has the ozone hole contributed to increased antarctic sea ice extent 1 since the 1970s sea ice extent has decreased dramatically in the northern hemisphere and increased slightly in the southern hemisphere a difference that is potentially explained by ozone depletion in the southern hemisphere stratosphere in this study we consider the impact of stratospheric ozone depletion on antarctic sea ice extent using a climate model forced with observed stratospheric ozone depletion from 1979 to 2005 contrary to expectations our model simulates a year round decrease in antarctic sea ice due to stratospheric ozone depletion the largest percentage sea ice decrease in our model occurs in the austral summer near the coast of antarctica due to a mechanism involving offshore ekman sea ice transport the largest absolute decrease is simulated in the austral winter away from the coast of antarctica in response to an ocean warming that is consistent with a poleward shift of thc large scale pattern of sea surface temperature our model results strongly suggest that processes not linked to stratospheric ozone depletion must be invoked to explain the observed increase in antarctic sea ice extent

beyond cold and warm an objective classification for maritime midlatitude fronts this study introduces a detailed and objective classification for mid latitude maritime fronts the classification is based on a principal component analysis pca to determine the dominant patterns of variability between fronts here fronts are defined as three dimensional frontal volumes which are detected in the era interim data set for a large number of locations in the atlantic pacific and indian oceans during both winter and summer in addition to the well established distinction between warm and cold fronts the pca exposes several new dimensions of variability a front intensity b surface fluxes and c along front transports linked to the intensity of the associated conveyor belts these new dimensions of variability are regionally and seasonally robust and a lagged composite analysis demonstrates that each of the new front types evolves in a dynamically characteristic way further the new front types can be related to established ones like katafronts and anafronts the new front types are finally redefined based on simple parameter thresholds to simplify their application in future studies

a revised jurassic radiolarian zonation for the south belt of the chichibu terrane western kyushu southwest japan abstract permian triassic and jurassic sedimentary and volcaniclastic rocks are distributed in the south belt of the chichibu terrane unfortunately they are not part of a sequence but are disordered masses of mappable units several sequences of jurassic age are found in the kuma massif on western kyushu the western part of the belt the radiolarian succession containing the sequences encompasses nearly the entire jurassic epoch detailed radiolarian successions from seven sections are discussed six sections consist mainly of bedded cherts and siliceous shales with minor terrigenous black shales one section consists of terrigenous black shales with oolitic limestone the radiolarian zonation presented here has been defined by the first and last appearances of age diagnostic species from stratigraphically coherent intervals thirteen radiolarian datum levels have been established defining ten zones and six subzones representing the lower to upper jurassic these zones are correlated with zones previously established by several workers for coeval strata of the world western tethys caucasus pacific coast of russia japan western pacific ocean and north america

antarctic sea ice climatology variability and late twentieth century change in ccsm4 abstracta preindustrial control run and an ensemble of twentieth century integrations of the community climate system model version 4 ccsm4 are evaluated for antarctic sea ice climatology modes of variability trends and covariance with related physical variables such as surface temperature and sea level pressure compared to observations the mean ice cover is too extensive in all months this is in part related to excessively strong westerly winds over 50 60 s which drive a large equatorward meridional ice transport and enhanced ice growth near the continent and also connected with a cold bias in the southern ocean in spite of these biases in the climatology the model s sea ice variability compares well to observations the leading mode of austral winter sea ice concentration exhibits a dipole structure with anomalies of opposite sign in the atlantic and pacific sectors both the el nino southern oscillation and the southern annular mode sam project onto this mode in twentieth century inte

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

a diagnostic case study of mei yu frontogenesis and development of wavelike frontal disturbances in the subtropical environment abstract during 6 7 june 2003 a mei yu front over southern china with active mesoscale convective systems mcss along it and to its south intensified rapidly in 24 h to possess a strong cyclonic circulation with relative vorticity centers reaching 1 7 10 4 s 1 and a low level jet llj of 22 5 m s 1 at 850 hpa moreover both the mass and wind fields and convection developed a wavelike structure at meso scale along the front using mainly gridded analyses from the european centre for medium range weather forecasts ecmwf the present study documented the evolution of this case and diagnosed the mechanisms responsible for its rapid intensification and the development of mesoscale disturbances using methods including the piecewise potential vorticity pv inversion results indicate that this mei yu front was characterized by strong horizontal shear and moderate temperature gradient and its development was not baroclinic in nature the initiation of a wavelike structure along the frontal shear zon

perspectives on moist baroclinic instability implications for the growth of monsoon depressions abstractlittle is known about the genesis and growth mechanisms of monsoon depressions despite the great importance of these storms for the hydrological cycle of the asian australian monsoon region of the few theoretical studies that have examined this issue most have attributed the amplification of monsoon depressions to some form of baroclinic instability or stable baroclinic growth highly modified by the diabatic effects of moist convection here a simple criterion namely the upshear tilt of potential vorticity anomalies is argued be necessary for dry or moist baroclinic growth reanalysis data are then used to assess whether a large ensemble of south asian monsoon depressions has vertical structures consistent with this criterion the evolution of these monsoon depressions is compared with that of ensembles of hurricanes and diabatic rossby waves the latter being prototypical examples of moist baroclinic instability during their amplification phase monsoon depressions do not exhibit an upshea

the spatial distribution and evolution characteristics of north atlantic cyclones a climatology of extratropical cyclones is produced using an objective method of identifying cyclones based on gradients of 1 km height wet bulb potential temperature cyclone track and genesis density statistics are analyzed and this method is found to compare well with other cyclone identification methods the north atlantic storm track is reproduced along with the major regions of genesis cyclones are grouped according to their genesis location and the corresponding lysis regions are identified most of the cyclones that cross western europe originate in the east atlantic where the baroclinicity and the sea surface temperature gradients are weak compared to the west atlantic east atlantic cyclones also have higher 1 km height relative vorticity and lower mean sea level pressure at their genesis point than west atlantic cyclones this is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of preexisting parent cyclones the evolution characteristics of composite west and east atlantic cyclones have been compared the ratio of their upper to lower level forcing indicates that type b cyclones are predominant in both the west and east atlantic with strong upper and lower level features among the remaining cyclones there is a higher proportion of type c cyclones in the east atlantic whereas types a and c are equally frequent in the west atlantic

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

interactions of north pacific tropical midlatitude and polar disturbances resulting in linked extreme weather events over north america in october 2007 abstractthis study uses observations and model reanalyses to examine the multiscale processes associated with four high impact extreme weather events ewes over north america during late october 2007 the ewes consisted of wind driven wildfires in california prolonged anomalous cold conditions in mexico linked to two cold surges heavy rainfall in the eastern united states and severe flood producing heavy rainfall in southern mexico the ewes involved a pronounced large scale flow reconfiguration across the north pacific and north america in conjunction with the formation of a high amplitude rossby wave train the flow reconfiguration involved perturbations to the north pacific jet stream linked to polar midlatitude and tropical disturbances including three tropopause level polar disturbances originating over northeastern asia transient extratropical cyclones a diabatic rossby vortex and western north pacific tropical cyclone kajiki eulerian and lagrangian diagnostics indicate that ridge amplifi

mesozoic tectonic evolution of the proto south china sea a perspective from radiolarian paleobiogeography abstract the proto south china sea pscs represents the lithosphere that formerly occupied the region southeast of south china where the present day south china sea is located the subduction and demise of the pscs have attracted wide attention whereas the pre subduction history particular the mesozoic of the region remains relatively neglected in this paper the radiolarian paleobiogeography of the region is analyzed to identify the paleobiogeographic affinity and paleo connectivity of the pscs with the pacific and tethys oceans during the mesozoic then the continent ocean configuration and tectonic evolution of the pscs and adjacent areas are discussed through the integration of paleobiogeographical results and associated paleomagnetic stratigraphic and petrologic data the main conclusions are as follows 1 during the triassic the pscs was situated in the transition zone between the pacific and tethys oceans and its paleobiogeography was influenced by both oceans the pscs was characterized by complex tectonic overprinting by the pacific and tethyan tectonic regimes 2 in the early middle jurassic the pscs was well connected to the pacific ocean but poorly connected to the tethys ocean consistent with the paleobiogeography of the pscs being mainly constrained by the pacific ocean the pscs was part of the paleo pacific slab 3 during the late jurassic cretaceous the pscs was in a semi closed environment the late jurassic early late cretaceous pscs was part of a west facing andean type subduction zone and the late late cretaceous pscs was situated in an extensional tectonic setting

early middle jurassic late aalenian radiolarian assemblage in a manganese nodule from the northern chichibu belt in the ino area kochi prefecture southwest japan abstract well preserved radiolarians were obtained from a manganese nodule collected from the northern chichibu belt in the ino area kochi prefecture southwestern japan this is the first discovery of manganese nodules containing radiolarians in the chichibu belt the radiolarian assemblage in the manganese nodule consists of 111 nassellarians and 110 spumellarians the assemblage contains 38 described species and 43 unknown morphotypes as shown by yao yao a 1997 faunal change of early middle jurassic radiolarians news of osaka micropaleontologists special volume no 10 155 182 in japanese with english abstract the assemblage suggests the late aalenian age based on the biostratigraphic data in japan and the western pacific it shows a low diversity of ring and disc shaped spumellarians like the genera hexasaturnalis parasaturnalis and orbiculiforma the genera paronaella parvicingula and parahsuum are highly diversified faunal composition of the examined assemblage in the chichibu belt is different from the contemporaneous assemblages in the mino and kuzumaki kamaishi belts this difference seems to indicate that the depositional regions of manganese nodules are different among the chichibu mino and kuzumaki kamaishi belts the examined manganese nodule may have been deposited during late aalenian time in a higher latitudinal area than its present location in the kuzumaki kamaishi belt judging by the number of species belonging to parvicingula

dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 dynamical aspects of the life cycle of the winter storm lothar 24 26 december 1999 are investigated with the aid of the european centre for medium range weather forecasts analysis data and mesoscale model simulations neither of these datasets capture the full amplitude of the observed extreme pressure fall and surface wind speeds but they do help identify a range of key dynamical and physical features that characterize the development of this unusual event the analysis and interpretation is primarily based upon the evolution of the lower and upper level potential vorticity pv field complemented by three dimensional trajectory calculations lothar originated in the western atlantic and travelled as a shallow low level cyclone of moderate intensity towards europe this translation took place below and slightly to the south of a very intense upper level jet and was accompanied by continuous and intense condensational heating that sustained a pronounced positive low level pv anomaly not unlike the concept of a diabatic rossby wave no significant pv anomalies were evident at the tropopause level during this early phase of the life cycle the surface cyclone intensified rapidly when the shallow cyclone approached the jet stream axis the circulation induced by the diabatically produced low tropospheric pv anomaly on steeply sloping isentropic surfaces that transect the intense upper level jet contributed significantly to the rapid formation of a narrow and deep tropopause fold this stratospheric pv anomaly virtually merged with the diabatically produced ephemeral pv feature to form a vertically aligned tower of positive pv at the time of maximum storm intensity a sensitivity study with a dry adiabatic hindcast simulation shows no pv tower configuration and only a very weak surface development and confirms the primary importance of the cloud diabatic heating for the tropopause fold formation and the rapid bottom up intensification of lothar a comparison of the anomalously high atlantic sea surface temperatures in december 1999 with the water vapour source regions for the latent heat release that accompanied the rapid intensification phase of lothar shows a close relationship this is of importance when discussing the possible implications of climate variability and change on the development of north atlantic winter storms copyright 2002 royal meteorological society

analysis of the slope of isentropic surfaces and its tendencies over the north atlantic the maintenance of baroclinicity along mid and high latitude storm tracks is a matter of ongoing debate using an isentropic framework a novel diagnostic based on the tendency equation for the slope of isentropic surfaces a measure of the potential for baroclinic development is presented the tendency comprises contributions from dynamic processes latent heat release radiation and subgrid scale turbulence which incorporates the effect of sensible heat fluxes a climatology of these tendencies over the north atlantic is compiled for the winters of 2009 and 2010 it is found that adiabatic tilting flattens the isentropic surfaces reflecting the action of growing baroclinic cyclones this tendency is balanced climatologically by the generation of slope by diabatic processes in the lower troposphere the most intense diabatic increase of slope is found along the oceanic frontal zone associated with the gulf stream and at higher latitudes in the labrador sea the nordic seas and the barents sea latent heat release and sensible heat fluxes both contribute substantially in these regions a quantitative analysis of cold air outbreaks emphasizes their important role in restoring the slope in the lower troposphere over the gulf stream region and off the sea ice edge at high latitudes in the upper troposphere latent heat release due to cloud microphysical processes is the dominant mechanism maintaining the slope

a classification of fastex cyclones using a height attributable quasi geostrophic vertical motion diagnostic a systematic and objective procedure is developed for applying the simple cyclone classification scheme of petterssen and smebye this method uses a height attributable solution of the quasi geostrophic equation to identify and quantify the relative importance of upper and lower tropospheric forcing and also the time trend in the horizontal spacing of the forcing at these two levels by applying this classification method to a sample of cyclogenesis events during their maximum intensification stage from the fronts and atlantic storm track experiment field experiment the type a and type b scheme of petterssen and smebye is reproduced and extended to include a type c type c consists of upper level dominated cyclones that form at high latitudes and in their initial stages resemble comma cloud type polar lows detailed examples of each of the three types are presented some cyclones can undergo more than one period of development and it is found that each development period can be classified as a different cyclogenesis category a or b these cyclones are classified as hybrid type a b there is some evidence that cyclone forecast accuracy depends on cyclone type thereby suggesting the potential for this method to be used to assign confidence levels for forecasts of cyclogenesis produced by numerical weather prediction models type b cyclones appear more difficult to predict because their development depends initially on the interaction between significant features in the upper and lower troposphere copyright 2002 royal meteorological society t d hewson s contribution is crown copyright

surface cyclones in the era 40 dataset 1958 2001 part i novel identification method and global climatology abstract a novel method is introduced to generate climatological frequency distributions of meteorological features from gridded datasets the method is used here to derive a climatology of extratropical cyclones from sea level pressure slp fields a simple and classical conception of cyclones is adopted where a cyclone is identified as the finite area that surrounds a local slp minimum and is enclosed by the outermost closed slp contour this cyclone identification procedure can be applied to individual time instants and climatologies of cyclone frequency fc are obtained by simple time averaging therefore unlike most other climatologies the method is not based on the application of a tracking algorithm and considers the size of cyclones in combination with a conventional cyclone center tracking algorithm that allows the determination of cyclone life times and the location of cyclogenesis and cyclolysis additional frequency fields can be obtained for special categories of cyclones that are gener

simulations of the extratropical transition of tropical cyclones contributions by the midlatitude upper level trough to reintensification abstract the extratropical cyclone development processes during the reintensification stage of an extratropical transition from a tropical cyclone tc are described using numerical simulations three control simulations without a tropical cyclone present examine the extratropical cyclogenesis associated with upper level troughs that are characterized as weak moderate and strong when no tropical cyclone is included in the simulation the minimum surface pressures attained with the weak moderate and strong troughs are 1003 991 and 977 mb respectively in all three cases the low tilts northwestward with height during intensification and the rainfall pattern and eventual occlusion are representative of classic extratropical cyclone development the interactions of a tropical cyclone with each of the three midlatitude circulation patterns are compared with the control simulations to illustrate the contributions to the extratropical transition of the tropical cyclone in the three trough with tc case

a newly proposed radiolarian zonation for the jurassic of japan abstract eight radiolarian zones are established on the basis of biostratigraphic investigations on the japanese jurassic these are theparahsuum sp c archicapsa pachyderma laxtorum jurassicum tricolocapsa plicarum tricolocapsa conexa stylocapsa spiralis cinguloturris carpatica andpseudodictyomitra primitiva zones in ascending order biohorizons reflecting evolutionary lineages are utilized where possible in defining the zonal boundaries in the case of absence of adequate lineages biohorizons of the first or last appearance of characteristic species are applied the zones are compared with the zones previously proposed by several workers in japan

a geochemical constraint on the formation process of a manganese carbonate nodule in the siliceous mudstone of the jurassic accretionary complex in the mino belt japan abstract manganese mn carbonate nodules which differ from seafloor mn nodules mainly composed of mno 2 are occasionally embedded in the form of a lens shape in the jurassic accretionary complexes such as the mino belt in japan the interpretation of the formation process of mn carbonate is still controversial particularly concerning whether the mn carbonate was formed primarily or secondarily in this study a fresh mn carbonate nodule incorporated into the red siliceous mudstone was collected for geochemical and sedimentological analysis the optical observation of thin sections indicates that the mn carbonate nodules are composed of abraded grains of rhodochrosite spherule with radiolarians and are sedimentary embedded in siliceous mudstone microfossil radiolarians from the mn carbonate nodules and the host red siliceous mudstone are dated as the bajocian but the radiolarians in the nodules are somewhat older than those in the host red siliceous mudstone geochemical analysis using the x ray absorption near edge structure on ce indicates the dominance of trivalent ce at present despite the observation of a positive ce anomaly in the paas normalized ree pattern of mn carbonate the ree adsorption experiment on synthesized mnco 3 does not show any distinctive positive ce anomaly and a thermodynamic calculation suggests the possible coexistence of rhodochrosite and spontaneous oxidation of ce a leaching experiment that can selectively decompose the carbonate phase demonstrated no ce anomaly in the carbonate phase of the mn carbonate and a poor contribution to the bulk ree concentration the carbon isotope data of mn carbonate nodule implied the dominance of inorganic marine carbonate origin with small contribution of organic decomposition the most plausible account of all of the observational and geochemical results is that the rhodochrosite grains were primarily formed on the depositional site and subsequently transferred to a different site where siliceous mudstone was deposited

the integral role of a diabatic rossby vortex in a heavy snowfall event abstract on 24 25 february 2005 a significant east coast cyclone deposited from 4 to nearly 12 in 10 30 cm of snow on parts of the northeastern united states the heaviest snowfall and most rapid deepening of the cyclone coincided with the favorable positioning of an upper level short wave trough immediately upstream of a preexisting surface cyclone the surface cyclone in question formed approximately 15 h before the heaviest snowfall along a coastal front in a region of frontogenesis and heavy precipitation the incipient surface cyclone subsequently intensified as it moved to the northeast consistently generating the strongest convection to the east northeast of the low level circulation center the use of potential vorticity pv inversion techniques and a suite of mesoscale model simulations illustrates that the early intensification of the incipient surface cyclone was primarily driven by diabatic effects and was not critically dependent on the upper level wave these facts taken in conjunct

a subtropical oceanic mesoscale convective vortex observed during sowmex timrex abstractthis study examines a subtropical oceanic mesoscale convective vortex mcv that occurred from 1800 utc 4 june to 1200 utc 6 june 2008 during intensive observing period iop 6 of the southwest monsoon experiment sowmex and the terrain influenced monsoon rainfall experiment timrex a dissipating mesoscale convective system reorganized within a nearly barotropic vorticity strip which formed as a southwesterly low level jet developed to the south of subsiding easterly flow over the southern taiwan strait a cyclonic circulation was revealed on the northern edge of the mesoscale rainband with a horizontal scale of 200 km an inner subvortex on a scale of 25 30 km with maximum shear vorticity of 3 10 3 s 1 was embedded in the stronger convection the vortex relative southerly flow helped create local potential instability favorable for downshear convection enhancement strong low level convergence suggests that stretching occurred within the mcv higher e air associated with significant pot

on a threefold classification of extratropical cyclogenesis a recently proposed extension to the twofold extratropical cyclogenesis classification scheme of petterssen and smebye is discussed a third class of extratropical cyclone type c is described in which initial development is controlled by a pre existing upper level potential vorticity pv anomaly in its early stages such a system is indistinguishable from the classical type b cyclone of the petterssen and smebye scheme however subsequent development cannot be understood in terms of a co operative interaction of the upper level feature with a low level baroclinic zone rather the cyclogenetic dynamics of type c systems are dominated by the action of strong midlevel latent heating such heating can generate important anomalies of pv that act to suppress the formation of a low level thermal anomaly and that interact destructively with the pre existing upper level feature candidate type c events are identified using recently developed height attributable quasi geostrophic vertical motion diagnostics the application of one such diagnostic to a climatology of instantaneous cyclonic features suggests that type c events may occur with reasonable frequency the generic behaviour of system types in the proposed threefold classification scheme is compared with the actual dynamics of some cyclones from the fronts and atlantic storm track experiment fastex the analysis is based on piecewise pv inversions and numerical simulations this approach is able to provide a good description of a case of standard type b development consistent with the qualitative description of petterssen and smebye and with the quasi geostrophic diagnostics within the same framework two systems are discussed whose behaviours do not fit the simple a b classification but are consistent with the proposed type c mechanism copyright 2003 royal meteorological society

reexamining the dynamics of short scale diabatic rossby waves and their role in midlatitude moist cyclogenesis abstract as a step toward a more comprehensive study of the physical processes that underlie explosive cyclogenesis a two dimensional semigeostrophic model with a now standard parameterization of latent heat release is used to diagnose the structure energetics and propagation characteristics of short scale diabatic normal modes in a moist baroclinic atmosphere with the eady basic state upon revisiting the inviscid problem it is found that when a thermodynamically consistent vertical profile of latent heat release is used the short wave cutoff vanishes and growth rates become independent of zonal wavelength for zonal wavelengths shorter than approximately 1900 km the destabilized short scale modes identified previously as diabatic rossby waves owe their existence to the continuous generation of potential vorticity by moist processes associated with warm air advection rising motion and latent heat release to determine if these short scale diabatic rossby wave modes continue to grow at small

life cycle study of a diabatic rossby wave as a precursor to rapid cyclogenesis in the north atlantic dynamics and forecast performance abstractthe life cycle of a north atlantic cyclone in december 2005 that included a rapid propagation phase as a diabatic rossby wave drw is investigated by means of operational analyses and deterministic forecasts from the ecmwf a quasigeostrophic omega diagnostic has been applied to assess the impact of upper level forcing during the genesis propagation and intensification phase respectively the system was generated in the gulf of mexico as a mesoscale convective vortex mcv influenced by vertical motion forcing from a nearby upper level trough the drw propagation phase was characterized by a shallow low level diabatically produced potential vorticity pv anomaly that rapidly propagated along the southern border of an intense baroclinic zone no significant upper level forcing could be identified during this phase of the development eventually explosive intensification occurred as the region of vertical motion forced by an approaching upper level trough reached the position of the drw the

middle jurassic radiolarian chert indarung padang district and its implications for the tectonic evolution of western sumatra indonesia abstract radiolaria from chert in the indarung area belong to the transhsuum hisuikyoense zone indicating an aalenian lower middle jurassic age carbonate in the area has been dated as upper jurassic to lower cretaceous from the occurrence of lovcenipora and overlying tuff has given a radiometric k ar age of 105 3 albian uppermost lower cretaceous the chert and carbonate are probably in tectonic contact with the chert faulted into the limestone during ene directed compression this comprises one of the best dated occurrences of allochthonous material in sumatra and confirms the accretion of oceanic material along the sunda margin during mid to late cretaceous times

the palette of fronts and cyclones within a baroclinic wave development abstract a study is undertaken of the concurrent development of fronts and cyclones within a growing baroclinic wave the dynamical framework for the study is that of the semigeostrophic adiabatic flow of a uniform potential vorticity atmosphere that is sandwiched between two horizontal plates on an f plane a three dimensional spectral model is used to examine the growth to finite amplitude of the normal modes of this system for basic states that comprise of a symmetric jetlike baroclinic flow with and without a superposition of a uniform barotropic shear of either cyclonic or anticyclonic vorticity it is demonstrated that the presence of such lateral shear in the ambient environment exerts a profound influence upon the ensuing palette of fronts and cyclones on the synoptic scale this flow component influences the scale and strength of the individual surface highs and lows and also modifies the extent of their lateral drift away from and their relative movement along the baroclinic zone aloft t

diabatic rossby waves in the southern hemisphere diabatic rossby waves drws are a special type of low level cyclone with a self maintaining mechanism given an environment of moderate or strong baroclinicity and abundant moisture under certain conditions these shallow cyclones associated with a cyclonic low level pv anomaly can serve as precursors for explosive cyclone intensification the present study is the first to investigate drws in the southern hemisphere sh two typical drw case studies are presented and a sophisticated algorithm is used to detect drws in operational analysis data from 2001 to 2012 drws occur in all ocean basins and seasons with a maximum in summer on average about four drws are found per month and 12 intensify explosively thereby they contribute 6 to the total set of explosively deepening extratropical cyclones in the sh drw tracks originate slightly closer to the equator than normal extratropical cyclones and they follow the convergence zones eastward and poleward this results in a climatological drw track density similar to a spiral from the western south pacific ending in the eastern south indian ocean broken only by the andes typical synoptic situations associated with drw genesis are identified the categories include i low level pv generation by upper level induced lifting ii low level jet induced diabatic pv generation and iii transformation of the low tropospheric pv anomaly from another system

a 10 yr climatology of diabatic rossby waves in the northern hemisphere abstractdiabatic rossby waves drws are low tropospheric positive potential vorticity pv anomalies in moist and sufficiently baroclinic regions they regenerate continuously by moist diabatic processes and potentially develop into explosively intensifying cyclones in this study a specific drw tracking algorithm is developed and applied to operational ecmwf analyses to compile a first climatology of drws in the northern hemisphere for the years 2001 10 drws are more frequent over the north pacific than over the north atlantic with on average 81 and 43 systems per year respectively less than 15 of these systems intensify explosively on average 12 per year over the pacific and 5 over the atlantic drws are most frequent in summer but most of the explosively intensifying drws occur in autumn and winter drws are generated typically between 30 50 n over the eastern parts of the continents and the western central parts of the oceans they propagate fairly zonally along the midlatitude baroclinic zone

the life cycle of an extratropical marine cyclone part ii mesoscale structure and diagnostics abstract this is the second of two articles describing the evolving structure and selected physical processes within an intense extratropical marine cyclone observed during the experiment on rapidly intensifying cyclones over the atlantic erica field program part i describes the 24 h frontal cyclone evolution through 6 h horizontal analyses of observations taken by specially deployed observing systems from air land and sea part ii presents frontal scale and precipitation structures and physical processes from analyses based primarily on research aircraft observations taken during three phases of the cyclone s life cycle horizontal analyses at 350 m above ground level describe the cyclone s mesoscale frontal baroclinic structure and associated flow patterns the vertical structure and evolution of the cyclone s cold front warm front and bent back front are illustrated in cross sectional analyses of potential temperature wind velocity potential vorticity pv front relative transverse flow vecto

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

the impact of coriolis approximations on the environmental sensitivity of idealized extratropical cyclones the precise influence of climate change on extratropical cyclone genesis and evolution is an important but as yet unsolved problem given their physical and economic impact on a large portion of the planet s population however extratropical cyclones are also affected by the competing influences of forcing mechanisms at a wide range of spatial scales complicating the problem while the advent of idealized numerical modeling has allowed great strides in addressing these complications and achieving some qualitative consensus in the literature there is still some quantitative disagreement about response magnitude and where local maxima and minima in the response may be located thus the advantages inherent in the variety of idealized numerical modeling methods used to address this problem are also a drawback as it can be difficult to draw one to one comparisons across experiments although the effects of particular model architecture choices such as microphysical and cumulus schemes are well documented others are less understood in this study we examine the role of coriolis approximations by comparing a new set of etc sensitivity experiments using a linear plane approximation to an existing set of extratropical sensitivity experiments using a constant f plane approximation etcs within the new plane experiment are found to generally decrease in strength with temperature as measured by both minimum sea level pressure and maximum eddy kinetic energy eke a small increase in eke is observed at the warmest temperatures likely due to diabatic influences disrupting flow within the warm conveyor belt while seemingly contradictory to the previous f plane results the two experiments are instead found to be qualitatively similar upon further inspection with an offset of approximately 8 k this offset is primarily due to the coriolis approximations although the initial stability profile affected by the coriolis approximation has a marginal influence

rossby wave initiation by recurving tropical cyclones in the western north pacific abstractthe interaction of recurving tropical cyclones tcs with midlatitude rossby waves during extratropical transition et can significantly alter the midlatitude flow configuration this study provides a climatological investigation of rossby wave initiation rwi by transitioning tcs in the specific configuration of an initially zonal midlatitude waveguide and elucidates physical processes governing ab initio flow amplification during et recurving tcs interacting with a zonally oriented waveguide in the western north pacific wnp basin from 1979 to 2013 are categorized into cases initiating rossby waves tc rwi or not tc norwi interactions with a zonally oriented waveguide occurred for 22 7 of the recurving tcs and one third of these resulted in tc rwi in the presence of a tc the probability of rwi on a zonally oriented waveguide is 3 times larger than in situations without a tc the occurrence of tc rwi exhibits a seasonality and is relatively more common during boreal summer than in aut

forcing of the antarctic circumpolar wave by el nino southern oscillation teleconnections we address several issues regarding the antarctic circumpolar wave acw these include the extent to which the acw is related to el nino southern oscillation enso cycles and the need to reconcile differences between the observed zonal wavenumber 2 pattern and the wavenumber 3 pattern found in coupled ocean atmosphere models in the present study we revisit the sea surface temperature sst signal of the observed acw we find that the associated sst variations may be decomposed into several empirical orthogonal functions eofs that are linearly independent the first four eofs describe 84 of the total variance on timescales of 3 7 years and superposition of sst signals of the four eofs reproduces sst signals of the observed acw given that eof analysis can only describe standing oscillations we then employ complex eof ceof analysis suitable for studying propagating waves the first two ceofs denoted ceofsst1 and 2 account for 70 of the total variance and the sst variability reconstructed from them again reproduces the observed acw the real part of ceofsst1 44 of the total variance is similar to the first real eof eofsst1 both eofsst1 and ceofsst1 may be identified with enso and have a wavenumber 2 zonal pattern in the southern middle to high latitudes ceofsst1 is the major constituent of the acw in the period of 1981 1997 the associated atmospheric circulation displays a pacific south america psa pattern statistical analyses demonstrate that the psa pattern teleconnected to enso is the major mechanism that forces this principal constituent of the acw ceofsst2 26 of the total variance has a zonal wavenumber 3 pattern in the same latitude band similar to that simulated by several coupled models we suggest that if enso is not adequately resolved in coupled models but structures with zonal wavenumber 3 pattern are then the modeled acw would appear to have a zonal wavenumber 3 pattern

a pv perspective on the vertical structure of mature midlatitude cyclones in the northern hemisphere development of extratropical cyclones can be seen as an interplay of three positive potential vorticity anomalies an upper level stratospheric intrusion low tropospheric diabatically produced potential vorticity pv and a warm anomaly at the surface acting as a surrogate pv anomaly this study based on the interim ecmwf re analysis era interim dataset quantifies the amplitude of the pv anomalies of mature extratropical cyclones in different regions in the northern hemisphere on a climatological basis a tracking algorithm is applied to sea level pressure slp fields to identify cyclone tracks surface potential temperatureanomalies duandverticalprofilesofpvanomalies dpvarecalculatedatthetimeofthecyclones minimumslpinaverticalcylinderaroundthesurfacecyclonecenter tocomparethecyclones characteristics they are grouped according to their location and intensity composite dpv profiles are calculated for each region and intensity class at the time of minimum slp and during the cyclone intensification phase in the maturestage allthree anomaliesare on averagelargerfor intense thanforweak wintercyclones e g 0 6 versus 0 2 potential vorticity units pvu 1 pvu 510 26 kk g 21 m 2 s 21 at lower levels and 1 5 versus 0 5 pvu at upper levels the regional variability of the cyclones vertical structure and the profile evolution is prominent cyclones in some regionsare moresensitiveto the amplitude ofa particularanomalythanin other regions values of du and low level dpv are on average larger in the western parts of the oceans than in the eastern parts results for summer are qualitatively similar except for distinctively weaker surface du values