As the Arctic continues to warm, a weakening of upper-tropospheric westerly winds is hypothesized to induce a meandering jet stream and slower propagation of Rossby waves. As such, current hypotheses suggest an increase in Greenland blocking due to increased stationarity of the high amplitude waves. These hypotheses have been supported observationally with the Greenland blocking index (GBI). However, given an expected increase in overall geopotential heights corresponding to increased temperatures in the region, we assess the robustness of trends in Greenland blocking using additional blocking metrics in addition to the GBI, which has largely been the focused blocking metric for this region to date. Our results show sensitivity of the GBI-based increases in blocking to global and zonally averaged 500-hPa geopotential heights, which results in inconsistent increasing trends over the 1979-2018 period when compared with other blocking metrics. Seasonal blocking frequencies of the GBI show a significant increase in blocking for JJA, though no significant trend in JJA blocking occurs for most metrics. Other indices suggest a decrease in blocking frequency in September-November (SON) and December-February (DJF), though these trends are not statistically significant. Yet, when smoothed using a 5-year running mean, these other metrics suggest an increase in both DJF and JJA blocking with a decrease only in SON blocking, which are consistent with findings of significant changes in GBI. We report no best metric for identifying Greenland blocking. Instead, we present some shortcomings of the different metrics used in this study. These results provide insight into selection of Greenland blocking events for future research, as over-or underestimation of blocking activity can impact estimates of surface mass balance of the ice sheet.

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Arctic Amplification is a fundamental feature of past, present, and modelled future climate. However, the causes of this “amplification” within Earth’s climate system are not fully understood. To date, warming in the Arctic has been most pronounced in autumn and winter seasons, with this trend predicted to continue based on model projections of future climate. Nevertheless, the mechanisms by which this will take place are numerous, interconnected. and complex. Will future Arctic Amplification be primarily driven by local, within-Arctic processes, or will external forces play a greater role in contributing to changing climate in this region? Motivated by this uncertainty in future Arctic climate, this review seeks to evaluate several of the key atmospheric circulation processes important to the ongoing discussion of Arctic amplification, focusing primarily on processes in the troposphere. Both local and remote drivers of Arctic amplification are considered, with specific focus given to high-latitude atmospheric blocking, poleward moisture transport, and tropical-high latitude subseasonal teleconnections. Impacts of circulation variability and moisture transport on sea ice, ice sheet surface mass balance, snow cover, and other surface cryospheric variables are reviewed and discussed. The future evolution of Arctic amplification is discussed in terms of projected future trends in atmospheric blocking and moisture transport and their coupling with the cryosphere. As high-latitude atmospheric circulation is strongly influenced by lower-latitude processes, the future state of tropical-to-Arctic teleconnections is also considered.

The increase in Greenland Ice Sheet (GrIS) surface runoff since the turn of the century has been linked to a rise in Greenland blocking frequency. However, a range of synoptic patterns can be considered blocked flow and efforts that summarize all blocking types indiscriminately likely fail to capture consequential differences in GrIS response. To account for these differences, we employ ERA5 reanalysis to identify summer blocking using two independent blocking metrics: the Greenland Blocking Index (GBI) and the blocking index of Pelly and Hoskins (2003, https://doi.org/10.1175/1520-0469(2003)060%3c0743:ANPOB%3e2.0.CO;2). We then conduct a self‐organizing map analysis to objectively classify synoptic conditions during Greenland blocking episodes and identify three primary blocking types: (a) a high‐amplitude Omega block, (b) a lower‐amplitude, stationary summer ridge, and (c) a cyclonic wave breaking pattern. Using Modèle Atmosphérique Régional output, we document the spatiotemporal progression of the surface energy and mass balance for each blocking type. Relative to all blocking episodes, summer ridge patterns produce more melt over the southern ice sheet, Omega blocks produce more melt across the northern ice sheet, and cyclonic wave breaking patterns produce more melt in northeast Greenland. Our results indicate that the recent trend in summer Greenland blocking was largely driven by an increase in Omega patterns and suggest that Omega blocks have played a central role in the recent acceleration of GrIS mass loss. Furthermore, the GBI exhibited a relative bias toward Omega patterns, which may help explain why it has measured stronger trends in summer Greenland blocking than other blocking metrics.

The exceptional atmospheric conditions that have accelerated Greenland Ice Sheet mass loss in recent decades have been repeatedly recognized as a possible dynamical response to Arctic amplification. Here, we present evidence of two potentially synergistic mechanisms linking high-latitude warming to the observed increase in Greenland blocking. Consistent with a prominent hypothesis associating Arctic amplification and persistent weather extremes, we show that the summer atmospheric circulation over the North Atlantic has become wavier and link this wavier flow to more prevalent Greenland blocking. While a concomitant decline in terrestrial snow cover has likely contributed to this mechanism by further amplifying warming at high latitudes, we also show that there is a direct stationary Rossby wave response to low spring North American snow cover that enforces an anomalous anticyclone over Greenland, thus helping to anchor the ridge over Greenland in this wavier atmospheric state.