Historical trends of seasonal Greenland blocking under different blocking metrics
Historical trends of seasonal Greenland blocking under different blocking metrics
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DOI：
10.1002/joc.6923
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发表时间：
2020-11
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影响因子：
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通讯作者：
L. Wachowicz;J. Preece;T. Mote;B. Barrett;G. Henderson
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文献类型：
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作者：
L. Wachowicz;J. Preece;T. Mote;B. Barrett;G. Henderson
随着北极持续变暖，对流层上部西风减弱被假设为诱导弯曲急流和罗斯贝波传播较慢。因此，目前的假设表明，由于高振幅波的平稳性增加，格陵兰岛阻塞增加。这些假设得到了格陵兰阻塞指数（GBI）的观测支持。然而，考虑到整体位势高度的预期增加对应于该地区气温的升高，我们评估了格陵兰岛阻塞趋势的稳健性，除了GBI之外，还使用了其他阻塞指标，GBI在很大程度上是该地区迄今为止的重点阻塞指标。我们的研究结果表明，基于GBI的阻塞增加对全球和纬向平均500 hPa位势高度的敏感性，这导致与其他阻塞指标相比，1979-2018年期间的增加趋势不一致。GBI的季节性阻塞频率显示JJA的阻塞显著增加，尽管大多数指标没有显著的JJA阻塞趋势。其他指标表明，阻塞频率在9月至11月（SON）和12月至2月（DJF）下降，尽管这些趋势在统计上并不显著。然而，当使用5年运行平均值进行平滑时，这些其他指标表明DJF和JJA阻滞增加，仅SON阻滞减少，这与GBI显著变化的结果一致。我们报告没有最好的指标来识别格陵兰岛阻塞。相反，我们提出了在这项研究中使用的不同指标的一些缺点。这些结果为未来的研究提供了对格陵兰阻塞事件的选择，因为阻塞活动的高估或低估可能会影响冰盖表面质量平衡的估计。
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 under‐estimation of blocking activity can impact estimates of surface mass balance of the ice sheet.