recent thermohaline trends of the atlantic waters inflowing to the mediterranean sea 1 a total of 5077 argo float profiles in the period 01 2002 05 2010 have been used to analyze salinity and temperature trends in the atlantic waters adjacent to the strait of gibraltar in order to identify the source of recent changes observed in the inflow to the mediterranean sea positive salinity trends of 0 038 0 009 year 1 and 0 013 0 003 year 1 have been found for the surface atlantic water and the eastern north atlantic central water respectively for temperature no significant trend is observed in the surface layer while positive trend of 0 05 0 02 c year is obtained for the thermocline waters the mediterranean water layer does not show any significant trend for the entire period but a switch from positive to negative trends is observed in year 2006 in contrast to previous findings these thermohaline variations are driven by intrinsic water masses changes instead of isopycnal vertical displacements probably related to an enhancement of the net freshwater losses in the area

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

physical and biogeochemical transports structure in the north atlantic subpolar gyre 1 physical mass heat and salt and biogeochemical nutrients oxygen alkalinity total inorganic carbon and anthropogenic carbon transports across the transoceanic world ocean circulation experiment woce a25 section in the subpolar north atlantic 4x line obtained previously alvarez et al 2002 2003 are reanalyzed to describe their regional and vertical structure the water mass distribution in the section is combined with the transport fields to provide the relative contribution from each water mass to the final transport values the water mass circulation pattern across the section is discussed within the context of the basin scale thermohaline circulation in the north atlantic eastern north atlantic central influenced antarctic intermediate mediterranean and subarctic intermediate waters flow northward with 10 3 5 6 1 7 and 2 9 sv respectively the total flux of lower deep water ldw across the section is 1 sv northward a portion of ldw flowing northward in the iberian basin recirculates southward within the eastern basin and about 0 7 sv flow into the western north atlantic about 7 sv of labrador seawater lsw from the labrador sea cross the 4x section within the north atlantic current and 12 sv of lsw from the irminger sea flow southward within the east greenland current denmark strait overflow water flows over the western flank of the irminger basin 1 5 sv and iceland scotland overflow water isow is mainly transported in the charlie gibbs fracture zone 6 sv isow remnants flow southward to the eastern basin contributing to the eastern basin deep ventilation lsw and the overflows transport cant southward across the section this southward cant transport is overcome by the northward transport in upper layers finally cant is injected into the subpolar gyre where it accumulates

mean full depth summer circulation and transports at the northern periphery of the atlantic ocean in the 2000s a mean state of the full depth summer circulation in the atlantic ocean in the region in between cape farewell greenland scotland and the greenland scotland ridge gsr is assessed by combining 2002 2008 yearly hydrographic measurements at 59 5 n mean dynamic topography satellite altimetry data and available estimates of the atlantic nordic seas exchange the mean absolute transports by the upper ocean mid depth and deep currents and the meridional overturning circulation moc 16 5 2 2 sv at 0 27 55 at 59 5 n are quantified in the density space inter basin and diapycnal volume fluxes in between the 59 5 n section and the gsr are then estimated from a box model the dominant components of the meridional exchange across 59 5 n are the north atlantic current nac 15 5 0 8 sv 0 27 55 east of the reykjanes ridge the northward irminger current ic 12 0 3 0 sv and southward western boundary current wbc 32 1 5 9 sv in the irminger sea and the deep water export from the northern iceland basin 3 7 0 8 sv 0 27 80 about 60 12 7 1 4 sv of waters carried in the moc upper limb 0 27 55 by the nac ic across 59 5 n 21 1 1 0 sv recirculates westward south of the gsr and feeds the wbc 80 10 2 1 7 sv of the recirculating nac ic derived upper ocean waters gains density of 0 27 55 and contributes to the moc lower limb accordingly the contribution of light to dense water conversion south of the gsr 10 sv to the moc lower limb at 59 5 n is one and a half times larger than the contribution of dense water production in the nordic seas 6 sv

amplitude phase and period variations of the quasi 2 day wave in the mesosphere and lower thermosphere over london canada 43 n 81 w during 1993 and 1994 because there is as yet no conclusive evidence pointing to the source of the quasi 2 day wave further observations are required in order to resolve questions about the generating mechanism as well as to better understand the role of the wave in the middle atmosphere in this paper we investigate the period amplitude phase and vertical wavelength for the quasi 2 day wave in the mesosphere and lower thermosphere using the university of western ontario 2 mhz radar near london canada and in addition we look at possible coupling with atmospheric tides the results of the present study bring out certain new aspects of the quasi 2 day wave at midlatitude in the northern hemisphere that have not been previously reported in particular we show that the period of the quasi 2 day wave determined from our study is smaller 46 47 hours than the 51 to 52 h period generally suggested by other northern hemisphere results and our periods also showed variability as a function of time we also draw attention to the annual variability and especially highlight the occurrence of the wave in nonsummer months for example a brief occurrence in april is not uncommon our study also contributes additional midlatitude geographical data that should aid in developing a better picture of the quasi 2 day wave

reversal of the 1960s to 1990s freshening trend in the northeast north atlantic and nordic seas hydrographic time series in the northeast north atlantic and nordic seas show that the freshening trend of the 1960s 1990s has completely reversed in the upper ocean since the 1990s temperature and salinity have rapidly increased in the atlantic inflow from the eastern subpolar gyre to the fram strait in 2003 2006 salinity values reached the previous maximum last observed around 1960 and temperature values exceeded records the mean properties of the atlantic inflow decrease northwards but variations seen in the eastern subpolar gyre at 57 n persist with the same amplitude and pattern along the pathways to fram strait time series correlations and extreme events suggest a time lag of 3 4 years over that distance this estimate allows predictions to be made the temperature of atlantic water in the fram strait may start to decline in 2007 or 2008 salinity a year later but both will remain high at least until 2010

decline of subpolar north atlantic circulation during the 1990s observations of sea surface height reveal that substantial changes have occurred over the past decade in the mid to high latitude north atlantic ocean topex poseidon altimeter data show that subpolar sea surface height increased during the 1990s and the geostrophic velocity derived from altimeter data exhibits declining subpolar gyre circulation combining the data from earlier satellites we find that subpolar circulation may have been weaker in the late 1990s than in the late 1970s and 1980s direct current meter observations in the boundary current of the labrador sea support the weakening circulation trend of the 1990s and together with hydrographic data show that the mid to late 1990s decline extends deep in the water column analysis of the local surface forcing suggests that the 1990s buoyancy forcing has a dynamic effect consistent with altimetric and hydrographic observations a weak thermohaline forcing allows the decay of the domed structure of subpolar isopycnals and weakening of circulation

climatology of the migrating terdiurnal tide tw3 in saber timed temperatures 1 the present paper is focused on the global spatial altitude and latitude structure and seasonal and interannual temporal variability of the migrating terdiurnal tide tw3 seen in 8 years 2002 2009 of observations of the kinetic temperature measured by the saber instrument on the timed satellite the tides migrating and nonmigrating and the planetary waves zonally traveling and stationary are simultaneously extracted from the satellite data it is found that the saber tw3 tide is dominated by different hough modes below and above 80 to 90 km height in the mesosphere it reflects mainly the evanescent feature of the first symmetric mode and in the lower thermosphere propagating modes with shorter vertical wavelengths dominate its structure the seasonal behavior of the terdiurnal tide at low latitudes is dominated by an annual variation with local summer amplification while that at midlatitudes is a combination of semiannual variation with maxima in equinoxes and an annual variability with winter enhancement the hough modes of the solar heating from waccm heating to a large extent determine the predominantly antisymmetric features of the saber tw3 tide during the solstice but are not able to explain well the predominant symmetric features in the equinoxes the tw3 tide reveals some interannual variability with a period of quasi 2 years which indicates an enhancement during the eastward phase of the stratospheric qbo

observation of a large amplitude wave and inversion layer leading to convective instability in the mesopause region over fort collins co 41 n 105 w 1 sodium resonance lidar observations on the night of nov 3 1997 ut recorded a temperature inversion with 80 k amplitude moving downward from 90 to 83 km with the maximum temperatures exceeding 280 k these are the highest temperatures and largest inversion layer observed in 10 years over fort collins colorado the inversion can be decomposed into a 50 k peak to peak amplitude oscillation with an apparent 8 hr period and 25 km vertical wavelength plus a residual 30 k inversion layer the temperature gradient above this maximum is near adiabatic from 88 100 km for 4 hours with multiple super adiabatic layers several km in depth streamlines derived from the sodium mixing ratio and the potential temperature both indicate a 10 km upward movement in the adiabatic region presumably a large amplitude upward propagating wave saturated when it reached the inversion layer just below the mesopause and broke leading to convective instabilities with large vertical and temporal scales

atmospheric impact of arctic sea ice loss in a coupled ocean atmosphere simulation the atmospheric response to an idealized decline in arctic sea ice is investigated in a novel fully coupled climatemodel experiment in this experimenttwo ensembles of single year model integrations are performed starting on 1 april the approximate start of the ice melt season by perturbing the initial conditions of sea ice thickness sit declines in both sea ice concentration and sit which result in sea ice distributions that are similar to the recent sea ice minima of 2007 and 2012 are induced in the ice loss regions there are strong 3k local increasesin sea surface temperature sst additionally there are remoteincreases in sst in the central north pacific and subpolar gyre in the north atlantic over the central arctic there are increases in surface air temperature sat of 8k due to increases in ocean atmosphere heatfluxes there are increases in sat over continental north america that are in good agreement with recent changes as seen by reanalysis data it is estimated that up to two thirds of the observed increase in sat in this region could be related to arctic sea ice loss in early summer there is a significant but weak atmospheric circulation response that projects onto the summer north atlantic oscillation nao in early summer and early autumn there is an equatorward shift of the eddy driven jet over the north atlantic as a result of a reduction in the meridional temperature gradients in winter there is no projection onto a particular phase of the nao

a decade long climatology of terdiurnal tides using timed saber observations 1 in this paper we globally characterize the solar terdiurnal tide in the 80 110 km region of earth s atmosphere through analysis of 10 years of temperature measurements made by the sounding of the atmosphere using broadband emission radiometry instrument on the thermosphere ionosphere mesosphere energetics and dynamics spacecraft the sun synchronous migrating component tw3 which is longitude independent and achieves maximum amplitudes of order of 5 k 10 k at 90 km 110 km not too different than the 7 15 k amplitudes that are typical of the migrating diurnal and semidiurnal tides in this region significant longitude variability 20 25 in terdiurnal temperature amplitudes also exists which is decomposed into zonal wave number components the largest of these te1 tw4 and tw5 reveal distinct seasonal latitudinal and height versus latitude patterns and interannual consistency in addition it is demonstrated that these particular components vary in ways that suggest that they originate from nonlinear interactions between diurnal and semidiurnal tides specifically between de3 and sw2 for te1 between dw2 and sw2 for tw4 and between dw1 and sw4 for tw5 we also demonstrate that the terdiurnal tides derived here are not influenced to any significant degree by aliasing due to the presence of other waves

climatic warming of atlantic intermediate waters abstract interdecadal temperature variability of the atlantic ocean is investigated by differencing hydrographic sections taken from the 1920s through the 1990s a comprehensive reanalysis of north atlantic sections and the inclusion of south atlantic sections show that warming seen previously in the north atlantic extends to the south atlantic the largest statistically significant changes occur on pressure surfaces between 1000 and 2000 decibars db over this pressure range and for latitudes between 32 s and 36 n temperatures have warmed by 0 5 c century 1 at 48 n a cooling of 3 c century 1 occurred between the 1950s and 1980s these isobaric temperature trends are decomposed into ones along surfaces of constant neutral density and ones due to the vertical movement of neutral surfaces the two components are associated with different processes in the southern north atlantic 8 36 n the subthermocline warming between the 1950s and 1980s appears to be due primarily to downward displacements of n

long term observations of north atlantic current transport at the gateway between western and eastern atlantic in the western north atlantic warm and saline water is brought by the north atlantic current nac from the subtropics into the subpolar gyre four inverted echo sounders with high precision pressure sensors pies were moored between 47 40 n and 52 30 n to study the main pathways of the nac from the western into the eastern basin the array configuration that forms three segments northern central and southern allows partitioning of the nac and some assessment of nac flow paths through the different mid atlantic ridge fracture zones we exploit the correlation between the nac transport measured between 2006 and 2010 and the geostrophic velocity from altimeter data to extend the time series of nac transports to the period from 1992 to 2013 the mean nac transport over the entire 21 years is 27 5 sv consisting of 60 warm water of subtropical origin and 40 subpolar water we did not find a significant trend in the total transport time series but individual segments had opposing trends leading to a more focused nac in the central subsection and decreasing transports in the southern and northern segments the spectral analysis exhibits several significant peaks the two most prominent are around 120 days identified as the time scale of meanders and eddies and at 4 9 years most likely related to the nao transport composites for the years of highest and lowest nao indices showed a significantly higher transport 2 9 sv during strong nao years mainly in the southern segment

the terdiurnal tide in the mesosphere and lower thermosphere over london canada 43 n 81 w radars have been used successfully for many years to measure atmospheric diurnal and semidiurnal tides but studies of the atmospheric terdiurnal tide have only rarely been reported to date in the literature in this paper we investigate the amplitude phase and vertical wavelength for the terdiurnal tide using the university of western ontario uwo 2 mhz radar near london canada emphasis is placed on short term monthly seasonal and annual variations of the terdiurnal tide the results of the present study bring out certain new aspects of the terdiurnal tide at midlatitudes in the northern hemisphere we show that terdiurnal tides have significant amplitudes in the mesosphere and lower thermosphere indeed the terdiurnal amplitudes are often comparable to the diurnal ones we also draw attention to the annual variability and especially highlight the occurrence of the terdiurnal tide in non winter months for example the occurrence of the terdiurnal tide in spring months is not uncommon thus it seems that the 8 hour component observed over london canada cannot be explained by the terdiurnal tide being due to solar heating alone particular cases of the terdiurnal tide are examined and the observed amplitude and phase profiles of the terdiurnal tide at certain times of the year are discussed in terms of nonlinear interaction between the diurnal and semidiurnal tides we suspect that this effect may also explain the fact that diurnal and semidiurnal tides at our station often seem suppressed relative to other sites thayaparan et al 1995a on the basis of our previous and present observations it is also possible that large terdiurnal amplitudes observed at certain times of the year may be partly explained in terms of tidal gravity wave interactions however this possibility needs to be further investigated in the future

intense warming and salinity modification of intermediate water masses in the southeastern corner of the bay of biscay for the period 1992 2003 1 the evolution of the intermediate water masses within the southeastern corner of the bay of biscay is studied from the shelf edge and slope stations of a hydrographic standard section northward from santander 43 30 43 54 n 3 47 w the section was sampled monthly from 1991 to autumn 2003 with some gaps more frequent in the early stages due to weather conditions data were systematically collected up to a 1000 m depth or to the maximum depth at the shallower stations showing a detailed picture of the variability in water masses below the mixing layer eastern north atlantic central water has warmed as a consequence of continuous deepening of the isopycnal levels changes in water properties at fixed isopycnal levels are less relevant and highly biased by a 1998 positive peak in temperature and salinity the warming trend found is 0 032 c per year on average on the other hand the mediterranean water has been modified along isopycnals variations 10 times greater than those due to isopycnal displacement increasing progressively both temperature and salinity for the period 1994 2001 the values found are around 0 020 c per year for temperature and 0 005 for salinity as a final picture all water masses below the mixing layer and down to a 1000 m depth in the southern bay of biscay have warmed up during the last decade at rates from two to six times greater than the those accepted for the north atlantic during the last half century

observational evidence of tidal gravity wave interactions using the uwo 2 mhz radar the degree of interaction between atmospheric gravity waves and tides is an issue which is of great importance in middle atmosphere studies it is especially important with regard to tidal variability which is frequently observed in the mesosphere and lower thermosphere but as yet has not been subject to adequate study in this paper we present some strong observational evidence of such interactions made with the uwo 2 mhz radar near london canada our observations show significant correlation between gravity waves and tides diurnal at certain times of the year and the nature of the correlation is intermittent and varies with time of year it is possible that differences between tidal amplitudes at sites with mesoscale separations may be explained in terms of such phenomena we also propose a simple model which is found to be consistent with the major features of the observed data

on the temporally varying northward penetration of mediterranean overflow water and eastward penetration of labrador sea water abstract historical hydrographic data in the eastern north atlantic are used to suggest a connection between the northward penetration of mediterranean overflow water mow and the location of the subpolar front the latter of which is shown to vary with the north atlantic oscillation nao during persistent high nao periods when the subpolar front moves eastward waters in the subpolar gyre essentially block the northward flowing mow preventing its entry into the subpolar gyre conversely during low nao periods the subpolar front moves westward allowing mow to penetrate past porcupine bank into the subpolar gyre the impacts of an intermittent penetration of mow into the subpolar gyre including the possible effect on water mass transformations remain to be investigated

long term hydrographic changes at 52 and 66 w in the north atlantic subtropical gyre caribbean abstract in july september 1997 two hydrographic lines were done in the western n atlantic along longitudes of 52 and 66 w as part of the woce one time hydrographic survey of the oceans each of these two lines approximately repeated earlier ones done during the international geophysical year s igy and the mid 1980s because of this repeated sampling long term hydrographic changes in the water masses can be examined in this report we focus on temperature and salinity changes within the subtropical gyre mainly between latitudes of 20 and 35 n and compare our results to those presented by bryden et al 1996 who examined changes along a zonal line at 24 n most recently occupied in 1992 since this most recent 24 n section in 1992 substantial changes have occurred in the western part of the subtropical gyre at the depths of the labrador sea water lsw in particular we see clear evidence for colder fresher labrador sea water throughout the gyre on our two recent sections that was not yet present in 1992 at similar longitudes along 24 n at shallower depths inhabited by waters that are an admixture of mediterranean mw and antarctic intermediate waters aaiw our recent survey shows an increase in salinity which can only be attributed to changes in water masses on potential temperature or neutral density surfaces furthermore waters above the mw aaiw layer and into the deeper part of the main pycnocline have continued to become saltier and warmer throughout the 40 year period spanned by our sections these latter changes have been dominantly due to a vertical sinking of density surfaces as t s changes in density surfaces are small but depths of individual t s horizons have increased with time the net change since the igy shows a mean temperature increase between 800 and 2500 m depth at a rate of 0 57 c century with a corresponding steric sea level rise of 1 mm yr and a net downward heave with small values near the top and bottom and a maximum rate of 2 7 m yr at 1800 m depth changes in the deep caribbean indicate a warming since the igy due to temperature increases of the inflowing source waters in the subtropical gyre at 1800m depth but no significant change in the deep salinity

warm and saline events embedded in the meridional circulation of the northern north atlantic 1 ocean state estimates from 1958 to 2005 from the simple ocean assimilation system soda system are analyzed to understand circulation between subtropical and subpolar atlantic and their connection with atmospheric forcing this analysis shows three periods 1960s around 1980 and 2000s with enhanced warm saline waters reaching high latitudes alternating with freshwater events originating at high latitudes it complements surface drifter and altimetry data showing the subtropical subpolar exchange leading to a significant temperature and salinity increase in the northeast atlantic after 2001 the warm water limb of the atlantic meridional overturning cell represented by soda expanded in density salinity space during these warm events tracer simulations using soda velocities also show decadal variation of the gulf stream waters reaching the subpolar gyre and nordic seas the negative phase of the north atlantic oscillation index usually invoked in such variability fails to predict the warming and salinization in the early 2000s with salinities not seen since the 1960s wind stress curl variability provided a linkage to this subtropical subpolar gyre exchange as illustrated using an idealized two layer circulation model the ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal in this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax hence the polar front moves westward opening an enhanced northward access of the subtropical waters in the eastern boundary current

terdiurnal tidelike variability in sporadic e layers 1 time series analysis was performed on a large database of ionosonde recordings taken over 12 years for the 6 month period from the beginning of may to the end of october when sporadic e layer occurrence is frequent the results show that in addition to the well known 24 and 12 hour tidal variations there is also a weaker but regular 8 hour periodicity in midlatitude sporadic e layers es statistically this terdiurnal periodicity is significant and occurs in both the sporadic e layer critical frequency foes and the layer virtual height h es becoming strongest around summer solstice and later in october after a minimum in september at times a weak 6 hour periodicity can also be present in es but its effects are much less significant than those of the 8 hour oscillation the 8 hour periodicity in es is attributed to the terdiurnal tide presumably acting through its vertical wind shear forcing of the metallic ions in the lower thermosphere the relation to the terdiurnal tide was inferred from simultaneous ionosonde recordings from three widely spaced stations in the same midlatitude zone showing the 8 hour oscillation to be present simultaneously in all ionosonde stations and have phases which are consistent with a westward propagating terdiurnal wave of zonal wave number 3 the present study establishes the regular occurrence of a terdiurnal tidelike oscillation in es which needs to be incorporated into the physics and modeling of sporadic e layer formation and dynamics

meteor radar observations of short term tidal variabilities in the low latitude mesosphere lower thermosphere evidence for nonlinear wave wave interactions 1 short term tidal variabilities in the mesosphere lower thermosphere mlt region using the meteor radar observations over trivandrum 8 5 n 77 e during march 2006 to february 2007 are discussed spectral analysis of daily averaged zonal and meridional winds revealed the presence of planetary waves with periods ranging from 2 to 30 days in the height region of 82 98 km the hourly zonal and meridional wind measurements are then used to estimate day to day diurnal tide amplitudes in the mlt region for the first time over this latitude spectral analysis of zonal and meridional diurnal tide amplitudes revealed tidal modulations at periods ranging from 2 to 30 days further during a strong episode of tidal modulation which is identified from the wavelet spectra a group of subsidiary spectral components around the diurnal tide is observed the presence of subsidiary spectral components around the diurnal tide has provided evidence for nonlinear interaction between tides and planetary waves to substantiate this result bispectral analysis is carried out which showed the nonlinear tide planetary wave interactions by revealing the presence of secondary waves exactly at the anticipated periods as the present observational site is very near to dip equator it is envisaged that the present results will have important implications in interpreting day to day variabilities in the equatorial ionosphere

observations of seasonal subduction at the iceland faroe front the polar front in the north atlantic is bound to the ridge between iceland and the faroe islands where about one half of the northward transport of warm atlantic water into the nordic seas occurs as well as about one sixth of the equatorward dense overflow we find a low salinity water mass at the surface of the iceland faroe front iff which in wintertime subducts along outcropping isopycnals and is found in much modified form on the atlantic side of the iceland faroe ridge ifr crest the features found on the atlantic side of the crest at depth have temperature and salinity characteristics which are clearly traceable to the surface outcrop of the iff the presence of coherent low salinity layers on the atlantic side of the ifr crest has not been previously reported warm waters above the ifr primarily feed the faroe current and injection of a low salinity water mass may play an early role in the water mass transformation taking place in the nordic seas the seasonality of the intrusive features suggests a link between winter convection mixed layer instability and deep frontal subduction these low salinity anomalies as well as a low oxygen water mass from the iceland basin can be used as tracers of the intermediate circulation over the ifr

societal need for improved understanding of climate change anthropogenic impacts and geo hazard warning drive development of ocean observatories in european seas society s needs for a network of in situ ocean observing systems cross many areas of earth and marine science here we review the science themes that benefit from data supplied from ocean observatories understanding from existing studies is fragmented to the extent that it lacks the coherent long term monitoring needed to address questions at the scales essential to understand climate change and improve geo hazard early warning data sets from the deep sea are particularly rare with long term data available from only a few locations worldwide these science areas have impacts on societal health and well being and our awareness of ocean function in a shifting climate substantial efforts are underway to realise a network of open ocean observatories around european seas that will operate over multiple decades some systems are already collecting high resolution data from surface water column seafloor and sub seafloor sensors linked to shore by satellite or cable connection in real or near real time along with samples and other data collected in a delayed mode we expect that such observatories will contribute to answering major ocean science questions including how can monitoring of factors such as seismic activity pore fluid chemistry and pressure and gas hydrate stability improve seismic slope failure and tsunami warning what aspects of physical oceanography biogeochemical cycling and ecosystems will be most sensitive to climatic and anthropogenic change what are natural versus anthropogenic changes most fundamentally how are marine processes that occur at differing scales related the development of ocean observatories provides a substantial opportunity for ocean science to evolve in europe here we also describe some basic attributes of network design observatory networks provide the means to coordinate and integrate the collection of standardised data capable of bridging measurement scales across a dispersed area in european seas adding needed certainty to estimates of future oceanic conditions observatory data can be analysed along with other data such as those from satellites drifting floats autonomous underwater vehicles model analysis and the known distribution and abundances of marine fauna in order to address some of the questions posed above standardised methods for information management are also becoming established to ensure better accessibility and traceability of these data sets and ultimately to increase their use for societal benefit the connection of ocean observatory effort into larger frameworks including the global earth observation system of systems geoss and the global monitoring of environment and security gmes is integral to its success it is in a greater integrated framework that the full potential of the component systems will be realised highlights societies increasingly depend on timely information on ecosystems and natural hazards data is needed to improve climate related uncertainty and geo hazard early warning observatory networks coordinate and integrate the collection of standardised data ocean observatories provide opportunity for ocean science to evolve

a dipole pattern of the sea surface height anomaly in the north atlantic 1990s 2000s 1 despite a long term trend of sea level rise continuing into the 2000s in the subpolar north atlantic variations in the sea surface height have behaved differently in both spatial and temporal domains a dipole pattern centered between the northern atlantic subpolar region and the region near the gulf stream was observed in the linear trends of the sea surface height anomaly ssha by applying the ensemble empirical mode decomposition eemd we found that this dipole pattern is mainly associated with the interannual to decadal ssha oscillations of the two regions which are 180 out of phase with each other over the time span of this study the low frequency variations of the ssha in the subpolar region are strongly inversely correlated with the cumulative north atlantic oscillation nao index r 0 84 in contrast with the gulf stream region which is positively correlated r 0 22 this therefore reveals an asymmetric response of the regional ssha to the cumulative nao forcing in which the subpolar variability leads that of the gulf stream region by 29 months moreover there is a remarkable reversal of the ssha trends from the 1990s to the 2000s which is unexpected given a weak and fluctuating nao behavior since mid 1990s such ssha variations in the 2000s might be related to the lagged variations of the atlantic meridional overturning circulation amoc

on the currents and transports connected with the atlantic meridional overturning circulation in the subpolar north atlantic results from an interannually forced 0 08 degrees eddy resolving simulation based on the hybrid coordinate ocean model in conjunction with a small but well determined transport database are used to investigate the currents and transports associated with the atlantic meridional overturning circulation amoc in the subpolar north atlantic spna the model results yield a consistent warming in the western spna since the early 1990s along with mean transports similar to those observed for the trans basin amoc across the world ocean circulation experiment hydrographic section ar19 16 4 sv and boundary currents at the exit of the labrador sea near 53 degrees n 39 0 sv and east of the grand banks near 43 degrees n 15 9 sv over a 34 year integration the model determined amoc across the ar19 section and the western boundary current near 53 degrees n both exhibit no systematic trend but some long term interannual and longer variabilities including a decadal transport variation of 3 4 sv from relatively high in the 1990s to low in the 2000s the decadal variability of the model boundary current transport near 53 degrees n lags the observed winter time north atlantic oscillation index by about 2 years and leads the model amoc across the ar19 section by about 1 year the model results also show that the long term variabilities are low compared to those on shorter time scales thus rapid sampling of the current over long time intervals is required to filter out high frequency variabilities in order to determine the lower frequency variabilities of interest

decadal water mass variations along 20 w in the northeastern atlantic ocean abstract water mass variations in the northeastern atlantic ocean along 20 w are analyzed with pentadal resolution over the past 15 years using data from four repeat occupations of a meridional hydrographic section running south from iceland the section was sampled in 1988 1993 1998 and 2003 the results are interpreted in the context of changes in air sea forcing ocean circulation and water properties associated with the north atlantic oscillation nao the nao index oscillated around zero from 1984 to 1988 was strongly positive from 1989 to 1995 after which it shifted to lower positive and occasionally negative values from 1996 to 2003 previously published studies suggest that after the 1995 1996 shift of the nao the subpolar gyre largely retreated to the northwest in the northeastern atlantic ocean resulting in an increasingly southeastern character of local water masses with time water property changes extending from the subpolar mode water spmw just below the seasonal pycnocline through the density range shared by mediterranean outflow water and subarctic intermediate water saiw along 20 w are consistent with changes in wind driven ocean circulation and air sea heat flux associated with shifts in the nao especially after accounting for ocean memory after periods of lower nao index the spmw is warmer saltier and lighter at these same times large increases of apparent oxygen utilization aou and potential vorticity are found at the spmw base consistent with spmw ventilation to lighter densities during lower nao index periods deeper and denser in the water column the cold fresh and dense saiw signature within the permanent pycnocline that was most strongly present in 1993 near the culmination of a period of high nao index is much reduced in 1988 and 1998 in 2003 after a prolonged period of lower nao index increasing influence of warmer saltier subtropical waters is clear within the permanent pycnocline the deep penetration of the changes implies that they are caused primarily by circulation changes resulting from nao associated wind shifts but changes in air sea heat flux could also have played a role

mechanisms underlying recent decadal changes in subpolar north atlantic ocean heat content the subpolar north atlantic spna is subject to strong decadal variability with implications for surface climate and its predictability in 2004 2005 spna decadal upper ocean and sea surface temperature trends reversed from warming during 1994 2004 to cooling over 2005 2015 this recent decadal trend reversal in spna ocean heat content ohc is studied using a physically consistent observationally constrained global ocean state estimate covering 1992 2015 the estimate s physical consistency facilitates quantitative causal attribution of ocean variations closed heat budget diagnostics reveal that the spna ohc trend reversal is the result of heat advection by midlatitude ocean circulation kinematic decompositions reveal that changes in the deep and intermediate vertical overturning circulation cannot account for the trend reversal but rather ocean heat transports by horizontal gyre circulations render the primary contributions the shift in horizontal gyre advection reflects anomalous circulation acting on the mean temperature gradients maximum covariance analysis mca reveals strong covariation between the anomalous horizontal gyre circulation and variations in the local wind stress curl suggestive of a sverdrup response results have implications for decadal predictability

modeling and analysis of the structure and generation of the terdiurnal tide the terdiurnal or 8 h tide has been seen in a number of midlatitude radar measurements and has recently been mapped globally at 95 km a series of calculations and model simulations are used to examine the processes responsible for generating this tide and for its strong hemispheric asymmetry the model tidal structure deviates significantly from the structure of a single hough mode in contrast to the diurnal tide the dominant cause of the hemispheric asymmetry is the sensitivity of the propagation to the background state particularly the static stability several conceptual views of the tide are explored to give a heuristic view of this asymmetry this analysis predicts that particular modes are prohibited from propagating in large regions of the summer mesosphere the tide occurs naturally in a three dimensional nonlinear model extending from the tropopause to the lower thermosphere the model tide shows a number of features in common with observations including amplitude maxima in midlatitudes a wintertime peak and zonal winds larger than meridional winds the tidal amplitude in the model is weaker than observed at 95 km several interactive model integrations are performed to determine the forcing mechanism for the tide these calculations indicate that the direct solar forcing of the terdiurnal tide is the dominant mechanism occurring in the model at middle and high latitudes nonlinear interactions contribute to the low latitude tide

on model differences and skill in predicting sea surface temperature in the nordic and barents seas the nordic seas and the barents sea is the atlantic ocean s gateway to the arctic ocean and the gulf stream s northern extension brings large amounts of heat into this region and modulates climate in northwestern europe we have investigated the predictive skill of initialized hindcast simulations performed with three state of the art climate prediction models within the cmip5 framework focusing on sea surface temperature sst in the nordic seas and barents sea but also on sea ice extent and the subpolar north atlantic upstream the hindcasts are compared with observation based sst for the period 1961 2010 all models have significant predictive skill in specific regions at certain lead times however among the three models there is little consistency concerning which regions that display predictive skill and at what lead times for instance in the eastern nordic seas only one model has significant skill in predicting observed sst variability at longer lead times 7 10 years this region is of particular promise in terms of predictability as observed thermohaline anomalies progress from the subpolar north atlantic to the fram strait within the time frame of a couple of years in the same model predictive skill appears to move northward along a similar route as forecast time progresses we attribute this to the northward advection of sst anomalies contributing to skill at longer lead times in the eastern nordic seas the skill at these lead times in particular beats that of persistence forecast again indicating the potential role of ocean circulation as a source for skill furthermore we discuss possible explanations for the difference in skill among models such as different model resolutions initialization techniques and model climatologies and variance

paleoliquefaction evidence for a strong holocene earthquake in south central indiana earthquake induced paleoliquefaction features in holocene sediments in south central indiana are evidence for strong shaking in the recent prehistoric past in an area where only infrequent low magnitude earthquakes have occurred during the 200 yr of the historic record distribution of liquefaction features and geotechnical analyses of liquefied sediments are the basis for estimating that an earthquake with a magnitude of 6 9 was centered near vallonia indiana radiometric archaeologic and stratigraphic relations bracket the event to between 3 7 ka and 4 2 ka b p evidence for a local source for strong shaking requires reassessment of earthquakes hazards in the southern indiana northern kentucky southwestern ohio area

terdiurnal surface pressure oscillations over the continental united states abstract the small terdiurnal pressure oscillation s3 p is determined over the conterminous united states by analyzing long time series of hourly barometer data from 180 stations spectral analysis of these time series reveals that the terdiurnal band is dominated by three or four spectral peaks separated in frequency by 1 cpy the central peak at 3 cpd is invariably smaller than the two immediate side peaks indicative of extraordinarily strong seasonal variations in the tide the largest terdiurnal tide occurs over the south central united states in winter where amplitudes exceed 300 bar summertime amplitudes are roughly one half as large summer and winter tides are almost completely out of phase with rapid 180 shifts occurring in the equinox seasons when amplitudes are very small

seasonal variations of the terdiurnal tide in the mesosphere and lower thermosphere a model study observations of the terdiurnal 8 hour tidal wind oscillations in the mesosphere and lower thermosphere mlt reveal strong seasonal and latitudinal variations the tidal amplitudes reach a maximum of about 15 20 m s 1 at midlatitudes in winter the vertical phase progression corresponds to very long vertical wavelengths during summer the amplitudes are typically weaker and the phases are less regular first simulations of the terdiurnal tide with the spectral mesosphere lower thermosphere model are presented the model explicitly accounts for the solar thermal excitation in the middle and upper atmosphere and reproduces the salient features of the terdiurnal wind oscillations well the preferential solar excitation of antisymmetric terdiurnal modes capable of propagating into the mlt combined with an asymmetric atmospheric response appears to be primarily responsible for the observed seasonal variations nonlinear interactions of the diurnal and semidiurnal tides are demonstrated to make a noticeable in situ contribution to the excitation of the terdiurnal tide at 95 100 km especially during equinox

rapid freshening of the deep north atlantic ocean over the past four decades the overflow and descent of cold dense water from the sills of the denmark strait and the faroe shetland channel into the north atlantic ocean is the principal means of ventilating the deep oceans and is therefore a key element of the global thermohaline circulation most computer simulations of the ocean system in a climate with increasing atmospheric greenhouse gas concentrations predict a weakening thermohaline circulation in the north atlantic as the subpolar seas become fresher and warmer1 2 3 and it is assumed that this signal will be transferred to the deep ocean by the two overflows from observations it has not been possible to detect whether the ocean s overturning circulation is changing but recent evidence suggests that the transport over the sills may be slackening4 here we show through the analysis of long hydrographic records that the system of overflow and entrainment that ventilates the deep atlantic has steadily changed over the past four decades we find that these changes have already led to sustained and widespread freshening of the deep ocean

northern north atlantic sea surface height and ocean heat content variability 1 the evolution of nearly 20 years of altimetric sea surface height ssh is investigated to understand its association with decadal to multidecadal variability of the north atlantic heat content altimetric ssh is dominated by an increase of about 14 cm in the labrador and irminger seas from 1993 to 2011 while the opposite has occurred over the gulf stream region over the same time period during the altimeter period the observed 0 700 m ocean heat content ohc in the subpolar gyre mirrors the increased ssh by its dominantly positive trend over a longer period 1955 2011 fluctuations in the subpolar ohc reflect atlantic multidecadal variability amv and can be attributed to advection driven by the wind stress gyre mode bringing more subtropical waters into the subpolar gyre the extended subpolar warming evident in ssh and ohc during the altimeter period represents transition of the amv from cold to warm phase in addition to the dominant trend the first empirical orthogonal function ssh time series shows an abrupt change 2009 2010 reaching a new minimum in 2010 the change coincides with the change in the meridional overturning circulation at 26 5 n as observed by the rapid rapid climate change project and with extreme behavior of the wind stress gyre mode and of atmospheric blocking while the general relationship between northern warming and atlantic meridional overturning circulation amoc volume transport remains undetermined the meridional heat and salt transport carried by amoc s arteries are rich with decade to century timescale variability

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

intense warming and salinification of intermediate waters of southern origin in the eastern subpolar north atlantic in the 1990s to mid 2000s 1 recent thermohaline changes in the layer of intermediate waters iw advected into the eastern subpolar north atlantic from lower latitudes are quantified using the data from the repeated transatlantic sections positive trends in temperature and salinity in the iw density class at 53 n 0 049 c a and 0 0088 a 1992 2002 and 60 n 0 044 c a and 0 0085 a 1997 2005 are derived the unexpectedly high rates of the iw warming and salinification cannot be explained solely by the long term and recent decadal changes at the intermediate levels in the midlatitude north atlantic and appear to be a consequence of the northward advance of the source water masses caused by the north atlantic oscillation induced contraction of the subpolar gyre

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

terdiurnal tide in the extended canadian middle atmospheric model cmam 1 we use the extended canadian middle atmosphere model cmam a general circulation model gcm to investigate the nature of the terdiurnal tide temperature and horizontal winds from a model run are analyzed to delineate the character of this tide for zonal wave numbers s 5 to 5 descriptions of the annual mean amplitudes seasonal variations and total tide superposed from the migrating and 10 nonmigrating components are provided the amplitudes and vertical wavelengths of the various components and the total terdiurnal tide are found to depend strongly on season latitude and altitude the migrating terdiurnal component maximizes at mid and high latitudes with significant amplitudes annual mean amplitude in wind temperature 10 m s k in the upper mesosphere and lower thermosphere mlt region between 80 and 100 km maximum amplitudes occur in winter in both hemispheres whereas above 100 km maximum amplitudes occur during solstices for the zonal wind field the nonmigrating terdiurnal components te5 te3 te4 tw4 and tw5 tend to peak at 50 n s with amplitudes between 2 and 8 m s the other nonmigrating components maximize in the polar regions with amplitudes of 2 10 m s possible generation mechanisms solar heating and nonlinear interactions for the migrating terdiurnal tide in the mlt region are also examined correlation analysis indicates that nonlinear interactions between the migrating diurnal and semidiurnal tides are unlikely to be the source of the migrating terdiurnal tide

evolution of subpolar north atlantic surface circulation since the early holocene inferred from planktic foraminifera faunal and stable isotope records abstract past changes in the surface flow regime of two main eastern north atlantic warm water pathways toward the nordic seas were reconstructed based on faunal analyses in combination with carbon and oxygen stable isotope measurements in planktic foraminifera the investigated sites in the surroundings of the faroe islands are located in the transitional area where surface waters of subpolar and subtropical origin mix before entering the arctic mediterranean in these areas large amplitude millennial variability in the characteristics of the upper water column appears modulated by changes in the intensity of the subpolar gyre circulation from 7 8 to 6 ka bp faunal records indicate a deep mixed layer which in conjunction with lighter 18 o values suggest that the inflowing atlantic waters were dominated by a relatively cooler and fresher water mass reflecting a strengthening of the subpolar gyre under conditions of enhanced positive nao like forcing and reduced meltwater input a shift in the hydrographic conditions occurred during the mid holocene centered at 5 ka bp at this time increasing upper water column stratification and the incipient differentiation of the stable isotopic signal of the iceland faroe and faroe shetland surface water masses suggest increasing influx of warmer more saline surface waters from the subtropical gyre as subpolar gyre circulation weakened the mid holocene decline in subpolar gyre strength is presumably related to a shift toward a low state of the nao like forcing associated with decreased solar irradiance later in the holocene from 4 ka bp to present the increased frequency and reduced amplitude of the surface hydrographic changes reflect corresponding fluctuations in subpolar gyre circulation these high frequency oscillations in subpolar gyre strength suggest increased surface circulation sensitivity to moderate freshwater fluxes to the labrador irminger sea basin highlighting the importance of the salinity balance in modulating subpolar gyre dynamics particularly under conditions of low nao atmospheric forcing

atmospheric response in summer linked to recent arctic sea ice loss since 2007 a large decline in arctic sea ice has been observed the large scale atmospheric circulation response to this decline is investigated in era interim reanalyses and hadgem3 climate model experiments in winter post 2007 observed circulation anomalies over the arctic north atlantic and eurasia are small compared to interannual variability in summer the post 2007 observed circulation is dominated by an anticyclonic anomaly over greenland which has a large signal to noise ratio climate model experiments driven by observed sst and sea ice anomalies are able to capture the summertime pattern of observed circulation anomalies although the magnitude is a third of that observed the experiments suggest high ssts and reduced sea ice in the labrador sea lead to positive temperature anomalies in the lower troposphere which weaken the westerlies over north america through thermal wind balance the experiments also capture cyclonic anomalies over northwest europe which are consistent with downstream rossby wave propagation

seasonal variations of mlt tides revealed by a meteor radar chain based on hough mode decomposition seasonal variations of different tides in the mesosphere and lower thermosphere are investigated from wind observations of a meteor radar chain on the basis of hough mode decomposition first the observed winds are decomposed into different diurnal semidiurnal and terdiurnal tidal components different seasonal patterns are revealed for each component pronounced semiannual oscillation sao is presented in the diurnal component while latitude dependent seasonal variation is found in the semidiurnal and terdiurnal components at the low midlatitude stations the semiannual annual oscillation is relatively stronger then hough mode decomposition is utilized to extract the dominant tidal modes of each decomposed component it is found that each component is dominated by one of its symmetric tidal modes with strong seasonal dependency apparent sao is observed in the dominant 1 1 mode 2 4 mode is strong in the autumn and winter months after the september equinox based on the extracted results we further map the three dimensional distribution latitude altitude season of each tidal component the mapped results are finally compared with the corresponding values observed by the thermosphere ionosphere mesosphere energetics and dynamics doppler interferometer tidi and modeled from the global scale wave model gswm each mapped tidal component agrees well with corresponding tidi observation in the seasonal variation meanwhile coincidences are found in the seasonal dependency of the diurnal component between the mapped values and the modeled results from gswm while difference between them exists in that of the semidiurnal one

warming and salinification of intermediate and deep waters in the irminger sea and iceland basin in 1997 2006 1 recent intra decadal changes in temperature and salinity of the labrador sea water and nordic overflow waters are quantified on the basis of the ctd data from the repeats of the zonal transatlantic section along 60 n carried out in 1997 2002 2004 and 2006 the revealed changes in general point to a rapid transition to the warmer saltier conditions at the intermediate and deeper levels in the irminger sea and iceland basin at the section latitude in 1997 2006 in particular substantial steady warming and salinification of the iceland scotland overflow water is revealed in both basins the latter result means an abrupt reversal or at least almost a decade long interruption of the long term freshening of this water lasted since the mid 1960s

transatlantic temperature and salinity changes at 24 5 n from 1957 to 2004 in 2004 a fifth occupation of a transatlantic section at 24 5 n allows us to examine decadal temperature and salinity changes using high quality full depth hydrographic data since 1957 waters shallower than 1750 dbar have been warming and salinifying at least since 1981 and in 2004 are significantly warmer and saltier than at any time since 1957 while deeper than 3000 dbar there has been continuous cooling and freshening since 1957 temperature and salinity changes at constant pressures are partitioned into changes on isopycnal surfaces and changes due to the vertical movement of the isopycnals warming in the western atlantic thermocline since 1957 at a rate of 0 0111 c yr dominates the transatlantic average while deep water has cooled and freshened at rates of 0 0021 c yr and 0 0003 psu yr respectively we argue that the shallower and deeper changes are consistent with a recently reported increased southward thermocline circulation and reduced southward flux of deep water

assessing variability in the size and strength of the north atlantic subpolar gyre recent studies on the size and strength of the north atlantic subpolar gyre spg offer contrasting assessments of the gyre s temporal variability studies that use empirical orthogonal function eof analyses of satellite sea surface height ssh report a rapid decline in spg size and strength since 1992 20 per decade while concurrent in situ observations report either no trend or a slight decline here we investigate this discrepancy by analyzing the size and strength of the spg with satellite ssh from 1993 to 2015 with two separate methods indirectly via eof analysis and more directly through measurements of the gyre center and boundary we define the boundary of the gyre as the largest closed contour of ssh the center as the minimum ssh and the strength as the difference between the ssh at the boundary and the center we identify a linear decline over the study period in the spg strength 5 1 per decade but find no statistically significant trend in the spg area the trend in the gyre strength is weaker than the eof based trend and is most likely below the level of detection of the in situ measurements we conclude that the variability previously identified as a sharp decline in spg circulation can be more appropriately attributed to basin wide sea level rise during the satellite altimetry period in addition we find that the properties of the eastern spg do not co vary with the spg size suggesting that spg dynamics do not control the strength of the inter gyre throughput

ocean change around greenland under a warming climate the impact of climate warming on the ocean near greenland is investigated with a high resolution coupled global climate model the ocean around greenland exhibits a strong warming in response to a four times increase of present day atmospheric co 2 levels the signal is intensified in the intermediate layer and regionally strongest in the greenland sea the projected changes in temperature are driven by changes affecting the large scale ocean circulation rather than changes of the local atmospheric heat forcing the ocean conditions examined here provide a background for the water masses in contact with the outlet glaciers around the greenland coast the future warming of the warm subtropical origin layer could thus lead to enhanced ice sheet melting although the signal could be mitigated by other effects including an enhanced stratification of the surface fresh layer applying a simple parameterization to estimate the change in melt rate along the greenland coast we find that ice sheet melting increases everywhere in response to the change in water mass properties although the melt rate changes show large variations in space the largest melting acceleration is found on the east coast between fram strait and denmark strait where both the parameterization applied to present day conditions and observations suggest moderate melting up to now these model results caution that the greenland ice sheet mass balance should be monitored everywhere and not only where melting occurs at the moment

origin formation and variability of the subpolar mode water located over the reykjanes ridge the origin and formation of the subpolar mode water spmw located over the reykjanes ridge in the north atlantic ocean and the variability of its properties over the period 1966 2004 are investigated through the use of a global eddy permitting 1 4 degrees ocean sea ice model and a lagrangian analysis tool the spmw is fed by subtropical and subpolar waters advected by the branches of the north atlantic current the spmw acquires its properties when its source waters enter the winter mixed layer in the iceland basin the spmw temperature variability is mainly explained by variations of the relative contributions of the subtropical and subpolar water transports to the total transport compared to the 1966 2004 mean lower higher subtropical water relative transport contribution leads to colder warmer spmw in the early 1990s in the late 1960s and late 1990s the intensity of the winter convection in the iceland basin also influences the spmw temperature through the amount of relatively cold intermediate waters of subtropical origin integrated in the spmw layer strong convection partly explains the cold spmw of the early 1990s the large increase in the spmw temperature in the late 1990s is due to both a decrease in the winter convection and an increase in the relative transport of the subtropical waters

on the occurrence and variability of the terdiurnal tide in the equatorial mesosphere and lower thermosphere and a comparison with the kyushu gcm 1 we studied the occurrence characteristics and variability of the terdiurnal tide 8 hour period in the equatorial mesosphere and lower thermosphere mlt using a meteor radar at koto tabang 0 2 s 100 3 e and mf radars at tirunelveli 8 7 n 77 8 e and pameungpeuk 7 4 s 107 4 e these locations one being located right over the equator and the other two at conjugate points around the equator within 10 form a unique experimental setup to study equatorial mlt dynamics the terdiurnal tide exists as a distinct wave signature at all three locations while the daily amplitudes can be as large as 15 m s 1 the monthly mean amplitudes lie between 1 and 10 m s 1 the amplitude of the terdiurnal tide at pameungpeuk is generally smaller than that observed at tirunelveli and koto tabang the seasonal variation in amplitude shows both annual and semiannual oscillations of 1 m s 1 at all three locations the present observations combined with previous reports indicate that the timing of the primary maximum of the terdiurnal tide amplitude shifts from autumn to late spring and early summer as one moves from high latitudes to the equator all with respect to the northern hemisphere the amplitudes and seasonal variation in the present observations show good comparison with that simulated by the general circulation model gcm developed by kyushu university japan this study supports the occurrence of nonlinear interaction between diurnal and semidiurnal tides and shows that gravity waves play an important role in the generation of the terdiurnal tide

assessing decadal changes in the deep western boundary current absolute transport southeast of cape farewell greenland from hydrography and altimetry 1 in earlier studies the decadal variability of the deep western boundary current dwbc transport in the vicinity of cape farewell greenland has been assessed from changes in the baroclinic velocities computed from hydrographic data and referenced to 1000 m depth the main limitation of using such an estimate as an index for the dwbc absolute transport variability comes from the unaccounted for decadal velocity changes at the reference level 1000 m these changes may substantially contribute to the dwbc absolute transport variability by compensating for or adding to the baroclinic transport changes to assess this contribution to variability we quantify the decadal velocity changes which occurred at 1000 m depth southeast of cape farewell since the mid 1990s the analysis combines estimates of the baroclinic velocity changes in the water column derived from repeat hydrography at similar to 59 5 degrees n and the velocity changes at the sea surface derived from altimetry an increase in the southward velocity at 1000 m above the dwbc between the periods of 1994 1997 and 2000 2007 is inferred it indicates that the increase in the dwbc absolute transport was larger than the 2 sv 1 sv 10 6 m 3 s 1 increase in its baroclinic component referenced to 1000 m this result and the observed coherence of the dwbc absolute and baroclinic transport changes between individual observations imply that the dwbc absolute transport variability in the region is underestimated but qualitatively well represented by its baroclinic component on decadal and shorter time scales

structure of the terdiurnal tide at 95 km satellite wind observations from the high resolution doppler interferometer hrdi instrument on the upper atmosphere research satellite uars are used to describe the latitudinal structure and seasonal variation of the terdiurnal 8 hour atmospheric tide at 95 km the amplitude of the annual average tide is 5 m s meridional and 15 m s zonal within the range observed 60 s to 60 n the maximum amplitudes are found during fall and winter at midlatitudes only weak temporal correlations with the diurnal and semidiurnal tides are seen on the monthly time scales resolved

hydrography and through flow in the north eastern north atlantic ocean the nansen project abstract the circulation and hydrography of the north eastern north atlantic has been studied with an emphasis on the upper layers and the deep water types which take part in the thermohaline overturning of the oceanic conveyor belt over 900 hydrographic stations were used for this study mainly from the 1987 1991 period the hydrographic properties of subpolar mode water in the upper layer which is transported towards the norwegian sea showed large regional variation the deep water mass was dominated by the cold inflow of deep water from the norwegian sea and by a cyclonic recirculation of lower deep water with a high antarctic bottom water content at intermediate levels the dominating water type was labrador sea water with only minor influence of mediterranean sea water in the permanent pycnocline traces of antarctic intermediate water were found geostrophic transports have been estimated and these agreed in order of magnitude with the local heat budget with current measurements with data from surface drifters and with the observed water mass modification a total of 23 sv of surface water entered the region of which 20 sv originated from the north atlantic current while 3 sv entered via an eastern boundary current of this total 13 sv of surface water left the area across the reykjanes ridge and 7 sv entered the norwegian sea while 3 sv was entrained by the cold overflow across the iceland scotland ridge approximately 1 4 sv of norwegian sea deep water was involved in the overflow into the iceland basin which with about 1 1 sv of entrained water and 1 1 sv recirculating lower deep water formed a deep northern boundary current in the iceland basin at intermediate depths where labrador sea water formed the dominant water type about 2 sv of entrained surface water contributed to a saline water mass which was transported westwards along the south icelandic slope