Predictability Changes of Stratospheric Circulations in Northern Hemisphere Winter

Ichimaru, Tomoko; Noguchi, Shunsuke; Hirooka, Toshihiko; Mukougawa, Hitoshi

doi:10.2151/jmsj.2016-001

Cited by 11 publications

(10 citation statements)

References 31 publications

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“…It is uncertain if the conclusion in this study based on this case can be generalized to other SSW events due to the peculiarities of the 2019 SSW event, which was initialized by wave‐1 but reinforced by wave‐3 and wave‐2 pulses leading to persistent splitting of the polar vortex. The relatively higher predictability of vortex displacement SSWs than vortex splitting events has been widely reported in previous studies (e.g., Ichimaru et al, ; Mukougawa & Hirooka, ; Rao et al, ; Taguchi, ) and similar predictability could be anticipated for this event during the peak‐1 period. The contribution of the rapid wave‐3 pulse to the SSW onset was also reported for the February 2005 warming event (Shi et al, ).…”

Section: Discussionsupporting

confidence: 84%

The 2019 New Year Stratospheric Sudden Warming and Its Real‐Time Predictions in Multiple S2S Models

et al. 2019

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Using multiple data sources, favorable conditions for the 2019 SSW event and its predictive skill from 11 subseasonal to seasonal (S2S) forecast models are explored in this study. This mixed‐type (displacement to split) SSW event occurred under moderate El Niño, easterly quasi‐biennial oscillation (QBO) together with solar minimum, and phases 4–6 of the Madden‐Julian oscillation (MJO). A strong positive PNA formed and developed in the troposphere before this SSW event, which is associated with enhanced and wave‐1‐dominated eddy heat flux. The predictive limit to this SSW onset is beyond 18 days in most S2S models, longer than the average predictive limit in existing literature. This high predictive skill may originate from the favorable initial conditions (QBO, MJO) and boundary conditions (moderate El Niño, solar minimum). Although some difference in the predictability of the 2019 SSW onset is found between models, most models well forecast its onset at a lead time of 18 days. More than 50% of the ensemble members initialized on 13 December forecast the zonal wind reversal, and the anomaly correlation for tropospheric heights during the SSW onset even exceed 0.7 in the multimodel ensemble (MME). In contrast, the predictability of the wave‐3 and wave‐2 pulses after the SSW onset, responsible for the standing split of the stratospheric polar vortex, is low in the forecast MMEs initialized before the SSW onset. It is a challenge for MMEs initialized before the SSW onset to well forecast the vortex splitting and its persistence 10–20 days after the SSW onset.

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Section: Discussionsupporting

confidence: 84%

The 2019 New Year Stratospheric Sudden Warming and Its Real‐Time Predictions in Multiple S2S Models

et al. 2019

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“…Kalnay, 2003). Therefore, we could estimate that the predictable period in the troposphere (levels below 100 hPa) is~7 to 9 days; This is consistent with other work (e.g., Ichimaru et al, 2016). On the other hand, the predictable period in the stratosphere is generally longer than that of the troposphere.…”

Section: Impact On Forecasting Circulation Anomalies After Sswssupporting

confidence: 90%

Impact of satellite observations on forecasting sudden stratospheric warmings

Noguchi

Kuroda

Mukougawa

et al. 2019

Preprint

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The observational impacts of satellite data assimilation on extended-range forecasts of sudden stratospheric warmings (SSWs) are investigated by conducting ensemble forecast experiments. We use two Japanese novel reanalysis products: the Japanese 55-year reanalysis (JRA-55) and its subset that assimilates conventional observations only (JRA-55C). A comparative examination on the reproducibility for SSWs between the two ensemble forecasts reveals that the impact of satellite observations is significant for forecasts starting 5 days before the SSW onset, with 20% less accuracy in the JRA-55C forecasts. Moreover, some of forecasts of vortex-splitting SSWs show a sudden appearance of deep difference, which lasts over a few months in the lower stratosphere and significantly affects the surface climate. These results highlight an important role of mesospheric and upper stratospheric circulations on the onset and development of SSWs. Plain Language Summary Satellite observations are valuable for producing initial conditions for numerical weather prediction (NWP) systems, especially over the upper stratosphere that typical upper-air observations cannot cover. However, many NWP models suffer from biases associated with unresolved processes. This study explores how the NWP system benefited from satellite data in forecasting the breakdown events of stratospheric polar vortexes/sudden stratospheric warmings (SSWs) by making many forecasts from typical initial conditions, both with and without satellite data. Due to unresolved bias over the upper stratosphere, some forecasts from no-satellite initial conditions miss the onset of SSWs and subsequent anomalous tropospheric conditions. Thus, the deteriorated grasp of the upper atmosphere in the absence of satellite observations degrades the deterministic predictability of extreme stratospheric events and following downward-propagating signals.

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“…Furthermore, Ichimaru et al . [] suggested by the analysis on several SSWs during 2001–2006 using the same ensemble forecast data set that the displacement type SSW tends to have a longer predictable period than the vortex splitting type SSW. On the other hand, by conducting deterministic hindcast experiments initialized at 1 day interval with a Hadley Center atmospheric general circulation model (HadGAM1) for four SSW events occurred in 1980s and 1990s, Marshall and Scaife [] indicated that there is no significant difference in the predictable period for the two types of the SSW.…”

Section: Introductionmentioning

confidence: 99%

Predictability of the stratospheric polar vortex breakdown: An ensemble reforecast experiment for the splitting event in January 2009

Noguchi

Mukougawa

Kuroda³

et al. 2016

JGR Atmospheres

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A series of ensemble reforecast experiments is conducted to investigate the predictability and the occurrence mechanism of a stratospheric sudden warming occurred in late January 2009, which is a typical polar vortex splitting event. To fully examine the rapid vortex splitting evolution and predictability variation, ensemble forecasts are carried out every day during January 2009. The vortex splitting event is reliably predicted by forecasts initialized after 6 days prior to the vortex breakup. It is also found that the propagating property of planetary waves within the stratosphere is a key to the successful prediction for the vortex splitting event. Planetary waves incoming from the troposphere are reflected back into the troposphere for failed forecasts, whereas they are absorbed within the stratosphere for succeeded forecasts. Composite analysis reveals the following reflection process of planetary waves for the failed forecast: Upward propagation of planetary wave activity from a tropospheric blocking over Alaska is weaker during initial prediction periods; then, the deceleration of the zonal wind in the upper stratosphere becomes weaker over Europe, which produces a preferable condition for the wave reflection; hence, subsequently incoming wave activity from the troposphere over Europe is reflected back over the Siberia inducing the eastward phase tilt of planetary waves, which shuts down the further upward propagation of planetary waves leading to the vortex splitting. Thus, this study shows that the stratospheric condition would be another important control factor for the occurrence of the vortex splitting event, besides anomalous tropospheric circulations enforcing upward propagation of planetary waves.It is also well known that SSWs are classified into the following two types based on the synoptic structure of the stratospheric circulation: "vortex displacement" type characterized by a shift of the polar vortex off the pole and "vortex splitting" type in which the polar vortex breaks up into two pieces [Charlton and Polvani, 2007]. It has been also revealed by several studies based on the composite of reanalysis data sets that the NOGUCHI ET AL.PREDICTABILITY OF VORTEX SPLITTING EVENT 3388

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Predictability Changes of Stratospheric Circulations in Northern Hemisphere Winter

Cited by 11 publications

References 31 publications

The 2019 New Year Stratospheric Sudden Warming and Its Real‐Time Predictions in Multiple S2S Models

The 2019 New Year Stratospheric Sudden Warming and Its Real‐Time Predictions in Multiple S2S Models

Impact of satellite observations on forecasting sudden stratospheric warmings

Predictability of the stratospheric polar vortex breakdown: An ensemble reforecast experiment for the splitting event in January 2009

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