In the summer of 2012, nearly the entire Greenland Ice Sheet (GIS) melted  as warm air and thin clouds moved over the GIS in association with an Atmospheric River (AR) (Bennartz et al. 2013, Neff et al. 2014).  More recently surface melt as well as rainfall have been observed at Summit Station Greenland.  While these events garner much media attention, systematic mass loss in the ablation zones around the ice sheet (particularly along the southwest coast), in the transition to the accumulation zone and vulnerable glacier systems (Mattingly et al. 2021) is important to forecast sea level rise.  In this analysis, we use a simple detection method to identify ARs along the Greenland west coast using reanalysis data at two points (60N/310W and 65N/305W) at 850 hPa, namely wind speed and direction and total integrated water vapor.  We show a comparison between ERA5, NCEP/NCAR, and the Twentieth Century Reanalysis to show the efficacy of this approach and the ability to track ARs over the past hundred years. The approach exploits the barrier effect of the GIS, which extends to about 700 hPa.
This use of reanalysis data is then coupled with the calculation of the fraction of melt in a series of latitude-longitude boxes at various locations around the ice sheet using the MEaSURES data set (Mote 2016) for the period 2000-2012. We then develop composite synoptic maps for geopotential height, total column water vapor, and Omega (for vertical velocity) for each class of event (e.g. strong ARs) and their subsequent evolution over 3 to 5 days. A key finding is that ARs that first impact the west coast later transport moisture to the SE coast leaving a residue of moisture along the west coast as the associated blocking high moves to the east.  In addition, we show how strong ARs along the west coast reflect geopotential height patterns very similar to those presented in (Gallagher et al. 2018) that are also associated with warmer temperature and increased opaque cloudiness at Summit Station.  Finally, we examine how various extreme events fit into this picture and affect the meteorology at Summit Station, including dramatic changes in boundary layer structure.

References

Bennartz, R., M. D. Shupe, D. D. Turner, V. P. Walden, K. Steffen, C. J. Cox, M. S. Kulie, N. B. Miller and C. Pettersen (2013). Nature 496(7443): 83-86.Gallagher, M. R., M. D. Shupe and N. B. Miller (2018. Journal of Climate."  31(21): 8895-8915.

Mattingly, K. S., T. L. Mote and X. Fettweis (2018). Journal of Geophysical Research: Atmospheres.

Mote, T. L. (2016). MEaSUREs Greenland Surface Melt Daily 25 km EASE-Grid 2.0, version 1. https://doi.org/10.5067/MEASURES/CRYOSPHERE/nsidc-0533.001.

Neff, W., G. P. Compo, F. M. Ralph and M. D. Shupe (2014). Journal of Geophysical Research-Atmospheres 119(11): 6520-6536.

Mattingly et al., EGU General Assembly 2021

How to cite: Neff, W., Shupe, M., Cox, C., and Gallagher, M.: Atmospheric Rivers and Surface Melt Events Over the Greenland Ice Sheet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3690, https://doi.org/10.5194/egusphere-egu23-3690, 2023.

Leads are Chanel-like openings in the sea-ice through which heat of several 100 Watt/m² is transferred from the ocean into the atmosphere. Even though leads account only for a view percent to the total ice coverage in polar regions, they modify the polar boundary layer significantly. Therefore, leads need to be considered in numerical weather and climate models. Since, generally leads are not explicitly resolved in these models it is important to understand the overall effect of leads of different sizes onto the boundary layer for different meteorological conditions.

With numerous Large-Eddy simulations, we investigated the dependency of the lead averaged surface heat flux on the lead width in a range between a few meters to several kilometers for different meteorological and surface conditions. Generally, we found under same temperature differences between ice and water and same meteorological conditions for small leads a decrease of lead averaged surface heat flux with lead width (as often observed in experimental studies), but for wider leads a significant increase.

We like to give some brief explanations of the possible causes for this behavior as well as to oppose these results to other former studies in this field, which might disagree to these in some points.

How to cite: Gryschka, M. and Mostafa, Z.: Turbulent heat exchange over polar leads – an LES study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8833, https://doi.org/10.5194/egusphere-egu23-8833, 2023.

Polar and sub-polar winters represent outstanding opportunities to study the PBL state in connection to the synoptic meteorological fields. In the high latitudes, the absence of a diurnal cycle combined with the presence of an anticyclone feature promotes surface radiative cooling resulting in the formation of a surface based temperature inversion (stably-stratified structure). Under such meteorological conditions, large scale subsidence promotes adiabatic compression (i.e., warming in upper levels) promoting the formation of elevated temperature inversions layers. This multilayered configuration represents a significant challenge for micro-scale/mesoscale modeling and air pollution dispersion as well as for the transport of the local contamination to the global arctic air shed. However, this structure is fragile and can be disrupted by dynamic and radiative effects caused by synoptic variability affecting the PBL state. Thus, significant changes in the PBL state are verified when synoptic situation changes (i.e, warm air advections and more mesoscale frontogenesis).

In this contribution, we describe the state of the PBL linked to the synoptic large scale variability using the high resolution thermodynamic profiling datasets from the 2022 ALPACA field experiment in Fairbanks, Alaska. High resolution synoptic scale reanalysis datasets are used to detail dynamic processes coupled to atmospheric dynamics in the PBL state.-

How to cite: Fochesatto, G. J., Keller, D., Dieudonné, E., Brett, N., Law, K., Bekki, S., Atkinson, D., Wellton, E., and Peterson, E.: The Effects of the Large Scale Synoptic fields in the High Latitude PBL states., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17118, https://doi.org/10.5194/egusphere-egu23-17118, 2023.

MOSAiC was a rare opportunity to obtain observational data on Arctic cyclones (ACs), with at least 22 ACs sampled during four of the five legs.  This presentation will illustrate how some of the AC cloud and boundary-layer characteristics produce both thermodynamic and dynamic impacts on the sea ice in the non-melt seasons.  Deep clouds associated with the ACs enhanced the downwelling radiation, with the surface radiation dependent on cloud height, temperature, and liquid water layers.  Underneath the warm fronts ahead of the ACs, this effect directly warmed the surface, sometimes to the extent of destabilizing the near-surface boundary layer.  Synoptically induced low-level jets (LLJs) found within AC warm sectors between the surface warm front and cold front often also provided warm-air advection down to a few hundred meters above the surface, which, in many cases, produced a stable lower boundary layer and enhanced downward sensible heat flux in these AC regions.  These effects in some mid-winter ACs produced near-surface temperature increases of 20° C or more compared to the surface temperatures prior to the ACs, with some, but not all, winter cases also producing strong thermal waves penetrating through the snow and ice and reducing sea-ice growth. 

In some ACs, a quasi-axisymmetric LLJ near the top of the boundary layer in the warm sector and then wrapping around the low center as a “bent-back” feature produces the appearance of two successive LLJs with greatly differing wind directions at the MOSAiC site.  The rapid change in wind speed and direction between these LLJ pairs produces a rapid change in the surface stress vector and imparts strong forcing on the sea ice.  During MOSAiC, strong ice deformation, lead formation, etc., was observed during the time periods between the two LLJs.  Hence, these LLJs not only play a role in the atmospheric thermal impacts on sea ice from ACs, but also on the dynamic impacts.

The broad relevance of Arctic Cyclone mesoscale features, such as low-level jets, warm-sector warm-air advection, and cloud macro and microstructure, to the sea-ice thermodynamic and dynamic environment during the MOSAiC field program will be illustrated with MOSAiC case-study observations, including basic meteorological measurements, rawinsondes, ARM remote sensors, surface energy budget measurements, and ice motion measurements.

How to cite: Persson, O., Cox, C., Gallagher, M., Shupe, M., Hutchings, J., Watkins, D., and Perovich, D.: Arctic Cyclone Cloud and Boundary-Layer Features Producing Thermodynamic and Dynamic Impacts on Arctic Sea Ice During MOSAiC, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17554, https://doi.org/10.5194/egusphere-egu23-17554, 2023.

Arctic clouds are poorly represented in climate models partly due to a lack of understanding of their source and nucleating capability of natural aerosol in the high Arctic. Recent field campaigns provided evidence of a source of sea salt aerosol (SSA) from blowing snow above sea ice, which can account for SSA winter/spring maxima observed in the polar regions. SSA emissions from sea ice sources can potentially influence regional climate via the indirect radiative effect, but contributions to cloud-forming particles, in particular, ice-nucleating particles (INP), are unknown. Here we report the first online spring-time observations of INPs in the Central Arctic. INP concentrations were on the order of a few tens [particle m^-3] activating between -38 and -15°C and were often associated with high wind speeds. Initial offline droplet assay analysis of snow on sea ice indicates the presence of potential INPs in winter/spring activating at -29 to -25°C. This is evidence that snow on sea ice represents a viable reservoir of INPs, which can be physically released via the blowing snow mechanism to the air above. We discuss sea ice sources of coarse SSA and INPs and their role in the lower atmosphere with a focus on blowing snow. To do this, we consider the comprehensive set of MOSAiC observations, including aerosol size and composition, airborne snow particles, and chemical and physical properties of both aerosol and snow on sea ice.

How to cite: Frey, M. M., Kirchgäßner, A., van den Heuvel, F., Lachlan-Cope, T., Stratmann, F., Wex, H., Macfarlane, A. R., Mirrielees, J., Pratt, K., Beck, I., Schmale, J., Nishimura, K., and Brooks, I.: Sea salt aerosol and ice nucleating particles (INP) in the Central Arctic during winter/spring – a discussion of a source from blowing snow above sea ice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9024, https://doi.org/10.5194/egusphere-egu23-9024, 2023.

Sea salt aerosols play a critical role in aerosol-radiation and aerosol-cloud interactions. Salty blowing snow has been hypothesized as an important source of sea salt aerosol in polar regions. The snow over sea ice can become salty by upward brine migration or deposition of sea spray produced from leads or transported from the ice edge. Wind-driven resuspension and sublimation of the snow is hypothesized to leave salty aerosol particles behind. Our understanding of aerosol emissions from blowing snow is based mainly on modeling studies, and direct observations to validate this process are sparse. The year-long Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, with its integrated measurements and sampling of frequent winter storms, is well suited to enhance our understanding of coupled Arctic system processes. Here, we focus on the impact of blowing snow and high wind speed events on aerosol number concentrations, size distributions, optical properties and cloud condensation nuclei (CCN) concentrations. Total aerosol number concentrations were significantly enhanced during high-wind speed periods, also concurrent with increased scattering aerosol coefficients and CCN concentrations. We further present a process-based characterization of the blowing snow events during MOSAiC and identify the influence of environmental variables on aerosol emissions. Our observations provide new insights into wind-driven aerosol in the central Arctic and may help to validate modelling studies and inform parameterization improvement particularly with respect to aerosol direct and indirect radiative forcing.

How to cite: Bergner, N., Beck, I., Pratt, K., Mirrielees, J., Creamean, J., Frey, M., Heutte, B., Angot, H., Arnold, S., Uin, J., Springston, S., Matrosov, S., Laurila, T., Jokinen, T., Quéléver, L., Pernov, J., Gong, X., Wang, J., and Schmale, J.: Characterization of blowing snow aerosol events in the central Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14641, https://doi.org/10.5194/egusphere-egu23-14641, 2023.

The Arctic region is undergoing considerable changes and is warming at a rate three to four times as fast as the rest of the world. Aerosols, which can originate from natural or anthropogenic sources, both of which can be locally emitted or long-range transported, play a crucial role in the Arctic radiative balance by directly absorbing or scattering incoming solar radiation or indirectly by changing cloud properties and modulating cloud formation mechanisms. Here, we investigate the sources of anthropogenic and natural aerosols in the central Arctic Ocean, using data collected during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition with a high-resolution time-of-flight aerosol mass spectrometer. Using positive matrix factorization on the organic fraction of aerosols during spring and summertime (March – July), we identified six distinct chemical sources of organic aerosols (OA): a hydrocarbon-like factor, a Haze factor, two factors related to two extreme events of warm and moist air mass intrusions (WAMI) in mid-April, an Arctic oxygenated factor, and a Marine factor. We also describe the geographical origin of these factors, inferred from a potential source contribution function applied on 3-hourly back-trajectories. Together, these results suggest that OA from Eurasian anthropogenic origin (including the two extreme WAMI events in mid-April) dominate the central Arctic OA budget until at least the month of May, where episodic spikes in naturally-sourced marine OA, originating from the Fram Strait marginal ice-zone start to become important through June and July. We also highlight a hitherto unreported highly-oxygenated organic factor, whose temporal variability is closely related to that of particulate ammonium (maximum concentration in May) and whose geographical origin, in the Canadian archipelagoes, could indicate a co-emission mechanism of organic aerosols and ammonia from Arctic seabird colonies.

How to cite: Heutte, B., Dada, L., Angot, H., El Haddad, I., Chen, G., Dällenbach, K. R., B. Pernov, J., Beck, I., Quéléver, L., Laurila, T., Jokinen, T., and Schmale, J.: Aerosol source identification in the spring and summertime central Arctic Ocean using high-resolution mass spectrometry during MOSAiC., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14320, https://doi.org/10.5194/egusphere-egu23-14320, 2023.

Understanding the mercury cycle in the Arctic is important due to the harmful bioaccumulation of its toxic form, methylmercury, in wildlife and ultimately Arctic residents. Gaseous elemental mercury (Hg(0)) is relatively well-mixed across the northern hemisphere atmosphere due to its long atmospheric lifetime. Hg(0) can be oxidized, especially in the Arctic spring during halogen-driven depletion events. The resulting gaseous oxidized mercury (Hg(II)) is relatively quickly deposited onto snow, either directly or via condensing onto particles, forming particulate mercury (PHg). It is generally understood that a large fraction of the deposited Hg(II) and PHg is photoreduced to Hg(0) and re-emitted to the atmosphere. However, mercury remaining in the snowpack till melt can become bioavailable through entering the ocean.

There is a severe lack of Hg(II) and PHg observations in the central Arctic, particularly over sea ice, limiting our understanding of the mercury cycle in that region and inhibiting us from quantifying mercury budgets in all environmental compartments and particularly where it unfolds its harmful neurotoxic effects. Moreover, most of the observational efforts aiming at creating process understanding focused on spring during mercury depletion events or the snow melt period, leaving large knowledge gaps for fall and winter.

Here, we show atmospheric observations of PHg during MOSAiC, measured with an aerosol mass spectrometer in fall and spring over the central Arctic pack ice. In both seasons, PHg concentrations correlate strongly with wind speed and chloride, suggesting a mechanical (wind-driven) process behind atmospheric PHg related partly to blowing snow. In addition, there are significant differences between fall and spring observations (e.g. no atmospheric mercury depletion events in fall), suggesting that various processes are at play.

This wind-driven process has hitherto not been reported and is different from observations at land-based stations as well as previous measurements over sea ice that ascribed the formation of PHg to adsorption of Hg(II) onto pre-existing aerosols or diamond dust rather than aerosolization from the snow pack. We hypothesize, based on snow chemical analyzes and literature, that the elevated halide content in snow on sea ice creates complexes of PHg, which are much harder to photoreduce than Hg(II), leading to a larger PHg content in snow. These processes of forming PHg and wind-driven aerosolization have implications for the mercury content of snow and the distances over which PHg is re-deposited after atmospheric transport given that the lifetime of PHg is about one order of magnitude larger than that of Hg(II) in the atmosphere. 

How to cite: Schmale, J., Angot, H., Heutte, B., Bergner, N., Archer, S., Bariteau, L., Beck, I., Blomquist, B., Boyer, M., Frey, M., Helmig, D., Howard, D., Jacobi, H.-W., Jokinen, T., Laurila, T., Pernov, J., Posman, K., Pratt, K., and Quelever, L.: New source mechanism for airborne particulate mercury in the central Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4112, https://doi.org/10.5194/egusphere-egu23-4112, 2023.

Local air pollution sources in the Arctic lead to poor air quality in Arctic cities, particularly during the winter months. Fairbanks in central Alaska, is a prime example of such an Arctic city which suffers from acute wintertime pollution episodes. The topography of Fairbanks (situated in a basin), coupled with strong surface-based temperature inversions, contributes to stable meteorological conditions that hinder the dispersion of pollutants and surface temperatures reaching -40 °C. These harsh winter conditions result in enhanced domestic and power plant combustion emissions. Stable meteorological regimes are frequently interspersed with less stable episodes, resulting in vertical mixing between surface and elevated inversion layers. However, there are many uncertainties in our understanding about pollution sources and secondary aerosol formation under cold, dark winter conditions, where photochemistry is limited. These issues were addressed through the collection of comprehensive datasets on atmospheric composition and meteorology in Fairbanks, during the international ALPACA (Alaskan Layered Pollution and Chemical Analysis) field campaign in January and February 2022. Data were collected at the surface and vertical profiles were collected using a tethered balloon (EPFL Helikite).

Here, we examine the relative contributions and distributions of power plant emissions, emitted above the surface, and surface emission sources to pollution levels in the Fairbanks region. The FLEXPART-Weather Research and Forecasting (WRF) Lagrangian particle dispersion model, driven by meteorological fields from WRF-Environmental Protection Agency (EPA, Alaska) simulations is deployed. Firstly, model runs are used to evaluate the transport and dispersion of emissions from power plants at several altitudes in and around Fairbanks. Surface-based and elevated temperature inversions, characteristic of the winter boundary layer in Fairbanks, are considered in a parameterisation of power plant plume injection heights, and temporal variations in these emissions is also taken into account. Secondly, the extent to which power plant emissions are contributing to surface pollution is investigated using power plant (point source) and sector-based surface EPA emissions at 1.3km resolution at hourly time resolution during the 2022 campaign period. Model results are evaluated against available vertical profile and ground-based observations from ALPACA 2022. Power plant plumes are simulated aloft at several ALPACA measurement sites, as validated by vertical profile observations. The simulations indicate that power plant emissions are mixed down towards the surface in some cases. These results also provide insights into relative source contributions from each power plant in Fairbanks within the vertical profile of the lower atmospheric boundary layer, which could be used as tool for source apportionment studies.

How to cite: Brett, N., Law, K. S., Arnold, S. R., Barret, B., Dieudonné, E., Fochesatto, G. J., Gilliam, R., Onishi, T., Bekki, S., Schmale, J., Pohorsky, R., Baccarini, A., D'Anna, B., Temime-Roussel, B., Decesari, S., Pappaccogli, G., Donateo, A., Scoto, F., Cesler-Maloney, M., and Huff, D. and the UAF & EPA Continued: Investigating the relative contributions of power plant and surface emissions to air pollution in Fairbanks, Alaska during the wintertime ALPACA 2022 campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6258, https://doi.org/10.5194/egusphere-egu23-6258, 2023.

The ALPACA (Alaskan Layered Pollution and Chemical Analysis) field campaign (January-February 2022) aimed to collect new data to document Arctic wintertime air pollution. State of the art instrumentation was deployed in Fairbanks, Alaska to characterise inorganic/organic aerosols, vertical layering and mixing of aerosols and precursors, and meteorology at sites influenced by local anthropogenic emissions and background Arctic Haze.

Vertical profiles of the boundary layer composition were collected from an instrumented tethered ballon (helikite) deployed at the UAF-Farm site in West Fairbanks. The Helikite payload included instruments dedicated to the characterisation of particles (concentration, composition, size distribution) and to measurement of trace gases with dedicated analysers for O3, CO and CO2 and a MICROMEGAS instrument. MICROMEGAS is a light-weight package based on low-cost Alphasense electrochemical sensors for trace gases (CO/O3/NO/NO2). This instrument was also deployed on the ground close to reference-grade trace gas analysers at the CTC measurement site in downtown Fairbanks, and onboard a vehicle for 2D-mapping of pollution within and around Fairbanks.

Low-cost electrochemical sensors are sensitive to temperature and humidity and require careful calibration and validation. We first introduce the calibration method based on multi-linear regression with the collocated CTC reference measurements. The performance (biases, correlation coefficients, RMSDs) of the calibrated data are then evaluated against CTC observations not used for the calibration. Cases of vertical helikite profiles with polluted layers related to specific dynamical conditions (temperature inversions, wind regimes…) are investigated. Tracer-tracer relationships (CO, NO, NO2 versus CO2 ; NOx versus Ox) together with meteorological observations are used to examine air mass origins (domestic combustion, vehicles, power plants), as well as dilution and chemical transformation of the sampled pollution plumes.

How to cite: Barret, B., Brett, N., Pohorsky, R., Baccarini, A., Schmale, J., Pappacogli, G., Scoto, F., Decesari, S., Donateo, A., Fochesatto, G. J., Simpson, W., Cesler-Maloney, M., Mao, J., Dieudoné, E., Bekki, S., Arnold, S., d'Anna, B., Medina, P., Busetto, M., and Law, K. S.: Vertical profiles of pollutants in Fairbanks, Alaska during the ALPACA 2022 field campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5706, https://doi.org/10.5194/egusphere-egu23-5706, 2023.

The Alaskan Layered Pollution and Chemical Analysis (ALPACA) field campaign investigated the sources and processing of wintertime urban pollution in Fairbanks, Alaska in January and February 2022. Several sites located around the city of Fairbanks collected data to study the underexplored cold and dark wintertime dynamical, physical and chemical processes driving air pollution, both outdoors and indoors. We deployed a tethered balloon system at a farm field site near the University of Alaska (UAF) to specifically investigate the vertical layering of pollution and influence of different emission altitudes on surface pollution levels.

The study site is located in a suburban area, west of downtown Fairbanks. Observational efforts there focused mainly on surface exchanges and the vertical distribution of pollutants in relation to the boundary layer structure, specifically under stable (inversion) conditions. Instruments at the UAF-farm provided continuous ground measurements of aerosol physical, optical and chemical properties, trace gases (O₃, CO, N₂O) and meteorology. The newly designed Modular Multiplatform Air Compatible Measurement System (MoMuCAMS) was deployed with a tethered-balloon (helikite) to sample air up to 350 m above ground level, providing information on the vertical distribution and mixing processes of atmospheric pollutants. Instruments onboard MoMuCAMS provided information on aerosol characteristics (particle number concentration, size distribution, absorption coefficient and chemical composition), trace gases (CO₂, O₃, CO, N₂O, NO_x), and meteorology. MoMuCAMS performed 21 flights between January 26 and February 25, 2021, collecting roughly 140 individual profiles of varying altitude under different boundary layer conditions, intercepting pollution plumes at different heights and of different composition. Given the suburban location of  the study site, we measured the influence of polluted air from the city and “cleaner” air from more remote origins.

We will show how the vertical structure of the atmosphere and the frequently occurring temperature inversions affect transport and dispersion of pollution at different heights and how different meteorological conditions affect local air circulation and pollution at the study site. 

How to cite: Pohorsky, R., Baccarini, A., Barret, B., Brett, N., Pappaccogli, G., Scoto, F., Donateo, A., Busetto, M., Bekki, S., Law, K., Decesari, S., Arnold, S., Fochesatto, J., Simpson, W., and Schmale, J.: Wintertime vertical distribution of air pollution in suburban Fairbanks during the ALPACA 2022 field campaign, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11403, https://doi.org/10.5194/egusphere-egu23-11403, 2023.

The climate change in the Arctic region seriously accelerated compared to the entire globe. Black carbon (BC) aerosol particles, which are one of the SLCFs (short-lived climate forcers) emitted from incomplete combustion processes, absorb solar radiation and have a large impact on the climate. In addition, deposited BC on snow and ice surface decreases surface albedo and contributes to snow melting and Arctic warming. However, a large spread among model estimations for BC in the Arctic remains because of the lack of observation as a constraint and differences among emission inventories.

Alaska in northern America has a large boreal forest. Forest fires in Alaska represent an important BC source for the Arctic and surrounding regions, especially for interior Alaska during the summer season. However, observation of BC in interior Alaska is not sufficient. In this presentation, we introduce our five-year-long observations of BC and CO in interior Alaska and our findings on the relationship between the BC/∆CO ratio and the forest fire intensity.

BC and CO monitoring at Poker Flat Research Range (PFRR; 65.12 N, 147.43 W) started in April 2016. PFRR is located in the centre of Alaska and is surrounded by evergreen needle-leave forests. Forest fires occur occasionally in the summer season and strongly affect BC and CO concentrations in PFRR. Median BC mass concentration through the observation period was 15.2 ng/m³ and did not show a clear seasonal variation. However, sporadically significant increases in BC were observed during summer. Comparing BC concentrations observed at PFRR with those at Denali (63.72 N, 149.0 W), Trapper creek (62.32 W, 153.15 W), and Barrow (71.32 N, 156.61 W), we found a weak correlation only for Denali (r² =0.3), indicating different air mass transport patterns as strong separated by high mountains particularly large differences between the interior and coastal regions in Alaska were noticed. On the other hand, the CO mixing ratio showed clear seasonal variation patterns, i.e. high in spring and low in summer. The median value of the CO mixing ratio was 124.7 ppb and significant increases were observed in the same period as BC, indicating the influences from the common emission sources. The median BC/∆CO ratio was 1.6 ng/m³/ppb and did not show clear seasonal variations. Furthermore, we quantitatively estimated the source contributions of BC using FLEXPART-WRF based on GFEDv4.1 inventory. As a result, FLEXPART-WRF represented high BC concentration periods with a relatively good correlation (r² =0.54) but underestimated approximately 17 %. Source estimation by FLEXPART-WRF indicated a strong contribution of forest fires from surrounding areas during the high BC concentration periods. We compared BC/∆CO and Fire Radiative Power observed in Alaska by MODIS. As a result, we found a positive relationship between these two values, indicating the increase of BC/∆CO with forest fire intensity. Our result suggests that the dependency of the BC and CO emission factors on the combustion intensity of forest fires should be taken into account to elaborate emission estimations from boreal forest fires.

How to cite: Kinase, T., Takigawa, M., Taketani, F., Kobayashi, H., Zhu, C., Kim, Y., and Kanaya, Y.: The long-term observation of black carbon and CO concentration in Alaska: Effect of forest fire emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11181, https://doi.org/10.5194/egusphere-egu23-11181, 2023.

A quantitative understanding of climate change in the polar regions being more extreme than at lower latitudes requires monitoring and modelling of key climate variables in these regions. Climate models disagree with observational datasets on the magnitude of the rate of Arctic amplification, and the representation of the chemistry and microphysics of aerosol particles in models is one of the contributing factors to the uncertainty in predicting polar climate. Aerosols represents one of the key model uncertainties through its impact on the surface energy balance via the scattering and absorption of solar radiation, and by its ability to influence cloud microphysics. Sea salt aerosol originating from the sublimation of blowing snow is a newly discovered source of aerosol particles above sea ice during winter and spring, and the hypothesised formation mechanism has been validated recently in the Antarctic. However, the lack of observations over a wide range of sea ice conditions including sub-micron sized particles has been a barrier towards accurately quantifying the mechanism of formation of SSA and the resulting SSA mass flux. Moreover, current blowing snow model parameterisations do not consider the spatial and temporal variability of sea ice and atmospheric state, which has a strong impact on the strength of the particle source from blowing snow across individual storms. In this study, we use observations from the MOSAIC (Multidisciplinary drifting Observatory for the Study of Arctic Climate) expedition (Oct 2019 to Sept 2020) and N-ICE2015 (Feb-June 2015) in the Arctic, and Weddell Sea measurements (June-October 2013) in the Antarctic to better constrain the blowing snow sea salt flux. We consider snow particle size distribution and snow salinity, which are both sensitive model parameters that govern the sea salt aerosol flux over sea ice. A gamma distribution fit is used to characterise the snow particle size distribution as a function of the 10-meter wind speed (ranging from the threshold wind speed (~5ms^-1) to 15ms^-1). Using the observations, we were able to better constrain the shape parameter of the gamma distribution, alpha, when compared to past studies.  We discuss the relationship between snow salinity and snow depth, to capture the influence of the changing sea ice and snowfall on blowing snow aerosol source. We implement these parametrisations derived from point measurements into a chemistry transport model (p-TOMCAT) to better capture the spatially and temporally variable blowing snow source across polar regions, which helps to accurately simulate the aerosol number and mass concentration, and sodium concentration in polar regions.

How to cite: Ranjithkumar, A., Duncan, E., Yang, X., Partridge, D., and Frey, M.: Modelling sea salt aerosol flux from blowing snow over a changing sea ice environment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6988, https://doi.org/10.5194/egusphere-egu23-6988, 2023.

Clouds have one of the most profound effects on Earth’s climate, yet they are still responsible for some of the biggest uncertainties in climate models. Cloud formation, radiative properties, thickness and lifetime are tightly interlinked with the presence of atmospheric particles (aerosols) and the formation of ice. Biological aerosols (bioaerosols) such as ice-nucleation proteins (INpro) produced by microorganisms are most efficient catalysts in the formation of ice and can trigger heterogenous freezing between -1°C and -15°C. Several studies have demonstrated that Arctic environments are a source of airborne INpro. Sea spray is one of the major sources of aerosols, which aside of the sea salt contain large amounts of organic material. These are ejected into the atmosphere through the process of wave breaking and bubble bursting of small bubbles, which eject drops from the sea surface microlayer (SML) to the atmosphere. Here, we present results derived from droplet freezing assays and amplicon sequencing combined with quantitative PCR, targeting the 16S rRNA gene from sea and aerosol samples collected along a transect from sub- to high Arctic Greenland (Baffin Bay). We demonstrate a positive correlation between INpro concentration and higher latitudes in sea bulk water (SBW) and SML. Additionally, we try to link specific taxonomic groups from the microbial communities to INpro production. Last, we aim to investigate if partitioning of specific taxonomic groups can be observed from SBW to SML and from SML to the atmosphere. Finally, we performed laboratorial sea-spray experiments simulating turbulent sea conditions. This study has the potential to help closing the current knowledge gap in understanding the partitioning of microorganisms from the sea to the atmosphere and unravel which microbes are the major contributors to atmospheric INpro and hence cloud formation.

How to cite: Castenschiold, C. D., Mignani, C., Christiansen, S., Alsved, M., Tesson, S., Löndahl, J., Bilde, M., Finster, K., and Šantl-Temkiv, T.: Linking Sea Spray, Bioaerosols and Ice-Nucleation Proteins in Arctic Marine Environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8027, https://doi.org/10.5194/egusphere-egu23-8027, 2023.

As a result of Arctic air temperatures rising at four times the global rate, the cryosphere is rapidly thawing, releasing greenhouse gas reservoirs and metabolically active greenhouse gas-producing microorganisms. In addition, thawing cryosphere elements, such as permafrost (i.e., ground that is frozen for at least two consecutive years) and ice wedges (i.e., frozen water accumulated in ground cracks due to expansion and contraction of permafrost), can be introduced into water systems by different mechanisms. These mechanisms can include thermokarst lake formation (i.e., ice-rich permafrost areas that thaw and create surface depressions that are filled with thawed ice) and the increasingly common permafrost landslides.

One of the hypotheses proposed in the multidisciplinary ARCSPIN (ARCtic Study of Permafrost Ice Nucleation) project is that microorganisms from thawed permafrost and ice wedges are discharged into water bodies in the Arctic region, and are ultimately released to the atmosphere through mechanisms such as thermokarst lake greenhouse gas bubble-bursting, and bubble-bursting due to higher wind-induced wave action on lakes, lagoons, and the open ocean. Additionally, these airborne biological particles can be a potential source of ice nucleating particles (INPs) active at warm temperatures (≥ -10^oC), potentially altering cloud properties in Arctic regions. Arctic clouds have strong effects on regional and global energy budgets, with cloud phase (i.e., liquid or ice) being a key modulator of their interactions with radiation. Arctic mixed-phase clouds (AMPCs) are prevalent and are key in the ocean-ice-atmosphere system affected by the delicate energy balance over frozen surfaces. Ice formation in AMPCs is highly sensitive to the quantity and effects of aerosols serving as INPs.

Here, we present results from a broad range of environmental samples collected during the ARCSPIN campaign in the Summer of 2021 in Northern Alaska (Utqiaġvik region), including air, water (i.e., sea, river, lagoon, and thermokarst lake), terrestrial (i.e., active layer, permafrost, ice wedge, and sediment), and vegetation samples. These samples were processed for 16S rRNA gene sequencing to identify and track microorganisms, showing for the first time how bioaerosols in Northern Alaska are influenced by terrestrial and water sources of the region. We additionally include results from published microbiome studies to perform source tracking analysis (Sourcetracker2), showing the potential long-range influence of ocean microorganisms, in particular, as bioaerosol sources in the Arctic. The obtained microbiome results are linked to meteorological conditions and air back trajectories calculated with NOAA’s HYSPLIT model.

Data generated from the ARCSPIN study in combination with the Community Earth System Model (CESM) will be used for parameterization development and to investigate potential impacts of this unique INP source on Arctic clouds, helping to understand sources and impacts of bioaerosols in the Arctic. 

How to cite: Nieto-Caballero, M., Hill, T. C. J., Barry, K. R., McCluskey, C. S., Douglas, T. A., DeMott, P. J., Kreidenweis, S. M., and Creamean, J. M.: Evidence of Ocean and Permafrost as Sources of Bioaerosols in the Alaskan Arctic Boundary Layer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10564, https://doi.org/10.5194/egusphere-egu23-10564, 2023.