scholarly journals The impact of wave-mean flow interaction on the Northern Hemisphere polar vortex after tropical volcanic eruptions

2016 ◽  
Vol 121 (10) ◽  
pp. 5281-5297 ◽  
Author(s):  
Matthias Bittner ◽  
Claudia Timmreck ◽  
Hauke Schmidt ◽  
Matthew Toohey ◽  
Kirstin Krüger
Keyword(s):  
Northern Hemisphere ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Mean Flow ◽  
Flow Interaction ◽  
The Impact

scholarly journals The impact of volcanic aerosols on stratospheric ozone and the Northern Hemisphere polar vortex: separating radiative from chemical effects under different climate conditions

2015 ◽  
Vol 15 (10) ◽  
pp. 14275-14314 ◽  
Author(s):  
S. Muthers ◽  
F. Arfeuille ◽  
C. C. Raible ◽  
E. Rozanov
Keyword(s):  
Northern Hemisphere ◽  
Climate Model ◽  
Stratospheric Ozone ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Radiative Heating ◽  
Dynamical Response ◽  
Climate Conditions ◽  
Column Ozone ◽  
The Impact

Abstract. After strong volcanic eruptions stratospheric ozone changes are modulated by heterogeneous chemical reactions (HET) and dynamical perturbations related to the radiative heating in the lower stratosphere (RAD). Here, we assess the relative importance of both processes as well as the effect of the resulting ozone changes on the dynamics using ensemble simulations with the atmosphere–ocean–chemistry–climate model (AOCCM) SOCOL-MPIOM forced by eruptions with different strength. The simulations are performed under present day and preindustrial conditions to investigate changes in the response behaviour. The results show that the HET effect is only relevant under present day conditions and causes a pronounced global reduction of column ozone. These ozone changes further lead to a slight weakening of the Northern Hemisphere (NH) polar vortex during mid-winter. Independent from the climate state the RAD mechanism changes the column ozone pattern with negative anomalies in the tropics and positive anomalies in the mid-latitudes. The influence of the climate state on the RAD mechanism significantly differs in the polar latitudes, where an amplified ozone depletion during the winter months is simulated under present day conditions. This is in contrast to the preindustrial state showing a positive column ozone response also in the polar area. The dynamical response of the stratosphere is clearly dominated by the RAD mechanism showing an intensification of the NH polar vortex in winter. Still under present day conditions ozone changes due to the RAD mechanism slightly reduce the response of the polar vortex after the eruption.

scholarly journals Coupling Modes among Action Centers of Wave–Mean Flow Interaction and Their Association with the AO/NAM

2012 ◽  
Vol 25 (2) ◽  
pp. 447-458 ◽  
Author(s):  
Nan Zhao ◽  
Sujie Liang ◽  
Yihui Ding
Keyword(s):  
Northern Hemisphere ◽  
Three Dimensional ◽  
Polar Vortex ◽  
The Arctic ◽  
Mean Flow ◽  
Annular Mode ◽  
Flow Interaction ◽  
Flow Interactions ◽  
Local Wave ◽  
The Arctic Oscillation

Abstract The Arctic Oscillation/Northern Hemisphere annular mode (AO/NAM) is attributed to wave–mean flow interaction over the extratropical region of the Northern Hemisphere. This wave–mean flow interaction is closely related to three atmospheric centers of action, corresponding to three regional oscillations: the NAO, the PNA, and the stratosphere polar vortex (SPV), respectively. It is then natural to infer that local wave–mean flow interactions at these three centers of action are dynamically coupled to each other and can thus explain the main aspects of the three-dimensional coherent structure of the annular mode, which also provides a possible way to understand how the local NAO–PNA–SPV perspective and the hemispheric AO/NAM perspective are interrelated. By using a linear stochastic model of coupled oscillators, this study suggests that two coupling modes among the PNA, NAO, and SPV are related to the two-dimensional pattern in sea level pressure of the AO. Although both of them may contribute to the AO/NAM, only one is related to the three-dimensional equivalent barotropic structure of the NAM, while the other one is mainly restricted to the troposphere. So the equivalent barotropic structure of the NAM, as usually revealed by the regression of the zonal wind against the AO index, is the manifestation of just one coupling mode. Another coupled mode is a baroclinic mode that resembles the NAM only in the troposphere. However, this similarity in spatial structures does not imply that the total variability of the AO/NAM index can be explained by those of the NAO–PNA–SPV or their coupling modes, because of the existence of the variability that may contribute to the AO/NAM, produced outside of these three regions. It is estimated that the coupling modes can jointly explain 44% of the variance of the AO/NAM index.

scholarly journals Enhanced Seasonal Prediction of European Winter Warming following Volcanic Eruptions

2009 ◽  
Vol 22 (23) ◽  
pp. 6168-6180 ◽  
Author(s):  
A. G. Marshall ◽  
A. A. Scaife ◽  
S. Ineson
Keyword(s):  
Climate Model ◽  
Initial Conditions ◽  
Polar Vortex ◽  
Volcanic Eruptions ◽  
Seasonal Prediction ◽  
The Arctic ◽  
Extended Model ◽  
Similar Response ◽  
Volcanic Aerosol ◽  
The Impact

Abstract The impact of explosive volcanic eruptions on the atmospheric circulation at high northern latitudes is assessed in two versions of the Met Office Hadley Centre’s atmospheric climate model. The standard version of the model extends to an altitude of around 40 km, while the extended version has enhanced stratospheric resolution and reaches 85-km altitude. Seasonal hindcasts initialized on 1 December produce a strengthening of the winter polar vortex and anomalous warming over northern Europe characteristic of the positive phase of the Arctic Oscillation (AO) when forced with volcanic aerosol following the 1963 Mount Agung, 1982 El Chichón, and 1991 Mount Pinatubo eruptions, as is observed. The AO signal in the extended model is of comparable strength to that in the standard model, showing that there is little impact from both increasing the vertical resolution in the stratosphere and extending the model domain to near the mesopause. The presence of this signal in the models, however, is likely due to the persistence of the observed signal from the initial conditions, because a similar set of experiments initiated with the same conditions, but with no volcanic aerosol forcing, exhibits a similar response as the forced runs. This suggests that the model has limited fidelity in capturing the response to volcanic aerosols on its own, consistent with previous studies on the impact of volcanic forcing in long climate simulations, but does support the premise that seasonal winter forecasts are substantially improved with the inclusion of stratospheric information.

scholarly journals Impact of solar vs. volcanic activity variations on tropospheric temperatures and precipitation during the Dalton Minimum

2013 ◽  
Vol 9 (6) ◽  
pp. 6179-6220 ◽  
Author(s):  
J. G. Anet ◽  
S. Muthers ◽  
E. V. Rozanov ◽  
C. C. Raible ◽  
A. Stenke ◽  
...  
Keyword(s):  
Northern Hemisphere ◽  
Solar Irradiance ◽  
Energetic Particle ◽  
Volcanic Eruptions ◽  
Hadley Cell ◽  
Particle Spectrum ◽  
Volcanic Aerosol ◽  
Mean Temperature ◽  
The Impact ◽  
Dalton Minimum

Abstract. The aim of this work is to elucidate the impact of changes in solar irradiance and energetic particles vs. volcanic eruptions on tropospheric global climate during the Dalton Minimum (DM, 1780–1840 AD). Separate variations in the (i) solar irradiance in the UV-C with wavelengths λ < 250 nm, (ii) irradiance at wavelengths λ > 250 nm, (iii) in energetic particle spectrum, and (iv) volcanic aerosol forcing were analyzed separately, and (v) in combination, by means of small ensemble calculations using a coupled atmosphere-ocean chemistry-climate-model. Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decrease global mean temperature by up to 0.5 K for 2–3 yr after the eruption. However, while the volcanic effect is clearly discernible in the southern hemispheric mean temperature, it is less significant in the Northern Hemisphere, partly because the two largest volcanic eruptions occurred in the SH tropics and during seasons when the aerosols were mainly transported southward, partly because of the higher northern internal variability. In the simulation including all forcings, temperatures are in reasonable agreement with the tree-ring-based temperature anomalies of the Northern Hemisphere. Interestingly, the model suggests that solar irradiance changes at λ < 250 nm and in energetic particle spectra have only insignificant impact on the climate during the Dalton Minimum. This downscales the importance of top-down processes (stemming from changes at λ < 250 nm) relative to bottom-up processes (from λ > 250 nm). Reduction of irradiance at λ > 250 nm leads to a significant (up to 2%) decrease of the ocean heat content (OHC) between the 0 and 300 m of depth, whereas the changes in irradiance at λ < 250 nm or in energetic particle have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 yr after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift of the intertropical convergence zone.

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.

scholarly journals Seasonal Variability of the Polar Stratospheric Vortex in an Idealized AGCM with Varying Tropospheric Wave Forcing

2015 ◽  
Vol 72 (6) ◽  
pp. 2248-2266 ◽  
Author(s):  
Aditi Sheshadri ◽  
R. Alan Plumb ◽  
Edwin P. Gerber
Keyword(s):  
Northern Hemisphere ◽  
Seasonal Variability ◽  
Seasonal Cycle ◽  
Bottom Topography ◽  
Polar Vortex ◽  
Equilibrium Temperature ◽  
Hemispheric Differences ◽  
Nonmonotonic Dependence ◽  
Wave Forcing ◽  
The Impact

Abstract The seasonal variability of the polar stratospheric vortex is studied in a simplified AGCM driven by specified equilibrium temperature distributions. Seasonal variations in equilibrium temperature are imposed in the stratosphere only, enabling the study of stratosphere–troposphere coupling on seasonal time scales, without the complication of an internal tropospheric seasonal cycle. The model is forced with different shapes and amplitudes of simple bottom topography, resulting in a range of stratospheric climates. The effect of these different kinds of topography on the seasonal variability of the strength of the polar vortex, the average timing and variability in timing of the final breakup of the vortex (final warming events), the conditions of occurrence and frequency of midwinter warming events, and the impact of the stratospheric seasonal cycle on the troposphere are explored. The inclusion of wavenumber-1 and wavenumber-2 topographies results in very different stratospheric seasonal variability. Hemispheric differences in stratospheric seasonal variability are recovered in the model with appropriate choices of wave-2 topography. In the model experiment with a realistic Northern Hemisphere–like frequency of midwinter warming events, the distribution of the intervals between these events suggests that the model has no year-to-year memory. When forced with wave-1 topography, the gross features of seasonal variability are similar to those forced with wave-2 topography, but the dependence on forcing magnitude is weaker. Further, the frequency of major warming events has a nonmonotonic dependence on forcing magnitude and never reaches the frequency observed in the Northern Hemisphere.

scholarly journals Mutual Interference of Local Gravity Wave Forcings in the Stratosphere

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1249
Author(s):  
Nadja Samtleben ◽  
Aleš Kuchař ◽  
Petr Šácha ◽  
Petr Pišoft ◽  
Christoph Jacobi
Keyword(s):  
Gravity Wave ◽  
Rocky Mountains ◽  
Middle Atmosphere ◽  
East Asian ◽  
Polar Vortex ◽  
Circulation Model ◽  
Global Circulation Model ◽  
Mean Flow ◽  
Destructive Effect ◽  
The Impact

Gravity wave (GW) breaking and associated GW drag is not uniformly distributed among latitudes and longitudes. In particular, regions of enhanced GW breaking, so-called GW hotspots, have been identified, major Northern Hemisphere examples being located above the Rocky Mountains, the Himalayas and the East Asian region. These hotspots influence the middle atmosphere circulation both individually and in combination. Their interference is here examined by performing simulations including (i) the respective single GW hotspots, (ii) two GW hotspots, and (iii) all three GW hotspots with a simplified global circulation model. The combined GW hotspots lead to a modification of the polar vortex in connection with a zonal mean flow decrease and an increase of the temperature at higher latitudes. The different combinations of GW hotspots mainly prevent the stationary planetary wave (SPW) 1 from propagating upward at midlatitudes leading to a decrease in energy and momentum transfer in the middle atmosphere caused by breaking SPW 1, and in turn to an acceleration of the zonal mean flow at lower latitudes. In contrast, the GW hotspot above the Rocky Mountains alone causes an increase in SPW 1 amplitude and Eliassen–Palm flux (EP flux), inducing enhanced negative EP divergence, decelerating the zonal mean flow at higher latitudes. Consequently, none of the combinations of different GW hotspots is comparable to the impact of the Rocky Mountains GW hotspot alone. The reason is that the GW hotspots mostly interfere nonlinearly. Depending on the longitudinal distance between two GW hotspots, the interference between the combined Rocky Mountains and East Asian GW hotspots is more additive than the interference between the combined Rocky Mountains and Himalaya GW hotspots. While the Rocky Mountains and the East Asian GW hotspots are longitudinally displaced by 105°, the Rocky Mountains are shifted by 170° to the Himalayas. Moreover, while the East Asian and the Himalayas are located side by side, the interference between these GW hotspots is the most nonlinear because they are latitudinally displaced by 20°. In general, the SPW activity, e.g., represented in SPW amplitudes, EP flux or Plumb flux, is strongly reduced, when the GW hotspots are interacting with each other. Thus, the interfering GW hotspots mostly have a destructive effect on SPW propagation and generation.

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

2020 ◽  
Vol 20 (17) ◽  
pp. 10531-10544
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, which is 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.

scholarly journals Minimal impact of model biases on northern hemisphere ENSO teleconnections

2020 ◽  
Author(s):  
Nicholas L. Tyrrell ◽  
Alexey Yu. Karpechko
Keyword(s):  
Northern Hemisphere ◽  
General Circulation ◽  
Southern Oscillation ◽  
Polar Vortex ◽  
Aleutian Low ◽  
Enso Events ◽  
Model Biases ◽  
The Impact ◽  
Strong Enso ◽  
Bias Corrections

Abstract. Correctly capturing the teleconnection between the El Niño–Southern Oscillation (ENSO) and Europe is of importance for seasonal prediction. Here we investigate how systematic model biases may affect this teleconnection. A two–step bias–correction process is applied to an atmospheric general circulation model to reduce errors in the climatology. The bias–corrections are applied to the troposphere and stratosphere separately and together to produce a range of climates. ENSO type sensitivity experiments are then performed to reveal the impact of differing climatologies on ENSO–Europe teleconnections. The bias–corrections do not affect the response of the tropical atmosphere, nor the Aleutian Low, to strong ENSO anomalies. However, the anomalous upward wave flux and the response of the northern hemisphere polar vortex differs between the climatologies. We attribute this to a reduced sensitivity of waves to the strength of the Aleutian Low. Despite the differing responses of the polar vortex, the NAO response is similar between the climatologies, implying that for strong ENSO events a stratospheric response may not be necessary for the ENSO–North Atlantic teleconnection.

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