Quasi-stationary planetary wave-mean flow interactions in the Northern Hemisphere stratosphere and their responses to ENSO events

2012 ◽  
Vol 55 (3) ◽  
pp. 405-417 ◽  
Author(s):  
XiaoQing Lan ◽  
Wen Chen ◽  
Lin Wang
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Mean Flow ◽  
Enso Events ◽  
Flow Interactions ◽  
Stationary Planetary Wave

Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

2021 ◽  
Author(s):  
Michal Kozubek ◽  
Peter Krizan
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Wave Number ◽  
Strong Activity ◽  
Key Characteristics ◽  
Zonal Wave Number ◽  
Show Difference ◽  
Temperature Enhancement ◽  
Stationary Planetary Wave

<p>An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.</p>

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 Comparison of Key Characteristics of Remarkable SSW Events in the Southern and Northern Hemisphere

Atmosphere ◽  
2020 ◽  
Vol 11 (10) ◽  
pp. 1063
Author(s):  
Michal Kozubek ◽  
Jan Lastovicka ◽  
Peter Krizan
Keyword(s):  
Northern Hemisphere ◽  
Planetary Wave ◽  
Polar Vortex ◽  
Wave Number ◽  
Strong Activity ◽  
Key Characteristics ◽  
Zonal Wave Number ◽  
Show Difference ◽  
Temperature Enhancement ◽  
Stationary Planetary Wave

An exceptionally strong sudden stratospheric warming (SSW) in the Southern Hemisphere (SH) during September 2019 was observed. Because SSW in the SH is very rare, comparison with the only recorded major SH SSW is done. According to World Meteorological Organization (WMO) definition, the SSW in 2019 has to be classified as minor. The cause of SSW in 2002 was very strong activity of stationary planetary wave with zonal wave-number (ZW) 2, which reached its maximum when the polar vortex split into two circulations with polar temperature enhancement by 30 K/week and it penetrated deeply to the lower stratosphere and upper troposphere. On the other hand, the minor SSW in 2019 involved an exceptionally strong wave-1 planetary wave and a large polar temperature enhancement by 50.8 K/week, but it affected mainly the middle and upper stratosphere. The strongest SSW in the Northern Hemisphere was observed in 2009. This study provides comparison of two strongest SSW in the SH and the strongest SSW in the NH to show difference between two hemispheres and possible impact to the lower or higher layers.

scholarly journals Stationary planetary wave propagation in Northern Hemisphere winter – climatological analysis of the refractive index

2007 ◽  
Vol 7 (1) ◽  
pp. 183-200 ◽  
Author(s):  
Q. Li ◽  
H.-F. Graf ◽  
M. A. Giorgetta
Keyword(s):  
Refractive Index ◽  
Wave Propagation ◽  
Northern Hemisphere ◽  
Planetary Wave ◽  
Planetary Waves ◽  
Mean Flow ◽  
Stratospheric Circulation ◽  
Hemisphere Winter ◽  
Planetary Wave Propagation ◽  
Northern Hemisphere Winter

Abstract. The probability density on a height-meridional plane of negative refractive index squared f(nk2<0) is introduced as a new analysis tool to investigate the climatology of the propagation conditions of stationary planetary waves based on NCEP/NCAR reanalysis data for 44 Northern Hemisphere boreal winters (1958–2002). This analysis addresses the control of the atmospheric state on planetary wave propagation. It is found that not only the variability of atmospheric stability with altitudes, but also the variability with latitudes has significant influence on planetary wave propagation. Eliassen-Palm flux and divergence are also analyzed to investigate the eddy activities and forcing on zonal mean flow. Only the ultra-long planetary waves with zonal wave number 1, 2 and 3 are investigated. In Northern Hemisphere winter the atmosphere shows a large possibility for stationary planetary waves to propagate from the troposphere to the stratosphere. On the other hand, waves induce eddy momentum flux in the subtropical troposphere and eddy heat flux in the subpolar stratosphere. Waves also exert eddy momentum forcing on the mean flow in the troposphere and stratosphere at middle and high latitudes. A similar analysis is also performed for stratospheric strong and weak polar vortex regimes, respectively. Anomalies of stratospheric circulation affect planetary wave propagation and waves also play an important role in constructing and maintaining of interannual variations of stratospheric circulation.

scholarly journals Aura MLS observations of the westward-propagating <i>s</i>=1, 16-day planetary wave in the middle atmosphere: climatology and cross-equatorial propagation

2010 ◽  
Vol 10 (10) ◽  
pp. 23197-23227 ◽  
Author(s):  
K. A. Day ◽  
R. E. Hibbins ◽  
N. J. Mitchell
Keyword(s):  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Wave Amplitude ◽  
Planetary Wave ◽  
High Latitudes ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Significant Wave ◽  
Zonal Wavenumber ◽  
Summer Time

Abstract. The Microwave Limb Sounder (MLS) on the Aura satellite has been used to measure temperatures in the stratosphere, mesosphere and lower thermosphere (MLT). The data used here are from August 2004 to June 2010 and latitudes 75° S to 75° N. The temperature data reveal the persistent presence of a westward propagating 16-day planetary wave with zonal wavenumber 1. The wave amplitude maximises in winter in the stratosphere and MLT at middle to high latitudes, where monthly-mean amplitudes can be as large as ~8 K. Significant wave amplitudes are observed in the summer-time MLT and at lower stratospheric heights of up to ~20 km at middle to high latitudes. Wave amplitudes in the Northern Hemisphere approach values twice as large as those in the Southern Hemisphere. Wave amplitudes are also closely related to climatological zonal winds and are largest in regions of strongest eastward flow. There is a~reduction in wave amplitudes at the stratopause. No significant wave amplitude is observed near the equator or in the strongly westward background winds of the atmosphere in summer. This behaviour is interpreted as a consequence of wave/mean-flow interactions. It has been suggested that the summer-time 16-day wave in the MLT is ducted across the equator from the winter hemisphere and that this ducting is modulated by the equatorial Quasi-Biennial Oscillation (QBO) in the westerly phase. Here we observe that the QBO modulates the 16-day wave in the polar summer-time MLT in the Northern Hemisphere as previously observed, but this modulation is not seen in the Southern Hemisphere.

scholarly journals Stationary planetary wave propagation in Northern Hemisphere winter – climatological analysis of the refractive index

2006 ◽  
Vol 6 (5) ◽  
pp. 9033-9067 ◽  
Author(s):  
Q. Li ◽  
H.-F. Graf ◽  
M. A. Giorgetta
Keyword(s):  
Refractive Index ◽  
Wave Propagation ◽  
Northern Hemisphere ◽  
Planetary Wave ◽  
Planetary Waves ◽  
Mean Flow ◽  
Stratospheric Circulation ◽  
Hemisphere Winter ◽  
Planetary Wave Propagation ◽  
Northern Hemisphere Winter

Abstract. The probability density on a height-meridional plane of negative refractive index squared f(nk2<0) is introduced as a new analysis tool to investigate the climatology of the propagation properties of stationary planetary waves based on NCEP/NCAR reanalysis data for 44 Northern Hemisphere boreal winters (1958–2002). This analysis shows the control of the atmospheric state on planetary wave propagation. It is found that not only the variability of atmospheric stability with altitudes, but also the variability with latitudes has significant influence on planetary wave propagation. Eliassen-Palm flux and divergence are also analyzed to investigate the eddy activities and forcing on zonal mean flow. Only the ultra-long planetary waves with zonal wave number 1, 2 and 3 are investigated. In Northern Hemisphere winter the atmosphere shows a large possibility for stationary planetary waves to propagate from the troposphere to the stratosphere. On the other hand, waves induce eddy momentum flux in the subtropical troposphere and eddy heat flux in the subpolar stratosphere. Waves also exert eddy momentum forcing on the mean flow in the troposphere and stratosphere at middle and high latitudes. A similar analysis is also performed for stratospheric strong and weak polar vortex regimes, respectively. Anomalies of stratospheric circulation affect planetary wave propagation and waves also play an important role in constructing and maintaining of interannual variations of stratospheric circulation.

scholarly journals Southern Annular Mode Dynamics in Observations and Models. Part II: Eddy Feedbacks

2013 ◽  
Vol 26 (14) ◽  
pp. 5220-5241 ◽  
Author(s):  
Isla R. Simpson ◽  
Theodore G. Shepherd ◽  
Peter Hitchcock ◽  
John F. Scinocca
Keyword(s):  
Negative Feedback ◽  
Planetary Wave ◽  
Southern Annular Mode ◽  
Summer Season ◽  
Substantial Contribution ◽  
Mean Flow ◽  
Annular Mode ◽  
Planetary Scale ◽  
Zonal Wavenumber ◽  
Climatological Circulation

Abstract Many global climate models (GCMs) have trouble simulating southern annular mode (SAM) variability correctly, particularly in the Southern Hemisphere summer season where it tends to be too persistent. In this two-part study, a suite of experiments with the Canadian Middle Atmosphere Model (CMAM) is analyzed to improve the understanding of the dynamics of SAM variability and its deficiencies in GCMs. Here, an examination of the eddy–mean flow feedbacks is presented by quantification of the feedback strength as a function of zonal scale and season using a new methodology that accounts for intraseasonal forcing of the SAM. In the observed atmosphere, in the summer season, a strong negative feedback by planetary-scale waves, in particular zonal wavenumber 3, is found in a localized region in the southwest Pacific. It cancels a large proportion of the positive feedback by synoptic- and smaller-scale eddies in the zonal mean, resulting in a very weak overall eddy feedback on the SAM. CMAM is deficient in this negative feedback by planetary-scale waves, making a substantial contribution to its bias in summertime SAM persistence. Furthermore, this bias is not alleviated by artificially improving the climatological circulation, suggesting that climatological circulation biases are not the cause of the planetary wave feedback deficiency in the model. Analysis of the summertime eddy feedbacks in the models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) confirms that this is indeed a common problem among GCMs, suggesting that understanding this planetary wave feedback and the reason for its deficiency in GCMs is key to improving the fidelity of simulated SAM variability in the summer season.

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