Displays

The Arctic has warmed more than twice as fast as the global average since the late 20^th century, a phenomenon known as Arctic amplification (AA).  Recently, there have been significant advances in understanding the physical contributions to AA and progress has been made in understanding the mechanisms linking AA to mid-latitude weather variability.  Observational studies overwhelmingly support that AA is contributing to winter continental cooling.  While Arctic warming is strongest at the surface, it extends throughout the mid-troposphere. In addition, the sea ice loss and associated warming is not uniform across the Arctic, but rather regionally focused including in the Barents-Kara Seas, a key region for disrupting the polar vortex.  The probability of severe winter weather increases across the Northern Hemisphere continents following polar vortex disruptions.  While some model experiments support the observational evidence, the majority of modeling results show little connection between AA and severe mid-latitude weather. Rather the excess warming generated in the Arctic due to sea ice loss and other mechanisms is not redistributed vertically in model simulations, but rather horizontally suggesting the export of excess heating from the Arctic to lower latitudes.  Divergent conclusions between model and observational studies, and even intra-model studies, continue to obfuscate a clear understanding of how AA is influencing mid-latitude weather.

How to cite: Cohen, J. and Zhang, X. and the Arctic mid-latitude linkages review paper: Divergent consensuses on Arctic amplification influence on mid-latitude severe winter weather, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2748, https://doi.org/10.5194/egusphere-egu2020-2748, 2020

The rapid warming of the Arctic, perhaps the most striking evidence of climate change, is believed to arise from increases in atmospheric concentration of greenhouse gases since the industrial revolution.  While the dominant role of carbon dioxide is undisputed, another important set of anthropogenic greenhouse gases was also being emitted over the second half of the twentieth century: ozone-depleting substances (ODS).  These compounds, in addition to causing the ozone hole over Antarctica, have long been recognized as powerful greenhouse gases.  However, their contribution to Arctic warming has not been quantified to date.  We do so here by analyzing ensembles of climate model integrations specifically designed for this purpose, spanning the period 1955-2005 when atmospheric concentrations of ODS increased rapidly.  We show that when ODS are kept fixed the forced Arctic surface warming, and the forced sea ice loss, are only half as large as when ODS are allowed to increase.  We also demonstrate that the large Arctic impact of ODS occurs primarily via direct radiative warming, not via ozone depletion.  Our findings reveal a substantial, and hitherto unrecognized, contribution of ODS to recent Arctic warming and highlight the importance of the Montreal Protocol as a major climate change mitigation treaty.

How to cite: Polvani, L., Previdi, M., England, M., Chiodo, G., and Smith, K.: Substantial twentieth-century Arctic warming caused by ozone-depleting substances, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3961, https://doi.org/10.5194/egusphere-egu2020-3961, 2020

Arctic sea ice melting processes in summer due to internal atmospheric variability have recently received considerable attention. A regional barotropic atmospheric process over Greenland and the Arctic Ocean in summer (June-July-August), featuring either a year-to-year change or a low-frequency trend toward geopotential height rise, has been identified as an essential contributor to September sea ice loss, in both observations and the CESM1 Large Ensemble (CESM-LE) of simulations [1-2]. This local melting is further found to be sensitive to remote sea surface temperature (SST) variability in the East Central Pacific [3]. Here, we utilize five available single-model large ensembles and 31 CMIP5 models’ pre-industrial control simulations to show that the same atmospheric process, resembling the observed one and the one found in the CESM-LE, also dominates internal sea ice variability on interannual to interdecadal time scales in pre-industrial, historical and future scenarios, regardless of the modeling environment. However, all models exhibit limitations in replicating the correct magnitude of the observed local atmosphere-sea ice coupling and its sensitivity to remote tropical SST variability. These biases cast a shadow over models’ credibility in simulating interactions of sea ice variability with the Arctic and global climate systems. Further efforts toward identifying possible causes of these model limitations may provide profound implications for alleviating the biases and improving interannual and decadal time scale sea ice prediction and future sea ice projection.

[1] Ding, Q., and Coauthors, (2017): Influence of high-latitude atmospheric circulation changes on summertime Arctic sea ice. Nat. Climate Change, 7, 289-295.

[2] Ding, Q., and Coauthors, (2019): Fingerprints of internal drivers of Arctic sea ice loss in observations and model simulations. Nat. Geosci., 12, 28–33.

[3] Baxter, I., and Coauthors, (2019): How tropical Pacific surface cooling contributed to accelerated sea ice melt from 2007 to 2012 as ice is thinned by anthropogenic forcing. J. Climate, 32, 8583–8602 https://doi.org/10.1175/JCLI-D-18-0783.1 

How to cite: Topal, D., Ding, Q., Mitchell, J., Baxter, I., Herein, M., Haszpra, T., Luo, R., and Li, Q.: An Internal Atmospheric Process Determining Summertime Arctic Sea Ice Melting in the Next Three Decades: Lessons Learnt from 5 Large Ensembles and CMIP5 Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4729, https://doi.org/10.5194/egusphere-egu2020-4729, 2020

The Arctic region shows some of the world's most significant signs of climate change. The atmospheric energy transport plays an important role for the Arctic climate; the atmospheric transport contributes an amount of energy into the Arctic that is comparable to that provided directly by the sun. From recently developed Fourier and wavelet based methods it has been found that the planetary component of the latent heat transport affects that Arctic surface temperatures stronger than the decomposed dry-static energy transport and the synoptic scale component of the latent heat transport. 

A large concern for humanity is that the climate change in polar regions will lead to significant melting of the ice sheets and glaciers. In fact the discharge water from the Greenland ice sheet has recently increased to the extent that this ice sheet is one of the major contributorsto sea-level rise. Here we test the hypothesis that the recent rapid increase in melt of the Greenland ice sheet is linked to a shift of planetary-scale waves transporting warm and humid air over the ice sheet.

The effect of the atmospheric energy transport is investigated by correlating the divergence of energy over the Greenland ice sheet with the surface mass balance of this ice sheet. The divergence of latent heat transport is found to correlate positively with the surface mass balance along the edges of the ice sheet, and negatively in the interior. This indicates that a convergence of latent at the edges of the ice sheet lead to a increased mass discharge from the ice sheet, whilst in the interior converging latent heat indicates an accumulation of mass to the ice sheet. 

To investigate the effect of transport by planetary and synoptic scale waves on the Greenland ice sheet surface mass balance the mass flux component of the transport divergence is decomposed into wavenumbers through the application of a Fourier series. The divergences of transport contributions of each wavenumber are then correlated with the surface mass balance of the Greenland ice sheet. The correlations between the surface-mass balance and divergence of transport contributions by different wavenumbers reveals the relative impact of atmospheric circulation systems, such as Rossby waves and cyclones, on the Greenland ice sheet mass balance. Further, identifying shifts in the circulation patterns over Greenland by applying self organizing maps, or similar methods, and investigations of how these circulation patterns affect the energy transport over Greenland by atmospheric waves of different scales are also pursued.
 
  

How to cite: Heiskanen, T. I. H. and Graversen, R. G.: The effect of latent heat transport by waves on Greenland Surface Mass Balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7006, https://doi.org/10.5194/egusphere-egu2020-7006, 2020

The current Arctic sea ice melting is accompanied by a significant Arctic warming, which could induce several climatic responses not limited to the high latitudes. These responses include changes in storm tracks, modification of the jet stream patterns as well as a stimulation of the planetary waves. The objective of this study is to determine the short-term changes on the extreme precipitation events over the high and mid-latitudes due to a sudden loss of Arctic sea ice. These changes are analysed using two different climate models (ECMWF-IFS and CNRM-CM6) at two different horizontal resolutions, that participate to the EU Horizon 2020 PRIMAVERA project. A common protocol in which the sea ice albedo is reduced to the ocean value is applied to simulate the sudden loss of Arctic sea ice. The results show an increase in drought duration in early winter over the southwestern North America in the ECMWF-IFS model at the two different horizontal resolutions and in the CNRM-CM6 at low resolution, and over the western part of the Mediterranean Basin in the ECMWF-IFS model. This increase can be understood by a stationary wave response due to Arctic sea ice loss which leads to an amplification of the subsidence over these two regions. Indeed, a northward shift of the North Atlantic High and North Pacific High is modelled in early winter. Thanks to these results, abrupt Arctic sea ice loss seems to play a role on the extreme precipitation events over mid-latitudes.

How to cite: Delhaye, S., Fichefet, T., Massonnet, F., Docquier, D., Chripko, S., Keeley, S., Msadek, R., and Roberts, C.: Impact of an abrupt Arctic sea ice loss on the extreme precipitation events in the midlatitudes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8283, https://doi.org/10.5194/egusphere-egu2020-8283, 2020

Modeling studies have shown that changes in sulphate aerosol emissions from both Europe and North America can have an impact on remote Arctic climate. The bulk of this response is driven by atmospheric changes, rather than through changes in meridional ocean heat transport. However, these simulations have focused on the Arctic response from an equilibrium perspective; i.e. the simulations are run for 200 years and the analyses are based on means of the last 50 years. While these simulations are useful to analyze the extent of contribution of mid-latitude aerosol emission changes, they cannot be used to investigate the mechanistic processes that initiate and drive the high-latitude response. We approach this problem by conducting two sets of initial condition ensemble simulations with >30 members for each set and focus our analysis on the first 30 years. Having a large number of ensemble members improves the signal-noise ratio and allows us to distinguish the model response to emission changes from internal variability. In the first set of simulations (control set), the aerosol emissions are set to year 2000. In the second set of simulations (perturbed set), we increase the European sulphate aerosol emissions to seven times the year 2000 value. We compare the two sets of simulations to evaluate the dynamical response of the atmosphere to the change in aerosol emissions. One of the key parameters that link the mid- and high-latitudes in the equilibrium response is the change in sea-ice area in the sub-polar latitudes. Reduced sea-ice coverage and greater open ocean area with lower mid-latitude aerosol emissions leads to increased ocean-atmosphere energy exchange and impacts the atmospheric meridional heat and energy budgets in the Arctic. We present the extent and seasonality of sea-ice changes for the first 30 years of our ensemble simulations and discuss their implications in the context of the mechanistical links between the mid- and high-latitudes.

How to cite: Krishnan, S., Ekman, A., Hansson, H.-C., and Riipinen, I.: What drives the Arctic response to mid-latitude sulphate aerosol emissions?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15906, https://doi.org/10.5194/egusphere-egu2020-15906, 2020

The recent rapid warming of the Arctic atmosphere and ocean and related sea ice decline have been associated with increasing occurrence of extreme weather events in the Arctic. Applying ERA-Interim reanalysis, we identify 100 days with largest positive and negative anomalies (compared to local climatology) in 2-m air temperature (T2m) in the Northern Hemisphere in winter during 2005-2019, and address various physical mechanisms contributing to these events. The mechanisms responsible for warm extremes in the Arctic are often associated with a meandering Polar front jet stream, favouring cases of large transports of heat and moisture from mid-latitudes to the Arctic. In addition, subsidence heating often contributes to warm extremes in the Arctic, allowing them to occur also under high-pressure conditions. The coldest T2m anomalies north of 30^oN mostly occur in regions that are also climatologically cold, i.e., cannot be strongly affected by cold-air advection. This suggests a dominating role local surface energy budget and boundary-layer processes.

Extreme weather events often interact with anomalies in sea ice concentration. Cases of strong winds transporting warm, moist air masses to the Arctic provide both dynamic and thermodynamic forcing for large sea ice anomalies, and during winter the openings in sea ice field contribute to air temperature extremes via large heat fluxes from the ocean to atmosphere.

Coldest winter extremes in mid-latitudes are typically associated with meandering jet stream and high-pressure blockings, but show differences between Central Europe, North America and northern China. In Central Europe the coldest events are typically associated with cold-air advection from the East or Northeast, whereas during the coldest events in North American East Coast the cold air is transported from the North. In northern China, the coldest events often occur under high-pressure conditions with weak winds. Accordingly, the role of cold-air advection is much smaller than in the case of the coldest events in North America.

How to cite: Vihma, T., Uotila, P., Naakka, T., and Nygård, T.: Occurrence and mechanisms of extreme winter air temperatures in the Arctic and surrounding continents, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19188, https://doi.org/10.5194/egusphere-egu2020-19188, 2020

This study assesses the ability of the Coupled Model Intercomparison Project phase 5 (CMIP5) simulations in capturing the interdecadal precipitation enhancement over the Yangtze River valley (YRV) and investigates the contributions of Arctic temperature and mid- to high-latitude warming to the interdecadal variability of the East Asian summer monsoon rainfall. Six CMIP5 historical simulations including models from the Canadian Centre for Climate Modeling and Analysis (CCCma), the Beijing Climate Center, the Max Planck Institute for Meteorology, the Meteorological Research Institute, the Met Office Hadley Centre, and NCAR are used. The NCEP–NCAR reanalysis and observed precipitation are also used for comparison.Among the sixCMIP5 simulations, only CCCma can approximately simulate the enhancement of interdecadal summer precipitation over the YRV in 1990–2005 relative to 1960–75; the various relationships between the summer precipitation and surface temperature (Ts), 850-hPa winds, and 500-hPa height field (H500); and the relationships between Ts and H500 determined using regression, correlation, and singular value decomposition (SVD) analyses. It is found that CCCma can reasonably simulate the interdecadal surface warming over the boreal mid- to high latitudes in winter, spring, and summer. The summer Baikal blocking anomaly is postulated to be the bridge that links the winter and spring surface warming over the mid- to high latitude and Arctic with the enhancement of summer precipitation over the YRV. Models that missed some or all of these relationships found in CCCma and the reanalysis failed to simulate the interdecadal enhancement of precipitation over the YRV. This points to the importance of Arctic and mid- to high-latitude processes on the interdecadal variability of the East Asian summer monsoon and the challenge for global climate models to correctly simulate the linkages.

How to cite: Li, Y. and Leung, L. R.: Interdecadal Connection between Arctic Temperature and Summer Precipitation over the Yangtze River Valley in the CMIP5 Historical Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2031, https://doi.org/10.5194/egusphere-egu2020-2031, 2020

Amplified Arctic warming and its relevance to mid-latitude cooling in winter have been intensively studied. Observational evidence has shown strong connections between decreasing sea ice and cooling over the Siberian/East Asian regions. However, the robustness of such connections remains a matter of discussion because modeling studies have shown divergent and controversial results. Here, we report a set of general circulation model experiments specifically designed to extract memory effects of land processes that can amplify sea ice–climate impacts. The results show that sea ice–induced cooling anomalies over the Eurasian continent are memorized in the snow amount and soil temperature fields, and they reemerge in the following winters to enhance negative Arctic Oscillation-like anomalies. The contribution from this memory effect is similar in magnitude to the direct effect of sea ice loss. The results emphasize the essential role of land processes in understanding and evaluating the Arctic–mid-latitude climate linkage.

How to cite: Nakamura, T., Yamazaki, K., Sato, T., and Ukita, J.: Memory effects of Eurasian land processes cause enhanced cooling in response to sea ice loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2284, https://doi.org/10.5194/egusphere-egu2020-2284, 2020

This study analysed the monsoon features of atmospheric circulation in the Barents and Kara Seas, the variability of atmospheric circulation, and anomalies in temperature, precipitation, and wind speed. In a cold period, the extreme winds are southerly winds that develop in the eastern parts of cyclones. In the warm season, the extreme speeds correspond to a northerly wind in the western periphery of cyclones. The regional circulation systems were divided into ten circulation weather types, separately for each sea. Their frequencies were compared with different indexes, describing the main modes of variability for the arctic region (the North Atlantic Oscillation, the summer North Atlantic Oscillation, the Scandinavia teleconnection pattern, the Siberian High). In the winter season, the monsoon currents from land to sea occur only when the North Atlantic Oscillation index is positive. With the prevalence of other modes of variability, the direction of the winds can be different, and this causes the monsoon regularity to be stochastic. In summer, the northern streams move on the western periphery of cyclones, regenerating and stabilizing over the Kara Sea.

The work was supported by the grant of the Russian Foundation for Basic Research (RFBR) [project number 18-05-60147] and this work was carried out as part of governmental assignment АААА-А16-116032810086-4.

How to cite: Kislov, A. and Matveeva, T.: On monsoon character of circulation over the Barents and Kara Seas , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2745, https://doi.org/10.5194/egusphere-egu2020-2745, 2020

Arctic sea ice has been retreating at fast pace in the last decades, with potential impacts on the weather and climate at mid and high latitudes, as well as the biosphere and society. Sea-ice loss is driven by anthropogenic global warming, atmospheric circulation changes, climate feedbacks, and ocean heat transport. To date, no clear consensus regarding the detailed impact of ocean heat transport on Arctic sea ice exists. Previous observational and modeling studies show that the poleward Atlantic Ocean heat transport and Arctic sea-ice area and volume are generally anti-correlated, suggesting a decrease in sea-ice area and volume with larger ocean heat transport. In turn, the changing sea ice may also affect ocean heat transport, but this effect has been much less studied. Our study explores the two-way interactions between ocean heat transport and Arctic sea ice. We use the EC-Earth global climate model, coupling the atmosphere and ocean, and perform different sensitivity experiments to gain insights into these interactions. The mechanisms by which ocean heat transport and Arctic sea ice interact are analyzed, and compared to observations. This study provides a way to better constrain model projections of Arctic sea ice, based on the relationships between ocean heat transport and Arctic sea ice.

How to cite: Docquier, D., Fuentes-Franco, R., Wyser, K., and Koenigk, T.: Interactions between ocean heat transport and Arctic sea ice, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3352, https://doi.org/10.5194/egusphere-egu2020-3352, 2020

As the land surface warms, a subsequent reduction in snow and ice cover reveals a less reflective surface that absorbs more solar radiation, which further enhances the initial warming. This positive feedback climate mechanism is the snow albedo feedback (SAF), which will exacerbate climate warming and is the second largest contributor to Arctic amplification. Snow albedo feedback will increase the sensitivity of climate change in the northern hemisphere, which affects the accuracy of climate models in simulation research of climate change, and further affects the credibility of future climate prediction results.

Using the latest generation of climate models from CMIP6 (Coupled Model Intercomparison Project Version 6), we analyze seasonal cycle snow albedo feedback in Northern Hemisphere extratropics. We find that the strongest SAF strength is in spring (mean: -1.34 %K^-1), second strongest is autumn (mean: -1.01 %K^-1), the weakest is in summer (mean: -0.18 %K^-1). Except summer, the SAF strength is approximately 0.15% K^-1 larger than CMIP5 models in the other three seasons. The spread of spring SAF strength (range: -1.09 to -1.37% K^-1) is larger than CMIP5 models. Oppositely, the spread of summer SAF strength (range: 0.20 to -0.56% K^-1) is smaller than CMIP5 models. When compared with CMIP5 models, the spread of autumn and winter SAF strength have not changed much.

How to cite: hu, J. and ji, D.: Evaluation of snow albedo feedback simulated by CMIP6 coupled climate models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4309, https://doi.org/10.5194/egusphere-egu2020-4309, 2020

The Arctic region is projected to experience amplified warming as well as strongly increasing precipitation rates. Equally important to trends in the mean climate are changes in interannual variability, but changes in precipitation fluctuations are highly uncertain and the associated processes unknown. Here we use various state-of-the-art global climate model simulations to show that interannual variability of Arctic precipitation will likely increase markedly (up to 40% over the 21^st century), especially in summer. This can be attributed to increased poleward atmospheric moisture transport variability associated with enhanced moisture content, possibly modulated by atmospheric dynamics. Because both the means and variability of Arctic precipitation will increase, years/seasons with excessive precipitation will occur more often, as will the associated impacts.

How to cite: Bintanja, R., van der Wiel, K., van der Linden, E., Reusen, J., Bogerd, L., Krikken, F., and Selten, F.: Strong future increases in Arctic precipitation variability linked to poleward moisture transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5301, https://doi.org/10.5194/egusphere-egu2020-5301, 2020

How to cite: Lanconelli, C., Cappucci, F., Mota, B., Gobron, N., Driemel, A., and Lupi, A.: Long-term trends of surface reflectance derived from models, satellite and in-situ observations over polar areas , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5830, https://doi.org/10.5194/egusphere-egu2020-5830, 2020

Single extreme weather events such as heavy storms or heat waves can have a major impact on Arctic surface temperatures, melting rates and sea-ice extent. If weather conditions in the Arctic become anomalous on the time scale of an entire season, this could affect the Arctic energy budget and sea ice coverage even more.

From a meteorological perspective, in a certain region an extreme season can be defined as a season when a specific meteorological parameter, such as surface temperature, reaches extremely high or low seasonal-mean values in this region. The dynamical processes leading to such anomalous seasons in the Arctic region as well as their possible change in a warmer climate have not yet been analysed in detail. Furthermore, it is yet unknown if climate models are able to correctly represent the processes leading to extreme seasons, which is an important aspect for the validation and potential further improvement of such models.

Here we focus on a detailed analysis of Arctic extreme seasons and their underlying atmospheric dynamics in the ERA5 reanalysis data set. Specifically, extreme seasons are determined based on departures from a transient climatology of four parameters (surface temperature, sea-ice extent, surface energy balance and net surface freshwater flux) in distinct regions of the Arctic with different climatological sea-ice extents. Using EOF analysis, the overall most extreme seasons, which occur as significantly anomalous for several parameters, are selected to perform extended case studies. Highly anomalous seasons occur on a broad range of spatial scales as well as for areas nearly covering the whole Arctic Ocean. The formation of small and large extreme seasons may vary significantly, including local processes as well as large-scale atmospheric features.

The winter of 1984/1985 shows one of the largest positive departure of surface temperature from the background warming trend together with a significant sea-ice reduction in the region of the High Arctic and the Greenland Sea. An analysis of the synoptic situation for this winter shows a slightly positive cyclone frequency anomaly over the Greenland Sea combined with a more pronounced negative cyclone frequency anomaly over the Kara-Barents Sea, favouring the advection of warm mid-latitude air masses towards the pole.

How to cite: Hartmuth, K., Papritz, L., Böttcher, M., and Wernli, H.: Dynamics and drivers of extreme seasons in the Arctic region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7635, https://doi.org/10.5194/egusphere-egu2020-7635, 2020

The wintertime warm Arctic-cold Eurasia (WACE) temperature trend during 1990-2010 was characterized by accelerating warming in the Arctic region, cooling in Eurasia and accelerating autumn/winter Arctic sea ice loss. We identify two atmospheric circulation modes over the North Atlantic-Northern Eurasian sector which displayed strong upward trends over the same period and can explain a large part of the observed decadal WACE pattern. Both modes bear a close resemblance to well-known teleconnection patterns and are relatively independent from anomalies in Arctic sea-ice cover. The first mode (PC1) captures the recent negative trends in the North Atlantic Oscillation and increased Greenland blocking frequency while the second mode (PC2) is reminiscent of a Rossby wave train and reflects an increased blocking frequency over the Urals and North Asia. We find that the loss in the Arctic sea ice and the upward trends in the PC1/PC2 together account for most of the decadal Arctic warming trend (>80%). However, the decadal Eurasian cooling trends may be primarily ascribed to the two circulation modes alone: all of the cooling in Siberia is contributed to by the PC1, and 65% of the cooling in East Asia by their combination (the contribution by PC2 doubles that by PC1). Enhanced intraseasonal activity of the two circulation modes increases blocking frequencies over Greenland, the Ural region and North Asia, which drive anomalous moisture/heat flux towards the Arctic and alter the downward longwave radiation. It weakens warm advection and enhances advection of Arctic cold airmass towards Eurasia.

How to cite: Ye, K. and Messori, G.: Two leading modes of wintertime atmospheric circulation drive the recent warm Arctic-cold Eurasia temperature pattern, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9705, https://doi.org/10.5194/egusphere-egu2020-9705, 2020

In North America and Asia, extreme cold weather characterized the winter of 2017–18. At the same time, the Pacific Arctic regions -- Chukchi and Bering Seas --experienced the historical lowest sea ice extent. Because the shape of the ice-free ocean appears as a hole in the larger ice cover, we refer to this sea ice hole as a warm hole. The jet stream dividing cold Arctic air from warm air deviated from normal zonal patterns northward into the ice-free areas north of the Bering Strait. Large southward jet stream pathways formed over Asia and America, allowing cold air to spread into Asia and the southern areas of North America. We hypothesise that the warm hole and Pacific atmospheric rivers were partially responsible for the cold winter. We used data analyses and numerical experiments to test this hypothesis. We propose a positive feedback mechanism between the sea ice anomaly and atmospheric river activity, with anomalous south winds toward the sea ice anomaly potentially leading to more warm water injected by the wind-driven current through the Bering Strait. Our findings suggest that Poleward propagation of the atmospheric rivers made upper air warm, leading to their upgliding, which further heated the overlying air, causing poleward jet meanders. As a part of this response the jet stream meandered southward over Asia and North America, resulting in cold intrusions.

We speculate that the positive feedback mechanism observed during the 2017–18 winter could recur in future years. This winter may be the first year when the warm hole shifted the dynamics of hemispheric climate to the new state, because ice retreat has not abated, and the warm hole would be expected to appear again and again. This would provide Eastern Eurasia and North America with cold winter in the new era of the warm hole. This study was recently published in Scientific Reports [1].

References

 [1] Tachibana, Y., K. K. Komatsu, V. A. Alexeev, L. Cai, and Y. Ando, Warm hole in Pacific Arctic sea ice cover forced mid-latitude Northern Hemisphere cooling during winter 2017-18, Scientific Reports, 9, 5567, DOI: 10.1038/s41598-019-41682-4 , (2019)

How to cite: Tachibana, Y., Komatsu, K., Alexeev, V., Cai, L., and Ando, Y.: Warm hole in Pacific Arctic sea ice cover forces mid-latitude Northern Hemisphere cooling during winter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11694, https://doi.org/10.5194/egusphere-egu2020-11694, 2020

The climate response to Arctic sea-ice loss is highly uncertain. There exists considerable disagreement between observational and modelling studies, and between models, for reasons that remain poorly understood. To make progress, the Polar Amplification Model Intercomparison Project (PAMIP) was designed to provide coordinated experiments, with consistent sea-ice loss applied in multiple models. Results from the PAMIP are presented, focussing on the robustness of the atmospheric response to Arctic sea-ice loss across models and, within individual models, the dependence of the response on the mean state.

In the troposphere, the mid-latitude jet is either weakened and/or shifted towards the equator in all models, albeit with varying magnitudes. We hypothesise that the magnitude of the jet response is sensitive to the atmospheric model resolution. To test this, and to more broadly identify the aspects of the atmospheric response that are sensitive to model resolution, we compare like-for-like experiments with two versions of the HadGEM3 model at low (N96) and high (N216) horizontal resolution.

The stratospheric polar vortex response to Arctic sea-ice loss is not consistent between models, and appears to be influenced by both the size of the ensemble for each model and the phase of the Quasi-Biennial Oscillation (QBO). The possible modulating effect of the QBO is further explored using new simulations with background atmospheric states representing the easterly and westerly QBO phases.

A surprising early result from the PAMIP simulations were sizeable changes in the Southern Hemisphere in response to Arctic sea-ice loss and significant changes in the Northern Hemisphere in response to Antarctic sea-ice loss, even in atmosphere-only model experiments. The robustness of such apparent interhemispheric connections across models, ensemble sizes and mean states is investigated.

How to cite: Walsh, A., Screen, J., Scaife, A., Smith, D., and Eade, R.: Model and state dependence of the atmospheric response to Arctic sea-ice loss, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11872, https://doi.org/10.5194/egusphere-egu2020-11872, 2020

Hudson Bay, along with James Bay, forms a significant section of the Canadian Sub-Arctic basin which experiences an annual event of Land-fast sea ice formation and melt. Here Landfast ice dynamics largely depends on the climatic and oceanographic conditions, along with coastal geomorphology. In this study, we attempt to investigate the annual cycle of land-fast sea ice formation and melt in the Hudson Bay and James Bay region by estimating the ice period, stages of development and extent. Through this study, we also emphasize the role of coastal morphology influencing ice stability. We have analysed over 2000 ice charts produced by the Canadian Ice Service (CIS) and satellite observations from Worldview and LANDSAT series. The Canadian Ice Service publishes charts of ice concentration and stages of development of Hudson Bay and James Bay on a monthly, weekly and daily scale. We observe the variation in land-fast ice dynamics by digitally extracting information from the daily and weekly ice charts produced by the CIS and satellite observation coupled with mean surface temperature throughout the period of study. Our results indicate landfast ice forming earlier and breaking later in the northern and north-western coastal margin of Hudson Bay as compared to the southern and eastern shore. James Bay experiences a relatively shorter ice season than Hudson Bay. Though time series analysis of break-up in the northern and north-western Hudson Bay shows a negative trend implying an earlier break-up in these regions. Southern and eastern Hudson Bay and James Bay have a positive trend implying a negligible change in the break-up period. The extent of landfast ice in the eastern coastal margins of Hudson Bay and James Bay was noted to be significantly more compared to the west, primarily due to the north to south and finally eastward movement of pack ice in the bay system. Complex coastal topography in the eastern coastal margin also contributes to the stability of these extended ice sheets. The study determines the description of the multiyear variability of land-fast sea ice under changing temperature regimes over the Canadian Sub-Arctic.

How to cite: Gupta, K., Mukhopadhyay, A., and Ehn, J.: Landfast ice in the Canadian Sub-Arctic: A Hudson-Bay wide study., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12232, https://doi.org/10.5194/egusphere-egu2020-12232, 2020

The minimum extent of arctic sea ice (SIE) in 2019 ranked second-to-lowest in history and is trending downward. Hence, there is an immediate need for flexible statistical modeling approaches that both explain endogenously the trend of SIE and permits its extrapolation to generate a long-run forecast. To that end, we propose the VARCTIC, which is a Vector Autoregression (VAR) specifically designed to capture and extrapolate feedback loops that characterize the Arctic system.  VARs are dynamic simultaneous systems of equations routinely estimated in economics to predict and understand the interactions of multiple macroeconomic time series. The VARCTIC is a compromise between fully structural/deterministic modeling and purely statistical approaches that usually offer little explanation of the underlying mechanism. Our "business as usual" completely unconditional forecast has September SIE hitting 0 around the middle of the century. By studying the impulse response functions of Bayesian VARs including different sets of variables, we single out CO2 shocks as main drivers of the long-run evolution of SIE. Additionally, we document that the corresponding responses of Sea Ice Albedo and Thickness largely amplify the long-run impact of CO2 on SIE.  Finally, we conduct conditional forecasts analysis of remedies like reducing CO2 emissions or the implementation of Albedo-enhancing Geo-Engineering technologies.

How to cite: Goulet Coulombe, P. and Göbel, M.: Modeling and Extrapolating Arctic Feedback Loops using Macroeconometric Techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12620, https://doi.org/10.5194/egusphere-egu2020-12620, 2020

At the end of December 2015, Storm Frank, a major Atlantic windstorm, intruded into the Arctic-circle along with warm air and a large amount of moisture, resulting in an unprecedented Arctic high-temperature phenomenon. In late January 2016, the Eurasian continent suffered a series of strong cold events. This study performed a synoptic analysis of a daily Northern Hemisphere SLP and 500hPa, 300hPa height anomaly using JRA-reanalysis data focusing on the process understanding of the sequential development and strengthening of Siberian high in association with the generation of the Ural blocking after the Arctic warming event. From synoptic analysis , we found that, within one month period, there exist several spells of Ural blocking occurrence instead of steady occupation of persistent high pressure over Ural Mountain region. The heat intrusion from midlatitude in association with Storm Frank caused a large wave breaking event over Atlantic sector of Arctic and initiated Ural blocking. The unprecedented warm temperature in early 10 days of January 2016 caused a large sea-ice loss and further heat injection from Barents/Kara seas helping anchoring the blocking over Ural Mountain region. In January 2016, several cold events over Eurasian continent well matched with the several spell of Ural blocking events. We suggest that daily scale interactions among warm advection, downward longwave radiation, sea-ice loss, and blocking occurrence need to be carefully considered to understand true nature of Arctic-Midlatitude linkage issue.

How to cite: Han, K., Ku, H., and Kim, B.: Process understanding of a linkage between East-Asian cold-surge wiith the unprecedented Arctic warming event in early 2016, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12794, https://doi.org/10.5194/egusphere-egu2020-12794, 2020

Mid-latitude continental weather and climate are strongly affected by the atmospheric circulation patterns such as Rossby waves and cyclones. For instance these patterns may lead to warm- and humid-air advection over western part of the continents in winter and cold-air advection in these regions during summer. By applying a newly developed method for splitting the atmospheric latent and dry-static energy transport into waves, hereby decomposing the energy transport into parts accomplished by e.g. Rossby waves and synoptic-scale weather systems, the effect of different atmospheric circulation patterns on Northern-Hemisphere continental climate is investigated.

Climate change and the associated Arctic temperature amplification may impact mid-latitude atmospheric circulation. Here we investigate the effect on Northern-Hemisphere continental climate from changes over recent decades in the atmospheric circulation patterns using the above-mentioned method.

How to cite: Graversen, R. G.: Impact of Rossby waves on Norther-Hemisphere continental climate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13463, https://doi.org/10.5194/egusphere-egu2020-13463, 2020

Black carbon (BC) and Brown Carbon (BrC) absorbs sunlight and heat the atmosphere. The heating rate (HR) can be determined from the divergence of the net radiative flux with altitude (vertical profiles) or from the modelling activity; however, it determination is, up to now, too sparse, does not account for light-absorbing-aerosol (LAA) speciation and for the influence of different cloudy sky conditions on the BC induced heating rate (HR) in the atmospheric layer below clouds. This work applies a new method (Ferrero et al., 2018) to experimentally determine (at high time resolution) the HR induced by the LAA from mid-latidudes to the Arctic along two years (2018-2019, June-August) of oceanographic cruises moving from 54°N to 81°N and from 2°W to 25°E.

The HR was experimentally determined at high time resolution and apportioned in the context of LAA species (BC, BrC), and sources (fossil fuel, FF; biomass burning, BB) as reported in Ferrero et al. (2018) equipping the Oceania vessel of the Polish Academy of Science  with the following instrumentation:

1) Aethalometer (AE-33, Magee Scientific, 7-λ), 2) Multiplexer-Radiometer-Irradiometer ROX (diffuse, direct and reflected radiance: 350-1000 nm, 1 nm resolution), 3) a SPN1 radiometer (global and diffuse radiation), 4) High volume sampler (TSP ECHO-PUF Tecora). Samples were analysed for ions (Dionex IC) and by EC/OC by using DRI Model 2015 Multi-Wavelength Thermal/Optical Carbon Analyzer. Radiometers were compensated for the ship pitch and roll by an automatic gimbal. AE33 absorption coefficient accuracy was determined through comparison with a MAAP (Thermo-Fischer).

The HR showed a clear latitudinal behavior with higher values in the harbor of Gdansk (0.29±0.01 K/day) followed by the Baltic Sea (0.04±0.01 K/day), the Norvegian Sea (0.01±0.01 K/day) and finally with the lowest values in the pure Arctic Ocean (0.003±0.001 K/day).

They followed the decrease of both BC concentrations and global radiation from 1189±21 ng/m³  and 230±6 W/m² (Gdansk) to 27±1 ng/m³ and 111±3 W/m² (Arctic Ocean). The latitunal gradient of the HR clearly demonstrate that the warming of the Arctic could be influenced by a heat transport. In this respect, the LAA added about 300 J/m³ at mid-latitudes and only 3 J/m³ close to the North Pole. Moreover, above the Arctic circle, 70% of the HR was due to the diffuse radiation induced by cloud presence, a condition that climate models in clear-sky assumption cannot capture. In addition, in the Arctic the BrC experienced an increase of 60% in determining the HR compared to mid-latitudes.

Acknowledgements: GEMMA Center - Project MIUR – Dipartimenti di Eccellenza 2018–2022.

Reference: Ferrero, L., et al (2018) Environ. Sci Tech., 52, 3546−3555

How to cite: Ferrero, L., Losi, N., Bigogno, A., Gregoric, A., Rigler, M., Močnik, G., Markuszewski, P., Makuch, P., Pakszys, P., Petelski, T., Zielinski, T., and Bolzacchini, E.: Experimental black and brown carbon heating rate and from mid-latitudes to the Arctic along two years (2018-2019) of research cruises: the energy gradient for the Arctic Amplification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18233, https://doi.org/10.5194/egusphere-egu2020-18233, 2020