MJO‐Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models

Garfinkel, Chaim I.; Schwartz, Chen

doi:10.1002/2017gl074470

Cited by 61 publications

(68 citation statements)

References 40 publications

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“…In turn, the adiabatic heat that is induced by the residual circulation downwelling in the polar region produced significant positive temperature anomalies in the stratosphere. In general, although MJO phases 2 and 3 are very important in the connection between MJO and SSW, which has been well established by the previous studies (Garfinkel et al, ; Garfinkel & Schwartz, ; Kang & Tziperman, ), these phases do not have a clear impact on the stratosphere when no SSW event is triggered. Instead, the linear teleconnection between the NH stratosphere and MJO phases 4 and 7 is clear during the period without an SSW event.…”

Section: Resultsmentioning

confidence: 62%

Response of the Northern Stratosphere to the Madden‐Julian Oscillation During Boreal Winter

Yang

Xue

et al. 2019

JGR Atmospheres

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In this study, the effects of the Madden‐Julian oscillation (MJO) on the northern stratosphere during boreal winter are investigated, especially in cases with the absence of a stratospheric sudden warming (SSW) event. During the wintertime, the polar cap temperature is expected to increase following MJO phase 2 (P2), P3, P4, and P7. However, the responses after P2 and P3 are much weaker if the dates from 50 days before to 50 days after the SSW central days are excluded from the composite. This result implies that the stratospheric polar warming following MJO P2 and P3 is sensitive to the occurrence of SSWs. After excluding the SSW events from the composite, the subsequent temperature anomalies strengthen and become more significant approximately 30 days after MJO P4 and 10 days after MJO P7. Planetary wave (PW) anomalies are enhanced in the midlatitudes of the upper troposphere, lagging MJO P4 by 15–25 days and lagging MJO P7 by 5–15 days. Thus, the upward propagation and dissipation of PWs in the stratosphere are significantly enhanced, further strengthening the Brewer‐Dobson circulation in the Northern Hemisphere stratosphere. The WN1, which is induced by the MJO in the stratosphere, is the dominant component of PW perturbation. The enhanced PW dissipation in the high latitudes of the stratosphere is weaker in terms of lagging MJO P4, so the zonal wind and temperature anomalies after MJO P4 are less significant in the polar region, especially in the lower stratosphere.

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Section: Resultsmentioning

confidence: 62%

Response of the Northern Stratosphere to the Madden‐Julian Oscillation During Boreal Winter

Yang

Xue

et al. 2019

JGR Atmospheres

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“…Another question unanswered in our study is how this SSW was related to remote forcing, such as the Madden-Julian oscillation (MJO). An MJO of large magnitude was observed in January 2018 before the SSW and in principle could have forced an SSW (e.g., Garfinkel & Schwartz, 2017). It is possible that ensemble members more accurately predicting the MJO would also be more successful in predicting SSW (Garfinkel & Schwartz, 2017).…”

Section: Resultsmentioning

confidence: 99%

Predicting Sudden Stratospheric Warming 2018 and Its Climate Impacts With a Multimodel Ensemble

Karpechko

Charlton‐Perez

Balmaseda

et al. 2018

Geophysical Research Letters

127

160

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Sudden stratospheric warmings (SSWs) are significant source of enhanced subseasonal predictability, but whether this source is untapped in operational models remains an open question. Here we report on the prediction of the SSW on 12 February 2018, its dynamical precursors, and surface climate impacts by an ensemble of dynamical forecast models. The ensemble forecast from 1 February predicted 3 times increased odds of an SSW compared to climatology, although the lead time for SSW prediction varied among individual models. Errors in the forecast location of a Ural high and underestimated magnitude of upward wave activity flux reduced SSW forecast skill. Although the SSW's downward influence was not well forecasted, the observed northern Eurasia cold anomaly following SSW was predicted, albeit with a weaker magnitude, due to persistent tropospheric anomalies. The ensemble forecast from 8 February predicted the SSW, its subsequent downward influence, and a long‐lasting cold anomaly at the surface.

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“…These impacts can occur either via vertically propagating Rossby waves directly associated with the MJO convection or indirectly from MJO‐extratropical tropospheric teleconnections that produce preferential wave patterns that excite planetary‐scale waves, which subsequently propagate into the polar stratosphere (e.g., Garfinkel et al, , ; Kang & Tziperman, ; Liu et al, ; Weare, ). Indeed, the MJO has been used as a skillful predictor for Northern Hemisphere sudden stratospheric warming events (Garfinkel & Schwartz, ; Schwartz & Garfinkel, ). These changes in the stratospheric polar vortex can then dynamically alter the tropospheric circulation and the NAO, as discussed above.…”

Section: Introductionmentioning

confidence: 99%

Tropospheric and Stratospheric Causal Pathways Between the MJO and NAO

et al. 2019

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Previous work has shown that the Madden‐Julian Oscillation (MJO) can influence the North Atlantic Oscillation (NAO) via a Rossby wave teleconnection that propagates through the troposphere (i.e., a tropospheric pathway). In addition, recent work suggests that the MJO can influence the stratospheric polar vortex, which is also known to influence the tropospheric NAO—thus, there likely exists a stratospheric pathway for MJO influence as well. Here, we apply two methods to shed more light on the pathways linking the MJO to the NAO. First, we use a traditional approach in climate science based on analyzing conditional probabilities. Second, we use methods from causal discovery theory based on probabilistic graphical models. Together, these two analysis approaches reveal that the MJO can impact the NAO via both a tropospheric and stratospheric pathway. The stratospheric pathway is shown to come about in two ways: First, both methods show that the MJO itself influences the strength of the stratospheric polar vortex on a timescale of ∼10 days, and then 5 days later the vortex can drive changes in the NAO. Second, the state of the stratospheric polar vortex acts to condition the NAO to be conducive (or not) to MJO influence. When the vortex is in a state that opposes the expected NAO response to the MJO, we find little influence of the MJO on the NAO, however, when the vortex supports the expected NAO response, the NAO is up to 30% more likely to be in a particular state following active MJO periods.

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MJO‐Related Tropical Convection Anomalies Lead to More Accurate Stratospheric Vortex Variability in Subseasonal Forecast Models

Cited by 61 publications

References 40 publications

Response of the Northern Stratosphere to the Madden‐Julian Oscillation During Boreal Winter

Response of the Northern Stratosphere to the Madden‐Julian Oscillation During Boreal Winter

Predicting Sudden Stratospheric Warming 2018 and Its Climate Impacts With a Multimodel Ensemble

Tropospheric and Stratospheric Causal Pathways Between the MJO and NAO

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