mountain torque events at the tibetan plateau the interaction of large scale wave systems with the tibetan plateau tp is investigated by regressing pressure potential temperature winds precipitation and selected fluxes in winter onto the three components toi of this massif s mountain torque on the basis of the 40 yr ecmwf reanalysis era 40 data events with respect to the equatorial greenwich axis of the global angular momentum exhibit by far the largest torques to1 which essentially represent north south pressure differences across the tp the axial torque to3 peaks when the surface pressure is high at the eastern slope of the tp the torque to2 with respect to the 90 e axis is closely related to to3 with to2 to3 the maximum minimum of to1 tends to occur about 1 day earlier than the minimum maximum of to2 all torque events are initiated by equivalent barotropic perturbations moving eastward along the northern rim of the tp in general the initial depression for example forms a southward protruding extension at the eastern slope of the tp and a new high grows near japan later the perturbation near japan moves eastward in to2 events but extends northward in to1 events these flow developments cannot be explained by theories of topographic instability the observed vertical motion at the lee slope is at best partly consistent with theories of linear quasigeostrophic wave motion along mountain slopes these findings lead the authors to test the eventual usefulness of linear theories by fitting the linear terms of a novel statistical equation for the potential temperature to the observed changes of and the torque to the observations this test indicates that the evolving regression patterns of can be explained by linear terms at least in specific domains in turn pressure tendency regressions at a selected level can be calculated on the basis of the linear tendencies above that level the formation of the lee trough appears to be mainly caused by horizontal warm air advection along the slopes but changes of the potential temperature above the height of the tp also contribute significantly to the pressure changes in the lee cold air advection aloft strengthens the japan high turbulent transports appear to be mainly responsible for the decay of the perturbations but data accuracy problems impede the analysis in particular the noisiness of the vertical motion fields affects the skill of the linear calculations

geochemistry and provenance of the middle ordovician austin glen member normanskill formation and the taconian orogeny in new england the austin glen member of the upper middle ordovician normanskill formation is a sandstone shale ysch succession deposited in the foreland of the taconian orogen petrographic major and trace element and nd pb isotopic data provide substantial constraints on its provenance lack of k feldspar and paucity of plagioclase in addition to the dominance of sedimentary rock fragments indicate that the source was dominated by recycled sedimentary components major and trace element data support this conclusion and indicate that the provenance of both shales and sandstones was the same no evidence of an ophiolitic or volcanic component was observed interpretation of nd isotopic characteristics are complicated by a partial resetting of the nd isotope system at about the time of sedimentation but indicate that the provenance of the austin glen member had a long term history of light rare earth element lree enrichment average tdm 1a8 ga furthermore nd isotopic compositions are extremely homogeneous end 8a1 0a6 1 s d n 23 at 450 ma the approximate depositional age indicating either a single source or very well mixed sources 207pb 204pb ratios are variable but within the range of pb isotopic compositions typically described as grenvillian the range of 207pb 204pb is greater than expected for the range of 206pb 204pb and suggests an additional component of pb possibly introduced during diagenesis the immediate source of the austin glen member may have been the accretionary prism that developed as older sediments of the laurentian margin were scraped off the basin oor incorporated within the accretionary prism and shed into the basin no evidence indicating the arrival of an undifferentiated island arc or continental fragment during the taconian orogeny has been found the data acquired during this study can be explained almost exclusively by grenville province source components but with possible additional contributions from older laurentian terranes and late proterozoic rift volcanics that are not readily quanti ed but likely to have been minor accordingly we conclude that the taconian orogeny in new england involved either 1 a continental arc that involved exclusively laurentia 2 collision of a continental block with identical geochemical characteristics as laurentia or 3 essentially no detritus from any exotic colliding block island arc or continental fragment reached the foreland basin at the time of austin glen deposition

local time and space scales of organized tropical deep convection the time and space scales of tropical deep convection are estimated via analysis of 3 hourly global cloud imagery gci data for 3 yr at 35 70 km resolution the emphasis is on estimating local time and space scales rather than traditional zonal wavenumber frequency spectra this is accomplished through estimation of local spatial lag autocorrelations the conditional probability of convection at neighboring points and the expected duration of convective events the spatial autocorrelation scale is found to be approximately 130 km and the mean duration of convective events approximately 5 5 h in the convectively active areas of the tropics there is a tendency for the spatial autocorrelation scales to be shorter over the continents than oceans 95 155 versus 110 170 km the expected duration of convective events likewise tends to be shorter 4 6 versus 5 7 h in the far western pacific these differences are sharp enough to legitimize the notion of the indonesian archipelago as an extended maritime continent with a distinctive shape consistent with many other studies the diurnal variation of the convection is also found to be strikingly different over the continents and oceans the diurnal amplitude over land is comparable to the long term mean raising the possibility of significant aliasing across timescales the simple analysis of this paper should be useful in evaluating and perhaps even improving the representation of convective processes in general circulation models

observed evolution of tropical deep convective events and their environment abstract using a compositing technique the temporal progression of tropical convective systems and the mean atmospheric state in their vicinity is constructed from a time series of geostationary satellite and operational rawinsonde data the technique establishes the stage in the life cycle of convection prevailing at a given place and time by a simple objective method using time series of satellite brightness temperature tb histograms collected from a region surrounding the site soundings are classified according to their placement in the convective life cycle and composites formed that represent the areal mean state of the convecting atmosphere at each stage for several scales of horizontal averaging the temporal structure found here for the mesoscale mean atmosphere closely resembles existing observations of the horizontal structure of a tropical squall line albeit with certain reductions in amplitude and stabilization rate this supports the generality of previous findings that the physical m

mountain drag along the gotthard section during alpex abstract an estimate of the time variation of the pressure drag component across the inner portion of the st gotthard section of the alps is derived for the special observational period march april 1982 of the alpex project surface pressure data obtained from a purpose designed mesoscale array of microbarograph stations are used and the results indicate that this drag component amounted to a value per unit area that varied on the order of 5 pa with a mean 0 78 pa it is shown that the phase variations of the time trace of the drag are directly related to synoptic scale flow developments however the magnitude of the drag is substantially influenced by mesoscale effects further an indication is given of the contribution to the drag of the effects of diurnal variation vertically propagating buoyancy waves and low level flow blocking deflection the order of magnitude of these drag values notwithstanding the potential errors in the estimates indicates that the alps exert a substantial influenc

numerical simulation of cyclone sidr using a cloud resolving model characteristics and formation process of an outer rainband abstractcyclone sidr one of the most devastating tropical cyclones that resulted in several thousand deaths and substantial damages developed in the north indian ocean and made landfall over the bangladesh coast on 15 november 2007 observation and simulation results show that sidr was embedded in a nonuniform environment and contained an intense outer rainband to the east of its center and a significant frontal band to the northwest a detailed study of the outer rainband is performed by numerical simulation the eastern band was a long quasi straight shape in the meridional direction that remained stationary relative to the cyclone center this band was composed of convective cells that developed southeast of the center within a synoptic scale convergence zone and propagated along the band toward the northeast quadrant the speed of the downwind propagating cells was greater than that of the cyclone which resulted in a convective cluster northeast of the center only the downwind portion of the band

an observational overview of dusty deep convection in martian dust storms abstractdeep convection as used in meteorology refers to the rapid ascent of air parcels in earth s troposphere driven by the buoyancy generated by phase change in water deep convection undergir

persistent nature of secondary diurnal modes of precipitation over oceanic and continental regimes abstract this investigation seeks a better understanding of the assorted mechanisms controlling the global distribution of diurnal precipitation variability based on the use of the tropical rainfall measuring mission trmm microwave radiometer and radar data the horizontal distributions of precipitation s diurnal cycle are derived from 8 yr of trmm microwave imager tmi and precipitation radar pr measurements involving three trmm standard rain retrieval algorithms the resultant distributions are analyzed at various spatiotemporal scales the results reveal both the prominent and expected late evening le to early morning em precipitation maxima over oceans and the counterpart prominent and expected mid to late afternoon mla maxima over continents moreover and not generally recognized the results reveal a widespread distribution of secondary maxima which generally mirror their counterpart regime s behavior occurring over both oceans and continents that is many ocean regions exhibit clear

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

structure of large scale convective anomalies over tropical oceans abstract geographical variations in the variance and cross correlation of monthly mean sea surface temperature sst outgoing longwave radiation olr a proxy for deep convection and vertical motion and convergence of winds at the surface and at 850 mb across the tropical indian and pacific oceans are examined within about 10 of the equator at most longitudes the variance of these quantities associated with the seasonal cycle is less than the variance associated with anomalies from the seasonal cycle largest variances in the sst and surface convergence data occur across the eastern near equatorial pacific whereas olr and 850 mb convergence variances are largest across the western pacific olr anomalies are significantly correlated with collocated sst and surface convergence anomalies from the date line eastward to the south american coast but are uncorrelated west of the date line the olr and 850 mb convergence anomalies are significantly correlated from about 120 w westward but are uncorrelated

interannual variability of deep convection over the tropical warm pool satellite data show that the total amount of deep convection was nearly constant from year to year over the warm pool region of the tropical indian and pacific oceans but the spatial distribution varied in the 1986 1987 warm el nino southern oscillation event the maximum of deep convective activity was over the high sea surface temperature sst of the west central pacific with a local minimum over the eastern indian ocean in the 1988 1989 cold enso event the maximum convective activity switched to the eastern indian ocean with a minimum over the west central pacific the sst changed very little over the eastern indian ocean from year to year and the centers of convective activity were always collocated with the four month mean low level westerlies in each year the latitude of the cloudy region of the intraseasonal oscillation iso varied interannually the interannual differences in deep convective activity over the warm pool were accounted for almost exclusively by the occurrence or nonoccurrence of extremely large long lasting deep mesoscale cloud systems cloud tops 208 k with horizontal dimensions 300 700 km such cloud systems occurred more frequently than normal over the western pacific during the warm enso event and over the eastern indian ocean during the cold event they occurred more frequently over the tropical eastern indian and western pacific oceans than over the maritime continent thus accounting for the seesaw pattern of the observed cold cloudiness between the two oceanic regions on both interannual and intraseasonal timescales

bridging the gap between the foreland and hinterland i geochronology and plate tectonic geometry of ordovician magmatism and terrane accretion on the laurentian margin of new england

comparison of three hydraulic property measurement methods hydraulic functions of soils may differ depending on the different measuring methods used the performance of three different methods for measuring soil hydraulic properties of a heterogeneous field were evaluated the experiments were conducted using three different sizes of undisturbed soil cores collected systematically along a 31 m long transect of a well drained sandy loam soil having three soil horizons ap 0 0 25 m c1 0 25 0 55 m c2 0 55 1 00 m the laboratory studies involved 1 detailed unsteady drainage flux experiments performed on fifteen columns of 1 m length and 0 3 m diameter 2 combined crust test and hot air methods applied to thirty columns of 0 2 m length and 0 2 m diameter and to a subset of sixty cylinders of 0 1 m length and 0 045 m diameter respectively taken from the ap horizon and 3 desorption experiments carried out on a total of one hundred eighty cores of 0 051 m length and 0 05 m diameter collected evenly from the three horizons mean soil hydraulic properties were inferred from experimental data characterizing either selected depths or the soil profile as a whole the results revealed considerable differences among estimated mean soil properties as obtained with different measuring techniques although the application of scaling theory substantially reduced variation in the measured pressure heads h and conductivities k the results revealed that scaling parameters determined from soil pressure head were not identical to scaling factors determined from hydraulic conductivity the results also show that k scaling factors in general were much more variable than h scaling factors and that the observed variability in scaling factors also depend upon the measurement technique used c 1997 elsevier science b v

a comparison of three measuring methods for estimating the saturated hydraulic conductivity in the shallow subsurface layer of mountain podzols abstract saturated hydraulic conductivity ks is a key input parameter for modeling water flow in soils well established methods exist but there is no methodological standard or benchmark this paper presents a comparison of three well established measurement methods which we used in the specific conditions of extremely heterogeneous mountain podzols the following devices were applied to undisturbed soil core samples diameter of 5 6 cm ks was estimated for a shallow subsurface ash gray layer the geometric mean values for ks measured using these three methods were gp 4 41 10 6 ms 1 sr 3 20 10 6 ms 1 and lp 7 09 10 6 ms 1 the mean values obtained using field methods were not statistically different the laboratory permeameter yielded slightly higher values than the field methods from the engineering perspective all tested methods provided similar mean values

water infiltration underneath single ring permeameters and hydraulic conductivity determination summary a single ring permeameter is suitable for measurement of soil hydraulic conductivity at a large field scale because of its simple structure easy operation portability small amount of recharging water and particularly because of its variable radius the authors established a simple single ring permeameter which consists of a hollow cylinder that is simply inserted into the top soil based on the theories of the philip and nestingen methods for single ring permeameter tests this paper presents new equations for describing 1 d infiltration within the inserted depth of the single ring infiltrometer and 3 d flow beyond the depth under both gravity and soil suction forces the soil hydraulic parameters of hydraulic conductivity and soil suction were optimized based on the declines of the ponded water depth within the single ring cylinder the new method was validated using numerical simulations of the declines of the water column within the cylinder through the variably saturated flow modflow vsf modflow the new method was then successfully applied in laboratory troughs and on a hillslope in huanjiang county northwest guangxi in southwest china the results demonstrate that the hydraulic conductivity determined by the new method is more accurate than those from the 1 d green ampt method and the 3 d nestingen method

an objective classification of saturn cloud features from cassini iss images abstract a k means clustering algorithm is applied to cassini imaging science subsystem continuum and methane band images of saturn s northern hemisphere to objectively classify regional albedo features and aid in their dynamical interpretation the procedure is based on a technique applied previously to visible infrared images of earth it provides a new perspective on giant planet cloud morphology and its relationship to the dynamics and a meteorological context for the analysis of other types of simultaneous saturn observations the method identifies 6 clusters that exhibit distinct morphology vertical structure and preferred latitudes of occurrence these correspond to areas dominated by deep convective cells low contrast areas some including thinner and thicker clouds possibly associated with baroclinic instability regions with possible isolated thin cirrus clouds darker areas due to thinner low level clouds or clearer skies due to downwelling or due to absorbing particles and fields of relatively shallow cumulus clouds the spatial associations among these cloud types suggest that dynamically there are three distinct types of latitude bands on saturn deep convectively disturbed latitudes in cyclonic shear regions poleward of the eastward jets convectively suppressed regions near and surrounding the westward jets and baroclinically unstable latitudes near eastward jet cores and in the anti cyclonic regions equatorward of them these are roughly analogous to some of the features of earth s tropics subtropics and midlatitudes respectively this classification may be more useful for dynamics purposes than the traditional belt zone partitioning temporal variations of feature contrast and cluster occurrence suggest that the upper tropospheric haze in the northern hemisphere may have thickened by 2014 the results suggest that routine use of clustering may be a worthwhile complement to many different types of planetary atmospheric data analysis

on the relationship between western maritime continent monsoon rainfall and enso during northern winter abstract several studies have reported that indonesian rainfall is poorly correlated with el nino southern oscillation enso events during the northern winter wet monsoon season this work studies the relationship between the nino 3 5 s 5 n 150 90 w sea surface temperature sst and the maritime continent monsoon rainfall during 1979 2002 the study indicates that the correlations are mostly negative except in the vicinity of sumatra and malay peninsula smp including the western sections of java and borneo where the correlations range from zero to weakly positive the monsoon rainfall during enso events is influenced by a pair of anomalous walker cells and a low level closed circulation centered near the philippines east of smp the rainfall is negatively correlated with nino 3 sst the anomalous low level wind over the indian ocean west of smp causes rainfall to also be correlated negatively with nino 3 sst but rainfall over smp is sheltered from this effect because of the high mountains along

potential minerals for determining u th pb chemical age using electron microprobe abstract after a decade of studies and development it is now accepted that reliable u th total pb isochron ages can be calculated for monazite using an electron microprobe at m scale either directly on thin sections or on separated grains mounted in polished section the potential for determining u th pb chemical ages from other u and th enriched phases has been investigated compared to chemical monazite dating results for which individual spot age precisions of 20 to 100 ma can be achieved from individual spot analyses using isochron plots for monazite the age homogeneity of a given population of data can be assessed and depending upon the number of analyses n 50 a precision of 5 to 10 ma can be obtained the u content in xenotime widely varies from less than 0 1 wt up to 3 wt but th rarely exceeds 1 wt as a consequence the amount of radiogenic pb produced during a given period remains significantly lower for xenotime than for monazite leading to a lower precision 20 ma on the mean ages xenotime however appears to remain as a closed system but common pb must be carefully checked furthermore the electron microprobe technique epma allows controlling any age discrepancy on xenotime grains as small as 10 20 m that cannot be dated by other isotopic methods such xenotime ages can be useful when studying the monazite xenotime equilibrium the electron microprobe is not the most reliable method for dating zircon since u and th concentrations are generally low and common pb is not negligible nevertheless the spatial resolution of epma coupled with isotope methods allows conclusive in situ studies about radiogenic pb mobility and metamictization thorite does not seem suitable for dating with either isotope methods or epma because of continuous radiogenic pb loss conversely the oxide phases thorianite and baddeleyite are robust minerals with closed systems they are rather rare and seem to incorporate negligible common pb making epma a method of choice for dating them for thorianite the precision on the mean age can be similar as that obtained for monazite or even better while the precision for baddeleyite cannot be significantly better than 20 to 50 ma due to the limited amount of u 0 1 and the lack of th

diagnostic studies of pacific surface winds abstract analyses are performed using surface winds derived from the monthly mean fsu pacific pseudo stress fields vorticity budget calculations reveal the relative contributions of various terms and allow simplification of the full momentum equations based on the simplified equations a procedure is developed for estimating surface pressure and then adjusting the winds the wind field adjustments fall well within the uncertainty of the data while allowing generally large imbalances in the vorticity budget to be removed completely further validation of the procedure is provided by comparisons between estimated and observed pressure anomalies the adjusted winds and pressure are then used to infer boundary layer and upper level forcing within the context of particular model formulations these forcing fields an compared with sea surface temperature outgoing longwave radiation and highly reflective cloud data in order to infer the dominant mechanisms contributing to observed surface circulation anom

diurnal cycle of the south pacific convergence zone in 30 years of satellite images 2015 american geophysical union a data set of three hourly south pacific convergence zone spcz location and extent from which ir temperature within the spcz may be obtained for 1980 2012 november april is used to examine the diurnal cycle of the spcz maximum spcz area occurs at 15 00 18 00 local standard time lst two minima in mean ir temperature are evident one at 13 00 16 00 lst nearly coinciding with the maximum in area and the second in the early morning hours at 05 00 07 00 lst when area is at a minimum the morning minimum in mean ir temperature is associated with a peak in deep convection while the afternoon minimum is associated with a peak in midlevel clouds on average the morning minimum in ir temperature dominates in the tropical regions of the spcz while the afternoon ir temperature minimum dominates in the subtropical regions of the spcz the relative strength of the two ir temperature minima is affected by the seasonal cycle intraseasonal variability associated with active madden julian oscillation events and interannual variability due to the el nino southern oscillation the morning ir temperature minimum becomes more dominant when the spcz is more frequently present or when the spcz is shifted toward the equator in terms of cloud height midlevel clouds dominate at all times in all regions of the spcz and peak in abundance between 15 00 18 00 lst low level clouds peak near midnight and then transition to high level clouds which peak between 03 00 06 00 lst just before sunrise

40ar 39ar dating of silurian and late devonian cleavages in lower greenschist facies rocks in the westminster terrane maryland usa 40 ar 39 ar dating of muscovite biotite and k feldspar combined with microstructural analysis of lower greenschist facies polymetamorphic phyllitic rocks and marbles were successfully used to decipher the thermal and tectonic histories of the westminster and adjacent terranes in western maryland the presence of unreset detrital muscovite in some samples demonstrates that temperatures in these rocks never exceeded the closure temperature for argon diffusion in muscovite 350 50 c minor biotite in some arkoses constrains the minimum metamorphic temperatures to 320 c these data show an early silurian ca 430 ma cleavage in the western part of the westminster terrane and a late devonian event ca 370 ma in the eastern westminster and adjacent potomac terranes these two cleavage domains are separated by the ne trending newly identified parrs ridge fault zone we propose that the sinistral transpressive collision of the carolina terrane with laurentia emplaced the western portion of the westminster terrane in the pennsylvania embayment along the martic fault where it was folded and cleaved at ca 430 ma but otherwise largely sheltered from later deformation the later late devonian dextral transpressive accretion of the outboard potomac terrane thrust rocks of the eastern westminster and potomac terranes to the west causing late devonian 360 370 ma s 2 cleavage in these rocks but only minimal discrete overprinting s 3 cleavages in rocks farther west final juxtaposition and thermal convergence of these terranes occurred along reactivated dextral strike slip faults in the alleghanian at ca 300 ma

tibet forcing of mid pleistocene synchronous enhancement of east asian winter and summer monsoons revealed by chinese loess record the mid pleistocene transition mpt of the global climate system marked by a shift of previously dominant 41 ka cycles to lately dominant 100 ka cycles roughly in the mid pleistocene is one of the fundamental enigma in the quaternary climate evolution the process and origin of the mpt remain of persistent interest and conjecture here we present high resolution astronomically tuned magnetic susceptibility ms and grain size records from a complete loess paleosol sequence at chaona on the central chinese loess plateau these two proxies are well known sensitive indicators to the east asian summer and winter monsoons respectively the records reveal a remarkable two step simultaneous enhancement of the east asian summer and winter monsoons at 0 9 ma and 0 64 ma respectively accompanied with an onset of a clear 100 ka cycle at 0 9 ma and of a final predominant 100 ka cycle starting at 0 64 ma the mid pleistocene stepwise rapid uplift of the tibetan plateau could be the mechanism driving the simultaneous enhancement of east asian summer and winter monsoons and the shift of the periodicities during the mpt by complex positive feedbacks 2012 university of washington

equatorial mountain torques and cold surge preconditioning the evolution of the two components of the equatorial mountain torque emt applied by mountains on the atmosphere is analyzed in the ncep reanalysis a strong lagged relationship between the emt component along the greenwich axis tm1 and the emt component along the 90 e axis tm2 is found with a pronounced signal on tm1 followed by a signal of opposite sign on tm2 it is shown that this result holds for themajor massifs antarctica the tibetan plateau the rockies and the andes if a suitable axis systemis used for each of them for the midlatitude mountains this relationship is in part associated with the development of cold surges following these results two hypotheses are made i the mountain forcing on the atmosphere is well measured by the regional emts and ii this forcing partly drives the cold surges to support these a purely dynamical linear model is proposed it is written on the sphere uses an f plane quasigeostrophic approximation and includes the mountain forcings in this model a positive negative peak in tm1 produced by a mountain massif in the northern southern hemisphere is due to a large scale high surface pressure anomaly poleward of the massif at a later stage high pressure and low temperature anomalies develop in the lower troposphere east of the mountain explaining the signal on tm2 and providing the favorable conditions for the cold surge development it is concluded that the emt is a good measure of the dynamical forcing of the atmospheric flow by the mountains and that the poleward forces exerted by mountains on the atmosphere are substantial drivers of the cold surges at least in their early stage therefore the emt time series can be an important diagnostic to assess the representation of mountains in general circulation models 2010 american meteorological society

diurnal and semidiurnal variations in global surface wind and divergence fields diurnal and semidiurnal variations in surface winds and wind divergence over the globe 50 s 70 n are documented using 3 hourly wind observations from 10 000 land stations and available marine reports during 1976 1997 a strong diurnal cycle in surface winds is found over land areas strongest over high terrain and in summer with an amplitude of 0 6 1 1 m s for wind speed and 0 5 0 7 m s for the zonal and meridional wind components surface wind speed peaks in the early afternoon over most of the globe it is suggested that increased downward turbulent mixing of momentum during the day could be one of the main causes for the early afternoon maximum of surface wind speed the diurnal anomalies of surface wind divergence tend to be out of phase in adjacent regions in particular land areas except for extreme inland locations exhibit maximum divergence around dawn 0600 0800 local solar time lst while nearby oceanic regions have their maximum divergence in the evening 1700 1900 lst thus there is evidence for a large scale diurnal circulation in which surface air rises and converges over the continents and sinks and diverges over nearby oceans in the afternoon and early evening and the opposite occurs in the early morning over the tropical atlantic and pacific oceans 10 s 10 n a zonally coherent pattern of maximum convergence divergence north south of the equator around 0900 1200 lst is generally similar to the latitudinal profile of the mean daily divergence indicative of an enhancement of the local hadley cell around 1030 lst relative to the daily mean another zonally coherent north south dipole occurs over the north pacific with maximum surface wind divergence convergence around 0600 0800 lst in the subtropics midlatitudes this phase pattern correlates with cloud cover over the two regions over the united states surface divergence peaks around 0600 lst in the west and the east and around 2000 lst in the center

regional distribution of deep clouds and cloud top altitudes over the indian subcontinent and the surrounding oceans 1 the bay of bengal bob and the east equatorial indian ocean are among the most intense deep convective regions over the tropics long term monthly mean distributions of deep clouds and the regional differences in the cloud top brightness temperature ctbt over the indian subcontinent and the surrounding oceanic regions the northern and eastern bob the southeast arabian sea and the eastern equatorial indian ocean are derived using national oceanic and atmospheric administration advanced very high resolution radiometer data for a period of 10 years and are compared with the direct observations of cloud top altitude cta using cloud aerosol lidar and infrared pathfinder satellite observation calipso the deepest clouds are found to occur over the northern bob nbob during the june august period the most probable ctbt in this region is 12 k lower than that over the other deep convective regions calipso observations also show that the frequency of occurrence of cta peaks at an altitude of 16 5 km over the nbob which is 1 km higher than that over the other regions strong convergence of horizontal wind between the surface and 200 hpa level and large divergence above combined with the most favorable sea surface temperature 28 c might be mainly responsible for the highest cta being observed over the nbob the annual variation of the base altitude and thickness of the tropical tropopause layer ttl and the upper tropospheric temperature are closely associated with the corresponding variations in the deep cloud fraction considerable fraction of deep clouds occurs within the ttl over the bob during the june august period

dynamical influence of the tibetan plateau on the winter monsoon over southeastern asia 1 previous studies have shown 1 that the tibetan plateau produces a significant fraction of the two components of the equatorial mountain torque emt in winter 2 that these torques are in part related to the east asian cold surges and 3 that the cold surges affect the convection over the maritime continent we show here that these relations are strong enough for the convection over the equatorial south china sea to be associated with significant signals on the two components of the emt that can precede by a few days and more the convection these signals are associated to surface pressure and temperature patterns that are strongly reminiscent of the east asian cold surges our results therefore show that the tibetan plateau couple dynamically the midlatitudes and the tropical region and that the vectors of this dynamical coupling are the cold surges this coupling also influences the convection over the northern bay of bengal mainland southeast asia and indonesia

u pb dating of major and accessory minerals formed during metamorphism and deformation of metapelites abstract u pb isotope analyses on major and accessory minerals from pelitic schists in of southwestern connecticut are used to date metamorphism and deformation most of the major minerals have 206 pb 204 pb ratios less than 100 however u pb mineral isochron and mineral whole rock isochrons constructed using aliquots of the same mineral yield concordant ages with uncertainties as low as 5 ma staurolite kyanite and garnet are older than metamorphic monazites and zircons these data are summarized below 5 mineral 206 pb 204 pb system the straits schist trap falls fm monazite zircon 207 pb 206 pb 379 384 ma 380 2 ma staurolite 48 623 238 u 206 pb 394 400 ma 398 5 ma garnet 22 46 238 u 206 pb 383 ma 414 10 ma 235 u 207 pb 418 ma 207 pb 206 pb 623 ma kyanite 21 27 238 u 206 pb 399 ma chlorite anatase ilmenite 20 27 238 u 206 pb 350 370 ma apatite quartz kspar 18 19 transposed pegmatitic intrusions in the straits schist yield monazites with u pb ages analytically indistinguishable from those of metamorphic monazites and zircons in the schists growth of monazite and zircon in the schists may be related to high t fluid influx associated with pegmatite intrusion age discordance in the garnets from the straits schist is most consistent with continuous loss of intermediate daughter products of the 238 u decay chain from about 420 ma to 380 ma garnets from the adjacent trap falls formation do not display this behavior

synoptic disturbances over the equatorial south china sea and western maritime continent during boreal winter abstract during boreal winter the maritime continent is a region of deep cumulus convection and heavy precipitation systems that play a major role in several global and regional scale processes over the western part of this region the synoptic scale borneo vortex the northeast cold surge and the intraseasonal madden julian oscillation mjo contribute to the variability in deep convection this work studies the impact on deep convection due to interactions among these three different motion systems furthermore the role of the unique topography of the region is examined with respect to the variability in the synoptic scale cold surge and borneo vortex on the synoptic scale the interaction of northeast winds with local topography and the dynamic response to the change in latitude contribute to the turning of the winds and localized patterns of deep convection in days without a borneo vortex deep convection tends to be suppressed over the south china sea and borneo and enhanced downstream over th

convection in gate the difficult problem of parameterizing tropical convection in large scale models of the atmosphere led to the global atmospheric research program s atlantic tropical experiment gate whose goal was to improve basic understanding of tropical convection and its role in the global atmospheric circulation a dense network of instrumented ships equipped with upper air sounding equipment and quantitative weather radars were located over the atlantic ocean in the intertropical convergence zone itcz just west of equatorial africa the ship network was supplemented by a fleet of research aircraft and a geosynchronous meteorological satellite the data obtained show that the deep convection in the itcz was concentrated in two types of cloud clusters rapidly moving squall clusters and slowly moving nonsquail clusters the clusters were characterized by large mid to upper level cloud shields or anvil clouds that emanated from penetrative cumulonimbus convection accompanying the deep cumulonimbus in each cluster was a log normal spectrum of smaller convective features ranging from moderate cumulonimbus down to tiny nonprecipitating cumulus the large cumulonimbus were typically grouped within a cluster into one or more mesoscale precipitation features or mpf s which were apparently triggered in mesoscale regions of intensified low level convergence as an mpf matured it developed a region of stratiform precipitation adjacent to its active deep convective cells the stratiform precipitation fell from the anvil cloud associated with the stratiform precipitation were a mesoscale downdraft below the anvil cloud and an apparent mesoscale updraft within the anvil cloud itself above the mesoscale downdraft these mesoscale drafts were distinct from the convective scale updrafts and downdrafts of the cumulus and cumulonimbus cells of the cluster downdrafts both convective scale and mesoscale filled the planetary boundary layer in the vicinity of cumulonimbus with stable air of low moist static energy these wakes of downdraft air exerted a strong control on where future convection broke out the results of gate show that to simulate the effects of tropical convection in large scale numerical models of the atmosphere a variety of phenomena must be accounted for including not only convective scale updrafts and downdrafts but anvil clouds with mesoscale updrafts and downdrafts downdraft induced boundary layer transformations and mesoscale convergence patterns experimentation with ways of including some of these features of tropical convection in large scale diagnostic and prognostic studies is under way but much work remains to be done

orbital controls on the el nino southern oscillation and the tropical climate the global synchroneity of glacial interglacial events is one of the major problems in understanding the link between milankovitch forcing and the climate of the late quaternary in this study we isolate a part of the climate system the tropical pacific and test its sensitivity to changes in solar forcing associated with changes in the earth s orbital parameters we use a simplified coupled ocean atmosphere model that is run for the past 150 000 years and forced with milankovitch changes in the solar insolation this system responds primarily to the precessional cycle in solar forcing and is capable of generating a mean response to the changes in the seasonal distribution of solar radiation even while the annual mean insolation is roughly constant the mean response to the precessional forcing is due to an interaction between an altered seasonal cycle and the el nifio southern oscillation enso changes in the enso behavior result in a mean tropical climate change the hypothesis is advanced that such a change in the tropical climate can generate a globally synchronous climate response to milankovitch forcing

22 year survey of tropical convection penetrating into the lower stratosphere 1 a 22 year survey of tropical convection penetrating into the stratosphere has been conducted using special subsets of the international satellite cloud climatology project cloud data set in addition to refined information about the geographic distribution of penetrating convective systems these results show that penetrating convection occurs predominantly in the larger organized mesoscale convective systems whereas smaller unorganized convective systems rarely penetrate durations of penetrating events are longest for the largest systems hurricanes and typhoons generally exceeding one day

evaluation of the model representation of the evolution of convective systems using satellite observations of outgoing longwave radiation 1 we introduce a technique for assessing the diurnal development of convective storm systems based on outgoing longwave radiation fields using the size distribution of the storms measured from a series of images we generate an array in the length scale time domain based on the standard score statistic it demonstrates succinctly the size evolution of storms as well as the dissipation kinematics it also provides evidence related to the temperature evolution of the cloud tops we apply this approach to a test case comparing observations made by the geostationary earth radiation budget instrument to output from the met office unified model run at two resolutions the 12 km resolution model produces peak convective activity on all length scales significantly earlier in the day than shown by the observations and no evidence for storms growing in size the 4 km resolution model shows realistic timing and growth evolution although the dissipation mechanism still differs from the observed data citation pearson k j r j hogan r p allan g m s lister and c e holloway 2010 evaluation of the model representation of the evolution of convective systems using satellite observations of outgoing longwave radiation j geophys res 115 d20206 doi 10 1029 2010jd014265

linear response of a stratified tropical atmosphere to convective forcing abstract the three dimensional response of the tropical atmosphere to an isolated heat source is investigated using a primitive equation model linearized about a resting basic state on an equatorial plane the model equations are solved by applying vertical and horizontal normal mode transforms the thermal forcing was chosen to simulate the convection which occurs over tropical south america during the southern hemisphere summer the vertical dependence of the forcing is such that the heating is zero at the top and bottom boundaries with a variable level of maximum beating the model results with steady forcing are compared with the average circulation over tropical south america for a 19 day period in the southern hemisphere summer of 1979 and it is shown that the model reproduces many aspects of the observed circulation the partition of the energy of the steady state response between the vertical modes is calculated and it is shown that the internal mode with an equivalent depth of 208 m is domina

a drive point application of the guelph permeameter method for coarse textured soils abstract the guelph permeameter gp is a widely used well auger hole method for in situ determination of field saturated hydraulic conductivity kfs and sorptive number in the vadose or unsaturated zone its application can be difficult however in gravelly materials which are problematic to auger and in un cohesive sandy materials which collapse during the augering process or upon wetting of the unlined well we circumvented these issues by replacing the gp well with a conically tipped well screen or drive point which is pushed driven rotated or vibrated to the desired depth we also developed a steady flow analysis to account for the fact that water discharge through the drive point screen is solely radial rather than both radial and vertical as in the original gp method the hydrus 2d numerical simulation model was used to determine appropriate shape values cdp for the drive point analysis and an empirical regression equation was developed to convert the discrete cdp values into continuous shape functions for porous materials with negligible moderate strong and very strong capillarity in a well sorted medium coarse sand the drive point method produced kfs and values which were plausible and consistent with other data from the field site the original gp method on the other hand under estimated the drive point results by factors of 2 1 3 1 which may have been caused by progressive collapse of the unlined gp well and or gradual sinking of the gp outflow tip into the unprotected well base it was concluded that the drive point gp method can provide convenient and accurate estimates of kfs and in materials where hydraulic properties are not substantially altered by the disturbance of drive point installation

on the role of sea surface temperature gradients in forcing low level winds and convergence in the tropics abstract we examine the importance of pressure gradients due to surface temperature gradients to low level p 700 mb flow and convergence in the tropics over time scales 1 month the latter plays a crucial role in determining the distribution of cumulonimbus convection and rainfall our approach is to consider a simple one layer model of the trade cumulus boundary layer wherein surface temperature gradients are mixed vertically consistent with ecmwf analyzed data the top of the layer is taken at 700 mb the influence from higher levels is intentionally suppressed by setting horizontal pressure gradients and frictional stresses to zero at the top of the layer horizontal convergence within the layer is taken up by cumulonimbus mass flux however the development of the cumulonimbus mass flux is associated with a short relaxation time o hr roughly the development time for such convection during this short time horizontal convergence acts to redistribute mass so as to reduce horizontal pressur

behavior of deep convective clouds in the tropical pacific deduced from isccp radiances abstract we analyze the properties of deep convection over the equatorial pacific and its relationship to sea surface temperature sst and surface wind divergence using isccp radiance data for july 1983 and january 1984 deep convective clouds dcc are diagnosed with both a combined visible infrared threshold method and an infrared only threshold method the visible channel is important in diagnosing deep convection in different regions with different surface and atmospheric properties because of the existence of large scale variations of dcc top altitudes the itcz and spcz exhibit changes in these two months that are characteristic of both the el nino and seasonal cycles deep convection is latitudinally confined to a much smaller spatial scale than that suggested by maps of outgoing longwave radiation diurnal variations of dcc cover and associated mesoscale cirrus anvil cloud cac cover are out of phase with deep convection peaking in the early morning throughout the equatorial pacific the diurna

time space characteristics of diurnal rainfall over borneo and surrounding oceans as observed by trmm pr abstract five years of tropical rainfall measuring mission trmm precipitation radar pr data were used to investigate the time and space characteristics of the diurnal cycle of rainfall over and around borneo an island in the maritime continent the diurnal cycle shows a systematic modulation that is associated with intraseasonal variability in the large scale circulation pattern with regimes associated with low level easterlies or westerlies over the island the lower tropospheric westerly easterly components correspond to periods of active inactive convection over the island that are associated with the passage of intraseasonal atmospheric disturbances related to the madden julian oscillation a striking feature is that rainfall activity propagates to the leeward side of the island between midnight and morning the inferred phase speed of the propagation is about 3 m s 1 in the easterly regime and 7 m s 1 in the westerly regime propagation occurs over the entire island causing a leeward enhan

mountain torques and northern hemisphere low frequency variability part i hemispheric aspects the ncep ncar reanalysis dataset for 1958 97 is used to analyze intraseasonal variations in mountain torques and the large scale atmospheric circulation patterns associated with them spectral analysis of the atmospheric angular momentum aam budget shows that the dominant variations of mountain torque have periodicities near 30 days and shorter while the dominant aam variations occur in the 40 60 day band this difference is due to the 40 60 day aam variations being primarily related to equatorial processes while mountain torque variations are associated mostly with extratropical processes the northern hemisphere nh mountain torque has enhanced power and significant spectral peaks in the 20 30 day band the signal in this band accounts for 33 of the nh mountain torque variance once the seasonal cycle has been removed lag composites of the nh 700 hpa geopotential heights based on the 20 30 day mountain torque signal show the latter to be associated with coherent large scale patterns that resemble lowfrequency oscillations identified in this band by previous authors the composite patterns that are in phase quadrature with the 20 30 day nh mountain torque have a pronounced zonally symmetric component these patterns are associated with substantial aam variations arguably driven by the nh mountain torque in this band principal component pc analysis of the nh 700 hpa heights shows that in the 20 30 day band the mountain torque is also in phase quadrature with the two leading pcs the first corresponds to changes in the midlatitude jet intensity near the subtropics while the second corresponds to the arctic oscillation the relationships with aam of the latter essentially occurs through the mass term mountain torques are furthermore nearly in phase with dominant patterns of low frequency variability that exhibit substantial pressure gradients across the rockies and the tibetan plateau

post taconic tilting and acadian structural overprint of the classic barrovian metamorphic gradient in dutchess county new york field mapping and 40ar 39ar age spectrum dating of white mica across the classic metamorphic gradient in dutchess county new york indicate that post peak metamorphic and structural events complicate the interpretation of this sequence as an intact taconic metamorphic field gradient oriented samples were collected and fabrics were measured along two 7 km transects these transects extend from west of the biotite zone west of clove mountain to the sillimanite zone swamp river valley in eastern dutchess county field and petrographic analysis reveals three pervasive foliations s1 s2 and s3 s1 is folded in the lower grade rocks of the sequence but is increasingly overprinted at garnet and higher zones by a penetrative foliation s2 s2 dips steeply to the se and is axial planar to folds in s1 s2 is overgrown by porphyroblasts of biotite biotite chloritoid biotite garnet staurolite kyanite sillimanite at respective metamorphic grades that appear to approximate peak temperature conditions s1 s2 and peak temperature conditions are constrained as late taconic based on a depositional age of 460 ma potter 1972 for the walloomsac formation and a staurolite age of 454 ma lanzirotti and hanson 1997 from kyanite sillimanite grade rocks s3 is a greenschist facies foliation composed of muscovite biotite chlorite that truncates or overprints s2 in garnet through sillimanite grade rocks in the eastern part of the study area s3 dips gently to the s se and becomes more penetrative to the east such that in the garnet zone s2 is overprinted by a weakly developed spaced s3 cleavage while in many samples in the staurolite and higher metamorphic zones s2 micas are significantly overprinted by s3 micas s3 is observed wrapping around and truncating peak temperature porphyroblasts three samples of lepidoblastic white mica with varying proportions of s1 s2 and s3 from the biotite through staurolite zone all produce 40ar 39ar age spectra suggesting closure ages of 385 ma these white mica ages are interpreted to represent the time of cooling through white mica closure 350 c the 40ar 39ar ages in conjunction with field mapping and petrographic analysis suggest that s3 developed in the devonian acadian orogeny furthermore the 40ar 39ar data constrains the timing of tilting and uplift of the ordovician barrovian sequence from the middle silurian to early devonian this study suggests mid crustal wedging during the salinic orogeny as a possible mechanism for tilting the rocks of this region and exposing the taconic aged barrovian field gradient at the surface today we conclude the low grade acadian metamorphic overprint of these rocks involved deformation that produced a new third cleavage that was coincident with regional cooling from peak taconic metamorphic conditions and thus required strain but no reheating during the acadian

the diurnal cycle of tropical convection the diurnal cycle of tropical convection is investigated with global cloud imagery constructed from 11 m radiance measurements taken aboard six satellites four harmonics of the diurnal cycle are resolved in the cloud imagery with about 50 km horizontal resolution to isolate deep convective activity from other processes which cause diurnal fluctuations in longwave radiance an index of deep convective activity is constructed by thresholding to brightness temperatures less than 230 k significant diurnal amplitude of deep convection is found only over tropical landmasses over the tropical oceans the diurnal cycle is weak and is barely discernible from the background red spectrum of convective variance nonetheless oceanic convection exhibits a systematic diurnal fluctuation with maximum intensity in the early morning nocturnal subsidence along the cloud free equator is postulated to play a role in forcing diurnal variation in the intertropical convergence zones other mechanisms are also implied to contribute as a similar early morning maximum in deep convection is seen even where no adjoining cloud free regions occur the diurnal cycle of deep convection is found to be organized on planetary scales predominantly in nonmigrating modes i e modes with phase speeds not equal to that of the sun the nonmigrating modes are postulated to be produced by the nonuniform distribution of convective centers the nonmigrating zonally symmetric component is found to be especially large while the role of this mode in forcing diurnal variations of the tropospheric circulation e g the hadley cell is questionable its role in modulating the ionospheric electric potential is well established discrepancies with the traditional notion that cloud to ground lightning is the dominant mechanism by which the earth is negatively charged are discussed in particular the probable role of nonlightning producing clouds e g the stratiform portion of convective complexes in diurnally modulating the negative charge on earth is discussed

ion microprobe u pb dating of hydrothermal xenotime from an episyenite evidence for rift related reactivation abstract hydrothermally intergrown xenotime monazite from an episyenite in the bohus granite southwest sweden has been analyzed in situ by ion microprobe although the analysed xenotime crystals are extremely small sometimes less than the ion beam diameter 17 m they retain relatively undisturbed u pb systems which yielded a 206 pb 238 u age of 252 8 ma the evolution of this episyenite involved an initial stage of quartz dissolution accompanied by albitization followed by a second stage of vug infilling and replacement of igneous fe ti phases the obtained age shows that the second alteration stage during which xenotime was precipitated was coeval with the thermal anomaly associated with permo carboniferous crustal thinning and the development of the nearby oslo rift moreover the development of the permeable episyenite structure must be ascribed to a preceding high temperature event most likely the post magmatic cooling of the host granite at 920 ma this study shows that u pb dating of young xenotimes may address geochronological problems though further work is required to characterize possible matrix effects which presently limit the accuracy of the method

modification of the boundary layer over the south china sea during a winter monex cold surge event abstract aircraft dropwindsonde and conventional sounding data have been used to document the boundary layer structure over the south china sea during the period of a 3 day moderate cold surge that occurred during the december 1918 winter monsoon experiment winter monex throughout the cold surge event equatorward deepening of the cumulus layer is observed over the northern south china sea to the south of a coastal cloud free region as cold air streaming of the coast encounter substantial surface sensible and latent heat fluxes following the onset of the cold surge the cumulus layer depth increases over the central south china sea however this depth decreases over the northern south china sea at a distance of 200 300 km from the china coast the depth and strength of the cumulus or subsidence inversion are greatest new the china coast 600 700 m 4 6 c and weaken toward the central south china sea 200 m 1 c whew they eventually become undetectable possible explanations for the observe

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

vertical structure of wintertime teleconnection patterns abstract orthogonal rotated principal component analysis of the wintertime northern hemisphere 5 day mean sea level pressure field yielded five modes which are of some dynamical interest one can be identified with the well known north atlantic oscillation and another with the pacific north american pattern three of the other modes are highly baroclinic in the sense that their sea level pressure patterns and their associated 500 mb height patterns are different in shape and opposite in polarity over substantial areas these more baroclinic patterns attain their largest amplitudes in the vicinity of the himalayas and rockies their spatial patterns evolve very differently in the lower and middle troposphere the sea level pressure patterns exhibit a distinctive eastward and or equatorward phase propagation parallel to contours of surface elevation along the northern and or eastern side of the mountain ranges while the corresponding 500 mb patterns evolve in a manner consistent with the concept of ros

interannual variations of outgoing ir associated with tropical circulation changes during 1974 78 abstract interannual variability of outgoing ir in the tropical pacific ocean is studied using measurements derived from the noaa scanning radiometer in addition to the usual mean maps seasonal anomaly maps are constructed from june july august 1974 december 1977 january february 1978 these ir anomalies are closely related to changes in convective cloudiness patterns time series representing the equatorial eastern pacific sea surface temperature sst anomalies and monthly anomalies at various locations are also plotted during this period a warming event occurs in which ssts in the eastern pacific rapidly become anomalously warm dramatic changes in outgoing ir occur simultaneously with this sst increase the region of convergence over indonesia shifts eastward and connects to a well developed intertropical convergence zone itcz the south pacific convergence zone spcz is also connected to the indonesian convergence zone but develops more slowly and does not reach its maximum strength unt

late taconian and pre acadian history of the new england appalachians of southwestern connecticut new u pb age determinations and field observations combined with published field relations refine the late taconian and pre acadian history of the new england appalachians of southwestern connecticut foliation within the camerons line shear zone was developed after 514 11 ma but prior to 445 1 5 ma this structure probably experienced renewed movement in the early silurian 437 2 ma as suggested by new xenotime growth in protomylonite metasedimentary and metavolcanic rocks east of camerons line were deposited were isoclinally folded and reached temperatures in excess of about 550 c before emplacement of small dioritic plutons of the 453 3 ma brookfield plutonic series igneous titanites in brookfield plutons cooled below u and pb diffusion e g 525 25 c in the latest ordovician to earliest silurian and were not reset in the acadian the newtown gneiss is a composite magmatic complex composed of quartz diorite 446 2 ma granodiorite 436 2 ma and granite 438 2 ma low 207 pb 204 pb feldspar isotopic compositions and 1150 ma zircon inheritance in the newtown gneiss and brookfield plutonic series are consistent with interaction with grenvillian crust or crustally derived material we propose that the newtown and harrison gneisses and possibly the brookfield plutonic series make up the plutonic roots of a late ordovician to early silurian 454 438 ma magmatic arc complex generated during subduction along the eastern north american continental margin magmatic activity was coeval with that in the bronson hill anticlinorium to the east ca 454 442 ma

alleviation of stationary biases in a gcm through a mountain drag parameterization scheme and a simple representation of mountain lift forces abstract the problem of the representation of the orientation of mountain forces in a gcm is examined first a series of winter simulations is presented with the laboratoire de meteorologie dynamique gcm where the model ground is flat and where the mountains are represented by applying forces to the flow that are either strictly opposite to the local wind i e a drag or strictly perpendicular to it i e a lift these experiments show that the drag forces improve the zonal wind but do not improve the steady planetary wave everywhere while the lift forces scarcely affect the zonal wind but force a steady planetary wave that is everywhere realistic the drag force is formulated following the realistic subgrid scale orographic sso scheme developed recently at ecmwf the lift force essentially enhances vortex stretching over large scale mountains to address issues concerning the representation of sso in gcms experiments with mean orography the ecmwf sso scheme and enhanced lift forces over mounta

persistent severe drought in southern china during winter spring 2011 large scale circulation patterns and possible impacting factors 1 severe drought persisted in southern china from january to may in 2011 in this study a statistical analysis is carried out to discuss the multiple possible impacting factors including la nina the north atlantic oscillation nao and the thermal condition of the tibetan plateau tp the la nina event in 2010 11 excited a lower tropospheric anomalous cyclone over the northwestern pacific weakening the northwestern pacific subtropical high and caused an eastward shift of the high as a result transportation of wet and warm moisture from tropical oceans to southern china decreased the la nina event also strengthened the upper tropospheric east asian jet stream and deepened the east asian trough favoring a southward intrusion of dry northerly flow from the siberia the la nina condition in the previous two seasons also seemed to provide precursory signals for the drought moreover in january may 2011 the nao was in a positive phase and it tended to excite stationary rossby waves that were distributed along the sub polar and subtropical waveguides respectively the sub polar one induced an anomalous anticyclone over the siberia favoring a southward intrusion of high latitude northerly flow to southern china the subtropical one associated possibly with the enhanced convection over the broad region from the mediterranean to sahara was favorable for an influence of upper tropospheric flow on southern china the tp might also exert an influence on the drought by weakening the westerly flow to the southern flank of tp and reducing water vapor transport from the bay of bengal to southern china

soil characterization in and around a proposed waste disposal facility at nuclear fuel complex hyderabad india generation of site specific hydrogeological parameters such as porosity bulk density hydraulic conductivity pore water velocity etc are the pre requisites to carry out studies on the low probability event of migration of radionuclides along with groundwater due to long term leaching from a waste disposal site in the present work the hydrogeological parameters are estimated for soil samples collected from various locations in and around a proposed solid waste disposal site at the nuclear fuel complex hyderabad india the groundwater velocity is estimated using darcy s law the range of values for hydraulic conductivity porosity and bulk density are determined to be 16 24 76 90 m day 1 average 48 12 m day 1 0 42 0 53 average 0 47 and 1 01 1 43 g cm 3 average 1 24 g cm 3 respectively using the estimated values of hydraulic conductivity porosity and the average value of hydraulic gradient between various wells at the site the average groundwater velocity has been estimated to be around 1 0 m day 1 which matches fairly well with the groundwater velocity estimated using radioactive tracer techniques these site specific results will be useful in the radiological impact assessment of a proposed near surface waste disposal facility at nuclear fuel complex hyderabad india

grenvillian provenance for the amphibolite grade trap falls formation implications for early paleozoic tectonic history of new england the trap falls formation is a sequence of interlayered quartzites and schists that crops out in the appalachian belt in southern connecticut and was deformed and metamorphosed to middle amphibolite grade during acadian orogenesis schists have high al2o3 and low cao na2o and k2o chemical index of alteration cia 68 70 consistent with a significant weathering history in the sediment source rare earth element ree patterns for both schists and quartzites parallel post archean average australian shale with light ree enrichment and well developed eu anomalies suggesting an average upper crustal source whole rock nd and pb isotopic analyses indicate old sources with depleted mantle model ages tdm from 1880 to 1660 ma 207pb 204pb from 15 62 to 15 87 and 206pb 204pb from 19 11 to 22 08 u pb ages for single grain and multigrain populations of detrital zircons range between 1113 and 992 ma the youngest of which defines a maximum depositional age for the trap falls formation u pb zircon ages ind

life cycle variations of mesoscale convective systems over the americas abstract using goes 7 isccp b3 satellite data for 1987 88 the authors studied the evolution of the morphological and radiative properties of clouds over the life cycles of deep convective systems cs over the americas at both tropical and middle latitudes a deep convective cloud system is identified by adjacent satellite image pixels with infrared brightness temperatures tir 245 k 28 c that at some time contain embedded convective clusters that are defined by pixel values of tir 218 k 55 c the first part of the analysis computes parameters for each convective system that describe the system areal size number of convective clusters fractional convective area average and maximum size of the convective clusters shape eccentricity and orientation mean tir variance of tir tir gradient and the mean variance and gradient of collocated visible reflectances when available the second part of the analysis searches a 5 5 region centered on each convective system but in the subsequent

variability of warm season cloud episodes over east asia based on gms infrared brightness temperature observations abstract the present study has used the geostationary meteorological satellite gms ir brightness temperature observations to investigate the regional and intraseasonal variability of east asian warm season cloud precipitation episodes in distance time space due to land sea contrast and latitudinal effects the data period was may august 1998 2001 and harmonic analysis was employed as the major tool for analysis the full domain of study 20 40 n 95 145 e was divided into northern and southern zones and into eastern and western sectors and statistics of episodes in each subregion were derived and compared for latitudinal effects episodes were found to be significantly larger in span and duration in northern 30 40 n than in southern 20 30 n zones in the northern zone the propagation characteristics were also stronger and remain evident even in midsummer while episodes south of 30 n reversed in direction and traveled westward in july and august for land sea contrast the may august tra

a climatology of warm season cloud patterns over east asia based on gms infrared brightness temperature observations abstract in the present study hourly infrared ir brightness temperatures observed by the geostationary meteorological satellite gms over the region 20 40 n 95 145 e in may august 1998 2001 are used to compile a climatology of warm season cloud precipitation episodes over east asia with a goal to better understand the characteristics of warm season convection and the behavior of these episodes results are compared with those obtained in north america using radar derived data the convection in east asia similar to that in north america is shown to also exhibit coherent patterns and characteristics of propagating events in the longitude time hovmoller space with a preferred phase speed of 10 25 m s 1 considerably faster than warm season synoptic scale waves near the eastern edge of the tibetan plateau convection was most active with a strong diurnal signal peaking in late afternoon or early evening then propagating eastward the zonal span and duration of episodes could reach 3000 km and

a severe drought event in northern china in winter 2008 2009 and the possible influences of la nina and tibetan plateau 1 severe drought occurred in northern china in winter 2008 09 and the la nina event might have exerted a major influence on the drought both correlation analysis and case investigation indicate that severe wintertime droughts in northern china mostly occur under la nina conditions the la nina event in 2008 2009 increased the differences in temperature and atmospheric pressure between the indo pacific oceans and the asian continent and intensified the northeasterly east asian winter monsoon flow in winter 2008 2009 the western pacific subtropical high was located farther south than normal associating with a southward shift of the intertropical convergence zone so that wet and warm flow could hardly reach northern china from the tropical oceans furthermore the la nina event in 2008 2009 strengthened the upstream portion of the upper tropospheric jet stream and the descending branch of the meridional cell over the subtropics causing a negative divergence anomaly to the northern side of the jet entrance as a result the airflow over northern china is more convergent divergent at the upper lower levels unfavorable for precipitation in winter 2008 2009 the surface and tropospheric temperatures over the tibetan plateau were above normal as a result the india burma trough was shallower and less active weakening the moisture transportation from the bay of bengal to eastern china this feature was possibly related to the less snow over the plateau results also show that both the nino3 4 sst and the tibet plateau temperature in the previous autumn can be considered indicators of the winter drought in northern china

impact of subgrid scale orography on equatorial angular momentum budget and the cold surges in a general circulation model abstractthe dynamical relations between equatorial atmospheric angular momentum eaam equatorial mountain torques and cold surges are analyzed in a general circulation model gcm first the authors show that the global eaam budget is well closed in the gcm much better than in the ncep ncar reanalysis they then confirm that the equatorial torques due to the tibetan plateau the rockies and the andes are well related to the cold surges developing over east asia north america and south america respectively for all these mountains a peak in the equatorial mountain torque components precedes by few days the development of a cold surge confirming that the cold surge s preconditioning is dynamically driven by large scale mountains the authors also analyze the contribution of the subgrid scale orography sso parameterizations and find that they contribute substantially to the torques in experiments where these parameterizations are almost entirely reduced over a given massif the authors find th

the relationship of low level winds and moisture to convection in the tropical pacific abstract strong convection in the tropical pacific is found to be enhanced when low level winds are westerly and poleward directed this means that winds which blow opposite to the normal easterly equatorward trade wind flow are associated with strong convection linear regression demonstrates that about 30 40 of the variance in conviction across the pacific during the 1982 83 el nino can be explained by low level precipitable water plus the low level winds

diurnal cycle of deep convection in super clusters embedded in the madden julian oscillation 1 the diurnal cycle of deep convection in the convectively active phase cap and convectively suppressed phase csp of the madden julian oscillation mjo was investigated using global infrared equivalent blackbody temperature tbb data from october 2000 to april 2005 we particularly focused on super clusters scs that occurred during the cap of the mjo to analyze the behavior of scs and the csp of the mjo statistically we created composites of tbb for each case four regions were examined 1 the indian ocean io 2 the ocean area of the maritime continent mco 3 the land area of the maritime continent mcl and 4 the western pacific wp the amplitude phase of the diurnal cycle of deeper convection in scs was larger than similar to that of the csp of the mjo this result is consistent with that found in a previous study however the diurnal cycle of deep convection in the csp of the mjo had a clear maximum peak especially over the mcl but that in scs had a broader maximum peak of deep convection especially in oceanic regions although the diurnal phase was similar between scs and the csp of the mjo this result statistically suggests that the organization of a convective system affects the diurnal cycle of its deep convection as described in a previous case study we also demonstrated that the difference in the diurnal cycle of deep convection in the io and wp regions arose from sea surface temperature differences in those regions

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c