the response of the southwest western australian wave climate to indian ocean climate variability knowledge of regional wave climates is critical for coastal planning management and protection in order to develop a regional wave climate it is important to understand the atmospheric systems responsible for wave generation this study examines the variability of the southwest western australian swwa shelf and nearshore wind wave climate and its relationship to southern hemisphere climate variability represented by various atmospheric indices the southern oscillation index soi the southern annular mode sam the indian ocean dipole mode index dmi the indian ocean subtropical dipole iosd the latitudinal position of the subtropical high pressure ridge strp and the corresponding intensity of the subtropical ridge stri a 21 year wave hindcast 1994 2014 of the swwa continental shelf was created using the third generation wave model simulating waves nearshore swan to analyse the seasonal and inter annual wave climate variability and its relationship to the atmospheric regime strong relationships between wave heights and the strp and the stri a moderate correlation between the wave climate and the sam and no significant correlation between soi dmi and iosd and the wave climate were found strong spatial seasonal and inter annual variability as well as seasonal longer term trends in the mean wave climate were studied and linked to the latitudinal changes in the subtropical high pressure ridge and the southern ocean storm belt as the southern ocean storm belt and the subtropical high pressure ridge shifted southward northward wave heights on the swwa shelf region decreased increased the wave height anomalies appear to be driven by the same atmospheric conditions that influence rainfall variability in swwa

the importance of atmospheric dynamics in the northern hemisphere wintertime climate response to changes in the earth s orbit milankovitch proposed that variations in the earth s orbit cause climate variability through a local thermodynamic response to changes in insolation this hypothesis is tested by examining variability in an atmospheric general circulation model coupled to an ocean mixed layer model subjected to the orbital forcing of the past 165 000 yr during northern hemisphere summer the model s response conforms to milankovitch s hypothesis with high low insolation generating warm cold temperatures throughout the hemisphere however during northern hemisphere winter the climate variations stemming from orbital forcing cannot be solely understood as a local thermodynamic response to radiation anomalies instead orbital forcing perturbs the atmospheric circulation in a pattern bearing a striking resemblance to the northern annular mode the primary mode of simulated and observed unforced atmospheric variability the hypothesized reason for this similarity is that the circulation response to orbital forcing reflects the same dynamics generating unforced variability these circulation anomalies are in turn responsible for significant fluctuations in other climate variables most of the simulated orbital signatures in wintertime surface air temperature over midlatitude continents are directly traceable not to local radiative forcing but to orbital excitation of the northern annular mode this has paleoclimate implications during the point of the model integration corresponding to the last interglacial eemian period the orbital excitation of this mode generates a 1 2 c warm surface air temperature anomaly over europe providing an explanation for the warm anomaly of comparable magnitude implied by the paleoclimate proxy record the results imply that interpretations of the paleoclimate record must account for changes in surface temperature driven not only by changes in insolation but also by perturbations in atmospheric dynamics

cross seasonal influence of the december february southern hemisphere annular mode on march may meridional circulation and precipitation abstractnew evidence suggests that interannual variability in zonal mean meridional circulation and precipitation can be partially attributed to the southern hemisphere annular mode sam the dominant mode of climate variability in the southern hemisphere sh extratropics a cross seasonal correlation exists between the december february djf sam and march may mam zonal mean meridional circulation and precipitation this correlation is not confined to the sh it also extends to the northern hemisphere nh subtropics when the preceding djf sam is positive counterclockwise and clockwise meridional cells accompanied by less and more precipitation occur alternately between the sh middle latitudes and nh subtropics in mam in particular less precipitation occurs in the sh middle latitudes the sh tropics and the nh subtropics but more precipitation occurs in the sh subtropics and the nh tropics a framework is built to explain the cross seasonal impact of sam related sst anomalies evidence indic

influence of the valley surroundings on valley wind dynamics abstractin a recent study the authors investigated the mechanisms leading to the formation of diurnal along valley winds in a valley formed by two isolated mountain ridges on a horizontal plain the main focus was on the relation between the valley heat budget and the valley plain pressure difference the present work investigates the influence of the valley surroundings on the evolution of the valley winds three valley plain configurations with identical valley volumes are studied a periodic valley an isolated valley on a plain the former case and an isolated valley entrenched in an elevated plateau according to the valley volume argument topographic amplification factor these three cases should develop identical temperature perturbations and thus similar along valley winds however substantial differences are found between the three cases in particular a much stronger daytime up valley wind and nighttime down valley wind for the plateau configuration the analysis demonstrates the importanc

extratropical transition of southwest pacific tropical cyclones part ii midlatitude circulation characteristics abstract this second of two papers on extratropical transition et over the southwest pacific ocean focuses on the variability of et a climatology of et onset based on a previously described objective technique shows that et commences 15 of latitude nearer the equator on average than similar cases from the northern hemisphere characteristic midlatitude circulation patterns accompanying et near 30 s are identified by means of empirical orthogonal function eof analysis of 50 storms the first eigenvector pattern explaining nearly half the circulation variability expresses relaxed and enhanced pressure gradients south of the storm that define composites similar to cradled and captured classifications previously described for the southeast indian ocean the second eof distinguishes redeveloping from weakening storms reintensifying storms were located beneath strong cyclonic vorticity advection cva near the equatorward entrance region of an upper jet whereas the upper jet was well to the west of

intraseasonal variability of wintertime frontal activity and its relationship with precipitation anomalies in the vicinity of south america the intraseasonal variability of the frontal activity and its connection with the variability of the atmospheric circulation and precipitation in the southern hemisphere is studied the frontal activity is defined as the relative vorticity times the local temperature gradient a band pass filter was applied to retain the intraseasonal timescales an empirical orthogonal function analysis was applied to the filtered frontal activity anomalies the two main modes show positive and negative centers located mainly over the southern pacific ocean and south american sector and are in quadrature with each other a similar pattern was found when the main modes of intraseasonal variability of the 500 hpa geopotential height were projected on the frontal activity suggesting that the variability of fronts are influenced by the variability of the large scale atmospheric circulation moreover the precipitation anomalies projected on the main modes of both frontal activity and 500 hpa geopotential height show similar structures especially over the southern pacific ocean and south america which may indicate that the variability of fronts controls the variability of precipitation the lagged regression of the time series of the frontal activity areally averaged over one of the centers of action against the frontal activity anomaly field shows at lags 8 and 8 a similar pattern suggesting a period of around 17 days for each mode moreover lagged regression between times series of frontal activity and precipitation anomalies reveals an opposite pattern between southeastern south america and southern chile being precipitation anomalies over these two regions anti correlated due to the frontal activity

atmosphere sea ice low frequency variability with a simple model of the southern hemisphere summary a simple primitive equation general circulation model sgcm is used as a representation of an aquaplanet with no orography to model constant southern hemisphere winter conditions the statistical signie cance of the decadal and quasi biennial variability is erst assessed in a long time sgcm run by means of a frequencydomain statistical decomposition the modelled long wave atmospheric pattern is then associated with the observed southern hemisphere annular mode as suggested by previous studies using the same sgcm a simple linear relationship between the low level wind and the ice velocity is then introduced into the sgcm to investigate the feedbacks between the sea ice cover and the baroclinic waves the zonal mean state reached by the sea ice cover in a long coupled run a few hundred years exhibits characteristics similar to the observations investigation of the low frequency variability in the coupled simulation leads to the following results 1 statistically signie cant variability is observed on interdecadal decadal interannual and quasi biennial time scales 2 interdecadal decadal and quasi biennial signals are associated with the atmospheric annular mode that forces changes in the northward extent of the sea ice cover at all southern ocean longitudes 3 the interannual signal 3 6 year period exhibits spatio temporal patterns and propagation speed similar to the wellknown antarctic circumpolar wave

indices of the southern hemisphere zonal wind abstract the time and spatial variation of the southern hemisphere 500 hpa zonal wind has been examined using spectral analysis bandpass filtering and empirical orthogonal function eof analysis applied to a 15 year sample of australian hemispheric analyses spectral analysis of the entire 15 year record of the 500 hpa zonal mean westerly wind shows significant peaks only on the seasonal and interannual time scales the mean segmented spectra for each season failed to show any additional significant peaks at higher frequencies or any significant differences between seasons the primary pattern of variation revealed by eof analysis shows similar behavior on synoptic to seasonal time scales with compensating departures occurring at intervals of 20 latitude the first eof has opposing peaks near 40 and 60 s and shows an equivalent barotropic pattern when correlated with individual grid point values at 500 hpa and mean sea level pressure correlations of the zonal pattern with regional anomalies reveal

dominant covarying climate signals in the southern ocean and antarctic sea ice influence during the last three decades abstracta composite dataset comprising geopotential height sea surface temperature zonal and meridional surface winds precipitation cloud cover surface air temperature latent plus sensible heat fluxes and sea ice concentration has been investigated with the aim of revealing the dominant time scales of variability from 1982 to 2013 three covarying climate signals associated with variations in the sea ice distribution around antarctica have been detected through the application of the multiple taper method with singular value decomposition mtm svd features of the established patterns of variation over the southern hemisphere extratropics have been identified in each of these three climate signals in the form of coupled or individual oscillations the climate patterns considered here are the southern annular mode sam the pacific south american psa teleconnection the semiannual oscillation sao and the zonal wavenumber 3 zw3 mode it is shown that most of the sea ice temporal variance i

multiple regimes and low frequency oscillations in the southern hemisphere s zonal mean flow abstract this paper studies multiple regimes and low frequency oscillations in the northern hemisphere zonal mean zonal flow in winter using 55 yr of daily observational data the probability density function estimated in the phase space spanned by the two leading empirical orthogonal functions exhibits two distinct statistically significant maxima the two regimes associated with these maxima describe persistent zonal flow states that are characterized by meridional displacements of the midlatitude jet poleward and equatorward of its time mean position the geopotential height anomalies of either regime have a pronounced zonally symmetric component but largest amplitude anomalies are located over the atlantic and pacific oceans high frequency synoptic transients participate in the maintenance of and transitions between these regimes significant oscillatory components with periods of 147 and 72 days are identified by spectral analysis of the zonal flow time series these oscillations are described b

preferred modes of variability and their relationship with climate change spatial structure of annular modes shows a remarkable resemblance to that of the recent trend in the observed circulation thompson et al this study performs a series of multilevel primitive equation model simulations to examine the extent to which the annular mode is capable of predicting changes in the zonal mean flow response to external heat perturbations each of these simulations represents a statistically steady state and differs from each other in the values of the imposed tropical heating h and high latitude cooling c defining the annular mode as the first empirical orthogonal function eof1 of zonal mean tropospheric zonal wind it is found that the climate predictability is generally high in the small c large h region of the parameter space but is markedly low in the large c small h region in the former region eof1 represents meridional meandering of the midlatitude jet while in the latter region eof1 and eof2 combine to represent coherent poleward propagation of zonal mean flow anomalies it is also found that the climate predictability tends to be higher with respect to changes in c than to changes in h the implications of these findings for the southern hemisphere climate predictability are also presented

trajectory modeling of modern dust transport to the southern ocean and antarctica aerosol deposition over the southern ocean and antarctica has the potential to alter marine productivity and thus ocean carbon uptake while also impacting radiative balance due to scattering and absorption from atmospheric particulates quantification of modern emission transport and deposition of terrestrial dust and other airborne material from southern hemisphere sources is challenging due to low emission levels and poor detection from remote sensing platforms here forward trajectory modeling is used to explore atmospheric transport independent of deposition processes from 1979 to 2013 trajectories are initiated from known arid dust source areas in south america patagonia australia and southern africa with detailed consideration of new zealand as a potential source results suggest that patagonian and new zealand dust and other aerosol emissions share strong atmospheric transport during all seasons allowing even potentially small new zealand emissions to contribute significantly to southern ocean and antarctic aerosol loading we find that atmospheric transport controlling distribution of dust and other aerosols shows distinct spatial variability new zealand and patagonia rapidly contribute a high proportion of trajectories to west antarctica while in interior east antarctica source contributions are limited and highly mixed the sensitivity of existing deep ice core sites to modern atmospheric transport is discussed finally interannual variability of poleward trajectory extension over the pacific and atlantic sectors of the southern ocean highlights the association of both tropical pacific sea surface temperature and high latitude wind variability e g the southern annular mode with transport of dust and other aerosols to the southern ocean and antarctica

an observational study of the intraseasonal poleward propagation of zonal mean flow anomalies abstract the poleward propagation of zonal mean relative angular momentum mr anomalies is examined using ncep ncar reanalysis data for both the winter and summer seasons of the northern and southern hemisphere this analysis is performed with a regression analysis using base latitudes in the subtropics midlatitudes and high latitudes it is found that the poleward mr anomaly propagation occurs at all latitudes with the propagation speed being greater in the subtropics and high latitudes compared to midlatitudes other fields such as eddy angular momentum flux convergence eddy heat flux friction torque and 300 mb streamfunction are regressed for the northern hemisphere winter and the southern hemisphere summer the main finding is that in the subtropics and midlatitudes the poleward mr anomaly propagation is primarily due to high frequency 10 day transient eddy angular momentum flux convergence and in high latitudes the propagation is mostly due to the summation of cross frequency and low fr

antarctic sea ice relationships with indices of the atmospheric circulation of the southern hemisphere a link between the antarctic sea ice extent and low frequency atmospheric variations particularly enso has been suggested by recent modeling and empirical studies this question is examined here using a high resolution by week by region data base of antarctic sea ice extent for the 1973 1982 period although of relatively short duration by northern hemisphere standards such a data base offers an opportunity rare in southern hemisphere climate studies the seaice variations are examined in the context of longer term indices of the large scale atmospheric circulation these are a southern oscillation index soi and an index of sea level pressure slp wavenumber one in the southern hemisphere extratropics the indices are updated through 1982 and their associations with regional scale pressure indices in the australia new zealand sector are also examined the 1973 1982 period is anomalous when compared with the period 1951 1972 correlation analysis of the monthly sea ice and circulation index values reveals that much of the apparent link between the ice and the soi suggested in previous studies arises from autocorrelations present in both data sets and the strong annual cycle of sea ice extent removing these effects from the data and re running the correlations reveals that most of the resulting significant associations between the ice and one or other of the circulation indices can probably be explained on the basis of chance in order to reconcile these findings with previous studies that show some strong ice circulation interactions on regional scales only those months in which significant correlations occur between both largescale circulation indices and the sea ice are examined further these occur preferentially in the ross and weddell sectors which constitute the regions contributing most to the variability of antarctic sea ice the analysis suggests that the sea ice extent changes lag the soi by several months but may precede changes in extratropical slp wavenumber one confirmation of these tentative regional ice extent circulation teleconnections necessarily awaits the forward extension of the high resolution sea ice data base beyond the 10 years available here

the pacific center of action of the northern hemisphere annular mode real or artifact the leading empirical orthogonal function eof of the sea level pressure slp field referred to as the arctic oscillation ao or northern hemisphere annular mode nam consists of a dipole between the polar cap region and the surrounding zonal ring centered along 458n embedded within the outer ring are centers of action over the euro atlantic and pacific sectors in which slp fluctuates in phase that the observed slp fluctuations at these two centers of action are virtually uncorrelated raises the question of whether the pacific center in the annular mode could be an artifact of eof analysis it is argued that sea level pressure fluctuations at the pacific and euro atlantic centers of action of the ao nam would be more strongly correlated were it not for the fact that slp variability over the north pacific is dominated by a pattern in which fluctuations over the north atlantic and north pacific are inversely related evidence of the coexistence of such a pattern which resembles an augmented version of the pacific north american pattern is presented

wave maintained annular modes of climate variability abstract the leading modes of month to month variability in the northern and southern hemispheres are examined by comparing a 100 yr run of the geophysical fluid dynamics laboratory gcm with the ncep ncar reanalyses of observations the model simulation is a control experiment in which the ssts are fixed to the climatological annual cycle without any interannual variability the leading modes contain a strong zonally symmetric or annular component that describes an expansion and contraction of the polar vortex as the midlatitude jet shifts equatorward and poleward this fluctuation is strongest during the winter months the structure and amplitude of the simulated modes are very similar to those derived from observations indicating that these modes arise from the internal dynamics of the atmosphere dynamical diagnosis of both observations and model simulation indicates that variations in the zonally symmetric flow associated with the annular modes are forced by eddy fluxes in the free troposphere while

intraseasonal variations in the southern hemisphere circulation abstract intraseasonal variations in the southern hemisphere atmospheric circulation have been examined through the application of a 10 50 day bandpass filter to daily ecmwf analyses for 1980 88 variations on this time scale contribute more than 40 of the daily variance in 500 hpa geopotential over much of the middle and high latitudes of the southern hemisphere eof analysis of the unnormalized variance for all seasons shows that 49 of this variance can be explained by zonal wave trains centered on the south pacific and southern atlantic indian oceans a high latitude mode of global extent and a wavenumber 3 pattern at midlatitudes these modes are essentially equivalent barotropic but slope westward with height so that the patterns at 100 hpa typically lag those at 1000 hpa by around 1o longitude there appears to be little interaction with the low latitude circulation all of the leading modes propagate eastward but the most consistent movement is shown by the south pacific wave train represented

the signature of the annular modes in the tropical troposphere the extratropical annular modes are coupled with a distinct pattern of climate anomalies that spans the circulation of the tropical troposphere the signature of the annular modes in the tropical troposphere exhibits a high degree of equatorial symmetry it is associated with upper tropospheric zonal wind anomalies centered about the equator midtropospheric temperature anomalies located 208n and 208s and opposing mean meridional circulation anomalies that span the subtropics of both hemispheres the linkages between the annular modes and the tropical circulation are only evident during the cold season months and are most robust in association with the northern hemisphere annular mode nam the coupling between the annular modes and the circulation of the tropical troposphere is consistent with forcing by waves originating at extratropical latitudes both annular modes are characterized by anomalies in the eddy momentum flux convergence at tropical latitudes that act to reinforce the changes in the tropical wind and temperature fields the most pronounced tropical anomalies lag indices of the annular modes by 2 weeks and are found over the eastern tropical pacific where climatological westerlies permit extratropical waves to propagate into the deep tropics the linkages between the nam and the tropical tropospheric circulation are

atmospheric teleconnections involving the southern ocean 1 i review the characteristic patterns of low frequency interannual and subdecadal variation in atmospheric circulation over the southern hemisphere sh extratropics and their climatic associations e g temperature precipitation winds sea surface temperatures ssts and sea ice conditions for the southern ocean the considerable spatial and temporal limitations of the observational database have strongly conditioned the pace of our understanding of sh teleconnections particularly for the pacific sector where the tropical el nino southern oscillation enso exerts a dominant influence an enso signal appears in the intensity interannual variations of the amundsen sea mean low pressure asl jet streams and long waves these variations comprise the so called pacific south america psa teleconnection patterns of low frequency variability in sh circulation that are mostly extratropical in origin but which can interact with enso are dominated by the zonally symmetric high latitude mode or antarctic oscillation aao the aao involves an alternation of atmospheric mass between middle and high southern latitudes a zonally asymmetric mode of wave number 1 is represented by an oscillation in pressure height between australian and south american sectors depicted by a trans polar circulation index a significant wave number 2 oscillation in the coupled atmosphere ocean ice system or antarctic circumpolar wave acw has a similar periodicity to enso and is strongest in the pacific sw atlantic sectors atmospheric teleconnections involving the southern ocean including those to enso show evidence of recent changes and the climatic implications of these are discussed

global influence of the northern hemisphere second mode of the zonal average of the zonal wind 1 the authors examine the impact of two zonal wind modes in the northern hemisphere northern annular mode nam and the second zonal wind mode on the global domain during the normal non el nino southern oscillation enso northern winter from 1981 2002 it is found that both modes are in association with tropical zonal wind anomalies but only the second zonal wind mode has significant linkage with the southern annular mode sam particularly leading about 6 19 days this kind of linkage can also be found in extended datasets but only evident since 1974

southern annular modes simulated by a climate model patterns mechanisms and uses abstract both high latitude hlm and low latitude modes llm of variability of zonal wind in the southern hemisphere have been identified through an analysis of a simulation for 1871 2200 by the csiro mark 3 climate model the extent to which these might both be described as annular modes based on their statistical patterns physical mechanisms and usefulness in climate study is assessed the modes are determined as eof1 and eof2 of vertically integrated zonal and monthly mean zonal wind for 1871 1970 these match well those from ecmwf re analysis era data and also from the earlier mark 2 model the mode index time series relate to largely annular patterns of local wind and surface pressure anomalies with hlm giving the familiar southern annular mode sam and other simulated quantities while modes calculated from 90 sectors are only moderately correlated mostly in the polar region for hlm the link increases with time scale there is little such relationship for llm a momentum equation

recent shifts in coastline change and shoreline stabilization linked to storm climate change since cuspate coastlines are especially sensitive to changes in wave climate they serve as potential indicators of initial responses to changing wave conditions previous work demonstrates that cape hatteras and cape lookout north carolina which are largely unaffected by shoreline stabilization efforts have become increasingly asymmetric over the past 30 years consistent with model predictions for coastline response to increases in atlantic ocean summer wave heights and resulting changes in the distribution of wave approach angles historic and recent shoreline change observations for cape fear north carolina and model simulations of coastline response to an increasingly asymmetric wave climate in the presence of beach nourishment produce comparable differences in shoreline change rates in response to changes in wave climate results suggest that the effect of beach nourishment is to compensate for and therefore to mask natural responses to wave climate change that might otherwise be discernible in patterns of shoreline change alone therefore this case study suggests that the effects of wave climate change on human modified coastlines may be detectable in the spatial and temporal patterns of shoreline stabilization activities similar analyses of cuspate features in areas where the change in wave climate is less pronounced i e fishing point maryland virginia and where local geology appears to exert control on coastline shape i e cape canaveral florida suggest that changes in shoreline configuration that may be arising from shifting wave climate are currently limited to sandy wave dominated coastlines where the change in wave climate has been most pronounced however if hurricane generated wave heights continue to increase large scale shifts in patterns of erosion and accretion will likely extend beyond sensitive cuspate features as the larger scale coastline shape comes into equilibrium with changing wave conditions copyright 2014 john wiley sons ltd

stationary atmospheric responses to an idealized sea surface temperature anomaly in the southern ocean abstractthe stationary atmospheric response to an idealized sea surface temperature anomaly ssta is studied with a quasigeostrophic atmospheric model of the southern hemisphere sensitivity of the stationary response to the midlatitude ssta location is determined and responses are decomposed on vertical modes the ssta almost directly forces baroclinic responses inducing warm air anomalies 40 50 downstream eastward to the ssta these baroclinic responses arise from an equilibrium between the ssta induced anomalous vortex stretching and i advection by the quasi stationary flow and ii dissipation by high frequency eddies the barotropic response consists of a midlatitude ridge trough and a south pole trough ridge for sstas localized from the drake passage to the western indian ocean from south of australia to the center of the pacific ocean this response can be further decomposed into i a zonally asymmetric component a quasi stationary wave train forced by a barotropic ridge downstream of

diabatic damping of zonal index variations abstractzonal index variations or north south shifts of the midlatitude jet are the dominant mode of zonal wind variability in the southern hemisphere previous studies have shown that synoptic time scale eddy momentum flux provides a positive feedback and acts to increase the persistence and low frequency variance of the zonal index however the impact of diabatic heating due to the precipitation associated with these eddies has not been investigated in this study regression analyses have been conducted to demonstrate that a robust precipitation anomaly can be found to accompany the jet and eddy momentum flux anomalies associated with a poleward shift of the jet with enhanced precipitation on the poleward flank of the jet and reduced precipitation on the equatorward flank diabatic heating associated with such a precipitation anomaly is expected to reduce the temperature gradient across the jet anomaly thus decreasing eddy generation and damping the anomaly this expectation is confirmed by three

nonstationary impacts of the southern annular mode on southern hemisphere climate abstract the temporal stability of the southern annular mode sam impacts on southern hemisphere climate during austral spring is analyzed results show changes in the typical hemispheric circulation pattern associated with sam particularly over south america and australia between the 1960s 70s and 1980s 90s in the first decades the sam positive phase is associated with an anomalous anticyclonic circulation developed in the southwestern subtropical atlantic that enhances moisture advection and promotes precipitation increase over southeastern south america sesa on the other hand during the last decades the anticyclonic anomaly induced by the sam s positive phase covers most of southern south america and the adjacent atlantic producing weakened moisture convergence and decreased precipitation over sesa as well as positive temperature anomaly advection over southern south america some stations in the australia new zealand sector and africa exhibit significant correlations between the sam and prec