Antarctic Peninsula warming and precipitation phase transition during atmospheric river events

Polar amplification has been pronounced in the Arctic with near-surface air temperatures increasing at more than twice the global warming rate during the last several decades. At the same time, over Antarctica temperature trends have exhibited a large regional variability. In particular, the Antarctic Peninsula (AP) stands out as having a warming rate much higher than the rest of the Antarctic ice sheet and other land areas in the Southern Hemisphere (SH). Future projections indicate that warming and ice loss will intensify in both polar regions with important impacts globally. In addition to the warming amplification, there has been also an enhancement of the polar water cycle with increases in poleward moisture transport and precipitation in both polar regions. An important process linking warming and precipitation enhancement is a shift towards more frequent rainfall compared to snowfall. Future projections show that the rain fraction will significantly increase in coastal Antarctica, especially in the AP. Atmospheric rivers (ARs), long corridors of intense moisture transport from subtropical and mid-latitude regions poleward, are known for their prominent role in both heat and moisture transport with impacts ranging from intense precipitation to temperature records and major melt events in Antarctica. Limited observations have hampered process understanding and correct representation of these extreme events in models. This presentation will give an overview of the enhanced observations targeting ARs in the AP (including surface meteorology, radiosonde, cloud and precipitation remote sensing, and radiative fluxes) as part of the Year of Polar Prediction (YOPP)-SH international collaborative effort. In-depth analysis of transport of heat and moisture, atmospheric vertical structure, cloud properties and precipitation phase transition from snowfall to rainfall during selected AR cases will be presented and compared with ERA5 reanalysis and high-resolution Polar-WRF model simulations. We will highlight three different local regimes around the AP: large-scale precipitation over the Southern Ocean north of the AP, orographic enhancement of precipitation in the western AP and the role of foehn, cloud/precipitation clearing and temperature increase in the northeastern AP.

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Cloud and precipitation microphysics evaluated with ERA-5 and Polar WRF over the northern Antarctic Peninsula

10.5194/egusphere-egu21-13058 ◽

2021 ◽

Author(s):

Anastasiia Chyhareva ◽

Svitlana Krakovska ◽

Irina Gorodetskaya ◽

Denis Pishniak ◽

Jonathan Wille ◽

...

Keyword(s):

Phase Transition ◽

Phase Transitions ◽

Antarctic Peninsula ◽

Large Scale ◽

Lower Troposphere ◽

Cloud Microphysics ◽

Orographic Enhancement ◽

Precipitation Type ◽

The Antarctic ◽

Precipitation Phase

Synoptic-scale atmospheric circulation that transports moisture from lower latitudes highly influences the Antarctic coastal climate, warming and moistening the lower troposphere and causing both precipitation and temperature increases. During recent decades, it has been shown that the highest warming rate over Antarctica is observed over the Antarctic Peninsula region. Heat and moisture transport from lower latitudes, particularly associated with atmospheric rivers (ARs), could play a crucial role in this warming. Among the most complex and understudied processes relate to microphysical properties of clouds and precipitation and understanding phase transitions during intense precipitation events associated with ARs and their representation in polar weather and climate models.The goal of this research is&#160; to investigate the temporal and spatial evolution of precipitation, including its intensity and phase transition and associated cloud properties during AR events over the Antarctic Peninsula in austral summer. We focus on two sites representing different regional and micro-climates around the Antarctic Peninsula - Escudero station, situated on King George Island at the northern tip of the peninsula, and Vernadsky station &#8211; located on Galindez Island at the western (upwind) side closer to the central part of the peninsula. Although both stations have typical maritime climate, the Vernadsky site is more affected by orographic enhancement of precipitation and cold air advection from the continent.We use ground-based observations of meteorology, conducted during The Year of Polar Prediction Special Observing Period (YOPP-SOP) in summer 2018/2019 over the Antarctic Peninsula region and compare against ERA-5 and AMPS Polar WRF. After evaluating ERA-5 reanalysis , it is used for large-scale analysis of clouds and precipitation type. The timings of precipitation phase transitions in ERA-5 and Polar WRF are determined for the grid cells where the two stations are located. Sensitivity to microphysics parameterization in Polar WRF is tested with several double moment cloud microphysics parameterization schemes.We analyze two cases with observed precipitation phase transitions, during the first week of December 2018. Higher precipitation amounts were observed over Vernadsky station during the first event and over Escudero during the second event. Total precipitation during the whole week is higher for Vernadsky station compared to Escudero station, related to the AR landfall position and strength, as well as the orographic enhancement at the upwind side of the Antarctic Peninsula ridge. This is confirmed by assessment of ERA-5 data. Comparison with the YOPP-SOP observations at Escudero shows that ERA-5 represents major precipitation type accurately and thus can be used for further study of precipitation microphysics. For Vernadsky station, ERA-5 showed a few cases of phase transition from snow to wet snow, associated with ARs events according to ERA-5 data; unfortunatly observations for comparison were lacking. Compared to ERA-5, Polar WRF shows a finer structure of precipitation fields disturbed by the mountains. We intend to test different parameterizations of cloud microphysics in Polar WRF with fine resolution against the complex of measurements at Vernadsky station in order to find the optimal configuration in the region to use during the upcoming winter YOPP in the Southern Hemisphere.

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Precipitation phase transition in austral summer over the Antarctic Peninsula

Ukrainian Antarctic Journal ◽

10.33275/1727-7485.1.2021.664 ◽

2021 ◽

pp. 32-46

Author(s):

A. Chyhareva ◽

◽

I. Gorodetskaya ◽

S. Krakovska ◽

D. Pishniak ◽

...

Keyword(s):

Phase Transition ◽

Phase Transitions ◽

Air Temperature ◽

Antarctic Peninsula ◽

Precipitation Amount ◽

Austral Summer ◽

Near Surface ◽

Atmospheric River ◽

Synoptic Conditions ◽

Precipitation Phase

Investigating precipitation phase transitions is crucial for improving our understanding of precipitation formation processes and impacts, particularly in Polar Regions. This study uses observational data and numerical modelling to investigate precipitation phase transitions in the western and northern Antarctic Peninsula (AP) during austral summer. The analysis is based on the ERA5 reanalysis product, dynamically downscaled using the Polar-WRF (Polar Weather Research and Forecasting) model, evaluated using regular meteorological observations and additional measurements made during the Year of Polar Prediction special observing period. We analyse three cases of extra-tropical cyclones bringing precipitation with phase transitions, observed at the Chilean station Professor Julio Escudero (King George Island, north of the AP) and the Ukrainian Antarctic Akademik Vernadsky station (western side of the AP) during the first week of December 2018. We use observed and modelled near-surface air temperature and pressure, precipitation amount and type, and vertical temperature profiles. Our results show that precipitation type (snow or rain) is well-represented by ERA5 and Polar-WRF, but both overestimate the total amount of precipitation. The ERA5 daily variability and vertical air temperature profile are close to the observed, while Polar-WRF underestimates temperature in the lower troposphere. However, ERA5 underestimates the temperature inversion, which is present during the atmospheric river event, while Polar-WRF represents that inversion well. The average weekly temperature, simulated with Polar-WRF, is lower compared to ERA5. The Polar-WRF fraction of snow in the total precipitation amount is higher than for ERA5; nevertheless, Polar-WRF represents the precipitation phase transition better than ERA5 during the event, associated with an atmospheric river. These case studies demonstrated a relationship between specific synoptic conditions and precipitation phase transitions at the AP, evaluated the ability of the state-of-the-art reanalysis and regional climate model to represent these events, and demonstrated the added value of combined analysis of observations from the western and northern AP, particularly for characterizing precipitation during synoptic events affecting the entire AP.

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Polar Amplification and Ice Free Conditions under 1.5, 2 and 3 °C of Global Warming as Simulated by CMIP5 and CMIP6 Models

Atmosphere ◽

10.3390/atmos12111494 ◽

2021 ◽

Vol 12 (11) ◽

pp. 1494

Author(s):

Fernanda Casagrande ◽

Francisco A. B. Neto ◽

Ronald B. de Souza ◽

Paulo Nobre

Keyword(s):

Global Warming ◽

Temperature Response ◽

Surface Air Temperature ◽

The Arctic ◽

Polar Regions ◽

High Latitudes ◽

Near Surface ◽

Polar Amplification ◽

Air Temperatures ◽

Average Rise

One of the most visible signs of global warming is the fast change in the polar regions. The increase in Arctic temperatures, for instance, is almost twice as large as the global average in recent decades. This phenomenon is known as the Arctic Amplification and reflects several mutually supporting processes. An equivalent albeit less studied phenomenon occurs in Antarctica. Here, we used numerical climate simulations obtained from CMIP5 and CMIP6 to investigate the effects of +1.5, 2 and 3 °C warming thresholds for sea ice changes and polar amplification. Our results show robust patterns of near-surface air-temperature response to global warming at high latitudes. The year in which the average air temperatures brought from CMIP5 and CMIP6 models rises by 1.5 °C is 2024. An average rise of 2 °C (3 °C) global warming occurs in 2042 (2063). The equivalent warming at northern (southern) high latitudes under scenarios of 1.5 °C global warming is about 3 °C (1.8 °C). In scenarios of 3 °C global warming, the equivalent warming in the Arctic (Antarctica) is close to 7 °C (3.5 °C). Ice-free conditions are found in all warming thresholds for both the Arctic and Antarctica, especially from the year 2030 onwards.

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The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

Climate of the Past Discussions ◽

10.5194/cpd-8-5293-2012 ◽

2012 ◽

Vol 8 (5) ◽

pp. 5293-5340 ◽

Cited By ~ 2

Author(s):

I. Nikolova ◽

Q. Yin ◽

A. Berger ◽

U. K. Singh ◽

M. P. Karami

Keyword(s):

Large Scale ◽

Climate Models ◽

Hydrological Cycle ◽

The Arctic ◽

Boreal Summer ◽

Interglacial Period ◽

Last Interglacial ◽

Proxy Data ◽

Vegetation Feedback ◽

Depth Analysis

Abstract. This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, LOVECLIM and CCSM3. The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated Pre-Industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the northern (southern) hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The arctic is warmer than PI through the whole year, resulting from its much higher summer insolation and its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice. In the tropical Pacific, the change in the SST annual cycle is suggested to be related to a minor shift towards an El Nino, slightly stronger for MIS-5 than for PI. Intensified African monsoon and vegetation feedback are responsible for the cooling during summer in North Africa and Arabian Peninsula. Over India precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara. A mix of forest and grassland occupies continents and expand deep in the high northern latitudes. Desert areas reduce significantly in Northern Hemisphere, but increase in North Australia. The simulated large-scale climate change during the last interglacial compares reasonably well with proxy data, giving credit to both models and reconstructions. However, discrepancies exist at some regional scales between the two models, indicating the necessity of more in depth analysis of the models and comparisons with proxy data.

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On the Use of Electromagnetics for Earth Imaging of the Polar Regions

Surveys in Geophysics ◽

10.1007/s10712-019-09570-8 ◽

2019 ◽

Vol 41 (1) ◽

pp. 5-45 ◽

Cited By ~ 4

Author(s):

Graham J. Hill

Keyword(s):

Electric Fields ◽

Measurement Errors ◽

Large Scale ◽

Broad Band ◽

High Energy ◽

Polar Regions ◽

Occupation Times ◽

Magnetotelluric Data ◽

Near Surface ◽

Snow And Ice

Abstract The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of ‘blizstatic’, localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s−1, the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions.

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Variability of Daily Maximum Wind Speed across China, 1975–2016: An Examination of Likely Causes

Journal of Climate ◽

10.1175/jcli-d-19-0603.1 ◽

2020 ◽

Vol 33 (7) ◽

pp. 2793-2816 ◽

Cited By ~ 1

Author(s):

Gangfeng Zhang ◽

Cesar Azorin-Molina ◽

Deliang Chen ◽

Jose A. Guijarro ◽

Feng Kong ◽

...

Keyword(s):

Wind Speed ◽

Large Scale ◽

Southern Oscillation ◽

Vertical Wind Shear ◽

Maximum Wind Speed ◽

The Arctic ◽

Risk Governance ◽

Daily Maximum ◽

Near Surface ◽

Maximum Wind

AbstractAssessing change in daily maximum wind speed and its likely causes is crucial for many applications such as wind power generation and wind disaster risk governance. Multidecadal variability of observed near-surface daily maximum wind speed (DMWS) from 778 stations over China is analyzed for 1975–2016. A robust homogenization protocol using the R package Climatol was applied to the DMWS observations. The homogenized dataset displayed a significant (p < 0.05) declining trend of −0.038 m s−1 decade−1 for all China annually, with decreases in winter (−0.355 m s−1 decade−1, p < 0.05) and autumn (−0.108 m s−1 decade−1; p < 0.05) and increases in summer (+0.272 m s−1 decade−1, p < 0.05) along with a weak recovery in spring (+0.032 m s−1 decade−1; p > 0.10); that is, DMWS declined during the cold semester (October–March) and increased during the warm semester (April–September). Correlation analysis of the Arctic Oscillation, the Southern Oscillation, and the west Pacific modes exhibited significant correlation with DMWS variability, unveiling their complementarity in modulating DMWS. Further, we explored potential physical processes relating to the atmospheric circulation changes and their impacts on DMWS and found that 1) overall weakened horizontal airflow [large-scale mean horizontal pressure gradient (from −0.24 to +0.02 hPa decade−1) and geostrophic wind speed (from −0.6 to +0.6 m s−1 decade−1)], 2) widely decreased atmospheric vertical momentum transport [atmospheric stratification thermal instability (from −3 to +1.5 decade−1) and vertical wind shear (from −0.4 to +0.2 m s−1 decade−1)], and 3) decreased extratropical cyclones frequency (from −0.3 to 0 month decade−1) are likely causes of DMWS change.

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Multiphysics dissipative waves as a multiscale precursor phenomenon to geodynamic instabilities

10.5194/egusphere-egu2020-20764 ◽

2020 ◽

Author(s):

Klaus Regenauer-Lieb ◽

Christoph Schrank ◽

Oliver Gaede ◽

Benjamin Marks ◽

Manman Hu ◽

...

Keyword(s):

Phase Transition ◽

Critical Point ◽

Large Scale ◽

Solid Mechanics ◽

Numerical Models ◽

Internal Variables ◽

Mechanical Pressure ◽

Compaction Bands ◽

First Order Theory ◽

Depth Analysis

We present the hypothesis that material instabilities based on multiscale and multiphysics dissipative waves hold the key for understanding the universality of physical phenomena that can be observed over many orders of scale. The approach is based on an extended version of the thermodynamic theory with internal variables (see related abstract by Antoine Jacquey et al. for session EMRP1.4 entitled: &#8220;Multiphysics of transient deformation processes leading to macroscopic instabilities in geomaterials&#8221;). The internal variables can, in many cases, shown to be related to order parameters in Lev Landau&#8217;s phase-transition theory. The extension presented in this contribution consists of replacing the jump condition for the symmetry-breaking order parameter at the critical point (e.g., density difference at the liquid-gas transition) through considering a second-order phase transition, where the internal variables change continuously from the critical point due to the propagation of material-damaging dissipative waves. This extension to the first-order theory allows assessing the dynamics of coupling the rates of chemical reactions, failure and fluid-flow as well as thermo-mechanical instabilities of materials. The approach gives physics-based insights into the processes that are commonly described by empirical relationships. Here, we present a first analytical model extended by numerical analyses and laboratory and field observations that show the existence of these precursor phenomena to large-scale instabilities. In the event that the propagating waves lead to a large-scale instability, the dissipation processes are predicted to leave tell-tale multi-scale structures in their wake, which can be used to decipher the dynamic processes underpinning the event.First analyses from a laboratory analogue experiment are presented, illustrating the slow speed of the waves and their peculiar dispersion relationships and reflection from boundaries. An idealized 1-D (oedometric) compaction experiment of a highly porous (45% porosity) carbonate rock investigates the emergence of localized compaction bands proposed to be formed by long-term resonant collision of the transient dissipation waves. Complementary numerical models of the phenomenon allow in-depth analysis of the dynamics and illustrate the physics of the formation of dissipative waves.For field application, we propose that a multiscale analysis - from the grain- over the outcrop- up to the lithospheric scale - can be used to extract quantitative information directly from natural deformation bands, fractures, and fault zones on, for example, the state of stress, the size of the underlying earthquakes, the flow and mechanical properties of the host rock, and the spatiotemporal evolution of fluid and mechanical pressure associated with faulting. The experimental investigation of the fundamental instability has broader applications in the fields of industrial processing of multiphase materials, civil, mechanical, and reservoir engineering and solid mechanics.

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Validation of the Aeolus Level-2B wind product over Northern Canada and the Arctic

10.5194/amt-2021-247 ◽

2021 ◽

Author(s):

Chih-Chun Chou ◽

Paul J. Kushner ◽

Stéphane Laroche ◽

Zen Mariani ◽

Peter Rodriguez ◽

...

Keyword(s):

Early Phase ◽

Weather Prediction ◽

European Space Agency ◽

Arctic Region ◽

The Arctic ◽

Horizontal Line ◽

Polar Regions ◽

Near Surface ◽

Northern Canada ◽

Space Agency

Abstract. In August 2018, the European Space Agency launched the Aeolus satellite, whose Atmospheric LAser Doppler INstrument (ALADIN) is the first spaceborne Doppler wind lidar to regularly measure vertical profiles of horizontal line-of-sight (HLOS) winds with global sampling. This mission is intended to assess improvement to numerical weather prediction provided by wind observations in regions poorly constrained by atmospheric mass, such as the tropics, but also, potentially, in polar regions such as the Arctic where direct wind observations are especially sparse. There remain gaps in the evaluation of the Aeolus products over the Arctic region, which is the focus of this contribution. Here, an assessment of the Aeolus Level-2B wind product is carried out from measurement stations in Canada’s north, to the pan-Arctic, with Aeolus data being compared to Ka-band radar measurements at Iqaluit, Nunavut; to radiosonde measurements over Northern Canada; to Environment and Climate Change Canada (ECCC)’s short-range forecast; and to the reanalysis product, ERA5, from the European Centre for Medium-Range Weather Forecasts (ECMWF). Periods covered include the early phase during the first laser nominal flight model (FM-A; 2018-09 to 2018-10), the early phase during the second flight laser (FM-B; 2019-08 to 2019-09), and the mid-FM-B periods (2019-12 to 2020-01). The adjusted r-square between Aeolus and other local datasets are around 0.9, except for somewhat lower values in comparison with the ground-based radar, presumably due to limited sampling. This consistency degraded by about 10 % for the Rayleigh winds in the summer, presumably due to scattering from the solar background. Over the pan-Arctic, consistency, with correlation greater than 0.8, is found in the Mie channel from the planetary boundary layer to the lower stratosphere (near surface to 16 km a.g.l.) and in the Rayleigh channel from the troposphere to the stratosphere (2 km to 25 km a.g.l.). Zonal and meridional projections of the HLOS winds are separated to account for the systematic changes in HLOS winds arising from sampling wind components from different viewing orientations in the ascending and descending phases. In all cases, Aeolus standard deviations are found to be 20 % greater than those from ECCC-B and ERA5. We found that L2B estimated error product for Aeolus is coherent with the differences between Aeolus and the other datasets, and can be used as a guide for expected consistency. Thus, our work confirms the quality of the Aeolus dataset over the Arctic and shows that the new Aeolus L2B wind product provides a valuable addition to current wind products in regions such as the Arctic Ocean region where few direct wind observations have been available to date.

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Decadal changes of wintertime poleward heat and moisture transport associated with the amplified Arctic warming

10.21203/rs.3.rs-264481/v1 ◽

2021 ◽

Author(s):

Xiaozhuo Sang ◽

Xiu-Qun Yang ◽

Lingfeng Tao ◽

Jiabei Fang ◽

Xuguang Sun

Keyword(s):

Heat Transport ◽

Moisture Transport ◽

Stationary Wave ◽

The Arctic ◽

Stationary Waves ◽

High Latitudes ◽

Arctic Warming ◽

Poleward Heat Transport ◽

Heat And Moisture ◽

Moisture Transports

Abstract The Arctic warming, especially during winter, has been almost twice as large as the global average since the late 1990s, which is known as the Arctic amplification. Yet linkage between the amplified Arctic warming and the midlatitude change is still under debate. This study examines the decadal changes of wintertime poleward heat and moisture transports between two 18-yr epochs (1999–2016 and 1981–1998) with five atmospheric reanalyses. It is found that the wintertime Arctic warming induces an amplification of the high latitude stationary wave component of zonal wavenumber one but a weakening of the wavenumber two. These stationary wave changes enhance poleward heat and moisture transports, which are conducive to further Arctic warming and moistening, acting as a positive feedback onto the Arctic warming. Meanwhile, the Arctic warming reduces atmospheric baroclinicity and thus weakens synoptic eddy activities in the high latitudes. The decreased transient eddy activities reduce poleward heat and moisture transports, which decrease the Arctic temperature and moisture, acting as a negative feedback onto the Arctic warming. The total poleward heat transport contributes little to the Arctic warming, since the increased poleward heat transport by stationary waves is nearly canceled by the decreased transport by transient eddies. However, the total poleward moisture transport increases over most areas of the high latitudes that is dominated by the increased transport by stationary waves, which provides a significant net positive feedback onto the Arctic warming and moistening. Such a poleward moisture transport feedback may be particularly crucial to the amplified Arctic warming during winter when the ice-albedo feedback vanishes.

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Moisture origin, transport pathways, and driving processes of intense wintertime moisture transport into the Arctic

10.5194/wcd-2021-57 ◽

2021 ◽

Author(s):

Lukas Papritz ◽

David Hauswirth ◽

Katharina Hartmuth

Keyword(s):

North Atlantic ◽

Moisture Transport ◽

Large Scale ◽

The Arctic ◽

Polar Cap ◽

Transport Pathways ◽

Moisture Sources ◽

The North ◽

Total Transport ◽

Air Streams

Abstract. Poleward moisture transport occurs in episodic, high-amplitude events with strong impacts on the Arctic and its climate system components such as sea ice. This study focuses on the origin of such events and examines the moisture sources, moisture transport pathways, and their linkage to the large-scale circulation. For that purpose, 597 events of intense zonal mean poleward moisture transport at 70° N (exceeding the 90th anomaly percentile) are identified and kinematic backward trajectories from 70° N are computed to pinpoint the moisture sources and characterize the air-streams accomplishing the transport. The bulk of the moisture transported into the polar cap during these events originates in the eastern North Atlantic with an uptake maximum poleward of 50° N. This asymmetry between ocean basins is a direct consequence of the fact that most of the moisture transport into the polar cap occurs in this sector. As a result of the fairly high-latitude origin of the moisture, the median time moisture spends in the atmosphere prior to reaching 70° N amounts to about 2.5 days. Trajectories further reveal an inverse relationship between moisture uptake latitude and the level at which moisture is injected into the polar cap, consistent with ascent of poleward flowing air in a baroclinic atmosphere. Focusing on events for which 75 % of the zonal mean moisture transport takes place in the North Atlantic east of Greenland (424 events) reveals that lower tropospheric moisture transport results predominantly from two types of air-streams: (i) cold, polar air advected from the Canadian Arctic over the North Atlantic and around Greenland, whereby the air is warmed and moistened by surface fluxes, and (ii) air subsiding from the mid-troposphere into the boundary layer. Both air-streams contribute about 36 % each to the total transport. The former dominates the moisture transport during events associated with an anomalously high frequency of cyclones east of Greenland (218 events), whereas the latter is more important in the presence of atmospheric blocking over Scandinavia and the Ural (145 events). A substantial portion of the moisture sources associated with both types of air-streams are located between Iceland, the British Isles, and Norway. Long-range moisture transport, accounting for 17 % of the total transport, is the dominant type of air-stream during events with weak forcing by baroclinic weather systems (64 events). Finally, mid-tropospheric moisture transport is invariably associated with (diabatically) ascending air and moisture origin in the central and western North Atlantic, including the Gulf Stream front, accounting for roughly 10 % of the total transport. In summary, our study reveals that moisture injections into the polar atmosphere are not primarily caused by the poleward transport of warm and humid air from low latitudes – a conclusion that applies in particular to cases where the transport is driven by baroclinic weather systems such as extratropical cyclones. Instead, it results from a combination of air-streams with pre-dominantly high-latitude or high-altitude origin and their interplay with large-scale weather systems (e.g., cyclones, blocks).

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