metamorphic evidence for tilt of the spuzzum pluton diminished basis for the baja british columbia concept to address the question of tilt versus translation as the mechanism responsible for discordance between paleomagnetic directions of cretaceous plutons in the british columbia coast plutonic complex and the north american reference direction metamorphic pressures around the margin of the spuzzum pluton have been determined pressures are derived from microprobe analyses and evaluation of exchange equilibria in the assemblage garnet biotite plagioclase aluminum silicate quartz samples studied come from eight localities in the contact aureole around the pluton and encompass the area of a previous paleomagnetic study the analyzed samples are coarse grained and exhibit textural features indicative of equilibrium crystallization following emplacement of the spuzzum pluton results of this study indicate a complicated tilt history for the spuzzum pluton with tilt first to the northeast then to the southwest the southwest tilt can fully explain the discordance of the paleomagnetic direction in the spuzzum but does not preclude translation however in view of the tilt history of this pluton the paleomagnetic data derived from it should not be used in an analysis of north south translation

structure of a frontal cyclone a diagnostic study of a mid latitude cyclone has been carried out using routinely available numerical weather prediction model products and imagery the cyclone was intense but not exceptionally so and the results are believed to have some generality the detailed description of the cyclone structure just before it began to deepen rapidly integrates concepts from a number of researchers into a common framework a dominant feature of the cyclone close to its centre was the cloud head a region of cloud with a sharp convex outer edge which formed poleward of the main polar front cloud band the cloud head was caused by two flows that entered it from the east ascending and fanning out within it one flow the cold conveyor belt brought low wet bulb potential temperature w air back into the cloud head from low levels ahead of the warm front the other flow was due to high w air that peeled off from the base of the main warm sector airflow i e part of the warm conveyor belt and travelled in the boundary layer back towards the cyclone centre first undercutting dry air that had earlier descended from the upper troposphere called a dry intrusion and then ascending at the upper boundary of the cloud head above the cold conveyor belt the transverse circulation that gave the ascent within the cloud head also led to the cold front fracturing along its length into two separate sharp surface cold fronts with a more diffuse frontal region in between frontal fracture the two sharp surface cold fronts were associated with narrow cold frontal rainbands line convection one of the line convection segments forming the southern edge of the cloud head the overrunning of the dry intrusion in the region of the frontal fracture led to a structure known as a split front in which an upper level humidity front began to run ahead of the position of the surface cold front a feature of the cyclone at this intermediate stage in its evolution was that a large proportion of the precipitation was being generated by ascent of relatively cold air the cold conveyor belt in the cloud head as part of the thermally indirect circulation at the left exit of a developing secondary upper level jet

mesoscale aspects of a dry intrusion within a vigorous cyclone the results of a diagnostic study using radar and satellite imagery together with surface reports and output from regional and mesoscale models are presented for an occasion of a rapidly deepening cyclone that crossed the british isles the study shows how air descended from near tropopause level in the form of mesoscale dry intrusions which appeared to overrun parts of the warm conveyor belt ahead of a surface cold front one of the dry intrusions is analysed in detail because it is thought to have led to the large changes that were observed in the character of the wide frontal rain band in some places the precipitation was entirely suppressed whilst in other places the precipitation became convective with a tornadic squall line developing although the effect of the dry intrusion was seen most clearly in the precipitation distribution as determined by radar the approach of the dry intrusion was also clearly detected in the satellite water vapour imagery and foreshadowed in the model forecasts the mesoscale model despite some limitations reproduced many of the observed mesoscale features it also provided insight into the detailed behaviour of the dry intrusion associated with the tornadic squall line it showed that the dry intrusion was characterized by a mesoscale filament of high potential vorticity pv which was extruded from the lower part of a large region of high pv near a low tropopause the extruded pv anomaly plunged to within a kilometre of the surface where it overran part of the warm conveyor belt the dry intrusion was also characterized by relatively low wet bulb potential temperature w and it led to potential instability where it overran the warm air the warm conveyor belt itself was characterized not only by a high w but also by a separate strip of high pv generated locally mainly by condensation the quality of the mesoscale model simulation gives grounds for optimism that such models are capable in principle of predicting severe mesoscale weather events when as in this case they are orchestrated by resolved larger scale dynamics

the presidents day snowstorm of 18 19 february 1979 a subsynoptic scale event abstract on 18 19 february 1979 a major east coast cyclone deposited a record breaking snowfall on the middle atlantic states the storm is noteworthy because of the failure of the operational prediction models to signal the intensity of the event the life cycle of the cyclone is reviewed with emphasis on the synoptic and mesoscale features and their possible linkage prior to cyclogenesis the synoptic pattern features a massive cold anticyclone near the great lakes with a broad baroclinic zone extending from texas eastward to the atlantic coast a region of enhanced lower tropospheric baroclinicity develops along the carolina coastal strip in response to significant oceanic sensible and latent heat fluxes which warm moisten and destabilize the boundary layer cyclogenesis is initiated along the coastal front as the result of lower tropospheric warm advection the importance of the coastal front is that it effectively steers the cyclone north northeastward parallel to the coast such that it eventually a

acceleration of near surface strong winds in a dry idealised extratropical cyclone to understand near surface strong winds in extratropical cyclones a simulation of a dry idealised baroclinic wave is presented the forces that accelerate the winds are analysed using the terms in the horizontal momentum equation two regions of strong near surface winds developed within the simulation one to the east of the low centre and the other to the southwest the flow to the east resembling the cold conveyor belt accelerated as it passed through the strong pressure gradient associated with the warm frontal zone this acceleration was reduced by friction near the surface the winds to the southwest were characterised by three airstreams one airstream consisted of air parcels that started north of the warm front near the surface accelerated north of the warm front encircled the low and continued to accelerate to the southwest of the low the increases in wind speed in this airstream also part of the cold conveyor belt resulted from the along flow pressure gradient force being greater than friction the second airstream consisted of air parcels that descended west of the cold front and maintained their speed during descent until they were slowed either by friction in the boundary layer or as they moved southward against the local pressure gradient between these two airstreams a third airstream was characterised by air parcels that accelerated during descent from the mid to lower troposphere whilst moving around the bent back front this airstream bears some resemblance to the sting jet and was accelerated by the pressure gradient force on descent until it encountered increased friction or moved against the local pressure gradient

high temperature arc parallel normal faulting and transtension at the roots of an obliquely convergent orogen structural and kinematic data from northern coastal british columbia 54 5 n document intra arc deformation patterns at mid crustal levels during and after emplacement of the coast mountains batholith major arc parallel displacements occurred along high temperature 700 c ductile normal faults and steep sinistral transtensional shear zones within an obliquely convergent margin strain patterns and pluton emplacement were controlled by 1 structural anisotropies in host rocks that predate batholith emplacement and 2 kinematic compatibility requirements created by simultaneous motion on curved pluton bounding shear zones these controls superseded a partitioning of the arc parallel and arc normal components of oblique plate convergence onto strike slip and thrust faults respectively

transpression between two warm mafic plates the queen charlotte fault revisited the queen charlotte fault is a transpressive transform plate boundary between the pacific and north american plates offshore western canada previous models for the accommodation of transpression include internal deformation of both plates adjacent to the plate boundary or oblique subduction of the oceanic plate the latter has been the preferred model both plates are warm and mafic and have similar mechanical structures new multichannel seismic reflection data show a near vertical queen charlotte fault down to the first water bottom multiple significant subsidence east of the queen charlotte fault a large melange where the fault is in a compressive left step and faulting which involves oceanic basement gravity modeling of profiles indicates that moho varies fairly smoothly across the plate boundary isostatic anomalies indicate that the pacific plate is flexed downward adjacent to the queen charlotte fault upward flexure of north america along with crust thickened relative to crust in the adjacent basin creates topography known as the queen charlotte islands combined with other regional studies these observations suggest that the plate boundary is a vertical strike slip fault and that transpression is taken up within each plate

mesoscale dynamics of a deepening secondary cyclone in fastex iop16 three dimensional structure retrieved from dropsonde data the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex intensive observation period iop 16 are documented using airborne dropsonde data the method proposed to recover the mesoscale analytical three dimensional 3 d dynamic fields from the dropsonde measurements is evaluated using simulated fields airborne in situ measurements and airborne doppler radar measurements these simulations and comparisons indicate that the method is able to resolve the mesoscale structures within the studied secondary cyclone both in the regions of clear air and precipitation it appears however that the most accurate description of the 3 d dynamic fields in both these regions would be obtained by combining doppler and dropsonde measurements the studied secondary cyclone is a fast moving frontal wave that developed on the trailing cold front of a parent low situated over greenland using the dropsonde derived 3 d fields the mesoscale flows involved in the organization of the secondary cyclone are described the potential vorticity and equivalent potential vorticity fields deduced from the basic analytical fields indicate that the atmosphere is roughly neutral to moist slantwise instability this configuration is known to significantly promote frontogenesis the vertical configuration of the jets and circulations within this secondary cyclone are compared with the coupling uncoupling scheme of shapiro a slight coupling is found between the thermally indirect circulation and the ageostrophic circulation the obtained coupling is however not as developed as in the ideal case described by shapiro which may explain the small upward velocities in our case airborne doppler radar and dropsonde measurements are combined so as to infer the multi scale processes involved in the mesoscale and convective scale organization of the atlantic secondary cyclones and to evaluate the new emerging theoretical interpretations of secondary cyclogenesis

the possible influence of upstream upper level baroclinic processes on the development of the qe ii storm abstract an analysis of the qe ii storm of 9 11 september 1978 presents evidence for the existence of upper level baroclinic processes upstream of the rapidly developing cyclone the analysis shows that a deepening shortwave trough was located 400 to 500 km upstream of the site of the storm 12 h prior to rapid cyclogenesis the trough was associated with 1 a polar jet marked by 65 m s 1 winds in its core and significant vertical and horizontal wind shear 2 positive vorticity advection and divergence at the 300 mb level and 3 an intense frontal zone that extended from 300 mb down to the surface it also appears that a tropopause fold likely extruded stratospheric air down to the 700 800 mb level 400 500 km upstream of the surface low and 12 h prior to the explosive development phase of the cyclone these findings raise questions about gyakum s assertion that the qe ii storm developed in an area in which the baroclinic support was confined to the lower troposphere and the related assertion by anthes e

the santa rosa event 40ar 39ar and paleomagnetic results from the valles rhyolite near jaramillo creek jemez mountains new mexico the jaramillo event was originally defined by doell and dalrymple in 1966 on the basis of k ar ages from sanidine in the normally transitionally and reversely magnetized rhyolite domes named cerro del abrigo cerro santa rosa i and cerro santa rosa ii respectively that erupted following collapse of the archetypal valles caldera new mexico we have collected new paleomagnetic data from the three domes and new 40 ar 39 ar laser fusion and furnace incremental heating experiments on sanidine crystals from the cerro santa rosa i rhyolite step wise alternating field and thermal demagnetization techniques applied to 52 samples from seven sites indicate that the original paleomagnetic results of doell and dalrymple science 152 1966 1060 1061 are valid cerro del abrigo is normally magnetized whereas the santa rosa i dome is transitional with an inclination of 363 toward the east and the santa rosa ii dome is of reversed polarity twenty five laser fusion experiments on sanidine crystals from the the cerro santa rosa i dome together with the saddle shaped spectrum obtained by incrementally heating the sanidine in a furnace reveal that this rhyolite contained a small but significant component of excess argon prior to eruption our preferred age of 936 8 ka 2c for the santa rosa i rhyolite is based on the concordant laser fusion isochron and incremental heating plateau ages this age is significantly older than was inferred on the basis of earlier laser fusion 40 ar 39 ar results that suggested a trapped component characterized by a 40 ar 36 ar ratio lower than the atmospheric value of 295 5 our new age distinguishes the santa rosa i dome by 65 kyr from the termination of the jaramillo normal subchron 1001 10 ka and by 37 kyr from basaltic lavas at haleakala and tahiti which record the kamikatsura event 899 6 ka moreover this determination is a factor of three more precise than the best previous estimate for a proposed geomagnetic event in this time period the cerro santa rosa i rhyolite dome once intimately linked with the end of the jaramillo event and the acceptance of plate tectonic theory now defines a highly resolved feature the santa rosa event in a terrestrial geomagnetic reversal time scale that is consistent with the global record of magnetic field intensity from marine sediments fl 2002 elsevier science b v all rights reserved

cenozoic thermal evolution and tectonics of the coast mountains of british columbia 1 fission track dating apparent uplift rates and patterns of uplift the high relief of the coast mountains of british columbia has been produced in part by rapid late neogene uplift the relationship of this uplift to the presently diverse and complex plate tectonic regime off the west coast of british columbia however is not clear cut to study this problem the areal patterns rates and total amounts of cenozoic uplift from 50 to 55 n have been determined by using fission track dating of zircon and apatite separated from rocks collected at high and low altitudes along several traverses through the mountains accepting closure temperatures of 105 c 10 c and 175 c 20 c for apatite and zircon respectively and a likely closure temperature difference between zircon and apatite of 70 15 c paleogeothermal gradients have been measured at kemano c km 35 ma ago and near ocean falls king island c km 20 ma ago subcrustal heat flow is suggested to have significantly increased in the late neogene near king island uplift rates in the axial part of the northern 52 55 n coast mountains were 0 1 0 2 km ma from 25 to 15 ma ago this uplift was temporally and tectonically related to part of the subsidence in the adjacent queen charlotte basin uplift rates increased somewhat in the late miocene to about 0 4 km ma probably due to passage of the anahim hot spot beneath the area late miocene recent erosion in the north 52 55 n has reduced summit altitudes and been more extensive than farther south despite this relicts of miocene river valleys and topography are still locally preserved partly beneath 7 10 ma basalts the area of the present southern 50 to 52 n coast mountains was near sea level and experienced very low uplift rates 0 5 km ma of the southern coast mountains the profile of this uplift was broadly plateaulike and this uplift led to the inversion of the miocene coastal topography middle cenozoic uplift from 52 to 55 n was probably the result of denudation and diminishing uplift after the terminal paleocene eocene orogenic episode which grossly thickened the crust this middle cenozoic erosion resulted in the restoration of a normal crustal thickness late neogene uplift in the coast mountains was the result of thermal expansion in the mantle caused by a mantle hot spot near 53 n and changes in the geometry of the subducted slab farther south

a bimodal volcanic plutonic system the zarembo island extrusive suite and the burnett inlet intrusive complex the zarembo island volcanic rocks and the burnett inlet plutonic complex in central southeastern alaska were investigated to determine if they are genetically related the zarembo island volcanic suite consists of basalt andesite and rhyolite lava flows which exhibit features that suggest simultaneous eruptions of mafic and felsic lavas five kilometres to the southeast the broadly layered burnett inlet plutonic complex consists of gabbro diorite and granite plutons that also show characteristics of contemporaneous mafic and felsic magmatism these bimodal volcanic and plutonic rocks are similar in age ranging from 18 5 to 21 5 ma both suites show a gap in silica concentration between 60 and 65 wt and have similar major trace and rare earth element composition both suites also show igneous layering either as interlayered basalt and rhyolite flows or as alternating gabbro and granite sheets additionally both groups contain magma mingling and mixing textures including mafic enclaves in felsic members and quartz xenocrysts rimmed by clinopyroxene in enclaves these characteristics suggest that the burnett inlet intrusive complex and the zarembo island volcanic suite represent an eroded shallow level plutonic center and its eruptive cover the style of volcanism and the bimodal nature of magmatism suggest that igneous activity occurred during crustal extension and thinning that accompanied strike slip tectonic motion in southeastern alaska during the tertiary the volcanic plutonic rock associations now exposed at the surface indicate that at least 7 of post 20 ma crustal tilting has affected the region and can help to explain aberrant paleomagnetic poles in mid cretaceous intrusions of the cordillera coast belt

a review of the structure and dynamics of upper level frontal zones abstract this article presents a review of upper level fronts with the intent of synthesizing observational and modeling studies into a conceptual and dynamical description of these fronts and their evolution relative to the life cycle of midlatitude baroclinic waves the discussion begins by tracing present day concepts concerning the structure of upper level frontal systems which are based on composite analyses of radiosonde and aircraft data from their origins in the pioneering analyses of upper air data in the 1930s perspectives from scales both smaller and larger than upper level frontal systems are provided respectively by considering the effects of turbulent processes on frontal structure and dynamics and by relating variations in frontal structure to the evolution of the baroclinic waves that provide the dynamical environment for upper level frontogenesis the dynamics of upper level fronts are shown to comprise the interactions between the primary geostrophic and secondary ageostrophic cir

tertiary extension and tilting in the queen charlotte islands evidence from dyke swarms and their paleomagnetism the queen charlotte islands form the western margin of the tertiary queen charlotte basin which is situated on the western margin of the north american plate they contain seven major dyke swarms of late eocene to miocene age a period when the relative motions of the pacific and the north american plates in this region were dominantly dextral strike slip transform margin with intervals of highly oblique divergence and convergence within each swarm dykes have a systematic trend however trends vary from swarm to swarm indicating that the stress field varied a total of 678 cores 1352 specimens were collected from 129 dykes in six swarms over a distance of about 200 km magnetic stability is variable one hundred and one dykes yielded records of the paleofield data are also reported from an oligocene pluton 5 sites 27 cores 52 specimens and miocene lavas 8 sites 52 cores 101 specimens both normal and reversed magnetizations occur but irrespective of sign the mean directions of remanen

kinematics and tectonic significance of transpressive structures within the coast plutonic complex british columbia abstract structural data from the coast plutonic complex near prince rupert british columbia are consistent with a deformational history dominated by dextral transpression from campanian to paleocene time penetrative east side up southwest directed ductile shearing produced moderately northeast plunging overturned kilometer scale isoclinal folds these folds are dextrally sheared and refolded into kilometer scale upright northwest plunging folds and steeply dipping transposed foliations with moderate to shallow northwest plunging lineations along their western side an east side up component to the transcurrent shearing is kinematically compatible with east side up shearing found within the great tonalite sill kinematic and geometric gradients and the spatial distribution of the finite stretching direction are interpreted to result from partitioning of transpression the location of these structures and overprinting relationships suggest the great tonalite sill intruded late kinematically into a crustal scale dextral transpressive shear zone these results indicate this shear zone could form part of the baja b c fault system that would have accommodated large northward displacements of the terranes making up western british columbia and southeast alaska this conclusion is based on 1 it is favorably located to accommodate the proposed displacements 2 deformation occurred during the time period of proposed large displacement 83 59 ma 3 the 15 km thickness of the shear zone indicates it records large displacements

mesoscale convective complexes over the united states during 1983 abstract enhanced infrared satellite imagery is used to document the occurrence of mesoscale convective complexes over the united states during 1983 thirty large convective systems are identified that display satellite observable characteristics which satisfy the mcc criteria described by maddox details of the life cycles of these 30 systems are given and four examples are discussed in the context of large scale midtropospheric features this is the third in a series of annual summaries assembled as a documentation for those interested in investigating the mesoscale convective weather systems that occur over the united states

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

convective activity in an extratropical cyclone and its warm conveyor belt a case study combining observations and a convection permitting model simulation warm conveyor belts wcbs are important lagrangian features in extratropical cyclones for the evolution of clouds precipitation and flow dynamics according to the classical concept wcbs rise continuously from the boundary layer to the upper troposphere with ascent rates of less than 50 hpa hr recent studies identified embedded convection in wcbs with ascent rates exceeding 50 hpa hr however its significance and characteristics have not yet been analysed systematically this study presents a detailed analysis of a frontal wave cyclone that occurred during the north atlantic waveguide and downstream impact experiment nawdex and investigates the occurrence of convection with ascent rates exceeding 100 200 hpa hr embedded in the wcb a set of diagnostics based on the combination of meteosat products ecmwf data and a convection permitting simulation reveals consistently that convection occurs frequently in the warm sector of the investigated cyclone in particular in the region of the wcb these convective regions are characterized by increased surface precipitation low values of convective available potential energy and significant large scale forcing for ascent indicating that this type of convection embedded in wcbs differs from classical air mass convection with higher vertical velocities this is qualitatively confirmed by airborne radar observations of the considered cyclone with reflectivities hardly exceeding 30 dbz in the investigated wcb the ascent is not continuous but characterized by intermittent periods of very strong or even convective ascent and occasionally by short periods of descent together these results provide a refined view on the concept of wcbs and its embedded convection

chemical air mass differences near fronts two case studies are presented of aircraft measurements ozone noy co and meteorological parameters in the vicinity of fronts located over the eastern side of the north atlantic ocean during spring 1994 the aim of these studies was twofold 1 to investigate whether frontal circulations can transport ozone from the boundary layer to the free troposphere in well defined layer and 2 to ascertain whether or not conveyor belts associated with extratropical cyclones exhibit well defined chemical signatures the first case study march 2 1994 sampled a well defined ozone enhanced layer within the free troposphere it is demonstrated that this air was transferred from the boundary layer to the free troposphere during the development of a baroclinic wave two warm conveyor belts sampled within this flight one associated with the developing baroclinic wave and the other with a mature low pressure system displayed clear and contrasting chemical signatures a consequence of their geographically different origins during the second case study april 25 1994 both the dry intrusion and the warm conveyor belt of a mature occluded low pressure system were sampled their chemical signatures in particular that of the dry intrusion showed that interleaving of the two airstreams had occurred probably in the vicinity of the occluded front it is thus demonstrated that chemical measurements within conveyor belts provide valuable information on the nature history and extent of these coherent flows

post 10 ma uplift and exhumation of the northern coast mountains british columbia apatite u th he ages reveal three distinct periods in the exhumation history of the northern coast mountains 54 n a well developed helium partial retention zone indicates little or no exhumation between ca 30 and 10 ma beginning at 10 ma and extending to at least 4 ma the range underwent steady but slow exhumation of 0 22 mm yr after which the exhumation rate increased by at least 70 an 85 km long he age traverse across the orogen at sea level shows that vertical offsets on post 10 ma faults are minor furthermore the sea level he ages 14 2 8 ma inversely correlate with local mean elevation along the traverse these data suggest that the coast mountains first appeared as a significant topographic feature only within the past few million years this history is not consistent with suggestions that uplift of the range resulted from formation of the queen charlotte basin in early middle miocene time we speculate that intense erosion by alpine and continental glaciation after 2 5 ma triggered isostatic uplift and creation of the modern topography of the coast mountains

mesoscale precipitation patterns in extratropical cyclones and implications for cyclone development analysis of the surface distribution of precipitation associated with intense extratropical cyclones reveals elongated maxima aligned with the steering flow rapidly intensifying cyclones create precipitation maxima which are better defined and contain more moisture than weaker cyclones the distributions are associated with the formation of a precipitation generating zone pgz aligned with the midtropospheric jet ahead of and parallel to the surface cold front extending southward from the surface low these zones tend to move along their axes and are host to the most frequent and intense convective activity in the extratropical cyclone hourly rain gage measurements at sites in their path indicate an average of three precipitation peaks in 16 storms studied although radar echoes disclose that many mesoscale structures with high reflectivity are simultaneously active it is hypothesized that formation of such zones is most pronounced when momentum transport out of the jet increases the advection of warm moist air at low levels thereby sustaining or increasing convective instability in this context the pgz becomes the dominant feature of the extratropical cyclone and is crucial to intensification

fragmentation of stratospheric intrusions evidence is presented pointing to the existence of rich and coherent subsynoptic and mesoscale flow features at tropopause levels these features are related to and evolve from the classical v shaped intrusions of stratospheric air down to tropospheric elevations it is shown that intrusions can develop into elongated 2000 3000 km and slender 200 km streamers and that thereafter such a streamer can roll up to form a train of stalactite shaped vortex subentities with an accompanying substantial thinning of the intervening filament in addition there are indications that the vortices themselves can develop a spirallike interior structure of interleaved stratospheric and tropospheric air these inferences are based upon two independent but complementary sources analysis of the potential vorticity distribution on tropopause transcending isentropic surfaces derived from the analysis fields of the european centre for medium range weather forecasts either directly or indirectly using a contour advection technique and imagery from the water vapor channel of the european space agency meteosat 4 satellite streamers were observed to occur with a frequency of approximately one per week over central and southern europe during the winter of 1991 1992 the fragmentation is linked to the instability or self development of a filament of enhanced potential vorticity and it can modify or instigate surface weather systems moreover by inducing a substantial and rapid enlargement of the intrusion s surface area it greatly enhances the potential for local irreversible mixing of stratospheric and tropospheric air

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

coastal and baja california paleomagnetism reconsidered systematic reappraisal of paleomagnetic data from upper mesozoic and lower cenozoic sedimentary rocks and igneous rocks of late mesozoic age in coastal and baja california indicates that pluton tilt and shallowing of paleomagnetic directions by sedimentary compaction resolve observed discordances with the north american apparent polar wander apw path when the best available reference paleopoles are used for comparison the hypothesis of major tectonic transport in excess of distances inherent in current models for evolution of the san andreas transform system is unnecessary and in conflict with geologic observations fresh insights derived from recent data sets and improved analysis include the following 1 the limited paleomagnetic data recording primary remanence for upper jurassic and lower cretaceous volcanic rocks in coastal california are concordant with the north american apw path 2 the tilt of the peninsular ranges batholith inferred from paleobarometric data eliminates its declination discordance and reduces its inclination discordance to a level where ovals of confidence for observed and expected paleomagnetic directions overlap 3 key cretaceous and paleogene red bed successions on the salinian block of coastal california and in baja california have yielded concordant paleolatitudes 4 the discordances of different apparent paleolatitudes inferred from cretaceous and paleogene marine sedimentary strata lie within a range that can be attributed to compaction shallowing on the basis of both experimental information and observations from elsewhere 5 turbidites are more susceptible to compaction shallowing than shelf and deltaic strata 6 the uniform rotation of paleomagnetic directions inferred previously for peninsular california is not supported by the full array of data now available from multiple localities 7 basement ties of the salinian block in california and of the baja california peninsula to the continental interior preclude any hypothesis for tectonic transport much in excess of san andreas transform slip

plate motions in the north pacific the 43 ma nonevent the hawaiian emperor seamount chain in the north pacific ocean is commonly considered to have been produced by motion of the pacific plate over a hotspot if the hotspot is assumed to have remained fixed in a mantle frame of reference the 60 change in trend between the hawaiian and emperor portions of the chain results from a change in motion direction of the pacific plate relative to the mantle at 43 ma during middle eocene time such a large and abrupt direction change should result in significant plate reorganizations and tectonic events in the pacific and surrounding plates but no evidence for these events can be found in addition in this paper it is shown that there were no changes in relative plate motions between pacific area plates that can be associated with the hawaiian emperor bend this is done by calculating motion of the pacific farallon and kula plates relative to asia and north america using the plate circuit farallon pacific antarctica africa north america asia with no major regional tectonic event at the time of the bend it is suggested that there was no plate reorganization at 43 ma and that the emperor portion of the seamount chain was formed by a nonstationary hotspot

a simple model for the synoptic analysis of cold fronts a split cold front model with an over running upper front or humidity front ahead of a surface front or humidity front is shown to provide a useful representation of the principal characteristics of many katafronts the use of such a model leads to more consistent analyses especially of cloud and rain than are achieved using unmodified classical concepts

age origin and significance of brittle faulting and pseudotachylyte along the coast shear zone prince rupert british columbia northwest striking brittle faults containing cataclasite fault gouge and in one location pseudotachylyte are common in the vicinity of the coast shear zone near prince rupert british columbia the pseudotachylyte locality found in a dextral strike slip fault zone along the coast shear zone contains spherulites alkali feldspar microlites and amygdules suggesting that the pseudotachylyte crystallized rapidly from a melt phase within 5 km of the surface 4 0 ar 3 9 ar incremental heating of the pseudotachylyte matrix yielded a weighted mean plateau of 29 8 0 6 ma and an inverse isochron of 29 8 1 5 ma with an 4 0 ar 3 6 ar intercept of 296 0 15 2 these results show that pseudotachylyte associated with brittle faulting can be dated precisely and imply that some dextral coast parallel displacement occurred across the coast shear zone in the oligocene and that the majority of exhumation in the coast mountains at the latitude of prince rupert 54 n was accomplished by 30 ma

mesoscale analysis of arc rainbands in a dry slot a series of almost concentric are shaped narrow rainbands was observed travelling at 140 km h 1 and producing severe wind gusts over parts of england their structure and environment have been analysed using radar and satellite imagery mesoscale model diagnostics surface observations and additional rawinsonde ascents obtained during the fronts and atlantic storm track experiment fastex the multiple rainband event is shown to have been associated with part of a dry intrusion characterized by a mesoscale vortex cold pool the event occurred within the dry slot region of a small frontal cyclone where the mesoscale pool of cold dry air was overrunning warm sector air continuous wind profiles from a uhf radar together with a well located rawinsonde at the epicentre of the arc rainbands showed that the major anomaly in the cold pool was an area of locally stronger winds 40 m s 1 at 800 hpa colocated with the temperature minimum at that level the observed orientation of the rainbands is explained in terms of the cold frontal structure at this level triggering ascent of the underlying warm moist air the multiple nature of the arc rainbands remains unexplained the possibilities of mesoscale gravity waves and conditional symmetric instability are both considered

high resolution observations of the trowal warm frontal region of two continental winter cyclones abstract this paper compares the structure of the trough of warm air aloft trowal warm frontal region of two continental wintertime cyclones the cyclones were observed over the central great lakes region during the lake induced convection experiment snowband dynamics project field campaign the cyclones had different origins with the first forming east of the colorado rockies and the second forming over the gulf of mexico they were associated with different upper level flow regimes one located just north of a nearly zonal jet and the other located just west of a nearly meridional jet both storms produced heavy swaths of snow across the states of illinois wisconsin and michigan high resolution observations of frontal structure were made during flights of the national center for atmospheric research electra aircraft using dropsondes and the electra doppler radar tail radar system the high resolution observations suggest a different arrangement of air masses in the trowal region compared with the

a lagrangian based analysis of extratropical cyclones ii a detailed case study a detailed case study analysis is undertaken of the occurrence of significant coherent ensembles of trajectories cets that accompany atlantic cyclogenesis the approach is based upon the lagrangian based analysis scheme introduced in part i the analysis reveals the existence of several distinct moist ascending and dry descending cets two types of moist ascending cets associated with strong condensational processes ascend from the boundary layer of the warm sector either in the close vicinity of the cyclone centre or in the trailing cold frontal region the latter is the main contributor to the precipitation along the cold front during the early phase of the development another type of moist cets distinguished by maximum water vapour flux travels at low levels through the warm sector and ascends to mid tropospheric levels in the warm frontal region where it produces strong precipitation around the time of maximum storm intensity cets with an upper level origin are linked to the classical dry intrusion different cets correspond to strong descent of upper level tropospheric air that penetrated to the lower troposphere the movement of stratospheric air toward the centre of the maturing cyclone and an event of stratosphere to troposphere exchange upstream of the upper level trough two different visualizations of time sequences of the moist ascending cets indicate that they represent well defined flexible tubes or airstreams that exist over a time period comparable with the duration of the main cyclone intensification they provide a translating flexible but coherent river bed for the quasi continuous ascent of moist boundary layer air to the upper troposphere these tubes are akin to the concept of warm conveyor belts and the present analysis method objectively diagnoses their geometrical and physical characteristics and potential vorticity pattern some consideration is also given to the relationship of cets and tropospheric rivers and to possible shortcomings of the approach

mesoscale analysis of a polar trough interacting with a polar front the interaction of a polar trough with a polar front can lead to a characteristic satellite cloud pattern commonly referred to as an instant occlusion the detailed structure and development of an event rather resembling an instant occlusion is analysed in this paper using routine data supplemented by additional radiosondes soundings and cloud imagery from noaa 7 and meteosat and radar network pictures the event presented differs from an instant occlusion as described by anderson and others in that a band of polar front cloud developed simultaneously with the band of cloud associated with the polar trough rather than being a pre existing feature thus we refer to it under the different name of pseudo occlusion in order to keep this distinction in mind a conceptual model of the pseudo occlusion is developed in which the key elements are i a moist relatively warm low level jet associated with the polar trough referred to as the polar trough conveyor belt and ii a major upper level jet streak associated with the polar front referred to as the polar front conveyor belt the two conveyor belts intersect almost at right angles precipitation associated with the polar front is predominantly from stratiform cloud whereas that associated with the polar trough is a mixture of stratiform and convective just on the poleward side of the upper jet the cloud top drops abruptly here dry air having recently descended beneath the tropopause fold suppresses the depth of the moist air associated with the polar trough conveyor belt this leads to a minimum in the intensity of precipitation between the rain areas associated with the trough and the front although the air overrunning the trough just on the poleward side of the polar front is dry as a result of earlier descent the air in this location is likely to have begun ascending as part of the indirect circulation in the exit region of the upper level jet streak the polar trough low level jet probably forms part of this circulation

passage of a tracer through frontal zones a model for the formation of forward sloping cold fronts it is shown that a forward sloping cold front may form in a simple two dimensional model of an atmospheric frontal zone through differential advection of dry and wet bulb potential temperature as such two frontal zones may coexist with opposing slopes this behaviour is manifest in the neutral eady edge wave which exhibits kata cold front behaviour while the unstable eady wave with an ana cold front does not generate a forward sloping cold front these results come about as a consequence of the wave like behaviour of the fronts in the model that is the ability of a front to propagate through the air locally as such they highlight the fact that a frontal zone need not be a barrier to airflow and that any air properties from water vapour to atmospheric pollution may pass through a front

high resolution analysis of frontal fracture abstract a mesoscale array of dropwindsondes released in a small rapidly deepening frontal wave cyclone in the eastern north atlantic during the fronts 92 experiment has been assimilated into a 17 km grid mesoscale model nested within the meteorological office s operational limited area model the mesoscale model reproduced the evolving cloud pattern with cloud head and dry slot seen in satellite imagery it also revealed a well defined evolution in the three dimensional thermodynamic structure associated with the process known as frontal fracture the frontal fracture was revealed most clearly in the pattern of wet bulb potential temperature w which was distorted by an effective differential rotation the rotation increasing with height this led to backward tilted w surfaces and ana cold frontal characteristics in the cloud head to the north of the center of rotation and to forward tilted w surfaces and kata cold frontal characteristics in the dry slot to the south of the center of rota

secondary cyclogenesis along an occluded front leading to damaging wind gusts windstorm kyrill january 2007 abstractwindstorm kyrill affected large parts of europe in january 2007 and caused widespread havoc and loss of life in this study the formation of a secondary cyclone kyrill ii along the occluded front of the mature cyclone kyrill and the occurrence of severe wind gusts as kyrill ii passed over germany are investigated with the help of high resolution regional climate model simulations kyrill underwent an explosive cyclogenesis south of greenland as the storm crossed poleward of an intense upper level jet stream later in its life cycle secondary cyclogenesis occurred just west of the british isles the formation of kyrill ii along the occluded front was associated i with frontolytic strain and ii with strong diabatic heating in combination with a developing upper level shortwave trough sensitivity studies with reduced latent heat release feature a similar development but a weaker secondary cyclone revealing the importance of diabatic processes during the formation of kyrill ii kyrill ii moved

the linkage between the warm and the cold conveyor belts in an idealized extratropical cyclone abstractthis study continues the investigation of airstreams in idealized moist baroclinic waves and addresses the formation of the cold conveyor belt ccb its linkage to the warm conveyor belt wcb and their impact on the development of a midlatitude cyclone the ccb is identified as a coherent bundle of trajectories characterized by weak ascent and a strong increase of potential vorticity pv along the flow in contrast to the wcb defined as the trajectories with maximum ascent the authors illuminate the role of the two conveyor belts in the formation of two strong pv anomalies that form in the upper wcb negative pv anomaly and lower troposphere ccb positive pv anomaly respectively and thereby establish a link between these airstreams and relevant aspects of the dynamics of extratropical cyclones the ccb moves close to the surface along the colder side of the bent back front and experiences a pv increase as it passes below a region of maximum latent heat release at midtropospheric level

stochastic determination of well capture zones a stochastic approach is adopted for characterizing the uncertainty in well capture zones in heterogeneous formations transmissivity is modeled as a random space function and a monte carlo approach is used to infer the probability distribution of the resulting stochastic capture zones through several numerical experiments the influence of the statistical parameters of transmissivity variation on the extent of uncertainty in the location of the capture zone is investigated two aquifer models are considered a fully confined aquifer and a leaky confined aquifer receiving recharge from above a connection is made with previous work on transport theory and the statistical parameters of the capture zone probability distribution are compared with those of a solute concentration plume

pacific and atlantic bomb like deepenings in mature phase a comparative study the mesoscale dynamics of a secondary cyclone sampled during the field phase of the fronts and atlantic storm track experiment fastex are documented using airborne doppler radar data the high quality of the mesoscale airborne doppler dataset collected within this secondary cyclone is highlighted this study demonstrates however the need to combine in the near future airborne doppler radar and dropsonde measurements in order to access multiscale processes involved in the mature stage of this fastex cyclone both in clear air and in precipitating regions the studied secondary cyclone developed on the trailing cold front of a parent low situated over greenland and underwent the most explosive deepening roughly 54 mb in 24 hours sampled in the multiscale sampling area during fastex the main flows responsible for the mesoscale organization of the cyclone are a warm airflow emerging from the base of the synoptic warm conveyor belt that generates the most active part of the cloud head a dry intrusion approaching in the dry slot the cyclone centre a cold conveyor belt that contributes to the upward mass transport towards the upper part of the polar front cloud band and a cold northerly flow in the western part of the cloud head which tends to wrap around the low centre and is likely to release convective instability through air sea interactions this study also documents a slight shift in position between the high vertical vorticity core associated with the active part of the cloud head and the location of the pressure minimum the detailed three dimensional structure of this atlantic secondary cyclone is also compared with that gathered within another bomb like deepening defined as more than a 24 mb surface pressure drop in 24 hours observed over the pacific ocean during the coastal observation and simulation with topography coast experiment some similarities are found the main differences appear to be linked to the warm seclusion that is exclusive to the studied pacific cyclone more pronounced ascending motions are found within the cloud head of the pacific reference case and the deepening results from a more constructive effect of geostrophic and non geostrophic processes than for the atlantic reference case

paleomagnetic evidence for displacement from the south of the coast plutonic complex british columbia the mid cretaceous spuzzum and porteau plutons of the coast plutonic complex of british columbia have two magnetizations a and b the a magnetization eight sites 83 specimens d 30 3 i 56 7 95 4 9 paleolatitude 37 5 n paleopole 65 0 n 14 9 w a95 6 2 is considered to have been acquired in the age range 105 90 ma this result differs from the field established for cratonic north america in this time range the difference could be caused either by previously undetected tilting about a horizontal axis of the plutons or by their rotation about a vertical axis and lateral displacement relative to the craton previously observed mid cretaceous magnetizations from other rock units from the western canadian cordillera and the cascades of washington united states are similarly discordant with respect to the craton this similarity over such a large area indicates that although local undetected tilting could be partly responsible it is unlikely to be the prime cause and we argue ther

the dichotomous structure of the warm conveyor belt the warm conveyor belt wcb of an extratropical cyclone generally splits into two branches one branch wcb1 turns anticyclonically into the downstream upper level tropospheric ridge while the second branch wcb2 wraps cyclonically around the cyclone centre here the wcb split in a typical north atlantic cold season cyclone is analysed using two numerical models the met office unified model and the cosmo model the wcb flow is defined using off line trajectory analysis the two models represent the wcb split consistently the split occurs early in the evolution of the wcb with wcb1 experiencing maximum ascent at lower latitudes and with higher moisture content than wcb2 wcb1 ascends abruptly along the cold front where the resolved ascent rates are greatest and there is also line convection in contrast wcb2 remains at lower levels for longer before undergoing saturated large scale ascent over the system s warm front the greater moisture in wcb1 inflow results in greater net potential temperature change from latent heat release which determines the final isentropic level of each branch wcb1 also exhibits lower outflow potential vorticity values than wcb2 complementary diagnostics in the two models are utilised to study the influence of individual diabatic processes on the wcb total diabatic heating rates along the wcb branches are comparable in the two models with microphysical processes in the large scale cloud schemes being the major contributor to this heating however the different convective parametrization schemes used by the models cause significantly different contributions to the total heating these results have implications for studies on the influence of the wcb outflow in rossby wave evolution and breaking key aspects are the net potential temperature change and the isentropic level of the outflow which together will influence the relative mass going into each wcb branch and the associated negative pv anomalies at the tropopause level flow

efficient approximate spectral method to delineate stochastic well capture zones in nonstationary groundwater flow systems summary this study presents an unconditional approximate spectral method asm to delineate well capture zones in nonstationary groundwater systems taking advantages of spectral theories in solving unmodeled small scale variability in hydraulic conductivity k the proposed spectral method can efficiently estimate flow uncertainties such velocity uncertainties associated with the concept of particle tracking can delineate well capture zones for groundwater systems with practical complexities and scales in this study the developed asm is assessed to quantify the accuracy of delineated well capture zones under a variety of conditions including bounded flow domains flow systems with multiple wells multiple hydraulic conductivity scales and nonstationary flows caused by complex sources and sinks in the modeling areas the asm solutions are systematically compared with the corresponding numerical solutions of nonstationary spectral method nsm and monte carlo simulation mcs simulation results reveal that the proposed asm is computationally efficient and the solutions of velocity variances agree well with the corresponding numerical solutions of nsm and mcs based on the simple and efficient approximations the developed asm can delineate accurately the mean and variance dynamics of capture zones in complex large scale groundwater flow systems

variation of frontal and precipitation structure along a cold front a diagnostic study is presented to illustrate the sequence of events in which a warm conveyor belt wcb flow is drawn into the circulation of a developing extratropical cyclone and interacts with dry air aloft to produce distinctive precipitation structures the poleward boundary of the upstream end of the wcb was associated with a classical ana cold frontal structure the other end of the wcb flow closer to the cyclone centre was overrun by a dry intrusion of low wet bulb potential temperature air to give a split kata cold front the orientation of the surface cold front i e the wcb boundary changed significantly between these two parts but the orientation of the surface geostrophic flow within the wcb changed relatively little between the two parts the surface cold front was characterized in most places by a narrow cold frontal rainband composed of shallow line convection elements precipitation cores aligned nearly parallel to the surface geostrophic flow in the wcb the changing relationship between the frontal orientation and the direction of the surface flow accounts for the fact that the line convection elements occurred end to end to give almost two dimensional line convection along the classical ana part of the cold front but were non aligned and widely spaced along the split cold front part

observations of the mesoscale sub structure in the cold air of a developing frontal cyclone observations from 58 dropwindsondes released in a mesoscale array during the fronts 92 experiment are interpreted in the context of satellite imagery to derive the mesoscale structure and evolution of parts of a frontal cyclone developing over the eastern north atlantic a conceptual model involving the intertwining of dry intrusion and cloud head flows is corroborated and is used to provide the framework for interpreting the detailed mesoscale behaviour in the cold air two distinct dry intrusions were responsible for two cold fronts trailing south westwards from the tip of the cloud head both were surface features at the beginning of our study but the leading one evolved into an upper front with mid level convection as the dry intrusion responsible for it overran the warm sector areas of both high and low potential vorticity were indicated within the dry intrusions upon encountering a critical level of zero system relative velocity at the top of the moist boundary layer the dry intrusions arrival was associated with the development of multiple dry and moist laminae near the top of the boundary layer the vertical wavelength of the laminae was about 1 km and they extended over 200 km in the front normal direction with a slope of typically 1 in 60 although most parts of the laminae were subsaturated their circulations combined with the double structure of the dry intrusions to produce multiple shallow cloud lines within the boundary layer these formed as an extension of the south western tip of the cloud head associated with the developing cyclone possible mechanisms for generating the observed structures are discussed

the relation of moist symmetric instability and upper level potential vorticity anomalies to the observed evolution of cloud heads the cloud head phenomenon has been known for some time as a precursor of rapid cyclogenesis based upon satellite imagery two stages of cloud head development are identified in this study that can be related to early and late stages of the associated cyclone weakly convex cloud heads emerge from the baroclinic zone at an early stage in cyclogenesis and strongly convex cloud heads develop in association with the rapid deepening of the cyclone trajectories are used to highlight the role of an upper level potential vorticity pv anomaly in the growth of the strongly convex cloud head and the main flow associated with the growth of the strongly convex cloud head is viewed using isentropic analysis the possible role of moist symmetric instability in the development of both weakly and strongly convex cloud heads is discussed and a new diagnostic for measuring the vertically integrated extent of realizable symmetric vrs instability based on the moist geostrophic pv is introduced royal meteorological society 2002 g j shutt s contribution is crown copyright

dynamics of a bomb like deepening secondary cyclone from airborne doppler radar during the second field phase of the coast coastal observations and simulations with topography experiment an extremely deep secondary cyclone was sampled over the open pacific ocean by an airborne doppler radar this secondary low led a few hours later to strong damage from central california to washington as it moved northward along the western us coast the present paper gives mesoscale dynamical insight into this deep secondary low it reveals a warm seclusion situation with the colder airflow that cyclonically encircles the low centre in quasi gradient wind balance state a conceptual representation of the mesoscale airflow circulation in the low centre area is given this study also validates new analysis methods developed to access three dimensional dynamical fields at mesoscale from airborne doppler radar measurements within secondary cyclones these methods will be used intensively to process airborne radar data gathered during the field phase of the fastex fronts and atlantic storm track experiment project so as to scrutinize multiscale processes involved in secondary cyclogenesis over the atlantic

structure and evolution of an isolated semi geostrophic cyclone the evolution and structure of an indealized low pressure system is studied within the framework of the semi geostrophic dynamics and in the limit of uniform potential vorticiy an isolated cyclone is grown from suitably chosen initial conditions rather than studying the evolution of a longitudinally periodic train of baroclinic systems it is shown that the resulting development is able to produce a range of flow features that compare favourably with observationally based conceptual models of cyclogenesis these features include in particular i the simultaneous occurrence of both a cold and a warm front whose alignment shows some of the characteristics of occluded frontal systems and is skin to the notion of a frontal fracture ii a dry descending air stream to the rear of the cyclone iii a narrow region of maximum ascent within the warm front an its bent back portion iv a poleward traveling air stream ahead of the cold front and v a shaped pattern of vertical lifting comparable with the cloud patterns as commonly observed in satellite pictures the evolving cyclone is analysed both form lagrangian and eulerian viewpoints it is demonstrated that lagrangian criteria exist that allow for the objective definition of air streams and flow patterns within developing cyclones the structures of cold and warm fronts at low levels are significantly affected by the different nature of the lagrangian trajectories within each of these regions in particular the air parcels in the warm frontal region are transported rapidly towards the centre of the low resulting in a low level warm front with an intrinsically three dimensional structure and an associated vorticity gradient in the along front direction

reexamining the cold conveyor belt abstract despite the popularity of the conveyor belt model for portraying the airflow through midlatitude cyclones questions arise as to the path of the cold conveyor belt the lower tropospheric airflow poleward of and underneath the warm front some studies beginning with carlson s analysis of the eastern u s cyclone of 5 december 1977 depict the cold conveyor belt moving westward reaching the northwest quadrant of the storm turning abruptly anticyclonically rising to jet level and departing the cyclone downstream hereafter the anticyclonic path other studies depict the cold conveyor belt reaching the northwest quadrant turning cyclonically around the low center and remaining in the lower troposphere the cyclonic path to clarify the path of the cold conveyor belt the present study reexamines carlson s analysis of the cold conveyor belt using an observational and mesoscale numerical modeling study of the 5 december 1977 cyclone this reexamination raises several previously unappreciated

uncertainties and implications of the late cretaceous and tertiary position of north america relative to the farallon kula and pacific plates we present updated global plate reconstructions and calculated uncertainties of the pacific kula and farallon vancouver plates relative to north america for selected times since 68 ma improved magnetic data from the indian ocean decrease the uncertainties in the global plate circuit approach these uncertainties are now considerably smaller than those inherent in equivalent reconstructions based on the assumption of fixed hotspots major differences between these results and those of others are due to our use of more detailed africa north america reconstructions separate vancouver and farallon plate reconstructions and the assumption of a rigid antarctica plate during cenozoic time the uncertainties in the relative positions of the pacific and north america plates since the time of anomaly 7 26 ma range up to 100 km in position or from 1 to 3 m y in time if the mendocino triple junction initiated at about 28 5 ma its position would have been at 31 3 n 130 km relative to fixed north america unacceptable overlap of oceanic crust of the pacific plate with continental crust of western north america in the anomaly 10 30 ma reconstruction is a minimum of 340 200 km along an azimuth of n60 e and may be accounted for by basin and range extension pacific north america displacement in the past 20 ma is found to be considerably less than that calculated by fixed hotspot reconstructions farallon vancouver north america convergence velocity decreased greatly between the times of anomalies 24 and 21 56 to 50 ma prior to the 43 ma age of the hawaiian emperor bend and the often quoted 40 ma end of the laramide orogeny a change in direction of farallon north america convergence occurred sometime between 50 and 42 ma and also may not correlate with the time of the hawaiian emperor bend the lack of data from subducted parts of the farallon and kula plates permits many possibilities regarding the position of the kula farallon ridge the age of subducted crust or the position of oceanic plateaus during the laramide orogeny leaving open the question of the relationship between plate tectonic scenarios and tectonic style during laramide time displacements of points on the various oceanic plates along the west coast of an arbitrarily fixed north america during the interval between anomalies 30 31 and 18 68 to 42 ma are found to be pacific plate 1700 200 km northward farallon plate 3200 400 km northeastward vancouver plate 3000 400 km northeastward kula plate if attached to the pacific plate after a24 time 2500 400 km northward

neogene tilting of crustal panels near wrangell alaska a late oligocene miocene igneous complex south and west of wrangell alaska contains mafic dikes that yield a discordant paleomagnetic direction inclination i 70 4 declination d 39 3 95 4 8 n 72 sites combined with local and regional geobarometric metamorphic and structural observations the discordant paleomagnetic direction indicates east side up tilt by 16 about a tilt axis with azimuth 8 neogene tilt of crustal blocks in the insular superterrane accounts for much of the paleomagnetic discordance in cretaceous plutons without the coastwise translation of 1000 km as suggested by the baja british columbia hypothesis

determination of a well head protection zone by stochastic inverse modelling abstract capture zones of wells play an important role in the protection of groundwater against pollution by persistent chemical compounds groundwater flow models can be used to delineate capture zones as however the accuracy and uniqueness of such models may be poor the outcome of a deterministic modelling exercise is likely to be unreliable in such a case stochastic modelling presents an alternative for the delineation of capture zones in this paper two methods are compared the unconditional and conditional monte carlo simulation in each method realizations of the aquifer characterized by a combination of recharge rates and transmissivity values are produced for each realization the capture zone of the well is determined by particle tracking by superposition of all capture zones produced a probability distribution is obtained that describes the probability of a point on the ground surface to belong to the capture zone this probability is given by the fraction of catchments among all realizations which contain the point conditioning the calculation with measured heads usually implies a zoning or spatial resolution of the transmissivity distribution the need for identification of large scale features for a meaningful zonation is stressed for a given zoned aquifer the influence of successively adding measured heads used to condition the stochasticsis studied with an increasing number of conditioning heads the probability distribution of the capture zone is shown to narrow this method allows the quantification of the value of measured head data

dry intrusions lagrangian climatology and dynamical impact on the planetary boundary layer abstractdry air intrusions dis are dry deeply descending airstreams from the upper troposphere toward the planetary boundary layer pbl the significance of dis spans a variety of aspects including the interaction with convection extratropical cyclones and fronts the pbl and extreme surface weather here a lagrangian definition for di trajectories is used and applied to ecmwf interim reanalysis era interim data based on the criterion of a minimum descent of 400 hpa during 48 h a first global lagrangian climatology of di trajectories is compiled for the years 1979 2014 allowing quantitative understanding of the occurrence and variability of dis as well as the dynamical and thermodynamical interactions that determine their impact dis occur mainly in winter while traveling equatorward from 40 50 latitude dis typically reach the lower troposphere with maximum frequencies of 10 in winter in the storm track regions as well as over the mediterranean sea arabian sea and eastern north pa

uncertainty estimation of well catchments in heterogeneous aquifers 1 the uncertainty in the boundary of two dimensional steady state well catchments due to the uncertainty of the spatially variable hydraulic conductivity field is investigated the well discharge rate and the areal recharge rate are assumed constant the catchment boundary is traced by backward particle tracking in the velocity field the uncertainty bandwidth of the catchment boundary is approximated in first order by formulating the time dependent longitudinal and transversal second moments of the particle displacements along and normal to the mean particle trajectory applications of the approach are presented for a set of simple configurations the results are compared with the results from unconditional numerical monte carlo simulations the comparison allows an assessment of the accuracy the applicability and the limits of the method the approximation corresponds quite well with the monte carlo simulations provided that the distance to the domain boundary is sufficiently large

batholith emplacement at mid crustal levels and its exhumation within an obliquely convergent margin abstract emplacement of the central part of the coast mountains batholith of northern coastal british columbia occurred within a regime characterized by oblique convergence between the farallon kula and north american plates we use new structural kinematic and u pb isotopic data to show that the locations geometry and mechanisms of pluton emplacement within this batholith were controlled by displacements within a network of normal faults and transtensional shear zones these data also show that the most active period of pluton emplacement from 67 to 51 ma coincided with a change in style of deformation within the batholith prior to 67 ma plutons were emplaced within an arc dominated by regional scale contractional shear zones in contrast emplacement of 67 51 ma plutons occurred in an arc increasingly dominated by normal faults with arc parallel to oblique displacement and by sinistral transtensional shear zones we have identified and mapped the structure of three plutonic complexes composed of 67 to 51 ma plutons the khyex sill complex arden lake plutonic complex and quottoon plutonic complex shear zone controlled emplacement of plutons within the batholith accounts for the widely different orientations and structural features that characterize plutons within these three complexes during and after this latest cretaceous paleogene period of intense plutonic activity and accompanying deformation the deep roots of the batholith were rapidly unroofed by ductile normal faulting prior to 50 ma

mesoscale dynamics of the trowal and warm frontal regions of two continental winter cyclones abstract the dynamic and thermodynamic structure and associated frontal circulations within the trowal and warm frontal regions of two extratropical winter cyclones are examined using numerical simulations in each cyclone the warm moist airstream originating in the warm sector was found to bifurcate upon reaching the warm front one branch of the flow turned anticyclonically eastward corresponding to the warm conveyor belt while the second branch turned cyclonically westward becoming the trowal airstream the dynamic forcing of vertical motion within the two airstreams was investigated using the fifth generation pennsylvania state university national center for atmospheric research mesoscale model mm5 both from an analysis of the sawyer eliassen se equation in two dimensions and from complete model solutions shearing deformation associated with the jet stream and the low level cyclonic flow dominated confluent deformation near the trowal in both cases the shearing deformation was accompanied

paleomagnetic results from the mogollon datil volcanic field southwestern new mexico and a refined mid tertiary reference pole for north america miocene oligocene rocks of the mogollon datil volcanic field in southwestern new mexico have yielded paleomagnetic data giving 61 site mean unit vgps and a paleomagnetic pole located at 81 9 n 143 6 e a95 4 5 k 17 6 this pole is indistinguishable from other mid tertiary reference poles for north america combining the mogollon datil data with vgp data from other studies of mid tertiary 20 40 ma rocks yields a paleomagnetic pole at 81 5 n 147 3 e n 239 a95 2 4 k 15 4 when divided into normal and reversed polarity subsets the data yield paleomagnetic poles that are statistically different at the 95 confidence level mcfadden and lowes 1981 the paleopole determined from reversely magnetized units located at 78 6 n 138 5 e n 125 a95 3 4 k 14 5 is 6 8 on the far side of the paleopole determined from normally magnetized units positioned at 84 2 n 166 4 e n 114 a95 3 3 k 17 0 when viewed from a common site location i e the western united states similar pole positions an differences are also seen in 10 ma subsets of this data set incomplete removal of a normal overprint on the reversely magnetized units appears unlikely to explain these results rather we suggest that the differences are consistent with the concept that differing harmonics may be associated with the two polarity states over the long term merrill and mcelhinny 1977 merrill et al 1979

a revised kinematic model for the relative motion between pacific oceanic plates and north america since the late cretaceous 1 the convergence between the pacific farallon and kula oceanic plates and the north american plate has provided a driving force for tectonic processes that have shaped the western margin of north america yet reconstructions of plate motion in the pacific basin have traditionally relied on the assumption of fixed hot spots in the last decade substantial cretaceous to paleogene motion between the pacific and atlantic hot spots has been recognized providing motivation to reevaluate the history of relative motion between pacific oceanic plates and north america by means of plate circuit reconstructions this paper presents new kinematic models based on two alternative plate circuits linking the pacific plate to north america since late cretaceous time when compared to models relying on fixity of pacific and indo atlantic hot spots our reconstructions suggest that the pacific kula and pacific farallon ridges were 600 1000 km closer to the western margin of north america and hence that the farallon and kula plates were smaller in late cretaceous to middle eocene time these findings cast significant doubt on the viability of a configuration of the farallon kula ridge that juxtaposes the kula plate with the southern part of the paleo north american margin during this time interval the results of our new reconstructions also suggest more oblique convergence between the farallon or kula plate and north america from the late cretaceous to the middle eocene related to the combination of dominantly northwest motion of the pacific plate and steady southwest motion of north america this provides an efficient mechanism for the coast parallel translation of some accreted terranes of north america it may also explain the structure of geological units in western north america such as the central belt of the franciscan complex which show a dominant coast parallel fabric formed during an interval coeval with the episode of oblique convergence

exhumation and tilting of the western metamorphic belt of the coast orogen in southern southeastern alaska the uplift history of the western metamorphic belt in southern southeastern alaska can be traced using emplacement depths and cooling ages of mid cretaceous plutons which intruded the metamorphic belt during the period 101 ma to 89 ma during the period 101 ma to 94 ma the rocks of the metamorphic belt now at the surface were buried to a depth of approximately 30 km pressure data indicate that by 89 ma the western portion of the metamorphic belt was at a shallower crustal level 23 km within the study area while the eastern side remained at a depth of approximately 30 km cooling curves constructed from minerals in mid cretaceous plutonic rocks indicate that the western side of the metamorphic belt cooled earlier than the eastern side an observation consistent with the inferred uplift history southwestward transport of metamorphic belt rocks within the hanging walls of thrust and high angle faults may have provided one mechanism for uplift during mid to late cretaceous time the eastern portion of the western metamorphic belt cooled rapidly at 55 ma probably in response to a period of rapid uplift the coast shear zone an early tertiary high angle fault with west side up displacement bounds the east side of the metamorphic belt we suggest tertiary uplift occurred by tilting of the metamorphic belt due to movement along this fault

reply to comment by m e beck and b a housen on paleomagnetism and geochronology of the ecstall pluton in the coast mountains of british columbia evidence for local deformation rather than large scale transport

paleomagnetic quantification of upper plate deformation during miocene detachment faulting in the mohave mountains arizona 1 paleomagnetic data from miocene 20 ma volcanic rocks and dikes of west central arizona reveal the tilt history of proterozoic crystalline rocks in the hanging wall of the chemehuevi whipple mountains detachment fault we obtained magnetization data from dikes and flows in two structural blocks encompassing crossman peak and standard wash in the mohave mountains in the crossman block the dike swarm records two components of primary magnetization 1 cnh a normal polarity high unblocking temperature or high coercivity component inclination i 48 5 declination d 6 4 and 2 crhm a reversed polarity high temperature or high coercivity component i 33 6 d 197 5 argon age spectra imply that the dikes have not been reheated above 300 c since their emplacement and a baked contact test suggests that the magnetization is likely to be miocene in age crhm deviates from the expected direction of the miocene axial dipole field and is best explained as a result of progressive tilting about the strike of the overlying andesite flows these data suggest that the crossman block was tilted 60 to the southwest prior to intrusion of the vertical dike swarm and the block continued to tilt during a magnetic field reversal to normal polarity cnh miocene dikes in the crossman block are roughly coplanar so the younger dikes with normal polarity magnetization intruded along planes of weakness parallel to the earlier reversed polarity swarm an alternative explanation involves cnh magnetization being acquired later during hydrothermal alteration associated with the final stages of dike emplacement in the standard wash block the primary component of magnetization is a dual polarity high temperature or high coercivity component swhl i 7 2 d 0 7 to produce agreement between the expected miocene magnetic direction and the swh component requires 1 correcting for a 56 tilt about the strike of flow bedding and 2 removing a counterclockwise vertical axis rotation of 20 the two rotations restore the standard wash dikes to vertical make parallel the dike layering in the crossman and standard wash blocks and align the strikes of bedding in both blocks geologic mapping geochemical evidence and paleomagnetic data are consistent with the upper plate of the mohave mountains having tilted in response to formation of the underlying detachment fault

the presidents day cyclone of 18 19 february 1979 influence of upstream trough amplification and associated tropopause folding on rapid cyclogenesis abstract a diagnostic analysis of an amplifying polar jet trough system and associated tropopause fold which preceded the 19 february 1979 presidents day cyclone is presented the analysis is based on conventional radiosonde data infrared and visible satellite imagery 6 7 m water vapor measurements from the temperature humidity infrared radiometer thir and ozone measurements from the total ozone mapping spectrometer toms the case study indicates that dynamically forced meso scale vertical circulations played an important role in the extrusion of stratospheric air along the axis of a polar jet and the subsequent development of the storm system specific findings include 1 tropopause folding accompanying an amplifying polar jet trough system occurred along the axis of the intensifying polar jet in response to subsidence forced by geostrophic deformation patterns associated with the jet streak 2 the folding process extruded dry stratosphere air marked by high values of potential vorticity dow

paleomagnetism and tectonics of the cretaceous mt stuart batholith of washington translation or tilt abstract the mt stuart batholith is a composite pluton of late cretaceous age that intrudes the crystalline north cascades terrane of northwestern washington its paleomagnetic direction d 10 0 i 45 5 95 4 9 is markedly different from the direction expected for cretaceous rocks from northwestern washington d 330 5 i 73 0 which means that the mt stuart batholith either has moved relative to the north american interior or has been tilted through a substantial angle or both since it acquired its magnetism either tilt or translation are possible geometrically but translation is more likely because 1 local geology apparently does not support tilt in the required direction 2 it probably is not possible for a panel of rock the size of the mt stuart batholith to tilt through the necessary angle ca 35 after its deeper parts have cooled sufficiently to retain remanent magnetization 3 the sense of paleomagnetic discordance found in the mt stuart batholith clockwise rotation of declination flattened inclination is identical to that found in nearly every other allochthonous terrane in the western north american cordillera including every other cretaceous batholith studied except the sierra nevada

testing terrane transport an inclusive approach to the baja b c controversy the baja british columbia hypothesis holds that a large segment of the western edge of northern north america baja b c was situated alongside california and northern mexico in middle cretaceous time was displaced northward in the late cretaceous and paleocene by north oblique convergence of the kula plate with north america and arrived near its present location by the early eocene a consistent body of paleomagnetic data supports this hypothesis however doubt persists and various crucial tests of a geologic nature have been proposed one such test concerns the provenance of zircons in cretaceous sedimentary basins of baja b c in this paper we use both paleomagnetic data and zircon occurrences to reconfirm the baja b c hypothesis we first argue that the only truly crucial tests yet performed have been paleomagnetic and that all such tests have been positive second we show that detrital zircon data from the upper cretaceous nanaimo group although not a crucial test provide valuable paleogeographic information available data demonstrate a change in detrital zircon provenance in the nanaimo group that closely matches the position of these rocks predicted by the baja b c hypothesis detrital zircons in the nanaimo group suggest a change from a southwestern north american source rich in grenville and 1 4 1 5 ga rocks to an increasing contribution from older parts of the craton such as the wyoming province together detrital zircons and paleomagnetic inclinations allow us to assemble a detailed schedule of northward tectonic transport of the baja b c terranes