a data study of the influence of the equatorial upper stratosphere on northern hemisphere stratospheric sudden warmings equatorial winds in the stratosphere are known to influence the frequency of stratospheric midwinter sudden warmings sudden warmings in turn influence the earth s climate both through their direct influence on polar temperatures and through the temperature dependence of ozone depletion in the lower stratosphere the conventional holton tan explanation for the equatorial influence on sudden warmings is in terms of the equatorial winds in the lower stratosphere 20 30 km acting as a waveguide for midlatitude planetary wave propagation this study employs stratospheric temperature analyses and equatorial rocketsonde wind data extending to 58 km to diagnose the relationship between the northern hemisphere polar temperatures and equatorial zonal winds at all height levels in the stratosphere in addition to the recognized holton tan relationship linking the polar temperatures to the quasi biennial oscillation in equatorial winds in the lower stratosphere a strong correlation of polar temperatures with equatorial winds in the upper stratosphere is found we suggest that this may be associated with the strength and vertical extent of the westerly phase of the semi annual oscillation in the upper stratosphere although the observations alone cannot provide a conclusive causal relationship the main diagnostic tools employed are correlation studies and composite analysis the results underline the need for continued high quality equatorial wind measurements at all stratospheric levels

detection of the secondary meridional circulation associated with the quasi biennial oscillation 1 the quasi biennial oscillation qbo signal in stratospheric zonal and meridional wind temperature and geopotential height fields is analyzed based on the use of the national centers for environmental prediction ncep reanalysis 1958 2001 the multitaper method singular value decomposition mtm svd a multivariate frequency domain analysis method is used to detect significant and spatially coherent narrowband oscillations the qbo is found as the most intense signal in the stratospheric zonal wind then the mtm svd method is used to determine the patterns induced by the qbo at every stratospheric level and data field the secondary meridional circulation associated with the qbo is identified in the obtained patterns this circulation can be characterized by negative positive temperature anomalies associated with adiabatic rising sinking motions over zones of easterly westerly wind shear and over the subtropics and midlatitudes while meridional convergence and divergence levels are found separated by a level of maximum zonal wind shear these vertical and meridional motions form quasi symmetric circulation cells over both hemispheres though less intense in the southern hemisphere

high rossby wave activity in austral winter 2002 modulation of the general circulation of the mlt during the macwave midas northern summer program 1 the seasonally and zonally averaged effects of the anomalously strong rossby wave activity in austral winter 2002 are estimated by a sensitivity experiment using an idealized general circulation model the approach focuses on the modulation of gravity wave saturation via the altered mean winds in the mesosphere and mlt in the northern summer mlt the effects consist of increased vertical gradients of the mean zonal wind and temperature as well as downward shifts of the residual circulation and the gravity wave induced frictional heating all these signals agree reasonably with observations obtained during the macwave midas program 2002

quasi biennial oscillation of short period planetary waves and polar night jet in winter antarctica observed in saber and merra 2 and mechanism study with a quasi geostrophic model

enso influences on southern hemisphere column ozone during the winter to spring transition 1 this study investigates how the el nino southern oscillation enso modulates the distribution of column ozone during the southern hemisphere sh winter to spring transition when a zonal asymmetry in column ozone develops near 55 s with a maximum south of australia enso differences in column ozone and planetary wave structure are explored for the average of seven el nino en versus six la nina ln events during 1982 2004 a westward shift in convection during ln corresponds to a 30 50 westward shift of sh planetary wave and column ozone patterns the extratropical lower stratospheric temperature anomalies are inversely correlated with tropical anomalies in similar longitude bands and are highly correlated with local column ozone anomalies the tropical signal is communicated to higher latitudes by modulating subtropical anticyclones with distinctive responses for en and ln years for each month during august and en a subtropical anticyclone extends from south america to south africa and the wave one asymmetry of the antarctic vortex is more pronounced and shifted eastward along with column ozone in september and en a strong anticyclone exists over south africa with a corresponding cold ozone poor anomaly in the stratosphere diminishing the western edge of the ozone maximum in october and ln a strong anticyclone exists over australia with an amplified trough on its poleward flank this trough is overlain by an ozone rich warm anomaly which expands the western edge of the ozone maximum and the polar vortex asymmetry is amplified and rotated westward

the evaluation of winds from geopotential height data in the stratosphere abstract several methods of obtaining horizontal wind fields in the extratropical stratosphere from geopotential height data are evaluated and compared to geostrophic estimates with focus on the poleward fluxes of momentum and heat and on the resulting eliassen palm ep flux divergence estimates winds derived from a coupled iterative solution of the zonal and meridional momentum equations balance winds are proposed and tested in addition to winds derived from linearizing these equations about the zonal mean flow linen winds comparison of the different analysis methods are made for a general circulation model simulation of the northern hemisphere nh winter stratosphere and for nh and southern hemisphere sh winter observational data the balance and linear wind estimates of poleward momentum flux are similar and substantially smaller than geostrophic values in the high latitude stratosphere neglect of local curvature effects is the primary cause of the geostrophic overestimate the relati

tropical sst preconditioning of the sh polar vortex during winter 2002 the response of the southern hemisphere sh polar atmosphere to the tropical sea surface temperature sst during the 2002 winter spring season is investigated by using a general circulation model gcm the sh stratospheric winter of 2002 was particularly unusual characterized by a weaker than normal polar vortex during the whole season it also registered at the end of september the first major warming yet observed in the sh this event is unexpected in the sh and it is supposed to be induced by a preconditioning of the polar vortex starting at the beginning of the winter atmospheric gcm experiments with prescribed sst boundary conditions are performed the sensitivity of the antarctic dynamics to the tropical sst of 2002 a year characterized by an el nino event of moderate intensity is studied and the uniqueness of the 2002 tropical oceanic condition is investigated through the comparison of the simulated response of the climatic system to 2002 and 1997 tropical sst 1997 being a year with a strong el nino event model results highlight a primary role played by the tropical sst of 2002 in the development of the peculiar characteristics of the antarctic dynamics during the winter months that appears to be a necessary condition for the generation of the anomalous destabilization of the polar vortex during the following spring results for june 2002 show a strong generation of vertically propagating waves resulting from the tropical sst that through the perturbation of the westerly jet at middle latitudes produces a preconditioning of the polar vortex by affecting the wave refraction index the particular structure of the tropical sst anomalies during the winter of 2002 is thought to have influenced the subsequent preconditioning of the stratospheric vortex

first lidar observations of quasi biennial oscillation induced interannual variations of gravity wave potential energy density at mcmurdo via a modulation of the antarctic polar vortex

propagation of the arctic oscillation from the stratosphere to the troposphere geopotential anomalies ranging from the earth s surface to the middle stratosphere in the northern hemisphere are dominated by a mode of variability known as the arctic oscillation ao the ao is represented herein by the leading mode the first empirical orthogonal function of low frequency variability of wintertime geopotential between 1000 and 10 hpa in the middle stratosphere the signature of the ao is a nearly zonally symmetric pattern representing a strong or weak polar vortex at 1000 hpa the ao is similar to the north atlantic oscillation but with more zonal symmetry especially at high latitudes in zonal mean zonal wind the ao is seen as a north south dipole centered on 40 45 n in zonal mean temperature it is seen as a deep warm or cold polar anomaly from the upper troposphere to 10 hpa the association of the ao pattern in the troposphere with modulation of the strength of the stratospheric polar vortex provides perhaps the best measure of coupling between the stratosphere and the troposphere by examining separately time series of ao signatures at tropospheric and stratospheric levels it is shown that ao anomalies typically appear first in the stratosphere and propagate downward the midwinter correlation between the 90 day low pass filtered 10 hpa anomaly and the 1000 hpa anomaly exceeds 0 65 when the surface anomaly time series is lagged by about three weeks the tropospheric signature of the ao anomaly is characterized by substantial changes to the storm tracks and strength of the midtropospheric flow especially over the north atlantic and europe the implications of large stratospheric anomalies as precursors to changes in tropospheric weather patterns are discussed

the southern oscillation part v the anomalies in the lower stratosphere of the northern hemisphere in winter and a comparison with the quasi biennial oscillation abstract the mean anomalies of 50 mb height in the northern winter for seven warm events in the southern oscillation show a weak polar vortex and an enhanced aleutian high in the mean for six cold events the polar vortex is unusually strong and the aleutian high is weakened and displaced far to the southwest these anomalies are consistent with the corresponding anomalies in sea level pressure pattern the warm events of 1963 and 1982 did not fit this pattern as in both years the polar vortex was cold and intense these events happened in years when volcanoes injected large amounts of gases and aerosols into the stratosphere and the temperature of the tropical stratosphere became unusually high in other warm events the temperature of the tropical stratosphere was abnormally low the mean anomalies of the quasi biennial oscillation for the winter as a whole west minus east phase computed from years with no cold or warm events are zonally symmetrical and shaped as four concentric regions with alternatin

a possible influence of the tropical quasi biennial oscillation on the variability of the extratropical circulation in the southern hemisphere 1 this study uses geopotential heights and zonal winds from the ncar ncep reanalysis and the naujokat tropical stratospheric zonal wind data set to evaluate the suggestion that the tropical quasi biennial oscillation qbo influenced the observed amplitude increase in zonal harmonic wave 1 in the southern hemisphere winter after 1975 fourier analysis was used to extract zonal wave 1 zw1 from the geopotential heights zw1 and the zonal winds were stratified by qbo phase and compared to those composited for years before and after 1975 the comparisons confirm that zw1 during the easterly phase of the qbo is larger than zw1 during the westerly phase the comparisons also suggest that the growth in zw1 seen after 1975 took place preferentially during winters with an easterly tropical qbo and weak stratospheric winds the change in zw1 is associated with surface level changes over the pacific and simultaneous upper level support by the easterly phase tropical qbo

turbulent stresses and secondary currents in a tidal forced channel with significant curvature and asymmetric bed forms acoustic doppler current profilers are deployed to measure both the mean flow and turbulent properties in a channel with significant curvature direct measurements of the reynolds stress show a significant asymmetry over the tidal cycle where stresses are enhanced during the flood tide and less prominent over the ebb tide this asymmetry is corroborated by logarithmic fits using 10 min averaged velocity data a smaller yet similar tendency asymmetry in drag coefficient is inferred by fitting the velocity and estimated large scale pressure gradient to a one dimensional along channel momentum balance this smaller asymmetry is consistent with recent modeling work simulating regional flows in the vicinity of the study site the asymmetry in drag suggests the importance of previously reported bed forms for this channel and demonstrates spatial and temporarily variations in bed stress secondary circulation patterns observed in a relatively straight section of channel appear driven by local curvature rather th

qbo effects on antarctic mesospheric winds and polar vortex dynamics 1 a dynamical link is demonstrated between the equatorial quasi biennial oscillation qbo and high latitude mesospheric zonal winds recorded by an imaging doppler interferometer idi at halley antarctica above 80 km eastward winds in winter an extension of the polar vortex into the mesosphere are strengthened under easterly 50 hpa qbo conditions this is similar to the holton tan effect in the stratosphere but working in opposition the weak winter time zonal winds are shown to differ by up to 2 6 m s dependent on qbo phase in spring zonal winds are most strongly correlated with the equatorial 25 hpa qbo and are significantly more westerly in november an extension of the qbo response in the stratosphere below it is suggested that qbo modulation of the vortex winds in the antarctic mesosphere is dependent on planetary wave activity from the antarctic in winter and arctic in spring

quasi biennial modulation of the southern ocean coherent mode empirical orthogonal function eof analysis of two independent southernocean sea level datasets for the period 1992 2002 shows that the coherent oceanicmode a zonally symmetric counterpart to the atmospheric southern annular mode sam consistently emerges as the predominant mode of variability and is revealedto be a reliable proxy for circumpolar transport upon subannual to interannualtime scales cross validation of the coherent mode from each dataset and that ofa global barotropic model demonstrates a high degree of correspondence betweensea level observations and model estimations and also indicates that the coherentoceanic mode is largely barotropically driven upon subannual time scales whilstbaroclinic oceanic effects predominate at longer periods both the coherent modeand transport are shown to be modi ed by the stratospheric quasi biennial oscilla tion qbo and a mechanism is described by which qbo dependent planetary waveactivity may be guided from the stratosphere towards the surface by high latitudeeasterly and westerly jets inducing wind anomalies that force sea level variabilitythrough equatorward ekman transport a longer 18 year tide gauge record fromthe vernadsky faraday station and a 22 year time series of sea level estimationsfrom an ocean general circulation model are used to show that qbo inducedsea level and transport variability may be modulated upon longer time scales by aquasi decadalcycleofsolaractivity copyright c 2010royalmeteorologicalsociety

quasi biennial oscillation influence on long period planetary waves in the antarctic upper mesosphere 1 long period planetary wave data derived from meteor wind observations recorded over a 12 year period with the superdarn radar at halley antarctica are presented and compared with the phase of the quasi biennial oscillation qbo throughout the equatorial stratosphere enhanced planetary wave activity in the antarctic upper mesosphere is found during the summer months when the qbo in the equatorial upper stratosphere is westerly and during the late winter when the qbo in the upper stratosphere is easterly these quasi biennial enhancements in planetary wave activity coincide with a reduction in strength by up to 30 of the late winter eastward winds in the antarctic upper mesosphere in addition when the qbo is in the correct phase for enhanced planetary wave activity in the upper mesosphere above halley planetary wave activity measured in the upper mesosphere of the high latitude northern hemisphere is reduced and vice versa these results clearly indicate significant interhemispheric propagation of planetary waves from the winter to summer hemispheres observational evidence that the stratospheric qbo induces a strong enough qbo in the equatorial upper mesosphere to act as a gate to the interhemispheric propagation of these long period waves is discussed in light of these results

the quasi biennial oscillation analysis using era 40 data 1 the era 40 data set is used to examine the equatorial quasi biennial oscillation qbo the data set extends from the ground to 0 1 hpa 65 km and covers a 44 year period january 1958 to december 2001 including 18 5 qbo cycles analysis of this data set of unprecedented spatial and temporal coverage has revealed a threefold structure in height in the qbo zonal wind anomalies at the equator in addition to the well known twofold structure in the lower and middle stratosphere that is easterlies overlying westerlies or vice versa there is a third anomaly in the upper stratosphere the sign of this upper stratospheric anomaly is the same as the lower stratospheric anomaly thus forming anomalies of alternating sign throughout the depth of the equatorial stratosphere the amplitude of this upper stratospheric anomaly is 10 m s 1 approximately one third of the amplitude of the lower stratospheric signal the frequency and descent rates of the east and west qbo phases are analyzed in detail with particular attention to any 11 year solar cycle influence in addition to the observed solar modulation of the duration of the qbo west phase the analysis shows a solar modulation of the mean descent rate of the easterly shear zone the mean time required for the easterly shear zone to descend from 20 to 44 hpa is 2 months less under solar maximum conditions than under solar minimum conditions 7 4 months versus 9 7 months this rapid descent of the easterly shear zone cuts short the west phase of the qbo in the lower stratosphere during solar maximum periods

quasi biennial modulation of the southern hemisphere stratospheric polar vortex observations reveal that the wintertime southern hemisphere stratospheric polar vortex is modulated by the phase of the equatorial quasi biennial oscillation qbo the high latitude southern stratosphere is shown to be slightly colder throughout the winter and the final warming occurs later when the qbo is in its west phase during may october the modulation of winds by the qbo is confined to midlatitudes at the edge of the polar vortex the difference between west and east phase composites of zonal mean wind during november at the time of the final warming in the southern hemisphere exceeded 14 ms 1 this difference is very similar to that in january in the northern hemisphere while northern hemisphere qbo effects are optimized using equatorial winds near 40 hpa southern hemisphere effects are best seen using 25 hpa winds

quasi biennial modulation of the semidiurnal tide in the upper mesosphere above halley antarctica we present an analysis of a long term archive of horizontal wind data derived from meteor wind observations from a superdarn radar at halley antarctica 76s 27w systematic differences between the 12 hour component in the meridional wind and the climatological mean are observed showing evidence of a quasi biennial modulation of the high latitude semidiurnal tide in the upper mesosphere the amplitude of the observed tides is enhanced when the equatorial stratospheric quasibiennial oscillation above 10 hpa is westerly this enhancement is greatest in the summertime tidal amplitudes when the zonal wavenumber one s 1 nonmigrating component dominates the semidiurnal wind field and is coincident with an enhancement of the summertime planetary wave activity in the upper mesosphere these observations strongly support the hypothesis that the s 1 component of the semidiurnal tide observed at high latitudes is due to a non linear interaction between the migrating s 2 semidiurnal tide and quasi stationary s 1 planetary waves

the extraordinarily strong and cold polar vortex in the early northern winter 2015 2016 the arctic polar vortex in the early winter 2015 16 was the strongest and coldest o f the la st 68 years using global reanalysis data satellite observations and mesospheric radar wind measurements over northern scandinavia we investigate the characteristics of the early sta g e polar vortex and relate them to previous winters we found a correlation between the planetary wave pw activity and the strength and temperature of the northern polar vor tex in the stratosphere and mesosphere in nov d ec 2015 a reduced pw generation in the troposphere and a stronger pw filtering in the troposphere and stratosphere caused by stronger zonal winds in mid latitudes resulted in a stronger polar vortex thi s effect was strengthened by the equator ward shift of pws due to the strong zonal wind in polar latitudes resulting in a southward shift of the eliassen palm flux divergence and hence inducinga decreased deceleration of th e polar vortex by pws

modulation of antarctic vortex composition by the quasi biennial oscillation using a decade of aura microwave limb sounder observations we show distinctly different n2o distributions in southern hemisphere winter that depend on the phase of the quasi biennial oscillation qbo composites of the nitrous oxide n2o anomalies calculated for westerly and easterly phases show that qbo generated variability originating in the subtropical middle stratosphere fills the midlatitude surf zone by late winter after the spring vortex breakup the anomaly is transported to the antarctic where it remains until the next vortex forms in fall trapped in the newly formed vortex the anomaly descends in isolation through fall and winter arriving in the antarctic lower stratosphere in september about 1 year after it formed this transport pathway explains previously reported variability of n2o and inorganic chlorine cly inside the antarctic vortex and demonstrates that the middle stratosphere qbo affects ozone depletion by modulating antarctic cly