a study of planetary waves in the southern winter troposphere and stratosphere part i wave structure and vertical propagation abstract planetary wave propagation in the southern winter troposphere and stratosphere is studied in an attempt to trace the origins of upward propagating disturbance daily geopotential girds from 1000 to 1 mb are analyzed for two 120 day winter seasons a cross correlation analysis technique is developed which allows coherent wave structure to be traced in time significant correlations are observed between the troposphere and stratosphere at finite time lags indicative of vertically propagating waves the observed vertical propagation time scales between the middle troposphere and middle stratosphere are on the order of 4 days for zonal wavenumber 1 k 1 1 2 days for k 2 and 1 day for k 3 the cross correlation analysis also delineates the meridional and vertical structures of the transient in time planetary waves zonal wavenumber 1 fluctuations exhibit a vertical out of phase relationship between the midlatitude troposphere and atmosphere three out of phase maxima in latitude are observed in

decadal variability of subpolar gyre transport and its reverberation in the north atlantic overturning 1 analyses of sea surface height ssh records based on satellite altimeter data and hydrographic properties have suggested a considerable weakening of the north atlantic subpolar gyre during the 1990s here we report hindcast simulations with high resolution ocean circulation models that demonstrate a close correspondence of the ssh changes with the volume transport of the boundary current system in the labrador sea the 1990s decline of about 15 of the long term mean appears as part of a decadal variability of the gyre transport driven by changes in both heat flux and wind stress associated with the north atlantic oscillation nao the changes in the subpolar gyre as manifested in the deep western boundary current off labrador reverberate in the strength of the meridional overturning circulation moc in the subtropical north atlantic suggesting the potential of a subpolar transport index as an element of a moc monitoring system

tropical midlatitude interaction on the time scale of 30 to 60 days during the northern summer of 1979 abstract the relationship between the low frequency oscillation of convective activity in the tropics and the intensity of planetary scale upper tropospheric 200 mb systems in the subtropics during the northern hemisphere nh summer is studied using data obtained in the first garp global experiment fgge the mid pacific trough and the south asian tibetan and mexican anticyclones undergo cycles of amplification and decay with the 30 60 day fluctuation of convective activities in the indonesia western pacific iwp region and in the intertropical covergence zone itcz over central america the thermal contrast between the asian continent and the north pacific and the resulting east west circulation show similar time variations this circulation regulates the intensity of the south asian anticyclone and the mid pacific trough divergent circulation associated with convection over central america maintains the mexican anticyclone the low frequency transients in the upper troposphere around the mid pa

variability of sea surface height and circulation in the north atlantic forcing mechanisms and linkages abstract simulations with a coarse resolution global ocean model during 1958 2004 are analyzed to understand the inter annual and decadal variability of the north atlantic analyses of empirical orthogonal functions eofs suggest relationships among basin scale variations of sea surface height ssh and depth integrated circulation and the winter north atlantic oscillation nao or the east atlantic pattern eap indices the linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability in the subpolar region variations of the gyre strength ssh in the central labrador sea and the nao index are highly correlated surface heat flux is important in driving variations of ssh and circulation in the upper ocean and decadal variations of the atlantic meridional overturning circulation amoc surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the amoc in the subtropical region momentum flux plays a dominant role in driving variations of the gyre circulation and amoc there is a strong correlation between gyre strength and ssh at bermuda

on the linkage of mesospheric planetary waves with those of the lower atmosphere and ionosphere a case study from indian low latitudes 1 in this paper we study the planetary scale wave features using concurrent observations of mesospheric wind and temperature ionospherich f and tropospheric wind from tirunelveli gadanki and kolhapur all located in the indian low latitudes made during february 2009 our investigations reveal that 3 to 5 day periodicity characterized as ultrafast kelvin ufk waves was persistent throughout the atmosphere during this period these waves show clear signatures of upward wave propagation from troposphere to the upper mesosphere linking the ionosphere through a clear correlation between mesospheric winds and h f variations we also note that the amplitude of this wave decreased as we moved away from the equator these results are the first of their kind from indian sector portraying the vertical as well as latitudinal characteristics of the 3 to 5 day ufk waves simultaneously from the troposphere to the ionosphere

shifting surface currents in the northern north atlantic ocean 1 analysis of surface drifter tracks in the north atlantic ocean from the time period 1990 to 2007 provides evidence that warm subtropical waters have recently increased their penetration toward the nordic seas prior to 2000 the warm water branches of the north atlantic current fed by the gulf stream turned southeastward in the eastern north atlantic since 2001 these paths have shifted toward the rockall trough through which the most saline north atlantic waters pass to the nordic seas these surface drifters are able to overcome the ekman drift which would force them southward under the westerly winds dominating the subpolar atlantic yet the changes in path cannot be accounted for by changes in ekman drift eddy kinetic energy from satellite altimetry shows increased energy along the shifted drifter pathways across the mid atlantic ridge since 2001 these near surface changes have occurred during continual weakening of the north atlantic subpolar gyre as seen by altimetry they are also consistent with the observed increase in temperature and salinity of the waters flowing northward into the nordic seas these findings suggest the changes in the vertical structure of the northern north atlantic ocean its dynamics and exchanges with the higher latitudes wind stress and its curl changes are discussed as a possible forcing of the changes in the pathways of the subtropical waters

simulated variability of the atlantic meridional overturning circulation to examine the multi annual to decadal scale variability of the atlantic meridional overturning circulation amoc we conducted a four member ensemble with a daily reanalysis forced medium resolution global version of the isopycnic coordinate ocean model micom and a 300 years integration with the fully coupled bergen climate model bcm the simulations of the amoc with both model systems yield a long term mean value of 18 sv and decadal variability with an amplitude of 1 3 sv the power spectrum of the inter annual to decadal scale variability of the amoc in bcm generally follows the theoretical red noise spectrum with indications of increased power near the 20 years period comparison with observational proxy indices for the amoc e g the thickness of the labrador sea water the strength of the baroclinic gyre circulation in the north atlantic ocean and the surface temperature anomalies along the mean path of the gulf stream shows similar trends and phasing of the variability indicating that the simulated amoc variability is robust and real mixing indices have been constructed for the labrador the irminger and the greenland iceland norwegian gin seas while convective mixing in the labrador and the gin seas are in opposite phase and linked to the nao as observations suggest the convective mixing in the irminger sea is in phase with or leads the labrador sea newly formed deep water is seen as a slow anomalous cold and fresh plume flowing southward along the western continental slope of the atlantic ocean with a return flow of warm and saline water on the surface in addition fast travelling topographically trapped waves propagate southward along the continental slope towards equator where they go east and continue along the eastern rim of the atlantic for both types of experiments the northern hemisphere sea level pressure and 2 m temperature anomaly patterns computed based on the difference between climate states with strong and weak amoc yields a nao like pattern with intensified icelandic low and azores high and a warming of 0 25 0 5 c of the central north atlantic sea surface temperature sst the reanalysis forced simulations indicate a coupling between the labrador sea water production rate and an equatorial atlantic sst index in accordance with observations this coupling is not identified in the coupled simulation

the circulation of eastern canadian seas abstract the eastern canadian seas including baffin bay the labrador sea and shelf the n e newfoundland shelf the scotian shelf and the gulf of st lawrence form an integrated hydro dynamical system the circulation is investigated using current meter data and a high resolution three dimensional coupled ice ocean circulation model cecom canadian east coast ocean model covering the entire area the model is forced with realistic atmosphere fluxes and the results are compared to the current meter data collected in four selected periods between 1987 and 2008 many features of the model current fields are similar to those from the previous regional circulation models for the shelves new findings from cecom include seasonal differences of the circulation around davis strait the detailed structure of the labrador current re circulation two cross shelf currents on the scotian shelf and strong currents in halibut channel which connects the waters of the western grand banks and scotian shelf the annual variation of the circulation is investigated both the model and data show the labrador current is strong in fall and weak in spring the outflow from the gulf of st lawrence through cabot strait and the currents on the inner scotian shelf are strong in winter and fall and weak in spring and are in phase with the labrador current the model currents are compared to observations using a qualitative method of visual comparison and a quantitative method based on statistical analysis the comparisons indicate that the main features of the current fields from the observations are successfully reproduced by the model the quantitative analysis indicates that the model currents are in reasonable agreement with the observations specifically a good agreement is found in the labrador shelf newfoundland shelf and flemish pass a fair agreement is found in davis strait the inner scotian shelf and sable bank however the agreement for cabot strait and the scotian shelf break is less satisfactory an analysis of the spatial variability of the current field suggests that the degree of agreement is closely related to the spatial variability of the current field the regions with low spatial variability generally have good agreements the volume and freshwater transports through several sections from the model are in good agreement with available estimates based on data

one to two month oscillations observed high latitude tropospheric and stratospheric response to tropical forcing abstract careful spectral correlation and coherence analyses of low frequency fluctuations in global geopotential height data are presented attention is paid to proper statistical assessments the main points are 1 one to two month oscillating quasi stationary wavetrains have recently been reported in the extratropical southern hemisphere troposphere as far south as the edge of antarctica however only weak correlations were observed with the supposed tropical forcing region leading to the question of whether the wavetrain is a response to tropical forcing or possibly due to in situ instabilities on 1 2 month time scales the present paper clears up this enigma with analyses of other tropical datasets which reveal clear correlation between low latitude source regions and the sh extratropical troposphere 2 an earlier investigation found strong correlations between 1 2 month oscillations in the upper stratosphere and tropical troposphere yet no vertical propagation was found directly above the tro

high resolution simulation of the boreal summer intraseasonal oscillation in met office unified model the present study investigates the fidelity and resolution sensitivity of met office unified model global atmosphere 3 0 in simulating the intra seasonal oscillation iso of the east asia and western north pacific summer monsoon two sets of model simulations at horizontal resolutions of n216 60km and n96 130km forced by observed daily high resolution sea surface temperature are examined and compared with the observations diagnostic results show that the model can well reproduce the gross spatio temporal features of observed summer iso over the east asia and western north pacific in terms of period dominant reof mode variance northward propagation cycle evolution and vertical structure the intra seasonal change in intensity and position of western north pacific subtropical high and upper troposphere westerly jet associated with the northward propagating isos are also reasonably captured in the model moreover increasing horizontal resolution improves most aspects of the iso simulation especially the intensity and northward propagation of the iso related convection and circulation systems further analysis indicates that the improvement as resolution increases is related to the weakening in background state of east asian summer monsoon which is due to the realistic simulation of land sea thermal contrast at higher resolution model this study suggests that enhanced model resolution can have some beneficial impacts on the iso simulation

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

the intraseasonal 30 50 day oscillation of the australian summer monsoon abstract the tropical intraseasonal 30 50 day oscillation manifests itself in the australian summer monsoon by a pronounced modulation of the monsoonal westerlies these 30 50 day fluctuations of the monsoonal westerlies are coherent with rainfall and olr across northern australia the olr fluctuation originates in the indian ocean and systematically propagates eastward at 5 m s 1 consistent with previous studies of the intraseasonal oscillation the detailed evolution of the intraseasonal oscillation of the monsoon is studied via composites of upper air data in and about the australian tropics during the summer periods 1957 87 91 events were identified at darwin australia the composite oscillation at darwin has a very deep baroclinic structure with westerlies extending up to 300 mb the westerly phase lasts about ten days and lags a similar duration rainfall event by about four days during the westerly phase the upper troposphere is warm and the extreme lower troposphere is cool this structure

sr o and pb isotope evidence for origin and evolution of etive igneous complex scotland a multi isotope approach has been applied to the origin of one of the largest and latest newer granite complexes of the scottish caledonides contributions from both mantle and unexposed late proterozoic lower continental crust are recognized indicating that granite magmatism is a mechanism for both primary crustal growth and reworking of older crustal rocks

intraseasonal variability of high resolution doppler imager winds in the equatorial mesosphere and lower thermosphere analyses of high resolution doppler imager hrdi daytime equatorial zonal winds indicate significant variability on time scales of 20 121 days these appear as transient oscillations in the equatorial zonal mean zonal wind between 70 and 100 km the oscillations are characterized by two maxima near 75 and 95 km that are out of phase separated by a minimum near 80 km these features move downward in time and exhibit equatorial symmetry with maximum values at the equator during 1994 maximum amplitudes of the intraseasonal oscillation are 20 m s 1 in january and 30 m s 1 in june the intraseasonal variability present in hrdi winds is qualitatively consistent with variations on similar timescales reported at christmas island it has been hypothesized that the wind patterns at christmas island result from modulated gravity wave driving eckermann et al 1997 the results of the present study strongly support this view

vertical and lateral propagation characteristics of intraseasonal oscillation from the tropical lower troposphere to upper mesosphere 1 using a mesosphere stratosphere troposphere mst radar and a rayleigh lidar collocated at the indian tropical station gadanki 13 5 n 79 2 e european centre for medium range weather forecasts ecmwf re analysis data and the horizontal wind velocities measured by the thermosphere ionosphere mesosphere energetics and dynamics timed doppler interferometer tidi instrument onboard the timed satellite the present study makes a report on the lateral and vertical propagation characteristics of an intraseasonal oscillation iso 20 40 day period band propagating from the lower troposphere to the upper mesosphere region during the winter november december january and february months of the years 2004 2005 it is found that the iso had its origin in the tropical lower troposphere and propagated laterally and vertically to the upper mesosphere through the subtropical latitudes by partial refraction and reflection processes about the subtropical westerly jet corresponding enhancements in the wavelet spectrum of outgoing long wave radiation olr noaa interpolated indicate that convective forces in the lower troposphere are one of the main sources for the generation of the iso from the phase of the iso in the horizontal winds as observed by the mst radar it is found that the iso propagated upward from the lower troposphere up to near the tropopause where it got sharply attenuated from the ecmwf data it is observed that the iso was refracted to the subtropical latitudes through the tropical tropopause from where it got radiated upward into the stratosphere the phase propagation of the filtered winds shows that the iso arched back toward the tropical latitudes and propagated to the mesospheric region

convection above the labrador continental slope the labrador sea is one of the few regions of the world ocean where deep convection takes place several moorings across the labrador continental slope just north of hamilton bank show that convection does take place within the labrador current mixing above the lower labrador slope is facilitated by the onshore along isopycnal intrusions of low potential vorticity eddies that weaken the stratification combined with baroclinic instability that sustains slanted mixing while restratifying the water column through horizontal fluxes above the shelf break the irminger seawater core is displaced onshore while the stratification weakens with the increase in isopycnal slope the change in stratification is partially due to the onshore shift of the classical labrador current baroclinic instability and possibly slantwise convection

first observations of intraseasonal oscillations in the equatorial mesosphere and lower thermosphere we present the first evidence of strong intraseasonal 10 100 day variability of the equatorial mesosphere and lower thermosphere drawn from spectral analysis of three years of radar wind measurements of the region at christmas island 2 n 157 w oscillations in the zonal wind as large as 20 m s 1 are observed with periods 60 days at 85 95 km amplitudes attenuate near 80 km then reintensify near 75 km where they are usually of longer period and are out of phase with the upper level oscillations oscillations with periods 35 40 days are also observed at 85 95 km these oscillations are transient and usually appear when the background flow is westward similar signals are not observed in the meridional winds these facts suggest that they could be kelvin waves similar to intraseasonal variability in the equatorial lower atmosphere associated with the madden julian oscillation somewhat different time height activity at 20 days could be related to the 1 3 rossby normal mode or the 20 25 day tropospheric oscillation as it is unlikely that any of these oscillations could propagate to these heights from the lower atmosphere we postulate that they arise due to variations in gravity wave activity and transmissivity induced by intraseasonal oscillations lower down which is transferred into the mean flow when these gravity waves dissipate in the mesosphere this may mean that this intraseasonal activity is a time varying mean wind rather than a forced planetary wave

vertical variation of low frequency oscillations in uhf radar derived winds at a tropical indian station 1 signatures of the low frequency intraseasonal oscillations and their vertical variation in the lower troposphere are studied using multilevel wind observations made at a tropical indian station pune 18 32 n 73 51 e from wind profiler uhf radar during the period june 2003 to may 2006 spectral analysis using fast fourier transform showed the presence of oscillations 30 40 days and 50 70 days in daily mean zonal winds and revealed their evolution in height period structures the 30 40 days oscillation mode has the largest amplitude compared to the other modes in zonal and meridional winds all oscillation modes have much less amplitude in the vertical wind component the high temporal 3 hourly zonal and meridional wind observations obtained during the southwest monsoon period june to september jjas during the years 2003 2004 and 2005 showed a prominent regime of oscillation namely 30 40 days and a moderate signature of 10 20 day mode in all three years it is seen that these oscillations are not occurring as a single frequency sinusoidal oscillation but are seen as broadband spectrum the amplitude of these wave modes showed significant vertical variation the vertical structures of radar observed intraseasonal oscillations 30 40 days mode and tropical rainfall measuring mission derived mean precipitation intensity during the monsoon period jjas during the years 2003 2005 showed a reasonable comparison the results presented in this study show significant intraseasonal and interannual variability in lower tropospheric winds which are closely related to the performance of the southwest monsoon

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

hydrography of the labrador sea during active convection the hydrographic structure of the labrador sea during wintertime convection is described the cruise part of the deep convection experiment took place in february march 1997 amidst an extended period of strong forcing in an otherwise moderate winter because the water column was preconditioned by previous strong winters the limited forcing was enough to cause convection to approximately 1500 m the change in heat storage along a transbasin section relative to an occupation done the previous october gives an average heat loss that is consistent with calibrated national centers for environmental prediction surface heat fluxes over that time period 200 wm 22 deep overturning was observed both seaward of the western continental slope which was expected as well as within the western boundary current itself something that had not been directly observed previously these two geographical regions separated by roughly the 3000 m isobath produce separate water mass products the offshore water mass is the familiar cold fresh dense classical labrador sea water lsw the boundary current water mass is a somewhat warmer saltier lighter vintage of classical lsw though in the far field it would be difficult to distinguish these products the offshore product was formed within the cyclonic recirculating gyre measured by lavender et al in a region that is limited to the north most likely by an eddy flux of buoyant water from the eastern boundary current the velocity measurements taken during the cruise provide a transport estimate of the boundary current throughput and offshore recirculation finally the overall trends in stratification of the observed mixed layers are described

the wind driven circulation quasi geostrophic simulations and theory for nonsymmetric winds abstract simulations of the wind driven ocean circulation carded out with an eddy resolving quasi geostrophic numerical model and symmetric idealized wind forcing have a large scale structure that is predicted wen by the steady nonlinear theory of rhines and young the sharp jet and inertial recirculation am often confined weft inside the region of closed hyperbolic characteristics defined by that theory and hence do not affect the sverdrup dynamics part of the gyre the characteristics make possible simple predictions about the development of the circulation including time dependence and eddy stirring by tilting the line of vanishing ekman pumping away from the east west orientation as it is tilted in the north atlantic and less so the north pacific we explore a family of circulations as the tilt of the wind held is increased characteristics originating at the eastern boundary begin to thread through the energetic region occupied by the free jet then extensive new branches of eddy driven f

zonal mean temperature variations inferred from saber measurements on timed compared with uars observations 1 in the zonal mean meridional winds of the upper mesosphere oscillations with periods between 1 and 4 months have been inferred from uars measurements and independently predicted with the numerical spectral model nsm the wind oscillations tend to be confined to low latitudes and appear to be driven at least in part by wave mean flow interactions winds across the equator should generate due to dynamical heating and cooling temperature oscillations with opposite phase in the two hemispheres investigating this phenomenon we have analyzed saber temperatures from timed in the altitude range between 55 and 95 km to delineate with an empirical model the year long variability of the migrating tides and zonal mean components the inferred seasonal variations of the diurnal tide characterized by amplitude maxima near equinox are in substantial agreement with uars observations and results from the nsm for the zonal mean the dominant seasonal variations in the saber temperatures with annual 12 months and semiannual 6 months periodicities agree well with those derived from uars measurements the intraseasonal variations with periods between 2 and 4 months have amplitudes close to 2 k almost half as large as those for the dominant seasonal variations their amplitudes are in qualitative agreement with the corresponding values inferred from uars during different years the saber and uars temperature variations reveal pronounced hemispherical asymmetries consistent with meridional wind oscillations across the equator the phase of the semiannual temperature oscillations from the nsm agrees with the observations from uars and saber however the amplitudes are systematically smaller which may indicate that planetary waves are more important than is allowed for in the model for the shorter period intraseasonal variations which can be generated by gravity wave drag the model results are generally in better agreement with the observations

an abrupt shift in the labrador current system in relation to winter nao events the behavior of the labrador current during the period from 1990 to 2007 is investigated with an eddy resolving circulation model for the north atlantic ocean an eof analysis of the model output suggests that the variability in the labrador current can be partitioned into a western labrador current wlc from the 300 2500 m isobaths and an eastern labrador current elc from the 2500 3300 m isobaths the model results demonstrate that the wlc transport experienced an abrupt increase during 2000 2002 consistent with data this differed significantly from the elc transport which was strong during the high winter nao north atlantic oscillation years 1990 95 and then steadily declined this elc trend is consistent with changes in the modelled atlantic meridional overturning circulation and convection depth our study proposes that the change in the wlc is due to a southwestward shift of the atmospheric circulation pattern starting in 2001 coincident with a change in the 2001 nao index and also in a westward shift of the action centers of the winter nao events this article is protected by copyright all rights reserved

heat budget in the north atlantic subpolar gyre impacts of atmospheric weather regimes on the 1995 warming event abstract in the mid 1990s the north atlantic subpolar gyre has shown a dramatic warming event that has been thoroughly investigated from observations and numerical simulations some studies suggest that it was due to an interannual wind driven weakening and shrinking of the gyre that facilitated the penetration of warm atlantic water the weakening of the gyre being attributed to changes in the north atlantic oscillation nao and in the east atlantic pattern which are the two dominant modes of atmospheric variability in the north atlantic however other studies suggest that the warming event was due to a decadal buoyancy driven strengthening of the meridional overturning circulation and subsequent intensification of the poleward heat transport in response to the positive nao conditions of 1988 1995 to reconcile this discrepancy the heat budget in the north atlantic subpolar gyre is reconstructed from four ocean hindcast simulations sharing the same modelling platform but using different settings the novelty of this work is the decomposition of the subpolar gyre into a western and an eastern subregion which is motivated by water mass distribution around reykjanes ridge and by the fact that deep convection only occurs in the western subpolar gyre in the western subpolar gyre the 1995 warming event is the decadal baroclinic ocean response to positive nao conditions from 1988 to 1995 the latter induced increased surface heat loss in the labrador sea that intensified deep convection hence strengthened the meridional overturning circulation and the associated poleward heat transport in the eastern subregion a concomittant warming is induced by an interannual barotropic adjustment of the gyre circulation to an abrupt switch from positive nao conditions in winter 1995 to negative nao conditions in winter 1996 indeed the gyre response to negative nao conditions is a cyclonic intergyre gyre that increases northward volume and heat transports at the southeastern limit of the subpolar gyre therefore the discrepancies found in the literature about the 1995 warming event of the north atlantic subpolar gyre are reconciled in the present work which suggests that the atmospheric drivers the mechanisms at stake and the associated timescales are different to the east and to the west of reykjanes ridge

a new collective view of oceanography of the arctic and north atlantic basins abstract we review some historical aspects of the major observational programs in the north atlantic and adjacent regions that contributed to establishing and maintaining the global ocean climate monitoring network the paper also presents the oceanic perspectives of climate change and touches the important issues of ocean climate variability on time scales from years to decades some elements of the improved understanding of the causes and mechanisms of variability in the subpolar north atlantic and adjacent seas are discussed in detail the sophistication of current oceanographic analysis especially in connection with the most recent technological breakthroughs notably the launch of the global array of profiling argo floats allows us to approach new challenges in ocean research we demonstrate how the ocean climate changes in the subpolar basins and polar seas correlate with variations in the major climate indices such as the north atlantic oscillation and atlantic multidecadal oscillation and discuss possible connections between the unprecedented changes in the arctic and greenland ice melt rates observed over the past decade and variability of hydrographic conditions in the labrador sea furthermore a synthesis of shipboard and argo measurements in the labrador sea reveals the effects of the regional climate trends such as freshening of the upper layer possible causes of which are also discussed on the winter convection in the labrador sea including its strength duration and spatial extent these changes could have a profound impact on the regional and planetary climates a section with the highlights of all papers comprising the special issue concludes the preface

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

intra seasonal oscillations observed in the mlt region above uk 52 n 2 w and esrange 68 n 21 e 1 analyses of intra seasonal oscillations i e oscillations with periods of 30 100 days in the mlt region made by meteor radars at middle uk five years of data and high latitudes esrange three years of data are presented in this work there is clear evidence of 75 day variability in the mean winds this intra seasonal oscillation appears to be a prominent feature of the mean zonal circulation and was observed quite regularly in the time intervals december 1996 september 2001 over uk and october 1999 december 2002 over esrange the intra seasonal oscillations observed over esrange are coherent in both amplitude and phase over the height range of 80 100 km covered by the radar they are especially strong in the range 90 97 km weaker near 87 88 km and stronger again near 81 km at these lower heights the intra seasonal oscillations are usually of longer period 80 days than and are out of phase with the oscillations at the upper heights we also note that this oscillation is a common feature in the meridional winds over the uk it is present but intermittent in the meridional winds over esrange

low latitude mesospheric mean winds observed by gadanki mesosphere stratosphere troposphere mst radar and comparison with rocket high resolution doppler imager hrdi and mf radar measurements and hwm93 1 low latitude mesospheric winds are investigated using data collected from 1995 to 2006 11 years by indian mst radar located at gadanki 13 5 n 79 2 e clear eastward and westward flow in zonal wind is noticed during solstices and equinoxes respectively the meridional wind shows equatorward flow below 75 km and poleward flow above 75 km quite consistent with that observed with other techniques the winds show a clear semiannual oscillation sao with maxima during equinoxes the strength of the sao during spring is larger than that of fall equinox and the first peak occurs at higher altitudes than the second peak the observed features are compared with other techniques namely rocket high resolution doppler imager hrdi and medium frequency mf radar and also with horizontal wind model hwm93 in general good comparison is seen among various techniques with some discrepancy observed in amplitudes interestingly decrease in eastward wind with time during winter months is noticed the significance of the present results lies in showing the consistency inconsistency of various experimental techniques to measure the middle atmospheric winds which are very important to assess the climate variability

extra tropical atmospheric response to enso in the cmip5 models the seasonal mean extra tropical atmospheric response to el nino southern oscillation enso is assessed in the historical and pre industrial control cmip5 simulations this analysis considers two types of el nino events characterized by positive sea surface temperature sst anomalies in either the central equatorial pacific cp or eastern equatorial pacific ep as well as ep and cp la nina events characterized by negative sst anomalies in the same two regions seasonal mean geopotential height anomalies in key regions typify the magnitude and structure of the disruption of the walker circulation cell in the tropical pacific upper tropospheric enso teleconnections and the polar stratospheric response in the cmip5 ensembles the magnitude of the walker cell disruption is correlated with the strength of the mid latitude responses in the upper troposphere i e the north pacific and south pacific lows strengthen during el nino events the simulated responses to el nino and la nina have opposite sign the seasonal mean extra tropical upper tropospheric responses to ep and cp events are indistinguishable the enso responses in the merra reanalysis lie within the model scatter of the historical simulations similar responses are simulated in the pre industrial and historical cmip5 simulations overall there is a weak correlation between the strength of the tropical response to enso and the strength of the polar stratospheric response enso related polar stratospheric variability is best simulated in the high top subset of models with a well resolved stratosphere