ca eskola component in clinopyroxene experimental studies at high pressures and high temperatures in multianvil apparatus abstract in order to investigate the pressure implications of silica exsolution from clinopyroxene in ultrahigh pressure metamorphic rocks we have measured systematically the values of the calcium eskola ca esk component of clinopyroxenes over a considerable range of pressure and temperature a series of anhydrous experiments using powdered glass of composition wt sio2 59 29 al2o3 23 12 mgo 5 44 cao 10 37 and na2o 1 78 were conducted in a walker style multianvil apparatus in the p t range of 6 12 gpa and 900 1200 c we find that all clinopyroxenes synthesized in equilibrium with garnet kyanite and sio2 coesite or stishovite are cation deficient the highest value of the ca esk component 32 38 mol is reached at 6 gpa followed by slight decrease beginning at 8 gpa as the pyroxene progressively dissolves into garnet and more rapid decrease at 10 12 gpa when stishovite becomes stable in the assemblage comparison of our data with those available in the literature which all together covers a wider range of p and t shows that the ca esk activity depends strongly on bulk chemistry especially the silica content in general integrated analyses of published experiments on similar compositions show that the ca esk component rises rapidly to its highest values from 1 to 4 6 gpa then slightly decreases to 9 gpa followed by remarkable decrease to 15 gpa culminating in replacement of pyroxene by garnet in equilibrium with stishovite we conclude that the sio2 exsolution lamellae observed in clinopyroxenes from many ultrahigh pressure terranes can be explained by destabilization of the ca esk component during decompression however because silica solubility in clinopyroxene reaches its maximum at 6 8 gpa the practical upper pressure limit that can be inferred from this system is 200 250 km

experimental study of subsolidus phase relations and mixing properties of pyroxene in the system cao al2o3 sio2 abstract subsolidus phase relations in the system cao al2o3 sio2 cas were experimentally determined with tight reversals of several univariant curves and with 14 equilibration experiments containing the assemblage pyroxene anorthite where pyroxene is a binary solid solution of ca tschermak cats caal2sio6 and ca eskola caes ca0 5alsi2o6 endmembers reversals were obtained on the following reactions bar c 3an gr 2ky q p 22t 700 3an cor gr 3ky p 21 8t 950 3cats gr 2cor p 55t 53900 and 6cats 1 x caesx 2 1 2x gr 4 1 2x cor 9xan observed slopes indicate 9 8 j mol k of al si disorder in ca tschermak pyroxene and 5 3 j mol k of al si disorder in anorthite at 1300 c it is suggested that al si disorder in anorthite increases by 1 9 j mol k from 700 c to 1300 c compositions of cats caes pyroxene in equilibrium with anorthite and pbo rich liquid were experimentally determined at 1400 1430 c and 22 7 30 8 kbar microprobe measurements gave compositions which are consistent with an ideal pyroxene solution and the following parameters for the reaction 3an 2cats 2caes j bar k 2rtln xcats xcaes 60200 86 4t 5 06 13 10 7p p 0 resulting in h0j 39 8 kj mol and s0 461 8 j mol k for the ca eskola endmember at 1300 c the obtained properties of the ca eskola component are necessary for thermobarometry based on pyroxene bearing assemblages containing plagioclase quartz or kyanite

large scale dynamics of the mesosphere and lower thermosphere an analysis using the extended canadian middle atmosphere model the extended canadian middle atmosphere model is used to investigate the large scale dynamics of the mesosphere and lower thermosphere mlt it is shown that the 4 day wave is substantially amplified in southern polar winter in the presence of instabilities arising from strong vertical shears in the mlt zonal mean zonal winds brought about by parameterized nonorographic gravity wave drag a weaker 4 day wave in northern polar winter is attributed to the weaker wind shears that result from weaker parameterized wave drag the 2 day wave also exhibits a strong dependence on zonal wind shears in agreement with previous modeling studies in the equatorial upper mesosphere the migrating diurnal tide provides most of the resolved westward wave forcing which varies semiannually in conjunction with the tide itself resolved forcing by eastward traveling disturbances is dominated by smaller scales nonmigrating tides and other planetary scale waves play only a minor role in the zonal mean zonal momentum budget in the tropics at these heights resolved waves are shown to play a significant role in the zonal mean meridional momentum budget in the mlt impacting significantly on gradient wind balance balance fails at low latitudes as a result of a strong reynolds stress associated with the migrating diurnal tide an effect which is most pronounced at equinox when the tide is strongest resolved and parameterized waves account for most of the imbalance at higher latitudes in summer this results in the gradient wind underestimating the actual eastward wind reversal by up to 40

a comparative study of mesospheric solar tides observed at adelaide and kyoto observations of winds in the upper mesosphere and lower thermosphere 80 110 km measured at the geographically conjugate locations of adelaide 35 s 138 e and kyoto 35 n 136 e in the years 1983 1985 are used to study hemispheric differences in the behavior of the solar diurnal and semidiurnal tides comparisons of the tidal amplitude and phase parameters show that there are distinct hemispheric asymmetries the diurnal tide is usually much larger in amplitude at adelaide and it exhibits a height structure which indicates a relatively larger contribution from the propagating 1 1 mode at this location comparisons with recent theoretical work suggest that while some of these differences may be due to hemispheric differences in forcing and or to interactions between the tide and the background winds in the middle atmosphere it is also possible that they indicate weaker turbulent induced damping of the 1 1 mode in the southern hemisphere the characteristics of the semidiurnal tide agree well at the two locations it is found that the zonal wind components are about 6 hours out of phase and the meridional components are in phase in all seasons this behavior taken together with the inferred vertical wavelengths which are greater than 100 km in summer and 45 80 km in winter indicates that there are strong contributions from the antisymmetric 2 3 mode probably forced by wind induced mode coupling from the symmetric 2 2 mode the phases near 90 km exhibit a bimodal or two state behavior with the phases being almost constant in one state near the june solstice and then making a rapid transition of between 4 and 6 hours to another phase stable state near the december solstice the duration of the state near the june solstice 6 8 months is longer than the duration of the state at the december solstice although the agreement between recent models and our observations is relatively good better agreement may be expected when more realistic wind distributions especially for the southern hemisphere are used in the models

observations of the two day wave in windii data during january 1993 analysis of variations in the zonal and meridional wind observed by the wind imaging interferometer windii on the upper atmosphere research satellite uars from january 19 to january 31 1993 reveal a strong quasi two day wave qtdw signature these observations were taken during the time of peak amplitude for this qtdw event wu et al 1993 and extend from 41 n to 71 s daytime and nighttime results are presented for the altitude ranges 90 to 150 km and 90 to 102 km respectively the qtdw is found to occur with significant amplitude well into the winter hemisphere and lower thermosphere its latitudinal structure below 103 km is found to be similar to that calculated by hagan et al 1993 using the background wind profile of portniagin and solov yeva 1992 the peak amplitude occurs at 94 km with a magnitude of about 50 m s for the meridional wind and 30 m s for the zonal wind mean profiles from the summer midlatitudes show a secondary maximum in amplitude near 115 km and a node at 130 km above 130 km the wave appears to be evanescent

momentum flux spectrum of convectively forced internal gravity waves and its application to gravity wave drag parameterization part ii impacts in a gcm waccm abstract impacts of a spectral parameterization of gravity wave drag gwd induced by cumulus convection gwdc in the ncar whole atmosphere community climate model waccm1b are investigated in the spectral gwdc parameterization reference wave momentum flux spectrum is launched at cloud top and analytically calculated based on the physical properties of convection and the large scale flow the cloud top wave momentum flux is strong mainly in the tropics and midlatitude storm track regions and exhibits anisotropy and spatiotemporal variability the anisotropy and variability are determined by the distributions and variations of convective activities the moving speed of convection and horizontal wind and stability in convection regions zonal mean zonal gwdc has a maximum of 13 27 37 50 m s 1 day 1 in the mesosphere in january july impacts of gwdc on zonal wind appear mainly in the low to midlatitudes of the upper stratosphere and mesosphere in these regions biases of zonal wind with respect to

correlation between the pacific north american pattern and the eastward propagation of sea surface temperature anomalies in the north pacific lag correlation and singular value decomposition analyses reveal that the pacific north american pattern is correlated with eastward propagating sea surface temperature sst anomalies in the north pacific the eastward movement of sst anomalies is also clear in one point lag correlation maps and longitude time plot of low pass filtered time series the timescale for the sst anomalies to travel across the north pacific is 1 year it is speculated that the propagation is related to the air sea interactions in the north pacific these findings provide observational support for the atmospheric bridge theory proposed by lau and nath 1994

gravity wave interactions with the diurnal propagating tide observations of the diurnal propagating solar tide in the mesosphere and lower thermosphere 50 150 km indicate substantial annual variations in tidal amplitudes observations and modeling efforts suggest that interactions with internal gravity waves can result in significant modifications of the diurnal tide herein a two dimensional 2 d linear steady state tidal model is used in conjunction with hybrid lindzen matsuno gravity wave parameterization to examine the role of gravity wave interactions in the seasonal variability of the diurnal tide in the mlt the analysis indicates that annual variations of the background atmosphere result in significant annual variations in the eddy diffusion and the diurnal harmonic of the momentum flux divergence wave stress produced by breaking gravity waves the seasonal variability in these two mechanisms can explain the observed semi annual variability in the diurnal tide amplitude minima at solstice and maxima at equinox the relative roles of wave stress and diffusion are examined and it is shown that both play important roles in tidal modification by damping its amplitude the effects of varying inputs to the gravity wave parameterization are explored

the seasonal variation of the propagating diurnal tide in the mesosphere and lower thermosphere part i the role of gravity waves and planetary waves abstract the seasonal variation of the propagating diurnal tide in the mesosphere and lower thermosphere is examined using results from a 2 yr simulation of the extended version of the canadian middle atmosphere model cmam the cmam is shown to be able to reproduce not only the observed semiannual amplitude variation of the tide in the lower thermosphere but also more subtle features such as amplitude maxima that are stronger in march april than in september october a 4 to 6 h shift in phase between winter and summer in the northern hemisphere and a weaker seasonal variation of phase in the southern hemisphere part i of this two part series of papers investigates the importance of two of the mechanisms that have been proposed to explain the observed variation of tidal amplitude namely 1 interactions with small scale gravity waves and 2 interactions with planetary scale waves like the quasi 2 day wave analysis of the tidal momentum and thermodynamic budgets shows that the direct effects of param

time gcm results for the quasi two day wave to understand how the quasi two day wave qtdw interacts with the mean flow and migrating tides we perturbed the lower boundary of the national center for atmospheric research thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm to excite the qtdw results from our initial model runs computed for a perpetual january 15th show wave amplitudes in wind and temperature that are in qualitative agreement with previous model results and observations the wave period and amplitude change over the duration of the model run and it is expected that this results from changes in the zonal mean zonal winds evidence supporting nonlinear interactions between the qtdw and the migrating tides is presented

forsterite diopside spinel liquid equilibria in the system cao mgo al2o3 sio2 at 20 kbar and petrological applications liquidus phase relationships in the caalal sio6 mg2sio4 camgsi2o6 caalsi2o8 portion of the simplified basalt tetrahedron in the cao mgo sio2 al2o3 system have been experimentally determined at 20 kbar pressure the fo diss sp li univariant curve that pierces the fo di an join and meets the fo diss enss sp li invariant point in the basalt tetrahedron extends all the way to and pierces the di fo cats join the limit of the simplified basalt tetrahedron toward the silica undersaturated portion

extended canadian middle atmosphere model zonal mean climatology and physical parameterizations 1 this paper describes the energetics and zonal mean state of the upward extension of the canadian middle atmosphere model which extends from the ground to 210 km the model includes realistic parameterizations of the major physical processes from the ground up to the lower thermosphere and exhibits a broad spectrum of geophysical variability the rationale for the extended model is to examine the nature of the physical and dynamical processes in the mesosphere lower thermosphere mlt region without the artificial effects of an imposed sponge layer which can modify the circulation in an unrealistic manner the zonal mean distributions of temperature and zonal wind are found to be in reasonable agreement with observations in most parts of the model domain below 150 km analysis of the global average energy and momentum budgets reveals a balance between solar extreme ultraviolet heating and molecular diffusion and a thermally direct viscous meridional circulation above 130 km with the viscosity coming from molecular diffusion and ion drag below 70 km radiative equilibrium prevails in the global mean in the mlt region between 70 and 120 km many processes contribute to the global energy budget at solstice there is a thermally indirect meridional circulation driven mainly by parameterized nonorographic gravity wave drag this circulation provides a net global cooling of up to 25 k d 1

experimentally determined stability of clinopyroxene garnet corundum in the system cao mgo al 2 o 3 sio 2

timescales for dust variability in the greenland ice core project grip ice core in the last 100 000 years the calcium representing dust concentration record of the last 100 000 years from the greenland ice core project grip ice core shows a huge dynamic range factor 100 the relationship between dust concentrations and temperature represented by the oxygen isotope ratio is not a simple one as has often been assumed a rapid alternation factor of 5 10 between low concentrations during the dansgaard oeschger interstadial periods and high levels in colder periods is superimposed on a long term trend encompassing a further factor of 5 10 within climate periods there is only a very weak relationship between ca concentration and temperature previous authors biscaye et al 1997 have suggested that the most likely source for the increased dust is eastern asia for the first time we consider each possible cause of both rapid and slow increases from source to deposition we suggest that to account for the size and rapidity of the fast changes significantly higher wind speed in the source area is required although changes in atmospheric residence time could also play a role for the slower long term variability changes in transport speed or possibly route are probably also involved changes in the size of the source area could give some change on longer time periods the probable importance of changes in source area wind speed almost simultaneous with greenland temperature changes confirms that climatic parameters in high and low latitudes were strongly coupled through the atmosphere during glacial climatic changes this adds to evidence that the atmospheric circulation system underwent almost instantaneous large scale changes during the last glacial period

enstatite jadeite join and its role in the earth s mantle phase relations on the enstatite jadeite join were experimentally determined at solidus temperatures and 90 152 kb and at 1400 2050 c 175 219 kb with a split sphere anvil apparatus ussa 2000 new findings include immiscibility in garnet and determination of the stability of naalsio4 calcium ferrite structure with stishovite a thermodynamic model for the enstatite jadeite join was developed to calculate a complete phase diagram for the join at 500 2500 c and 0 270 kb the results indicate that the two major discontinuities in the earth s mantle at 400 and 670 km depths could correspond respectively to the formation and the breakdown of garnet with a pyroxene composition a model for a chondritic upper mantle is proposed in which large scale chemical and mineral layering was produced by fractionation of liquidus phases in a magma ocean solidification was completed at 400 km depth by crystallization of sodium enriched residual melts which produced a pyroxene layer at 300 400 km depths

the northern hemisphere tropospheric response to changes in the gravity wave drag scheme in a perpetual january gcm the sensitivity of a general circulation model climatology to changes in the gravity wave drag scheme is investigated with particular emphasis being placed upon the northern hemisphere wintertime tropospheric circulation it is found that by weakening the upper level drag the ferrel cell circulation intensifies to the north resulting in a greater than 10 k cooling in the region of the arctic tropopause the poleward side of the northern hemisphere sub tropical jet intensifies in the region of 60 70 n and a poleward shift is observed in the eddy meridional momentum flux a large part of the response is zonally asymmetric with the aleutian and icelandic lows becoming shallower with weakened upper level gravity wave drag by comparing the results of a gravity wave drag scheme having a wave breaking vertical profile with those of a simple uniform drag profile scheme it appears that the tropospheric response to weakened upper level drag depends very little upon the choice of vertical drag profile in the troposphere

the atlanto pacific multidecade oscillation and its imprint on the global temperature record results from a multiregression analysis of the global and sea surface temperature anomalies for the period 1950 2011 are presented where among the independent variables multidecade oscillation signals over various oceanic areas are included these indices are defined in analogy with the atlantic multidecadal oscillation amo index unexpectedly we find that a strong multidecade oscillation signal echoing the amo is also present in the western and northwestern pacific region the results indicate that naturally induced climate variations seem to be dominated by two internal variability modes of the ocean atmosphere system amo and el nino southern oscillation with a marked geographical dichotomy in their respective areas of dominance as the amo index is directly derived from sst data the finding that the amo signal is present on a large fraction of the global oceanic surface casts doubt on its use as an independent explanatory variable in regression analyses of the global surface temperature anomalies

sensitivity of mesospheric mean flow planetary waves and tides to strength of gravity wave drag a global circulation model which extends from the surface to 125 km is used to study how the strength of gravity wave drag affects the dynamics of the mesosphere the strength of gravity wave drag has a strong influence on the zonal mean state of the mesosphere in particular the magnitude and variability of the summer mesopause temperature and the shear on the top of the mesospheric jets this change in the zonal mean state strongly affects the susceptibility of the mesosphere to baroclinic and or barotropic instability and hence the formation of the 2 day wave the 2 day wave in turn interacts nonlinearly with the diurnal tide producing secondary waves and a reduction in amplitude of the diurnal tide previous studies with quasi linear mechanistic tidal models have captured some semiannual variation in tidal amplitude through direct interactions between tides and gravity waves our fully nonlinear global circulation model results support an alternative explanation in terms of interactions between planetary waves and tides

exsolution of garnet within clinopyroxene of mantle eclogites major and trace element chemistry eclogite xenoliths from the mantle have experienced a wide variety of processes and p t conditions many of which are recorded in the mineral compositions and textures exsolution of garnet from clinopyroxene is one such texture occurring in a minority of mantle eclogites new analyses of clinopyroxene and garnet of eclogite xenoliths from kimberlites at bellsbank south africa and obnazhennaya yakutia russia are presented here and these are combined with data from the literature exsolution of garnet from clinopyroxene is generally lamellar although lens shaped garnets are also present major and trace element characteristics show a wide range of compositions and include eclogite groups a b and c rare earth element ree concentrations of garnet and pyroxene were determined by sims and the ree patterns are subtly different from those in ordinary eclogites differences include the absence of prominent eu anomalies in samples of this study and differences in the slopes of chondrite normalized ree patterns it is possible that these signatures are unique to exsolved eclogites a result of subsolidus elemental partitioning during exsolution some reconstructed whole rock compositions are aluminuous comparison with ordinary eclogites shows only minor differences implying a similar origin if the immediate precursor to the exsolved eclogites was a monomineralic pyroxenite the excess aluminium was tied up in tschermak s molecule although the occasional presence of kyanite exsolution lamellae is indicative of a ca eskola component reconstructed pyroxenes from kyanite and corundum rich samples contain unrealistic amounts of aluminium for mantle pyroxenes a protolith or parental pyroxene threshold of 24 al2o3 may exist above which as in a plagioclase cumulate the final assemblage is kyanite and or corundum bearing

observed temperature two day wave and its relatives near the stratopause the two day wave is observed in the upper atmosphere research satellitemicrowave limb sounder temperature data around 40 58 km between december 1991 and september 1994 the two day wave temperature signature is most significant after each solstice when the derived easterly winds near the stratopause extend across the equator to at least 208 latitude in the winter hemisphere and the zonal mean winds near the equator are inertially unstable with observed inertial instability disturbances the observed two day wave consists of a 2 0 day period zonal wavenumber 3 and a 1 8 day period zonal wavenumber 4 component named 3 2 0 and 4 1 8 respectively the 3 2 0 component is dominant during two of the three available austral summers but its amplitude is much weaker than the 4 1 8 component during the two observed boreal summers during the austral summers correspondence between amplification of the two day wave temperature signatures regions of reversed potential vorticity gradient due to meridional curvature of the zonal mean flow and the critical lines for the 3 2 0 and 4 1 8 modes suggest barotropic instability as a source of both wave components momentum redistribution by observed inertial instability appears to barotropically destabilize the equatorward flank of the easterly jet where the wave components subsequently grow during the boreal summers the 4 1 8 component appears to be excited by instability that is associated with vertical shear and curvature of the flow seated above the observational domain the boreal 3 2 0 mode appears unrelated to the zonal flow instability within the observational domain and may reflect a normal mode like response during these periods

intraseasonal and interannual variability of the quasi 2 day wave in the northern hemisphere summer mesosphere this study uses global synoptic meteorological fields from a high altitude data assimilation system to investigate the quasi 2 day wave q2dw and migrating diurnal tide during the northern hemisphere nh summers of 2007 2009 by applying a two dimensional fast fourier transform to meridional wind and temperature fields we identify q2dw source regions and diagnose propagation of q2dw activity into the upper mesosphere and lower thermosphere we find that the q2dw in nh summer is composed primarily of westward propagating zonal wave number 3 and wave number 4 components that originate within baroclinically unstable regions along the equatorward flank of the summer midlatitude easterly jet the amplitude of the wave number 3 q2dw tends to peak in july while the amplitude of the wave number 4 q2dw tends to peak in late june and again in early august the seasonal mean q2dw amplitudes are largest in 2009 when the amplitude of the migrating diurnal tide in the upper mesosphere near 30 n was relatively weak however there is no evidence of rapid amplification of the q2dw via nonlinear interaction with the diurnal tide instead variations of q2dw amplitudes during nh summer appear to be linked to variations in the strength and location of the mesospheric easterly jet from one summer to the next with a stronger jet producing larger q2dw amplitudes linear instability model calculations based on the assimilated wind fields indicate that the fastest growing modes are zonal wave numbers 3 and 4 with periods near 2 days that originate in the vicinity of the easterly jet

a three dimensional mountain wave imaged in satellite radiance throughout the stratosphere evidence of the effects of directional wind shear swath scanned thermal radiances from the advanced microwave sounding units amsu a on the noaa and aqua satellites are used to image the horizontal temperature structure of a long wavelength mountain wave that formed over southern scandinavia on 14 january 2003 data from all six stratospheric channels show this wave propagating through the full depth of the stratosphere in channels 9 11 altitudes 20 90 hpa the imaged wave has a phase structure broadly consistent with a stationary wave radiated by the southeastward flow over and above the quasi elliptical terrain of southern norway channel 12 radiances at 10 hpa however show a remarkable abrupt change in imaged wave structure the horizontal wavelength contracts phase lines rotate anticlockwise by 30 40 and peak activity migrates to the south to lie over denmark and northern germany similar structure persists in channels 13 and 14 at 2 5 hpa with progessively increasing radiance amplitudes these features are stable over the 10 hours of amsu a measurements from five separate overpasses and are validated against independent radiances acquired by the atmospheric infrared sounder airs and retrieved airs amsu a temperature profiles from the aqua overpass this change at the channel 11 12 interface coincides with an onset of anticlockwise rotation backing and intensification of background stratospheric winds with height fourier ray and spatial ray modelling incorporating these directionally sheared winds and simplified orographic forcing reproduce the salient features of the observations but only after wave induced temperature perturbations have been converted to channel radiances using a forward model the differential visibility of various components of this three dimensional mountain wave to the amsu a channel weighting functions has a first order impact on the observations at heights above 10 hpa once that is factored in the combined observations and modelling provide direct experimental support for the shutts model s predictions of how backing wind vectors affect the vertical evolution of three dimensional mountain waves implications of these observations for orographic gravity wave drag parametrization are briefly discussed copyright 2007 royal meteorological society

coordinated investigation of summer time mid latitude descending e layer es perturbations using na lidar ionosonde and meteor wind radar observations over logan utah 41 7 n 111 8 w 1 it is well known that there is a strong correlation between the formation of a descending sporadic e layer es and the occurrence of large upper atmospheric zonal wind shears most likely driven by solar thermal tides and or gravity waves we present new results of es perturbation events captured between 13 and 17 july 2011 ut days 194 198 as part of a coordinated campaign using a wind temperature na lidar at utah state university 41 7on 111 8 w and a canadian advanced digital ionosonde cadi scientific instrumentation ltd saskatoon saskatchewan canada and skiymet meteor wind radar both located at nearby bear lake observatory 41 9 n 111 4 w during this period the cadi detected strong descending es on 2 days 195 and 197 when large modulations of the top side mesospheric na layer occurred in synchronism with strong oscillations in the ionosonde e region echoes a weakening in the descending e layer echoes was observed on the other 2 days 196 and 198 coincident with a large reduction in the zonal diurnal and semidiurnal amplitudes above 95 km both tidal components were found to have comparable contributions to the total zonal wind shear that was critical for es formation and its downward propagation further investigation indicates that the weakening tidal amplitudes and the occurrence of the es events were also influenced by a strong quasi two day period modulation suggesting significant quasi two day wave qtdw interactions with the tides indeed a nonlinear wave wave interaction induced 16 hour period child wave was also detected with amplitude comparable to that of the prevailing tides these interaction processes and their associated effects are consistent with earlier thermosphere ionosphere mesosphere electrodynamics general circulation model studies of nonlinear interactions between the migrating tidal waves and the qtdw and were probably responsible for the observed damping of the tidal amplitudes resulting in the disruption of the es

diurnal variations of temperature and winds inferred from timed and uars measurements 1 owing to their sampling properties in local solar time both the timed and uars spacecrafts provide the opportunity to quantitatively study the mesospheric thermal tides the information though is limited because it takes the timed instruments 2 months to cover the full range of 24 hours almost twice as long as uars we present here the results of an analysis in which the seasonal and global scale variations of amplitude and phase for the migrating diurnal tide are retrieved from atmospheric temperature and wind measurements on the timed saber tidi and uars mls hrdi satellites comparisons are made with results from the numerical spectral model nsm which is characterized in part by the parameterization of small scale gravity waves at 60 km and above the amplitude and phase variations of the diurnal tide from the nsm agree generally well with those derived from the saber temperatures in the saber temperature amplitudes at around 60 km there are evident asymmetries in latitude with respect to the equator which are not apparent in the mls data near 55 km or in the nsm the asymmetry in the saber temperatures disappears above 60 km for the meridional winds of the migrating diurnal tide derived from tidi the phase and relative amplitude variation with latitude and season are in qualitative agreement with the hrdi measurements and the nsm the amplitudes from tidi winds are systematically smaller but this may in part be due to interannual variations however the results for the zonal winds from tidi more often do not agree well with those from hrdi or the nsm

the character of polar tidal signatures in the extended canadian middle atmosphere model the characteristics of the diurnal semidiurnal and terdiurnal tides zonal wave numbers 5 to 5 in temperature and zonal wind in the polar mesosphere and lower thermosphere region as simulated by the extended canadian middle atmosphere model are examined the most significant diurnal semidiurnal and terdiurnal tides in the polar regions are ds0 dw1 and de1 sw3 sw2 sw1 ss0 se1 and se2 and tw3 ts0 and tw1 respectively and their latitudinal structures seasonal variations and hemispheric asymmetries noted of these components ds0 tw1 ts0 and tw3 exhibit a seasonally symmetric variation with both hemispheres strengthening simultaneously on the other hand dw1 strengthens asymmetrically so that when one hemisphere is strong the other is weak the remainder show no seasonal tendency but vacillate on shorter than seasonal time scales in a symmetric or antisymmetric manner at different times of the year global scale correlations of the amplitudes of the migrating tides dw1 sw2 and the stationary planetary wave 1 and the assumed child nonmigrating tides are also examined the results indicate that the correlations are highly time scale dependent and the significant correlations seen with the original time series are mainly due to longer term variations 18 days there are no consistent global correlations associated with the short term variations 18 days among these waves

observations of the quasi 2 day wave from the high resolution doppler imager on uars a strong westward traveling oscillation with a period of 2 days and zonal wave number 3 is observed in the mesospheric and lower thermospheric winds from the high resolution doppler imager on the upper atmosphere research satellite the important events happen in january july and september october of which the occurrence in january is the strongest with an amplitude over 60ms 1 detailed analyses for the periods of january 1992 and january 1993 reveal a cause and effect relationship in the wave developing process at 95km the global structures of the wave amplitude and phase are also presented

observations of the 2 day wave in nmc stratospheric analyses abstract observational characteristics of the 2 day wave a westward propagating zonal wave 3 oscillation in the summer subtropical upper stratosphere and mesosphere are studied based on five years of national meteorological center nmc operational stratospheric analyses these data show episodic occurrence of the 2 day wave in the upper stratosphere in january centered near 20 s and july august centered near 20 n these episodes are strongly correlated with observed reversals of the zonal mean potential vorticity gradient near the core of the summer easterly jet consistent with previous suggestions that the 2 day wave is generated by an in situ instability of this jet on the other hand the horizontal and vertical structure of the waves is very similar to that calculated by salby for a global normal mode rossby wave the combination of normal mode structure and instability signature suggests that the 2 day wave is a near resonant mode forced by dynamical instability

short term variability in the migrating diurnal tide caused by interactions with the quasi 2 day wave 1 the migrating diurnal tide is one of the dominant dynamical features in the low latitudes of the earth s mesosphere and lower thermosphere mlt region representing the atmospheric response to the largest component of solar forcing ground based observations of the tide have resolved short term variations attributed to nonlinear interactions between the tide and planetary waves that are also in the region using the ncar thermosphere ionosphere mesosphere electrodynamics general circulation model time gcm we simulate a quasi 2 day wave qtdw event under late january conditions in this case sideband sum and difference child waves are resolved indicating that a nonlinear interaction is occurring between the qtdw and the tide the migrating diurnal tide in the mlt displays local amplitude decreases of 20 40 as well as a shortening of vertical wavelength by roughly 4 km examining the physical mechanisms driving the interaction nonlinear advection is found to result in amplification of the tide in some regions and damping in others manifesting as increased smoothing of the tidal structure when the qtdw is present in the mlt additionally the qtdw also enhances the easterly summer mean wind jet that can also account for changes in tidal amplitude and vertical wavelength we find that qtdw induced background atmosphere changes in time gcm can drive tidal variability at levels greater than nonlinear advection a possibility not previously considered

alleviation of a systematic westerly bias in general circulation and numerical weather prediction models through an orographic gravity wave drag parametrization systematic westerly biases in the northern hemisphere wintertime flow of the meteorological office 15 layer operational model and 11 layer general circulation model are described evidence that the failure to parametrize subgrid scale orographic gravity wave drag may account for such biases is presented this evidence is taken from aircraft studies surface pressure drag measurements and studies of the zonally averaged momentum budget a parametrization scheme is described in which the surface stress is proportional to the near surface wind speed and static stability and to the variance of subgrid scale orography the stress is absorbed in the vertical by considering the influence of such gravity wave activity on static stability and vertical wind shear a richardson number dependent wave breaking formulation is devised and the vertical stress profile determined by a saturation hypothesis whereby the breaking waves are maintained at marginal stability it is shown that wave breaking preferentially occurs in the boundary layer and in the lower stratosphere results from a simple zonally symmetric model show how the adjustment to thermal wind balance with a wave drag in the stratosphere warms polar regions by adiabatic descent and decelerates the mean westerlies in the troposphere the influence of the parametrization scheme on integrations of the 11 layer model is described and found to be generally beneficial in a discussion of the reasons why this problem has only recently emerged it is suggested that the satisfactory northern hemisphere winter circulations of previous coarser general circulation models were due to a compensation implied by underestimating both the surface drag and the horizontal flux of momentum by explicitly resolved large scale eddies

seasonal variations of the diurnal tide induced by gravity wave filtering wind measurements with the uars spacecraft show that between 90 and 100 km altitude the fundamental diurnal tide is modulated semi annually with peak amplitudes of almost 100 m s near equinox more than a factor of two larger than during solstice applying hines doppler spread parameterization dsp for small scale gravity waves gw we present results from a numerical spectral model nsm to describe the seasonal variations in the mean zonal circulation interacting self consistently with the diurnal tide with the dsp the gw momentum source increases the amplitude of the tide at altitudes above 70 km in contrast to the rayleigh friction parameterization that causes damping since the tide absorbs gw momentum it reduces the wave generated semi annual oscillations sao in the mean zonal winds at equatorial latitudes outside the tropics gw momentum is absorbed by the mean zonal winds that peak near the summer and winter solstices as a result the gw reach the upper mesosphere with more momentum during equinox periods and thus cause a seasonal modulation of the tide that is predominately semi annual

simulation of large scale dynamics in the mesosphere and lower thermosphere with the doppler spread parameterization of gravity waves 2 eddy mixing and the diurnal tide turbulence is thought to be produced by gravity waves that become unstable in the upper atmosphere owing to a relatively short vertical wavelength of the solar diurnal tide turbulent viscous type mixing is expected to be particularly important for tidal dissipation in the mesosphere and lower thermosphere mlt within the doppler spread parameterization dsp of gravity waves the vertical eddy exchange coefficients may be calculated from the gw energy deposition rate the dsp as implemented in the spectral mesosphere lower thermosphere model is shown to provide realistic simulations of both the diurnal tide and turbulent mixing in the mlt in particular the vertical structure and seasonal variations of eddy mixing agree well with in situ observations and independent estimates from global thermal balance the seasonal variations of turbulence are found to be primarily responsible for a strong semiannual variation of the diurnal tide in agreement with recent satellite observations

a large discontinuity in the mid twentieth century in observed global mean surface temperature the record of global sea surface temperatures spanning the past century provides key evidence for global warming and is much scrutinized with a view to distinguishing between anthropogenic and natural climate variability it has been assumed that this record is now largely free of substantial uncorrected instrument biases not so according to a team assembled from four of the world s leading climate research institutes they have identified a pronounced discontinuity in the record a sudden drop of about 0 3 c in global sea surface temperature in 1945 that coincides with a significant change in the shipboard instrumentation used to collect the data this discontinuity is 40 as large as the century long upward trend in temperatures so correcting for it is likely to change the overall record and its interpretation substantially a pronounced discontinuity in the record of global sea surface temperatures has been identified the marked drop in global sea surface temperature in 1945 coincides with a significant change in the shipboard instrumentation that was used to collect the source data at that time this discontinuity is 40 as large as the century long upward trend in temperatures so correcting for it is likely to change the overall record and its interpretation particularly in the middle 20th century data sets used to monitor the earth s climate indicate that the surface of the earth warmed from 1910 to 1940 cooled slightly from 1940 to 1970 and then warmed markedly from 1970 onward1 the weak cooling apparent in the middle part of the century has been interpreted in the context of a variety of physical factors such as atmosphere ocean interactions and anthropogenic emissions of sulphate aerosols2 here we call attention to a previously overlooked discontinuity in the record at 1945 which is a prominent feature of the cooling trend in the mid twentieth century the discontinuity is evident in published versions of the global mean temperature time series1 but stands out more clearly after the data are filtered for the effects of internal climate variability we argue that the abrupt temperature drop of 0 3 c in 1945 is the apparent result of uncorrected instrumental biases in the sea surface temperature record corrections for the discontinuity are expected to alter the character of mid twentieth century temperature variability but not estimates of the century long trend in global mean temperatures

the quasi two day wave observed in the equatorial middle atmosphere an oscillation with a period near 2 days is found in radar wind measurements made in the upper mesosphere and lower thermosphere at christmas island 2 n 157 w in the central pacific the oscillation is particularly strong in the meridional wind component and seems to be present almost continuously ir the 80 100 km height region although some intermittency is evident wave amplitudes are especially large about one month after the solstices in july august and in january february at times coincident with large 2 day wave events in the summer mesosphere at extratropical latitudes power spectral and complex demodulation techniques are used to study the amplitude and frequency variations of the oscillation as a function of height and time downward phase propagation is found consistent with upward energy propagation and with a vertical wavelength of about 70 km an unusual feature is a shift in wave period from near 50 hours in july august to 48 hours in january february when the largest amplitudes up to 45 m s 1 are observed a 16 hour oscillation is also found at times when the 2 day wave amplitudes are largest the observations are consistent with the 2 day wave being a manifestation of the 3 0 rossby gravity normal mode another weaker oscillation is also found in the meridional wind field at a period near 44 hours this oscillation may be due to the 2 0 normal mode

the summer wind field between 80 and 93 km observed by the mst radar at poker flat alaska 65 n abstract results of an analysis of the summertime wind field between 80 93 km over poker flat alaska are presented the data were obtained using the large but as yet incomplete mst radar at poker flat and cover the periods 17 june 13 july 1979 and 22 june 22 july 1980 zonal and meridional mean wind profiles and tidal components during these periods are examined and are compared with other observations at comparable latitudes as well as with current theoretical profiles while our results agree reasonably closely with other observations and theory some discrepancies exist and are discussed in addition to the expected 8 12 and 24 h components of atmospheric motions we find strong evidence for a 16 h component particularly during the 1979 data period in addition we show examples of the average power spectrum of wind fluctuations from 3 min to 8 days these spectra not only show the expected tidal peaks but show also that the spectral energy density is continuous between the shortest 8 h t

garnet pyroxene equilibria in the system cao mgo al 2 o 3 sio 2 cmas prospects for simplified t independent lherzolite barometry and an eclogite barometer new experimental data on compositions of garnets in two pyroxene garnet assemblages in the system cao mgo al2o3 sio2 cmas are presented for conditions between 1 100 and 1 570 c and 30 to 50 kb garnets in these assemblages become less calcic with increasing pressure garnet orthopyroxene barometry al solubility barometry pertinent to geobarometry for garnet lherzolites has been evaluated with a set of experimental data covering the range 900 to 1 570 c and 15 to 100 kb various formulations of this barometer work well to 75 kb phase equilibria are not sufficient to positively verify the thermodynamic validity of any of such models empirical garnet orthopyroxene barometry at least in the system cmas can be formulated to obtain a pressure estimate without previous temperature estimation p kb 34 4 19 175 1n x al m1 17 702 1n x ca m2 the potential application of an analogous garnetclinopyroxene equilibrium is limited because the amount of ca tschermaks in natural clinopyroxenes is usually quite small in garnet lherzolites and many eclogites the ca mg exchange between garnet and clinopyroxene appears however sufficiently sensitive to pressure to allow calibration of a cmas barometer the reaction 3camgsi2o6 mg3al2si3o12 3mg2si2o6 ca3al2si3o12 has a v o of 3 5 cm3 the total pressure dependency of this reaction is however closer to a theoretical v o of about 5 cm3 when excess volume properties of the phases involved are taken into account we have calibrated such a barometer mean error of estimate 2 8 kb for assemblages with pyrope rich py 80 garnets and orthopyroxenes this may provide the basis for a geobarometer for eclogites from kimberlites

effective diffusivity in the middle atmosphere based on general circulation model winds 1 the mixing of a passive tracer in the stratosphere and lower mesosphere is studied on the basis of the effective diffusivity which is obtained in the framework of the tracer based coordinate system this characteristic is proportional to the average diffusion flux over lagrangian contours and inversely proportional to the mean tracer gradient the tracer distribution used in the calculation of the effective diffusivity is obtained after integration of the advection diffusion equation using general circulation model winds and a new numerical advection scheme with small numerical diffusivity using some theoretical and experimental arguments it is shown that the interpretation of the seasonal variability of the effective diffusivity field cannot be done on the basis of the momentary wind field alone but some flow history should be taken into account the climatology of the effective diffusivity for different months is presented up to the lower mesosphere and compared with previous studies in the stratosphere some new features of the effective diffusivity distribution are obtained for example there is a local maximum of the effective diffusivity at midlatitudes of the northern hemisphere of the summer middle stratosphere the effective diffusivity fields in the lower mesosphere show a strong increase of the mean effective diffusivity from the upper stratosphere to the lower mesosphere and the existence of a complex latitudinal structure of the effective diffusivity at mesospheric heights in the lower mesosphere there is a marked interannual variability during the southern hemisphere easterly wind development a possible explanation for the obtained structure is discussed on the basis of in situ rossby wave generation and rossby wave breaking effects

petrology of two diamondiferous eclogite xenoliths from the lahtojoki kimberlite pipe eastern finland abstract diamondiferous group a eclogites constitute a minor portion of the mantle derived xenoliths in the eastern finland kimberlites they have been derived from the depth interval 150 230 km where they are inferred to occur as thin layers or small pods within coarse grained garnet peridotites the chemical and isotopic composition of minerals suggest that they represent proterozoic mantle derived melts or cumulates rather than subducted oceanic lithosphere during magma ascent and emplacement of the kimberlites the eclogite xenoliths were mechanically and chemically rounded judging from the types of surface markings in addition those octahedral crystal faces of diamonds that were partially exposed from the rounded eclogite xenolith became covered by trigons and overlain by microlamination due to their reaction with the kimberlite magma the diamonds bear evidence of pervasive plastic deformation which is not however evident in the eclogite host this suggests that annealing at ambient lithospheric temperatures has effectively recrystallised the silicates while the diamond has retained its lattice imperfections and thus still has the potential to yield information about ancient mantle deformation one of our samples is estimated to contain approximately 90 000 ct ton diamond implying that some diamonds occur within very high grade pods or thin seams in the lithospheric mantle to our knowledge this is one of the most diamondiferous samples described

on the pacific decadal oscillation and the atlantic multidecadal oscillation might they be related 1 the nature of the pacific decadal oscillation pdo is investigated based upon analyses of sea surface temperature observations over the last century the pdo is suggested to be comprised of a 20 year quasi periodic oscillation and a lower frequency component with a characteristic timescale of 60 years the 20 year quasi periodic oscillation is clearly identified as a phase locked signal at the eastern boundary of the pacific basin which could be interpreted as the signature of an ocean basin mode we demonstrate that the 60 year component of the pdo is strongly time lag correlated with the atlantic multidecadal oscillation amo on this timescale the amo is shown to lead the pdo by approximately 13 years or to lag the pdo by 17 years this relation suggests that the amo and the 60 year component of the pdo are signatures of the same oscillation cycle

satellite observations of thermospheric tides results from the wind imaging interferometer on uars thermospheric winds measured by the wind imaging interferometer windii on the upper atmosphere research satellite are analyzed for migrating solar tides the data cover a 2 year period commencing february 1992 and are obtained from the atomic oxygen o 1s 557 7 nm emission which provides observations of the 90 to 200 km altitude range during daytime and the 90 to 110 km range at night the subtropical lower thermosphere is dominated by the diurnal propagating tide which exhibits a vertical wavelength of approximately 22 km grows in amplitude up to 95 km and decays rapidly above where molecular diffusion greatly reduces the vertical shears although the phase remains fairly uniform throughout the year a pronounced semiannual oscillation is observed in the diurnal tide amplitude at both 20 n and 20 s the meridional and zonal wind components attain their maximum values at equinox of approximately 70 and 40 m s respectively while the solstitial minima are nearly a factor of 2 smaller at 35 n the diurnal tide semiannual amplitude oscillation is still present in the lower thermosphere but above 100 km it is replaced by an annual cycle with a maximum in july and august this contrasts with 35 s where the july august peak is absent and the semiannual oscillation extends to 110 km at midlatitudes the zonal and meridional winds are of similar magnitude and no significant hemispheric asymmetries in amplitudes are observed in the lower thermosphere the semidiurnal tide amplitude exhibits an annual oscillation with maximum values of 30 to 40 m s occurring in june july near 100 km at 35 n 35 s and the equator a bimodal structure in the seasonal variation of the semidiurnal phase is observed this feature is characterized by rapid equinoctial transitions and is particularly well defined at the equator examination of the equatorial middle thermosphere indicates that the semidiurnal tide attains its maximum amplitude at 140 km and exhibits a vertical wavelength of approximately 60 km these findings indicate the predominance of the antisymmetric 2 3 hough mode in the tropics

improved extended reconstruction of sst 1854 1997 abstract an improved sst reconstruction for the 1854 1997 period is developed compared to the version 1 analysis in the western tropical pacific the tropical atlantic and indian oceans more variance is resolved in the new analysis this improved analysis also uses sea ice concentrations to improve the high latitude sst analysis and a modified historical bias correction for the 1939 41 period in addition the new analysis includes an improved error estimate analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling the near global average sst in the new analysis is consistent with the version 1 reconstruction the 95 confidence uncertainty for the near global average is 0 4 c or more in the nineteenth century near 0 2 c for the first half of the twentieth century and 0 1 c or less after 1950

the extended canadian middle atmosphere model first results from the extended canadian middle atmosphere model are presented the model extends from the surface to the middle thermosphere and includes relevant physical parameterizations to simulate unresolved gravity waves a non orographic gravity wave drag parameterization has also been implemented results from a two year simulation are discussed and are shown to be in good qualitative agreement with upper atmosphere research satellite wind observations the realistic features which are reproduced include the reversal of the mesospheric jets and the semi annual variation of the migrating diurnal tide in the low latitude mesosphere

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

quantification of the gravity wave forcing of the migrating diurnal tide in a gravity wave resolving general circulation model 1 the interaction of gravity waves gws and the migrating diurnal tide are studied in a gw resolving general circulation model gcm by calculating the tidal components of zonal wind accelerations and equivalent rayleigh friction due to tidal induced gw dissipation two 15 day periods for perpetual equinoctial and solstice simulations are analyzed which are performed with the japanese atmospheric general circulation model for upper atmosphere research jaguar high resolution gcm the model can directly simulate gws with horizontal wavelengths greater than about 190 km and thus reproduce the general features of the mean winds and temperatures from the surface to the mesosphere and lower thermosphere mlt the amplitudes of the migrating diurnal tide are successfully simulated during both seasons and the tidal winds affect the altitudes of gw dissipation in the low latitude mlt the tidal component of gw forcing has maximal values of about 15 m s 1 d 1 near the maximal vertical shears of the tidal winds and generally works to shorten the vertical wavelength of the migrating diurnal tide the phase relationship between the tidal winds and the tidal induced gw forcing is not exactly 90 out of phase causing amplification suppression of the tide the gw forcing amplifies the migrating diurnal tide during the equinox while during the solstice it suppresses the tidal winds in the upper mesosphere of both hemispheres this difference in behavior can be attributed to a seasonal variation of the mean zonal winds because combination of the mean and tidal winds affects the altitudes of gw dissipation

excess silica in omphacite and the formation of free silica in eclogite silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite however mechanisms other than exsolution might produce free silica and the possible mechanisms depend in part on the nature and definition of excess silica excess silica may occur in both stoichiometric and non stoichiometric pyroxene although the issue has been debated we show that all common definitions of excess silica in non stoichiometric clinopyroxene are internally consistent interchangeable and therefore equivalent the excess silica content of pyroxene is easily illustrated in a three component condensed composition space and may be plotted directly from a structural formula unit or recalculated end members in order to evaluate possible mechanisms for the formation of free silica in eclogite we examined the net transfer reactions in model eclogites using a thompson reaction space we show that there are at least three broad classes of reactions that release free silica in eclogite i vacancy consumption in non stoichiometric pyroxene ii dissolution of ti phases in pyroxene or garnet iii reactions between accessory phases and either pyroxene or garnet we suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility but also of titanium solubility and the possible roles of accessory phases and inclusions on the balance of free silica

observations of the diurnal tide from space abstract this study presents a climatology of mesospheric and lower thermospheric diurnal tidal winds obtained with the high resolution doppler imager hrdi on the upper atmosphere research satellite uars the observations reveal that although tidal structures are present at all times like the prevailing zonal winds they exhibit significant semiannual as well as other shorter term variations in amplitude results are presented for a period extending over more than one year from november 1991 to july 1993 the 1 1 diurnal tidal amplitude of the meridional component characterized by the value at an altitude of 90 km and a latitude of 22 ranges from a minimum at solstice of less than 20 m s 1 to an equinox maximum of over 70 m s 1 the vertical wavelength and phase of the tide show only slight variations throughout the year with a suggestion of semiannual variations in both

effects of horizontal geometrical spreading on the parameterization of orographic gravity wave drag part i numerical transform solutions abstractnumerical transform solutions for hydrostatic gravity waves generated by both uniform and sheared flow over elliptical obstacles are used to quantify effects of horizontal geometrical spreading on amplitude evolution with height both vertical displacement and steepness amplitudes are considered because of their close connections to drag parameterizations in weather and climate models novel diagnostics quantify the location and value of the largest wavefield amplitudes most likely to break at each altitude these horizontal locations do not stray far from the obstacle peak even at high altitudes resulting vertical profiles of wave amplitude are normalized to remove density and refraction effects thereby quantifying the horizontal geometrical spreading contribution currently absent from parameterizations horizontal geometrical spreading produces monotonic amplitude decreases with height through wave action conservation as waves propagate into progressively larger horizontal areas accumulated

impact of a spectral gravity wave parameterization on the stratosphere in the met office unified model abstract the impact of a parameterized spectrum of gravity waves on the simulation of the stratosphere in the met office unified model um is investigated in the extratropical mesosphere the gravity wave forcing acts against the mean zonal wind and it dominates over the resolved wave forcing in the extratropical stratosphere the gravity wave forcing gives a small acceleration in the direction of the mean zonal wind both summer and winter stratospheric jets have improved maximum strength and tilt with height when the parameterized gravity wave forcing is included although the southern winter jet is still more vertically aligned than in observational analyses the timing of the seasonal breakdown of the southern winter vortex is also improved by the addition of gravity wave forcing in the tropics the most obvious impact is that the model reproduces the quasi biennial oscillation qbo with a realistic mean and range of periods it also reproduces most of the observed asymmetries between the easterl