sea ice motion in response to geostrophic winds it is an old rule of thumb that sea ice moves with a speed of about 2 of the surface wind and about 45 to the right of the wind a similar relationship between the ice velocity and the geostrophic wind is examined here it is found that only about half of the long term several month average ice motion is directly related to the geostrophic wind the other half being due to the mean ocean circulation on shorter time scales and in all seasons more than 70 of the variance of the ice velocity in the central arctic ocean is explained by the geostrophic wind within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion the spatial variations in ice velocity are also partly explained by the geostrophic wind about half of the variance in the large scale ice vorticity and shear are accounted for on the other hand none of the large scale ice divergence can be explained by the wind the long term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

ablation of avalanched and undisturbed snow himalaya mountains pakistan avalanche deposits represent a significant storage of winter snow on the south slope of the himalaya mountains pakistan complicating the annual snowmelt cycle because of the differences in ablation of avalanche transported snow and undisturbed snow measurements show very high rates of melting of both snow types particularly of avalanche snow late in the melt season the high rates are a function of the low latitude of the study area and the low elevation of the avalanche snow deposits as well as heat release by condensation air temperature was closely correlated with daily snowmelt and appears to hold promise as a predictor however data constraints prevent an energy balance analysis of this relationship gravimetric measurements show that condensation is important in the snow surface energy exchange and can represent a significant source of energy for snowmelt rainfall during warm conditions also makes a more significant contribution to snowmelt than shown in previous studies the derived temperature based melt factors or coefficients compare well with published figures from other mountain areas but their confidence limits are sufficiently wide to produce significant errors in the prediction of basin snowmelt runoff

retrograding wintertime low frequency disturbances over the north pacific ocean abstract retrograding westward moving features over the middle and high latitudes of the northern hemisphere during winter are examined in observations and data from a gcm simulation using complex principal component analysis the first eigenvector of the low frequency middle troposphere geopotential height over the north pacific has a zonal scale of 120 160 deg longitude and a dipole like meridional structure with maximum amplitude over the gulf of alaska and the bering sea these disturbances propagate westward and go through a life cycle of growth and decay over a period of about three weeks the temporal evolution of the energy and its conversions during the life cycle of the simulated pacific disturbances are composited using the time dependent coefficient of the principal component analysis as an index for their occurrence the composite energy cycle indicates that the kinetic and available potential energy of these disturbances grow and decay together both baroclinic and barotropic conversion

the pinal schist southeast arizona usa contraction of a palaeoproterozoic rift basin the palaeoproterozoic pinal schist of southeast arizona comprises mainly greenschist facies turbiditic metasedimentary rocks with associated volcanic rocks the deformation history of the pinal schist includes foliation and elongation lineation development within sedimentary protoliths during early basin contraction followed by gentle warping of the metamorphosed sediments into upright regional scale horizontal folds with 10 km wavelengths continued contraction caused development of shear zones approximately parallel to anticlinal axial surfaces and syn kinematic granitic rocks intruded into anticlinal cores such shear zones occur throughout southeast arizona in the turbiditic rocks of the pinal schist as well as in rocks of more continental character associated with the tonto basin supergroup in the mazatzal mountains it is proposed that shear zone distribution in both the pinal schist and the adjacent tonto basin supergroup reflects control by a pre existing rift margin the pinal schist and tonto basin supergroup therefore represent distal and proximal rift margin facies respectively reactivation of early extensional faults as reverse shear zones during margin contraction controls shear zone distribution in southeast arizona with deformation character changing from ductile to brittle with shallowing crustal level this model explains shear zone and lithological distribution and deformational style in southeast arizona and it also implies a continuum of sediment deposition and deformation throughout this part of the mazatzal orogeny

the link between the north atlantic oscillation and arctic sea ice export through fram strait abstract recently hilmer and jung have shown that the wintertime link between the north atlantic oscillation nao and the sea ice export through fram strait changed from zero correlation 1958 77 to about 0 7 1978 97 during the last four decades in the current study the authors focus on the question of how the two phenomena are linked in a long term context during wintertime december march this is done on a statistical basis using data from a century scale control integration of the coupled general circulation model echam4 opyc3 along with historical sea level pressure data for the period 1908 97 from the results of this study there is less indication that a significant link on interannual and decadal timescales between the nao and the sea ice export through fram strait is a characteristic property of the climate system at least under present day climate conditions this missing link can be explained by a vanishing net impact of the nao on sea ice thickness as well as sea ice drift near fram st

the pinal schist of southern arizona a paleoproterozoic forearc complex with evidence of spreading ridge trench interaction at ca 1 65 ga and a proterozoic arc obduction event the pinal terrane of southern arizona is composed mostly of quartz sericite schists meta wackes metavolcanic rocks and granitoid and gneissic rocks with minor meta chert meta conglomerate and carbonate rocks various tectonic settings have been suggested for the origin of this terrane the existence of tectonic melanges within the terrane the presence of granitic rocks in close proximity to the melanges the presence of both oceanic and arc like metavolcanic rocks within the terrane the age distributions of igneous and meta igneous rocks within the terrane the deformational patterns within the terrane and the width of the terrane all support a model in which the terrane was formed as a forearc subduction complex that experienced a ridge subduction event at ca 1 65 ga the pinal terrane was likely the forearc subduction complex to the mazatzal arc terrane which lies immediately to the north regional variations in the mineralogy of metavolcanic and metasedimentary rocks exposed within the terrane together with structural data suggest the terrane may have experienced an arc obduction event in the proterozoic after the ridge subduction event if it did most of this arc terrane was eroded off the pinal terrane in the 300 m y following the obduction event and prior to deposition of the apache group at ca 1 32 ga there is a paleoproterozoic arc terrane exposed in northern mexico that may represent remnants of an obducted arc terrane high pressure high temperature metamorphic rocks e g blueschists have not been identified within the pinal terrane

sea ice velocity in the fram strait monitored by moored instruments 1 the fram strait sea ice velocity was measured by means of a new method using moored doppler current meters in the period 1996 2000 almost 3 years of ice velocity observations near 79 n 5 w are analyzed the average southward ice velocity was 0 16 m s the correlation between the ice velocity and the cross strait sea level pressure slp difference was r 0 76 for daily means and r 0 79 for monthly means the same cross strait slp difference exhibits a positive trend since 1950 of 10 of the mean per decade by a simple linear model we compute mean sea ice area flux to 850 000 km2 year for the period 1950 2000 ice thickness monitored by means of upward looking sonars since 1990 is also discussed the combined data gave a monthly ice volume flux of 200 km3 during the last decade with no significant trend

characteristics of winter cyclone activity in the northern north atlantic insights from observations and regional modeling 1 fields from the ncep ncar reanalysis are used in conjunction with simulations from polar mm5 to examine regional processes contributing to cyclone development in the sub arctic arctic sector of the north atlantic strong deepening of systems 6 hpa 6 hours is especially common south of the tip of greenland and in the vicinity of the mean icelandic low il a secondary maximum is located just south of svalbard composite analyses of strongly deepening systems in these areas point to the influence of pronounced preexisting low level temperature gradients linked to ocean currents the sea ice margin and ocean land contrasts the area of preferred deepening near svalbard corresponds to the northernmost penetration of open water in the north atlantic impacts of greenland s orography are prominent in the synoptic complexity of the region typical synoptic situations examined as case studies include splitting or bifurcation of cyclones at the southern tip of greenland orographic cyclogenesis in the lee of greenland at the location of the mean il and deepening of preexisting systems near the il orographic influences are clearly captured in polar mm5 simulations for which control runs of the three cases are compared to runs for which the orography of greenland is removed

geochemistry and tectonic setting of lower proterozoic supracrustal rocks of the pinal schist southeastern arizona two lithologic assemblages are identified in the early proterozoic 1700 ma supracrustal rocks of the pinal schist in southeastern arizona a western assemblage is composed largely of quartz wacke turbidites and an eastern assemblage includes bimodal volcanics and variable amounts of sediment chiefly feldspathic quartzite and conglomerate basalts from the eastern assemblage have incompatible element distributions similar to those found in basalts from continental margin arcs or evolved oceanic arcs whereas those from the western assemblage have distributions similar to within plate or back arc basin basalts felsic volcanics range in composition from rhyodacite to rhyolite and exhibit incompatible element distributions similar to those found in felsic volcanics from continental rifts and back arc basins near continents provenance studies of sediments from both assemblages indicate sources rich in granite and felsic volcanics the quartz wackes are similar in composition to sediments from continental margin arcs and associated back arc basins an increase in mafic components in these rocks from north to south in the pinal basin may reflect compositional polarity in an arc system the eastern assemblage may represent remnants of a major northeast trending continental margin arc system and the western assemblage may have been deposited in an intra arc basin or a northwest trending aulacogen which opened on the southwest

dipole anomaly in the winter arctic atmosphere and its association with sea ice motion abstract this paper identified an atmospheric circulation anomaly dipole structure anomaly in the arctic atmosphere and its relationship with winter sea ice motion based on the international arctic buoy program iabp dataset 1979 98 and datasets from the national centers for environmental prediction ncep and the national center for atmospheric research ncar for the period 1960 2002 the dipole anomaly corresponds to the second leading mode of eof of monthly mean sea level pressure slp north of 70 n during the winter season october march and accounts for 13 of the variance one of its two anomalous centers is stably occupied between the kara sea and laptev sea the other is situated from the canadian archipelago through greenland extending southeastward to the nordic seas the dipole anomaly differs from one described in other papers that can be attributed to an eastward shift of the center of action of the north atlantic oscillation the finding shows that the dipole anomaly also differs from

atmospheric forcing of fram strait sea ice export a closer look fram strait is the primary region of sea ice export from the arctic and therefore plays an important role in regulating the amount of sea ice and freshwater within the arctic we investigate the variability of fram strait sea ice motion and the role of atmospheric circulation forcing using daily data during the period 1979 2006 the most prominent atmospheric driver of anomalous sea ice motion across fram strait is an east west dipole pattern of sea level pressure slp anomalies with centers of action located over the barents sea and greenland this pattern also observed in synoptic studies is associated with anomalous meridional winds across fram strait and is thus physically consistent with forcing changes in sea ice motion the association between the slp dipole pattern and fram strait ice motion is maximized at 0 lag persists year round and is strongest on time scales of 10 60 days the slp dipole pattern is the second empirical orthogonal function eof of daily slp anomalies in both winter and summer when the analysis is repeated with monthly data only the barents center of the slp dipole remains significantly correlated with fram strait sea ice motion however after removing the leading eof of monthly slp variability e g the north atlantic oscillation the full east west dipole pattern is recovered no significant slp forcing of fram strait ice motion is found in summer using monthly data even when the leading eof is removed our results highlight the importance of high frequency atmospheric variability in forcing fram strait sea ice motion

a link between fram strait sea ice export and atmospheric planetary wave phase 1 a link is found between the variability of fram strait sea ice export and the phase of zonal wave 1 in slp for the period 1958 1997 previous studies have found that the link between ice export through fram strait and the nao is inconsistent over time scales longer than the last two decades inconsistent and low correlations are also found between fram strait ice export and the ao index the phase of zonal wave 1 explains 60 70 of the simulated ice export variance after the removal of two anomalous phases in 1966 and 1967 unlike the nao and ao links these high variances are consistent for both the first and second halves of the 40 year period this consistency is attributed to the sensitivity of wave 1 phase to the presence of secondary low pressure systems in the barents sea that serve to drive arctic sea ice southward through fram strait

chronologic and isotopic framework for early proterozoic crustal evolution in the eastern mojave desert region se california the early proterozoic geologic evolution of the eastern mojave desert region as defined by characteristics of its supracrustal rocks granitoids metamorphism structural history and pb and nd isotopic signature contrasts sharply with other proterozoic provinces of the southwestern united states the oldest supracrustal rocks of the mojave desert region contain zircons over 2 0 ga corroborating nd isotopic evidence for a much older crust here than elsewhere in the southwestern united states granitoids widely emplaced within these supracrustal rocks range from 1 76 to 1 64 ga the earlier plutons and surrounding supracrustal rocks were metamorphosed to granulite and high amphibolite facies throughout the province at about 1705 ma in a migmatite producing event that we term informally the ivanpah orogeny subsequent granitoids emplaced from 1 69 to 1 67 ga were voluminous along a north trending belt in the middle of the mojave province younger plutons were emplaced at about 1 66 ga in several places and at about 1 64 ga along the extreme southern part of the province commonalities between the proterozoic evolutions of the mojave and arizona crustal provinces do not conclusively establish the time that the provinces were juxtaposed the data only suggest that the juxtaposition occurred between about 1 76 and 1 64 ga

crustal growth in southern arizona u pb geochronologic and sm nd isotopic evidence for addition of the paleoproterozoic cochise block to the mazatzal province terranes composed of arc related igneous and sedimentary rocks were accreted onto the continental margin of southwestern north america from 1 9 to 1 6 ga they formed the yavapai mazatzal province in arizona of which the so called pinal schist and associated rocks in southeastern arizona form an integral part 148 u pb analyses on magmatic and detrital zircons were performed on 21 samples to constrain timing of geologic events in paleoproterozoic time in the area of southeastern arizona 25 sm nd whole rock analyses were made to infer sources of sedimentary and igneous rocks our results allow us to delineate a suture zone between the pinal tectonostratigraphic unit pinal block which consists primarily of basinal metaturbiditic rocks and a southeastern allochthonous juvenile volcano sedimentary domain the location of the suture is constrained by lithologic contrast across the boundary an increase in age of detrital zircons a marked decrease of end t and an intervening subduction complex swift and force this issue we propose the name cochise block for the southeastern part because it represents a faultbound allochthonous tectonic unit in the cochise block we document volcanic activity from about 1630 to 1647 ma quartzitic sedimentary rocks were largely derived from almost contemporaneous volcanic rocks and show detrital zircon ages from 1630 to 1729 ma with the majority 85 percent between 1630 to 1674 ma quartzites and intermediate to felsic metavolcanic rocks show a tight cluster of end t values 2 9 3 8 close to the depleted mantle model and therefore represent juvenile additions to the crust post tectonic metabasalts with end 1500 4 5 are interpreted as being derived from a depleted upper mantle source around 1 5 ga in the pinal block detrital zircons yield values from 1678 to 1731 ma end t values of metapelites and wackes range from 0 2 to 2 3 values decrease from southeast to northwest indicating progressive input of more evolved material toward the craton our data suggest that sedimentation within the pinal block was proximal to the continental margin and occurred later than 1 68 ga and ended before the intrusion of granitoids at 1 65 ga we show that the north american crust grew rapidly and progressively by addition of juvenile but evolved metavolcanic arc rocks and derived quartz rich metasedimentary rocks as documented in the cochise block timespans between depleted mantle model age and zircon crystallization on the order of 50 my attest to rapid crustal processing during this significant time of crustal growth

subduction margin assemblages in the proterozoic pinal and cochise blocks southeastern arizona protoliths of paleoproterozoic rocks broadly referred to as pinal schist in the johnny lyon hills and the dragoon and little dragoon mountains of cochise county arizona include intrusive and subaqueous extrusive mafic rocks turbiditic clastic rocks and highly deformed sedimentary rocks visually similar to phanerozoic melanges the combination of these lithologies and their present spatial distribution clastic rocks to the northwest separated by a region of melange from mafic igneous rocks to the southeast is suggestive of an assemblage formed at a subduction type continental margin protoliths of the mafic rock sequence about 700 m thick consist upward from its base of composite diabase dikes pillow lavas and pillow breccias and pelitic sedimentary rocks it may be an ophiolite fragment the clastic rocks though complexly deformed form a largely coherent mostly northwest younging sequence a fault bounded deformed belt present between the mafic and the clastic rocks includes pre metamorphic melange and broken formation the study area falls along or near previously suggested boundaries between lithotectonic assemblages within the precambrian rocks of southeastern arizona our results provide insight into the location and nature of the boundary and strongly suggest the presence of a suture zone juxtaposing predominantly metavolcanic rocks to the southeast against predominantly metasedimentary rocks to the northwest consistent with the terminology used by eisele and isachsen this issue we adopt the terms cochise block and pinal block for the regions to the southeast and northwest of the suture respectively

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

eddy driven recirculation of atlantic water in fram strait eddy resolving regional ocean model results in conjunction with synthetic float trajectories and observations provide new insights into the recirculation of the atlantic water aw in fram strait that significantly impacts the redistribution of oceanic heat between the nordic seas and the arctic ocean the simulations confirm the existence of a cyclonic gyre around the molloy hole near 80 n suggesting that most of the aw within the west spitsbergen current recirculates there while colder aw recirculates in a westward mean flow south of 79 n that primarily relates to the eastern rim of the greenland sea gyre the fraction of waters recirculating in the northern branch roughly doubles during winter coinciding with a seasonal increase of eddy activity along the yermak plateau slope that also facilitates subduction of aw beneath the ice edge in this area

evidence for a recent change in the link between the north atlantic oscillation and arctic sea ice export evidence for a recent change in the link between the north atlantic oscillation nao and arctic sea ice export through fram strait during wintertime djfm is presented from the analysis of simulated arctic sea ice and observations for the period 1958 1997 whereas no correlation between the two time series is found from 1958 to 1977 r 0 1 the correlation increased significantly thereafter r 0 7 1978 1997 the increased coherency between the nao and arctic sea ice export through fram strait during the last two decades resulted from anomalous meridional wind components near fram strait which were associated with the more easterly position of the nao s centers of interannual variability compared to 1958 1977

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

wintertime westward traveling planetary scale perturbations over the euro atlantic region the features of the wintertime westward traveling planetary scale perturbations over the euro atlantic region are examined through the use of space time spectral analysis applied to the 500 hpa geopotential height field the intention is to understand the nature of these phenomena and the performance of climate models data from both ecmwf re analyses and a simulation from the arpege general circulation model are used westward traveling planetary scale transients are found over the region as local perturbations resembling rossby normal modes with a maximum power over the eastern atlantic the westward traveling planetary scale transients north of 40 n have periods larger than 20 days south of this latitude wave periods are shifted to a band around 10 days so that they can be related to subtropical transient waves the atmospheric model used like other models which exhibit reasonable mean climatic properties tend to have less overall intraseasonal variability than observed nevertheless the model is able to capture most of the features of the westward traveling low frequency transients the differences in basic state partially produced by scale interactions would lead to the generation of westward traveling waves in the model distinct from the observed however it is suggested that the improvement of the present model version with regard to previous model versions is due to a better simulation of the time mean state the reasonable simulation of the synoptic scale variability south of 50 n and thus of its barotropic forcing on the basic state may also help to explain the realistic westward traveling transients in the model

the dynamics of euro atlantic blocking onsets the mechanisms leading to euro atlantic blocking are investigated using 31 winters of 500 hpa geopotential height from nmc and ecmwf daily analyses and a 30 000 day perpetual winter run from a simple 3 level quasi geostropic model a composite analysis of the atmospheric flow during days preceding blocking events is carried out it indicates that euro atlantic blocking events have two simultaneous main precursors a high latitude retrograding wave number 1 pattern at planetary scale and an enhanced baroclinic wavetrain travelling across the north atlantic at synoptic scale these phenomena are identified both in observed and in simulated data the nonlinear interactions between small scale large scale and the mean flow during the establishment of the blocking anomaly are examined by a budget analysis of the quasi geostrophic potential vorticity equation these diagnostics demonstrate that wave wave interactions contribute to about 50 of the local amplification of the blocking anomaly while wave mean flow interactions contribute to propagation of the large and small scale anomalies and their phase locking finally the question is addressed as to whether the two precursors are necessary and sufficient conditions for blocking onsets by performing various sets of initial value experiments performed with the quasi geostrophic model these experiments show that the two precursors occur simultaneously but only the synoptic scale baroclinic wavetrain is necessary to trigger euro atlantic blocking

relationship between sea ice motion and geostrophic wind in the northern hemisphere this paper presents maps showing the relationship between sea ice motion derived from defense meteorological satellite program dmsp special sensor microwave imager ssm i imagery and the geostrophic wind in the northern hemisphere for seven winters 1991 92 1997 98 the sea ice motion is highly correlated with the geostrophic wind except for some coastal regions overall the direction of the ice motion is nearly parallel to the wind an obvious contrast between seasonal ice zones and the interior of the arctic is observed in the speed reduction factor ratio of ice speed to wind speed which is probably caused by the spatial variation of internal ice stress surface ocean currents are also derived by subtracting the wind effect from the ice motion

deformational styles in the proterozoic pinal schist pinal peak arizona microstructural and quartz caxis analyses a 5 km thick north dipping shear zone in the pinal peak map area near globe arizona reveals contact metamorphism of the pinal schist through intrusion of the proterozoic madera diorite in pinal schist sillimanite and rare andalusite occur in the metamorphic aureole around the diorite but not elsewhere in this or adjoining map areas where metamorphic grade is interpreted to be low greenschist facies deformation was synchronous in the schist and the diorite and is recorded by a well developed generally n and nw trending elongation lineation field interpretations of ductile deformation fabrics generally indicate top to the south or reverse present day coordinates displacement microstructures in the pinal schist the madera diorite and the pinal madera contact zone include s c fabrics mica fish asymmetric type tails on porphyroclasts and grain shape and lattice preferred mineral orientation most of which indicate top to the south locally se to sw displacement consistent with field

a striking example of the atmosphere s leading traveling pattern abstract conventional and complex empirical orthogonal function eof techniques show that for at least four months during the fall and winter of 1979 80 a large amplitude large scale traveling flow anomaly existed in the troposphere and stratosphere this feature evolved in a cyclic manner exhibiting an average period of about 23 days its phase propagation was toward the west while its amplitude was concentrated in a broad envelope centered over canada the phenomenon was equivalent barotropic in the troposphere and increased in amplitude with altitude it represented about 25 of the variance of geopotential heights in the troposphere and stratosphere for the months of november through march the meridional and zonal structure of the zonal wavenumber one component of the traveling anomaly is similar to that of the theoretical 16 day wave however it is distinct from that theoretical mode in that its period is longer and in the troposphere zonal wave two makes a large contribution to its structur

arctic sea ice reemergence the role of large scale oceanic and atmospheric variability abstractarctic sea ice reemergence is a phenomenon in which spring sea ice anomalies are positively correlated with fall anomalies despite a loss of correlation over the intervening summer months this work employs a novel data analysis algorithm for high dimensional multivariate datasets coupled nonlinear laplacian spectral analysis nlsa to investigate the regional and temporal aspects of this reemergence phenomenon coupled nlsa modes of variability of sea ice concentration sic sea surface temperature sst and sea level pressure slp are studied in the arctic sector of a comprehensive climate model and in observations it is found that low dimensional families of nlsa modes are able to efficiently reproduce the prominent lagged correlation features of the raw sea ice data in both the model and observations these families provide an sst sea ice reemergence mechanism in which melt season spring sea ice anomalies are imprinted as sst anomalies and stored over the summer months allowing for

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

clastic metasediments of the early proterozoic broken hill group new south wales australia geochemistry provenance and metallogenic significance whole rock analyses of samples of pelite psammite and psammopelite from the early proterozoic broken hill group willyama supergroup in the broken hill block new south wales australia reveal distinctive geochemical signatures major element data show high al2o3 and k2o low mgo and na2o and relatively high fe2o3tmgo ratios compared to average early proterozoic clastic metasediments high field strength elements hfse are especially abundant including nb most 15 27 ppm ta most 1 0 2 2 ppm th 17 36 ppm hf 4 15 ppm and zr most 170 400 ppm y 33 74 ppm is also high concentrations of ferromagnesian elements are generally low sc 20 ppm ni 62 ppm co 26 ppm cr most 100 ppm data for rare earth elements rees show high abundances of light rees lacn 116 250 chondrite lacn 437 in one sample high lacnybcn ratios 5 6 13 9 and large negative eu anomalies eueu 0 32 0 57 the geochemical data indicate derivation of the metasedimentary rocks of the broken hill group by the erosion mainly of felsic igneous or meta igneous rocks high concentrations of hfse y and rees in the metasediments suggest a provenance dominanted by anorogenic granites and or rhyolites including those with a type chemistry likely sources of the metasediments were the rhyolitic to rhyodacitic protoliths of local quartz feldspar biotite garnet gneisses e g potosi type gneiss that occur within the lower part of the willyama supergroup or chemically similar basement rocks in the region alternative sources may have included early proterozoic anorogenic granites and or rhyolites in the mount isa and or pine creek blocks of northern australia or in the gawler craton of south australia metallogenic considerations suggest that the metasediments of the broken hill block formed enriched source rocks during the generation of pegmatite hosted deposits and concentrations of la ce nb ta th and sn in the region li be b w and u in pegmatite minerals of the district may have been acquired during granulite facies metamorphism of the local metasediments

dramatic interannual changes of perennial arctic sea ice linked to abnormal summer storm activity 1 the perennial september arctic sea ice cover exhibits large interannual variability with changes of over a million square kilometers from one year to the next here we explore the role of changes in arctic cyclone activity and related factors in driving these pronounced year to year changes in perennial sea ice cover strong relationships are revealed between the september sea ice changes and the number of cyclones in the preceding late spring and early summer in particular fewer cyclones over the central arctic ocean during the months of may june and july appear to favor a low sea ice area at the end of the melt season years with large losses of sea ice are characterized by abnormal cyclone distributions and tracks they lack the normal maximum in cyclone activity over the central arctic ocean and cyclones that track from eurasia into the central arctic are largely absent fewer storms are associated with above average mean sea level pressure strengthened anticyclonic winds an intensification of the transpolar drift stream and reduced cloud cover all of which favor ice melt it is also shown that a strengthening of the central arctic cyclone maximum helps preserve the ice cover although the association is weaker than that between low cyclone activity and reduced sea ice the results suggest that changes in cyclone occurrence during late spring and early summer have preconditioning effects on the sea ice cover and exert a strong influence on the amount of sea ice that survives the melt season

a seesaw structure in slp anomalies between the beaufort sea and the barents sea 1 this paper reveals a new mode of winter october march monthly mean atmospheric intraseasonal variability characterized by a seesaw structure in sea level pressure slp anomalies between the barents sea and the beaufort sea with an equivalent barotropic structure the beaufort high varies out of phase with the siberian high compared to the arctic oscillation ao and the dipole anomaly the effect of this mode on fram strait sea ice flux is the most important so far although it accounts for only 9 1 of the variance the beaufort high itself is not crucial for sea ice flux through fram strait

meridional flow variability over the nordic seas in the arctic oscillation framework an anomalous recurring atmospheric circulation pattern of high relevance for the climate of the nordic seas and siberia is identified it is found as the second empirical orthogonal function eof of monthly winter sea level pressure slp anomalies poleward of 30 n where the leading eof is the arctic oscillation ao the most prominent centre of action of the circulation pattern is located over the barents region this barents oscillation bo is shown to have a high temporal correlation with the sensible heat loss of the nordic seas r 0 76 the bo also correlates to eurasian surface air temperature sat anomalies with r 0 72 after the ao related sat variations are removed by means of a linear regression two sets of slp composites are constructed where one is based on low and high nordic seas heat loss months and the other is based on warm and cold eurasian months patterns reminiscent of the bo emerge in the two composites when ao related variability is removed

geochemical and detrital mode evidence for two sources of early proterozoic sedimentary rocks from the tonto basin supergroup central arizona the tonto basin supergroup includes up to 6 5 km of early proterozoic sedimentary and volcanic rocks that were deposited in a relatively short period of time at about 1 7 ga in central arizona moderate correlations of rare earth elements ree and ti with al2o3 and ree distributions in detrital sediments of this supergroup suggest that these elements are contained chiefly in clay mica and or zircon fractions ree distributions including negative eu anomalies in most tonto basin sediments are similar to those in phanerozoic shales weak to moderate correlations of fe sc ni and co to al2o3 also suggest a clay mica control of these elements detrital modes and geochemical characteristics of sediments indicate two dominant sources for sedimentary rocks of the tonto basin supergroup a granitoid source and a volcanic source the granitoid source was important during deposition of the upper part of the succession the mazatzal group as shown by increases in k2o al2o3 and th in pelites with stratigraphic height and increases in zr and hf and decreases in eu eu cr and ni in in pelites of the maverick shale sediment provenance characteristics and paleocurrent indicators are consistent with deposition of the supergroup in a continental margin back arc basin the granitoid sediment source appears to have been the north american craton on the north and the volcanic source a more local source from an arc on the south

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

the role of fram strait winter cyclones on sea ice flux and on spitsbergen air temperatures 1 the link between high latitude atlantic winter cyclone activity and both the climate of spitsbergen and fram strait ice export is examined cyclones are more frequent over fram strait in relatively mild low ice export winters and are associated with south southwesterly flow around anomalous high pressure over scandinavia there is an increased tendency for cyclogenesis to occur off the northeast greenland coast and east greenland current in those winters fram strait cyclones then typically continue into the western arctic basin north of greenland and canada anomalously cold high ice export winters have higher cyclone activity in the barents sea and eurasia side of the arctic basin cyclones in mild winters have close proximity to spitsbergen and may simultaneously advect arctic sea ice across fram strait possibly accounting for the low under 30 shared variance in winter time series of temperatures and sea ice export

outflow of arctic ocean sea ice into the greenland and barents seas 1979 2007 abstract twenty nine years of arctic sea ice outflow into the greenland and barents seas are summarized outflow is computed at three passages fram strait between svalbard and franz josef land s fjl and between franz josef land and severnaya zemlya fjl sz ice drift at the flux gates has been reprocessed using a consistent and updated time series of passive microwave brightness temperature and ice concentration ic fields over the record the mean annual area outflow at the fram strait is 706 113 103 km2 it was highest in 1994 95 1002 103 km2 when the north atlantic oscillation nao index was near its 29 yr peak the strength of the transpolar drift stream tds was high during the late 1980s through the mid 1990s there is no statistically significant trend in the fram strait area flux even though there is a positive trend in the gradient of cross strait sea level pressure the outflow has not increased because of a negative trend in ic seasonally the area outflow during recent sum

a fram strait cyclone properties and impact on ice drift as measured by aircraft and buoys 1 atmospheric cyclones in the fram strait affect the sea ice transport from the arctic ocean into the atlantic ocean during the field experiment framzy in april 1999 a fram strait cyclone and its impact on the ice drift was measured using a research aircraft and an array of 15 ice buoys the synoptic scale cyclone moved from the south into the area it was discernible up to 500 hpa in the pressure field but the horizontal temperature contrast of up to 16 k between the warm and cold sides was confined to the lowest 500 m the average ice drift was 0 21 ms 1 toward 200 but increased to 0 6 ms 1 during the cyclone passage the ice drift amounted to 1 6 of the geostrophic wind with a turning angle of 51 on the average comparisons between the aircraft measurements and operational weather model analyses show an insufficient representation of the temperature inversion and indicate an underestimate of wind speed and thus momentum transfer to the sea ice

the greenland sea jet a mechanism for wind driven sea ice export through fram strait 1 we present a mechanism for wind driven sea ice export from the arctic ocean through fram strait for the period 1979 2007 using the output of a high resolution regional atmospheric climate model by explicitly calculating the components of the atmospheric momentum budget we show that not large scale synoptic forcing lsc but mainly thermal wind forcing thw causes the persistent northerly jet the greenland sea jet over fram strait the jet results from horizontal temperature gradients in the atmospheric boundary layer abl set up between cold abl air over the sea ice covered western greenland sea and the relatively warmer abl over the ice free eastern greenland sea from 1993 onwards we find a negative trend in thw due to a stronger response to climate warming of the abl over the sea ice covered ocean compared to that over the ice free ocean although on average lsc is smaller than thw year to year variations in lsc explain most of the interannual variability in the sea ice area flux through fram strait r 0 81 a small positive trend is found for lsc partly compensating the decrease in thw in recent years