scholarly journals Siberian Snow Forcing in a Dynamically Bias-Corrected Model

2020 ◽  
Vol 33 (24) ◽  
pp. 10455-10467
Author(s):  
Nicholas L. Tyrrell ◽  
Alexey Yu. Karpechko ◽  
Sebastian Rast
Keyword(s):  
Northern Hemisphere ◽  
Polar Vortex ◽  
Atmospheric Model ◽  
Stratospheric Polar Vortex ◽  
Surface Response ◽  
Eurasian Snow ◽  
And Control ◽  
Enhanced Surface ◽  
Dynamic Variables ◽  
Bias Corrections

AbstractWe investigate the effect of systematic model biases on teleconnections influencing the Northern Hemisphere wintertime circulation. We perform a two-step nudging and bias-correcting scheme for the dynamic variables of the ECHAM6 atmospheric model to reduce errors in the model climatology relative to ERA-Interim. One result is a significant increase in the strength of the Northern Hemisphere wintertime stratospheric polar vortex, reducing errors in the December–February mean zonal stratospheric winds by up to 75%. The bias corrections are applied to the full atmosphere or the stratosphere only. We compare the response of the bias-corrected and control runs to an increase in Siberian snow cover in October—a surface forcing that, in our experiments, weakens the stratospheric polar vortex from October to December. We find that despite large differences in the vortex strength the magnitude of the stratospheric weakening is similar among the different climatologies, with some differences in the timing and length of the response. Differences are more pronounced in the stratosphere–troposphere coupling, and the subsequent surface response. The snow forcing with the stratosphere-only bias corrections results in a stratospheric response that is comparable to control, yet with an enhanced surface response that extends into early January. The full-atmosphere bias correction’s snow response also has a comparable stratospheric response but a somewhat suppressed surface response. Despite these differences, our results show an overall small sensitivity of the Eurasian snow teleconnection to the background climatology.

The stratospheric response and surface influence in a bias-corrected model.

2020 ◽  
Author(s):  
Nicholas Tyrrell ◽  
Alexey Karpechko ◽  
Sebastian Rast
Keyword(s):  
Northern Hemisphere ◽  
Polar Vortex ◽  
Atmospheric Model ◽  
Quasi Biennial Oscillation ◽  
Stratospheric Polar Vortex ◽  
Surface Response ◽  
Model Biases ◽  
Increased Strength ◽  
And Control ◽  
Bias Corrections

<p>We investigate the effect of systematic model biases on teleconnections influencing the Northern Hemisphere wintertime circulation. We perform a two-step nudging and bias-correcting scheme for the dynamic variables of the ECHAM6 atmospheric model to reduce errors in the model climatology relative to ERA-Interim. The developed scheme is efficient in removing errors in model’s climatology. In particular, large negative bias in December-February mean zonal stratospheric winds is reduced by up to 75%, significantly increasing the strength of the Northern Hemisphere wintertime stratospheric polar vortex. <!-- I think calling increase in vortex strength ”a result” somewhat shifts the focus. The result is reduced error, not increased strength. I mean technically it is the same, but perception of the result is a bit different. What do you think? -->The bias-corrections are applied to the full atmosphere or stratosphere only.</p><p>We compare the response of bias-corrected and control runs to internal stratospheric variability and surface forcings that are important on seasonal timescales: Siberian snow cover in October; the Quasi-Biennial Oscillation (QBO); and ENSO. We find the bias-corrected model has the potential for a strengthened and more realistic response to the teleconnections, either in the stratospheric or surface response. In particular, the bias-corrected model has a strong QBO teleconnection which modulates the extratropical polar vortex and sea level pressure variability in a manner similar to that seen in observations. The Siberian snow forcing with the stratosphere-only bias-corrections also leads to an enhanced surface response relative to the control.<!-- Given considerable remaining biases in tropospheric waves in the stratosphere-only bias corrected run I would not overemphasize the results in this particular run especially because full bias-corrected run does not show large surface response. But it is Ok to mention this result in the abstract. --> The mechanism behind the sensitivity of the teleconnections to model biases is discussed.</p>

scholarly journals Nonlinear response of Northern Hemisphere stratospheric polar vortex to the Indo–Pacific warm pool (IPWP) Niño

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Xin Zhou ◽  
Quanliang Chen ◽  
Fei Xie ◽  
Jianping Li ◽  
Minggang Li ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Temperature Response ◽  
Polar Vortex ◽  
Warm Pool ◽  
Boreal Winter ◽  
Linear Wave ◽  
Stationary Waves ◽  
Stratospheric Polar Vortex ◽  
Pacific Warm Pool ◽  
Tropical Sea

Abstract Variations in tropical sea surface temperatures (SST) have pronounced impacts on the stratospheric polar vortex, with the role of El Niño being the focus of much research interest. However, the Indo–Pacific warm pool (IPWP), which is the warmest body of seawater in the world, has received less attention. The IPWP has been warming in recent years. This paper presents for the first time the remarkable nonlinearity in Northern Hemisphere (NH) stratospheric circulation and temperature response to IPWP warming (the so-called IPWP Niño) in boreal winter. The magnitude of NH stratospheric vortex weakening is strong and significant in case of moderate IPWP Niño, but is weak and insignificant in strong IPWP Niño case. This phenomenon is robust in both the historical simulations and observations. An idealized model experiments forced with linear varying SST forcing in the IPWP region isolate the nonlinearities arising from IPWP Niño strength. Westward extension of precipitation into the Maritime Continent drives attenuation and westward shift of extratropical waves during strong IPWP Niño events. Linear wave interference analysis reveals this leads to weak interference between the climatological and anomalous stationary waves and thereby a weak response of the stratospheric vortex. These findings imply a distinct stratospheric vortex response to the IPWP Niño, and provide extended implications for the surface climate in the NH.

scholarly journals The effect of interactive ozone chemistry on weak and strong stratospheric polar vortex events

2020 ◽  
Author(s):  
Jessica Oehrlein ◽  
Gabriel Chiodo ◽  
Lorenzo M. Polvani
Keyword(s):  
Climate Variability ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
Winter Climate ◽  
The Impact

Abstract. Modeling and observational studies have reported effects of stratospheric ozone extremes on Northern Hemisphere spring climate. Recent work has further suggested that the coupling of ozone chemistry and dynamics amplifies the surface response to midwinter sudden stratospheric warmings (SSWs). Here, we study the importance of interactive ozone chemistry in representing the stratospheric polar vortex and Northern Hemisphere winter surface climate variability. We contrast two simulations from the interactive and specified chemistry (and thus ozone) versions of the Whole Atmosphere Community Climate Model, designed to isolate the impact of interactive ozone on polar vortex variability. In particular, we analyze the response with and without interactive chemistry to midwinter SSWs, March SSWs, and strong polar vortex events (SPVs). With interactive chemistry, the stratospheric polar vortex is stronger, and more SPVs occur, but we find little effect on the frequency of midwinter SSWs. At the surface, interactive chemistry results in a pattern resembling a more negative North Atlantic Oscillation following midwinter SSWs, but with little impact on the surface signatures of late winter SSWs and SPVs. These results suggest that including interactive ozone chemistry is important for representing North Atlantic and European winter climate variability.

High vs. low latitude influence on seasonal stratospheric pathways in the atmospheric model ICON

2021 ◽  
Author(s):  
Raphael Köhler ◽  
Dörthe Handorf ◽  
Ralf Jaiser ◽  
Klaus Dethloff
Keyword(s):  
Large Scale ◽  
Arctic Oscillation ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Atmospheric Model ◽  
The Arctic ◽  
Late Winter ◽  
Stratospheric Polar Vortex ◽  
Enso Events ◽  
Hemisphere Winter

<p>Stratospheric pathways play an important role in connecting distant anomaly patterns to each other on seasonal timescales. As long-lived stratospheric extreme events can influence the large-scale tropospheric circulation on timescales of multiple weeks, stratospheric pathways have been identified as one of the main potential sources for subseasonal to seasonal predictability in mid-latitudes. These pathways have been shown to connect Arctic anomalies to lower latitudes and vice versa. However, there is an ongoing discussion on how strong these stratospheric pathways are and how they exactly work.</p><p> </p><p>In this context, we investigate two strongly discussed stratospheric pathways by analysing a suite of seasonal experiments with the atmospheric model ICON: On the one hand, the effect of El Niño-Southern Oscillation (ENSO) on the stratospheric polar vortex, and thus the circulation in mid and high latitudes in winter. And on the other hand, the effect of a rapidly changing Arctic on lower latitudes via the stratosphere. The former effect is simulated realistically by ICON, and the results from the ensemble simulations suggest that ENSO has an effect on the large-scale Northern Hemisphere winter circulation. The ICON experiments and the reanalysis exhibit a weakened stratospheric vortex in warm ENSO years. Furthermore, in particular in winter, warm ENSO events favour the negative phase of the Arctic Oscillation, whereas cold events favour the positive phase. The ICON simulations also suggest a significant effect of ENSO on the Atlantic-European sector in late winter. Unlike the effect of ENSO, ICON simulations and the reanalysis do not agree on the stratospheric pathway for Arctic-midlatitude linkages. Whereas the reanalysis exhibits a weakening of the stratospheric vortex in midwinter and a connected tropospheric negative Arctic Oscillation circulation response to amplified Arctic warming, this is not the case in the ICON simulations. Implications and potential reasons for this discrepancy are further analysed and discussed in this work.  </p>

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