interdecadal change in the north atlantic storm track during boreal summer around the mid 2000s role of the atmospheric internal processes the first eof mode eof1 of summer storm track activity over the north atlantic is characterized by a dipole structure with negative storm track anomalies over the south coast of greenland extending northeast across iceland to the norwegian sea and positive anomalies over coastal western europe this study shows that a significant interdecadal change in the north atlantic storm track during boreal summer occurred around the mid 2000s after the mid 2000s the eof1 occurs more frequently at its positive phase which is associated with an interdecadal increase in the geopotential height anomalies around greenland on the intra seasonal timescale the anticyclonic anomalies around greenland are crucial for the occurrence of positive eof1 events via triggering eastward propagating rossby waves therefore the interdecadal increase in the geopotential height anomalies around greenland tends to facilitate the occurrence of the positive eof1 event and is therefore a key driver of the interdecadal change in the summer storm track activity over the north atlantic further analysis indicates that the development of anticyclonic anomalies around greenland is maintained by the self interaction among the low and high frequency transients themselves moreover the anomalous synoptic eddy activities associated with the change in storm tracks can in turn amplify and maintain the rossby waves triggered by the anticyclonic anomalies around greenland in the synoptic scale eddy feedback process

distribution of clay minerals along a weathered pyroclastic profile hong kong abstract the distribution of clay minerals along a weathered profile developed over crystal vitric tuffs are examined by x ray diffractometry xrd and scanning electron microscopy sem techniques chlorite and illite are the most abundant clay minerals in fresh and moderately decomposed rocks respectively chlorite is limited to fresh samples whereas illite and trace amounts of interstratified illite smectite are ubiquitous along the profile halloysite and kaolinite are the dominant clay minerals in highly to completely decomposed rocks halloysite clusters in moderately decomposed samples provide clear evidence of crystallization from solution whereas vermiform kaolinite books reveal evidence of transformation from illite in most samples in general as the intensity of weathering increases a kaolin to illite and kaolinite to halloysite ratios increase and b the morphology of halloysite varies from spheriodal clusters to tubular aggregates it is concluded that the nature type and abundance of clay minerals along the profile result from complex combinations of several different processes controlled mainly by three factors the pre weathering alteration history of parent rock the degree of weathering and microenvironmental conditions the relative role of each factor can vary significantly within the same profile as evidenced by mineralogical and petrographical characteristics the nature and type of clay minerals in fresh and moderately decomposed rocks can be attributed to pre weathering hydrothermal and or deuteric alterations on the other hand the degree of weathering regulates the nature type and abundance of clay minerals particularly kaolin group minerals in highly to completely decomposed rocks sesquioxides are sensitive to microenvironmetal conditions and can modify the distribution of clay minerals regardless of the degree of weathering of the rock

genesis of altered conway granite grus in new hampshire usa abstract increased pedologic interest in grus has created a need for better understanding of geologic and pedogenic processes producing such materials progress in this area is hindered by the incomplete understanding of pedogenic processes as well as the fact that some of the properties of grus may be created through any of several pathways hydrothermal alteration is one important example of a geologic process which may produce characteristics similar to those created by pedogenesis this process is not often considered by soil scientists because of their unfamiliarity with the geologic environments which engender such conditions and the petrographic evidence specific to these processes this study uses petrographic evidence of microfracturing silicification and sericitization indicative of hydrothermal alteration in conjunction with igneous structural geology to enhance traditional pedologic assessments of weathering and soil genesis in the conway granite grus this interdisciplinary approach led to the interpretation that the grus was a product of hydrothermal alteration rather than paleopedogenesis as had been proposed previously more importantly this study demonstrates that interpretations of soil weathering paleosol occurrences and grus genesis in a variety of locations can be enhanced by such considerations

relationship between cyclone tracks anticyclone tracks and baroclinic waveguides abstract this study presents observational results concerning the structure and evolution of high frequency fluctuations with periods shorter than 6 days in the geopotential height field the results are based on a statistical analysis of 1000 500 and 250 mb height fields derived from twice daily nmc final analyses over the northern hemisphere for the 20 winters 1964 65 through 1983 84 the disturbances assume the form of waves elongated in the meridional direction with a mean wavelength of 4000 km a westward tilt with height and a mean eastward phase propagation of 12 1 5 m s 1 these results support an interpretation in terms of finite amplitude baroclinic waves whose structure and evolution varies with geographical location over the continents and especially along the eastern slopes of the rockies and the tibetan plateau the waves show marked departures in structure and evolution from those over the oceans in particular we find evidence of a systematic influence of the terrain in steering the

atmospheric response to zonal variations in midlatitude sst transient and stationary eddies and their feedback midwinter storm track response to zonal variations in midlatitude sea surface temperatures ssts has been investigated using an atmospheric general circulation model under aquaplanet and perpetual january conditions zonal wavenumber 1 sst variations with a meridionally confined structure are placed at various latitudes having these sst variations centered at 308n leads to a zonally localized storm track while the storm track becomes nearly zonally uniform when the same sst forcing is moved farther north at 408 and 508n large small baroclinic energy conversion north of the warm cold sst anomaly near the axis of the storm track near 408n is responsible for the large small storm growth the equatorward transfer of eddy kinetic energy by the ageostrophic motion and the mechanical damping are important to diminish the storm track activity in the zonal direction significant stationary eddies form in the upper troposphere with a ridge trough northeast of the warm cold sst anomaly at 308n heat and vorticity budget analyses indicate that zonally localized condensational heating in the storm track is the major cause for these stationary eddies which in turn exert a positive feedback to maintain the localized storm track by strengthening the vertical shear near the surface these results indicate an active role of synoptic eddies in inducing deep tropospheric scale response to midlatitude sst variations finally the application of the model results to the real atmosphere is discussed

storm track dynamics this paper reviews the current state of observational theoretical and modeling knowledge of the midlatitude storm tracks of the northern hemisphere cool season observed storm track structures and variations form the first part of the review the climatological storm track structure is described and the seasonal interannual and interdecadal storm track variations are discussed in particular the observation that the pacific storm track exhibits a marked minimum during midwinter when the background baroclinicity is strongest and a new finding that storm tracks exhibit notable variations in their intensity on decadal timescales are highlighted as challenges that any comprehensive storm track theory or model has to be able to address physical processes important to storm track dynamics make up the second part of the review the roles played by baroclinic processes linear instability downstream development barotropic modulation and diabatic heating are discussed understanding of these processes forms the core of our current theoretical knowledge of storm track dynamics and provides a context within which both observational and modeling results can be interpreted the eddy energy budget is presented to show that all of these processes are important in the maintenance of the storm tracks the final part of the review deals with the ability to model storm tracks the success as well as remaining problems in idealized storm track modeling which is based on a linearized dynamical system are discussed perhaps on a more pragmatic side it is pointed out that while the current generation of atmospheric general circulation models faithfully reproduce the climatological storm track structure and to a certain extent the seasonal and enso related interannual variations of storm tracks in depth comparisons between observed and modeled storm track variations are still lacking

summer arctic atmospheric circulation response to spring eurasian snow cover and its possible linkage to accelerated sea ice decrease abstractanticyclonic circulation has intensified over the arctic ocean in summer during recent decades however the underlying mechanism is as yet not well understood here it is shown that earlier spring eurasian snowmelt leads to anomalously negative sea level pressure slp over eurasia and positive slp over the arctic which has strong projection on the negative phase of the northern annular mode nam in summer through the wave mean flow interaction specifically earlier spring snowmelt over eurasia leads to a warmer land surface because of reduced surface albedo the warmed surface amplifies stationary rossby waves leading to a deceleration of the subpolar jet as a consequence rising motion is enhanced over the land and compensating subsidence and adiabatic heating occur in the arctic troposphere forming the negative nam the intensified anticyclonic circulation has played a contributing role in accelerating the sea ice decline observed during the last two decades the results here provid

characteristics of wave packets in the upper troposphere part i northern hemisphere winter abstract gridded data produced by the ecmwf reanalysis project have been analyzed to document the properties of wave packets in the northern hemisphere winter midlatitude upper troposphere based on results from earlier investigations 300 hpa meridional wind variations were chosen for analysis wave packet envelopes were also defined by performing complex demodulation on the wind data the properties of the wave packets are mainly illustrated using time lagged one point correlation maps performed both on and wave packet envelopes the results show that over most regions in the northern hemisphere winter with the exception of the deep tropics and near the aleutian low medium scale waves dominant wavenumber 5 8 exhibit the characteristics of downstream development and occur within wave trains that propagate with eastward group velocities much faster than the phase speeds of individual phases of the waves their group velocity is highly correlated with the local time mean 200 400 hpa wind while the

interdecadal variations of the silk road pattern abstractbased on several reanalysis and observational datasets this study suggests that the silk road pattern srp a major teleconnection pattern stretching across eurasia in the boreal summer shows clear interdecadal variations that explain approximately 50 of its total variance the interdecadal srp features a strong barotropic wave train along the asian subtropical jet resembling its interannual counterpart additionally it features a second weak wave train over the northern part of eurasia leading to larger meridional scale than its interannual counterpart the interdecadal srp contributes approximately 40 of the summer surface air temperature s variance with little uncertainty and 10 20 of the summer precipitation s variance with greater uncertainty over large domains of eurasia the interdecadal srp shows two regime shifts in 1972 and 1997 the latter shift explains over 40 of the observed rainfall reduction over northeastern asia and over 40 of the observed warming over eastern europe

the role of stationary eddies in shaping midlatitude storm tracks transient and stationary eddies shape the extratropical climate through their transport of heat moisture and momentum in the zonal mean the transports by transient eddies dominate over those by stationary eddies but this is not necessarily the case locally in particular in storm track entrance and exit regions during winter stationary eddies and their interactions with the mean flow dominate the atmospheric energy transport here it is shown that stationary eddies can shape storm tracks and control where they terminate by modifying local baroclinicity simulations with an idealized aquaplanet gcm show that zonally localized surface heating alone e g ocean heat flux convergence gives rise to storm tracks which have a well defined length scale that is similar to that of earth s storm tracks the storm tracks terminate downstream of the surface heating even in the absence of continents at a distance controlled by the stationary rossby wavelength scale stationary eddies play a dual role within about half a rossby wavelength downstream of the heating region stationary eddy energy fluxes increase the baroclinicity and therefore contribute to energizing the storm track farther downstream enhanced poleward and upward energy transport by stationary eddies reduces the baroclinicity by reducing the meridional temperature gradients and enhancing the static stability transports both of sensible and latent heat water vapor play important roles in determining where storm tracks terminate

effect of granite crystal grain size on soil properties and pedogenic processes along a lithosequence this study generated new insight into the effect of bedrock grain sizes on pedogenesis under identical topographic and climatic environment the physico chemical and mineralogical properties of two adjacent typic dystrochrepts usda 1999 respectively developed from fine and coarse textured granites were compared this research study was performed in the morvan mountains france analysis of the two underlying bedrocks revealed similar chemical and mineralogical properties with the crystal grain size being the only parameter which differed in these soils bedrock played the key role in the particle size fraction distribution the main factor controlling water retention in the soils weathering reactions of clay minerals were more marked in the fine textured granite soil in this soil both clay mineral swelling and mica transformation into expansible phyllosilicates were greater compared to the coarse textured granite soil in the clay fraction of the fine textured granite soil there were smaller amounts of low crystallised fe and al minerals with higher carbon content in the topsoil as compared to the coarse granite soil the exchangeable cation analysis of the fine textured granite soil revealed a higher proportion of base saturation and a smaller proportion of altit than in coarse textured granite soil which could be explained by preferential leaching of al cations the decrease in exchangeable al the higher swelling of the smectitic layer and the smaller proportion of fe and al oxy hydroxides could be explained by the complexing acid conditions which increased mineral weathering and al leaching the higher water retention increased the time of contact between minerals and the soil solution and the higher carbon content in the topsoil could have enhanced the complexing acid conditions resume d auteur

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

the dynamics of nao teleconnection pattern growth and decay this investigation performs both diagnostic analyses with ncep ncar re analysis data and forced barotropic model calculations to examine the dynamical mechanisms associated with the growth and decay of the north atlantic oscillation nao teleconnection pattern the diagnostic calculations include projection and composite analyses of each term in the stream function tendency equation the results of the analyses reveal a complete life cycle of growth and decay within approximately two weeks the positive nao phase is found to develop after anomalous wavetrain propagation across the north pacific to the east coast of north america this contrasts with the negative nao phase which appeared to develop in situ both high frequency period 10 days transient eddy fluxes drive the nao growth after the nao anomaly attains its maximum amplitude the high frequency transient eddy fluxes continue to drive the nao anomaly in a manner that is consistent with a positive feedback process the decay of the nao occurs through both the divergence term and the low frequency transient eddy fluxes the temporal and spatial properties of the divergence term are found to be consistent with ekman pumping these results illustrate many important differences between the nao and pacific north american pna teleconnection patterns perhaps most striking being that the nao life cycle is dominated by nonlinear processes whereas the pna evolution is primarily linear in addition the relation between the nao and the zonal index is discussed copyright 2003 royal meteorological society

weathering of granites in a temperate climate nw portugal granitic saprolites and arenization abstract saprolites or in situ weathering products from granitoid rocks of northwest portugal were studied by means of x ray diffraction xrd of their clay fraction and observations of polished thin sections combined with transmission electron microscopy tem scanning electron microscopy with energy dispersive spectrometer sem eds microanalyses their principal features are 1 depths of more than 10 m 2 mean material loss of 40 as calculated by an isovolumetric method 3 low clay content mean value of 7 and a high degree of mineralogical evolution the clay fraction is characterized by a predominance of kaolinite and gibbsite with subordinate 2 1 minerals illite chlorite vermiculitic mixed layers vermiculite the significance of the secondary minerals in granitic saprolites from northwest portugal is compared to published data from atlantic europe this allows the definition of a climatic zonality for weathering products and identifies arenization as an important weathering process

the recent shift in early summer arctic atmospheric circulation 1 the last six years 2007 2012 show a persistent change in early summer arctic wind patterns relative to previous decades the persistent pattern which has been previously recognized as the arctic dipole ad is characterized by relatively low sea level pressure over the siberian arctic with high pressure over the beaufort sea extending across northern north america and over greenland pressure differences peak in june in a search for a proximate cause for the newly persistent ad pattern we note that the composite 700 hpa geopotential height field during june 2007 2012 exhibits a positive anomaly only on the north american side of the arctic thus creating the enhanced mean meridional flow across the arctic coupled impacts of the new persistent pattern are increased sea ice loss in summer long lived positive temperature anomalies and ice sheet loss in west greenland and a possible increase in arctic subarctic weather linkages through higheramplitude upper level flow the north american location of increased 700 hpa positive anomalies suggests that a regional atmospheric blocking mechanism is responsible for the presence of the ad pattern consistent with observations of unprecedented high pressure anomalies over greenland since 2007 2012 american geophysical union all rights reserved

the variability of the atlantic storm track and the north atlantic oscillation a link between intraseasonal and interannual variability abstract the winter mean north atlantic oscillation nao index has been mostly positive since the 1980s with a linear upward trend during the period from 1978 to 1990 p1 and a linear downward trend during the period from 1991 to 2009 p2 further calculations show that the atlantic storm track eddy activity is more intense during p2 than during p1 which is statistically significant at the 90 confidence level for a t test this study proposes a hypothesis that the change in the trend of the positive nao index from p1 to p2 may be associated with the marked intensification of the atlantic storm track during p2 a generalized nonlinear nao model is used to explain the observed trend of the positive nao index within p2 it is found that even when the atlantic storm track eddies are less intense a positive phase nao event can form under the eddy forcing if the planetary scale wave has an initial value with a low over high dipole structure during p1 and p2 a blocking flow can occur in the downstream si

weathering and pedogenesis in the sila grande massif calabria south italy from field scale to micromorphology abstract weathering and soil features in the upland landscapes developed on granitic terrains of the sila grande massif calabria south italy have been studied in this work the attempt to link field scale and micromorphological observations in order to better understand the main weathering processes and their controlling factors is revealed to be very powerful six soil profiles in the area around the cecita lake representative of different geomorphological units were characterised by field work optical microscopy and sem eds analysis a strong influence on weathering and pedogenesis by micro scale features of primary minerals and parent rock fabrics is shown key roles are played also by relief in the development and preservation or stripping of regolith soil mantles in relation to natural and man induced phenomena by time controlling rates and degree of development of the main weathering features by climate in terms of type and intensity of dominant processes

asymmetric influence of boreal spring arctic oscillation on subsequent enso previous studies have suggested that the boreal spring arctic oscillation ao could exert a significant influence on the outbreak of el nino southern oscillation enso during the following winter this study further reveals that the influence of the spring ao on the subsequent enso is asymmetric when the spring ao is in its high phase significant el nino like sea surface temperature sst warming anomalies are observed over the tropical central eastern pacific in the following winter however when the spring ao is in its low phase negative sst anomalies over the tropical central eastern pacific are weak and statistically insignificant this asymmetric influence is attributed to the asymmetric features of both the atmospheric circulation anomalies in spring and atmospheric heating anomalies over the subtropical north pacific from spring to summer for the high ao phase composite the anomalous cyclonic circulation over the subtropical western north pacific and the related westerly wind anomalies to its south over the tropical western pacific are strong and significant in spring the tropical zonal wind anomalies would trigger enso events via the excitation of an eastward propagating kelvin wave meanwhile the atmospheric heating anomalies over the subtropical north pacific play an important role in sustaining the westerly wind over the tropical western pacific from spring to summer in contrast the counterparts in the low ao phase composite are weak and statistically insignificant our results indicate that the phase of spring ao should be taken into account when using spring ao as a predictor for enso

interdecadal variations in northern hemisphere winter storm track intensity abstract in this paper the interannual variations in the northern hemisphere winter storm tracks have been examined based on 51 winters december january february of ncep ncar reanalysis data the leading empirical orthogonal function eof corresponds to the simultaneous strengthening weakening of both the pacific and atlantic storm tracks interannual and month to month variations in the pacific and atlantic storm tracks are found to be significantly correlated the principal component associated with the leading hemispheric eof exhibits pronounced interdecadal variability there appears to be a transition during the early 1970s from a weak storm track state prior to 1972 73 to a strong storm track state subsequently decadal mean storm track intensity during the 1990s is about 30 stronger than that during the late 1960s and early 1970s the relationship between variations in storm track intensity and low frequency seasonal mean flow anomalies has also been examined it is shown that storm track va

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

tectonic evolution of a crustal scale oblique ramp hellenides thrust belt greece abstract this study investigates the tectonic evolution of the omalos transverse zone which served as a crustal scale oblique ramp in the external hellenides thrust belt on crete island the omalos oblique ramp developed above an inherited mesozoic fault zone that strikes ne sw oblique to the regional ssw directed tectonic transport during the early miocene pleistocene evolution of the thrust belt the oblique ramp was repeatedly reactivated localizing deformation above the inherited structure geological and structural mapping combined with kinematic analysis of ductile and brittle structures suggest that the omalos oblique ramp generated a local kinematic field which deviated significantly from the regional kinematic pattern in the thrust belt the most conspicuous feature in the tectonic evolution of the oblique ramp is a change from a ductile wrench dominated to a brittle primarily reverse faulting regime across the brittle ductile transition followed by brittle wrench deformation after the final exhumation of high pressure hp rocks deflections of transport and compression orientations from the regional pattern are attributed to buttressing against basement cover offsets produced by the pre existing fault zone to oblique ramping and to transfer faulting respectively our findings are potentially applicable to other examples of crustal scale oblique thrust ramps in various tectonic settings

on the existence of storm tracks abstract given that middle latitude weather systems transport heat in a manner such as to weaken the baroclinicity that is thought to be crucial to their growth it is perhaps surprising that concentrated regions of such eddy activity i e storm tracks are found in the northern hemisphere winter the existence and possible self maintenance of storm tracks is investigated using a linear stationary wave model with storm track region forcings taken from data averaged over a number of winters it is found that the direct thermal effect of the eddies does indeed act against the existence of the storm track their vorticity fluxes lead to some reduction of this effect it is argued that the mean diabatic heating in the storm track region is an indirect eddy effect this heating is found to maintain the mean maximum in baroclinicity in the region further the mean low level flow induced by the eddy effects is such as to enhance the warm western oceanic boundary currents that are crucial to the existence of t

organization of storm track anomalies by recurring low frequency circulation anomalies abstract from previous studies it is known that anomalous momentum fluxes by bandpass eddies are important in maintaining long lasting tropospheric flow anomalies evidence is presented that suggests that these anomalous fluxes do not occur at random but happen because the structure of storm track activity is modified by the presence of prominent low frequency large scale circulation anomalies this behavior is noted in an extended integration of a perpetual january simulation with a general circulation model gcm because nonlinear feedbacks between low and high frequency variability make it difficult to establish causal relationships between these two ranges of variability a model is constructed that approximates the storm track activity that would be expected to accompany a given low frequency without including the feedback of the high frequencies onto the low frequency state this model is based on the linearized primitive equations and uses a series of short integrations from random initial condi