The role of stationary and transient planetary waves in the maintenance of stratospheric polar vortex regimes in Northern Hemisphere winter

2010 ◽  
Vol 28 (1) ◽  
pp. 187-194 ◽  
Author(s):  
Qian Li ◽  
Hans-F. Graf ◽  
Xuefeng Cui
Keyword(s):  
Northern Hemisphere ◽  
Polar Vortex ◽  
Planetary Waves ◽  
Stratospheric Polar Vortex ◽  
Hemisphere Winter ◽  
Northern Hemisphere Winter

scholarly journals The Unusual Midwinter Warming in the Southern Hemisphere Stratosphere 2002: A Comparison to Northern Hemisphere Phenomena

2005 ◽  
Vol 62 (3) ◽  
pp. 603-613 ◽  
Author(s):  
Kirstin Krüger ◽  
Barbara Naujokat ◽  
Karin Labitzke
Keyword(s):  
Detailed Analysis ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Traveling Waves ◽  
Dominant Role ◽  
Polar Vortex ◽  
Planetary Waves ◽  
Wave Forcing ◽  
Northern Winter

Abstract A strong midwinter warming occurred in the Southern Hemisphere (SH) stratosphere in September 2002. Based on experiences from the Northern Hemisphere (NH), this event can be defined as a major warming with a breakdown of the polar vortex in midwinter, which has never been detected so far in the SH since observations began at the earliest in the 1940s. Minor midwinter warmings occasionally occurred in the SH, but a strong interannual variability, as is present in winter and spring in the NH, has been explicitly associated with the spring reversals. A detailed analysis of this winter reveals the dominant role of eastward-traveling waves and their interaction with quasi-stationary planetary waves forced in the troposphere. Such wave forcing, finally leading to the sudden breakdown of the vortex, is a familiar feature of the northern winter stratosphere. Therefore, the unusual development of this Antarctic winter is described in the context of more than 50 Arctic winters, concentrating on winters with similar wave perturbations. The relevance of preconditioning of major warmings by traveling and quasi-stationary planetary waves is discussed for both hemispheres.

scholarly journals The role of the tropical West Pacific in the extreme Northern Hemisphere winter of 2013/2014

2016 ◽  
Vol 121 (4) ◽  
pp. 1698-1714 ◽  
Author(s):  
Peter A. G. Watson ◽  
Antje Weisheimer ◽  
Jeff R. Knight ◽  
T. N. Palmer
Keyword(s):  
Northern Hemisphere ◽  
West Pacific ◽  
Hemisphere Winter ◽  
Northern Hemisphere Winter

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 On the Linkages between the Tropospheric Isentropic Slope and Eddy Fluxes of Heat during Northern Hemisphere Winter

2012 ◽  
Vol 69 (6) ◽  
pp. 1811-1823 ◽  
Author(s):  
David W. J. Thompson ◽  
Thomas Birner
Keyword(s):  
Northern Hemisphere ◽  
Low Frequency ◽  
Lower Troposphere ◽  
Heat Fluxes ◽  
Daily Data ◽  
Synoptic Eddies ◽  
Eddy Fluxes ◽  
Hemisphere Winter ◽  
Northern Hemisphere Winter

Abstract Previous studies have demonstrated the key role of baroclinicity and thus the isentropic slope in determining the climatological-mean distribution of the tropospheric eddy fluxes of heat. Here the authors examine the role of variability in the isentropic slope in driving variations in the tropospheric eddy fluxes of heat about their long-term mean during Northern Hemisphere winter. On month-to-month time scales, the lower-tropospheric isentropic slope and eddy fluxes of heat are not significantly correlated when all eddies are included in the analysis. But the isentropic slope and heat fluxes are closely linked when the data are filtered to isolate the fluxes due to synoptic (&lt;10 days) and low-frequency (&gt;10 days) time scale waves. Anomalously steep isentropic slopes are characterized by anomalously poleward heat fluxes by synoptic eddies but anomalously equatorward heat fluxes by low-frequency eddies. Lag regressions based on daily data reveal that 1) variations in the isentropic slope precede by several days variations in the heat fluxes by synoptic eddies and 2) variations in the heat fluxes due to both synoptic and low-frequency eddies precede by several days similarly signed variations in the momentum flux at the tropopause level. The results suggest that seemingly modest changes in the tropospheric isentropic slope drive significant changes in the synoptic eddy heat fluxes and thus in the generation of baroclinic wave activity in the lower troposphere. The linkages have implications for understanding the extratropical tropospheric eddy response to a range of processes, including anthropogenic climate change, stratospheric variability, and extratropical sea surface temperature anomalies.

scholarly journals The Role of Warm Conveyor Belts for the Intensification of Extratropical Cyclones in Northern Hemisphere Winter

2016 ◽  
Vol 73 (10) ◽  
pp. 3997-4020 ◽  
Author(s):  
Hanin Binder ◽  
Maxi Boettcher ◽  
Hanna Joos ◽  
Heini Wernli
Keyword(s):  
Northern Hemisphere ◽  
Extratropical Cyclones ◽  
Cyclone Center ◽  
Explosive Cyclones ◽  
Conveyor Belts ◽  
Upper Level ◽  
Hemisphere Winter ◽  
Warm Conveyor Belts ◽  
Northern Hemisphere Winter

Abstract The role of warm conveyor belts (WCBs) and their associated positive low-level potential vorticity (PV) anomalies are investigated for extratropical cyclones in Northern Hemisphere winter, using ERA-Interim and composite techniques. The Spearman correlation coefficient of 0.68 implies a moderate to strong correlation between cyclone intensification and WCB strength. Hereby, cyclone intensification is quantified by the normalized maximum 24-h central sea level pressure deepening and WCB strength by the WCB air mass associated with the cyclone’s 24-h period of strongest deepening. Explosively intensifying cyclones typically have strong WCBs and pronounced WCB-related PV production in the cyclone center; they are associated with a WCB of type W2, which ascends close to the cyclone center. Cyclones with similar WCB strength but weak intensification are either diabatic Rossby waves, which do not interact with an upper-level disturbance, or cyclones where much of the WCB-related PV production occurs far from the cyclone center and thereby does not contribute strongly to cyclone deepening (WCB of type W1, which ascends mainly along the cold front). The category of explosively intensifying cyclones with weak WCBs is inhomogeneous but often characterized by a very low tropopause or latent heating independent of WCBs. These findings reveal that (i) diabatic PV production in WCBs is essential for the intensification of many explosive cyclones, (ii) the importance of WCBs for cyclone development strongly depends on the location of the PV production relative to the cyclone center, and (iii) a minority of explosive cyclones is not associated with WCBs.

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