mechanisms limiting the northward extent of the northern summer monsoons over north america asia and africa abstract mechanisms determining the poleward extent of summer monsoon convergence zones for north america asia and africa are examined in an intermediate atmospheric model coupled with a simple land model and a mixed layer ocean observations show that thermodynamical factors associated with the net heat flux into the atmospheric column provide favorable conditions for the monsoon convergence zone to extend farther poleward than actually occurs to understand the discrepancy a series of experiments are designed to test the importance of mechanisms previously examined in the south american case by the authors namely soil moisture ventilation and the interactive rodwell hoskins mechanism the latter refers to the interaction between baroclinic rossby wave dynamics and convective heating in north america experiments suggest that ventilation by both temperature and moisture advection is a leading effect the interactive rodwell hoskins mechanism tends to favor east coast rainfall and west coast dryne

the alberta foreland basin relationship between stratigraphy and cordilleran terrane accretion events a foreland basin sequence resulting from accretion of a terrane to a continental passive margin ideally should be unconformity bounded with a shallowing upward pattern like the classic flysch to molasse sequence of alpine foreland basins the basal unconformity is cut as the peripheral bulge associated with lithospheric flexure migrates cratonward ahead of the basin and the advancing overthrusts the shallowing occurs because sediment supply at first is low early stages of accretion near the continental slope generate little or no topography above sea level later stages result in significant tectonic uplift and much sediment is shed into the foreland filling the basin the upper unconformity is cut as lithospheric bending stresses are relaxed following overthrusting and reduction of the flexural load on the lithosphere through erosion and or tectonic denudation of the overthrusts causes regional uplift or basin rebound actual sequences show differences from this idealized version in that i

apatite fission track thermochronometry from central alberta implications for the thermal history of the western canada sedimentary basin apatite separated from 47 cretaceous and tertiary drill core and surface samples from the foreland basin strata of the western canada sedimentary basin wcsb have been analyzed for their apatite fission track aft age and confined track length distribution thermal histories of the fission track data were then estimated using a constrained random search inversion technique based on the durango apatite annealing model most importantly this technique provides an estimate of the peak postdepositional temperature experienced by each sample with error bounds determined by the precision of the fission track data most apatite samples retain at least some tracks that formed prior to the time of maximum cenozoic burial assumed to be coincident with maximum temperature seven apatite samples were fully annealed during burial during or following the laramide orogeny and provide a minimum age of 42 ma for heating lower cretaceous samples from near the deformation front were fully annealed and attained temperatures of at least 119 138 c during maximum burial in contrast stratigraphically equivalent samples at the northeastern end of the transect near the cold lake heavy oil and tar sand deposits did not exceed 80 c paleogeothermal gradients calculated using bounded estimates of the peak temperatures experienced by the samples together with maximum burial estimates from coal moisture studies range from 20 c km near the deformation front to as high as 60 c km near the cratonic edge of the basin this variation has the same trend as present geothermal gradients which range from 30 c km to 45 c km but indicates a greater contrast at the end of the laramide the results are consistent with the concept of heat transport by basinal scale fluid flow

orographic effects of the tibetan plateau on the east asian summer monsoon an energetic perspective this paper investigates the dynamical processes through which the tibetan plateau tp influences the east asian summer monsoon easm within the framework of the moist static energy mse budget using both observations and atmospheric general circulation model agcm simulations the focus is on the most prominent feature of the easm the so called meiyu baiu mb which is characterized by a well defined southwest northeast elongated quasi stationary rainfall band spanning from eastern china to japan and into the northwestern pacific ocean between mid june and mid july observational analyses of the mse budget of the mb front indicate that horizontal advection of moist enthalpy and primarily of dry enthalpy sustains the front in a region of otherwise negative net energy input into the atmospheric column a decomposition of the horizontal dry enthalpy advection into mean transient and stationary eddy fluxes identifies the longitudinal thermal gradient due to zonal asymmetries and the meridional stationary eddy velocity as the most influential factors determining the pattern of horizontal moist enthalpy advection numerical simulations in which the tp is either retained or removed show that the tp influences the stationary enthalpy flux and hence the mb front primarily by changing the meridional stationary eddy velocity with reinforced southerly wind over the mb region and northerly wind to its north changes in the longitudinal thermal gradient are mainly confined to the near downstream of the tp with the resulting changes in zonal warm air advection having a lesser impact on the rainfall in the extended mb region

temporal variations in the cooling and denudation history of the hunza plutonic complex karakoram batholith revealed by 40ar 39ar thermochronology the 40ar 39ar thermochronology of the late cretaceous hunza plutonic complex reveals an episodic cooling and denudation history for this regional scale pluton the 40ar 39ar analyses of biotites from a vertical relief section of 3200 m reveal a pulse of rapid cooling at 20 ma in the interval of 110 27 ma age elevation distributions suggest denudation rates of the order of 0 02 0 003 mm yr at 20 ma denudation rates increased significantly to 2 7 0 7 mm yr then returned to much slower rates until 12 ma a second pulse of rapid cooling beginning at 12 ma is revealed by inverse numerical modeling of multidiffusion domain alkali feldspars from a vertical section of 1700 m decreasing in elevation these samples record the onset of rapid cooling at 12 9 and 7 ma respectively all of the alkali feldspars record a period of nearly isothermal conditions prior to the onset of rapid cooling when rates increased to 30 c m y assuming a geothermal gradient of 30 c km these cooling rates translate into denudation rates of 1 0 mm yr apatite fission track analysis indicates denudation rates of 0 7 0 1 mm yr over the interval of 6 6 ma to 2 4 ma in agreement with the alkali feldspar data these data suggest denudation of 2 9 0 4 km since the plio pleistocene together the alkali feldspar and apatite data indicate that a minimum of 10 km of overburden has been removed since the mid late miocene an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type exit to leave the system paper 95tc02424 temporal variations in the cooling and denudation history of the hunza plutonic complex karakoram batholith revealed by 40ar 39ar thermochronology m a krol p k zeitler g poupeau and a pecher diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

discussion on mississippi valley type lead zinc deposits through geological time implications from recent age dating research by d l leach d bradley m t lewchuk d t a symons g de marsily and j brannon 2001 mineralium deposita 36 711 740

subtropical anticyclones and summer monsoons the summer subtropical circulation in the lower troposphere is characterized by continental monsoon rains and anticyclones over the oceans in winter the subtropical circulation is more strongly dominated by the zonally averaged flow and its interactions with orography here the mechanics of the summer and winter lowertropospheric subtropical circulation are explored through the use of a primitive equation model and comparison with observations by prescribing in the model the heatings associated with several of the world s monsoons it is confirmed that the equatorward portion of each subtropical anticyclone may be viewed as the kelvin wave response to the monsoon heating over the continent to the west a poleward flowing low level jet into a monsoon such as the great plains jet is required for sverdrup vorticity balance this jet effectively closes off the subtropical anticyclone to the east and also transports moisture into the monsoon region the low level jet into north america induced by its monsoon heating is augmented by a remote response to the asian monsoon heating the rossby wave response to the west of subtropical monsoon heating interacting with the midlatitude westerlies produces a region of adiabatic descent it is demonstrated here that a local diabatic enhancement can lead to a strengthening of the descent longitudinal mountain chains act to block the westerly flow and also tend to produce descent in this region below the descent sverdrup vorticity balance implies equatorward flow that closes off the subtropical anticyclone to the west and induces cool upwelling in the ocean through ekman transport feedbacks involving for example sea surface temperatures may further enhance the descent in these regions the conclusion is that the mediterranean type climates of regions such as california and chile may be induced remotely by the monsoon to the east hence it can be argued that the subtropical circulation in summer comprises a set of weakly interacting monsoon systems each involving monsoon rains a low level poleward jet a subtropical anticyclone to the east and descent and equatorward flow to the west in winter it is demonstrated how the nonlinear interaction between the strong zonal mean circulation associated with the winter hadley cell and the mountains can define many of the large scale features of the subtropical circulation the blocking effect of the longitudinal mountain chains is shown to be very important subsequent diabatic effects such as a local diabatic enhancement would appear to be essential for producing the observed amplitude of these features

a diabatically driven mesoscale vortex in the lee of the tibetan plateau abstract an analysis of a diabatically driven and long lived midtropospheric vortex in the lee of the tibetan plateau during 24 27 june 1987 is presented the large scale conditions were characterized by the westward expansion of the 500 mb western pacific subtropical high and the amplification of a trough in the lee of the plateau embedded within the lee trough three mesoscale convective systems mcss developed a vortex emerged following the dissipation of one mcs with its strongest circulation located in the 400 500 mb layer low level warm advection and surface sensible and latent heating contributed to the convective initiation weak wind and weak ambient vorticity conditions inside the lee trough provided a favorable environment for these mcss and the vortex to develop and evolve the organized vortex circulation featured a coherent core of cyclonic vorticity extending from near the surface to 300 mb with virtually no vertical tilt the air in the vicinity of the vortex was very moist and the

geochronologic studies in central new england ii post acadian hinged and differential uplift sup 40 ar sup 39 ar analyses of muscovite biotite and k feldspar from central new england reveal a remarkable pattern of mineral ages the ages are progressively younger from central to western new hampshire and rise sharply near the vermont border to ages more typical of post acadian cooling this distribution is attributed to differential uplift via isostatic rebound of an anomalously thickened crust at the bronson hill anticlinorium this explanation requires that between 6 and 8 km of normal fault motion has occurred on structures in western new hampshire not previously recognized to have accommodated this kind or magnitude of displacement this hinged differential uplift occurred from approximately 360 170 ma and is consistent with a time constant for rebound of approximately 80 m y

modeling secondary oil migration with core scale data viking formation alberta basin the viking formation in the alberta basin contains approximately 88 7 x 106 m3 5 579 x 108 bbl of recoverable oil which migrated more than 200 km as indicated by oil source rock correlation simulating the mechanisms controlling secondary oil migration hydrodynamics buoyancy and permeability heterogeneity is beneficial for exploration but it remains extremely difficult to predict oil occurrences although core scale petrophysical data for the viking formation are abundant 69 000 core plugs the extent of fracture permeability and permeability alteration due to diagenesis are unknown moreover sampling bias may affect the permeability distribution in unpredictable ways numerical simulations of oil migration were conducted using the highest core plug measurement of permeability from each borehole to obtain an upper bound on oil migration velocities this permeability model is not appropriate for simulating stratigraphic entrapment of oil but it does reveal that core scale data are in the appropriate range of magnitude to have allowed significant oil migration regional groundwater flow was essential for charging several of the largest and most distant oil fields in the viking formation maximum core plug permeability data are useful for modeling the extent of secondary oil migration and may have applications to fluid flow and transport modeling in other foreland settings

on the seasonality of the hadley cell abstract the annual march of the climatological mean meridional circulations mmcs in the ncep ncar reanalyses is dominated by two components of roughly comparable mean squared amplitude 1 a seasonally invariant pair of hadley cells with rising motion centered near and just to the north of the equator and subsidence in the subtropics and 2 a seasonally reversing sinusoidally varying solsticial cell with ascent in the outer tropics of the summer hemisphere and subsidence in the outer tropics of the winter hemisphere the meridional structure and seasonal evolution of the solsticial cell are suggestive of a close association with the monsoons these results are consistent with previous analyses of the mean meridional circulation based on radiosonde data

investigation of a large scale mode of ocean atmosphere variability and its relation to tropical pacific sea surface temperature anomalies abstract by examining the linearly coupled atmospheric and oceanic signals related to interannual variability in sea surface temperatures and upper air wind fields a hemispheric scale ocean atmosphere teleconnection mode is isolated that is significantly correlated with equatorial pacific ssts 12 months later the interannual component of this teleconnection mode is related to a basin scale dipole in the upper air wind fields stretching across the extratropical pacific with additional anomalies extending from the eastern tropical pacific over north america and into the atlantic basin in addition it is related to variability in the sst field with warm anomalies found over the tropical subtropical western pacific as well as the equatorial eastern pacific also there are related cold anomalies over the extratropical central north pacific that extend down into the central subtropical tropical pacific diagnostic studies investigating the ocean atmosphere structure for this mode of variability indicate th

the mechanical impact of the tibetan plateau on the seasonal evolution of the south asian monsoon the impact of the tibetan plateau on the south asian monsoon is examined using a hierarchy of atmospheric general circulation models during the premonsoon season and monsoon onset april june when westerly winds over the southern tibetan plateau are still strong the tibetan plateau triggers early monsoon rainfalldownstream particularlyoverthebay ofbengalandsouth china the downstreammoist convection is accompanied by strong monsoonal low level winds in experiments where the tibetan plateau is removed monsoon onset occurs about a month later but the monsoon circulation becomes progressively stronger and reaches comparable strength during the mature phase during the mature and decaying phase of monsoon july september when westerly winds over the southern tibetan plateau almost disappear monsoon circulation strength is not much affected by the presence of the tibetan plateau a dry dynamical core with east west oriented narrow mountains in the subtropics consistently simulates downstream convergence with background zonal westerlies over the mountain in a moist atmosphere the mechanically driven downstream convergence is expected to be associated with significant moisture convergence the authors speculate that the mechanically driven downstream convergence in the presence of the

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

mesoscale analyses of the sichuan flood catastrophe 11 15 july 1981 abstract during the period 11 15 july 1981 heavy rainfall occurred over the sichuan basin in china resulting in severe floods that took a large toll in human life and property damage synoptic analyses indicate that early in this period the southerly monsoon flow was particularly strong near the basin because of a favorable positioning of the pacific subtropical high and the indian monsoon depression the passage of a deep midlatitude trough from the lake baikal region brought colder drier air from siberia into southwest china the siberian air stream met the monsoon current over the eastern plateau and the sichuan basin creating a region of large scale low level convergence mesoscale analyses show that the flood was directly related to the extreme development of a long lived mesoscale vortex called south sw vortex by chinese meteorologists over the basin as it merged with another mesoscale vortex generated over the tibetan plateau mesoscale heat and moisture budgets suggest that the latent hea

early cretaceous denudation related to convergent tectonics in the baikal region se siberia we present 24 new apatite fission track aft ages and 18 track length measurements from the baikal region se siberia most samples have aft ages between 140 and 100 ma with relatively high mean track lengths c 13 2 m the relationship between aft ages elevation and mean track lengths indicate that the samples record rapid cooling during the early cretaceous 140 120 ma as also shown by thermal history inversion of track length distributions cooling took place during a late jurassic early cretaceous orogenic phase related to closure of the mongol okhotsk ocean and reflected in the exhumation of metamorphic core complexes followed by thrusting and reverse faulting basin inversion and large vertical motions the variation in aft ages throughout the study area can be partly explained by differences in geothermal structure but differential denudation also played a role minimum amounts of early cretaceous denudation are estimated at 2 3 km

apatite fission track analysis of oligocene strata in south texas u s a testing annealing models analysis of apatite fission track data from forty seven surface and subsurface samples of fine grained sandstone to pebbly conglomerate from the oligocene catahoula gueydan frio and vicksburg formations documents the response of fission track ages and track length distributions to simple post depositional thermal histories characterized by monotonic heating data from outcrop samples document that the apatite component was derived from source areas characterized by rapid cooling through the temperature range from 120 to 50 c during the early tertiary the apatite population is characterized by a log normal chlorine distribution mean 0 3 wt 0 3 wt consisting predominantly of low cl apatites 80 is 0 5 wt mean track lengths from core samples decrease systematically with increasing depth and temperature the decrease in apatite fission track ages with increasing depth and temperature is less systematic due to the scatter in inherited ages at the time of deposition no tracks were observed in apatite from samples at temperatures above 130 c mean track lengths for the south texas data agree well with those for a similar data set from the otway basin southeastern australia for present day temperatures of 70 c at higher temperatures mean lengths are 1 to 9 m longer than those observed from the otway basin this discrepancy is interpreted to reflect up to 40 ma longer residence times at maximum burial temperatures for the otway basin samples standard deviations about mean lengths are also lower than observed in the otway basin study consistent with the wider variation of cl contents mean 0 8 wt 0 7 wt that characterize apatite from the otway basin recently published apatite fission track annealing models predict significantly different mean track length vs present day temperature profiles for thermal histories believed to be representative of those experienced by sampled south texas strata because of the large uncertainties attributed to present day temperatures 10 c the predicted mean length vs temperature trends for these models essentially fall within or on the uncertainty envelope for the observed trend residuals of predicted minus observed mean lengths suggest that the previously published carlson composite parameter model using an initial mean length of 15 8 m instead of 16 5 m or the crowley et al model for track length reduction down to 11 m provide the best estimates of mean track length reduction over geologic time scales for near end member f apatite populations

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

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

evidence for differential unroofing in the adirondack mountains new york state determined by apatite fission track thermochronology abstract apatite fission track ages of 168 83 ma for 39 samples of proterozoic crystalline rocks three samples of cambrian potsdam sandstone and one cretaceous lamprophyre dike from the adirondack mountains in new york state indicate that unroofing in this region occurred from late jurassic through early cretaceous samples from the high peaks section of the adirondack massif yielded the oldest apatite fission track ages 168 135 ma indicating that it was exhumed first unroofing along the northern northwestern and southwestern margins of the adirondacks began slightly later as shown by younger apatite fission track ages 146 114 ma determined for these rocks this delay in exhumation may have resulted from burial of the peripheral regions by sediment shed from the high peaks apatite fission track ages for samples from the southeastern adirondacks are distinctly younger 112 83 ma than those determined for the rest of the adirondack region these younger apatite fission track ages are from a sec

zircon la icpms geochronology of the cornubian batholith sw england abstract available u pb age data for the cornubian batholith of sw england is based almost entirely on monazite and xenotime and very little zircon u pb age data has been published as a result no zircon inheritance data is available for the batholith by which the nature of the unexposed basement of the rhenohercynian zone in sw england might be constrained zircon la icpms data for the cornubian batholith provides concordia ages bodmin moor granite 316 4 ma carnmenellis granite 313 3 ma dartmoor granite 310 ma st austell granite 305 5 ma and land s end granite 300 5 ma that are consistently 20 30 ma older than previously published emplacement ages for the batholith and unrealistic in terms of geologic relative age relationships with respect to the country rock this discrepancy is likely as a consequence of minor pre granitic pb inheritance several of the batholith s granite plutons contain a component of late devonian inheritance that may record rift related lower crustal melting or arc related magmatism associated with subduction of the rheic ocean in addition the older granites likely contain mesoproterozoic inheritance although the highly discordant nature of the mesoproterozoic ages precludes their use in assigning an affinity to the rhenohercynian basement in sw england

the relationship between track shortening and fission track age reduction in apatite combined influences of inherent instability annealing anisotropy length bias and system calibration abstract the relationship between reduced track density 0 and reduced mean confined track length l l 0 during annealing has been studied for both spontaneous and induced tracks in four apatite samples with different chemical composition compositional range and origin and with spontaneous tracks giving mean confined track lengths varying from 14 5 m down to 12 3 m in all four apatites induced tracks show a relationship between l l 0 and 0 composed of two regions at higher values the two appear to be equal while at lower values l l 0 is greater than 0 this can be understood qualitatively in terms of the anisotropy of annealing and the bias against revelation of short tracks data from three apatites of uniform composition show near identical relationships in a sample showing a range of apatite compositions the point of divergence from the 1 1 relationship is somewhat higher than in the uniform composition apatites because individual grains anneal at different rates and the presence of highly annealed grains affects the track density more strongly than the mean track length spontaneous tracks show similar relationships to those observed for induced tracks in each sample when the data are renormalised to allow for the natural annealing present in the spontaneous tracks previous studies which led to the idea of length reduction without density reduction for spontaneous tracks did not renormalise density data as well as length data thereby distorting the apparent relationship data for the multi compositional apatite sample where annealing has taken place in geological conditions also agrees with the laboratory annealing data for both spontaneous and induced tracks this consistency suggests that a single process is responsible in all three cases implying that a laboratory based description of annealing can be applied to geological conditions with confidence recognition that spontaneous tracks in apatite are commonly annealed suggests that in general the fission track age should be interpreted as a reflection of both the time over which tracks have been retained and the distribution of etchable track lengths since the latter is a manifestation of the thermal history the fission track age should be interpreted in similar terms

the formation mechanism of the bonin high in august the bonin high is a subtropical anticyclone that is predominant near japan in the summer this anticyclone is associated with an equivalent barotropic structure often extending throughout the entire troposphere although the equivalent barotropic structure of the bonin high has been known for years among synopticians because of its importance to the summer climate in east asia there are few dynamical explanations for such a structure the present paper attempts to provide a formation mechanism for the deep ridge near japan we propose a new hypothesis that this equivalent barotropic ridge near japan is formed as a result of the propagation of stationary rossby waves along the asian jet in the upper troposphere the silk road pattern first the monthly mean climatology is examined in order to demonstrate this hypothesis it is shown that the enhanced asian jet in august is favourable for the propagation of stationary rossby waves and that the regions of descent over the eastern mediterranean sea and the aral sea act as two major wave sources second a primitive equation model is used to simulate the climatology of august the model successfully simulates the bonin high with an equivalent barotropic structure the upper tropospheric ridge is found to be enhanced by a height anomaly of more than 80 m at 200 hpa when a wave packet arrives sensitivity experiments are conducted to show that the removal of the diabatic cooling over the asian jet suppresses the silk road pattern and formation of an equivalent barotropic ridge near japan while the removal of the diabatic heating in the western pacific does not copyright 2003 royal meteorological society

minerological and o isotope studies of diagenesis and porewater evolution in continental sandstones cretaceous belly river group alberta canada abstract the mineralogy and o isotope geochemistry of diagenetic phases from continental sandstones of the upper cretaceous belly river group west central and south western alberta have been determined diagenesis of the continental sandstones is dominated by crystallization of clay minerals including fe rich chlorite 18 o 3 3 to 9 3 i s c s and illite 18 o 9 5 to 10 7 kaolinite 18 o 5 9 to 12 7 s i and smectite 18 o 11 0 to 14 0 other diagenetic phases include quartz overgrowths 18 o 12 0 to 21 0 and calcite 18 o 8 5 to 12 9 13 c x02212 14 3 to 2 0 chlorite generally crystallized first in the paragenetic sequence followed by quartz i s calcite and kaolinite and then s i and smectite interpretation of these data suggests that early diagenesis occurred in the presence of low 18 o meteoric water whose 18 o value rose moderately during subsequent burial highest burial temperatures 110 c were probably achieved in the south western portion of the study area and are reflected by the appearance of r1 ordered i s in this locality post laramide influx of meteoric water subsequently resulted in a substantially lower porewater 18 o value values of 18 o for diagenetic minerals from the continental sandstones and immediately underlying deltaic and shoreline basal sandstones are systematically lower by 1 to 6 than equivalent phases from the lower cretaceous marine sandstones of the viking formation relative differences in the oxygen isotopic compositions of connate waters freshwater vs sea water have been preserved surviving 18 o enrichment during burial and 18 o depletion during post laramide influx of meteoric water while substantial meteoric dilution of the porewater has occurred flushing of evolved connate waters has not been complete

oxygen isotope studies of diagenesis and pore water evolution in the western canada sedimentary basin evidence from the upper cretaceous basal belly river sandstone alberta abstract the oxygen isotope compositions and paragenetic sequence of diagenetic minerals from the upper cretaceous basal belly river sandstone southwestern alberta have been used to identify changes in pore water composition during diagenesis these changes can be related to major geologic events within the western canada sedimentary basin low 18o meteoric water has played an important role in the diagenesis of these upper cretaceous rocks on a basinwide scale during deposition and early diagenesis and following uplift of the basin in early eocene time diagenetic phases include early chlorite 18o 6 1 to 8 3 and calcite 18osmow 21 0 13cpdb 1 6 followed by quartz overgrowths 18o 13 1 to 18 0 calcite 18osmow 10 4 to 14 4 13cpdb 10 6 to 1 2 and then kaolinite 18o 7 8 to 11 9 illite smectite 18o 10 9 to 13 1 and smectite 18o 12 6 to 13 7 the interpretation of these results is that shallow diagenesis early in the burial history chlorite calcite occurred in the presence of brackish or fresh water with burial the 18o value of the pore water increased due to water rock interaction burial diagenesis was terminated in the early eocene by uplift laramide orogeny recharge of the basin by low 18o meteoric water occurred at this time the meteoric water then became involved in the formation of diagenetic quartz and calcite at or near maximum burial temperatures and in the crystallization at lower temperatures of kaolinite illite smectite and smectite as post eocene cooling and erosion progressed

coal quality coal rank variation and its relation to reconstructed overburden upper cretaceous and tertiary plains coals alberta canada near surface coals in the alberta plains occur in upper cretaceous and tertiary sediments the former represented by the belly river group horseshoe canyon formation and wapiti formation and the latter by the scollard member of the paskapoo formation statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations the coals discussed range in rank from subbituminous c to high volatile bituminous c these coals are variable in ash content and low in sulfur content the relationships among calorific value dry basis in kj kg and ash dry basis in and calorific value moist mineral matter free basis in kj kg and equilibrium moisture meq in were determined to be cvd 29 677 315 17 ashd and cvmmmf 31 816 442 05 meq respectively the maximum depth of coal seam burial dob in m was reconstructed on the basis of previously published graphs relating the equilibrium moisture loss to depth of coal seam burial using the relationship log10meq 1 865 0 000416 dob a least squares regression analysis of calorific value mmmf basis in k kg on the calculated depth of burial dob in m yielded the equation cvmmmf 14 748 6 25 dob indicating a coalification gradient determined on the reconstructed overburden of 6 25 kj kg m 0 82 btu lb ft of depth or overburden near surface coals in the alberta plains increase in rank toward the west southwest toward the foothills and mountains region because of progressively greater amounts of overburden that existed in that direction during the tertiary erosion has since removed between 900 and 1 900 m 3 000 and 6 200 ft of sediment with the greatest amount of removal occurring in a west southwest direction

the jameson land basin east greenland a fission track study of the tectonic and thermal evolution in the cenozoic north atlantic spreading regime abstract the late mesozoic and cenozoic thermal history of the jameson land basin is constrained by new apatite and zircon fission track ft data of surface permian to jurassic sedimentary rocks the results show a general regional thermal evolution related to burial to temperatures close to and in excess of the maximum temperatures of the apatite annealing interval 125 c followed by cooling mainly due to cenozoic uplift and erosion faulting and differential movements in the basin generally occurred after cooling below the apatite partial annealing zone paz 75 125 c however in the northern part of the basin the data suggest a thicker sediment cover or localized heating related to an earlier fracture zone both apatite ft analysis and vitrinite reflectance values reveal a postmature signature for the studied rocks in the northeastern jameson land and premature to mature for the western central and southern jameson land rocks with respect to generation of hydrocarbons the chemical variations of apatite enhance the possibility of recognizing sample positions near maximum temperatures in the paz furthermore the pb zn mineralization pattern closely follows the tertiary maturity trend given by the ft data the type and distribution of mineralization suggest that it was influenced by the regional thermal evolution of the basin in the northeast domain circulating fluids may have overprinted the regional thermal record before ca 20 ma basaltic dyke and sill intrusions 55 45 ma locally caused resetting of apatite ft ages but generally the direct influence from upper crustal magmatic activity played only a minor role the thermal evolution in northeast jameson land is related to the late tectonic evolution of the northeast atlantic involving a change in ridge position at ca 25 ma which followed the passage of the proto icelandic mantle plume at 63 40 ma

diagenesis and isotopic evolution of porewaters in the alberta deep basin the falher member and cadomin formation abstract diagenesis and porewater evolution in the alberta deep basin have been studied by combining results from petrologic stable isotope and fluid inclusion analyses of diagenetic minerals four stages of diagenesis and porewater evolution corresponding to burial and subsequent uplift and erosion have been identified in the falher member of the spirit river formation and the cadomin formation stage 1 deposition and burial is marked by early precipitation of hematite siderite or chlorite and the dissolution of unstable detrital grains followed by later albitization precipitation of illite and local calcite cement and pressure solution of chert grains during this stage 18o values of porewaters in the falher member increased from 10 3 to 3 infiltration of saline fluids from pre cretaceous units may have produced porewaters in the cadomin formation with 18o values as high as 4 to 7 stage 2 maximum burial and relief is dominated by precipitation of quartz druse in conglomerates and horizontal fractures porefluids during stage 2 had 18o values of 3 at 190 c 2 3 wt dissolved solids in the falher member and at 150 c in the cadomin formation during stage 3 uplift and erosion precipitation of dickite occurred in both the falher member and the cadomin formation from evolved meteoric water as temperatures and 18o values of the porewater decreased in addition precipitation of ankerite and calcite was initiated in the falher member as the influx of evolved meteoric water continued finally in stage 4 maximum generation of methane from interbedded coals methane saturation of the porespaces marked the end of diagenesis in the down dip gas saturated part of the deep basin

gas maturity and alteration systematics across the western canada sedimentary basin from four mud gas isotope depth profiles abstract carbon isotope and molecular compositions of mississippian to upper cretaceous mud gases have been examined from four depth profiles across the western canada sedimentary basin wcsb the profiles range from the shallow oil sands in the east r 0 0 25 to the very mature sediments in the overthrust zone to the west r 0 2 5 in the undisturbed wcsb 13 c 1 13 c 2 and 13 c 2 13 c 3 cross plots show three maturity and alteration trends 1 pre cretaceous gas sourced from type ii kerogen 2 cretaceous colorado group gas and 3 lower cretaceous mannville group biodegraded gas a fourth set of distinctly different maturity trends is recognized for lower cretaceous gas sourced from type iii kerogen in the disturbed belt of the wcsb displacement of these latter maturity trends to high 13 c 2 values suggests that the sampled gas was trapped after earlier formed gas escaped probably as a result of overthrusting unusually 13 c enriched gas 13 c 1 34 13 c 2 13 and 13 c 3 0 from the gething formation in the disturbed belt is the result of late stage gas cracking in a closed system in general gas maturity is consistent with the maturity of the host sediments in the wcsb suggesting that migration and mixing of gases was not pervasive on a broad regional and stratigraphic scale the deep basin portion of the wcsb is an exception here extensive cross formational homogenization of gases has occurred in addition to updip migration along the most permeable stratigraphic units

evidence from apatite fission track analysis for regional cretaceous cooling in the ouachita mountain fold belt and arkoma basin of arkansas geologic note 1 a reconnaissance study involving apatite fission track analysis of surface paleozoic sedimentary and cretaceous intrusive rocks was undertaken to evaluate the low temperature thermal history of the ouachita mountain fold belt and arkoma basin of arkansas paleozoic rocks have apparent apatite fission track ages ranging from 184 or 12 ma to 95 or 11 ma with mean track lengths in the range of 12 95 or 0 17 micrometers to 13 51 or 0 13 micrometers indicating that these samples have undergone significant postdepositional annealing cretaceous samples have apatite fission track ages between 104 or 4 and 88 or 6 ma that are concordant with rb sr and k ar ages and mean track lengths in the range 14 69 or 0 16 micrometers to 15 36 or 0 10 microme ers indicating that these rocks cooled rapidly to paleotemperatures below 50 60 degrees c following their emplacement and have subsequently remained cool paleozoic strata of the ouachita mountain fold belt and arkoma basin in arkansas are inferred to have undergone regional cooling from paleotemperatures greater than 110 degrees c beginning in the early cretaceous to paleotemperatures generally less than 80 90 degrees c prior to the intrusion of alkaline plutons along the western margin of the mississippi embayment during the middle cretaceous whether regional cooling during the cretaceous was caused by uplift and erosion or whether a dramatic reduction in the paleogeothermal gradient was involved remains uncertain although a significant component of uplift and erosion is inferred from independent geological observations the results of this study indicate that paleozoic rocks of the ouachita mountain fold belt and arkoma basin of ar ansas were exposed to maximum paleotemperatures during late paleozoic burial prior to the emplacement of cretaceous plutons in the region

sensitivity of east asian monsoon climate to the uplift of the tibetan plateau abstract using the cola center for ocean land atmosphere studies general circulation model a series of numerical experiments were conducted to examine the impact of uplift of the tibetan plateau on the evolution of the monsoon climate in east asia an attempt was made to isolate the effect of the plateau uplift from the changes in other forcing mechanisms we examined the spatial and temporal variation patterns of a variety of climatic variables and indices including monsoon intensity sea level pressure surface and upper air winds temperature at different levels precipitation air humidity and soil moisture our results suggest that the evolution of the east asia monsoon may be more sensitive to the uplift of the tibetan plateau than that of the south asia monsoon moreover the effect of the plateau uplift on the east asia winter monsoon is more significant than that on the summer monsoon in the northern part of east asia north china the formation of the monsoon climate is marked mainly by the establishment of the northerly winds in winter or the winter monsoon system corresponding to the uplift of the plateau when the height reaches approximately 50 of its current elevation on the other hand the establishment of the monsoon climate in the southern part of east asia the yangtze river valley and the area south of it may be much earlier than that in the northern part

the development mechanism for tibetan plateau warm vortices abstract the low level cyclonic vortices which form over the tibetan plateau in the summer monsoon season are major rain producing systems and have the potential to trigger cyclogenesis on the lee side when they move off the plateau two cases of the plateau vortices which occurred in july 1979 are studied the characteristics of the vertical structure in their developing stage and the circulation condition favorable for the eastward movement in the mature stage are diagnosed and presented by use of fgge iiib datasets numerical simulations with real data were performed using the gfdl limited area mesoscale simulation model results suggest that the latent heating is an essential driving force for the development of the vortices studied here the analysis of a continuous cisk model with a basic state resembling that actually observed over the summer plateau shows that the predicted unstable mode has a preferred scale growth rate and vertical structure all of which are qualitatively comparable to observ

geothermal gradients hydrodynamics and hydrocarbon occurrences alberta canada using coal rank data and the demonstrated genetic link between the present hydrodynamic regime and geothermal gradient pattern it is possible to reconstruct the geothermal history of alberta over the past 60 m y palinspastic adjustment for tectonic compression caused by the major laramide thrusting shows that the predeformation isoreflectance lines increased logarithmically with depth in the late paleocene the geothermal gradient was about 23 c km 1 25 f 100 ft in the eastern alberta plains compared to about 30 c km 1 65 f 100 ft in the western alberta plains a regional trend opposite to the post laramide trends reconstruction of the early eocene surface indicates western uplands with geothermal gradients as low as 21 c km 1 15 f 00 ft and eastern lowlands with geothermal gradients of 27 c km 1 5 f 100 ft compared to the present situation this represents an enhanced topographic surface and a subdued geothermal gradient pattern the genetic relations of topography water table elevation hydrodynamic regime and geothermal gradient pattern in both the early eocene and the present conform to a model developed for any compacted sedimentary basin with subaerial relief in this model on a regional scale high topographic areas have high water table elevations with correspondingly high potentiometric surfaces these areas control the regional recharge of cold meteoric water and hence have low geothermal gradients areas of medium elevation exhibit regional lateral flow and intermediate geothermal gradients regional topographic lows correspond with low potentiometric surfaces and the regional discharge of warm formation waters from deep in the basin results in high geothermal gradients local topographic featur s cause perturbations in this picture study of both the regional pattern and fine detail of the early eocene and present topographic surfaces and geothermal gradient patterns shows the validity of the model the result of the second laramide orogenic pulse was therefore to reverse the geothermal gradient pattern resulting mainly from compaction flow and to impose a topographically controlled hydrodynamic regime with flow in the same direction but with a 9 c km 0 5 f 100 ft decreased geothermal gradient in western alberta and a 4 c km 0 2 f 100 ft increased geothermal gradient in eastern alberta as erosion proceeded during the tertiary the entire alberta basin warmed up until the present temperature regime was attained study of some major hydrocarbon occurrences shows a genetic link between the hydrocarbon occurrence and the present fluid regime which itself is controlled by the present topography for at least the significant upper cretaceous shallow gas reserves in southeastern alberta however their position may already have been determined as early as the beginning of the eocene by the topographic surface at that time therefore the extent to which the present topographic surface is responsible for hydrocarbon accumulation through gravity induced cross formational flow remains unknown because this process was operative as long ago as the early eocene what does not ap ear to be in doubt is the fact that gravity induced cross formational flow does control the hydrodynamic regime which in turn influences the geothermal gradient pattern and the accumulation of hydrocarbons

seasonality and interannual variability of the westerly jet in the tibetan plateau region abstract in this study 40 yr ecmwf re analysis era 40 data are used for the description of the seasonal cycle and the interannual variability of the westerly jet in the tibetan plateau region to complement results based on the analysis of monthly mean horizontal wind speeds an occurrence based jet climatology is constructed by identifying the locations of the jet axes at 6 hourly intervals throughout 1958 2001 thus a dataset describing the highly transient and localized features of jet variability is obtained during winter and summer the westerly jet is located respectively to the south and north of the tibetan plateau during the spring and autumn seasons there are jet transitions from south to north and vice versa the median dates for these transitions are 28 april and 12 october the spring transition is associated with large interannual variations while the fall transition occurs more reliably within a 3 week period the strength of the jet exhibits a peculiar seasonal cycle during northw

exploiting radiation damage control on apatite u th he dates in cratonic regions abstract apatites from four pairs of samples of precambrian basement from the western canadian shield were analyzed by u th he thermochronometry to test for the influence of radiation damage on apatite u th he dates in this cratonic region recent studies have demonstrated that the accumulation of radiation damage increases the apatite he retentivity so that apatites with a span of effective u concentrations eu that experienced the same thermal history may be characterized by a range of closure temperatures in this investigation each sample pair consisted of a mafic dike cross cutting felsic gneisses from a single outcrop or nearby outcrops that contained apatites with a span of eu the apatites yielded u th he dates from 846 to 123 ma and were positively correlated with eu within each sample pair these results can be explained using a model that tracks the evolution of he mobility in response to the accumulation of radiation damage when coupled with regional geological constraints the data appear to require partial to complete he loss due to burial and reheating in phanerozoic time new apatite fission track dates and length data were obtained for five of these samples the apatite fission track dates are proterozoic regardless of apatite eu thermal history simulations indicate that the apatite fission track data are compatible with the u th he results although the thermal histories are not identical in detail and the fission track results alone do not require phanerozoic heating together the data are consistent with burial of this region by 1 km of phanerozoic strata that were subsequently denuded thus pointing toward significant phanerozoic deposition in the north american cratonic interior hundreds of kilometers east of where previously documented the results suggest that exploiting radiation damage control on apatite u th he dates through investigation of surface sample apatites with a span of closure temperatures can impose tighter restrictions on thermal histories in low relief cratonic landscapes than was previously possible

burial cementation in the swan hills formation devonian rosevear field alberta canada abstract saddle dolomite anhydrite and coarsely crystalline late mosaic calcite cements in the devonian swan hills formation at the rosevear field in alberta canada are interpreted from petrographic and geochemical evidence as the products of burial diagenesis these inferred burial cements are commonly found as a partial to complete filling of moldic and vuggy porosity in massive replacement dolostones fluid inclusions th 125 159 c tm 18 to 22 c 87sr 86sr ratios 0 7101 0 7115 enrichment in ba and zn and light 18o values 6 to 11 2 pdb suggest that saddle dolomite precipitated from hot radiogenic brine with salinities six times greater than seawater ions for saddle dolomite precipitation may have been sourced from off reef shales the precambrian basement middle devonian halite mesozoic clastics and swan hills replacement dolomite undergoing pressure solution in the presence of a normal paleogeothermal gradient 30 c km saddle dolomite would have formed in the late cretaceous paleocene at depths of 3 5 km this time corresponds to the emplacement of gas at the rosevear field dolomite hosted anhydrite cement with nonradiogenic 87sr 86sr 0 7083 and low 34s compositions 15 to 23 cdt has been quantitatively modeled using a two component mixing equation to constrain fluid and ion sources the results indicate that ions for cementation were derived from fluids that passed through and dissolved middle devonian anhydrite this produced a sr rich brine with nonradiogenic 87sr86sr and low 34s these fluids mixed with radiogenic formation water already in the reservoir to precipitate anhydrite cement with the observed isotopic composition fluid inclusions th 90 to 170 c tm 6 to 17 c and elevated 87sr 86sr compositions 0 7105 0 7173 in coarsely crystalline late mosaic calcite support precipitation during the hydrological transformation of the western canada basin into a topographically controlled flow regime the reduced precipitation temperatures of some fluid inclusions in late mosaic calcite compared to saddle dolomite may be attributed to the decrease in western basin paleogeothermal gradients following the laramide orogeny the presence of calcitized anhydrite coarsely crystalline calcite with light 13c values 5 4 to 13 2 pdb s enriched pyrite and 8 h2s in reservoir gases provide evidence for thermochemical sulfate reduction during burial diagenesis at rosevear

subnormal geothermal gradients in the great valley forearc basin california during franciscan subduction a fission track study outboard parts of forearcs commonly have subnormal geothermal gradients because relatively cold lithosphere subducts beneath them the strata of the 10 to 15 km thick late jurassic tertiary great valley forearc basin accumulated in the forearc of the franciscan subduction zone of coastal california in this study paleogeothermal gradients in this basin were reconstructed to constrain the tectonic history of the convergent plate margin backstripping was used to reconstruct the burial histories of outcropping basin strata and apatite fission track analysis was used to determine the maximum burial temperatures experienced by 64 rock samples plots of maximum burial temperatures versus maximum burial depths indicate earliest tertiary time of deepest burial forearc basin geothermal gradients of about 9 c km backstripping shows that strata from the lower parts of two sections were deeply buried 6 5 km for the period 90 65 ma without experiencing high temperatures 105 c indicating that gradients were at least moderately subnormal throughout that period the data permit gradients no greater than about 15 c km at 90 ma decreasing to no greater than about 9 c km at 65 ma lower strata in another section were probably deeply buried without experiencing high temperatures from 130 or 120 ma until the latest cretaceous or early tertiary indicating that subnormal gradients probably existed throughout that period k ar ages of franciscan complex blueschists indicate subnormal gradients in the california forearc in the late jurassic and early cretaceous fission track data from the sierra nevada indicate subnormal gradients in the early and middle cenozoic and modern heat flow patterns indicate subnormal gradients in the late cenozoic together these indicators suggest that thermal gradients in the forearc were continuously subnormal from the initiation of franciscan subduction in the late jurassic until the termination of subduction in the late cenozoic gradients in the range that would permit blueschist facies metamorphism in the franciscan complex were thus long lived the broad range of k ar ages noted for franciscan blueschists need not reflect multiple discrete metamorphic events but are also consistent with a continuous extended period of high p t conditions blueschists need not have been uplifted soon after metamorphism to avoid overprinting by normal p t conditions but rather may have remained at depth for extended periods preliminary modeling indicates that an interruption in subduction of longer than 5 20 m y should cause detectable heating of forearc basin strata while a much shorter interruption should heat accretionary wedge rocks since there is no evidence of such heating it appears that convergence at the franciscan trench was essentially continuous if allochthonous terranes traveled northward parallel to the california margin during the late jurassic to late cenozoic period of franciscan subduction they apparently did so during oblique subduction not during extended interludes of pure transform motion

thermal and tectonic history of selected taranaki basin new zealand wells assessed by apatite fission track analysis apatite fission track analysis afta has been applied to samples from four hydrocarbon well sections to study the thermal and tectonic history and the hydrocarbon prospectivity of the southern part of the taranaki basin new zealand data from three of the wells 1 fresne 1 north tasman 1 surville show that the successions were exposed to higher temperatures in the past through deeper burial cooling from elevated paleotemperatures was effected by late miocene uplift and erosion of 3 0 or 0 3 km of section in 1 fresne or 2 0 or 0 5 km in 1 surville and 1 0 or 0 3 km in 1 north tasman in the fourth well 1 kupe formations are currently at their maximum temperatures since deposition afta provides unique constraints on the timing of hydrocarbon generation in relation to trap formation the proposed source rocks in 1 fresne passed through the oil formation window 100 150 degrees c and into the zone of gas production 150 220 degrees c during the middle miocene prior to the formation of potential trapping structures those in 1 north tasman passed into the oil formation zone about the same time and source rocks in 1 surville have probably never been heated enough to produce oil afta indicates considerable prospectivity remains in the region of 1 kupe where generation would have occurred after trap formation

large scale dynamics of the meiyu baiu rainband environmental forcing by the westerly jet abstract meiyu baiu is the major rainy season from central china to japan brought by a zonally elongated rainband from june to mid july large scale characteristics and environmental forcing of this important phenomenon are investigated based on a reanalysis dataset the meiyu baiu rainband is accompanied by a trough of sea level pressure horizontal shears and sharp moisture gradients near the surface a westerly jet tilted northward with height and large northeastward moisture transport from the south the analysis here reveals the westerly jet as an important culprit for meiyu baiu along the rainband mean ascending motion corresponds well with a band of warm horizontal temperature advection in the midtroposphere throughout summer this adiabatic induction of upward motion originates from the advection of warm air by the westerlies from the eastern flank of the tibetan plateau the ascending motion both induces convection and is enhanced by the resultant condensational heating the westerly jet anch

ocean atmosphere land feedbacks in an idealized monsoon summary an intermediate complexity atmospheric model coupled with a simple land surface model and a mixedlayer ocean model is used to investigate the processes involved in an idealized monsoon occumng on a single rectangular continent idealized divergences of ocean heat transports are specified as an annual average q flux in this simple coupled configuration the mechanisms that affect land ocean contrast and in turn the seasonal movement of the continental convergence zones are examined these include soil moisture feedbacks cooling of tropical oceans by ocean transport ventilation defined as the import into continental regions of low moist static energy air from ocean regions where heat storage opposes summer warming and the interactive rodwellhoskins mechanism in which rossby wave induced subsidence to the west of monsoon heating interacts with the convection zone the fixed ocean transports have a substantial impact on the continental convection if q flux is set to zero subtropical subsidence and ventilation tend to substantially limit the poleward movement of summer monsoon rainfall when land hydrology feedbacks are active the drying of subtropical continents disfavours continental convection even in the tropics when ocean transports are included tropical oceans are slightly disfavoured as regions for producing convection which by contrast favours continental convection the monsoon circulation then produces moisture transport from the ocean regions that allows substantial progression of convection into the subtropics over the eastern portion of the continent the western portion of the continent tends to have a dry region of characteristic shape this east west asymmetry is partly due to the interactive rodwell hoskins mechanism the ventilation is of at least equal importance in producing east west asymmetry and is the single most important process in limiting the poleward extent of the continental convection zone

the importance of sea level fluctuations in the formation of linear conglomerate bodies carrot creek member of cardium formation cretaceous western interior seaway alberta canada abstract the raven river member of the cardium formation turonian upper cretaceous in the carrot creek area of alberta contains two coarsening upward sequences of marine mudstones and sandstones the lower sequence coarsens from black mudstones into bioturbated fine grained sandstones and is capped by a gritty siderite horizon which probably indicates a pause in deposition the sandstones of the upper sequence contain hummocky cross stratification suggesting open marine deposition below fairweather wave base the two sequences are scoured to variable depths by a major erosion surface which has a relative relief of up to 20 m a structure map and three dimensional mesh diagrams of this surface suggest four topographic elements a relatively high terrace a bevel at which und rlying beds are truncated and a series of bumps and hollows these are interpreted to represent a remnant erosional topography which gradually fades away into the final topographic element the smooth basin plain the erosion surface is covered with conglomerate assigned to the carrot creek member of the cardium the conglomerate thickness reaches about 20 m against the bevel and in some of the hollows but usually thins to a veneer on the terrace on top of the bumps and on the distal basin floor the conglomerate bodies are relatively long and narrow and trend northwest southeast they are overlain by marine mudstones of the dismal rat member the elongate conglomerate bodies appear at first sight to be another case of western interior seaway offshore bars encased in marine mudstones many tens of kilometers seaward of time equivalent shoreline deposits however the erosion surface indicates that the conglomerates are not genetically part of the underlying coarsening upward sequence we propose a rapid relative lowering of sea level following deposition of the hummocky cross stratified sandstones the shoreline advanced many kilometers northeastward into the basin and during stillstand wave erosion cut a new shoreface profile the bevel during this lowstand incised rivers supplied gravel to the shoreface waves worked the gravel alongshore against the bevel and into the erosional hollows subsequent transgres ion spread some gravel southwestward back across the terrace storms transported gravel stringers into the transgressive muds accumulating in the hollows other erosional surfaces of this type exist in alberta at the cardium viking and bad heart horizons and in new mexico at the gallup tocito horizon suggesting that sea level changes and shoreface incision may be an alternative explanation for other long narrow offshore bars encased in marine shales

effects of mountain uplift on east asian summer climate investigated by a coupled atmosphere ocean gcm abstract to study the effects of progressive mountain uplift on east asian summer climate a series of coupled general circulation model cgcm experiments were performed eight different mountain heights were used 0 no mountain 20 40 60 80 100 control run 120 and 140 the land sea distribution is the same for all experiments and mountain heights are varied uniformly over the entire globe systematic changes in precipitation pattern and circulation fields as well as sea surface temperature sst appeared with progressive mountain uplift in summertime precipitation area moves inland on the asian continent with mountain uplift while the pacific subtropical anticyclone and associated trade winds become stronger the mountain uplift resulted in an sst increase over the western tropical pacific and the maritime continent and an sst decrease over the western indian ocean and the central subtropical pacific there is a drastic change in the east asian circulations with the threshold value

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

northern monashee mountains omineca crystalline belt british columbia timing of metamorphism anatexis and tectonic denudation the northern monashee mountains lie at the northern termination of a north south zone of eocene extension in the southern omineca crystalline belt of british columbia isotopic structural and petrogenetic studies in the northern monashee mountains document middle to late cretaceous regional metamorphism two episodes of crustal anatexis and a period of rapid cooling coincident with middle eocene extension partial melting of geochemically and isotopically similar pelitic sources produced peraluminous granites during and postdating regional metamorphism at 100 ma and 63 ma respectively rb sr muscovite whole rock isochrons from the younger granites give an age of 62 5 2 0 ma rb sr isochron and u pb mineral ages are similar indicating that the 63 ma granites were emplaced into a terrane that had cooled to 500 c or less by 63 ma hornblende muscovite and biotite k ar and apatite fission track mineral cooling ages from the northern monashee mountains are are 76 3 5 8 n 7 51 4 3 5 n 6 55 1 2 7 n 10 and 45 0 2 9 n 3 ma respectively mean age and standard deviation accelerated cooling beginning with the emplacement of 63 ma granites and ending at 45 ma occurred in response to ramping along a crustal scale thrust fault followed by offset on the middle eocene offset on the middle eocene north thompson normal fault

isomerization and aromatization of hydrocarbons and the paleothermometry and burial history of alberta foreland basin the hydrocarbon fractions extracted from 34 cretaceous shales from a cross section of the alberta basin have been analyzed using gas chromatography mass spectrometry particular attention has been paid to the extents to which three temperature dependent geochemical reactions have occurred isomerization of steranes at c 20 isomerization of hopanes at c 22 and aromatization of c ring monoaromatic steroid hydrocarbons estimates of the kinetic constants of these reactions have been published previously therefore constraints may be put on the maximum temperature experienced by the sediments and the time for which this temperature existed the subsidence history of the alberta basin is simulated using a lithospheric flexural model in which the lithosphere is downwarped by the loading of overthrusts in the adjacent cordilleran orogene when overthrusting ceases erosion of the overthrusted region lightens the load and the lithosphere rebounds causing uplift and erosion of the foreland basin major overthrusting and therefore deep burial occurred during the laramide orogeny of late cretaceous to mid tertiary time the extent of chemical reactions suggests that the present maturity of the cretaceous shales is almost entirely a reflection of burial and heating during the laramide orogeny in a manner that is consistent with the lithospheric flexural model for the basin the chemical reactions suggest that the paleogeothermal gradient increased systematically away from the foothills of the rocky mountains along the profile studied that a similar trend exists today suggests this situation has persisted at least since the early stages of the laramide orogeny this variation is best explained by advective heat transfer water entering the basin in the faulted and topographically higher foothills is heated at depth thereby depressing the geothermal gradient this hot water then migrates updip and away from the foothills to enhance the geothermal gradients in the edmonton area and beyond the route of the migrating hot water is similar to that taken by hydrocarbons from devonian and cretaceous source rocks in the deep basin updip to the oil and tar sand accumulations of alberta