Arctic amplification has been proposed to influence midlatitude weather via a range of pathways. One hypothesis that has garnered wide public interest is that the weakening of the midlatitude temperature gradient due to Arctic warming causes larger meanders in the jet stream and so more intense weather extremes. However, previous work with idealized model simulations indicated that polar warming reduces waviness.

A variety of metrics have been developed to describe jet waviness, with some focused on jet geometry and others on the magnitude of the associated geopotential anomalies. Recent studies analyzing sea-ice loss and global warming simulations indicate that the response to polar warming may depend on its depth, with deeper warming having a larger effect on midlatitudes. Here we perform a variety of dry idealized model simulations in which we apply polar warming of different depths and latitudinal extents and assess the behavior of these different metrics.

Eddy heat transport decreases regardless of how polar warming is applied. However, unexpectedly we find that metrics relating to geometry (jet sinuosity, meander area) indicate a robust increase in jet waviness with polar warming. Meanwhile Local Wave Activity suggests increased waviness if warming is confined to the poles, but decreased waviness if warming extends into the midlatitudes. The apparent disagreement between metrics can be reconciled by assessing the changes in midlatitude geopotential gradient in the different simulations. Overall, these idealized simulations indicate that polar amplification could cause an increase in jet meandering, characterized by a shift of geopotential anomalies to smaller spatial scales and lower frequencies. However, the heat transport achieved and magnitude of pressure anomalies generated depend predominantly on the equator-to-pole temperature difference and geopotential gradient. Implications for weather extremes are discussed.

How to cite: Geen, R., Thomson, S., Screen, J., and Vallis, G.: Perceived midlatitude jet waviness response to polar warming is sensitive to warming structure and metric choice, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2569, https://doi.org/10.5194/egusphere-egu23-2569, 2023.

Using a large ensemble of simulations from the Polar Amplification Model Intercomparison Project (PAMIP) and Coupled Model Intercomparison Project Phase 6 (CMIP6), we compare the response of winter-mean precipitation and daily extremes across the North Hemisphere in response to future Arctic sea-ice loss and global ocean warming. North Atlantic-Northwest Europe is simulated to become drier in response to future Arctic sea-ice loss, with reduced precipitation intensity and more dry days. A wetting response to sea-ice loss is simulated over the midlatitude Atlantic Ocean. These responses are robust across the eight models analysed, albeit with differences in their magnitude and spatial pattern. The precipitation response to global ocean warming is broadly opposite in sign, but larger in magnitude, compared to the response to sea-ice loss, over these regions. The precipitation responses to both sea-ice loss and ocean warming are strongly related to coincident changes in storm density and intensity. More specifically, an equatorward shift of the storm tracks in response to sea-ice loss and poleward shift of the storm tracks in response to ocean warming. The linear combination of the responses of future Arctic sea-ice loss and global ocean warming explain well the spatial pattern of the precipitation change at 2 ºC global warming projected in CMIP6. Our results suggest that projected future precipitation change over North Atlantic-Northwest Europe reflects a ‘tug-of-war’ between Arctic sea-ice loss and global ocean warming, but the latter dominates over the former.

How to cite: Yu, H., Screen, J., Hay, S., Catto, J., and Xu, M.: Winter Precipitation Responses to Projected Arctic Sea-Ice Loss and Global Ocean Warming and Their Opposing Influences over Northwest Europe, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1247, https://doi.org/10.5194/egusphere-egu23-1247, 2023.

A rapidly warming Arctic and mild cold mid-latitude continents have been one of the main characteristics of the Northern Hemisphere winter during the last two decades. However, the factors contributing this warm Arctic-cold continent (WACC) pattern remain unclear, although anomalies in blocking highs and the Arctic oscillation (AO) are possible factors. This study revealed that the mode with high-latitude concurrent blockings (HCBs) is more consistent with the WACC pattern than the AO. In the HCB mode, a strong anticyclonic anomalous circulation over the Arctic Circle, excited by the strong HCBs over the Ural Mountains and the North Pacific, changes the polar atmospheric circulation and redistributes both momentum and heat to give a warmer Arctic than in the AO mode. A weak polar night jet and a poleward shift in the subtropical westerly jet result in mild cold mid-latitude continents. However, these features are not seen in the AO mode, which is characterized by cool continents and a warm Greenland. Besides, human activities may also be contributed to the interdecadal WACC because there is an interdecadal increase in the WACC pattern with HCBs in the CMIP6 simulations with human activities. These results suggest that the role of HCBs should be highly paid attention in winter mid-high latitude extreme events in recent decades.

How to cite: Zhao, L. and Qu, J.: Enhanced High-Latitude Concurrent Blockings Cause the Warm Arctic-Cold Continent Pattern, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6700, https://doi.org/10.5194/egusphere-egu23-6700, 2023.

Rapid Arctic warming and sea-ice loss have been observed in recent decades, and these trends are likely to continue in the future. Research has shown that Arctic changes affect weather and climate across the Northern Hemisphere. These changes, especially those in the extreme ends, can adversely impact communities and ecosystems. Recent development of the Polar Amplification Model Intercomparison Project (PAMIP) means that large ensembles of standardised climate experiments are now available for examining the effects of future Arctic changes on extreme weather in a coordinated way. Based on present-day and future (2°C global mean warming above pre-industrial levels) PAMIP model simulations, I will show the projected responses of winter hot and cold extremes (at the 20-year return period) to future Arctic sea-ice loss and ocean warming separately. I will focus on land areas in the Northern Hemispheric mid- and high latitudes where responses are expected to be largest. I will discuss the importance of considering the effect of sea-ice concentration loss together with that from ocean warming, which is not routinely done in the literature.

How to cite: Lo, E., Mitchell, D., Watson, P. A. G., and Screen, J. A.: Effects of future Arctic sea-ice loss and ocean warming on winter temperature extremes in the Northern Hemisphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6779, https://doi.org/10.5194/egusphere-egu23-6779, 2023.

Based on reanalysis datasets and sea-ice sensitivity experiments, this study has pointed out that the autumn sea ice loss in East Siberian-Chukchi-Beaufort (EsCB) Seas significantly increases the frequency of winter extreme low temperature over western-central China. Autumn sea ice loss warms the troposphere and generates anticyclonic anomaly over the Arctic region one month later. Under the effects of synoptic eddy-mean flow interaction and anomalous upward propagated planetary wave 2, the Arctic anticyclonic anomaly strengthens and develops toward Greenland-Northern Europe, accompanied by a weakened stratospheric polar vortex. In winter, following intra-seasonal downward propagation of stratospheric anomalies, the Northern European positive geopotential anomalies enhance and expand downstream within 7 days, favoring Arctic cold air east of Novaya Zemlya southward (the hyperpolar path) accumulating in Siberia around Lake of Baikal. In the subsequent 2~3 days, these cold anomalies rapidly intrude western-central China and induce abrupt sharp cooling, thus more frequent extreme low temperature there.

How to cite: Ding, S., Wu, B., Chen, W., Graf, H.-F., and Zhang, X.: Possible linkage between winter extreme low temperature over central-western China and autumn sea ice loss, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10688, https://doi.org/10.5194/egusphere-egu23-10688, 2023.

Recent studies have widely discussed arctic warming and its effect on the temperature variability over Eurasia. They agreed that Eurasia is cold while the arctic is warm during the boreal winter. Yet, the differences in month-to-month features and their predictability have not been examined. In this research, we categorized Arctic vertical warming into four types – Deep Arctic Warming (DAW), Shallow Arctic Warming (SAW), Arctic Warming Aloft, and Others – based on the vertical temperature distribution in the Barents-Kara Sea. And we discussed two significant events, DAW and SAW, which are closely related to the cold event over East Asia. The result shows that the temperature variability over East Asia associated with the Arctic events is significant in January and February but not in December. The multi-model ensemble of seasonal prediction models can distinguish the four types of Arctic events well than the individual models. In contrast, the individual models show better skill in reproducing the circulation patterns associated with the DAW than MME. Models tend to exhibit higher predictability over Eurasia in January and February compared to December. We suggest that this is partly due to the models' better representation of DAW in those months,  which is helpful for the better simulation of Arctic-midlatitude linkage. 

How to cite: Kim, G., Lee, W.-S., and Kim, B.-M.: The Effect of Arctic Vertical Warming on East Asia temperature variability on a monthly time scale and its predictability., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4694, https://doi.org/10.5194/egusphere-egu23-4694, 2023.

Across the winters of global warming and Arctic amplification (AA) era,  the frequency of extreme cold events in East Asia (EA) showed an upward trend. Here we constructed regional AA index in the winters of 1979–2019, and examine the atmospheric driver that linked with strong AA scenarios and cold extreme in EA. Results show that the local atmospheric blocking is key drivers for regional AA occurrence on the intraseasonal timescale. Ural-Siberia blocking, which is tightly linked to the warming over Barents-Kara Seas (BK), is the primary atmospheric mode when regional AA corresponds with extreme East Asian cold days. However, when there is no warming over BK during the associated cold days in EA, the warming over western hemisphere become prominent, accompanied by the negative phase of the North Atlantic Oscillation (NAO−) and blocking dipole system located at mid-Siberian and East Asian continent. Under this circulation configuration, not only does EA exhibits extremely cooling, but also northeastern North America experiences significant cold anomalies. Furthermore, precursor signals at 2–10 days are found between NAO− and each regional AA event when the days of BK warming are excluded. Our results highlight the importance of atmospheric circulation on linking the warming of different Arctic sectors and cold extremes in the mid-latitude continent, and point out the independent role of NAO− and BKS warming on regional AA.

How to cite: Zhuo, W., Yao, Y., Luo, D., Simmonds, I., and Fei, H.: The key atmospheric drivers linking regional Arctic amplification with East Asian cold extremes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4628, https://doi.org/10.5194/egusphere-egu23-4628, 2023.

To quantify the relative contributions of Arctic sea ice and unforced atmospheric internal variability to “warm Arctic, cold East Asia” (WACE), this study analyses three sets of large-ensemble simulations carried out by the Norwegian Earth System Model with a coupled atmosphere-land surface model, forced by seasonal sea ice conditions from preindustrial, present-day, and future periods. Each ensemble-member within the same set uses the same forcing but with small perturbations to the atmospheric initial state. Hence, the difference between the present-day (or future) ensemble-mean and the preindustrial ensemble-mean provides the ice-loss-induced response, while the difference of the individual members within the present-day (or future) set is the effect of atmospheric internal variability.

Results indicate that both present-day and future sea ice loss can force a negative phase of the Arctic Oscillation with a WACE pattern in winter. The magnitude of ice-induced Arctic warming is over four times larger than the ice-induced East Asian cooling, the latter with a magnitude that is about 30% of the observed cooling. Sea ice loss contributes about 60% (80%) of Arctic winter warming for the present-day (future) climate. Atmospheric internal variability can also induce a WACE pattern with comparable magnitudes between Arctic and East Asia. Ice-loss-induced East Asian cooling can easily be masked by atmospheric internal variability effects because random atmospheric internal variability may induce warming with larger magnitude. Observed WACE pattern occurs as a result of both Arctic sea ice loss and atmospheric internal variability, with the former  dominating Arctic warming and the latter dominating  East Asian cooling.

How to cite: He, S., Drange, H., Furevik, T., Wang, H., Fan, K., Graff, L. S., and Orsolini, Y.: Relative impacts of sea ice loss and atmospheric internal variability on winter Arctic to East Asian surface air temperature based on large-ensemble simulations with NorESM2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15812, https://doi.org/10.5194/egusphere-egu23-15812, 2023.

This study investigates the differences in atmospheric responses to Arctic sea ice anomalies between simulations from six (atmospheric-only) models contributing to the Polar Amplification Model Intercomparison Project and one long control simulation (piControl from CMIP6) from the same six (coupled) models. We perform a composite analysis between years of low and high Arctic sea ice extent in the piControl and consider four different types of experiment in the PAMIP where only the sea ice concentration is changed (pdSST-futArcSIC, pdSST-futBKSeasSIC, pdSST-futOkhotskSIC and pdSST-pdArcSIC) to examine the associated atmospheric circulation changes owing to an Arctic sea ice loss. A negative change in the North Atlantic Oscillation (NAO) pattern emerges in winter, linked to the so-called stratospheric pathway, and is mainly due to the sea ice anomaly in the Barents-Kara Seas. The results in the PAMIP experiments support these findings, except that the intensity is lower than in the piControl composite analysis. This work highlights that the atmospheric circulation responses to Arctic sea ice loss in a long control simulation (CMIP6) show similarities with the responses of a coordinated set of numerical model experiments with prescribed sea ice (PAMIP). However, the atmospheric responses in the numerical models with prescribed sea ice display weaker changes than in CMIP6. The role of the atmosphere-ocean coupling and of the initial sea ice condition could be the main reasons for this difference in intensity.

How to cite: Delhaye, S., Massonnet, F., Fichefet, T., Msadek, R., Terray, L., and Screen, J.: Consistent atmospheric circulation responses due to Arctic sea ice loss between prescribed sea ice simulations and single long control simulations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12191, https://doi.org/10.5194/egusphere-egu23-12191, 2023.