observations of a cut off low over southern australia the structure and evolution of an intense cut off low is documented in detail unprecedented for the australian region by combining high time resolution radiosonde profiles with co located wind profiler observations and routine australian bureau of meteorology analyses the cut off low develops over the ocean south of australia and subsequently interacts with a subtropical frontal system over the central part of the continent throughout the period of observation the strongest temperature gradients lay through the subtropics moreover the subtropical temperature gradients strengthened while the midlatitude temperature gradients associated with the cut off low weakened the australian bureau of meteorology s 150 km regional assimilation and prognosis system analyses capture the broad scale structure and evolution of the system reasonably well the system documented here is similar in structure to the instant occlusion investigated by browning and hill 1985 the major difference being that our cut off low develops poleward of a subtropical front the cut off low was cold cored and produced a very deep tropopause fold over adelaide the tropopause descended to an altitude of about 5 km and the temperature at 500 hpa fell to 30 c the western edge of the low level cold dome was marked by a strong secondary warm front which passed over adelaide about 8 hours after the tropopause height minimum the warm front was characterized at the surface by an absolute minimum in the pressure and a temperature rise of about 7 c significantly this increase in temperature took place in the early hours of the morning against the diurnal trend the cut off low produced very high rainfalls resulting in flash flooding and much damage in the adelaide hills area the most severe convection took place in the region behind the lowered tropopause around the passage of the warm front

role of subduction erosion in the generation of andean magmas subduction erosion or scraping off of the continental crust by subducting oceanic lithosphere is an important tectonic process along parts of the andean convergent plate boundary estimated rates of subduction erosion increase northward north of the southem andes due to decreasing subduction angle and decreasing sediment supply to the trench west of the central andes subduction erosion may remove as much as 535 km 3 of crust per 1 km of trench per 1 m y or 7 vol of the subducting oceanic lithosphere the higher 87 sr 86 sr ratios of mafic magmas erupted north of the southern andes may be explained by the higher rates of subduction erosion and increased amounts of contamination of the sub arc mantle magma source

jet streaks in the gulf stream mesoscale alongstream speed changes of the gulf stream are diagnosed from an array of current meters at depths 400 700 and 1000 m near 688w during the development of steep ratio of amplitude to wavelength o 1 meanders speed maxima jet streaks are generally found between trough and crest axes in steep meanders with local speed minima near the trough and crest axes speed changes along streamlines can be quite dramatic speed changes along the jet axis between jet streaks and local minima in excess of 0 60 0 40 and 0 35 m s 21 are observed at depth 400 700 and 1000 m respectively this is in comparison with peak speeds in a frontal coordinates system mean of 1 22 0 67 and 0 28 m s21 at depth 400 700 and 1000 m respectively from a previous study the presence of the jet streaks can be explained kinematically as a superposition of the gulf stream and barotropic vortices the development of these jet streaks in relation to the developing steep meanders differs from the canonical picture of jet streak baroclinic wave development in the atmospheric jet stream in that the jet streaks in the gulf stream are predominantly fixed in place with respect to meanders as they steepen

crustal xenoliths from calbuco volcano andean southern volcanic zone implications for crustal composition and magma crust interaction crustal xenoliths in the 1961 andesite flow of calbuco volcano in the southern southern volcanic zone ssvz of the andes consist predominantly of pyroxene granulites and hornblende gabbronorites the granulites contain plagioclase pyroxene magnetite amphibole and have pronounced granoblastic textures small amounts of relict amphibole surrounded by pyroxene plagioclase magnetite glass symplectites are found in some specimens these and similar textures in the gabbronorites are interpreted as evidence of dehydration melting mineral and bulk rock geochemical data indicate that the granulites are derived from an incompatible trace element depleted basaltic protolith that underwent two stages of metamorphism a moderate pressure high temperature stage accompanied by melting and melt extraction from some samples followed by thermal metamorphism after entrainment in the calbuco andesite lavas high nd t values 4 0 to 8 6 nd isotope model ages of 1 7 2 0 ga and trace element characteristics like chondrite normalized la yb and la nb 1 indicate that the protoliths were oceanic basalts similar oceanic metabasalts of greenschist to amphibolite facies are found in the paleozoic metamorphic belt that underlies the chilean coastal ranges mineral and bulk rock compositions of the gabbronorite xenoliths indicate that they are cognate crystallizing from the basaltic andesite magma at calbuco crystallization pressures for the gabbros based on total al contents in amphibole are 6 8 kbar these pressures point to middle to lower crustal storage of the calbuco magma neither granulite nor gabbro xenoliths have the appropriate geochemical characteristics to be contaminants of calbuco andesites although an ancient sedimentary contaminant is indicated by the lava compositions the presence of oceanic metabasaltic xenoliths together with the sedimentary isotopic imprint suggests that the lower crust beneath the volcano is analogous to the coastal metamorphic belt which is an accretionary complex of intercalated basalts and sediments that formed along the paleozoic gondwanan margin if this is the case the geochemical composition of the lower and middle crust beneath the ssvz is significantly different from that of most recent ssvz volcanic rocks

transient shallow reservoirs beneath small eruptive centres constraints from mg fe interdiffusion in olivine abstract small eruptive centres commonly have more primitive lavas than those associated with stratovolcanoes an observation that has been taken to indicate a short magma residence in the crust relative to those reservoirs below stratovolcanoes the caburgua cones of the andean southern volcanic zone from a basaltic small eruptive centre where this can be tested here we use melts simulations and the available thermobarometry data to determine the conditions of olivine crystal rim formation and the mg fe diffusion modelling to determine the magma residence times of those rims in the crust results yield timescales varying from a few days to dozens of days and if freezing is to be avoided can only be explained by some form of storage or slow transport through at least one shallow magma body the longest durations of magma residence seen in the olivine rim zones are up to 471 days these timescales are shorter than those estimated decadal from the nearby more differentiated and well established stratovolcano villarrica which has a dominantly basaltic andesite composition for caburgua cones we propose the existence of a transient reservoir in contrast to a long lived reservoir such as that inferred beneath the adjacent villarrica stratovolcano

the impact of moist frontogenesis and tropopause undulation on the intensity size and structural changes of hurricane sandy 2012 abstractthis study examines the relative roles of moist frontogenesis and tropopause undulation in determining the intensity size and structural changes of hurricane sandy using a high resolution cloud resolving model a 138 h simulation reproduces sandy s four distinct development stages i rapid intensification ii weakening iii steady maximum surface wind but with large continued sea level pressure slp falls and iv reintensification results show typical correlations between intensity changes sea surface temperature and vertical wind shear during the first two stages the large slp falls during the last two stages are mostly caused by sandy s northward movement into lower tropopause regions associated with an eastward propagating midlatitude trough where the associated lower stratospheric warm air wraps into the storm and its surrounding areas the steady maximum surface wind occurs because of the widespread slp falls with weak gradients lacking significant inward advection of absolute

three dimensional structure along the inverted palaeoproterozoic fiery creek fault system mount isa terrane australia abstract the nw dipping fiery creek fault system located in the northern mount isa terrane comprises numerous sub parallel faults that record multiple episodes of palaeo to mesoproterozoic movement hanging wall wedge shaped stratal geometries and marked stratal thickness variation across the fault system indicate that the earliest movement occurred during episodic intracontinental extension mount isa rift event ca 1710 1655 ma reactivation of the fault system during regional shortening and basin inversion associated with the mesoproterozoic isan orogeny ca 1590 1500 ma resulted in complex three dimensional hanging wall geometries and highly variable strain in the hanging wall strata along the fault system this has resulted in the development of discrete hanging wall deformation compartments that are characterised by different structural styles high strain compartments are characterised by relatively intense folding and the development of break back thrusts whereas low strain compartments are only weakly folded variations in hanging wall strain are attributed to selective reactivation of normal fault segments controlled by the pre inversion fault dip and lithological contrasts across the faults variation of the pre inversion fault dip is interpreted to have been caused by episodic tilt block rotation during crustal extension moderately dipping faults active early in the mount isa rift event show the greatest degree of reactivation whereas younger and steeper normal faults have behaved as buttresses during inversion with strain focussed in zones of upright folding in the hanging wall

recent volcanism in the puyehue cordon caulle region southern andes chile 40 5 s petrogenesis of evolved lavas

effective stratification for pseudoadiabatic ascent effective stratification can be interpreted as the resistance to upward motion of saturated air parcels experiencing condensation previously published expressions for effective stratification conflict with each other and the most widely distributed expression contains an o 1 error a derivation of effective stratification is presented that exposes its physical interpretation and that reveals the origin of the flaw in the incorrect derivation

precipitation over greenland retrieved by a dynamic method and its relation to cyclonic activity abstract in order to calculate the vertical motion over some high mountain regions such as greenland an equation without the quasigeostrophic approximation in coordinates has been developed a dynamic method for retrieving precipitation over greenland is based on this equation the retrieved annual mean precipitation distribution for 1987 and 1988 is in very good agreement with the observed annual accumulation pattern over the greenland ice sheet the major weather system producing precipitation over greenland is the frontal cyclone based on the precipitation characteristics greenland can be divided into five subregions precipitation over the north coastal and central interior regions primarily occurs in summer for the three other subregions if the composite monthly mean sea level pressure charts for high and low monthly precipitation amounts are constructed a clear relationship between precipitation and cyclonic activity emerges if a mean cyclone exists in the labrador sea heavy precipita

eruption dynamics of the 22 23 april 2015 calbuco volcano southern chile analyses of tephra fall deposits abstract after 54 years since its last major eruption in 1961 calbuco volcano ensenada southern chile reawakened with few hours of warning on 22 april 2015 at 18 05 local time the main explosive eruption consisted of two eruption pulses lasting 1 5 and 6 h each one on 22 and 23 april producing stratospheric 15 km height eruption columns the erupted materials correspond to porphyritic basaltic andesite 55 wt of sio2 the tephra fall affected mainly the area northeast of the volcano and the finest ash was deposited over southern chile and patagonia argentina we studied the tephra fall deposits of both pulses in terms of stratigraphy distribution volume emplacement dynamics and eruption source parameters here we show field observations that have been made 5 470 km downwind and distinguish five layers layers a b b1 c and d representing different stages of the eruption evolution eruption onset layer a pulse 1 followed by the first paroxysmal event layer b pulse 1 in some places interbedded by layer b1 tentatively representing the sedimentation of a secondary plume during the end of pulse 1 we recognized a second paroxysm layer c pulse 2 followed by the waning of the eruption layer d pulse 2 the total calculated bulk tephra fall deposit volume is 0 27 0 007 km3 0 11 0 13 km3 dense rock equivalent 38 of which was erupted during the first phase and 62 during the second pulse this eruption was a magnitude 4 45 event vei 4 eruption of subplinian type

dehydration melting and water saturated melting of basaltic and andesitic greenstones and amphibolites at 1 3 and 6 9 kb

calbuco volcano and minor eruptive centers distributed along the liquine ofqui fault zone chile 41 42 s contrasting origin of andesitic and basaltic magma in the southern volcanic zone of the andes calbuco volcano is a late pleistocene holocene composite stratovolcano located at 41 20 s in the southern region of the southern volcanic zone of the andes ssvz 37 46 s in contrast to basalt and basaltic andesite which are the dominant lava types on the volcanic front from 37 to 42 s calbuco lavas are porphyritic andesites which contain a wide variety of crustal xenoliths they have sio2 contents in the 55 60 range and have comparatively low k2o rb ba th and lref abundances relative to other ssvz centers incompatible element abundance ratios are similar to those of most ssvz volcanics but 87sr 86sr and 143nd 144nd are respectively higher and lower than those of adjacent volcanic centers basalts from nearby osorno stratovolcano 25 km to the northeast are similar to other basaltic ssvz volcanoes however basalts from several minor eruptive centers mec located east of calbuco and osorno volcano along the liquine ofqui fault zone lofz are enriched in ba nb th and lree and have higher la yb and lower ba la k la and rb la 87sr 86sr and 143nd 144nd in mec basalts are respectively lower and higher than those of osorno and calbuco lavas we suggest that mec basalts were produced by lower extents of mantle melting than basalts from osorno and other ssvz stratovolcanoes probably as a result of lower water content in the source of mec basalts calbuco andesites formed from basaltic parents similar to osorno basalts by moderate pressure crystallization of a hornblende bearing assemblage accompanied by crustal assimilation hornblende stability in the calbuco andesites was promoted by the assimilation of hydrous metasedimentary crustal rocks which are also an appropriate endmember for isotopic trends together with magma storage at mid crustal depths the unique characteristics of calbuco volcano i e the stability of hornblende at andesitic sio2 contents low 143nd 144nd and high 87sr 86sr and abundant crustal xenoliths provide evidence for crustal assimilation that is not apparent at more northerly volcanoes in the ssvz

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

petrology of the plio quaternary volcanism of the south central and meridional andes plio quaternary volcanoes lay upon a continental crust which is thick and of precambrian paleozoic age in the south central andes sca 18 28 s whereas it is relatively thin and of mesozoic cenozoic age in the meridional andes ma 32 42 s eleven calc alkaline volcanic massifs or groups of small volcanoes and two shoshonitic volcanoes have been studied in the sca eleven calc alkaline volcanic massifs have been studied in the ma one alkaline volcano has been approached in argentinian patagonia calc alkaline lavas are mostly andesites and dacites in the sca and high al basalts and basic andesites in the ma shoshonitic lavas are absarokites shoshonites and banakites no cognate xenoliths were found in the lavas the texture of the lavas is microlitic with abundant calc alkaline lavas or rare shoshonitic lavas phenocrysts distribution of phenocrysts opposes calc alkaline lavas of the sca with hornblende and biotite to those of the ma with olivine in calc alkaline lavas plagioclase is the most abundant mineral phase from high al basalts an90 to rhyolites an20 olivine is fo78 65 phenocrysts in basic lavas clinopyroxene ca mg rich augite and orthopyroxene bronzite show little compositional variation with lava differentiation amphibole is pargasitic or edenetic hornblende crystal clots which result from resorption of hornblende are found biotite is ti rich phenocrysts of quartz are found in rhyolites and rimmed by pyroxenes in basic lavas of the sca microlites of magnetite are ubiquitous and phenocrysts occur only in the sca in the sca geothermometers and geobarometers give the following results equilibration temperatures which decrease from 1000 c in andesites to 900 c in dacites h2o pressures vary between 1 and 4 kbar and oxygen fugacities are higher than the ni nio buffer basic lavas may have equilibrated at 50 km depth in shoshonitic lavas plagioclase and k feldspar are present olivine is fo85 phenocrysts and fo65 microlites clinopyroxene is cr rich orthopyroxene is bronzite in shoshonites microlites and banakites microlites and phenocrysts hornblende is pargasitic biotite is t rich in banakites conditions of differentiation of the lavas are high temperatures 850 1050 c water pressures inferior to 2 kbar oxygen fugacities above the ni nio buffer and total pressures which correspond to depths of 80 120 km major and trace element distributions emphasize differences between calc alkaline associations of the sca and ma and between calc alkaline and shoshonitic associations in shoshonitic lavas decreases in mgo and ni cao and cr al2o3 and sr correspond to respective olivine clinopyroxene and plagioclase fractionations incompatible elements circum pacific characteristics high al2o3 constant na2o3 increasing k2o with differentiation andean characteristics low cao and peculiar characteristics ma lavas have lower mgo olivine fractionation in the sca lavas have lower tio2 and feo fractionations of magnetite pyroxenes and hornblende the origin of the andean magmatism is not consistent with single stage models anatexis of continental crust crystal fractionation of basaltic magma under amphibolite or eclogite facies partial melting of peridotitic upper mantle material a three stage model is proposed the first stage consists of partial melting of upper mantle material loss in fluids of the subducted oceanic crust induces the melting bubbles of primary magma are generated the second stage consists of selective crustal contamination during the stay of the magma at the base of the continental crust the third stage consists of low pressure crystal fractionation which governs the differentiation of the lava series the present model considers transversal and longitudinal zonation of the andes high degrees of melting low rate of contamination and reduced crystal fractionation characterize the ma whereas low degrees of melting high rate of contamination and considerable crystal fractionation characterize the sca garnet is involved in the genesis of shoshonitic lavas

combined sr o isotope relationships and petrogenesis of andean volcanics of south america active andesitic type volcanism in the southern andes lat 42 36 s is characterized by low sr and o isotopic compositions which fall in the range 87sr 86sr 0 7036 0 7043 18o 5 2 6 8 in contrast volcanic centres in the central andes lat 24 21 s are significantly enriched in both 87sr and 18o we present the first combined sr and o isotope study of the southern volcanic zone svz in chile crustal thickness 40 km 1 and of the southern part of the central volcanic zone cvz in the borderlands of bolivia chile and argentina crustal thickness 60 70 km 1 only one of 13 volcanic centres studied lascar exhibits a correlated increase in both 87sr and 18o parallel with the basalt andesite rhyolite compositional change indicative of contamination by upper crust through a fractional crystallization assimilation mechanism the other centres of the cvz for which there is an overall sr o correlation document the variable contamination of mantle derived magmas at depth in the lower crust which had been thickened by mesozoic and earlier plutonism

water saturated and undersaturated melting of metaluminous and peraluminous crustal compositions at 10 kb evidence for the origin of silicic magmas in the taupo volcanic zone new zealand and other occurrences

reply to comment on crustal contributions to arc magmatism in the andes of central chile by w hildreth and s moorbath

crustal sources involved in continental arc magmatism a case study of volcan mocho choshuenco southern chile volcan mocho choshuenco a pleistocene holocene basaltic andesite to dacite shield volcano located at lat 40 s in the southern volcanic zone svz of the andes is built on the thinnest svz continental crust 30 km which consists largely of paleozoic sedimentary and metamorphic rocks and mesozoic plutons sr pb nd and o isotopic ratios of mocho choshuenco lavas 87 sr 86 sr 0 70399 to 0 70422 206 pb 204 pb 18 57 to 18 61 207 pb 204 pb 15 60 to 15 63 208 pb 204 pb 38 45 to 38 57 143 nd 144 nd 0 512787 to 0 512881 18 o 5 8 to 6 8 standard mean ocean water are similar to those of other svz centers and exhibit no correlation with indices of differentiation however incompatible trace element systematics indicate that evolved lavas have been contaminated by crustal plutonic rocks by 5 to 15 rb ba k ba rb la and k la ratios increase with increasing sio 2 content as a result of assimilation of orogenic calc alkalic plutonic rocks enriched in rb and k relative to ba and la xenoliths of plutonic rocks recovered from mocho choshuenco lavas are slightly more radiogenic in 87 sr 86 sr less radiogenic in 143 nd 144 nd and comparable in pb isotopic ratios and they have variable 18 o contents 87 sr 86 sr 0 70482 to 0 70557 206 pb 204 pb 18 60 to 18 64 207 pb 204 pb 15 60 to 15 62 208 pb 204 pb 38 53 to 38 56 143 nd 144 nd 0 512686 18 o 3 3 to 5 5 smow contamination of mocho choshuenco parental magmas by crustal melts with small isotopic contrast imposed little variation on isotopic heterogeneities existing in the parental compositions these heterogeneities probably were produced during magma crust interaction at the crust mantle boundary or in the lower crust

an early autumn polar low formation over the norwegian sea around october 15 1993 an unusual polar low formation took place over the norwegian sea the evolution is studied by means of the hirlam forecasting model at the danish meteorological institute satellite imagery and observations the investigation to some extent based on generalized forms of the equations for omega and geopotential tendency reveals that the disturbance forms initially by baroclinic instability along a frontal zone within a maritime polar air mass and in close proximity of an intense extratropical cyclone during its growth to a polar low air sea interaction seems to work in conjunction with the baroclinic process a parallel forecast with the latent heat set to zero shows that heating of the atmosphere associated with precipitation is necessary for the polar low formation

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

geochemical variations in andean basaltic and silicic lavas from the villarrica lanin volcanic chain 39 5 s an evaluation of source heterogeneity fractional crystallization and crustal assimilation at 39 5 s in the southern volcanic zone of the andes three pleistocene recent stratovolcanoes villarrica quetrupillan and lanin form a trend perpendicular to the strike of the andes 275 to 325 km from the peru chile trench basalts from villarrica and lanin are geochemically distinct the latter have higher incompatible element abundances and la sm but lower ba la and alkali metal la ratios these differences are consistent with our previously proposed models involving a a west to east decrease in an alkali metal rich high ba la slab derived component which causes an across strike decrease in degree of melting or b a west to east increase in the contamination of subduction related magma by enriched subcontinental lithospheric mantle silicic and mafic lavas from the stratovolcanoes have overlapping sr nd and o isotopic ratios silicic lavas also have geochemical differences that parallel those of their associated basalts e g rhyolite from villarrica has lower la sm and incompatible element contents than high sio2 andesite from lanin at each volcano the most silicic lavas can be modelled by closed system fractional crystallization while andesites are best explained by magma mixing apparently crustal contamination was not an important process in deriving the evolved lavas basaltic flows from small scoria cones 20 35 km from villarrica volcano have high incompatible element contents and low ba la like lanin basalts but trend to higher k rb 356 855 and lower 87sr 86sr 0 70361 0 70400 than basalts from either stratovolcano however all basalts have similar nd pb and o isotope ratios the best explanation for the unique features of the cones is that the sources of svz magmas e g slab derived fluids or melts of the subcontinental lithospheric mantle have varying alkali metal and radiogenic sr contents these heterogeneities are not manifested in stratovolcano basalts because of extensive subcrustal pooling and mixing this model is preferable to one involving crustal contamination because it can account for variable sr isotope ratios and uniform nd and pb isotope ratios among the basalts and the divergence of the cones from across strike geochemical trends defined by the stratovolcanoes

new age controls on the tephrochronology of the southernmost andean southern volcanic zone chile the chronology of over 50 tephra layers preserved in a lake sediment core from laguna la trapananda llt in the southern portion of the andean southern volcanic zone ssvz chile is constrained by new radiocarbon age determinations which span the period from late pleistocene glacial retreat to the late holocene the tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the ssvz volcanoes mentolat hudson maca and potentially cay the new age determinations are used to estimate the ages of the 50 tephra in the llt core as well as those from the other previously described lake cores in the area by a bayesian statistical method the results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost ssvz they indicate that there was essentially no increase in the rate of eruptions from late glacial to recent times due to deglaciation they also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic paleoecologic archaeologic and tephrochronologic studies in central patagonia

cyclolysis a diagnosis of two extratropical cyclones abstract this paper presents a diagnosis of the slow decay of two extratropical cyclones that occurred over the central united states in march and november 1999 results reveal that vertical superposition of the cyclone and upper level troughs is not required for cyclone decay to occur in both cases decay commenced while the upper level trough was still upstream from and thus upper level cyclonic vorticity was present above the cyclone failure of the upstream tilt in both trough systems to yield cyclone intensification was attributed largely to the advection of cold air primarily at lower to middle levels into each cyclone s interior also of interest is the fact that latent heat release also contributed to the decay of both cyclones this latter result was a consequence of the location of the cyclones in the outer portion of their respective heating regions finally more rapid decay of the two cyclones was prevented by middle and lower tropospheric adiabatic warming that occurred in the statical

tropopause undulations and the development of extratropical cyclones part ii diagnostic analysis and conceptual model abstract a case study of a developing cyclone is used to show that the three dimensional distribution of height change during development can be strongly sensitive to temperature changes which occur in the lower stratosphere in association with an evolving tropopause undulation quantitative analysis of the storm with a geopotential height tendency equation indicates that a synergistic process developed between the stratosphere and troposphere whereby the vertical motion pattern maintained and intensified the upper level temperature anomalies while the subsequent upper level temperature advection led to an enhanced vertical circulation using the results of this diagnostic study a conceptual model is constructed the conceptual model is based on the hydrostatic and wind field adjustments that occur as tropopause undulations propagate over favored regions of tropospheric warm advection and less stable air

comment on crustal contributions to arc magmatism in the andes of central chile by w hildreth and s moorbath in their paper crustal contributions to arc magmatism in the andes of central chile hildreth and moorbath conclude that the stratovolcanos forming the volcanic front at the northern end between 33 37 5 s of the southern volcanic zone svz 33 46 s of the andes show along arc changes in isotopic and elemental ratios that demonstrate a northward increase in crustal contributions to magma genesis stern et al 1984a b futa and stern 1988 and stern 1988 previously reached this same conclusion by comparing the chemistry of three of the northernmost volcanos in the svz between 33 34 s with those from south of 36 s however the processes by which crustal components are incorporated in andean magmas and specifically what is causing crustal components to be incorporated in increasing amounts in the magmas erupted at the northern end of the svz remain controversial with regard to andean volcanism in general hildreth and moorbath suggest that although the principal magma source is presumed to lie within the mantle wedge fluxed by a slab derived contribution the base level isotopic and chemical values for each volcano are established by blending of subcrustal and deep crustal magmas in zones of melting assimilation storage and homogenization mash at the mantle crust transition they further suggest that the along arc changes in isotopic and elemental ratios observed at the northern end of the svz are due to changing composition age and most significantly increased proportional contribution of the lowermost crust in conjunction with increased depth to the mash zone as the crust thickens northward below the volcanic front in contrast stern et al 1984a futa and stern 1988 and stern 1988 1991 argue that the distinctive petrochemical characteristics of the volcanoes at the northernmost end of the svz reflect a northward change in the composition and amount of continental components subducted into the mantle source region hildreth and moorbath s preference for intra crustal upper plate influence on the along arc variations in magma chemistry at the northern end of the svz appears to be based on both geological and geochemical arguments that i find in many cases debatable i discuss these separately below followed by a brief comment on the relative effectiveness of lower crustal mash versus mantle source region contamination processes in explaining along arc chemical variations observed in andean magmas

attribution and its application to mesoscale structure associated with tropopause folds it is important in meteorology to be able to establish a link between various features this link in its strongest form would be referred to as cause and effect but this is extremely difficult to establish for atmospheric flows a weaker but nonetheless powerful link is attribution which attempts to provide a way to associate various fundamental features such as potential vorticity anomalies to weather events involving regions of ascent attribution is not new and it is implicit in the way that atmospheric evolution is usually described in this paper an attempt is made to define more precisely what are the steps and assumptions being made in such a method these ideas become more concrete by applying them to a simple model of a two dimensional front at which there is a tropopause fold the aim is to find the vertical motion attributable to the descended tropopause fold in an extra tropical cyclone this is the first step in a longer programme of research designed to provide a test of the hypothesis that such a descended tropopause can trigger mesoscale phenomena such as convection and cyclones

structure and evolution of subtropical cyclone anita as evaluated by heat and vorticity budgets this paper explores the evolution of subtropical cyclone anita which occurred near the east coast of brazil 19 s 37 w in march 2010 thermodynamic and dynamic processes during anita s lifecycle are investigated using the heat and vorticity budget equations the cyclone developed with hybrid characteristics and moved anomalously to the southwest where it coupled with an upper level cut off low during the mature phase this coupling was the main dynamical mechanism for further cyclone deepening anita then remained quasi stationary about 30 s 47 w for two days due to an upper level dipole pattern which prevented earlier displacement of the upper level low counterpart when the dipole pattern dissipated the cyclone moved southeast and underwent extratropical transition whilst merging with a mid latitude frontal cyclone diabatic heating and horizontal temperature advection are found to be essential for the subtropical development during extratropical transition it is instead diabatic cooling together with adiabatic cooling and warm air advection that act as the main mechanisms to influence the local temperature tendencies at low levels low level cyclonic tendencies were mostly due to convergent flow and the residual vorticity partially destroyed the vorticity tendencies produced by the divergence term moreover in regions and levels where convection could explain some of the vorticity tendencies it is found that apparent sinks of cyclonic vorticity were related to negative vorticity due to divergence i e convergent flow whilst apparent sources were related to positive vorticity due to divergence i e divergent flow

postseismic coastal uplift in southern chile tide gage records at puerto montt referenced to a mareograph in talcahuano indicate a large at least 75 cm postseismic uplift of the region following the 1960 mw 9 5 event field observations carried out in 1989 at the same locations of previous measurements in 1968 are consistent with tide gage records the postseismic elevation changes are modeled as the result of propagating creep on the downdip extension of the coseismic fault for a 30 e fault dip minimum square error indicates a fault creep velocity of 4 6 km yr and slip amplitude of 3 5 m