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

sedimentary furrows and organized flow structure a study in lake superior investigations of the geology and physical limnology of a field of sedimentary furrows in lake superior have provided information on the characteristics of these bedforms and their relationship to the wind driven currents and associated turbulence structures in the bottom boundary layer the results generally support the existing conceptual model for furrow formation furrows in the study area 2 km2 at 100 m depth are spaced 20 l 00 m apart and exceed 800 m long the troughs being 0 5 m deep and 3 5 m wide sediment cores collected by submersible are poorly sorted cohesive terrigenous silts with a mean grain size of 20 pm relative to sediments in the interfurrow area those in the trough contain higher fractions of sand and coarse debris and accumulate at a rate 15 slower strong bottom currents speed 6 cm s l usually flow within 20 of the furrow direction and are most frequent between late october and early february when wind forced currents reach the bottom annual peak speeds approach 30 cm s l the relationship of the current and temperature records to the wind field is consistent with predictions of coastal jet theory profiling current meters deployed on either side of a furrow showed near bottom cross stream flow converging over the furrow with divergence higher in the boundary layer when the current speed exceeded 6 cm s l a preliminary numerical model exhibits a cross stream flow pattern consistent with the profiler observations

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

deformation in the vicinity of ice divides calculs numeriques aux elements finis de la variation de la vitesse horizontale avec la profondeur au voisinage d une difference de la glace symetrique isotherme et ou glissement sur un lit plat

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

color banding on georges bank as viewed by coastal zone color scanner observations of georges bank by coastal zone color scanner czcs show bandlike patterns that appear to be related to the large sand dunes and ridges which dominate the bottom topography there ship measurements of temperature and chlorophyll on georges bank in july 1979 also reflect the influence of the underwater dune fields the cause of the banding in the czcs data is unknown but is speculated to be the creation of alternating zones of divergence and convergence by tidal currents as the water flows over the underwater dune trough configuration the banding observed by czcs appears to be seasonal following the sequence of primary production in the gulf of maine and is believed to be important to biological processes as a site of new production and or as an effective transport mechanism any future models that attempt to interrelate tidal mixing and primary production must consider bottom topography and secondary flows

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

gravity waves in the troposphere and stratosphere during the macwave midas summer rocket program 1 combining data taken during the macwave summer rocket campaign at the andoya rocket range 69 3 n 16 0 e with a lidar radiosondes falling spheres and vhf radars at andoya and at the esrange the gravity wave content of the troposphere and stratosphere during the campaign nights was analyzed the lidar yielded vertical wavelengths and periods of gravity waves in the stratosphere a stokes parameter analysis was performed for the radiosonde and falling sphere data to estimate propagation directions of the gravity waves the wave content in the troposphere was inferred by applying wavelet and cross spectral methods to the radar data we found propagation conditions and spectra of the waves to vary with height following the change in the background wind the waves were excited both at the ground and in the tropopause lower stratosphere region

southern hemisphere summer mesopause responses to el nino southern oscillation abstractin the southern hemisphere sh polar region satellite observations reveal a significant upper mesosphere cooling and a lower thermosphere warming during warm enso events in december an opposite pattern is observed in the tropical mesopause region the observed upper mesosphere cooling agrees with a climate model simulation analysis of the simulation suggests that enhanced planetary wave pw dissipation in the northern hemisphere nh high latitude stratosphere during el nino strengthens the brewer dobson circulation and cools the equatorial stratosphere this increases the magnitude of the sh stratosphere meridional temperature gradient and thus causes the anomalous stratospheric easterly zonal wind and early breakdown of the sh stratospheric polar vortex the resulting perturbation to gravity wave gw filtering causes anomalous sh mesospheric eastward gw forcing and polar upwelling and cooling in addition constructive inference of enso and quasi biennial oscillation qbo could lead to st

classification of sedimentary furrows and a model for furrow initiation and evolution sedimentary furrows are longitudinal bed forms which form in fine grained cohesive sediments of the deep sea floor as well as in similar sediments in estuaries and in large lakes deep sea furrows have been observed where bottom currents often flow in one direction at 5 to 20 cm sec currents are much stronger greater than 50 cm sec in furrowed estuarine environments but sediment accumulation rates are higher a review of furrows studied in a variety of locations and environments suggests that these bed forms fall into two broad morphological classes those developed in muddy cohesive sediments tend to have steep walls and flat floors while those developed in carbonate rich cohesive sediments are broad and have gently sloping walls at abyssal depths furrows can often be detected by their distinctive echo patterns on 3 5 khz echo sounders a series of similar evenly spaced hyperbolic echoes which often have their apices tangent to the sea floor however different furrow cross sections may generate distinctive hyperbolic echo patterns a model for furrow initiation and development in muddy cohesive sediments suggests that furrows develop in depositional environments swept by recurring directionally stable and episodically strong currents furrows are initiated when secondary circulations in the boundary layer align coarse generally light debris in sand ribbon like bed forms as the coarse light sediments move along the sea floor they abrade small longitudinal troughs into the muds the grooves may fill in during intervals between strong current events if sedimentation rates are too high once a furrow is established on the sea floor further development may be controlled by the balance between sediment deposition and erosion where deposition occurs continuously and erosion occurs only episodically during brief periods of increased current strength narrow furrows width 1 5 to 1 15 of spacing appear to develop where deposition exceeds erosion whereas wide furrows width 1 2 of spacing develop where erosion exceeds or equals deposition dissolution may play an important role in the formation and evolution of furrows in carbonate rich cohesive sediments secondary circulation patterns over established furrows may be strongly controlled by bed form topography

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

climatological effects of orography and land sea heating contrasts on the gravity wave driven circulation of the mesosphere abstract on the basis of permanent january simulations performed with an idealized general circulation model for the troposphere and middle atmosphere the sensibility of the general circulation to orographic and thermal forcing of large scale stationary waves is assessed gravity waves are parameterized following lindzen s saturation theory up to the stratopause present model results coincide with earlier estimates confirming that the boreal winter zonal mean climate does crucially depend on the combined action of orography and land sea heating contrasts since in turn the propagation and breakdown of internal gravity waves is strongly modulated by the background horizontal winds the mesospheric response to stationary wave forcing turns out be substantial as well it is found that in the climatological zonal mean a warmer polar night stratosphere is accompanied by lower temperatures in the mesosphere up to about 80 km the temperature signal induced by stationary wave forcing changes sign again in

trends of mesospheric gravity waves at northern middle latitudes during summer 1 recent investigations of the seasonal variation of the activity of gravity waves in the mesosphere lower thermosphere mlt at middle and high latitudes suggest a semiannual variation with maxima during winter and summer and minima during the equinoxes it is generally assumed that this annual cycle is determined by filtering processes due to the background winds in the stratosphere and lower mesosphere on the other side long term observations of mesospheric winds at juliusruh 55 n 13 e since 1990 indicate a stable increase of westward directed winds below 80 km negative trends during summer as e g clearly evident in monthly means in july here we are studying how these long term changes of winds are related to trends of the activity of gravity waves gw with periods between 3 6 hours our results show that the observed zonal wind trend at about 75 km during july goes along with an enhancement of the gw activity at altitudes above 80 km indeed also the year to year variation of maxima of the observed westward directed winds at altitudes near 75 km and the gw activity at about 80 km are significantly correlated our results stimulate the further study of long term wind changes and corresponding gravity wave trends

suspended sediment signatures induced by shallow water undulating bottom topography near surface signatures of suspended sediment concentration ssc related to submerged bed forms displayed in visible band data gathered by space borne imaging sensors are described detailed acoustic doppler current profiler adcp data of vertical current velocity component echo intensity modulation of ssc and related oceanographic and meteorological observations in a tidal inlet of the north sea have been analyzed to understand the associated hydrodynamics of the optical imaging mechanism theoretical considerations based on the navier stokes and sediment continuity equations have been carried out as a first approximation these theoretical results explain signatures of enhanced ssc of in situ measurements and analyzed space borne images strong currents flowing over steep bottom topography are able to stir up the sediments to form both a general continuum of ssc and localized pulses of higher ssc in the vicinity of the causative bed feature itself the strain rate equivalent to the current gradient is an important parameter describing near water surface oceanographic and meteorological phenomena in the visible and microwave part of the electromagnetic spectrum observed by shore and ship based as well as air and space borne remote sensing systems significant disagreements between theoretical results of the strain rate generated by the surface current and in situ observations at the crests of submerged ridges and sand waves were identified possible explanations could be first the current velocity may not be barotropic near the crests of such bed forms and second mass conservation may not only be maintained through an acceleration or deceleration of the flow this implies that active up and downwelling effects of the three dimensional current field can also play a significant role for hydrodynamic interaction between current and underwater bed forms

holocene accumulation and ice sheet dynamics in central west antarctica 1 we derive depth age relationships across the ice divide between the ross and amundsen seas by tracking radar detected layers from the byrd ice core and a dated 105 m core near the divide the depth age relationships and an ice flow model are used to establish histories of accumulation and ice sheet dynamics over the past 8000 years results show that accumulation was approximately 30 higher than today from 5000 to 3000 years ago antarctic climate variability today is dominated by periodic fluctuations in strength of the circumpolar vortex which raises the possibility that the vortex was systematically weaker during the period of high accumulation accumulation today decreases almost linearly across the divide it is unlikely that this pattern has changed through the holocene the radar detected stratigraphy shows no evidence of the arched layers that are expected beneath a stable divide that is frozen to its bed implying that the divide has also been migrating and or the basal ice has been sliding through the holocene we cannot rule out the possibility of sliding because the basal ice is near its pressure melting point other evidence indicates that divide migration is likely the ross sea sector is now near steady state but it had a strong negative imbalance 200 years ago when kamb ice stream was active in contrast recent speedups of pine island and thwaites glaciers have likely caused the mass balance of the amundsen sea sector to become negative the divide is likely migrating toward the ross sea today

ice flow between the greenland ice core project and greenland ice sheet project 2 boreholes in central greenland the ice flow between the greenland ice core project grip and greenland ice sheet project 2 gisp2 boreholes in the summit region of central greenland is modeled with a steady state finite element model the model calculates the free ice sheet surface and the coupled ice flow and temperature fields along the flow line between the boreholes three dimensional effects are expressed in terms of the divergence of the flow and included in the coupled stress and temperature fields in addition to ice core data several geophysical surface programs have provided data that are used to constrain the model the modeled isochrones resemble the bedrock structure along the flow line but rise at the divide the rise at the divide is not seen in internal layers found by surface radio echo sounding an ice particle originally deposited at the surface moves through different stress and temperature regimes a set of trajectory lines are followed from the surface to the boreholes in order to follow the variation of stress deviators temperature and deformation along with the ice movement these variations along a trajectory line constitute a history of the corresponding ice layer the difference between the history of ice layers found in the grip and gisp2 boreholes is mainly due to the shear stress which is 3 4 times higher for gisp2 ice than for grip ice furthermore the grip ice experiences a nonzero longitudinal stress deviator much longer than the gisp2 ice

ocean surface patterns above sea floor bedforms as recorded by radar southern bight of north sea abstract airborne radar observations of the southern bight of the north sea have revealed sea surface patterns that reflect a constructional sea floor topography of tide built sand waves and sand ridges the patterns result from local horizontal differences in the amplitude of water surface waves with wavelengths less than 1 cm such modulations result from surface convergences and divergences as the water flows across structures on the ocean floor three sand ridges were observed which form a topological series defined by side slope asymmetry and sand wave pattern depth appears to be the controlling variable with shallow water leading to the steepest slopes most intense asymmetry and the most marked separation of sand waves into ebb and flood dominated domains

modelling the mean barotropic circulation in the bay of fundy and gulf of maine abstract two dimensional nonlinear numerical models are used to study the residual barotropic circulation generated by tides and steady winds in the bay of fundy and gulf of maine the first a multi grid model is used to examine the bay of fundy with a coarse look at the gulf of maine the circulation in the upper bay of fundy is predominantly tidally driven the model clearly reproduces the major gyres observed at the head of the bay steady wind stresses have some effect on the strength of these currents but little cited on the pattern the counterclockwise gyre observed in the body of the bay of fundy is not reproduced in the model the second model covers the lower bay of fundy and the gulf of maine with a single fine grid and is used to look at details in the gulf of maine a clockwise circulation around georges bank and nantucket shoals is clearly indicated from tidal forcing alone as is a gyre over the shallow part of browns bnak different steady wind stress fields give rise to variations in

acoustical study of the spatial distribution of plankton on georges bank and the relationship between volume backscattering strength and the taxonomic composition of the plankton abstract high frequency 420 khz sound was used to study the volume backscattering from plankton and micronekton over georges bank as part of a study designed to determine the correlation length scales of plankton spatial patterns in relation to physical structure and to intercompare different kinds of sampling and remote sensing instrumentation two physically distinct areas were studied a well mixed area in a shallow portion of the bank and a stratified area on the deeper southern flank of the bank a submersible echo sounder with a down looking transducer was mounted in a towed v fin volume backscattering data were collected from near the sea surface to the bottom 40 80 m vertical and horizontal volume backscattering structure in the stratified region differed from that in the well mixed area in both mean and variance providing evidence that physical forcing of the pattern varied significantly between the two areas internal waves appeared to modulate the depth of dense mid depth volume scattering layers in the stratified sites in the mixed area there was little horizontal layering or coarse scale horizontal structure however fine scale vertical lineations were evident with horizontal length scales on the order of the depth of the water column one hypothesis to explain these vertical lineations in the well mixed areas involves the development of secondary vertical circulation cells associated with the tidal flows over a rough bottom although volume backscattering at the stratified sites was 4 7 times higher than at the mixed site there was no significant difference in mocness multiple opening closing net and environmental sensing system collected biovolumes between these locations the difference in volume backscattering was due to differences in both the acoustic scattering properties of zooplankton taxa and the taxonomic composition of the plankton between the sites correlations between taxon abundance and volume scattering were positive and significant only for pteropods and euphausiid larvae the abundances of copepods chaetognaths fish larvae and amphipods were not significantly correlated with volume scattering when taxon specific model predictions of acoustic backscattering cross section developed by stanton et al ices journal of marine science 51 1994 505 512 were used with field collected individual size and abundance data to predict measured volume backscattering data good agreement was found between observed and predicted volume backscattering strengths

steady thermomechanical flow along two dimensional flow lines in large grounded ice sheets a thermomechanical flow model has been developed in order to perform simultaneous calculations of the surface elevation and the distribution of stresses velocities and temperatures along two dimensional flow lines on large grounded ice sheets in order to solve the complex system of full thermomechanical coupled equations the following approximations have been made a coordinate scaling giving a lead order reduced model and an iteration procedure which decouples the energy balance equation from the rest of the equations glen s flow law is used as the constitutive relationship between stresses and deformation in the model and it is found that the longitudinal deviatoric stresses have a significant role in the lead order equations at the ice divide the solution shows that the velocity stress and temperature distributions change rapidly here the basal temperature increases creating a hot spot the surface strain rates increase 50 and the horizontal velocity profile is concave near the base with an inflection point away from the ice divide basal temperature increases and in the example presented here the basal temperature reaches the pressure melting point after 2 3 of the lateral extent and basal sliding begins to influence the flow in the ablation region it is seen that the heat produced by internal deformation is of the same order of magnitude as the geothermal heat flux from the bedrock

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

mesospheric planetary waves over antarctica during 2002 1 wind measurements from a series of atmospheric radars located around antarctica have been used to characterize the mesospheric planetary wave field during the winter of 2002 combining winds from the medium frequency mf radar at rothera 68 s 68 w and the superdarn high frequency meteor wind radars at halley 76 s 27 w sanae 72 s 3 w and syowa 69 s 40 e stations we have been able to measure the period wavenumber and propagation direction of the most prominent planetary waves the results show that the planetary wave field before the unusual stratospheric warming in 2002 was dominated by a very long period 43 days westward and upward propagating zonal planetary wavenumber 1 however after the stratospheric warming events began in late winter the character of the wave field changed and a shorter period 14 days westward zonal wavenumber 1 became established it would appear that the previously reported oscillations of the mesospheric hydroxyl airglow temperatures at rothera and halley which were strongly anti correlated to the meridional wind were the result of these planetary waves

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 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 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

attribution of ionospheric vertical plasma drift perturbations to large scale waves and the dependence on solar activity 1 in this study we quantify the contribution of individual large scale waves to ionospheric electrodynamics and examine the dependence of the ionospheric perturbations on solar activity we focus on migrating diurnal tide dw1 plus mean winds migrating semidiurnal tide sw2 quasi stationary planetary wave one qspw1 and nonmigrating semidiurnal westward wave one sw1 under northern winter conditions when qspw1 and sw1 are climatologically strong from thermosphere ionosphere mesosphere electrodynamics general circulation model simulations under solar minimum conditions it is found that the mean winds and dw1 produce a wave two pattern in equatorial vertical e bdrift that is upward in the morning and around dusk the modeled sw2 also produces a wave two pattern in the ionospheric vertical drift that is nearly a half wave cycle out of phase with that due to mean winds and dw1 sw1 can cause large vertical drifts around dawn while qspw1 does not have any direct impact on the vertical drift wind components of both sw2 and sw1 become large at middle to high latitudes in the e region and kernel functions obtained from numerical experiments reveal that they can significantly affect the equatorial ion drift likely through modulating the e region wind dynamo the most evident changes of total ionospheric vertical drift when solar activity is increased are seen around dawn and dusk reflecting the more dominant role of large f region pedersen conductivity and of the f region dynamo under high solar activity therefore the lower atmosphere driving of the ionospheric variability is more evident under solar minimum conditions not only because variability is more identifiable in a quieter background but also because the e region wind dynamo is more significant these numerical experiments also demonstrate that the amplitudes phases and latitudinal and vertical structures of large scale waves are important in quantifying the ionospheric responses