Examining the Relationship between Tropopause Polar Vortices and Tornado Outbreaks
Examining the Relationship between Tropopause Polar Vortices and Tornado Outbreaks
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DOI：
10.1175/waf-d-21-0058.1
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发表时间：
2021-10-01
影响因子：
2.9
通讯作者：
Bluestein, Howard B.
中科院分区：
文献类型：
--
作者：
Bray, Matthew T.;Cavallo, Steven M.;Bluestein, Howard B.
众所周知，中纬度急流条纹会产生广泛支持龙卷风爆发的条件，包括迫使大规模上升、增加风切变和降低静态稳定性。尽管许多过程可能会引发急流条纹，但我们在这里重点关注极地急流和对流层顶极地涡流（TPV）之间相互作用所产生的急流极大值。 TPV 源自北极，是对流层顶的长期环流，可以平流进入中纬度地区。我们假设，假设存在其他支持龙卷风发展的环境条件，当这些涡流与射流相互作用时，它们可能会为龙卷风爆发提供上升和切变的补充强迫。通过使用俄克拉荷马州、伊利诺伊州和阿拉巴马州这三个州的一组严重龙卷风爆发日的案例，我们发现大约三分之二的龙卷风爆发中存在涡流喷射条纹结构（1250 公里内）。这些涡旋通常起源于北极（即 TPV），并在爆发前一周通过平流进入中纬度地区，穿过北太平洋进入阿拉斯加湾，然后沿着北美海岸转向赤道。这些漩涡比平均水平更强烈、寿命更长。我们进一步证明，在天气尺度上，爆发区域存在统计上显着的风切变、准地转上升强迫和低静态稳定性模式。此外，我们发现与龙卷风事件相关的 TPV 最常发生在春季，并且与非龙卷风 TPV 案例相比，与更大的低水平湿度相关。 意义声明 美国的龙卷风爆发有可能造成重大生命和财产损失。为了确保有足够的准备时间并最大限度地减少这些损失，在这些事件发生之前对其进行预测至关重要；然而，目前很难提前几天预测龙卷风的爆发。这项工作调查了对流层顶极涡 (TPV) 等大气特征与美国龙卷风爆发之间的潜在联系。由于其物理特性，TPV 有可能提前几周进行预测。尽管需要进一步的工作来证实这种联系，但我们的研究结果可以为未来龙卷风爆发的长期预测提供工具。
Midlatitude jet streaks are known to produce conditions broadly supportive of tornado outbreaks, including forcing for large-scale ascent, increased wind shear, and decreased static stability. Although many processes may initiate a jet streak, we focus here on the development of jet maxima by interactions between the polar jet and tropopause polar vortices (TPVs). Originating from the Arctic, TPVs are long-lived circulations on the tropopause, which can be advected into the midlatitudes. We hypothesize that when these vortices interact with the jet, they may contribute supplemental forcing for ascent and shear to tornado outbreaks, assuming other environmental conditions supportive of tornado development exist. Using a case set of significant tornado outbreak days from three states-Oklahoma, Illinois, and Alabama-we show that a vortex-jet streak structure is present (within 1250 km) in around two-thirds of tornado outbreaks. These vortices are commonly Arctic in origin (i.e., are TPVs) and are advected through a consistent path of entry into the midlatitudes in the week before the outbreak, moving across the northern Pacific and into the Gulf of Alaska before turning equatorward along the North American coast. These vortices are shown to be more intense and longer-lived than average. We further demonstrate that statistically significant patterns of wind shear, quasigeostrophic forcing for ascent, and low static stability are present over the outbreak regions on the synoptic scale. In addition, we find that TPVs associated with tornadic events occur most often in the spring and are associated with greater low-level moisture when compared to non-tornadic TPV cases.SIGNIFICANCE STATEMENt Tornado outbreaks over the United States have the potential to cause significant loss of life and property. To ensure adequate preparation time and minimize these losses, forecasting these events well before their occurrence is essential; however, it is currently difficult to predict tornado outbreaks more than a few days in advance. This work investigates a potential connection between atmospheric features known as tropopause polar vortices (TPVs) and tornado outbreaks in the United States. Due to their physical characteristics, TPVs have the potential to be forecasted up to weeks in advance. Although further work will be needed to confirm this link, our findings could provide a tool for long-term prediction of future tornado outbreaks.