at a second AR on 10 June. Both ARs were documented from ice stations.

A major uncertainty was the navigation in the ice during late winter and this also tuned out to be the most difficult part of the deployment. The ice was thick and hard to break, the size of the largest ice floes was much larger than expected and short-term variations of the ice pressure made navigation very difficult. The maximum latitude obtained was ~80.5 °N, hence, we stayed in the Fram Strait ice pack. Also, only two brief ARs were encountered, less than expected. In spite of this we were able to gain a large amount of unique observations, both from the icebreaker when in transit and from two ice camps.

How to cite: Tjernström, M., Zieger, P., and Murto, S. and the ARTofMELT Science Team: Arctic spring and the onset of sea-ice melt: Early impressions from the ARTofMELT expedition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15627, https://doi.org/10.5194/egusphere-egu24-15627, 2024.

14:25–14:35
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EGU24-5124
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ECS
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Highlight
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On-site presentation
Philipp Anhaus, Christian Katlein, Marcel Nicolaus, Noémie Planat, and Martin Schiller

A trend towards earlier sea-ice melt is detected in many ice-covered regions in the Arctic. The timing of the melt onset has a strong impact on the sea-ice energy budget. Melt onset changes the radiative properties of the ice due to increasing snow wetness and meltwater. So far, satellite passive microwave data are used to detect the melt onset. We analyzed transmitted radiation spectra as collected underneath drifting sea-ice using a remotely operated vehicle during the ARTofMELT expedition in the Fram Strait in spring 2023. We colocated those spectra with measurements of snow depth, sea ice and surface topography, chlorophyll-a concentration in the water column, and with aerial images. This combined dataset enables us to track down possible subsurface pathways and accumulation pools of meltwater. Areas of low snow load and depressed surface topography are characterized by higher transmitted radiation compared to areas with a thick snow cover. Those areas overlapped with areas that showed the first signs of surface melt. Chlorophyll-a concentrations varied only slightly in magnitude and did not match with the heterogeneous pattern of snow depth and ice topography. Here we discuss how to disentangle the influences of chlorophyll a and the subsurface meltwater on the spectral shape of transmitted radiation. We propose that upon successful disentanglement, the spectra can be used as an indicator for subsurface melting. Our study suggests that sea-ice melting starts subsurface and that measurements of transmitted solar radiation spectra could be used to identify the melt onset prior to surface melting. This can provide an interesting complementary information on melt occurrence and on the location of the water in the snowpack in addition to satellite passive microwave data.

How to cite: Anhaus, P., Katlein, C., Nicolaus, M., Planat, N., and Schiller, M.: Is spring melting in the Arctic detectable by under-ice radiation?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5124, https://doi.org/10.5194/egusphere-egu24-5124, 2024.

14:35–14:45
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EGU24-12340
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ECS
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Virtual presentation
Thibault Desjonquères, Leif E. B. Eriksson, Malin Johansson, Denis Demchev, Truls Karlsen, Timo Vihma, and Bing Cheng

In May-June 2023 the ARTofMELT 2023 expedition took place, with the aim to capture the melt onset in the Arctic Ocean. For the sea ice dynamics part of the cruise, in-situ observations were collected to co-inside with satellite observations, enabling studies of changes in drift patterns, capture the breakup of ice floes and studies of changes in backscatter signatures in satellite images as a consequence of melt onset. 

Seven OpenMETbuoys-v2021 and three SIMBA buoys, were placed on four first-year ice floes, away from the Marginal Ice Zone (MIZ). The OpenMETbuoys, equipped with GNSS (Global Navigation Satellite Systems), gyro, and accelerometer, facilitated horizontal motion, rotation, potential deformation, and wave action analysis. SIMBA buoys, with GNSS and thermistor strings, focused on temperature effects connected to melt onset. Three OpenMETbuoys and one SIMBA buoy were deployed on two larger floes. The two remaining drifters were deployed on individual floes. Deploying multiple buoys on each floe allowed detailed examination of small-scale drift changes, convergence, divergence, rotational patterns, frequencies, and connections to satellite Synthetic Aperture Radar (SAR) images. This deployment provides insights into the remaining wave energy in the pack ice. 

Low noise Radarsat Constellation Missions (RCM) SAR images in dual polarization (HH+VV or HH+HV) were acquired to overlap with the campaign in space and time. The temperature sensors onboard the SIMBA buoys enables us to connect changes in  backscatter values in the SAR images from the winter conditions into the early melt season and help define limitations for the SAR sea ice drift retrieval algorithm. 

Initial findings from wave and GNSS data offer insights into the condition of ice floes, including dislocation, disintegration, melting, and interactions with neighboring floes. The dislocation of the floes is indicated by the physical dissociation of the buoys present on the same floe. The OpenMETbuoys' recorded wave height and wave period indicate the drifter's location: on ice, in a transition phase on a small piece of ice or floating in the water between pieces of brash ice, or in open water.

Regarding the two bigger floes, on the first one, the drifters were launched 2023-05-22. An OpenMET drifter was dislocated from the rest of the floe on the 26th of May, and was in the transition phase on the 1st of July. The two remaining drifters were separated on the 29th of May. The last OpenMET drifter reached the transition phase on the 25th of May. The drifters on the second floe were launched 2023-05-28. The first dislocation occurred on the 8th of June, the second one on the 18th of June. The two remaining OpenMET drifters on this floe reached the transition phase on the 13th of June and 15th of June. The third floe contained a SIMBA drifter launched 2023-06-06 and the fourth one an OpenMETbuoy launched 2023-05-28. The latter reached the transition phase on the 10th of June.

How to cite: Desjonquères, T., Eriksson, L. E. B., Johansson, M., Demchev, D., Karlsen, T., Vihma, T., and Cheng, B.: Sea ice drift and wave pattern analysis of the early melt onset during the ARTofMELT cruise 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12340, https://doi.org/10.5194/egusphere-egu24-12340, 2024.

14:45–14:55
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EGU24-11158
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ECS
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On-site presentation
Sonja Murto and Michael Tjernström

A 6-week long expedition ARTofMELT (Atmospheric rivers and the onset of Arctic sea-ice melt) with the Swedish Icebreaker Oden took place in the Arctic Ocean during late winter and spring of 2023. The aim was to collect observations and study processes leading up to the sea-ice melt onset. One of the targets was to assess the role of atmospheric rivers (ARs), i.e., southerly warm and moist-air injections, in advancing the melt-timing. This paper presents the synoptic situation during the expedition, based on observations measured onboard Oden and reanalysis data (ERA5). Additionally, the origin and paths of airmasses reaching Oden are determined using 7-day backward trajectories computed with the Lagrangian analysis tool LAGRANTO. The meteorological conditions were quite dynamic during these 35 days, strongly influenced by several (at least 6) surface cyclones passing Oden and only two warming events accompanied by rather weak ARs were observed, the latter one leading to the melt onset at the end of the expedition.

 

Based on meteorological conditions from 6-hourly launched radiosoundings, the expedition can be divided into six periods. The first short period encompasses the first days of the expedition, when Oden was located at the marginal ice zone. The winds were variable, mainly southerly, and it was moist with slightly below-freezing temperatures. As Oden was moving northwestwards, a one-week cold (~-15 - -10) and dry period followed. This period was mainly governed by northerly winds, guided by a persistent family of surface cyclones located over the Laptev and Kara Seas. The first major storm, that coincided with an atmospheric blocking over Scandinavia, was related to a cyclone forming to the southwest of Greenland and moving northeast, bringing winds over 25 m/s as it hit Oden on 13 May.  Northerly winds followed after the stormed had passed, guided by a surface pressure dipole between a high over Greenland and a low over the Arctic Ocean.

 

The first one-week long ice camp was built at the end of the second period, extending into the third period. A low-pressure over Greenland and high-pressure and an upper-level blocking over Scandinavia resulted in a pathway for a transient warm-air mass from the south, and melting was observed for the first-time. However, this warming was only temporary, as temperatures dropped below freezing after the AR had passed. Several weaker storms governed this third milder period, ending with the second major storm associated with a cyclone on 25 May. Again, winds turned northerly after the storm passed, which made the entry to the fourth longer, colder and drier period. The second 2-week long ice camp was established at the beginning of this period and expanded over the two last periods. These captured the forecasted (6 June) and the real melt onset (10 June). A surface pressure dipole with a high over Greenland and a low over the Arctic Ocean dominated at the beginning of the fifth period, and warm but dry air aloft was observed. As the winds turned southerly, the melt-onset period was characterized as warm and moist.

How to cite: Murto, S. and Tjernström, M.: Synoptic situation during the ARTofMELT 2023 spring expedition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11158, https://doi.org/10.5194/egusphere-egu24-11158, 2024.

14:55–15:05
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EGU24-19946
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Highlight
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On-site presentation
Falk Pätzold, Lutz Bretschneider, Magnus Asmussen, Barbara Altstädter, Evelyn Jäkel, Hendrik Stapel, Tim Sperzel, Manfred Wendisch, Birgit Wehner, Ralf Käthner, and Astrid Lampert

In the Arctic climate system, the onset of melting is a crucial point, and timing is still difficult to predict. Therefore, the expedition ARTofMELT was dedicated to exploring atmospheric conditions and processes that are involved in triggering the onset of melting.

The helicopter borne sensor system HELIPOD was deployed in this expedition to measure the spatial variability of atmospheric dynamics, radiation, aerosols, trace gases and surface properties on a horizontal scale up to 40 km around the icebreaker ODEN. During the ARTofMELT23 expedition, the HELIPOD conducted 12 measurement flights in the FRAM strait around 80° North and the prime meridian between 9 May and 9 June 2023 with 26.5 hours in the air. The flights covered an area of about 20 NM around the location of the icebreaker ODEN and a vertical range from 50 m to 2700 m above sea level. The flight patterns were aligned parallel and perpendicular to dominating directions as the sea ice edge and the wind direction. In one case a cloud layer edge apparently structured the atmospheric situation. The flights covered pre-melt onset conditions, refreezing situations and the melt onset. Synoptic air mass changes were probed as well.    

The presentation gives an overview of the temporal changes of the ambient conditions during the research flights, and a first assessment of the flights during transient weather situations.

How to cite: Pätzold, F., Bretschneider, L., Asmussen, M., Altstädter, B., Jäkel, E., Stapel, H., Sperzel, T., Wendisch, M., Wehner, B., Käthner, R., and Lampert, A.: Helicopter borne measurements during melt onset in the Fram strait as part of ARTofMELT23, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19946, https://doi.org/10.5194/egusphere-egu24-19946, 2024.

15:05–15:15
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EGU24-5372
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On-site presentation
Hélène Angot, Marion Réveillet, and Julia Schmale and the MOSAiC team

Warm and moist intrusions (WAMIs) into the central Arctic, predominantly observed in winter and early spring, are becoming more frequent, significantly affecting the region’s near-surface energy budget. This study focuses on the deposition pulses of black carbon (BC) triggered by WAMIs and their subsequent impact on snow properties and melting during the summer, using a modeling approach and comprehensive datasets from the 2019–2020 Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition. Our findings reveal that WAMIs induce episodes of intense BC wet deposition in the central Arctic shoulder season (Nov–Apr) due to transported pollution and moisture. We demonstrate that WAMIs result in exceptionally high BC deposition (> 4 orders of magnitude compared to typical winter/spring conditions) across an area of nearly 1 million km2, approximately 20% of the central Arctic Ocean. Furthermore, we establish a direct connection between these winter/spring BC deposition pulses and subsequent summer increases in absorbed solar energy (> 4 W/m2) and snowpack melt rate (+15%). Despite their sporadic occurrence (only 8% of the time), WAMIs play a significant role in the central Arctic surface energy budget through the BC snow albedo effect.

How to cite: Angot, H., Réveillet, M., and Schmale, J. and the MOSAiC team: Impact of warm and moist intrusions on black carbon deposition and summer snow melt in the central Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5372, https://doi.org/10.5194/egusphere-egu24-5372, 2024.

15:15–15:25
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EGU24-17193
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ECS
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On-site presentation
Jennie Spicker Schmidt, Marianne Glasius, Camille Mavis, Jessie Creamean, Gabriel Freitas, Paul Zieger, Kai Finster, and Tina Šantl-Temkiv

The Arctic is a particularly vulnerable region on Earth, where climate change takes place at an intense pace. Clouds represent an essential element within the Arctic atmosphere and play a crucial role in the regional radiative balance. The physical properties of clouds are tightly interlinked with the presence of aerosols that can serve as cloud condensation nuclei (CCN) and as ice nucleating particles (INPs), which facilitate the formation of cloud droplets and ice crystals, respectively. Consequently, they affect cloud thickness, lifetime, and albedo.

More studies propose that various biological aerosols e.g., aerosolized microbial cells, proteinaceous compounds and fragments actively contribute to cloud processes serving as INPs active at high subzero temperatures (>-15°C). However, our understanding of microorganisms responsible for producing compounds serving as INPs, their source environments, and their level of activity, remains highly uncertain.

Given the profound impact of climate change in the Arctic region, understanding the role of biological INPs in the atmosphere becomes particularly critical during Arctic melt season. Here, we present an overview of bioaerosol observations and sources tracking from the recent Arctic expedition ”Atmospheric rivers and the onset of Arctic melt” (ARTofMELT 2023).

Biological INPs are thought to originate from the ocean and meltwater sources during the Arctic Spring and Summer. To assess the potential contribution of these sources to INP active aerosols, aerosols were generated from bulk seawater and sea ice melt water with a temperature-controlled sea spray simulation chamber. The presence of microorganisms in the bulk water and aerosol was quantified using flow cytometry and qPCR while the composition of the microbial communities was determined by amplicon sequencing. Additionally, fluorescent bioaerosols generated by the chamber were  analyzed using a Multiparameter Bioaerosol Spectrometer (MBS). Simultaneously, ambient air samples were analyzed for the presence of microbial cells, bioaerosols, and the composition of the collected microbial community. The ice nucleating properties of water, sea ice melt, and aerosols from the chamber and ambient aerosol were also measured to determine their relevance for Arctic cloud formation.

Preliminary results from the ambient measurements revealed low concentrations of airborne bacterial cells and highly active INPs. From the sea spray simulations, we found that ice melt, snow melt and seawater samples generated a high flux of bacterial cells which were accompanied by INPs active predominantly at low freezing temperatures (<-15°C). Therefore, it seems that the local sea spray is not a likely source of proteinaceous INPs detected in the Arctic spring atmosphere, which will be further explored through bacterial community analysis. Our results will thus provide comprehensive insights into the contribution of local and long-range transported sources of bioaerosols to the Arctic.

How to cite: Schmidt, J. S., Glasius, M., Mavis, C., Creamean, J., Freitas, G., Zieger, P., Finster, K., and Šantl-Temkiv, T.: The composition and sources of airborne bacteria and proteinaceous Ice Nucleating Particles in the High Arctic marine region during Spring, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17193, https://doi.org/10.5194/egusphere-egu24-17193, 2024.

15:25–15:35
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EGU24-19851
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ECS
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On-site presentation
Gabriel Freitas, Kouji Adachi, Julia Asplund, Jessie Creamean, Fredrik Mattsson, Camille Mavis, Lovisa Nilsson, Matthew Salter, Jennie Spiecker Schmidt, Tina Šantl-Temkiv, and Paul Zieger

The Arctic has been experiencing a rise in ambient temperature several times higher than the global average. This warming trend has led to a continuous decline in sea ice coverage and snowpack prevalence. Aerosol sources, such as those from the open ocean and tundra, have become more prevalent throughout the year. These sources emit primary biological aerosol particles (bioaerosols) some of which exhibit ice nucleating properties at high temperatures (>-15C). Ice nucleating particles (INPs) play a crucial role in cloud ice formation, affecting cloud physical and optical properties, as well as their lifetime. Consequently, this has a substantial impact on the Arctic climate. 

During the ARTofMELT2023 expedition (“Atmospheric Rivers and the Onset of Sea Ice Melt 2023”) conducted aboard the Swedish icebreaker Oden in the Atlantic sector of the Arctic Ocean, we assessed the relative importance of several natural bioaerosol sources, such as sea ice, snow melt (to simulate melt ponds) and bulk ocean water. This involved several sea spray simulation chamber and nebulizer experiments, referred to as “source experiments”. The aerosol particles generated in the 61 source experiments conducted were analyzed using single-particle ultraviolet fluorescence spectroscopy along with other complementary aerosol measurements. These included particle size, black carbon content, particle chemical composition, as well as the microbial community and INP concentration of emitted particles. Additionally, filter samples were obtained for transmission electron microscopy (TEM) analysis. 

Our findings indicate that sea ice and snow melt are more significant sources of bioaerosols compared to the bulk ocean water, including the sea surface microlayer, indicating the potential importance of melt ponds as a local Arctic bioaerosol source. Furthermore, we found significant differences in the chemical composition, black carbon content and size distribution of the various analyzed aerosol sources.

How to cite: Freitas, G., Adachi, K., Asplund, J., Creamean, J., Mattsson, F., Mavis, C., Nilsson, L., Salter, M., Spiecker Schmidt, J., Šantl-Temkiv, T., and Zieger, P.: Characteristics of natural Arctic aerosols emitted from a wide range of local sources during ARTofMELT2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19851, https://doi.org/10.5194/egusphere-egu24-19851, 2024.

15:35–15:45
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EGU24-3662
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ECS
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On-site presentation
Samantha Rush, Chang-Ho Lee, Kitack Lee, Penny Vlahos, and Lauren Barrett

The Arctic Ocean is one of the most rapidly changing environments on the planet as sea ice extent and thickness have declined extensively over the last 40 years. It is predicted that by 2050, Arctic summers will become mostly ice-free, and the Arctic Ocean will be dominated by seasonally annual, rather than multiyear, sea ice. Arctic sea ice serves as a mediator of biogeochemical processes globally, though the impacts of increased ice melt and water column freshening on Arctic biogeochemistry are uncertain. Specifically, declining sea ice raises significant concerns regarding the future carbon uptake potential of the Arctic and the buffering capacity, or alkalinity, of seawater. Boron (B) is a major element in seawater, and in the form of the borate ion, it serves as the third largest contributor to alkalinity. Boron concentrations in the open ocean are typically conservative and accounted for through relationships with other water components, such as with salinity (S) in the boron to salinity ratio (B/S). Well established B/S ratios have been defined for the open ocean; however, salinity variability can create discrepancies in the open ocean boron corrections for alkalinity. In 2021, work in the marginal ice zone of the Bering and Chukchi Seas revealed non-conservative boron behavior and significant alkalinity system inaccuracies based on the deviation in computed B/S ratios in ice cores and brine. In this study, we investigate the B/S ratio in ice melt zone waters, snow, brine, annual, and multiyear sea ice from the eastern Arctic basin. A total of 169 samples were collected during the onset on melt (May-June 2023) on the ARTofMELT expedition across a range of salinities (2 - 63). High salinity samples (S>29) included 1 lead, 7 brine, 16 under-ice, and 28 open ocean water samples. Low salinity samples (S<29) included 1 brine, 10 snow, and 106 ice core samples. Excluding snow, results indicate deviations from the accepted open ocean B/S ratio (0.1336 mg/kg). For both the entire high salinity sample set and the open ocean subset within it, the B/S average value (0.1304 ± 0.001 mg/kg) was lower. For low salinity samples, the average B/S value (0.1328 ± 0.003) was higher than the high salinity sample value but still lower than the accepted field value. The range of B/S ratios was much larger in low salinity samples (0.1260-0.1425 mg/kg) than high salinity samples (0.1275-0.1350 mg/kg); however, both ranges were significantly smaller than the 2021 B/S ratio range (0.0900-0.1850 mg/kg). The smaller deviation from the accepted B/S ratio in this study resulted in carbon system analysis inaccuracies less than 2 µmol/kg across the entire salinity range. We present the computed B/S ratios and the differences in these datasets using the δ18O isotopic ratios to understand the heterogeneity of western, annual ice in the marginal ice zone and eastern, multiyear ice in pack ice regions. The marked distinction in the datasets allows potential insight into boron concentrations and the conversion of total alkalinity to carbonate alkalinity across current and future systemic climate-change shifts in the Arctic.

How to cite: Rush, S., Lee, C.-H., Lee, K., Vlahos, P., and Barrett, L.: Non-conservative nature of Boron in low salinity Arctic ice and ice melt zones, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3662, https://doi.org/10.5194/egusphere-egu24-3662, 2024.

Posters on site: Thu, 18 Apr, 10:45–12:30 | Hall X5

Display time: Thu, 18 Apr 08:30–Thu, 18 Apr 12:30
X5.117
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EGU24-11515
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ECS
Cort Zang, Megan Willis, Julia Asplund, Fredrik Mattsson, Paul Zieger, and Michael Tjernström

The sources, composition, and reactive transformation of reactive organic carbon (ROC, non-methane organic carbon) as well as the processing, abundances, and distribution of organosulfur compounds in the Arctic marine atmosphere are unconstrained partially due to a lack of targeted measurements.  Understanding the emission, transport and processing of ROC and organosulfur compounds is important for improving our understanding of the impacts of gaseous precursors on aerosol nucleation and growth, and atmospheric oxidation capacity. There is a shift in aerosol size distribution that occurs with the Arctic spring-to-summer transition period and there are very few Arctic marine measurements of trace gases during this same period. Constraining the composition of organosulfur compounds and ROC is important for understanding the drivers in the shift of aerosol size distribution.

We present shipborne gas-phase measurements of ROC and organosulfur compounds in the Arctic marine atmosphere as part of the Atmospheric Rivers and the onseT of sea ice MELT (ARTofMELT) campaign. ARTofMELT took place from May 7th to June 15th of 2023 over pack ice and within the marginal ice zone between 78 and 81°N in the Fram Strait. We deployed a reagent ion switching chemical ionization mass spectrometer to target ROC and organosulfur compounds using H­3O+ ionization for the detection of reduced compounds and NH4+ ionization for the detection oxidized species. The measurements encompass a variety of different conditions including ozone depleted air masses (<10ppbv), cloud influenced air masses, a range of aerosol concentrations, and air masses with southern and northern airmass history with influences from biologically rich marine regions as well as transport from over pack ice. Additionally, measurements of ROC show the presence of ≥C5 organics in the environment with implications for aerosol size and growth. Here, we show an overview of our measurements and some initial observations of the ROC present during the campaign.

How to cite: Zang, C., Willis, M., Asplund, J., Mattsson, F., Zieger, P., and Tjernström, M.: Overview of SMÄLTA: Secondary Marine Aerosol precursors and Links to aerosol growth at ice-melT onset in the Arctic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11515, https://doi.org/10.5194/egusphere-egu24-11515, 2024.

X5.118
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EGU24-4403
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ECS
Theresa Mathes and Andreas Held

The Arctic region is warming rapidly, and aerosol-cloud-sea-ice interactions are considered to be one of the key features of the Arctic climate system. It is therefore crucial to identify Arctic particle sources and sinks in order to study their impact on cloud formation and properties. Scott and Levin (1972) were the first to describe open leads as potential sources of atmospheric particles and thus a local source of particle emissions in the central Arctic. Held et al. (2011) found that open leads and ice ridges in particular emit high levels of particles. Particle concentrations have also been shown to be altered by the intrusion of warm and moist air masses and can be strongly enhanced in turbulence-dominated cases (You et al., 2022). Despite significant progress in Arctic research in recent years, there is still a lack of information on near-surface particle concentrations over different surface types, especially before and during the ice-melting period.

Here, we present measurements of near-surface particle concentration profiles to help to quantify the vertical aerosol exchange between Arctic sea ice and the atmosphere. In spring 2023, during the research cruise ARTofMELT on board the icebreaker Oden, we successfully carried out vertical particle measurements. From 17 May to 9 June 2023, near-surface particle concentration profiles were measured during 16 individual measurement periods. Due to the early season, measurements could be taken both before and during the melting process.

For the profile measurements, an aersol inlet was automatically moved up and down by a 1.50 m linear actuator. A plate was attached to the lift to hold sensors for the distance, wind and temperature as well as the aerosol inlet. An  box containing the condensation particle counter (CPC 3007, TSI, St. Paul, MN, USA) was connected to the inlet. Total particle number concentrations with a lower cut-off diameter of 10 nm were then determined at six different heights from 6 cm above the surface to 1.30 m. These measurements were carried out on the ice close to an open lead or surrounded by a closed ice surface.

Figure 1 shows an example for two days of fluxes at 79.8 ° N and 1.9° W. Due to the proximity to the open lead, an emission (red) of aerosols predominates, which is partially alternated by a deposition (blue). The flow calculations are based on 26 height profiles measured on 17 May and 24 on 18 May.

We thank our colleagues from Leibniz Institute for Tropospheric Research, Stockholm University, Swedish polar research secretariat as well as all expedition participants who provided insight and expertise that greatly assisted the research.

Held, A., Brooks, I.M., Leck, C., and Tjernström, M. (2011) On the potential contribution of open lead particle emissions to the central Arctic aerosol concentration. Atmos.Chem.Phys. 11, 3093-3105.
Scott, W. D. and Z. Levin (1972) Open channels in sea ice as ion sources. Science 177, 425-426.
You, C., Tjernström, M., Devasthale, A. (2022) Warm and moist air intrusions into the winter Arctic: a Lagrangian view on the near-surface energy budgets. Atmos.Chem.Phys. 22, 8037–8057.

How to cite: Mathes, T. and Held, A.: Near-surface particle concentration profiles above the Arctic sea ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4403, https://doi.org/10.5194/egusphere-egu24-4403, 2024.

X5.119
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EGU24-5901
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ECS
Lea Haberstock, Julia Asplund, Almuth Neuberger, Luisa Ickes, Gabriel Freitas, Fredrik Mattsson, Darrel Baumgardner, Ilona Riipinen, and Paul Zieger

Aerosol-cloud interactions play a crucial role in the Arctic’s radiative budget. During the campaign ‘Atmospheric rivers and the onset of sea ice melt’ (ARTofMELT 2023) we aimed to improve our understanding of aerosol-cloud interactions by conducting in-situ measurements of microphysical and chemical properties of aerosols, cloud droplets, and precipitation in the Arctic during the onset of sea ice melt. A ground-based fog and aerosol spectrometer (GFAS) and a fog monitor (FM-120) from Droplet Measurement Technologies (DMT) were used to measure among other things droplet size, number concentration, and liquid water content. Precipitation was measured with a meteorological particle spectrometer (MPS, DMT). Throughout the campaign, we observed several fog and blowing snow events, along with occasional precipitation. These events provided an opportunity to investigate and compare the distinctive microphysical properties associated with each event. Our findings reveal significant variations in the size distribution and particle phase of blowing snow, precipitation, and fog.

How to cite: Haberstock, L., Asplund, J., Neuberger, A., Ickes, L., Freitas, G., Mattsson, F., Baumgardner, D., Riipinen, I., and Zieger, P.: Aerosol-Cloud-Precipitation Interactions in the Arctic: Insights from the ARTofMELT Campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5901, https://doi.org/10.5194/egusphere-egu24-5901, 2024.

X5.120
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EGU24-20594
Jessie Creamean and the MOSAiC and ARTofMELT field teams

Aerosol particles and clouds play a critical role in regulating radiation reaching the Arctic, which is warming faster than anywhere else globally. However, the magnitude of their effects is not adequately quantified, especially in the Arctic Ocean over sea ice. Specifically, particles generated from open leads, melt ponds, and the snow-covered sea ice surfaces remain poorly understood, yet could have significant impacts on cloud condensation nuclei (CCN) and ice nucleating particle (INP) concentrations, and thus, central Arctic cloud formation. While marine biological processes have been demonstrated to be potentially key primary aerosol sources in the Arctic summer, exact sources and emission processes of these particles remain highly uncertain. 

For this presentation, we provide an overview of aerosol observations from two recent Arctic field campaigns: the 2019–2020 Multidisciplinary drifting Observatory for Study of Arctic Climate (MOSAiC) and the 2023 Atmospheric rivers and the onset of Arctic melt (ARTofMELT) expeditions. We highlight preliminary findings focused on aerosols that have the potential to impact cloud phase and lifetime over the Arctic Ocean, specifically those from local sources in the early spring and summer melt periods. The evolution of open water within the pack ice in late spring and the Arctic melt season coincides with an increase in aerosol particle concentration, which may be attributed to biological activity within seawater and sea ice. However, the emission of aerosol particles is contingent on features like open leads and melt ponds, and whether they are covered by snow, freshwater melt layers, or ice lids. This integrative study involves the use of detailed aerosol, meteorological, oceanographic, and sea ice observations from MOSAiC and ARTofMELT. Overall, this work will enable us to assess local aerosol processes associated with cloud formation to better understand the Arctic system through a holistic approach.

How to cite: Creamean, J. and the MOSAiC and ARTofMELT field teams: Sea ice, snow caps, and freshwater lenses: The hurdles local Arctic aerosols must overcome to become airborne, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20594, https://doi.org/10.5194/egusphere-egu24-20594, 2024.

X5.121
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EGU24-5950
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ECS
Julia Asplund, Lea Haberstock, Jessica Matthew, Fredrik Mattson, Lovisa Nilsson, Erik Swietlicki, Megan Willis, Cort Zang, and Paul Zieger

Aerosol- cloud interactions remain among the most uncertain key parameters in the fast-changing Arctic climate system, in large part due to a lack of observational data from this hardly accessible region. The spring-summer transition is a particularly under sampled time period, due to harsh ice conditions. Here, we present five weeks of aerosol size distribution measurements over the spring Arctic pack ice, including more than 30 hours of in-cloud data, obtained during the ARTofMELT 2023 expedition. A setup of three inlets, including a whole-air, an interstitial, and a counterflow virtual impactor inlet, were used to cover the full aerosol population as well as both the activated and interstitial aerosol when in cloud. We will show an overview of the collected observations and the link between the size distribution properties and parallel measured aerosol parameters such as chemical tracers, as well as an air mass source analysis. Fog events were recorded during a range of aerosol conditions, allowing us to study the activated fraction when concentrations span from under 20 particles per cc, to over 150. The dataset also features several distinct regimes where different processes such as blowing snow, new particle formation, and secondary ice production dominate or influence the aerosol population, and we will demonstrate how the regimes are characterized by the dominant mode of the size distribution.

How to cite: Asplund, J., Haberstock, L., Matthew, J., Mattson, F., Nilsson, L., Swietlicki, E., Willis, M., Zang, C., and Zieger, P.: What we can learn from aerosol size distribution measurements over the spring Arctic pack ice, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5950, https://doi.org/10.5194/egusphere-egu24-5950, 2024.

X5.122
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EGU24-17977
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ECS
Lovisa Nilsson, August Thomasson, Paul Zieger, Julia Asplund, Pontus Roldin, Fredrik Mattson, Erik Ahlberg, and Erik Swietlicki

Few expeditions have ventured into the Arctic to observe the processes that take place in the transition from winter to summer. Particularly, direct observations of aerosol-cloud interactions are scarce, and comprise a large source of uncertainty in radiative forcing estimations in the Arctic.

Light absorbing aerosol particles, such as black carbon (BC) from incomplete combustion, exert a positive forcing upon direct absorption of sunlight, and affect clouds by serving as cloud condensation nuclei (CCN). During the icebreaker expedition ARTofMELT in spring 2023, we measured BC with a multi-angle absorption photometer (MAAP) and a single particle soot photometer (SP2) for five weeks. The two instruments differ by principle and can be used to inform on complementary aspects of the light absorbing aerosol. For example, the MAAP provides the total mass concentrations of so-called equivalent BC (eBC), whereas the single particle instrument SP2 determines the mass of individual refractory BC (rBC) aggregates. Most of the time, the MAAP and SP2 sampled the total BC concentration on the same inlet (whole-air). However, during cloud-events, the SP2 measured downstream of a counterflow virtual impactor (CVI) inlet that samples just cloud droplets or ice crystals without the interstitial or non-activated aerosol.

Our first results indicate overall low out-of-cloud BC mass concentrations for both instruments (median and interquartile range, IQR: 4.4 (1.6-8.5) ngm-3 for the MAAP and 2.5 (1.2-4.7) ngm-3 for the SP2). The variation in mass concentration was small, although the tendency of a gradual decrease was observed towards the onset of the melt.

The SP2 instrument enables studies of the BC mass size distribution. For example, during a cloud event we observed that the geometric mean diameter (GMD, mass equivalent diameter) shifted from smaller (171 nm, whole-air inlet) to larger sizes (175-192 nm), as the SP2 switched to sampling the cloud-residual BC (CVI inlet). Further investigation is needed to examine the underlying causes for this observation (e.g. variation in airmass origin). 

The total aerosol concentration is influenced by local natural sources and production from gaseous precursors, as opposed to the BC concentration which is mainly affected by anthropogenic activities. BC source footprints from the Lagrangian dispersion model FLEXPART, indicate little influence from industrialized regions during the whole campaign. This may explain the comparably low median concentration of rBC-particles (1.1 cm-3, IQR: 0.5-2.1) to the total aerosol number concentration (in the range ~20-150 cm-3).

How to cite: Nilsson, L., Thomasson, A., Zieger, P., Asplund, J., Roldin, P., Mattson, F., Ahlberg, E., and Swietlicki, E.: Springtime observations of black carbon aerosols in and outside of low-level Arctic clouds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17977, https://doi.org/10.5194/egusphere-egu24-17977, 2024.

X5.123
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EGU24-5162
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ECS
The Partitioning Processes of Sea Ice Associated Ice Nucleation Particles Impacting the Arctic Clouds 
(withdrawn)
Lasse Z. Jensen, Eva R. Kjærgaard, Martina D’Agostino, Dorte Søgaard, Bernadette Rosati, Merete Bilde, Lars C. Lund-Hansen, Kai Finster, and Tina Šantl-Temkiv
X5.124
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EGU24-17589
Jean Lac and Hélène Chepfer

Low-liquid stratiform clouds are ubiquitous in the Arctic. Their high surface longwave warming induces change in the surface radiative budget that might have effects on the sea-ice melt especially during transitioning seasons. In particular, low liquid clouds formed in Spring may trigger early melt onset that might have an impact on the following evolution of the sea-ice during summer. 

However, relatively little is known about the existence and the drivers of such clouds in the early melt season. Here we used 13 years of space based lidar cloud profile observations with complementary data to show that the predominance of low clouds happens in May. First, we showed that the low cloud fraction reaches 75% of the Arctic Ocean in May over the sea-ice only with a low interannual variability. This cover increase in May seems to be homogeneous over the whole Arctic Ocean. Second, we investigated potential early summer drivers forming those low liquid clouds. One feature is the moisture sources that could explain the availability of such liquid droplets to form liquid clouds. While the other feature is the boundary layer structure, that might affect the stability and the ocean/atmosphere interaction over sea-ice leads.  

Overall, this study suggests a peak of Arctic low liquid clouds occurring in May that might impact the sea-ice summer melt by triggering early Spring melt. 

How to cite: Lac, J. and Chepfer, H.: Intense formation of low liquid clouds over the Arctic sea-ice during May.  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17589, https://doi.org/10.5194/egusphere-egu24-17589, 2024.

X5.125
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EGU24-21926
Jeff Welker, Ben Kopec, Eric Klein, Julia Muchowski, Timo Vihma, Paul Zieger, Falk Paetzold, Astrid Lampert, Penny Vlahos, John Prytherch, Valtteri Hyöky, and Truls Karlsen

Transitions periods between seasons in the Arctic are phases when the atmosphere-sea ice-ocean interactions are heightened, especially during these periods of exceptional warming.  These transition periods may be accompanied by shifts in atmospheric transport patterns, the distribution of sea ice and extreme events, such as atmospheric rivers.  Atmospheric Rivers may act as accelerants of sea ice melt and its redistribution, leading to spatial complexity in ice-ocean-atmosphere exchanges of mass and energy.

As part of an interdisciplinary team aboard the I/B Oden from early May to mid-June, four main water isotope measurement packages were collected to maximize collaborations and to resolve nuisances of the Arctic System throughout the cruise track between Svalbard and NE Greenland (Figure 1).  First, in order to delineate longitudinal distribution of the warm and salty W Svalbard current compared to the cold and fresh E Greenland current, we continuously measured the near surface water δ18O, δ2H and d-excess values. Second, in order to source water vapor and moisture sources from the warm, moist, and isotopically enriched subpolar & N Atlantic, compared to cold, dry and isotopically depleted Arctic air, we also continuously measured the δ18O, δ2H and d-excess values of water vapor collected from the ship’s, bow-mounted, eddy covariance tower. Third, in order to understand the horizontal and altitudinal patterns of water vapor parcels that surround the ship; in-situ water vapor isotopes were measured during fHeliPod flight lines that extended up to 30 km N-S-E-W of the Oden and from ~ 50 m above the sea ice and open water to over 2k in altitude.  Fourth, in order to delineate the source of moisture (sea water vs. meteoric water) throughout the sea ice core profiles and the patterns and sources of moisture in the snow pack profiles; ice cores and snow pits were collected (drilled) and dug at ~10 different locations and water isotope samples were analyzed for δ18O, δ2H and d-excess values back in the laboratory.

Four major discoveries will be presented: A) mixing of the surface W Svalbard and NE Greenland current is found to be farther east than previously reported and the surface water masses may differ by up to 5 ‰ δ18O during spring; B) water vapor isotopes responded at hourly time scales as moisture sources during Atmospheric River events begin with northward fluxes of warm, moist air masses but passing cyclones deliver N-S cold-dry, isotopically depleted water vapor in extreme Arctic-sourced storm events lasting a day or more; C) Horizontal and vertical transects during Heliopod flights captured horizontal and altitudinal variation in water vapor isotopes during periods when the weather of the ship was dominated by cold-dry Arctic air, interrupted by periods when the ship was experiencing pulses of warm, moist, and high humidity conditions; D) ice cores and snow packs exhibit vertical isotopic variation indicative of different moisture sources and morphogenesis processes.

How to cite: Welker, J., Kopec, B., Klein, E., Muchowski, J., Vihma, T., Zieger, P., Paetzold, F., Lampert, A., Vlahos, P., Prytherch, J., Hyöky, V., and Karlsen, T.: Water Isotope measurements contribute to the understanding of atmospheric, sea ice, ocean interactions during the ArtofMelt expedition, Fram Strait, spring 2023, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21926, https://doi.org/10.5194/egusphere-egu24-21926, 2024.

X5.126
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EGU24-3232
Abhay Devasthale and Michael Tjernström

Given the high rate of sea ice loss and the Arctic amplification, the dynamical processes responsible for airmass transport into or out of the Arctic, thus affecting the seasonal melt and recovery of sea ice, need to be understood and scrutinized from different observational perspectives. In a classical, rather binary view of transport “into or out of the Arctic”, a lot of attention in the recent years has rightfully been given on understanding the role of heat and moisture transport into the Arctic in regulating the sea ice melt. However, the cold and dry Arctic airmasses with long residence times are more than occasionally transported out of the Arctic over the open ocean waters, creating one of the most spectacular air mass transformations: the marine cold air outbreaks (MCAOs). The most tangible manifestation of MCAOs are the convectively rolled, narrow cloud streets formed over open water off the edges of the Arctic sea ice in the Nordic and Barents Seas, seen vividly in visible satellite imageries. MCAOs can also locally influence the onset of sea ice melt as they often happen in spring.  

By combining nearly 20 years of remotely sensed data from the hyperspectral Atmospheric Infrared Sounder (AIRS), the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth’s Radiant Energy System (CERES) instruments onboard NASA’s Aqua satellite, this study presents a climatological view of the vertical structure of atmosphere and the cloud radiative effects during MCAOs in the northeast Atlantic.

How to cite: Devasthale, A. and Tjernström, M.: A climatological satellite view of marine cold air outbreaks in the northeast Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3232, https://doi.org/10.5194/egusphere-egu24-3232, 2024.