Do split and displacement sudden stratospheric warmings have different annular mode signatures?

Maycock, Amanda C.; Hitchcock, Peter B.

doi:10.1002/2015gl066754

Cited by 91 publications

(119 citation statements)

References 28 publications

(46 reference statements)

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“…strong and weak events, long and short. Similarly, over‐persistence of long SSWs compared to ECMWF ERA‐40 reanalyses has been noted by Maycock and Hitchcock () in a 1,000‐year climate model simulation. A first interpretation may be that the radiative damping time‐scale in the stratosphere is too long in the forecast model.…”

Section: Discussion and Summarysupporting

confidence: 72%

“…Note that we do not attempt to distinguish between vortex splits and displacements, given the limited size of our ensemble of events. In a long climate model simulation, Maycock and Hitchcock () found no differences in the surface signatures that were robust to the criteria used for classifying events and, for a given method of defining splits and displacements, the model data only showed small statistically robust differences. For each of the four categories, compositing is performed with respect to either the initial or the end day (the first or last day when the PC1 meets the above‐mentioned criterion).…”

Section: Seasonal Forecasts From the Ecmwf System 4 And Ancillary Rementioning

confidence: 99%

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Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model

Orsolini

Nishii

Nakamura

2018

Quart J Royal Meteoro Soc

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Previous studies have documented extreme stratospheric polar vortex events, but the factors governing their duration have received little attention. Here, we investigate weak and strong stratospheric polar vortex events simulated in ensemble reforecasts for the Northern Hemisphere winter with the seasonal forecast model (System 4) of the European Centre for Medium‐Range Weather Forecasting, in comparison with the European Reanalysis Interim dataset. The individual strong and weak vortex events are classified into short and long events. A composite analysis is conducted for each of the four categories of events with respect to their initial or end days. We examine the characteristics of each category in the forecast model and reanalyses, including anomalous zonal‐mean zonal winds, heat and wave‐activity fluxes, lower‐tropospheric temperature and surface pressure, as well as the synoptic evolution of upper‐tropospheric anomalies during the precursory and decaying stages. The main findings are: (a) the forecast System 4 is found to produce both short and long anomalous vortex events in comparable amplitude to the reanalyses, but the polar zonal wind anomalies are more persistent, for each of the four categories considered; (b) short events penetrate as deep as the long events right at their onset, but they rapidly decay under a wave forcing that is less sustained than in the long events; (c) subtle differences in the synoptic evolution of blocking Highs and Lows over both oceanic basins or over Northern Eurasia or America appear to condition the duration of the forcing; and (d) during such short events, characteristic surface or lower‐tropospheric signatures of the annular mode paradigm arising from the downward stratospheric influence are not allowed sufficient time to develop.

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Section: Discussion and Summarysupporting

confidence: 72%

Section: Seasonal Forecasts From the Ecmwf System 4 And Ancillary Rementioning

confidence: 99%

Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model

Orsolini

Nishii

Nakamura

2018

Quart J Royal Meteoro Soc

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“…Previous work has suggested that split‐ and displacement‐type SSW events, which exhibit some different characteristics in many upper‐level atmospheric features, could have different impacts on surface climate (Lehtonen & Karpechko, ; Mitchell et al, ), though long model simulations show little significant difference in the surface climate response (Jucker, ; Maycock & Hitchcock, ). Given the sample size of observed SSWs in our analysis, a full analysis of these differences using observational data is not robust.…”

Section: Discussionmentioning

confidence: 99%

Observed Relationships Between Sudden Stratospheric Warmings and European Climate Extremes

et al. 2019

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Sudden stratospheric warmings (SSWs) have been linked with anomalously cold temperatures at the surface in the middle to high latitudes of the Northern Hemisphere as climatological westerly winds in the stratosphere tend to weaken and turn easterly. However, previous studies have largely relied on reanalyses and model simulations to infer the role of SSWs on surface climate and SSW relationships with extremes have not been fully analyzed. Here, we use observed daily gridded temperature and precipitation data over Europe to comprehensively examine the response of climate extremes to the occurrence of SSWs. We show that for much of Scandinavia, winters with SSWs are on average at least 1 °C cooler, but the coldest day and night of winter is on average at least 2 °C colder than in non‐SSW winters. Anomalously high pressure over Scandinavia reduces precipitation on the northern Atlantic coast but increases overall rainfall and the number of wet days in southern Europe. In the 60 days after SSWs, cold extremes are more intense over Scandinavia with anomalously high pressure and drier conditions prevailing. Over southern Europe there is a tendency toward lower pressure, increased precipitation and more wet days. The surface response in cold temperature extremes over northwest Europe to the 2018 SSW was stronger than observed for any SSW during 1979–2016. Our analysis shows that SSWs have an effect not only on mean climate but also extremes over much of Europe. Only with carefully designed analyses are the relationships between SSWs and climate means and extremes detectable above synoptic‐scale variability.

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“…Mitchell et al (2011) used extreme value theory and 2-D moment diagnostics to characterize Arctic and Antarctic polar vortices and showed that moment diagnostics were a useful measure of vortex variability and could be used to help distinguish vortex-split/displacement SSWs. Many studies of the polar vortex, stratospheric variability, and their connections have since made extensive use of geometric and moment diagnostics for studies based on modeling (e.g., Liu and Scott, 2015;, reanalyses (e.g., Hannachi et al, 2011;Mitchell et al, 2013;Seviour et al, 2013), and climate model data (e.g., Maycock & Hitchcock, 2015;Seviour et al, 2017;Zhang et al, 2016) Since stratospheric polar vortices are easily defined in dynamical fields and because their geometry provides insight into their dynamics, computer vision techniques are ideal for analyzing their behavior. The field of computer vision has sought to develop algorithms by which computers can perform tasks that the human eye does naturally.…”

Section: 1002/2017jd027556mentioning

confidence: 99%

“…Mitchell et al () used extreme value theory and 2‐D moment diagnostics to characterize Arctic and Antarctic polar vortices and showed that moment diagnostics were a useful measure of vortex variability and could be used to help distinguish vortex‐split/displacement SSWs. Many studies of the polar vortex, stratospheric variability, and their connections have since made extensive use of geometric and moment diagnostics for studies based on modeling (e.g., Liu and Scott, ; Matthewman & Esler, ), reanalyses (e.g., Hannachi et al, ; Mitchell et al, ; Seviour et al, ), and climate model data (e.g., Maycock & Hitchcock, ; Seviour et al, ; Zhang et al, )…”

Section: Introductionmentioning

confidence: 99%

Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques

Lawrence

Manney

2018

JGR Atmospheres

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Computer vision techniques are used to characterize the Arctic stratospheric polar vortex in 38 years of reanalysis data. Such techniques are typically applied to analyses of digital images, but they represent powerful tools that are more widely applicable: basic techniques and considerations for geophysical applications are outlined herein. Segmentation, descriptive, and tracking algorithms are combined in the Characterization and Analysis of Vortex Evolution using Algorithms for Region Tracking (CAVE‐ART) package, which was developed to comprehensively describe dynamical and geometrical evolution of polar vortices. CAVE‐ART can characterize and track multiple vortex regions through time, providing an extensive suite of region, moments, and edge diagnostics for each. CAVE‐ART is valuable for identifying vortex‐splitting events including, but not limited to, previously cataloged vortex‐split sudden stratospheric warmings. An algorithm for identifying such events detects 52 potential events between 1980 and 2017; of these, 38 are subjectively classified as distinct “split‐like” events. The algorithm based on CAVE‐ART is also compared with moment‐based methods previously used to detect split events. Furthermore, vortex edge‐averaged wind speeds from CAVE‐ART are used to define extreme weak and strong polar vortex events over multiple vertical levels; this allows characterization of their occurrence frequencies and extents in time and altitude. Weak and strong events show distinct signatures in CAVE‐ART diagnostics: in contrast to weak events, strong vortices are more cylindrical and pole centered, and less filamented, than the climatological state. These results from CAVE‐ART exemplify the value of computer vision techniques for analysis of geophysical phenomena.

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Do split and displacement sudden stratospheric warmings have different annular mode signatures?

Cited by 91 publications

References 28 publications

Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model

Duration and decay of Arctic stratospheric vortex events in the ECMWF seasonal forecast model

Observed Relationships Between Sudden Stratospheric Warmings and European Climate Extremes

Characterizing Stratospheric Polar Vortex Variability With Computer Vision Techniques

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