The Spring Transition of the North Pacific Jet and its Relation to Deep Stratosphere-to-Troposphere Mass Transport over Western North America

Breeden, Melissa L.; Butler, Amy H.; Albers, John R.; Sprenger, Michael; Langford, A. O.

doi:10.5194/acp-2020-604

Cited by 6 publications

(12 citation statements)

References 31 publications

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“…in stratosphere-troposphere coupling in austral spring. Consideration of the timing of the FSW in both hemispheres may be important for how much stratospheric ozone is transported via deep stratospheric intrusions to the surface in spring (Albers et al, 2018;Breeden et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

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Butler

2021

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Every spring, the stratospheric polar vortex transitions from its westerly wintertime state to its easterly summertime state due to seasonal changes in incoming solar radiation, an event known as the "final stratospheric warming" (FSW). While FSWs tend to be less abrupt than reversals of the boreal polar vortex in midwinter, known as sudden stratospheric warming (SSW) events, their timing and characteristics can be significantly modulated by atmospheric planetary-scale waves. Just like SSWs, FSWs have been found to have predictable surface impacts. While SSWs are commonly classified according to their wave geometry, either by how the vortex evolves (whether the vortex displaces off the pole or splits into two vortices) or by the dominant wavenumber of the vortex just prior to the SSW (wave-1 versus wave-2), little is known about the wave geometry of FSW events. We here show that FSW events for both hemispheres in most cases exhibit a clear wave geometry. Most FSWs can be classified into wave-1 or wave-2 events, but wave-3 also plays a significant role in both hemispheres. Additionally, we find that in the Northern Hemisphere, wave-2 events are more likely to occur later in the spring, while in the Southern Hemisphere, wave-1 or wave-2 events show no clear preference in timing. The FSW enhances total column ozone over the pole of both hemispheres during spring, but the spatial distribution of ozone anomalies can be influenced by the wave geometry and the timing of the event. We also describe the stratosphere's downward influence on surface weather following wave-1 and wave-2 FSW events. Significant differences between the tropospheric response to wave-1 and wave-2 FSW events occur over North America and over the Southern Ocean, while no significant differences are found over the North Atlantic region, Europe, and Antarctica. IntroductionThe polar stratosphere exhibits a distinct seasonal cycle featuring a wintertime polar vortex, that is, strong circumpolar westerly winds that form in late summer and decay the following spring, which is ultimately due to the seasonal cycle of incoming solar radiation. While the formation of the polar vortex occurs very predictably each year in late summer of both hemispheres (late August in the Northern and mid-February in the Southern Hemisphere), the timing of the spring weakening of the vortex, the so-called final stratospheric warming (FSW) event, is more variable (Black et al., 2006;Black and McDaniel, 2007a). The FSW marks the reversal of the climatological winter westerlies to summer easterlies in the stratosphere, and its timing varies 1

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Section: Discussionmentioning

confidence: 99%

Response to reviewers

Butler

2021

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“…5 and Supplement S5). This implies that the transport anomalies outlined next are more predictable, and hence the composites more heavily weighted, for the periods before the jet undergoes its spring transition (Newman and Sardeshmukh 1998;Breeden et al 2020).…”

Section: Potential Predictability Of Jet Shifts and Transportmentioning

confidence: 98%

“…That the STTPBL is weaker is not entirely surprising because while a high percentage of upper level breaking waves extend downwards to the mid-to upper troposphere, subsequently causing associated STT500 and TME, only a small subset of these waves will achieve the needed amplitude and depth to extend all the way to the PBL. Moreover, transport to the STTPBL is also dependent on the depth of the PBL, which tends to be relatively shallow until late spring to early summer when convective heating begins to increase (Seidel et al 2012;Škerlak et al 2014;Breeden et al 2020). Nevertheless, all of the composites provide a basis for the expectation that Pacific jet variability can be used as a predictor for transport over landmasses of interest, including the western United States, southern Alaska, and Japan.…”

Section: Retrospective Analysismentioning

confidence: 99%

“…This means that the variability, and as we will show, the predictability, of both types of transport are dependent on the seasonal cycle of the Pacific jet. Sometime between early March and late April, the Pacific jet undergoes a transitionwhich typically occurs very abruptlyfrom being strong and largely zonally contiguous between Asia and North America to being weak, with a discontinuity in the jet that spans most of the Pacific basin (Nakamura 1992;Newman and Sardeshmukh1998;Hoskins and Hodges 2019;Breeden et al 2020). The characteristics of this transition, and its relationship to forms of low-frequency variability that might be predictable on subseasonal timescales (e.g., ENSO) have been explored in the context of STT of mass and ozone.…”

mentioning

confidence: 99%

“…The characteristics of this transition, and its relationship to forms of low-frequency variability that might be predictable on subseasonal timescales (e.g., ENSO) have been explored in the context of STT of mass and ozone. For example, Breeden et al 2020 demonstrated that early season jet transitions (mid-to-late March), which are more common during La Niña conditions, are characterized by enhanced mass transport to the PBL (see also, Lin et al 2015 and references therein).…”

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Subseasonal prediction of springtime Pacific-North American transport using upper-level wind forecasts

Albers¹,

Butler²,

Breeden³

et al. 2020

Preprint

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Abstract. Forecasts of Pacific jet variability are used to predict stratosphere-to-troposphere transport (STT) and tropical-to-extratropical moisture exports (TME) during boreal spring over the Pacific-North American region. A retrospective analysis first documents the regionality of STT and TME for different Pacific jet patterns. Using these results as a guide, Pacific jet hindcasts, based on zonal-wind forecasts from the European Centre for Medium-Range Weather Forecasting Integrated Forecasting System, are utilized to test whether STT and TME over specific geographic regions may be predictable for subseasonal forecast leads (3–6 weeks ahead of time). Large anomalies in STT to the mid-troposphere over the North Pacific, TME to the west coast of the United States, and TME over Japan are found to have the best potential for subseasonal predictability using upper-level wind forecasts. STT to the planetary boundary layer over the intermountain west of the United States is also potentially predictable for subseasonal leads, but likely only in the context of shifts in the probability of extreme events. While STT and TME forecasts match verifications quite well in terms of spatial structure and anomaly sign, the number of anomalous transport days is underestimated compared to observations. The underestimation of the number of anomalous transport days exhibits a strong seasonal cycle, which becomes progressively worse as spring progresses into summer.

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What's in a Name? On the Use and Significance of the Term “Polar Vortex”

Manney

Butler

Lawrence

et al. 2022

Geophysical Research Letters

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This commentary appears in the Special Collection focusing on the Arctic stratospheric "polar vortex" in 2019/2020. But how clear are we about what constitutes a "polar vortex"? Confusion persists in the popular press about what a polar vortex is and how polar vortices relate to extreme weather events. This confusion stems in part from imprecise descriptions by the scientific community.In January 2014, a cold air outbreak (CAO) set record-low minimum temperatures throughout the south central and eastern US (e.g., Screen et al., 2015). Headlines hailed it as "the polar vortex," and this language became commonplace in news and popular science media. At the time, the term "polar vortex" in scientific literature typically described the stratospheric polar vortex (see, e.g., Lillo et al., 2021;Waugh et al., 2017, for discussion of this), but some studies used the term to describe the "tropospheric polar vortex" (e.g., Wallace et al., 2014;Yu & Zhang, 2015), in both cases often without further qualification. Waugh et al. (2017) sought to dispel confusion, describing the stratospheric and tropospheric "circumpolar" vortices as these terms had been commonly used in scientific literature, highlighting their differences and relationships to extreme weather events, and providing recommendations for describing them. While this work is widely cited, the two concepts are still often confused, including on educational websites and in climate change communication studies (e.g.,

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The Spring Transition of the North Pacific Jet and its Relation to Deep Stratosphere-to-Troposphere Mass Transport over Western North America

Cited by 6 publications

References 31 publications

Response to reviewers

Response to reviewers

Subseasonal prediction of springtime Pacific-North American transport using upper-level wind forecasts

What's in a Name? On the Use and Significance of the Term “Polar Vortex”

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