a p t t d discontinuity in east central nepal implications for the evolution of the himalayan mid crust abstract rock specimens collected from lower middle and upper portions of the exhumed himalayan mid crust in the upper tama kosi region of east central nepal yield pressure temperature time deformation p t t d paths that demonstrate the presence of a structural metamorphic and geochronologic discontinuity a p t t d path from below the discontinuity defines a loading path with deformation at staurolite grade metamorphic conditions occurring at 10 8 ma p t t d paths from above the discontinuity in contrast record an earlier and protracted metamorphic history that includes decompressional heating monazite ages from specimens collected above the discontinuity constrain prograde garnet growth to be 21 ma with decompression related garnet breakdown initiating at c 19 ma and likely continuing until c 15 ma these contrasting p t t d histories separated by a tectonometamorphic discontinuity are consistent with an evolutionary model for the himalaya in which rocks above the discontinuity were metamorphosed in the deep hinterland of the orogen and deformed during lateral extrusion from beneath tibet while rocks below the discontinuity were deformed and metamorphosed later within the shallower foreland of the orogen these results demonstrate the spatial and temporal relationships and compatibility between lateral midcrustal extrusive flow and wedge taper processes within an evolving orogen

an arctic ocean cold core eddy detailed physical and chemical observations were obtained during september 1997 of a cold core eddy situated in the southern central canada basin of the arctic ocean the eddy was about 20 km in diameter had maximum current speeds exceeding 20 cm s 21 and extended from the base of the upper mixed layer near 40 m down to 400 m excess salt in the eddy core was consistent with addition of brine from 1mo f ice formation core tracer distributions indicated a lifetime exceeding 1 year and were consistent with an origin as near surface pacific water with some admixed terrestrial runoff the eddy was probably formed in association with a polynya along the alaskan chukchi sea coast through local water densification from surface ice formation followed by development of frontal instabilities formation and subsequent migration of such eddies which may have lifetimes of several years provide a mechanism for transporting water from the beaufort and chukchi sea coastal and shelf regions into the interior canada basin and for contributing to maintenance of the permanent halocline present light ice conditions throughout the arctic ocean favor the formation of such eddies and may contribute to enhanced ventilation of the halocline waters

monazite xenotime garnet equilibrium in metapelites and a new monazite garnet thermometer prograde suites of pelitic rocks were examined with electron microprobe introduction and laser ablation inductively coupled plasma mass spectrometry to monazite ce la th po4 plays an important role in determine the systematics of element partitioning between coexisting studies of igneous and metamorphic petrogenesis foremonazite xenotime and garnet monazite grains that grew in most monazite is used to date specific events in a equilibrium with xenotime are enriched in y and dy compared with petrogenetic sequence e g parrish 1990 harrison et al monazite that grew in xenotime absent assemblages y and heavy 1997 hawkins bowring 1999 foster et al 2000 rare earth element contents of monazite coexisting with xenotime monazite may contain a large percentage of the sample increase with rising temperature monazite xenotime y gd and rare earth element ree budget and thus exert an y dy partitioning is systematic within a metamorphic grade and important influence on the evolution of melt composition increases slightly with increasing metamorphic grade suggesting wark miller 1993 bea 1996 the thermobarometric that monazite xenotime pairs approached partitioning equilibrium potential of monazite coexisting with xenotime has been garnet and monazite in both xenotime bearing and xenotime absent recognized leading to calibration of monazite geoassemblages show a strong r 0 94 systematic relationship thermometers gratz heinrich 1997 1998 heinrich between inverse temperature and ln keq for the net transfer equiet al 1997 andrehs heinrich 1998 in addition the librium yag oh ap 25 4 qtz 5 4 grs 5 4 an recognition that nearly all lead in monazite is radiogenic 3ypo4 mnz 1 2h2o suggesting that garnet and monazite parrish 1990 montel et al 1994 has led to development crystallized in compositional equilibrium the following temand application of electron microprobe monazite dating perature keq relationship for the equilibrium above has been derived techniques suzuki adachi 1991 montel et al 1996 williams et al 1999 t c 1 45p bars 447772 32052 567 40 rln keq 273 15 full realization of monazite as a thermochronometer requires detailed understanding of the specific reactions responsible for its formation previous studies of monazite with a precision of some 30 c for temperature estimates our petrogenesis have focused on monazite compositional observations suggest that major and accessory phases interact in a zonation zhu o nions 1999a 1999b monazite coupled fashion during metamorphism and also approach a state growth kinetics ayers et al 1999 behavior of monazite of compositional equilibrium as reactions proceed during hydrothermal alteration poitrasson et al 1996 crowley ghent 1999 and melting events watt 1995 or to a limited extent the influence of major phase mineral assemblage in monazite reactivity zhu

a long lived mesoscale convective complex part i the mountain generated component abstract using data collected during colorado state university s south park area cumulus experiment in 1977 a sequence of multi scale convective events leading to the formation of a mesoscale convective complex is described in the first phase surface based cool advection in the elevated mountain basin delayed the full transition of the morning boundary layer into a deep mixed layer until well after convective instability was reached over the adjacent ridges the second phase was earmarked by the formation of convective precipitation echoes at hot spots over the high mountain terrain two groups of cells then propagated eastward across the mountain basin forming a line of discrete cells which moved across the foothills toward the high plains the cells further intensified at the foothills high plains interface and formed a still larger north south line of thunderstorms in the third phase this north south line of thunderstorms evolved into an expanding meso scale convective cluster as it contin

discovery of a crystalline basement and early ordovician marine transgression in the karakorum mountain range pakistan a granite pluton intruding low grade quartzites and migmatites lies north of the karakorum axial batholith of cretaceous to miocene age the pluton is covered by transgressive litharenite and slate that contain a fairly rich assemblage of acritarchs of arenigian age early ordovician belonging to the peri gondwana biogeographic province this is the first time that crystalline basement has been found in karakorum and acritarchs in central asia these discoveries add new evidence that the karakorum microplate together with the helmand block of central afghanistan and the lhasa block of tibet belongs to a cimmerian domain at the northern fringe of gondwana

mesoscale air motions associated with a tropical squall line abstract composites of radar and wind observations in a coordinate system attached to a moving tropical squall line confirm that such a squall system is composed of two separate circulation features a convective squall line region and a stratiform anvil region the squall line region is characterized by mesoscale boundary layer convergence which feeds deep convective updrafts and mid to upper level divergence associated with outflow from the cells the anvil region is characterized by mid level convergence which feeds both a mesoscale downdraft below the anvil and a mesoscale updraft within the anvil cloud before this study the mesoscale updraft in the anvil cloud of the tropical squall system had been somewhat speculative and both the anvil updraft and downdraft had been inferred only qualitatively the occurrence of the anvil updraft is now proven and quantitative profiles of the mesoscale anvil updraft and downdraft have been obtained

evidence for the role of the lid and underunning in an outbreak of tornadic thunderstorms abstract on the last day of may 1985 a series of tornadic thunderstorms devastated pans of ohio pennsylvania new york and ontario canada analysis of this outbreak reveals that a lid which moved from the southwestern united states the previous day played a major role in enabling the latent instability to achieve large values severe convection began along the edge of the lid underrunning in a region experiencing baroclinically forced ascent associated with a migrating jet streak this paper discusses the role of the lid in the development of the latent instability the relationship between underrunning and the migrating jet streak and the effects of terrain on the evolution of latent instability and on the formation of the lid finally we present a climatological study of the lid in order to show why the convection was so severe yet so unusual in this part of the country

building the hindu kush monazite records of terrane accretion plutonism and the evolution of the himalaya karakoram tibet orogen in situ u th pb la icp ms monazite ages from the hindu kush of nw pakistan provide new petrochronologic constraints on the tectonic evolution of the himalaya karakoram tibet orogen monazites from two adjacent garnet staurolite schist specimens yield multiple age populations that record the major mesozoic and cenozoic deformational magmatic and metamorphic events along the southern margin of eurasia these include the accretion of the hindu kush sw pamir to eurasia during the late triassic followed by the accretion of the karakoram terrane in the early jurassic younger jurassic and cretaceous ages record the development of an andean style volcanic arc along the southern eurasian margin which ended with the docking of the kohistan island arc and the emplacement of the kohistan ladakh batholith during the late cretaceous the initial eocene collision of india with eurasia was followed by widespread high temperature metamorphism and anatexis associated with crustal thickening within the himalaya system in the late oligocene and early miocene

warm core vortex amplification over land abstract a convectively generated mesoscale vortex that was instrumental in initiating and organizing five successive mesoscale convective systems over a period of three days is documented two of these convective systems were especially intense and resulted in widespread heavy rain with localized flooding based upon radar and satellite data the detectable size of the vortex became much larger following the strong convective developments nearly tripling its initial diameter over its three day life cycle during nighttime when convection typically intensified within the vortex movement of the system tended to slow following dissipation of the convection in the morning the daytime movement accelerated cross sections of potential vorticity taken through the vortex center clearly show a maximum at midlevels and a well defined minimum directly above the vortex and the potential vorticity maximum were essentially colocated and the system was nearly axisymmetric in the vertical over the three day life

reconnaissance geology in upper chitral baroghil and karambar districts northern karakorum pakistan during the summer of 1992 a geological expedition crossed the northern karakorum range in northern pakistan from the chitral to karambar valleys from the villages of mastuj to imit some of the areas visited were geologically unknown a number of structural units were crossed belonging to the karakorum block or to other crustal blocks north of it they are a the axial batholith in which three plutonic bodies have been identified and b the northern sedimentary belt nsb in which three major tectonostratigraphic units form thrust stacks dipping to the north their internal stratigraphy and structural style are partly different the most complete contains a crystalline basement transgressed by a marine succession during the early ordovician the youngest strata are represented by the reshun conglomerate of inferred cretaceous age the northernmost unit of the nsb is tightly folded whereas the central one forms a monocline vertical faults mainly strike slip dissect the thrusted slabs metamorphic deformation is absent or reaches only the anchizone in the studied sector of the karakorum nsb to the north of the karakorum proper there are several other tectonic units separated by vertical faults they are from south to north a the tas kupruk zone with metavolcanics of basaltic to latibasaltic composition b the atark unit mostly consisting of massive carbonate rocks of mesozoic age and c the wakhan slates which consist of a thick widespread succession of dark slates metasiltites and sandstones the fine grained elastic rocks are supposed to be palaeozoic to early triassic in age the wakhan slates are intruded by plutons belonging to the east hindu kush batholith from which a single k ar age on muscovite gave a jurassic age

middle late jurassic tectonostratigraphic evolution of central asia implications for the collision of the karakoram lhasa block with asia mesozoic basins in different regions of central asia provide important records for investigating relationships between intraplate deformation in central asia and tectonic processes at asian boundaries the present study gives a review of the stratigraphic and structural evolution of basins in different regions of central asia during the middle late jurassic it is shown that basins and mountain belts in northwest china experienced compressional deformation and were wholly or partially uplifted during the late middle late jurassic compared to extensively distributed middle jurassic coal bearing strata in northwest china upper jurassic strata characterized by red mudstones and conglomerates have a much smaller distribution in the mean time the tibet pamir plateau also underwent a folding and uplift event and upper jurassic sedimentary rocks are generally missing in the pamir and western tibet the intense compressional deformation and uplift event of the late middle late jurassic from the tibet pamir plateau to northwest china requires a new tectonic model as proposed here we suggest that the karakoram and lhasa blocks were a single giant block which was accreted to asia in the late middle jurassic earliest cretaceous and cross cut by the karakoram fault in the cenozoic during the callovian the western part of the karakoram lhasa block initially collided with the southern asian margin collision and continued convergence during the late middle late jurassic caused sinistral strike slip faulting along the central badakhshan fault and south tian shan suture accommodating crustal shortening in areas to the southeast of the faults the pamir western tibet tarim block qilian qaidam block and bei shan meanwhile the northeastward transpressional motion of the tarim block produced strong compressional stresses to areas north of the tarim block the kyrgyz tian shan central tian shan junggar basin and turfan basin with the northward movement of the karakoram lhasa block the eastern part of the karakoram lhasa block began to collide with the southern asian margin during the latest jurassic earliest cretaceous resulting in strong crustal deformation and thickening in east asia and central asia

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

the spatial and temporal variability of convective storms over the northeast united states during the warm season abstract a spatial and temporal climatology of convective storms over the northeast united states during the warm season april september is presented using composite national operational weather radar nowrad data at 2 km grid spacing from 1996 to 2007 as well as cloud to ground lightning from the national lightning data network nldn on a 10 km grid from 2001 to 2007 there are preferred regions for convective storms within new york s hudson river valley western and southeastern pennsylvania central new jersey and across the delmarva peninsula a favored initiation area during the early afternoon is the immediate lee of the appalachians with a tendency for these convective systems to move eastward to the coast by late evening there is a sharp gradient in convective frequency within 20 km of the coast on average as a result of the relatively stable marine boundary layer but as the sea surface warms by midsummer this convective activity increases near the coast with a nocturnal 0600 1200 utc c

diurnal boundary layer development over sloping terrain abstract a one dimensional prognostic model of the atmospheric boundary layer coupled to a surface energy budget is described which utilizes a profile formulation non local for exchange coefficients in the daytime convective boundary layer and an exchange coefficient scheme based on local richardson number for the stable nocturnal boundary layer this combined local and non local model is used to simulate the full diurnal cycle of the boundary layer behavior of days 33 34 of the wangara experiment results of the simulation indicate that these simplified exchange coefficient schemes simulate the mean features of the boundary layer as well as the more complex and computationally expensive higher order closure models this diurnal boundary layer formulation is incorporated into a two dimensional mesoscale model employing a terrain following coordinate system to examine boundary layer behavior over sloping terrain similar to that of the great plains of the united states particular emphasis is placed on th

processes controlling the structure and longevity of two quasi linear convective systems crossing the southern new england coast abstractthis paper explores the structural evolution and physical processes that explain the modification of two quasi linear convective systems qlcss that encountered the densely populated new york city atlantic coastal region one qlcs on 31 may 2002 traversed the atlantic coastal boundary with little change in its intensity producing widespread severe wind damage across new york city and long island during this event warm air advection at 925 hpa helped destabilize the layer above this level over the coastal zone while the marine boundary layer deepened below this level the 0 3 km line perpendicular vertical wind shear was relatively strong which supported ascent along the leading edge of the diabatically generated cold pool the surface based convective system became slightly elevated as it moved over the marine waters in contrast the 23 july 2002 qlcs decayed upon encountering the atlantic coastline despite its coincidence with a surface cold front the most unstable cape values during thi

tectonic significance of 24 ma crustal melting in the eastern hindu kush pakistan northward directed subduction has continued beneath the hindu kush from the mesozoic when the region formed part of the southern margin of asia until today the kohistan arc was accreted at ca 100 ma followed by the indian plate at 54 50 ma after the india asia collision a regional crustal melting event occurred at ca 25 21 ma to the east of the hindu kush in the karakoram range producing the baltoro pluton in the eastern hindu kush range most of the granitoids appear to be subduction related plutons that predate the india asia collision however the gharam chasma pluton is a two mica garnet tourmaline leucogranite that has intruded into staurolite grade schists and sillimanite k feldspar grade migmatites u pb ages on monazite xenotime and uraninite from undeformed samples of the gharam chasma pluton and a leucogranite dike that crosscuts the migmatites indicate that crustal melting occurred at ca 24 ma synchronous with the baltoro melting event this age also provides an upper limit on the age of the regional staurolite grade metamorphism in the eastern hindu kush

the interaction of simulated squall lines with idealized mountain ridges abstract numerical simulations of squall lines traversing sinusoidal mountain ridges are performed using the advanced regional prediction system cloud resolving model precipitation and updraft strength are enhanced through orographic ascent as a squall line approaches a ridge the simulated squall line then weakens as it descends the ridge because some of the cold pool is blocked by the terrain resulting in less lift along the gust front and weaker convective cells the flow within the cold pool accelerates slightly and the depth of the cold air decreases owing to upstream blocking transitioning the flow in the cold pool head from subcritical to supercritical then back to subcritical at the bottom of the ridge a hydraulic jump forms when the flow transitions the second time enabling the development of a new convective line downwind of the mountain these new updrafts grow and eventually replace the older updrafts that weakened during descent this process results in the discrete propagation of a squ

cooling exhumation and deformation in the hindu kush nw pakistan new constraints from preliminary 40ar 39ar and fission track analyses abstract asian crust in the hindu kush region in northern pakistan records a protracted history of rifting subduction and collision not commonly preserved within the himalaya because of this it is key to understanding the development of the southern eurasian margin both prior to and after collision with india new mica 40ar 39ar and apatite fission track geochronologic data from this region provide constraints on the kinematics of the hindu kush 40ar 39ar muscovite and biotite ages from the late cambrian kafiristan pluton are 379 7 1 7 ma and 47 2 0 3 ma respectively the muscovite age may record cooling or partial resetting while the biotite age is interpreted to record a thermal disruption associated with the early stages of continental collision in the himalayan system a 111 0 0 6 ma muscovite age from the northern part of the tirich mir pluton 123 ma old u pb is interpreted to indicate a recrystallization event 12 myrs after its intrusion in addition a younger muscovite age of 47 5 0 2 ma was derived from the opposite side of the same pluton in the immediate hanging wall of the tirich mir fault this eocene age is interpreted to represent the time of recrystallization during fault re activation in the early stages of india asia continent continent collision 40ar 39ar biotite analysis from the buni zom pluton yields an age of 61 6 1 1 ma and is interpreted to reflect cooling at mid upper crustal levels subsequent to the pluton s emplacement in the middle cretaceous finally 17 1 21 3 ma 40ar 39ar ages from the garam chasma pluton and surrounding metapelites indicate cooling immediately following crystallization of the leucogranite body in the earliest miocene latest oligocene the younger cooling history is resolved by fission track dating of apatite aft in the vicinity of the bounding tirich mir fault the tirich mir pluton yields an aft age of 1 4 0 3 ma which is consistent with active exhumation associated with the surface uplift of the 7700 m tirich mir peak the garam chasma pluton has a young age of 3 5 0 2 ma which also records rapid rock uplift and exhumation in the area finally an aft age of 9 1 2 1 ma was extracted from a metapelite in the footwall of an east verging thrust fault separating it from the garam chasma pluton to the west the difference in ages pliocene vs late miocene reflect differential cooling exhumation paths across that structure

old origin for an active mountain range geology and geochronology of the eastern hindu kush pakistan prior to accretion of the kohistan island arc during the late cretaceous and final suturing of india with asia at ca 50 ma the hindu kush mountains along the border of afghanistan and northwest pakistan were situated on the active southern margin of asia geology and geochronology of the eastern hindu kush range in pakistan demonstrate that localized crustal melting and leucogranite intrusion took place in the gharam chasma area at ca 24 ma more regionally developed and widespread deformation metamorphism and magmatism took place before collision between both india and the kohistan island arc with asia ca 195 ma u pb monazite ages on a deformed leucogranite dike from the upper lutkho valley indicate an early jurassic phase of crustal melting u pb monazite ages of 135 126 ma on a staurolite schist from near gharam chasma are interpreted as a minimum age for staurolite grade metamorphism within the tirich mir fault zone pegmatite dikes crosscut the staurolite schists u pb dating of uraninites from one of these pegmatite dikes reveals an age of 114 2 ma monazites from the same rock give ages of 125 121 ma possibly due to inheritance of older cores these jurassic early cretaceous constraints on metamorphism and magmatism relate to subduction and accretion processes perhaps including the suturing of the karakoram and hindu kush terranes along the tirich mir fault in general high temperature low pressure metamorphism and subduction related granitoid magmatism in the eastern hindu kush suggest a high thermal gradient in an active margin setting from early jurassic to cretaceous time

triple doppler analysis of a discretely propagating long lived high plains squall line abstract a nonsevere squall line that developed on 21 june 1993 along the northern foothills of the colorado rocky mountains is analyzed using a series of triple doppler analyses this squall line developed in a relatively dry environment characterized by weak low level but strong upper level vertical shear of the horizontal winds the drier thermodynamic profile as characterized by a higher lifting condensation level and weak low level shear resulted in convection forming not along but rather 7 10 km behind the leading edge of the shallow cold pool the strong upper level shear established a predominantly leading anvil this led to a suppression zone immediately ahead of the leading line which in turn resulted in a discrete mode of propagation of the squall line three different cycles were observed each cycle had a distinct line of convective cells that initiate intensify and then decay in each case the new cells developed 20 40 km out ahead of the decaying line of the previous cycle many studi

a climatology of the structure evolution and propagation of midlatitude cyclones in the southeast united states abstractthe seasonal and interannual variability of the structure evolution and propagation of midlatitude cyclones in the southeast united states are studied using a composite analysis in the upper levels the composites show that the axis of the wintertime upper level trough remains north south oriented and propagates eastward along 40 n while the summertime upper level trough has a much slower propagation at a farther north latitude and an axis that is tilted in the northeast southwest direction upper level circulation changes are consistent with a shift from wintertime cyclonic behavior to summertime anticyclonic behavior midlatitude cyclones significant changes in the low level structure and precipitation patterns of midlatitude cyclones ensue from these upper level changes while the winter composite is characterized by eastward propagating midlatitude cyclones that extend deep into the subtropics the summer composite is characterized by semistationary midlatitude troughs that only briefl

tectono metamorphic evolution of the karakorum metamorphic complex dassu askole area ne pakistan exhumation of mid crustal ht mp gneisses in a convergent context the south karakorum margin east of the himalayan syntaxis consist of an e w elongated zone of young 10 3 ma high grade metamorphic rocks m2 and related migmatitic domes this late tectono metamorphic event post dates the palaeogene 55 37 ma phase of thickening of the belt featured by nw se structures and associated m1 amphibolite facies metamorphism 0 7 gpa 700 c this m2 metamorphism is characterised by low pressure high temperature conditions coeval with migmatite formation in response to a thermal increase of c 150 c compared to m1 culminating at a temperature of c 770 c and a pressure of 0 5 0 6 gpa rapid exhumation of migmatitic domes at a rate of 5 mm yr 1 was accommodated by vertical extrusion in the core of e w crustal scale folds these crustal scale folds formed in response to n s syn collisional shortening and were enhanced by thermal weakening of the migmatised continental crust m2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid crustal level such relationships between a mantle related magmatism and a high temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted indian slab since 20 ma

organizational modes of midlatitude mesoscale convective systems this paper discusses common modes of mesoscale convective organization using 2 km national composite reflectivity data the authors investigated linear mesoscale convective systems mcss that occurred in the central united states during may 1996 and may 1997 based upon the radar observed characteristics of 88 linear mcss the authors propose a new taxonomy comprising convective lines with trailing ts leading ls and parallel ps stratiform precipitation while the ts archetype was found to be the dominant mode of linear mcs organization the ls and ps archetypes composed nearly 40 of the studied population in this paper the authors document the characteristics of each linear mcs class and use operational surface and upper air data to describe their different environments in particular wind profiler data reveal that the stratiform precipitation arrangement associated with each class was roughly consistent with the advection of hydrometeors implied by the mean middle and upper tropospheric storm relative winds which were significantly different among the three mcs modes case study examples are presented for both the ls and ps classes which have received relatively little attention to this point as well the authors give a general overview of the synoptic scale meteorology accompanying linear mcss in this study which was generally similar to that observed by previous investigators

the new york bight jet climatology and dynamical evolution abstract this paper describes the southerly new york bight nyb jet 11 17 m s 1 that develops primarily during the warm season just above the surface offshore east of the northern new jersey coast and south of long island the nyb observations from two offshore buoys are used to develop a 9 yr climatology of 134 jet events from 1997 to 2006 there is a seasonal maximum 2 5 events per month during june and july with a skew toward the spring months the wind directions for the jet trace out a nearly elliptical orbit for the 24 h period around the time of jet maximum at 2300 utc 1900 eastern daylight time edt on average composites reveal that the nyb jet occurs on days with southwesterly synoptic flow and the jet is part of a larger scale 200 300 km wind enhancement offshore of the mid atlantic and northeast u s coasts during the early evening hours high resolution observations surface mesonet aircraft soundings and a terminal doppler weather radar and weather research and forecastin

metamorphic history of the south tibetan detachment system mt everest region revealed by rscm thermometry and phase equilibria modelling this study combines microstructural observations with raman spectroscopy on carbonaceous material rscm phase equilibria modelling and u pb dating of titanite to delineate the metamorphic history of a well exposed section through the south tibetan detachment system stds in the dzakaa chu valley of southern tibet in the hanging wall of the stds undeformed tibetan sedimentary series rocks consistently record peak metamorphic temperatures of 340 c temperatures increase down section reaching 650 c at the base of the shear zone defining an apparent metamorphic field gradient of 310 c km 1 across the entire structure u th pb geochronological data indicate that metamorphism and deformation at high temperatures occurred over a protracted period from at least 20 to 13 ma deformation within this 1 km thick zone of distributed top down to the northeast ductile shear included a strong component of vertical shortening and was responsible for significant condensing of palaeo isotherms along the upper margin of the greater himalayan series ghs we interpret the preservation of such a high metamorphic gradient to be the result of a progressive up section migration in the locus of deformation within the zone this segment of the stds provides a detailed thermal and kinematic record of the exhumation of footwall ghs rocks from beneath the southern margin of the tibetan plateau

insights into the evolution of the hindu kush kohistan karakoram from modern river sand detrital geo and thermochronological studies the hindu kush kohistan karakoram region is critical to understanding the long term accretion history of the south asian margin pre and post india asia collision and the impact of these collisions on the development of high topography however knowledge about this region remains incomplete due to sparse studies here we present a study comprising detrital zircon u pb geochronology detrital muscovite 40ar 39ar thermochronology and numerical modeling on 40ar 39ar dates the study identifies zircon u pb age peaks at 200 ma 110 130 ma 60 80 ma and 28 40 ma supporting the polyphase collisions and crustal growth in the south asian margin modeling study reveals fast cooling erosion at 115 129 ma 69 71 ma 27 35 ma and 8 ma which are synchronous with collision related crustal growth indicating the significant impact of accretion both prior to and post india asia collision this study along with studies in eastern karakoram reveals along strike variations in erosion and exhumation with young since late miocene intense erosion focusing on the east central karakoram we suggest that this east west spatial variation in exhumation may have been associated with more intense crustal shortening and thus the greater crustal thickness topographic relief and altitude observed in the eastern compared to western karakoram

ice edge eddies in the fram strait marginal ice zone five prominent ice edge eddies in fram strait on the scale of 30 to 40 kilometers were observed over deep water within 77 n to 79 n and 5 w to 3 e the use of remote sensing a satellite tracked buoy and in situ oceanographic measurements showed the presence of eddies with orbital speeds of 30 to 40 centimeters per second and lifetimes of at least 20 days ice ablation measurements made within one of these ice ocean eddies indicated that melting which proceeded at rates of 20 to 40 centimeters per day is an important process in determining the ice edge position these studies give new insight on the formation propagation and dissipation of ice edge eddies

anatomy age and evolution of a collisional mountain belt the baltoro granite batholith and karakoram metamorphic complex pakistani karakoram abstract geological mapping and u th pb geochronology from the karakoram metamorphic complex and baltoro granite batholith has resulted in more detailed timing constraints on tectonic evolution of asian crust during and following collision and accretion of the kohistan arc and the indian plate to the southern margin of asia crustal thickening along the karakoram resulted in polyphase deformation metamorphism and melting u pb zircon and monazite ages show that kyanite and sillimanite grade metamorphism in the baltoro region peaked during oligocene early miocene c 28 22 ma times at structurally deeper levels sillimanite grade migmatites of the dassu dome have pliocene c 5 4 3 5 ma ages new u pb ages from crustal melt biotite muscovite garnet leucogranites from the trango towers cathedral peak and paiyu peak across the baltoro batholith range from 19 8 0 5 ma to perhaps as young as 14 ma using data from both the hunza and baltoro regions we suggest that regional high grade metamorphism was diachronous in space and time and could have lasted continuously for at least 37 ma c 50 13 ma or as much as 50 ma c 63 13 ma along the southern margin of the asian plate in the karakoram crustal melting along the baltoro granite batholith spanned at least 13 ma 26 4 13 ma supplementary material analytical methods and description of u th pb data of samples are available at http www geolsoc org uk sup18382

pre mesozoic alpine basements their place in the european paleozoic framework prior to their alpine overprinting most of the pre mesozoic basement areas in alpine orogenic structures shared a complex evolution starting with neoproterozoic sediments that are thought to have received detrital input from both west and east gondwanan cratonic sources a subsequent neoproterozoic cambrian active margin setting at the gondwana margin was followed by a cambrian ordovician rifting period including an ordovician cordillera like active margin setting during the late ordovician and silurian periods the future alpine domains recorded crustal extension along the gondwana margin announcing the future opening of the paleotethys oceanic domain most areas then underwent variscan orogenic events including continental subduction and collisions with avalonian type basement areas along laurussia and the juxtaposition and the duplication of terrane assemblages during strike slip accompanied by contemporaneous crustal shortening and the subduction of paleotethys under laurussia thereafter the final pangea assemblage underwent triassic and jurassic extension followed by tertiary shortening and leading to the buildup of the alpine mountain chain recent plate tectonic reconstructions place the alpine domains in their supposed initial cambrian ordovician positions in the eastern part of the gondwana margin where a stronger interference with the chinese blocks is proposed at least from the ordovician onward for the visean time of the variscan continental collision the distinction of the former tectonic lower plate situation is traceable but becomes blurred through the subsequent oblique subduction of paleotethys under laurussia accompanied by large scale strike slip since the pennsylvanian this global collisional scenario has been replaced by subsequent and ongoing shortening and strike slip under rising geothermal conditions and all of this occurred before all these puzzle elements underwent the complex alpine reorganization

wind driven freshwater buildup and release in the beaufort gyre constrained by mesoscale eddies recently the beaufort gyre has accumulated over 20 km3 of freshwater in response to strong anticyclonic atmospheric winds that have prevailed over the gyre for almost two decades here we explore key physical processes affecting the accumulation and release of freshwater within an idealized eddy resolving model of the beaufort gyre we demonstrate that a realistic halocline can be achieved when its deepening tendency due to ekman pumping is counteracted by the cumulative action of mesoscale eddies based on this balance we derive analytical scalings for the depth of the halocline and its spin up time scale and emphasize their explicit dependence on eddy dynamics our study further suggests that the beaufort gyre is currently in a state of high sensitivity to atmospheric winds however an intensification of surface stress would inevitably lead to a saturation of the freshwater content a constraint inherently set by the intricacies of the mesoscale eddy dynamics

five generations of monazite in langtang gneisses implications for chronology of the himalayan metamorphic core monazite grains from greater himalayan sequence gneisses langtang valley nepal were chemically mapped and then dated in situ via th pb ion microprobe analysis correlation of ages and chemistry reveals at least five different generations of monazite ranging from c 9 to 300 ma petrological models of monazite chemistry provide a link between these generations and the thermal evolution of these rocks yielding an age for the melting of greater himalayan rocks within the main central thrust sheet c 16 ma and for the timing of thrust sheet emplacement that are younger than commonly viewed chemical characterization of monazite is vital prior to chronological microanalysis and many ages previously reported for monazite from the greater himalayan sequence are interpretationally ambiguous

stratigraphic evidence for an early collision between northwest india and asia the collision of india with asia1 had a profound influence on late cretaceous and cenozoic oceanography2 climate3 fauna extinctions4 and the motion of at least some of the earth s litho spheric plates5 as the collision ended a period of rapid indo asian convergence6 a precise knowledge of its timing when the crust of the neo tethys ocean was completely subducted7 at some point along the plate boundary is important for understanding its wider consequences but current estimates of the collision age range from 65 to 38 myr before present6 8 11 here we report the results of extensive biostratigraphic analyses from waziristan and kurram in northwest pakistan which show that accretionary prism and trench strata were first thrust onto the northwest indian passive margin after 66 myr but before 55 5 myr after this time volcanic arc fragments the accretionary prism trench material and imbricates of the north indian slope were raised to shallow water depths and overlapped by upper palaeocene shallow water carbonates and shales12 14 indicative of post collision thrusting in this region finally both the suture and the indian craton were overlapped by continuous unconformable upper lower eocene shallow marine strata demonstrating that suturing was complete by 49 myr

characterizing thunderstorm gust fronts near complex terrain abstractfire safety aviation wind energy and structural engineering operations are impacted by thunderstorm outflow boundaries or gust fronts gfs particularly when they occur in mountainous te

lateral mixing across ice meltwater fronts of the chukchi sea shelf summer and fall hydrographic sections in the northeastern chukchi sea frequently capture 5 20 m thick intrapycnocline lenses or horizontal plumes of warm moderately salty summer bering sea water flowing northward from bering strait these features occur within the shallow 20 m depth pycnocline separating cold dilute surface meltwater from near freezing salty winter formed waters beneath the pycnocline an idealized numerical model suggests that the features arise from eddies and meanders generated by instability of the surface front separating meltwater from bering sea water warm bering sea water is transported across the front and into the pycnocline by the cross frontal velocities associated with the instabilities the accompanying lateral eddy heat fluxes may be important both in summer for promoting ice melt and in fall by delaying the onset of ice formation over portions of this shelf lateral heat flux magnitudes depend upon the stratification of the bering sea water

characterizing the eddy field in the arctic ocean halocline ice tethered profilers itp deployed in the arctic ocean between 2004 and 2013 have provided detailed temperature and salinity measurements of an assortment of halocline eddies a total of 127 mesoscale eddies have been detected 95 of which were anticyclones the majority of which had anomalously cold cores these cold core anticyclonic eddies were observed in the beaufort gyre region canadian water eddies and the vicinity of the transpolar drift stream eurasian water eddies an arctic wide calculation of the first baroclinic rossby deformation radius rd has been made using itp data coupled with climatology rd 13 km in the canadian water and 8 km in the eurasian water the observed eddies are found to have scales comparable to rd halocline eddies are in cyclogeostrophic balance and can be described by a rankine vortex with maximum azimuthal speeds between 0 05 and 0 4 m s the relationship between radius and thickness for the eddies is consistent with adjustment to the ambient stratification eddies may be divided into four groups each characterized by distinct core depths and core temperature and salinity properties suggesting multiple source regions and enabling speculation of varying formation mechanisms

age of crystallization and cooling of the k2 gneiss in the baltoro karakoram the mountains of k2 8611 m and broad peak 8047 m in the baltoro karakoram northern pakistan are composed of plagioclase homblende and biotite hornblende k feldspar orthogneisses and amphibolite facies paragneisses intruded by garnet biotite muscovite tourmaline leucogranitic veins a u pb zircon age of 115 120 ma was obtained on an orthogneiss from the south face of k2 40 ar 39 ar analysis on hornblende yields a plateau age of 90 6 1 8 ma consistent with a mid cretaceous phase of magmatism concomitant with early subduction related components of the karakoram batholith muztagh tower unit hunza plutonic unit we interpret the k2 gneiss as representing a culmination of mid crustal rocks along a discontinuous but wide zone north of the karakoram batholith

rainfall occurrence in the u s warm season the diurnal cycle the diurnal occurrence of warm season rainfall over the u s mainland is examined particularly in light of forcings at multiple scales the analysis is based on a radar dataset of 12 seasons duration covering the u s mainland from the continental divide eastward the dataset resolves 2 km features at 15 min intervals thus providing a detailed view of both large and regional scale diurnal patterns as well as the statistics of events underlying these patterns the results confirm recent findings with respect to the role of propagating rainfall systems and the high frequency at which these are excited by sensible heating over elevated terrain between the rockies and the appalachians 60 of midsummer rainfall occurs in this manner most rainfall in the central united states is nocturnal and may be attributed to the following three main forcings 1 the passage of eastward propagating rainfall systems with origins near the continental divide at 105 w 2 a nocturnal reversal of the mountain plains solenoid which is associated with widespread ascent over the plains and 3 the transport of energetic air and moisture convergence by the great plains low level jet other features of interest include effects of the appalachians semidiurnal signals of regional significance and the impact of breezes along the gulf of mexico a modest effort was put forth to discern signals associated with el nino and the southern oscillation while tendencies in precipitation patterns are observed the record is too short to draw conclusions of general significance

diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes over contiguous north china the diurnal evolution and distribution of warm season convective storms in different prevailing wind regimes at the 925 hpa and 500 hpa levels over contiguous north china have been studied using a climatology based on radar reflectivity mosaics soundings and reanalysis data from 15 may to 15 september in 2008 2011 in the wind regimes at the 925 hpa level the frequency of occurrence of convection is highest for south southwesterly flows followed by that for south southeasterly flows the low level southerly warm and moist flow over the foothills and plains favors initiation and intensification of convection resulting from topographic forcing among the wind regimes at the 500 hpa level the frequency of occurrence of convection shows a pronounced maximum for west southwesterly flows and most of these storms initiate and develop over the foothills and plains convection in the wind regime shows the morphology and slowly east southeastward moving characteristics of well organized longer lived systems with environmental conditions conducive to vertical wind shear and instability at the 500 hpa level the high frequency of occurrence of convection for west southwesterly flows is followed by that for west northwesterly flows under west northwesterly flows convective storms initiated over mountains located to the northwest in the early afternoon move rapidly to the plains in the southeast of the study region these storms show the primary formation characteristics of shorter lived convection and intensify noticeably as they move from the mountains to the foothills and plains

the spatial and temporal distribution of organized convective structures over the northeast and their ambient conditions abstract organized convective structures over the northeastern united states were classified for two warm seasons may august using 2 km composite radar i e the national operational weather radar nowrad data nine structures were identified three types of cellular convection clusters of cells isolated cells and broken lines five types of linear convection lines with no stratiform precipitation lines with trailing stratiform precipitation lines with parallel stratiform precipitation lines with leading stratiform precipitation and bow echoes and one nonlinear system the occurrence of all structures decreases from the western appalachian slopes eastward to the atlantic coast isolated cellular convection forms primarily during the morning to late afternoon 1200 2100 utc mainly over the high terrain clusters of cells form primarily over the appalachians and the atlantic coastal plain during the daytime 1200 0000 utc linear convection is favored from midafternoon to early evening 18

convective episodes in the east central united states nine years of composited radar data are investigated to assess the presence of organized convective episodes in the east central united states in the eastern united states the afternoon maximum in thunderstorms is ubiquitous over land however after removing this principal diurnal peak from the radar data the presence and motion of organized convective systems becomes apparent in both temporally averaged fields and in the statistics of convective episodes identified by an objective algorithm convective echoes are diurnally maximized over the appalachian chain and are repeatedly observed to move toward the east partly as a result of this the daily maximum in storms is delayed over the piedmont and coastal plain relative to the appalachian mountains and the atlantic coast during the 9 yr studied the objective algorithm identified 2128 total convective episodes 236 yr 1 with several recurring behaviors many systems developed over the elevated terrain during the afternoon and moved eastward often to the coastline and even offshore in addition numerous systems formed to the west of the appalachian mountains and moved into and across the eastern u s study domain in particular many nocturnal convective systems from the central united states entered the western side of the study domain frequently arriving at the eastern mountains around the next day s afternoon maximum in storm frequency a fraction of such well timed systems succeeded in crossing the appalachians and continuing across the piedmont and coastal plain convective episodes were most frequent during the high instability low shear months of summer which dominate the year round statistics even so an important result is that the episodes still occurred almost exclusively in above average vertical wind shear despite the overall dominance of the diurnal cycle the data show that adequate shear in the region frequently leads to long lived convective episodes with mesoscale organization

the cimmerian geopuzzle new data from south pamir based on its permian triassic stratigraphic and biotic evolution we correlate the se pamir to the karakoram terrane and we consider them equivalent along with the central pamir to the qiantang terrane of tibet all of palaeozoic gondwanan ancestry we prove the occurrence of a marked cimmerian unconformity documented by lowermost jurassic deposits suturing intensively faulted and folded permian and triassic units which suggests that the south pamir collided around the t j boundary with the central pamir along the rushan pshart suture collision of the karakoram to the south pamir happened slightly later along the wakhan tirich boundary zone progressive time shifting of deformation can be related to the complex setting of the cimmerian belt which was subdivided into minor blocks by incipient oceanic basins providing strong crustal mobility terra nova 25 352 360 2013

deterioration of perennial sea ice in the beaufort gyre from 2003 to 2012 and its impact on the oceanic freshwater cycle time series of ice draft from 2003 to 2012 from moored sonar data are used to investigate variability and describe the reduction of the perennial sea ice cover in the beaufort gyre bg culminating in the extreme minimum in 2012 negative trends in median ice drafts and most ice fractions are observed while open water and thinnest ice fractions 0 3 m have increased attesting to the ablation or removal of the older sea ice from the bg over the 9 year period monthly anomalies indicate a shift occurred toward thinner ice after 2007 in which the thicker ice evident at the northern stations was reduced differences in the ice characteristics between all of the stations also diminished so that the ice cover throughout the region became statistically homogenous the moored data are used in a relationship with satellite radiometer data to estimate ice volume changes throughout the bg summer solid fresh water content decreased drastically in consecutive years from 730 km3 in 2006 to 570 km3 in 2007 and to 240 km3 in 2008 after a short rebound solid fresh water fell below 220 km3 in 2012 meanwhile hydrographic data indicate that liquid fresh water in the bg in summer increased 5410 km3 from 2003 to 2010 and decreased at least 210 km3 by 2012 the reduction of both solid and liquid fresh water components indicates a net export of approximately 320 km3 of fresh water from the region occurred between 2010 and 2012 suggesting that the anticyclonic atmosphere ocean circulation has weakened

shallow and intermediate depth earthquakes in the hindu kush region across the afghan pakistan border abstract we investigated the spatio temporal seismicity parameters of shallow 0 70 km and intermediate 70 300 km depth earthquakes in the hindu kush region which is characterized by the occurrence of large earthquakes in a small zone of intense activity by way of comparison intermediate depth earthquakes dominate the hindu kush seismicity using a catalogue of 3820 earthquakes we determined the various earthquake histograms time series plots variations of frequency magnitude distribution b value and seismicity rate changes z value both time periods encompassing pre and post 1964 subsets of earthquakes differ significantly in terms of reporting earthquakes b and z value for shallow and intermediate seismicity the b values appear to be lower 1 07 and 0 90 for intermediate depth earthquakes than do the b values produced by shallow earthquakes 1 32 and 1 06 using the pre and post 1964 data sets the three low b value

wave disturbances and their role in the maintenance structure and evolution of a mesoscale convection system abstractthis study investigates a nocturnal mesoscale convective system mcs observed during the plains elevated convection at night pecan field campaign a series of wavelike features were obse

major intrusive stages in afghanistan typology age and geodynamic setting afghanistan straddles the gondwana eurasia boundary most of its major structural areas comprise large plutonic belts based on some 700 major element analyses the typology of the eleven main plutonic belts has been determined these belts differ from each other on the whole they display a very broad range of petrographic types from nepheline syenites and gabbros to leucocratic muscovite tourmaline granites and a wide diversity of magmatic associations from cafemic or alumino cafemic associations of various types tholeiitic calc alkaline subalkaline i e monzonitic alkaline peralkaline to various aluminous ones taking into account the typology of the belts and chronological data four major intrusive stages have been recognized and related to the geodynamic evolution of afghanistan and central asia 1 aluminous lower palaeozoic ca 500 ma stage related to linear crustal thinning at the gondwana scale 2 cafemic and alumino cafemic triassic ca 230 ma stage related to southward dipping subduction of oceanic crust beneath an island arc involving a large continental strip detached from the southern asia margin 3 cafemic and alumino cafemic cretaceous ca 100 ma stage dominantly related to subduction of oceanic crust under marginal gondwana fragments 4 eocene oligocene stage ca 35 ma induced by the india eurasia collision including two quite different groups of intrusives a a cafemic and alumino cafemic group related to extensional phenomena dominantly associated with the westward extrusion of central afghanistan along the herat fault these phenomena occurred on both sides of the gondwana palaeozoic asia boundary b an aluminous group resulting from crustal thickening in marginal gondwana fragments

the potential role of atmospheric bores and gravity waves in the initiation and maintenance of nocturnal convection over the southern great plains abstractthis investigation explores the relationship among bores gravity waves and convection within the nocturnal environment through the utilization of measurements taken during the internation

the structure evolution and dynamics of a nocturnal convective system simulated using the wrf arw model abstractprevious studies have documented a nocturnal maximum in thunderstorm frequency during the summer across the central united states forecast skill for these systems remains relatively low and the explanation for this nocturnal maximum is still an area of active debate this study utilized the wrf arw model to simulate a nocturnal mesoscale convective system that occurred over the southern great plains on 3 4 june 2013 a low level jet transported a narrow corridor of air above the nocturnal boundary layer with convective instability that exceeded what was observed in the daytime boundary layer the storm was elevated and associated with bores that assisted in the maintenance of the system three dimensional variations in the system s structure were found along the cold pool which were examined using convective system dynamics and wave theory shallow lifting occurred on the southern flank of the storm conversely the southeastern flank had deep lifting with favorable integrated vertical shear ov

the generation of a mesoscale convective system from mountain convection a mesoscale convective system mcs that formed just to the east of denver is investigated with a nonhydrostatic numerical model to determine which processes were important in its initiation the mcs developed from outflow from previous convective activity in the rocky mountains to the west model results indicate that this outflow was necessary for the development of the mcs even though a convergence line was already present in the area where the mcs developed a simulation with a 3 km grid spacing more fully resolves the convective activity in the mountains but the development of the mcs can be simulated with a 6 67 km grid cloud effects on solar radiation and ice sedimentation both influence the strength of the outflow from the mountain convection but only the ice sedimentation makes a significant impact on the development of the mcs after its initiation the frequent convective activity in the rocky mountains during the warm season provides outflow that would make mcs generation favorable in this region thus there is a close connection between mountain convective activity and mcs generation the implications of such a connection are discussed and possible directions of future research are indicated

numerical study of an observed orogenic mesoscale convective system part 1 simulated genesis and comparison with observations abstract the interaction of topographically induced thermally and mechanically driven diurnal flow regimes in the lee of the rockies is shown to lead to the growth of a mesoscale convective system mcs an organic mcs observed during the 1977 combined south park area cumulus experiment and high plains experiment is numerically simulated with a two dimensional nonhydrostatic cloud model covering spatial scales of 1000 km in this numerical investigation meso meso and meso scales of motion are represented simultaneously as a result interesting features of cloud mesoscale interaction are predicted that cannot be represented in cloud parameterization frameworks based on the results of this simulation a six stage conceptual model of orogenic development is given

eddies in the western arctic ocean from spaceborne sar observations over open ocean and marginal ice zones the western arctic ocean is a host to major ocean circulation systems many of which generate eddies that can transport water masses and corresponding tracers over long distances from their formation sites however comprehensive observations of critical eddy characteristics are currently not available and are limited to spatially and temporally sparse in situ observations here we use high resolution spaceborne synthetic aperture radar measurements to detect eddies from their surface imprints in ice free sea surface roughness and in sea ice patterns throughout marginal ice zones we provide the first estimate of eddy characteristics extending over the seasonally ice free and marginal ice zone regions of the western arctic ocean including their locations diameters and monthly distribution using available synthetic aperture radar data we identified over 4 000 open ocean eddies as well as over 3 500 eddies in marginal ice zones from june to october in 2007 2011 and 2016 eddies range in size between 0 5 and 100 km and are frequently found over the shelf and near continental slopes but also present in the deep canada basin and over the chukchi plateau we find that cyclonic eddies are twice more frequent compared to anticyclonic eddies at the surface distinct from the dominating anticyclonic eddies observed at depth by in situ moorings and ice tethered profilers our study supports the notion that eddies are ubiquitous in the western arctic ocean even in the presence of sea ice and emphasizes the need for improved ocean observations and modeling at eddy scales

coherent regeneration and the role of water vapor and shear in a long lived convective episode abstract in a recent radar based climatological study of warm season precipitation over the continental united states carbone et al found a high frequency of long lived coherent rainfall episodes many of the events were of longer duration than normally associated with mesoscale convective complexes and exhibited phase speeds 10 m s 1 in excess of the phase speed associated with synoptic systems the observations led to the speculation that cold pool dynamics and wavelike propagation mechanisms were responsible for the longevity of the systems one of the long lived episodes included in the statistics of the carbone et al study is described here occurring on 14 15 july 1998 the system lasted 50 h and traveled over 2800 km at its peak intensity the system was a bow echo producing damaging wind large hail and local flash flooding an interesting aspect of the event was an abrupt 90 turn in the storm s orientation and propagation vector midway through its life the environmental factors that led t

the detection and significance of diurnal pressure and potential vorticity anomalies east of the rockies abstract harmonic analysis of pressure temperature and precipitation data from 1000 automated surface observing system asos stations reveals a mix of stationary and east west moving disturbances east of the rockies optimization of the pressure data using a temperature based tide assumption separates a strong sun following continentally enhanced tide from a smaller eastward propagating wave epw the latter signal moves at a similar speed to the previously discovered eastward moving precipitation systems analysis of asos summer precipitation data confirms eastward propagation but east of 90 w it shows nonpropagating diurnal convection at a fixed local time i e 1800 lst analysis of winter days still finds the epw suggesting that it is the cause and not the result of the propagating precipitation a possible mechanism for the epw is developed from the linear bousinesq equations with heating and wind shear solutions show eastward moving diurnal pulses of potential vorticity pv generated by

cretaceous evolution of the central asian proto paratethys sea tectonic eustatic and climatic controls the timing and mechanisms of the cretaceous sea incursions into central asia are still poorly constrained we provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of cretaceous records of the proto paratethys sea fluctuations in the tajik and tarim basins the early cretaceous marine incursion in the western tajik basin was followed by major marine incursions during the cenomanian ca 100 ma and santonian ca 86 ma that reached far into the eastern tajik and tarim basins these marine incursions were separated by a turonian coniacian ca 92 86 ma regression basin wide tectonic subsidence analyses imply that the early cretaceous sea incursion into the tajik basin was related to increased pamir tectonism we find that thrusting along the northern edge of the pamir at ca 130 90 ma resulted in increased subsidence in a retro arc basin setting this tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the cenomanian ca 100 ma the following turonian coniacian ca 92 86 ma major regression driven by eustasy coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting the santonian ca 86 ma major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west siberian basin an early maastrichtian cooling ca 71 70 ma potentially connected to global late cretaceous trends is inferred from the replacement of mollusk rich limestones by bryozoan and echinoderm rich limestones

initiation of precipitation episodes relative to elevated terrain abstract the western and central united states experience a pronounced diurnal cycle in rainfall during the warm season over the higher terrain west of 105 w most precipitation occurs in the afternoon whereas the central united states experiences more nocturnal events this coherent phase transition between the rocky mountains and the u s great plains is well defined for all warm seasons between 1996 and 2003 provided that the rainfall observations are remapped relative to the elevated terrain in the western united states prior to north south averaging due to the westward shift of the continental divide north of 42 n and its intersection with the warm season storm track for 2002 the diurnal coherence greatly improves after remapping the 2002 rainfall observations this speaks to the long range influence of orography on precipitation frequency and suggests that the primary east west corridor of precipitation for an individual warm season intersects the cordillera over a fairly narrow latitude range

gulf stream eddy characteristics in a high resolution ocean model 1 a detailed statistical study of the mesoscale eddy activity in the gulf stream gs region is performed based on a high resolution multidecadal regional ocean model hindcast an eddy detection and tracking method that can be used to capture eddy features from large datasets is presented this method is applied to the 50 year model hindcast within a domain with the most energetic eddy activity along the gs detection results are then analyzed to investigate the kinematic properties and temporal variability of gs mesoscale eddies the studied kinematic properties include the eddy size duration intensity propagation and spatial distribution on average cyclonic eddies are smaller in size but more energetic and remain coherent longer than anticyclonic ones cyclonic eddies generally travel further from the generation sites and have a strong tendency for westward propagation with a small equatorward deflection anticyclonic eddies remain near their generation locations and tend to propagate northward the temporal evolution of eddy properties for long lived eddies lifetime 90 days is also examined for both cyclonic and anticyclonic eddies the size increases rapidly to their maximum value within the first 20 days at which point they begin to slowly decay in terms of intensity cyclonic eddies show a quasi linear decay while the anticyclonic ones reach a quasi steady state after 3 4 months of a more rapid decay finally the seasonal variability of the gs mesoscale eddies is explored in autumn and winter both types of eddies are more numerous and larger but less intense while in spring they are more intense but less numerous and generally smaller several possible mechanisms including the wind stress thermal forcing and topographic influence are considered to explain the seasonal cycle of eddy variability

impact of environmental variations on simulated squall lines interacting with terrain abstractthe complex evolution of convective systems crossing or attempting to cross mountainous terrain represents a substantial forecasting challenge this study examines the processes associated with environments of crossing squall lines which were able to redevelop strong convection in the lee of a mountain barrier and noncrossing squall lines which were not able to redevelop strong convection downstream of the barrier in particular numerical simulations of mature convective systems crossing idealized terrain roughly approximating the appalachian mountains were used to test the first order impact of variations in the vertical wind profile upon system maintenance by itself the wind profile showed no ability to uniquely discriminate between simulated crossing and noncrossing squall lines each test revealed a similar pattern of orographic enhancement suppression and lee reinvigoration in which a hydraulic jump deepened the system s cold pool and renewed the low level lifting increasing th

coastal ocean fronts and eddies imaged with ers 1 synthetic aperture radar ers 1 c band synthetic aperture radar sar data were collected during the norwegian continental shelf experiment norcsex both in november 1991 during the ers 1 commissioning phase and at different seasons in 1992 and 1993 characteristic sar image expressions are observed in relation to perturbation of the surface current short wave interaction across the norwegian coastal current front for winds less than 10 12 rn s 1 in situ measurements document the existence of alternating zones of convergence and divergence coexisting with a strong near surface current shear of nearly 4f where f is the coriolis parameter across a distance of a few kilometers under calm to moderate winds i e 4 7 rn s 1 characteristic expressions of upper ocean circulation features also include the manifestation of eddies through the presence of surface film which damps the bragg waves comparison of a near coincident national oceanic and atmospheric administration advanced very high resolution radiometer image and an ers 1 sar image supports the interpretation that surface current fronts are imaged by sar in combination with an sar image simulation model the relative quantitative importance of shear convergence and divergence along the front is examined although the model formulation is simple and the absolute magnitude of the perturbations is uncertain the study shows that the sar images can sometimes be used to interpret frontal dynamics including growth and decay of meanders

a radar based climatology of mesoscale convective systems in the united states abstractthis research applies an automated mesoscale convective system mcs segmentation classification and tracking approach to composite radar reflectivity mosaic images that cover the contigu

changing source regions of magmas and crustal growth in the trans himalayas evidence from the chalt volcanics and kohistan batholith kohistan northern pakistan the kohistan batholith and chalt volcanics form a major part of the kohistan island arc terrane in northern pakistan they record some 70 80 ma of magmatism within the northwestern himalayan orogen the chalt volcanics are albian aptian mid cretaceous and currently available rbsr age data for the batholith indicate an intrusive age span of 102 to 30 ma the volcanics are composed of medium k calc alkaline andesites and low k high mg tholeiites some of which have boninitic and basaltic komatiitic chemistry three intrusive stages are recognised in the batholith 1 110 90 ma comprises low k trondhjemites and medium high k calc alkaline gabbro diorites with associated hornblendite cumulates 2 85 40 ma comprises low high k calc alkaline gabbro diorites with hornblendite cumulates granodiorites and granites and 3 circa 30 ma comprises biotite muscovite garnet leucogranites 87sr 86sr0 for the batholith range between 0 7039 and 0 7052 four magmatic source regions sce 1 sce 4 have been identified sce 1 is a variably metasomatised mantle wedge situated above an active subduction zone during stages 1 and 2 sce 2 is a harzburgite depleted with respect to major elements and incompatibles whilst retaining subduction related trace element ratios sce 2 melted during stage 1 within a fore arc position during the subduction of young hot oceanic crust to provide the necessary extra thermal input for harzburgite anatexis melts from sce 2 produced the high mg tholeiitic volcanics sce 3 melted during stage 1 to produce the low k trondhjemites and it is envisaged as incompatible element depleted primitive arc crust with a similar composition to the depleted chalt volcanics sce 4 melted at 30 ma during stage 3 as india underthrust eurasia frictional heating and dehydration of the indian plate caused crustal anatexis within the deep kohistan arc and these melts formed the stage 3 leucogranites the low 87sr 86sr initial ratios for the great bulk 95 of the batholith indicate that it represents a major juvenile addition to the continental crust this conclusion has important implications for crustal growth theories of island arc accretion and batholith underplating