Verification of Subseasonal-to-Seasonal Forecasts for Major Stratospheric Sudden Warmings in Northern Winter from 1998/99 to 2012/13

Taguchi, Masakazu

doi:10.1007/s00376-019-9195-6

Cited by 13 publications

(20 citation statements)

References 23 publications

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“…Taguchi [13] compared S2S multi-system forecasts for five characteristic MSSWs, and showed that some systems are more skillful than others. More comprehensive comparisons using more MSSWs obtained consistent results [14,15]. Studies for two recent cases, MSSW in January 2019 and minor SSW in September 2019 in the Southern Hemisphere, revealed prolonged predictable time limits of about 18 days or longer for these cases [16,17], compared with the typical range between 5 and 15 days [1].…”

Section: Introductionmentioning

confidence: 65%

“…The present case study has taken a different approach, that is, investigated false alarms of an MSSW by real-time S2S forecasts for the 2017/2018 Northern Hemisphere winter season. The target ECMWF system is one of the systems that were shown to have relatively good skill in forecasting real MSSWs [13][14][15][16].…”

Section: Summary and Discussionmentioning

confidence: 99%

“…We chose the ECMWF system for this study, because it provides relatively abundant data in terms of initialization frequency and ensemble size [9]. The system was also shown to be one of the best systems in the S2S project database in forecasting MSSWs [13][14][15][16]. The initialization frequency is every 3 or 4 days.…”

Section: Datamentioning

confidence: 99%

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A Study of False Alarms of a Major Sudden Stratospheric Warming by Real-Time Subseasonal-to-Seasonal Forecasts for the 2017/2018 Northern Winter

Taguchi¹

2020

Atmosphere

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This study investigates false alarms of a major sudden stratospheric warming (MSSW) by real-time subseasonal-to-seasonal forecast data of the European Centre for Medium-Range Weather Forecasts system for the 2017/2018 Northern Hemisphere winter season. The analysis reveals two false alarm cases in the season, one in early December and the other in early February. Each case is characterized by ensembles of which a considerable part of the members (MSSW members) show an MSSW, that is, reversal of the zonal mean zonal wind in the extratropical stratosphere on similar calendar dates. Ensemble forecasts that are initialized earlier or later basically lack an MSSW, demonstrating clear intraseasonal variability in the frequency of forecasted MSSWs. For each false alarm case, the MSSW member mean field shows equatorward displacement of the polar vortex around the onset date. For both cases, the MSSW members accompany stronger wave activity in the lower stratosphere than other non-MSSW members and reanalysis data. They are further associated with higher geopotential height than the non-MSSW members, in the upper troposphere over northeastern Canada and Greenland before the first case, and lower height over northeastern Eurasia before the second case. These are located over the ridge and trough, respectively, of the climatological planetary wave of zonal wave number one, and are consistent with the increased wave activity.

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Section: Introductionmentioning

confidence: 65%

Section: Summary and Discussionmentioning

confidence: 99%

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A Study of False Alarms of a Major Sudden Stratospheric Warming by Real-Time Subseasonal-to-Seasonal Forecasts for the 2017/2018 Northern Winter

Taguchi¹

2020

Atmosphere

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“…Comparing the average predictability of SSWs (e.g., Domeisen et al., 2020a; Rao et al., 2019, 2020; Taguchi, 2020) and that of the strong polar vortex in March 2020, the cold state of the Arctic stratosphere is forecasted even in unfavorable conditions (i.e., easterly QBO above 50 hPa). On the other hand, predictability may be further enhanced were conditions for vortex intensification more favorable.…”

Section: Summary and Discussionmentioning

confidence: 99%

“…The gradual downward propagation of the NAM signal from the stratosphere to the troposphere increases our chance of accurately predicting surface weather on the S2S timescale (Sigmond et al., 2013; Tripathi et al., 2015, 2016). Due to the possible downward impact of the extreme stratospheric events such as SSWs and SFWs, predictability of those warming events has attracted wide interest in literature most recently (e.g., Butler et al., 2019; Domeisen et al., 2020a, 2020b; Karpechko et al., 2018; Rao et al., 2018, 2020; Taguchi, 2020). The potential for improved predictability associated with strong polar vortex events, on the other hand, has received comparatively less attention.…”

Section: Introductionmentioning

confidence: 99%

The Strong Stratospheric Polar Vortex in March 2020 in Sub‐Seasonal to Seasonal Models: Implications for Empirical Prediction of the Low Arctic Total Ozone Extreme

Rao

Garfinkel

2021

JGR Atmospheres

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Using reanalysis and real‐time forecasts from 11 sub‐seasonal to seasonal (S2S) models, the strong stratospheric polar vortex in March 2020 coupled with Arctic ozone loss and their predictability are reported in this study. Arctic ozone reached a minimum value in March 2020 similar to the events in 1997 and 2011. Upward propagation of waves into the stratosphere in winter–early spring was anomalously weak, and the weakened Brewer‐Dobson circulation transported less ozone‐rich air to the Arctic stratosphere in November 2019–March 2020, which contributes around 40% of the total Arctic ozone loss in March, with the residual mainly explained by the chemical loss. Anomalous upwelling in the Arctic further cooled and intensified the polar vortex for ozone depletion and weak mixing, preventing recovery of ozone in early spring 2020. The polar vortex intensity and Arctic total ozone are strongly coupled, so a prediction of Arctic total ozone becomes possible for S2S models using metrics of the polar vortex as a proxy. The prediction of the strong stratospheric polar vortex in late March 2020 is assessed for four common initializations (February 27, March 5, March 12, and March 19) for S2S models. Displacement of the polar vortex toward the Western Hemisphere can only be forecasted in the two later initializations, and its intensity anomaly is underestimated in nearly all of those forecasts. Therefore, the empirical model using the S2S outputs also underestimates the Arctic total ozone. Despite this underestimation, this extremely strong polar vortex event led to improved surface predictability on subseasonal timescales: near‐surface temperature and precipitation are well forecasted 2–3 weeks in advance.

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Sudden Stratospheric Warmings

Baldwin

Ayarzagüena

Birner³

et al. 2020

Preprint

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Sudden stratospheric warmings (SSWs) are impressive fluid dynamical events in which large and rapid temperature increases in the winter polar stratosphere (∼10-50 km) are associated with a complete reversal of the climatological wintertime westerly winds. SSWs are caused by the breaking of planetary-scale waves that propagate upwards from the troposphere. During an SSW, the polar vortex breaks down, accompanied by rapid descent and warming of air in polar latitudes, mirrored by ascent and cooling above the warming. The rapid warming and descent of the polar air column affect tropospheric weather, shifting jet streams, storm tracks, and the Northern Annular Mode, making cold air outbreaks over North America and Eurasia more likely. SSWs affect the atmosphere above the stratosphere, producing widespread effects on atmospheric chemistry, temperatures, winds, neutral (nonionized) particles and electron densities, and electric fields. These effects span both hemispheres. Given their crucial role in the whole atmosphere, SSWs are also seen as a key process to analyze in climate change studies and subseasonal to seasonal prediction. This work reviews the current knowledge on the most important aspects of SSWs, from the historical background to dynamical processes, modeling, chemistry, and impact on other atmospheric layers.

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Verification of Subseasonal-to-Seasonal Forecasts for Major Stratospheric Sudden Warmings in Northern Winter from 1998/99 to 2012/13

Cited by 13 publications

References 23 publications

A Study of False Alarms of a Major Sudden Stratospheric Warming by Real-Time Subseasonal-to-Seasonal Forecasts for the 2017/2018 Northern Winter

A Study of False Alarms of a Major Sudden Stratospheric Warming by Real-Time Subseasonal-to-Seasonal Forecasts for the 2017/2018 Northern Winter

The Strong Stratospheric Polar Vortex in March 2020 in Sub‐Seasonal to Seasonal Models: Implications for Empirical Prediction of the Low Arctic Total Ozone Extreme

Sudden Stratospheric Warmings

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