the north pacific as a regulator of summertime climate over eurasia and north america abstract the role of the north pacific as a regulator of boreal summer climate over eurasia and north america is investigated using observational data two summertime interannual climate modes associated with sea surface temperature sst variability in the north pacific are identified the first mode shows an elongated zone of warm cold sst anomalies in the central north pacific along 40 n with temporal variability significantly correlated with el nino during the preceding spring but its subsequent evolution is quite different from el nino the second mode exhibits a seesaw sst variation between the northern and southern north pacific and is independent of el nino both modes are linked to coherent sst anomalies over the north atlantic suggesting the presence of an atmospheric bridge linking the two extratropical oceans using the principal component of the most dominant mode as the north pacific index npi composite analyses show that the positive negative phase of npi features a warm cold

mineralogical and isotopic evidence for phenocryst matrix disequilibrium in the garner mountain andesite petrographic trace element and isotopic evidence demonstrates that magma mixing preceded the eruption of the garner mountain andesite the flow contains reversely zoned plagioclase phenocrysts and amphibole pseudomorphs composed of plagioclase clinopyroxene orthopyroxene and opaque oxides partially resorbed quartz grains are also present in contrast to the isotopically uniform matrix plagioclase phenocrysts have 87sr 86sr ratios that correlate negatively with matrix sr and positively with matrix rb abundances these observations demonstrate increasing isotopic disequilibrium between the plagioclase and matrix in the more evolved varieties of the flow

the large scale horizontal structure of the antarctic circumpolar current from fgge drifters the last decade of research in the southern ocean has shown that the antarctic circumpolar current acc is a complex system composed of narrow high speed currents separated by broad quiescent zones the circumpolar nature of this structure was examined using position and velocity data obtained from approximately 300 surface drifting buoys deployed in the southern ocean during the first garp global experiment fgge the distribution of buoys on 1 1 squares shows that in some regions most notably south of australia the buoys form three coherent bands of high buoy density which are separated by regions of low buoy density the latitudes of these bands coincide with those of the subtropical front subantarctic front and polar front to further examine the relationship between these fronts and buoy distribution locations of the three fronts determined from historical hydrographic data were used to partition the buoys into zonal bands corresponding to front and nonfront regions a mean buoy density and mean near surface speed were then computed for each zonal band high buoy densities were associated with all three fronts in the region south of australia other regions also showed a tendency although not as pronounced for buoys to accumulate in fronts the mean near surface speeds suggest that the subantarctic and polar fronts are circumpolar moreover the mean near surface speeds associated with the three frontal regions differ speeds within the subantarctic and polar front regions are approximately twice that associated with the subtropical front

blocking highs over asia and monsoon droughts over india severe summer droughts of the indian subcontinent have been found to accompany prolonged breaks in the south west monsoon data from the years of severe drought suggest that the associated breaks were due to upper tropospheric blocking ridges over east asia we present here a model for the evolution of two such blocking ridges the east asia eabr and the west asia wabr apparently an intense wabr the initiator of the monsoon break precedes the formation of the eabr this cycle could be a way of predicting years of intense drought or monsoon activity

classification seasonality and persistence of low frequency atmospheric circulation patterns abstract orthogonally rotated principle component analysis rpca of northern hemisphere 1 month mean 700 mb heights is used to identify and describe the seasonality and persistence of the major modes of interannual variability the analysis is detailed and comprehensive in that 1 a high resolution approximately equal area 358 point grid is used for the virtually maximum possible 35 year period of record 2 a positive bias in the nmc data base in the early 1950s in the subtropics is largely eliminated for the first time and 3 homogeneous separate analyses of each month of the year are carried out detailing the mouth to month changes in the dominant circulation patterns winter results are similar to those of other recent rpca and teleconnection studies except that some less obvious patterns are identified and further detail of the better known patterns is provided two north south dipole patterns are found over the pacific ocean west pacific oscillation and east pacific pattern and over the atla

satellite tracked drift buoy observations of the near surface flow in the eastern mid latitude north pacific the surface and near surface 30 m currents of the eastern mid latitude pacific obtained from 32 satellite tracked drifting buoys during the period june 1976 through august 1977 are discussed these observations of oceanic currents are merged with and are compared to fleet numerical weather center s daily estimates of surface winds for the same period statistical comparisons of these data sets reveal that the drifters move systematically approximately 30 to the right of the surface wind at approximately 1 5 of the wind speed this relationship between drifter movement and surface winds occurs during the entire period except for the summer months of 1976 when independent of the surface winds the buoy trajectories indicate mesoscale eddy motions with 100 km and 30 day time and space scales respectively drifter liftimes exceeded that of the 9 m diameter parachute drogues set at 30 m depth thus enabling a comparison of the currents derived from the drifter motions at the surface and 30 m these comparisons reveal no systematic difference in the drifter motions with and without drogues these results suggest a rather uniform flow in the upper 30 m during periods of steady winds the estimates of the nature of near surface currents obtained from the drifters differ from those predicted by ekman s classical theory of wind driven flow in that there is no evidence of either a reduction in speed or change in direction of the currents over the upper 30 m

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

surface circulation and kinetic energy distributions in the southern hemisphere oceans from fgge drifting buoys abstract trajectories of approximately 300 satellite tracked drifting buoys deployed throughout the southern hemisphere oceans during the fiat garp global experiment fgge have been analyzed to infer the mean surface circulation and kinetic energy distributions of the surface flow the resulting picture of mean surface circulation is consistent with expectations based on compilations of historical observations of currents and the density field the distribution of kinetic energy of the mean flow is highly zonal in character with high values in the persistent zonal flows of the antarctic circumpolar current and the south equatorial currents and low values in the broad intervening zone using statistics based on 5 squares the western boundary currents do not emerge as dominant features of the mean flow on the other hand these currents do appear to be a major source of eddy kinetic energy most eddy kinetic energy appears to be due to fluctuations with periods less than one month both mean and eddy kin

baroclinic volume transport in the southern ocean abstract a new map of the baroclinic volume transport to 3000 m has been produced for the southern ocean making use of all available historic hydrographic data in the area the map complements the geopotential height anomaly map of gordon et al 1978 the construction of the transport map was facilitated by the strong vertical coherence of the flow found for the whole ocean area

the summertime annular mode in the northern hemisphere and its linkage to the winter mode 1 the seasonal variations of the northern hemisphere annular mode nam are investigated through empirical orthogonal function analysis of the zonally averaged geopotential height fields for each individual calendar month patterns of the winter and summer nams differ not only in the geopotential height fields but also in the mean meridional circulation and eddy structure the summer nam has a smaller meridional scale and is displaced poleward as compared to the winter nam the antinode on the lower latitude side in the summer nam is at the nodal latitude of the winter nam the summer nam is more strongly related to surface air temperatures over eurasia than the original arctic oscillation the summer nam is a wave driven internal atmospheric mode that is maintained by both stationary and transient waves the summer nam is associated with the arctic front polar jet and storm track around the arctic ocean the winter to summer linkage described by m ogi et al can be interpreted as a preferred transition from one polarity of the winter annular mode to the same polarity of the summer annular mode the spring cryosphere i e snow in eurasia and sea ice in the barents sea plays a supporting role in this transition index terms 1620 global change climate dynamics 3309 3309 meteorology and atmospheric dynamics climatology 1620 3319 meteorology and atmospheric dynamics general circulation 3349 meteorology and atmospheric dynamics polar meteorology keywords northern hemisphere s annular mode arctic oscillation winter to summer link

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

processes of multibathyal aragonite undersaturation in the arctic ocean during three years of study 2010 2012 the western arctic ocean was found to have unique aragonite saturation profiles with up to three distinct aragonite undersaturation zones this complexity is produced as inflow of atlantic and pacific derived water masses mix with arctic derived waters which are further modified by physiochemical and biological processes the shallowest aragonite undersaturation zone from the surface to 30 m depth is characterized by relatively low alkalinity and other dissolved ions besides local influence of biological processes on aragonite undersaturation of shallow coastal waters the nature of this zone is consistent with dilution by sea ice melt and invasion of anthropogenic co2 from the atmosphere a second undersaturated zone at 90 220 m depth salinity 31 8 35 4 occurs within the arctic halocline and is characterized by elevated pco2 and nutrients the nature of this horizon is consistent with remineralization of organic matter on shallow continental shelves bordering the canada basin and the input of the nutrients and co2 entrained by currents from the pacific inlet finally the deepest aragonite undersaturation zone is at greater than 2000 m depth and is controlled by similar processes as deep aragonite saturation horizons in the atlantic and pacific oceans the comparatively shallow depth of this deepest aragonite saturation horizon in the arctic is maintained by relatively low temperatures and stable chemical composition understanding the mechanisms controlling the distribution of these aragonite undersaturation zones and the timescales over which they operate will be crucial to refine predictive models this article is protected by copyright all rights reserved

a complex magma mixing origin for rocks erupted in 1915 lassen peak california the eruption of lassen peak in may 1915 produced four volcanic introduction rock types within 3 days and in the following order 1 hybrid magma mixing is an important process among interblack dacite lava containing 2 undercooled andesitic inclusions mediate magmas in volcanic arcs e g turner 3 compositionally banded pumice with dark andesite and light campbell 1986 philpotts 1990 and references therein dacite bands and 4 unbanded light dacite all types represent laboratory studies of synthetic analogs of silicate magma stages of a complex mixing process between basaltic andesite systems and mathematical modeling of mixing viscous and dacite that was interrupted by the eruption they contain liquids have suggested a range of possible mixing mechdisequilibrium phenocryst assemblages characterized by the coanisms e g cashman bergantz 1991 however use existence of magnesian olivine and quartz and by reacted and of these results to interpret magmatic systems is limited unreacted phenocrysts derived from the dacite the petrography and by the applicability of synthetic analogs to magmatic crystal chemistry of the phenocrysts and the variation in rock conditions and by the imprecise knowledge of the effective compositions indicate that basaltic andesite intruded dacite magma viscosity of silicate liquid crystal mixtures at magmatic and partially hybridized with it phenocrysts from the dacite magma temperatures and pressures if magmas mix incompletely were reacted cooling crystallization and vesiculation of the hybrid i e mingle features such as compositional banding or andesite magma converted it to a layer of mafic foam the decreased undercooled inclusions are usually apparent but if they density of the andesite magma destabilized and disrupted the foam mix completely mineralogical disequilibrium may be the blobs of foam rose into and were further cooled by the overlying dacite magma forming the andesitic inclusions disaggregation of only direct evidence for a mixing origin andesitic inclusions in the host dacite produced the black dacite and if the thermal and compositional contrasts between light dacite magmas formation of foam was a dynamic process two magmas are great and the ratio of silicic to mafic removal of foam propagated the foam layer downward into the magma is large there is little interaction between them hybrid andesite magma eventually the thermal and compositional and the mafic magma is undercooled e g bacon 1986 contrasts between the hybrid andesite and black dacite magmas were many undercooled inclusions contain reacted phereduced then they mixed directly forming the dark andesite magma nocrysts inherited from their host silicic magma heiken about 40 50 andesitic inclusions were disaggregated into the eichelberger 1980 and bacon 1986 pointed out host dacite to produce the hybrid black dacite thus disaggregation that undercooled inclusions are typically formed from of inclusions into small fragments and individual crystals can be hybrid magmas in general the formation of undercooled an efficient magma mixing process disaggregation of undercooled inclusions retards further mixing sakuyama 1984 inclusions carrying reacted host magma phenocrysts produces cothompson dungan 1985 sparks marshall 1986 existing reacted and unreacted phenocryst populations koyaguchi blake 1991 however fragmentation and or disaggregation of undercooled inclusions plays an important role in hybridization in some magma systems thompson dungan 1985 coulon et al 1986 clynne christiansen 1987 clynne 1989 linneman myers

rossby wave propagation and teleconnection patterns in the austral winter abstract observational evidence of and theoretical support for the northern and southern hemisphere teleconnection patterns in the austral southern hemisphere winter are examined through an upper troposphere streamfunction teleconnectivity map and time lag cross correlation analysis using ecmwf initialized analysis 2oo hpa winds for the 11 june august periods from 1979 to 1989 as was previously found for the northern hemisphere winter the regions of strong teleconnectivity particularly in the winter hemisphere tend to he oriented in the zonal direction and coincide with the location of the major jet streams although equatorward propagation from the northern and southern hemispheres is observed little evidence of cross equatorial propagation has been found for comparison the response of a barotropic model linearized about a climatological 300 hpa june august time mean flow to localized forcing is determined it is found that the activity tends to be trapped inside each of the southern hemisphere

micro scale heterogeneity of andesite from chilungshan northern taiwan evidence from melt inclusions geochronology and hf o isotopes of zircons abstract the chilungshan andesite belongs to the chilung volcano group in northern taiwan and constitutes the western end of the island chains of the ryukyu arc chemically it is a normal medium k calc alkaline andesite shrimp dating of magmatic zircons yielded an emplacement 206 pb 238 u age of 1 04 0 06 ma with e hf t of 6 1 to 13 4 and 18 o of 5 02 to 6 28 the zircons contain inherited cores and felsic to andesitic silicate melt glass inclusions besides apatite quartz k feldspar biotite garnet fe mg minerals pyroxene or hornblende and plagioclase with variable an values plagioclase phenocrysts also contain quartz k feldspar and felsic melt inclusions this study confirms the presence of micro scale heterogeneity in the andesite as a result of mixing between mantle derived and continental material contamination of continental crust occurs either within the magma chamber at a medium to deep crustal level and or during dehydration and melting of a subducted oceanic slab and overlying sediments in an island arc environment

sub solidus dehydration of amphiboles in an andesitic magma several petrologic experiments have demonstrated that in igneous and metamorphic reactions amphibole minerals can break down by a subsolidus dehydration reaction but evidence for the reaction in natural rocks has been lacking evidence for the breakdown of an edenite pargasite amphibole by a subsolidus dehydration reaction has now been found in an andesite flow from garner mountain southern cascase range the andesite contains one modal percent of crystal clots formed of crystallites of opx cpx plag k spar opaque and quartz the crystal clots retain the original amphibole morphology and intra clot pyroxenes are aligned with crystallographic c parallel to c in the amphibole precursor these conditions would not be duplicated by a melting reaction microprobe analyses of the bulk clot and the intra clot minerals suggest the solid state reaction 100 amph 10 sio2 55 cpx 33 plag 22 opx 1 opq 1 kspar pyroxene thermometry of the andesite groundmass pyroxenes and the intra clot pyroxenes demonstrates that the amphibole dehydration reaction occurred in the xenocrystic amphiboles as a result of heating by the near solidus andesite magma

generation and evolution of a cyclonic ring at drake passage in early 1979 abstract an equatorward meander in the antarctic polar front at drake passage was observed to amplify and pinch off during january and early february 1979 forming a cold core cyclonic current fins with a radius of 50 km this ring appeared to move directly across the passage parallel to a submarine ridge before turning northeastward upon reaching a gap between the ridge and the south american continental rise its net motion was across the polar frontal zone and the ring was last observed to be pushing through the subantarctic front geostrophic surface speeds of up to 90 cm s 1 relative to 3500 m wore observed where the northern sector of the ring and the subantarctic front were in proximity a stability analysis of the banded flow regime across drake passage suggests that necessary conditions for baroclinic instability exist everywhere within the zonal current and those for barotropic instability exist adjacent to the fronts the beat and salt anomalies of this ring relative to the polar frontal zone

the subantarctic and polar fronts in relation to deep water masses through the southwestern atlantic the two principal fronts within the antarctic circumpolar current acc the subantarctic front saf and the polar front pf are investigated with respect to their spatial patterns and relations to deep water masses from the northern drake passage to the western and southern argentine basin observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters east of drake passage the width of the polar frontal zone pfz increases rapidly when the saf turns sharply northward as a part of the falkland malvinas current while the pf remains oriented mainly toward the northeast found within this region of the pfz are mesoscale eddies the upper layers of which consist of subantarctic mode water from the pacific the contrasts in upper layer water properties that identify the saf can be traced the entire length of the falkland current to the brazil falkland confluence zone and then southward to the southern argentine basin there the saf turns eastward and later but perhaps not always merges with the pf north of ewing bank to form a single intense current core strongly influenced by bottom topography at times this eastward current loops southward through a gap in the falkland ridge into the georgia basin thereby supplying relatively warm and salty subantarctic water to the antarctic zone east of the gap the two fronts become separated and are once again distinct features in the vicinity of the islas orcadas rise at depth within drake passage and the western scotia sea the saf and pf are not lateral boundaries between distinct water masses but are instead identified by enhanced vertical displacements of property isopleths with the northward turn of the saf east of drake passage a thick layer of circumpolar deep water cdw is advected over the falkland plateau into the argentine basin there it is joined by waters entering the argentine basin via a deep spreading route through the georgia basin denser cdw deep water from the weddell sea and episodically deep water from the southeastern pacific ocean together these waters form a northward flow off the patagonian shelf that extends from the sea surface to the bottom most of which turns back toward the south with the falkland current return also flowing south along the seaward side of the falkland current return well away from the western boundary is the main core of north atlantic deep water nadw detatched masses of nadw are observed within the cdw at the western boundary as well as within the acc south of the saf in the south central argentine basin

drifter trajectories through a current meter array at drake passage six low profile undrogued buoys drifted through the drake passage during 1979 where an extensive array of current meters was moored geostrophic currents at the buoy positions are estimated by extrapolating the shallow 40 hour low pass filtered current measurements to the surface by using vertical shear relationships derived from hydrographie stations taken over a 5 year period within the passage the buoy tracks are also filtered followed by the removal of the extrapolated geostrophic currents the residual drifts are then compared with the 10 m winds which are estimated twice daily by applying the similarity theory for a neutral barotropic boundary layer to sea level atmospheric pressure fields the residual drifts are found to respond within a few hours to variations in the wind buoy motions against the interior flow persisting for as long as 6 days along with loops and reversals which are not observed in the subsurface currents are well accounted for by the wind during times of nearly steady wind conditions the residual drift is found to average 3 4 1 4 of the 10 m wind speed at 25 0 12 0 to the left of the wind