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Given growing interest in extreme high‐latitude weather events, we use records from nine meteorological stations and atmospheric reanalysis data to examine extreme daily precipitation events (leading, 99th and 95th percentile) over Arctic Canada. Leading events span 90 mm at Cape Dyer, along the southeast coast of Baffin Island, to 26 mm at Sachs Harbour, on the southwest coast of Banks Island. The 95th percentiles range from 20 to 30% of leading event sizes. Extreme events are most common on or near the month of climatological peak precipitation. Contrasting with Eurasian continental sites having a July precipitation peak corresponding to the seasonal peak in precipitable water, seasonal cycles in precipitation and the frequency of extremes over Arctic Canada are more varied, reflecting marine influences. At Cape Dyer and Clyde River, mean precipitation and the frequency of extremes peak in October when the atmosphere is quickly cooling, promoting strong evaporation from Baffin Bay. At all stations, leading events involved snowfall and strong winds and were associated with cyclone passages (mostly of relatively strong storms). They also involved strong vapour fluxes, sometimes associated with atmospheric rivers or their remnants. The most unusual sequence of events identified here occurred at Clyde River, where the three largest recorded precipitation events occurred in April of 1977. Obtaining first‐hand accounts of this series of events has proven elusive. Identified links between extreme events and atmospheric rivers demonstrates the need to better understand how the characteristics of such features will change in the future. [ABSTRACT FROM AUTHOR]

We utilize statistically modeled ocean heat transports through the Bering Strait along with additional predictors to create skillful predictions of sea ice retreat and advance dates in the Chukchi Sea. Interannual variability of June and September oceanic heat transports through the strait can be captured using modeled Ekman transports, surface winds, and sea surface temperatures. At one‐month leads, our models can explain 41% and 79% of sea ice retreat and advance date variance with root mean squared errors (RMSEs) of 10.2 and 12.8 days respectively. At 4‐month leads, our models can respectively capture 37% and 73% of sea ice retreat and advance date variance with RMSEs of 8.5 and 14.6 days. These findings offer a path toward operational forecasts of sea ice retreat and advance dates in the Chukchi Sea in the absence of direct, readily available observations of heat transports in the strait. Plain Language Summary: The Chukchi Sea is a key region for shipping and other growing economic activities in the Arctic. Seasonal sea ice conditions in the region are strongly determined by the oceanic heat transport into the Chukchi Sea from the north Pacific Ocean via the Bering Strait. However, seasonal predictions of sea ice are hampered by the lack of high quality, real‐time, observations of Bering Strait water properties. We address this limitation by statistically modeling Bering Strait volume and heat transports and then using these models to forecast sea ice retreat and advance dates in the Chukchi Sea. Skillful sea ice forecasts in this critical region have the potential to increase the navigability of Arctic waters. Key Points: Variability in Bering Strait volume transports can be captured using surface winds and Ekman transports in the East Siberian and Bering SeasBering Sea sea surface temperatures, along with modeled volume transports, can capture Bering Strait ocean heat transport variabilityModeled ocean heat transports can be used to skillfully forecast sea ice retreat and advance dates with 1 and 4‐month lead times [ABSTRACT FROM AUTHOR]

The Arctic frontal zone (AFZ) is a narrow band of strong horizontal temperature gradients that develops along the Arctic Ocean coastline each summer in response to differential heating of the atmosphere over adjacent land and ocean surfaces. Past research has linked baroclinicity within the AFZ to summer Arctic cyclone development, especially by intensifying storms that migrate northward from the Eurasian continent. This study uses the Community Earth System Model Large Ensemble in conjunction with an advanced cyclone detection and tracking algorithm to assess how the AFZ, summer Arctic cyclone activity, and the relationship between them respond to warming under the representative concentration pathway 8.5 (RCP8.5) scenario. Under this strong warming scenario, the AFZ remains a significant cyclone intensifier. Changes to the AFZ are largely restricted to June, when earlier snowmelt leads to strengthening of land-ocean temperature contrasts. This strengthening is accompanied by enhanced cyclogenesis along the east Siberian coast, but no change is observed for overall cyclone frequency over the Arctic Ocean. However, simultaneous changes to subpolar storm tracks impact Arctic cyclone activity in all summer months, sometimes in opposition to the impact of the AFZ. In June, the storms migrating poleward to the Arctic Ocean become weaker under RCP8.5, leading to lower Arctic cyclone intensity. In July and August, the poleward shift of the North Pacific storm track enhances cyclone activity in the Beaufort and Chukchi Seas. [ABSTRACT FROM AUTHOR]

There is growing recognition that reductions in Arctic sea ice extent will influence patterns of atmospheric circulation both within and beyond the Arctic. We explore the impact of 2007 ice conditions (the second lowest Arctic sea ice extent in the satellite era) on atmospheric circulation and surface temperatures and fluxes through a series of model experiments with the NCAR Community Atmospheric Model version 3 ( CAM3). Two 30-year simulations were performed; one using climatological sea ice extent for the end of the 20th century and other using observed sea ice extent from 2007. Circulation differences over the Northern Hemisphere were most prominent during autumn and winter with lower sea level pressure ( SLP) and tropospheric pressure simulated over much of the Arctic for the 2007 sea ice experiment. The atmospheric response to 2007 ice conditions was much weaker during summer, with negative SLP anomalies simulated from Alaska across the Arctic to Greenland. Higher temperatures and larger surface fluxes to the atmosphere in areas of anomalous open water were also simulated. CAM3 experiment results were compared to observed SLP anomalies from the National Center for Environmental Prediction/National Center for Atmospheric Research ( NCEP/ NCAR) Reanalysis data. The observed SLP anomalies during spring are nearly opposite to those simulated. In summer, large differences were shown between the observed and simulated SLP also, suggesting that the sea ice conditions in the months preceding and during the summer of 2007 were not responsible for creating an atmospheric circulation pattern which favoured the large observed sea ice loss. The simulated and observed atmospheric circulation anomalies during autumn and winter were more similar than spring and summer, with the exception of a strong high pressure system in the Beaufort Sea which was not simulated, suggesting that the forced atmospheric response to reduced sea ice was in part responsible for the observed atmospheric circulation anomalies during autumn and winter. [ABSTRACT FROM AUTHOR]

Abstract: The past decade has seen substantial advances in understanding Arctic amplification — that trends and variability in surface air temperature tend to be larger in the Arctic region than for the Northern Hemisphere or globe as a whole. We provide a synthesis of research on Arctic amplification, starting with a historical context and then addressing recent insights into processes and key impacts, based on analysis of the instrumental record, modeling studies, and paleoclimate reconstructions. Arctic amplification is now recognized as an inherent characteristic of the global climate system, with multiple intertwined causes operating on a spectrum of spatial and temporal scales. These include, but are not limited to, changes in sea ice extent that impact heat fluxes between the ocean and the atmosphere, atmospheric and oceanic heat transports, cloud cover and water vapor that alter the longwave radiation flux to the surface, soot on snow and heightened black carbon aerosol concentrations. Strong warming over the Arctic Ocean during the past decade in autumn and winter, clearly associated with reduced sea ice extent, is but the most recent manifestation of the phenomenon. Indeed, periods of Arctic amplification are evident from analysis of both warm and cool periods over at least the past three million years. Arctic amplification being observed today is expected to become stronger in coming decades, invoking changes in atmospheric circulation, vegetation and the carbon cycle, with impacts both within and beyond the Arctic. [Copyright &y& Elsevier]

The article focuses on changes in arctic sea-ice. Satellite passive microwave (PMW) sensors are cited for estimating sea-ice extent and concentration. Difficulties in assessing uncertainties in sea-ice thickness estimates are explained together with major developments in modeling and the causes of biases in simulated sea-ice extent. The contribution of natural multi-year and decadal climate variability in the rapid decline of the Arctic ice extent and thickness is examined along with the need to develop strategies for optimizing regional projections.

Arctic sea ice mass budgets for the twentieth century and projected changes through the twenty-first century are assessed from 14 coupled global climate models. Large inter-model scatter in contemporary mass budgets is strongly related to variations in absorbed solar radiation, due in large part to differences in the surface albedo simulation. Over the twenty-first century, all models simulate a decrease in ice volume resulting from increased annual net melt (melt minus growth), partially compensated by reduced transport to lower latitudes. Despite this general agreement, the models vary considerably regarding the magnitude of ice volume loss and the relative roles of changing melt and growth in driving it. Projected changes in sea ice mass budgets depend in part on the initial (mid twentieth century) ice conditions; models with thicker initial ice generally exhibit larger volume losses. Pointing to the importance of evolving surface albedo and cloud properties, inter-model scatter in changing net ice melt is significantly related to changes in downwelling longwave and absorbed shortwave radiation. These factors, along with the simulated mean and spatial distribution of ice thickness, contribute to a large inter-model scatter in the projected onset of seasonally ice-free conditions. [ABSTRACT FROM AUTHOR]

ABSTRACT Calculations of a thermal front parameter using NCEP-NCAR reanalysis data over the period 1979-98 reveal a relative maximum in frontal frequencies during summer along northern Eurasia from about 60 degrees to 70 degrees N, best expressed over the eastern half of the continent. A similar relative maximum is found over Alaska, which is present year-round although best expressed in summer. These high-latitude features can be clearly distinguished from the polar frontal zone in the mid-latitudes of the Pacific basin and collectively resemble the summertime "Arctic frontal zone" discussed in several early studies. While some separation between high- and midlatitude frontal activity is observed in all seasons, the summer season is distinguished by the development of an attendant mean baroclinic zone aligned roughly along the Arctic Ocean coastline and associated wind maxima in the upper troposphere. The regions of maximum summer frontal frequency correspond to preferred areas of cyclogenesis and to where the summertime contribution to annual precipitation is most dominant. Cyclones generated in association with the Eurasian frontal zone often track into the central Arctic Ocean, where they may have an impact on the sea-ice circulation. Development of the summertime Eurasian frontal zone and the summertime strengthening of the Alaskan feature appear to be largely driven by differential heating between the cold Arctic Ocean and warm snow-free land. Frontal activity also shows an association with orography. Several studies have argued that the location of the summer Arctic frontal zone may be in part determined by discontinuities in energy exchange along... [ABSTRACT FROM AUTHOR]

An improved monthly precipitation climatology for the Arctic is developed by blending the Legates and Willmott gridded product with measurements from Russian "North Pole" drifting stations and gauge-corrected station data for Eurasia and Canada. The improved climatology is used to examine the accuracy of mean precipitation forecasts from the National Centers for Environmental Prediction (NCEP) and European Reanalysis Agency (ERA) reanalysis models, based on data for the period 1979--88. Both models capture the major spatial features of annual mean precipitation and general aspects of the seasonal cycle but with some notable errors. Both underestimate precipitation over the Atlantic side of the Arctic. NCEP overestimates annual totals over land areas and to a somewhat lesser extent over the central Arctic Ocean. Except for the North Atlantic-- Scandinavia sector, the NCEP model also depicts the seasonal precipitation maximum consistently one month early in July. Overall, the ERA predictions are better. Both models perform best during winter and worst during summer. The most significant problem with the NCEP model is a severe oversimulation of summer precipitation over land areas, due to excessive convective precipitation. Further investigation for July reveals that both the NCEP analyses and 12-h forecasts are too wet below about 850 mb and have more negative low-level temperature gradients as compared to available rawinsonde profiles. This suggests that low-level observations are not being effectively incorporated in the analyses. Given this finding, the high humidities are consistent with excessive surface evaporation rates. This problem may in turn relate to soil moisture, which NCEP updates by the modeled precipitation. If soil moisture is too high, this would favor excessive evaporation and high low-level humidities, fostering excessive precipitation, in turn keeping soil moisture and evaporation rates high. The NCEP down-welling shortwave... [ABSTRACT FROM AUTHOR]

Measurements from the Russian "North Pole" series of drifting stations, the United States drifting stations "T-3" and "Arlis II," land stations, and, where necessary, over the northern North Atlantic and coastal Greenland, empirically derived values from earlier Russian studies are used to compile a new gridded monthly climatology of global (downwelling shortwave) radiation for the region north of 658N. Spatio-temporal patterns of fluxes and effective cloud transmittance are examined and comparisons are made with fields from the National Centers for Environmental Prediction--National Center for Atmospheric Research (NCEP--NCAR) reanalysis and those derived from the International Satellite Cloud Climatology Project (ISCCP) C2 (monthly) cloud product. All months examined (March--October) show peak fluxes over the Greenland ice sheet. March, September, and October feature a strong zonal component. Other months exhibit an asymmetric pattern related to cloud fraction and optical depth, manifested by an Atlantic side flux minimum. For June, the month of maximum insolation, fluxes increase from less than 200 W m 22 in the Norwegian and Barents seas to more than 300 W m 22 over the Pacific side of central Arctic Ocean extending into the Beaufort Sea. June fluxes of more than 340 W m 22 are found over the Greenland ice sheet. Effective cloud transmittance, taken as the ratio of the observed flux to the modeled clear sky flux, is examined for April--September. Values for the Atlantic sector range from 0.50--0.60, contrasting with the central Arctic Ocean where values peak in April at 0.75--0.80, falling to 0.60-- 0.65 during late summer and early autumn. A relative Beaufort Sea maximum is well expressed during June. The NCEP--NCAR and ISCCP products capture 50%--60% of the observed spatial variance in global radiation during most months. However, the NCEP--fluxes are consistently high, with Arctic Ocean errors in excess of 60 W m 22 during summer, reflect. [ABSTRACT FROM AUTHOR]

September Arctic sea ice extent over the period of satellite observations has a strong downward trend, accompanied by pronounced interannual variability with a detrended 1 year lag autocorrelation of essentially zero. We argue that through a combination of thinning and associated processes related to a warming climate (a stronger albedo feedback, a longer melt season, the lack of especially cold winters) the downward trend itself is steepening. The lack of autocorrelation manifests both the inherent large variability in summer atmospheric circulation patterns and that oceanic heat loss in winter acts as a negative (stabilizing) feedback, albeit insufficient to counter the steepening trend. These findings have implications for seasonal ice forecasting. In particular, while advances in observing sea ice thickness and assimilating thickness into coupled forecast systems have improved forecast skill, there remains an inherent limit to predictability owing to the largely chaotic nature of atmospheric variability. [ABSTRACT FROM AUTHOR]

Abstract: Arctic amplification, the observation that surface air temperature changes in the Arctic exceed those of the Northern Hemisphere as a whole, is a pervasive feature of climate models, and has recently emerged in observational data relative to the warming trend of the past century. The magnitude of Arctic amplification is an important, but poorly constrained variable necessary to estimate global average temperature change over the next century. Here we evaluate the mechanisms responsible for Arctic amplification on Quaternary timescales, and review evidence from four intervals in the past 3 Ma for which sufficient paleoclimate data and model simulations are available to estimate the magnitude of Arctic amplification under climate states both warmer and colder than present. Despite differences in forcings and feedbacks for these reconstructions compared to today, the Arctic temperature change consistently exceeds the Northern Hemisphere average by a factor of 3–4, suggesting that Arctic warming will continue to greatly exceed the global average over the coming century, with concomitant reductions in terrestrial ice masses and, consequently, an increasing rate of sea level rise. [Copyright &y& Elsevier]

As assessed over the period of satellite observations, October 1978 to present, there are downward linear trends in Arctic sea ice extent for all months, largest at the end of the melt season in September. The ice cover is also thinning. Downward trends in extent and thickness have been accompanied by pronounced interannual and multiyear variability, forced by both the atmosphere and ocean. As the ice thins, its response to atmospheric and oceanic forcing may be changing. In support of a busier Arctic, there is a growing need to predict ice conditions on a variety of time and space scales. A major challenge to providing seasonal scale predictions is the 7-10 days limit of numerical weather prediction. While a seasonally ice-free Arctic Ocean is likely well within this century, there is much uncertainty in the timing. This reflects differences in climate model structure, the unknown evolution of anthropogenic forcing, and natural climate variability. In sharp contrast to the Arctic, Antarctic sea ice extent, while highly variable, has increased slightly over the period of satellite observations. The reasons for this different behavior remain to be resolved, but responses to changing atmospheric circulation patterns appear to play a strong role., (© 2018 New York Academy of Sciences.)