What's in a name? On the use and significance of the term “polar

manuscript submitted to Geophysical Research Letters

What’s in a name? On the use and signiﬁcance of the1

term “polar vortex”2

Gloria L. Manney

1,2

, Amy H. Butler

, Zachary D. Lawrence

4,5,6

, Krzysztof3

Wargan

7,8

, Michelle L. Santee

NorthWest Research Associates, Socorro, NM, USA5

New Mexico Institute of Mining and Technology, Socorro, NM, USA6

NOAA Chemical Sciences Laboratory, Boulder, CO, USA7

Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA8

NOAA Physical Sciences Laboratory, Boulder, CO, USA9

NorthWest Research Associates, Boulder, CO, USA10

NASA Goddard Space Flight Center, Greenbelt, MD, USA11

Science Systems and Applications, Inc., Lanham, MD, USA12

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA13

Key Points:14

•

The stratospheric polar vortex is a well-deﬁned feature dominating the cool-season15

circulation in each hemisphere from ∼15–50 km altitude16

•

The tropospheric circulation does not constitute a single coherent structure and17

is most aptly described by regional jet stream variations18

•

Accuracy in deﬁning and describing “the polar vortex” and its eﬀects is key to im-19

proving understanding by non-specialist audiences20

Corresponding author: Gloria L. Manney, [email protected]

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manuscript submitted to Geophysical Research Letters

Abstract21

Mainstream and popular science media are rife with misunderstandings about what a22

“polar vortex” is. The term most aptly describes the stratospheric polar vortex, a sin-23

gle feature dominating the cool-season circulation from ∼15–50 km. Regional jet stream24

variations dominate the tropospheric circulation, which is not well-described as a polar25

vortex; indeed, there is no single consistent deﬁnition of a tropospheric polar vortex in26

the literature. Stratospheric polar vortex disturbances profoundly inﬂuence extreme weather27

events, including cold air outbreaks (CAOs). How the stratospheric polar vortex aﬀects28

tropospheric jets, whose local excursions drive CAOs, is not fully understood. Public-29

facing parts of publications describing research on this topic are not always clear about30

how the “polar vortex” is deﬁned; greater clarity could improve communications both31

within the community and with non-specialist audiences.32

Plain Language Summary33

What is a “polar vortex”? The atmospheric science community most commonly34

uses this term to describe the stratospheric polar vortex, a band of winds extending from35

about 15 to 50 km altitude that ﬂows around the pole of each hemisphere during their36

respective fall through spring seasons. However, the term “polar vortex” has been used37

in mainstream media and popular science platforms to instead describe local variations38

in the upper tropospheric jet streams (winds that blow most strongly between about 839

and 13 km altitude) and even individual extreme cold weather events. We argue that the40

term should be used only in reference to the stratospheric polar vortex, which is a sin-41

gle feature that predominantly controls dynamical and chemical variability in the win-42

ter polar stratosphere. The stratospheric polar vortex is related to but distinct from more43

regional jet stream excursions and associated weather extremes; further study is needed44

to fully understand these relationships.45

1 The stratospheric polar vortex, tropospheric jet streams, and cold46

air outbreaks47

This commentary appears in the Special Collection focusing on the Arctic strato-48

spheric “polar vortex” in 2019/2020. But how clear are we about what constitutes a “po-49

lar vortex”? Confusion persists in the popular press about what a polar vortex is and50

how they relate to extreme weather events. This confusion stems in part from impre-51

cise descriptions by the scientiﬁc community.52

In January 2014, a cold air outbreak (CAO) set record-low minimum temperatures53

throughout the south central and eastern US (e.g., Screen et al., 2015). Headlines hailed54

it as “the polar vortex”, and this language became commonplace in news and popular55

science media. At the time, the term “polar vortex” in scientiﬁc literature typically de-56

scribed the stratospheric polar vortex (see, e.g., Waugh et al., 2017; Lillo et al., 2021,57

for discussion of this), but some studies used the term to describe the “tropospheric po-58

lar vortex” (e.g., Wallace et al., 2014; Yu & Zhang, 2015), in both cases often without59

further qualiﬁcation. Waugh et al. (2017) sought to dispel confusion, describing the strato-60

spheric and tropospheric “circumpolar” vortices as these terms had been commonly used61

in scientiﬁc literature, highlighting their diﬀerences and relationships to extreme weather62

events, and providing recommendations for describing them. While this work is widely63

cited, the two concepts are still often confused, including on educational websites and64

in climate change communication studies (e.g., Shepherd, 2016; Lyons et al., 2018; UC-65

Davis, 2019; UCAR, 2021). Even recent papers within the atmospheric science commu-66

nity are not always clear about which circulation feature(s) they are discussing, and some67

use the term “polar vortex” to describe synoptic-scale disturbances associated with CAOs,68

echoing the inaccurate usage in popular media (e.g., Bushra & Rohli, 2019, 2021; Over-69

land & Wang, 2019; Dai et al., 2021; Jiang, 2021; Juzbaˇsi´c et al., 2021; K¨om¨u¸sc¨u & O˘guz,70

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manuscript submitted to Geophysical Research Letters

2021; Nielsen-Gammon et al., 2021; Overland, 2021; Zhang et al., 2021; Xiong et al., 2021).71

Sometimes the most public-facing parts of research papers (abstracts, plain language sum-72

maries, key points) do not clearly deﬁne how the term “polar vortex” is used.73

Figure 1 shows characteristics of the stratospheric and tropospheric circulation on74

two occasions the popular press described CAOs as a polar vortex “outbreak” or “at-75

tack”, but which were associated with very diﬀerent stratospheric polar vortex condi-76

tions. This ﬁgure shows the stratospheric polar vortex, upper tropospheric jet streams,77

and the circulation that is sometimes described as a “tropospheric polar vortex” (i.e.,78

the 2 and 3 PVU potential vorticity contours on the 330-K isentropic surface, one pos-79

sible deﬁnition discussed by Waugh et al., 2017).80

The stratospheric polar vortex is bounded by the polar night jet, a band of strong81

eastward winds throughout the stratosphere that forms in fall in each hemisphere and82

vanishes in spring. Diﬀerent diagnostics of the stratospheric polar vortex edge (e.g., Lawrence83

& Manney, 2018) select similar physically meaningful boundaries (Fig. 1a, left, deﬁned84

using a potential vorticity contour coincident with the strongest potential vorticity gra-85

dients, as in Lawrence et al. (2018)). The stratospheric polar vortex constitutes a sin-86

gle feature that dominates the circulation and transport throughout the polar stratosphere87

from fall through spring.88

The so-called “tropospheric polar vortex”, as most often deﬁned, exists year-round,89

but no single deﬁnition uniquely identiﬁes it or the altitude(s) at which it exists (the char-90

acteristics described herein do not depend substantially on which of numerous deﬁnitions91

is used). We show one common deﬁnition (Waugh et al., 2017, and references therein)92

whereby its edge follows the axis of an upper tropospheric jet on an isentropic surface93

in the middle to upper troposphere. The maximum winds of these jets are very local-94

ized in altitude compared to the stratospheric polar night jet, and they vary strongly with95

longitude (e.g., Manney, Hegglin, et al., 2011; Manney et al., 2014, Fig. 1a). Because re-96

gional variability of discontinuous jet streams governs the extratropical tropospheric cir-97

culation, “tropospheric polar vortex” deﬁnitions do not describe a single dominant cir-98

cumpolar circulation. Further confusion arises from the distinction between tropospheric99

“polar” (primarily eddy driven) and “subtropical” (largely radiatively driven) jets. While100

some recent papers and popular science pieces identify the “tropospheric polar vortex”101

with the tropospheric polar jet (e.g., Waugh et al., 2017; Bushra & Rohli, 2021; UCAR,102

2021), numerous studies show that tropospheric jets are not well-represented by this sim-103

pliﬁed conceptual division but rather form a seasonally and regionally varying complex104

with hybrid radiatively and eddy-driven features that is rarely continuous around the105

globe (S. Lee & Kim, 2003; Manney et al., 2014; Spensberger & Spengler, 2020, and ref-106

erences therein).107

These diﬀerences are reﬂected in windspeeds (Fig. 1a,b), which peak sharply along108

the stratospheric polar vortex edge; in contrast, a “tropospheric polar vortex” deﬁned109

as noted above meanders through regions of weak and strong winds, leading to a broad,110

ﬂat distribution of “vortex-edge” windspeeds. Potential vorticity gradients (indicating111

polar vortex strength) are consistently strong along the circumference of the stratospheric112

polar vortex but have many localized maxima in small portions of the “tropospheric vor-113

tex” edge and elsewhere in the extratropics (Figure 1c). This results in relatively stronger114

mean potential vorticity gradients along the stratospheric vortex edge, versus weaker mean115

potential vorticity gradients and most frequent values near zero in the troposphere (Fig. 1d).116

Further, tropospheric windspeeds (Fig. 1a) often show a single jet (or no strong jet) be-117

cause separate tropospheric polar and subtropical jets do not always exist. A “tropo-118

spheric polar vortex” might therefore follow the polar jet in one region but the subtrop-119

ical jet in another, thus traversing regimes controlled by diﬀerent dynamical processes.120

The stratospheric polar vortex is critical for transport, chemical processing, con-121

ﬁnement of processed air, and ozone loss. Processes promoting ozone depletion are com-122

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monly analyzed from a vortex-centered perspective because the stratospheric vortex rep-123

resents a strong transport barrier, isolating air primed for ozone destruction (e.g., Schoe-124

berl et al., 1992; Manney, Santee, et al., 2011; Manney et al., 2020); the amount of po-125

lar ozone loss in a given spring depends critically on the strength and coldness of the win-126

ter/spring stratospheric polar vortex. In contrast, upper tropospheric ozone variability127

is dominated by regional variations in stratosphere-troposphere exchange and the amount128

of lower stratospheric ozone available for transport into the troposphere (e.g., Albers et129

al., 2018; Olsen et al., 2019; Breeden et al., 2021). Figures 1e and 1f illustrate these dif-130

ferences: Ozone gradients change abruptly across the stratospheric polar vortex edge but131

are quite uniform within it. In contrast, ozone gradients are strong in many localized re-132

gions within the “tropospheric polar vortex”, with highly variable gradients often ap-133

pearing well poleward of the “vortex” edge. These characteristics are reﬂected in sharply-134

peaked ozone distributions along the stratospheric polar vortex edge, and large variabil-135

ity in ozone along the “tropospheric vortex” edge (Fig. 1f). Note that the broad change136

from uniform gradients to highly variable gradients across the “tropospheric vortex edge”137

as deﬁned here is a reﬂection of vertical ozone gradients and the tilt of the 330 K isen-138

tropic surface in the subtropics.139

Stratosphere-troposphere coupling (e.g., Baldwin & Dunkerton, 2001; Kidston et140

al., 2015) dynamically links variability of the polar vortex to extremes at the surface (e.g.,141

Domeisen & Butler, 2020). For example, extreme stratospheric polar vortex disruptions142

(sudden stratospheric warmings, SSWs) are associated with increased risk of mid-latitude143

CAOs (e.g., Butler et al., 2017; King et al., 2019; Baldwin et al., 2021; Huang et al., 2021),144

and unusually strong stratospheric polar vortices are associated with anomalously high145

extratropical surface temperatures (including heat waves and destructive wildﬁres) (Limpasuvan146

et al., 2005; Lawrence et al., 2020; Overland & Wang, 2021). Because radiative timescales147

are longer in the lower stratosphere, disruptions to the circulation can persist there for148

weeks to months, potentially providing subseasonal-to-seasonal forecast skill for extremes149

like CAOs (e.g., Domeisen et al., 2019). Using information about the stratospheric po-150

lar vortex to predict CAOs is, however, complicated because the timing and location of151

individual CAOs varies signiﬁcantly following polar vortex disruptions, perhaps related152

to details of the stratospheric polar vortex characteristics and evolution. Recent work153

suggests that Eurasian CAOs are more closely linked to SSWs, while North American154

CAOs are more strongly associated with stratospheric polar vortex elongation that might155

or might not accompany an SSW (e.g., Kretschmer et al., 2018; S. H. Lee et al., 2019;156

Cohen, Agel, Barlow, Garﬁnkel, & White, 2021). It is worth emphasizing that CAOs can157

occur during both strong and weak stratospheric polar vortex conditions (e.g., S. H. Lee158

et al., 2019; Cohen, Agel, Barlow, Furtado, et al., 2021): Figure 1 shows a CAO (Jan-159

uary 2014) linked to a strong (but distorted) stratospheric vortex and one (February 2021)160

following an SSW.161

CAOs are often termed “polar vortex events” in the news, popular science media,162

and less specialized peer-reviewed papers (e.g., Lyons et al., 2018, on communication of163

climate change risks), but the dynamical processes involved argue that they are best de-164

scribed as equatorward excursions of the tropospheric jets and southward advection of165

cold Arctic air. These features are not generally correlated with the strength of any glob-166

ally deﬁned “tropospheric polar vortex” (e.g., Cellitti et al., 2006; Waugh et al., 2017;167

Bushra & Rohli, 2021), so the utility of the latter concept in relation to CAOs is ques-168

tionable. CAOs in some regions are indeed more likely, and more likely to be severe, fol-169

lowing SSWs (e.g., King et al., 2019; S. H. Lee et al., 2019; Huang et al., 2021), explain-170

ing why the media often hails reports of an SSW with “the polar vortex is coming” even171

though an SSW actually represents a rapid deceleration, or disappearance, of the strato-172

spheric polar vortex winds. While the relationship to stratospheric polar vortex distur-173

bances can improve lead times for probabilistic forecasts of CAO occurrence, more ex-174

tensive mechanistic understanding of how stratospheric polar vortex anomalies aﬀect re-175

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manuscript submitted to Geophysical Research Letters

gional excursions of tropospheric jet streams is needed to further improve prediction of176

when and where CAOs will occur.177

The term “polar vortex” is used in another way that is not directly related to any178

planetary-scale circumpolar vortex, but is related to many CAOs (e.g., Lillo et al., 2021).179

A “tropopause polar vortex” (TPV) is a sub-synoptic-scale feature characterized by a180

deep depression of the tropopause (sometimes to near the surface) bounded by an “Arc-181

tic jet stream” poleward of and below the tropospheric polar jet (Shapiro et al., 1987).182

Lillo et al. (2021) showed that the North American CAO in late January 2019 resulted183

directly from a TPV moving southward from its high-latitude origins; TPVs play a role184

in many (but by no means all) CAOs (e.g., Papritz et al., 2019; Biernat et al., 2021). While185

the existence of yet another feature termed a “polar vortex” may engender confusion,186

the direct link of these localized vortices to CAOs emphasizes the importance of local/regional187

circulation anomalies (and associated jet stream excursions) to extreme weather events.188

Points such as those above regarding the stratospheric polar vortex have been high-189

lighted in studies using theoretical ﬂuid-dynamical or dynamical systems approaches (e.g.,190

Scott & Dritschel, 2006; Serra et al., 2017; Mester & Esler, 2020). It is not clear that sim-191

ilar approaches could usefully describe what some have termed a “tropospheric polar vor-192

tex”.193

2 Best Practices for Describing the Polar Vortex194

It is clearly appropriate and useful to describe the stratospheric polar vortex as dom-195

inating stratospheric cool-season variability and exerting inﬂuence on the surface on sub-196

seasonal to seasonal timescales, including probabilistic links to extreme weather events.197

Jet stream excursions and related troughs and ridges are suitable for describing the gen-198

esis and evolution of CAOs, whereas the concept of a “tropospheric polar vortex” is typ-199

ically not helpful in describing extreme weather events or elucidating their causes. We200

conclude:201

•

The term “polar vortex” is most appropriate for describing the stratospheric po-202

lar vortex, but given its broad use and misuse, “stratospheric” should be speci-203

ﬁed explicitly.204

•

The stratospheric polar vortex is a climatological feature that exists throughout205

the cool seasons (though sometimes temporarily disrupted) and thus should not206

be described as an “event” with a sub-seasonal time scale.207

•

The tropospheric circulation, especially in relation to extreme weather events, can208

most clearly be described in relation to the tropospheric jet streams, without in-209

voking the term “tropospheric polar vortex”. More accurate and appropriate ter-210

minology for referring to such events would be “Arctic cold air outbreak” (or more211

simply a CAO) or a “polar front”.212

•

While the term “tropopause polar vortex” has been used to describe sub-synoptic213

scale vortices that are sometimes linked to CAOs, local features might be more214

clearly described in relation to their provenance, e.g., a “Canadian tropopause vor-215

tex”.216

•

Scientists should be careful in the public-facing parts of our communications (e.g.,217

titles, abstracts, plain language summaries, web sites) to be clear and precise about218

what we mean by the term “polar vortex”.219

•

In communications with the media, atmospheric scientists should emphasize that220

stratospheric polar vortex variability is indeed helpful in predicting CAOs and other221

extreme weather events, but stratospheric inﬂuence is exerted via regional jet stream222

variations that cannot in themselves be called a “polar vortex”.223

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Further study is needed to elucidate the relationship of stratospheric polar vortex vari-224

ations to underlying regional tropospheric jet stream variations and ultimately to extreme225

weather events. The stratospheric polar vortex and tropospheric jet streams play impor-226

tant, but distinct, roles in understanding and forecasting extreme weather events. Ac-227

curate description of these features is thus critical to improving communication, both228

within the scientiﬁc community and with the public, regarding events that can have pro-229

found human impacts.230

Acknowledgments231

We thank the MLS team at JPL, especially Brian Knosp, Luis Mill´an, and Ryan Fuller,232

for data management, processing, and analysis support; NASA’s GMAO for the MERRA-2233

dataset; Ken Minschwaner, Jessica George, and Kody Gray for helpful discussions; and234

two anonymous reviewers for their insightful comments. We are grateful to B. J. Hoskins,235

M. E. McIntyre, and A. W. Robertson (Hoskins et al., 1985) for inspiring the title of this236

commentary. G.L.M. was partially supported by the JPL Microwave Limb Sounder team237

under a JPL subcontract to NWRA. Z.D.L. was partially supported under a NWS OSTI238

Weeks 3–4 Project (NA20NWS4680051). G.L.M. and Z.D.L. were partially supported239

by NSF Climate and Large-scale Dynamics Grant #2015906. K.W. was supported by240

NASA’s GMAO core funding. Work at the Jet Propulsion Laboratory, California Insti-241

tute of Technology, was carried out under a contract with the National Aeronautics and242

Open Research244

The MERRA2 data set used here is publicly available: https://disc.gsfc.nasa245

.gov/datasets?project=MERRA-2 (Global Modeling and Assimilation Oﬃce (GMAO),246

2015).247

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manuscript submitted to Geophysical Research Letters

References248

Albers, J. R., Perlwitz, J., Butler, A. H., Birner, T., Kiladis, G. N., Lawrence,249

Z. D., . . . Dias, J. (2018). Mechanisms governing interannual variability of250

stratosphere-to-troposphere ozone transport. J. Geophys. Res., 123 (1), 234–251

260. Retrieved from https://agupubs.onlinelibrary.wiley.com/doi/abs/252

10.1002/2017JD026890 doi: https://doi.org/10.1002/2017JD026890253

Baldwin, M. P., Ayarzag¨uena, B., Birner, T., Butchart, N., Butler, A. H., Charlton-254

Perez, A. J., . . . Pedatella, N. M. (2021). Sudden stratospheric warm-255

ings. Rev. Geophys., 59 (1), e2020RG000708. Retrieved from https://256

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020RG000708257

(e2020RG000708 10.1029/2020RG000708) doi: https://doi.org/10.1029/258

2020RG000708259

Baldwin, M. P., & Dunkerton, T. J. (2001). Stratospheric harbingers of anomalous260

weather regimes. Science, 294 , 581–584.261

Biernat, K. A., Bosart, L. F., & Keyser, D. (2021). A climatological analysis of the262

linkages between tropopause polar vortices, cold pools, and cold air outbreaks263

over the central and eastern United States. Mon. Weather Rev., 149 (1), 189–264

206. Retrieved from https://journals.ametsoc.org/view/journals/mwre/265

149/1/mwr-d-20-0191.1.xml doi: 10.1175/MWR-D-20-0191.1266

Breeden, M. L., Butler, A. H., Albers, J. R., Sprenger, M., & Langford, A. O.267

(2021). The spring transition of the North Paciﬁc jet and its relation to268

deep stratosphere-to-troposphere mass transport over western North Amer-269

ica. Atmos. Chem. Phys., 21 (4), 2781–2794. Retrieved from https://acp270

.copernicus.org/articles/21/2781/2021/ doi: 10.5194/acp-21-2781-2021271

Bushra, N., & Rohli, R. V. (2019). An objective procedure for delineating the272

circumpolar vortex. Earth and Space Science, 6 (5), 774-783. Retrieved273

from https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/274

2019EA000590 doi: https://doi.org/10.1029/2019EA000590275

Bushra, N., & Rohli, R. V. (2021). Relationship between atmospheric tele-276

connections and the northern hemisphere’s circumpolar vortex. Earth277

and Space Science, 8 (9), e2021EA001802. Retrieved from https://278

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2021EA001802279

(e2021EA001802 2021EA001802) doi: https://doi.org/10.1029/2021EA001802280

Butler, A. H., Sjoberg, J. P., Seidel, D. J., & Rosenlof, K. H. (2017). A sudden281

stratospheric warming compendium. Earth System Science Data, 9 (1), 63–76.282

Retrieved from https://www.earth-syst-sci-data.net/9/63/2017/ doi: 10283

.5194/essd-9-63-2017284

Cellitti, M. P., Walsh, J. E., Rauber, R. M., & Portis, D. H. (2006). Extreme285

cold air outbreaks over the United States, the polar vortex, and the large-286

scale circulation. J. Geophys. Res., 111 (D2). Retrieved from https://287

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2005JD006273 doi:288

https://doi.org/10.1029/2005JD006273289

Cohen, J. L., Agel, L., Barlow, M., Garﬁnkel, C. I., & White, I. (2021). Linking Arc-290

tic variability and change with extreme winter weather in the United States.291

Science, 373 (6559), 1116–1121. Retrieved from https://www.science.org/292

doi/abs/10.1126/science.abi9167 doi: 10.1126/science.abi9167293

Cohen, J. L., Agel, L. A., Barlow, M. A., Furtado, J. C., Kretschmer, M., &294

Matthias, V. (2021). The ”Polar Vortex” winter of 2013/14. In AGU Fall295

Meeting 2021.296

Dai, G., Li, C., Han, Z., Luo, D., & Yao, Y. (2021, May). The nature and pre-297

dictability of the East Asian extreme cold events of 2020/21. Adv. Atmos. Sci..298

Retrieved from https://doi.org/10.1007/s00376-021-1057-3299

Domeisen, D. I., & Butler, A. H. (2020, December). Stratospheric drivers of extreme300

events at the Earth’s surface. Comm. Earth Environ., 1 (1), 59. Retrieved from301

https://doi.org/10.1038/s43247-020-00060-z302

–7–

manuscript submitted to Geophysical Research Letters

Domeisen, D. I., Butler, A. H., Charlton-Perez, A. J., Ayarzag¨uena, B., Baldwin,303

M. P., Dunn-Sigouin, E., . . . Taguchi, M. (2019). The role of the strato-304

sphere in subseasonal to seasonal prediction Part II: Predictability arising from305

stratosphere - troposphere coupling. J. Geophys. Res., n/a(n/a). Retrieved306

from https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/307

2019JD030923 doi: 10.1029/2019JD030923308

Gelaro, R., McCarty, W., Surez, M. J., Todling, R., Molod, A., Takacs, L., . . .309

Zhao, B. (2017). The Modern-Era Retrospective Analysis for Research310

and Applications, Version-2 (MERRA-2). J. Clim., 30 , 5419–5454. doi:311

doi:10.1175/JCLI-D-16-0758.1312

Global Modeling and Assimilation Oﬃce (GMAO). (2015). Merra-2313

inst3 3d asm nv: 3d, 3-hourly,instantaneous, model-level, assimilation, as-314

similated meteorological ﬁelds v5.12.4, greenbelt, md, usa, Goddard Earth Sci-315

ences Data and Information Services Center (GES DISC), accessed 1 novem-316

ber 2015. doi: 10.5067/WWQSXQ8IVFW8317

Hoskins, B. J., McIntyre, M. E., & Robertson, A. W. (1985). On the use and signiﬁ-318

cance of isentropic potential vorticity maps. Q. J. R. Meteorol. Soc., 111 , 877–319

946.320

Huang, J., Hitchcock, P., Maycock, A. C., McKenna, C. M., & Tian, W. (2021,321

July). Northern hemisphere cold air outbreaks are more likely to be severe322

during weak polar vortex conditions. Comm. Earth Env., 2 (1), 147. Retrieved323

from https://doi.org/10.1038/s43247-021-00215-6324

Jiang, J. H. (2021). Polar vortex linked to atmospheric circulation at daily scale.325

Retrieved from https://eos.org/editor-highlights/polar-vortex-linked326

-to-atmospheric-circulation-at-daily-scale?utm campaign=ealert327

(EOS Editors’ Highlight)328

Juzbaˇsi´c, A., Kryjov, V. N., & Ahn, J. B. (2021, apr). On the anomalous devel-329

opment of the extremely intense positive Arctic oscillation of the 2019–2020330

winter. Env. Res. Lett., 16 (5), 055008. Retrieved from https://doi.org/331

10.1088/1748-9326/abe434 doi: 10.1088/1748-9326/abe434332

Kidston, J., Scaife, A. A., Hardiman, S. C., Mitchell, D. M., Butchart, N., Bald-333

win, M. P., & Gray, L. J. (2015). Stratospheric inﬂuence on tropospheric334

jet streams, storm tracks and surface weather. Nature Geoscience, 8 . doi:335

http://dx.doi.org/10.1038/ngeo2424336

King, A. D., Butler, A. H., Jucker, M., Earl, N. O., & Rudeva, I. (2019). Observed337

relationships between sudden stratospheric warmings and European climate338

extremes. J. Geophys. Res., 124 (24), 13943–13961. Retrieved from https://339

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JD030480 doi:340

https://doi.org/10.1029/2019JD030480341

K¨om¨u¸sc¨u, A.

U., & O˘guz, K. (2021, August). Analysis of cold anomalies observed342

over Turkey during the 2018/2019 winter in relation to polar vortex and other343

atmospheric patterns. Meteorol. Atmos. Phys., 133 (4), 1327–1354. Retrieved344

from https://doi.org/10.1007/s00703-021-00806-0345

Kretschmer, M., Cohen, J., Mattias, V., Runge, J., & Coumou, D. (2018). The dif-346

ferent stratospheric inﬂuence on cold-extremes in Eurasia and North America.347

npj Clim Atmos Sci, 1 . doi: 10.1038/s41612-018-0054-4348

Lawrence, Z. D., & Manney, G. L. (2018). Characterizing stratospheric polar349

vortex variability with computer vision techniques. Journal of Geophysical Re-350

search: Atmospheres, 123 (3), 1510–1535. Retrieved from http://dx.doi.org/351

10.1002/2017JD027556 (2017JD027556) doi: 10.1002/2017JD027556352

Lawrence, Z. D., Manney, G. L., & Wargan, K. (2018). Reanalysis intercomparisons353

of stratospheric polar processing diagnostics. Atmos. Chem. Phys., 18 , 13547–354

13579. doi: 10.5194/acp-18-13547-2018355

Lawrence, Z. D., Perlwitz, J., Butler, A. H., Manney, G. L., Newman, P. A.,356

Lee, S. H., & Nash, E. R. (2020). The remarkably strong Arctic strato-357

–8–

manuscript submitted to Geophysical Research Letters

spheric polar vortex of winter 2020: Links to record-breaking Arctic oscil-358

lation and ozone loss. J. Geophys. Res., 125 (22), e2020JD033271. Re-359

trieved from https://agupubs.onlinelibrary.wiley.com/doi/abs/360

10.1029/2020JD033271 (e2020JD033271 10.1029/2020JD033271) doi:361

https://doi.org/10.1029/2020JD033271362

Lee, S., & Kim, H.-K. (2003). The dynamical relationship betweem subtropical and363

eddy-driven jets. J. Atmos. Sci., 60 , 1490–1503.364

Lee, S. H., Furtado, J. C., & Charlton-Perez, A. J. (2019). Wintertime North Amer-365

ican weather regimes andtheArctic stratospheric polar vortex. Geophys. Res.366

Lett., 46 (24), 14892–14900. Retrieved from https://agupubs.onlinelibrary367

.wiley.com/doi/abs/10.1029/2019GL085592 doi: https://doi.org/10.1029/368

2019GL085592369

Lillo, S. P., Cavallo, S. M., Parsons, D. B., & Riedel, C. (2021). The role of a370

tropopause polar vortex in the generation of the January 2019 extreme Arc-371

tic outbreak. J. Atmos. Sci., 78 (9), 2801–2821. Retrieved from https://372

journals.ametsoc.org/view/journals/atsc/78/9/JAS-D-20-0285.1.xml373

doi: 10.1175/JAS-D-20-0285.1374

Limpasuvan, V., Hartmann, D. L., Thompson, D. W. J., Jeev, K., & Yung,375

Y. L. (2005). Stratosphere-troposphere evolution during polar vortex376

intensiﬁcation. J. Geophys. Res., 110 (D24). Retrieved from https://377

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2005JD006302 doi:378

https://doi.org/10.1029/2005JD006302379

Lyons, B. A., Hasell, A., & Stroud, N. J. (2018). Enduring extremes? polar vortex,380

drought, and climate change beliefs. Environmental Communication, 12 (7),381

876–894. Retrieved from https://doi.org/10.1080/17524032.2018.1520735382

doi: 10.1080/17524032.2018.1520735383

Manney, G. L., Hegglin, M. I., Daﬀer, W. H., Santee, M. L., Ray, E. A., Pawson, S.,384

. . . Walker, K. A. (2011). Jet characterization in the upper troposphere/lower385

stratosphere (UTLS): Applications to climatology and transport studies. At-386

mos. Chem. Phys., 11 , 6115–6137.387

Manney, G. L., Hegglin, M. I., Daﬀer, W. H., Schwartz, M. J., Santee, M. L., &388

Pawson, S. (2014). Climatology of upper tropospheric/lower stratospheric389

(UTLS) jets and tropopauses in MERRA. J. Clim., 27 , 3248-3271.390

Manney, G. L., Livesey, N. J., Santee, M. L., Froidevaux, L., Lambert, A., Lawrence,391

Z. D., . . . Fuller, R. A. (2020). Record-low Arctic stratospheric ozone in392

2020: MLS observations of chemical processes and comparisons with pre-393

vious extreme winters. Geophys. Res. Lett., 47 (16), e2020GL089063. Re-394

trieved from https://agupubs.onlinelibrary.wiley.com/doi/abs/395

10.1029/2020GL089063 (e2020GL089063 10.1029/2020GL089063) doi:396

https://doi.org/10.1029/2020GL089063397

Manney, G. L., Santee, M. L., Rex, M., Livesey, N. J., Pitts, M. C., Veefkind, P., . . .398

Zinoviev, N. S. (2011). Unprecedented Arctic ozone loss in 2011. Nature, 478 ,399

469–475.400

Mester, M., & Esler, J. G. (2020). Dynamical elliptical diagnostics of the Antarctic401

polar vortex. J. Atmos. Sci., 77 (3), 1167–1180. Retrieved from https://402

journals.ametsoc.org/view/journals/atsc/77/3/jas-d-19-0232.1.xml403

doi: 10.1175/JAS-D-19-0232.1404

Nielsen-Gammon, J., Bolinger, R., Attard, H., Bentley, A., Brown, V., Fuhrmann,405

C., . . . Tollefson, W. (2021). Evaluation of the February 2021 south-central big406

freeze. In AGU Fall Meeting 2021.407

Olsen, M. A., Manney, G. L., & Liu, J. (2019). The ENSO and QBO impact on408

ozone variability and stratosphere-troposphere exchange relative to the sub-409

tropical jets. J. Geophys. Res., 124 (13), 7379–7392. Retrieved from https://410

agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019JD030435 doi:411

10.1029/2019JD030435412

–9–

manuscript submitted to Geophysical Research Letters

Overland, J. E. (2021, October). Rare events in the Arctic. Climatic Change,413

168 (3), 27. Retrieved from https://doi.org/10.1007/s10584-021-03238-2414

Overland, J. E., & Wang, M. (2019). Impact of the winter polar vortex on greater415

North America. Intl. J. Climatol., 39 (15), 5815–5821. Retrieved from416

https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/joc.6174417

doi: https://doi.org/10.1002/joc.6174418

Overland, J. E., & Wang, M. (2021). The 2020 Siberian heat wave. Intl. J. Clima-419

tol., 41 (S1), E2341–E2346. Retrieved from https://rmets.onlinelibrary420

.wiley.com/doi/abs/10.1002/joc.6850 doi: https://doi.org/10.1002/421

joc.6850422

Papritz, L., Rouges, E., Aemisegger, F., & Wernli, H. (2019). On the thermo-423

dynamic preconditioning of Arctic air masses and the role of tropopause424

polar vortices for cold air outbreaks from Fram Strait. J. Geophys. Res.,425

124 (21), 11033–11050. Retrieved from https://agupubs.onlinelibrary426

.wiley.com/doi/abs/10.1029/2019JD030570 doi: https://doi.org/10.1029/427

2019JD030570428

Schoeberl, M. R., Lait, L. R., Newman, P. A., & Rosenﬁeld, J. E. (1992). The struc-429

ture of the polar vortex. J. Geophys. Res., 97 , 7859–7882.430

Scott, R. K., & Dritschel, D. G. (2006). Vortexvortex interactions in the431

winter stratosphere. J. Atmos. Sci., 63 (2), 726–740. Retrieved from432

https://journals.ametsoc.org/view/journals/atsc/63/2/jas3632.1.xml433

doi: 10.1175/JAS3632.1434

Screen, J. A., Deser, C., & Sun, L. (2015). Reduced risk of North American cold435

extremes due to continued Arctic sea ice loss. Bull. Am. Meteor. Soc., 96 (9),436

1489–1503. Retrieved from https://journals.ametsoc.org/view/journals/437

bams/96/9/bams-d-14-00185.1.xml doi: 10.1175/BAMS-D-14-00185.1438

Serra, M., Sathe, P., Beron-Vera, F., & Haller, G. (2017). Uncovering the edge of439

the polar vortex. J. Atmos. Sci., 74 (11), 3871–3885. Retrieved from https://440

journals.ametsoc.org/view/journals/atsc/74/11/jas-d-17-0052.1.xml441

doi: 10.1175/JAS-D-17-0052.1442

Shapiro, M. A., Hampel, T., & Krueger, A. J. (1987). The Arctic tropopause fold.443

Mon. Weather Rev., 115 (2), 444–454. Retrieved from https://journals444

.ametsoc.org/view/journals/mwre/115/2/1520-0493 1987 115 0444 tatf445

2 0 co 2.xml doi: 10.1175/1520-0493(1987)115h0444:TATFi2.0.CO;2446

Shepherd, M. (2016). 12 weather and climate concepts that confuse the public.447

Retrieved from https://www.forbes.com/sites/marshallshepherd/2016/448

12/13/12-weather-and-climate-concepts-that-confuse-the-public/449

?sh=2943e192350b450

Spensberger, C., & Spengler, T. (2020, 07). Feature-Based Jet Variability in the Up-451

per Troposphere. J. Clim., 33 (16), 6849–6871. Retrieved from https://doi452

.org/10.1175/JCLI-D-19-0715.1 doi: 10.1175/JCLI-D-19-0715.1453

UCAR. (2021). Why the polar vortex keeps breaking out of the arctic. Retrieved454

from https://scied.ucar.edu/learning-zone/climate-change-impacts/455

why-polar-vortex-keeps-breaking-out-arctic456

UCDavis. (2019). What is the polar vortex? Retrieved from https://457

climatechange.ucdavis.edu/climate-change-definitions/what-is-the458

-polar-vortex/459

Wallace, J. M., Held, I. M., Thompson, D. W., Trenberth, K. E., & Walsh, J. E.460

(2014). Global warming and winter weather. Science, 343 (6172), 729–730.461

Waugh, D. W., Sobel, A. H., & Polvani, L. M. (2017). What is the polar vortex462

and how does it inﬂuence weather? Bull. Am. Meteor. Soc., 98 (1), 37–44. Re-463

trieved from https://doi.org/10.1175/BAMS-D-15-00212.1 doi: 10.1175/464

BAMS-D-15-00212.1465

Xiong, X., Liu, X., Wu, W., Yang, Q., & Zhou, D. K. (2021). Polar vortex outbreak466

air transport: Observation using satellite IR sounder derived ozone product467

–10–

manuscript submitted to Geophysical Research Letters

and comparison with model. In AGU Meeting Fall 2021.468

Yu, B., & Zhang, X. (2015). A physical analysis of the severe 2013/2014 cold win-469

ter in North America. J. Geophys. Res., 120 (19), 10,149–10,165. Retrieved470

from https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/471

2015JD023116 doi: 10.1002/2015JD023116472

Zhang, X., Fu, Y., Han, Z., Overland, J. E., Rinke, A., Tang, H., . . . Wang, M.473

(2021, August). Extreme cold events from East Asia to North America in win-474

ter 2020/21: Comparisons, causes, and future implications. Adv. Atmos. Sci..475

Retrieved from https://doi.org/10.1007/s00376-021-1229-1476

–11–

manuscript submitted to Geophysical Research Letters

Figure 1. Characteristics of (left to right) 6 Jan 2014 and 16 Feb 2021 stratospheric and

upper tropospheric circulations: (a) Windspeeds (colorﬁll) and two potential vorticity (PV)

contours representing the stratospheric polar vortex edge (green) and boundary of tropospheric

“global” circulation (orange). (b) Windspeed histograms along the “vortex edge” (most equator-

ward PV contour shown in (a)); vertical lines show mean around that PV contour. (c) Normal-

ized PV gradient magnitudes. (d) Normalized PV gradient magnitude along the “vortex edge”

(hemispheric mean is 1 by deﬁnition; vertical lines as in (b)). (e) Normalized ozone gradient

magnitudes. (f) Normalized ozone mixing ratios along the “vortex edge” (vertical lines as in (b)).

Cyan contours in (c) and (e) show “vortex edge” PV. 600 K (330 K) ﬁelds are shown for strato-

sphere (troposphere), except windspeeds are at 345 K (near level of maximum tropospheric jet

stream winds). Data are from MERRA-2 (Gelaro et al., 2017).

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