paleolatitudes determined from paleomagnetic data from vertical cores most of the paleomagnetic data available from oceanic plates consist of measurements of inclination but not declination from azimuthally unoriented vertical cores similarly the basic paleomagnetic data to be analyzed from crustal blocks that have rotated by varying amounts about vertical axes are a set of paleoinclinations a new method is proposed for determining the paleocolatitude of a sampling site and the associated confidence limits paleomagnetic inclinations are first converted to paleocolatitudes and averaged to produce a mean colatitude after showing that this mean is biased we derive a paleocolatitude correction to remove the bias using a model for geomagnetic secular variation based on the latitude dependence of secular variation during the past 5 million years after testing the validity of the model by applying it to paleomagnetic data from quaternary lavas for which both inclination and declination are known we apply the method to inclination only paleomagnetic data from suiko seamount the most complete data set from a drilling site the method is then applied to paleomagnetic data from all deep sea drilling project sites for the pacific plate to obtain for each site an unbiased mean paleocolatitude and its confidence limits these paleocolatitudes and confidence limits are then used as input for a least squares analysis to obtain early and late cretaceous poles for the pacific plate and 95 confidence limits for these poles it is shown that the scatter of individual site paleocolatitudes about the best fit pole is consistent with the confidence limits at each site as determined by the new method of analysis

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

three different downstream fates of the boreal summer mjos on their passages over the maritime continent the boreal summer mjos exhibit three distinctive downstream evolutions on their passages over the maritime continent mc i smoothly transitioning from indian ocean io to western pacific type i ii rapidly decayed over the mc type ii and iii significantly intensified over the mc type iii during the life cycles of type i and iii mjos basin wide overturning circulations connect the convective dipoles between western and eastern north pacific for type ii mjo regional overturning circulations connect the convective dipoles between the io and western north pacific wnp for type i and iii mjos the associated convection over eastern io is able to generate strong kevin wave responses and significant positive sst anomalies over the mc and western pacific on the other hand for type ii mjo in the io a persistent convection lingers around the wnp it intensifies westerly monsoon flows thus preventing the generation of coherent positive sst anomalies ahead of the io mjo convection it also blocks the formation of a robust kelvin wave response over the mc and western pacific by delaying the northeastward migrations of the dry phase the convection of type i and iii mjos at eastern io is able to generate positive boundary layer moisture anomalies along with positive column integrated moisture tendencies over the mc and western pacific thus allowing them to propagate eastward smoothly on the other hand the type ii mjo convection in eastern io is associated with a very dry troposphere and negative column integrated moisture tendency over western pacific which result in the rapid decay of convection over the mc these results emphasize the important roles of robust kelvin wave responses and positive sst anomalies on the eastward propagation of boreal summer mjos over the mc through moistening the troposphere ahead of the convection

paleogene evolution of the kodiak islands alaska consequences of ridge trench interaction in a more southerly latitude the kodiak islands of alaska are principally composed of a late cretaceous and paleogene complex of accreted deep sea rocks an early paleocene magmatic event invaded the accretionary complex with mid ocean ridge basalt morb andesite and granodiorite geochemical evidence suggests both the andesite and granodiorite are mixtures of morb and sediment the volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter the granodioritic intrusions with k ar ages as old as 62 ma postdate emplacement of the early paleocene sedimentary and volcanic rocks interaction of the subduction complex with the kula farallon ridge most simply explains this early paleocene magmatic episode paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40 3 6 north latitude which is 25 3 9 south of the expected position of the kodiak islands relative to north america the magmatic arc presently northwest of the kodiak accretionary complex was active during the late cretaceous and early paleocene diminished after the ridge trench interaction and resurged from late eocene into miocene time the magmatic resurgence is coeval with the obductive offscraping of eocene to oligocene submarine fan deposits in the kodiak islands the petrology of these fan deposits indicates they are the most likely proximal equivalent for the zodiac fan thereby limiting its relative motion with respect to the kodiak islands possible models accounting for the northward motion of the kodiak accretionary complex include 1 coupling the accretionary complex and possibly related arc to the northward moving kula plate and closing an ocean basin north of the arc in paleogene time 2 emplacing the kodiak accretionary complex at the northward limit of the paleomagnetic data with subsequent northward motion accomplished by closure of a small back arc basin and or intracontinental shortening and 3 transcurrent faulting and northward motion of the kodiak accretionary complex without the presently adjacent arc

accretion of southern alaska abstract paleomagnetic data from southern alaska indicate that the wrangellia and peninsular terranes collided with central alaska probably by 65 ma ago and certainly no later than 55 ma ago the accretion of these terranes to the mainland was followed by the arrival of the ghost rocks volcanic assemblage at the southern margin of kodiak island poleward movement of these terranes can be explained by rapid motion of the kula oceanic plate mainly from 85 to 43 ma ago according to recent reconstructions derived from the hot spot reference frame after accretion much of southwestern alaska underwent a counterclockwise rotation of about 50 as indicated by paleomagnetic poles from volcanic rocks of late cretaceous and early tertiary age compression between north america and asia during opening of the north atlantic 68 44 ma ago may account for the rotation

overprint magnetizations in support of northward displacement of the chugach prince william terrane alaska widespread discrepancies between geologic and paleomagnetic estimates of northward displacement are ubiquitous in reconstructions of the north american cordillera in southern alaska this discrepancy persists into paleogene time paleomagnetic data indicate that the mesozoic arc complex of the southern alaska terrane was in place by late cretaceous early tertiary time while the outboard mesozoic and tertiary accretionary complex of the chugach prince william terrane still lay far to the south the apparent tertiary displacement of the chugach prince william terrane is difficult to reconcile with most apparent geologic constraints i studied the paleomagnetism of early tertiary mafic volcanic rocks from prince william sound alaska in an attempt to corroborate the meager paleomagnetic database i sampled at knight island and glacier island and found overprint magnetizations at knight island the paleomagnetic directions are too scattered for tectonic interpretation at glacier island i found three overprint magnetizations the type 1 magnetization has a normal direction and is concordant with the expected direction for north america the type 2n magnetization yields a characteristic direction which is too scattered for tectonic interpretation the type 2r magnetization is reversed and implies 17 10 of northward displacement with respect to north america assuming that the magnetization was acquired at 55 ma and the ophiolite was not subsequently tilted the type 2r magnetization agrees remarkably well with paleomagnetic results from the nearby resurrection peninsula in terms of inferred displacement paleotrend of the sheeted dike complex and reversed polarity of magnetization the type 1 magnetization was subsequently acquired after the chugach prince william terrane arrived in southern alaska

circulation anomalies associated with tropical convection during northern winter abstract lagged cross correlations between outgoing longwave radiation olr and national meteorological center global analyses are utilized to isolate the preferred upper level and surface circulation anomalies associated with tropical convection during northern winter three intraseasonal time scales are studied 30 70 14 30 and 6 14 days in the 30 70 day band the upper level circulation signals are zonally elongated with zonal wavenumbers 0 2 dominant higher frequency signals are dominated by zonal wavenumbers 5 and 6 in the 14 30 day band convection over the eastern hemisphere is associated with upper level anticyclones in the subtropics and appears to be linked in some cases to midlatitude wave trains the strongest signals are for convection over africa australia and the eastern indian ocean only weak signals are seen for convection over indonesia in these regions of upper level easterlies olr anomalies peak prior to the maximum anomalies in wind suggesting forcing of the circulation b

dynamical linkage of tropical and subtropical weather systems to the intraseasonal oscillations of the indian summer monsoon rainfall part i observations the indian summer monsoon rainfall ismr over the western ghats wg and the bay of bengal bob is marked by the intraseasonal oscillations isos with preferred 10 20 day and 30 50 day bands on the basis of pentad climate prediction center merged analysis precipitation and daily sea level pressure and winds at 850 hpa derived from european center for medium range weather forecast reanalysis we present the structure and evolution of the isos linked to the ismr variations over the wg and the bob and the associated anomalies of the atmospheric circulation using the approaches of wavelet analysis bandpass filtering and composite analysis this study reveals that the activities of both the intertropical convergence zone itcz and the western pacific subtropical high wpsh contribute strongly to the structure and propagation of the isos on intraseasonal time scales northward development and propagation of the itcz plays a critical role in the northward propagating isos but not in the westward propagating bob 10 20 day isos the latter isos may be linked instead to the activity of synoptic scale weather systems to the east over the western tropical pacific the enhanced itcz in the tropical indian ocean plays a strong role in the sudden strengthening of the wpsh during the transition from the break to active phase of the 30 50 day isos we find that the strong wpsh in the asian summer monsoon season with generally northward advance and eastward withdrawal promotes the formation of a northwest to southeast tilted anomalous rainfall belt over the east asian tropical summer monsoon region and the western tropical pacific in the 30 50 day low frequency band positive negative elongated rainfall anomalies with an unbroken northwest southeast tilt strong easterly westerly anomalies in the tropical pacific and northward advance and eastward movement of strong weak wpsh are favorable for maintaining the eastward propagation of the 30 50 day isos in the pacific daily high resolution sea surface temperature obtained from the national oceanic and atmospheric administration is used to explain the propagation features of the 10 20 day isos in the indian ocean

paleomagnetism of the late triassic hound island volcanics revisited the collision and accretion of the alexander terrane profoundly influenced the geologic history of alaska and western canada however the terrane s displacement history is only poorly constrained by sparse paleomagnetic studies we studied the paleomagnetism of the hound island volcanics in order to evaluate the location of the alexander terrane in late triassic time we collected 618 samples at 102 sites in and near the keku strait alaska from the late triassic hound island volcanics the permian pybus formation and 23 ma gabbroic intrusions we found three components of magnetization in the hound island volcanics the high temperature component component a resides in hematite and magnetite and was found only in highly oxidized lava flows in a geographically restricted area we think it is primary or acquired soon after eruption of the lavas principally because the directions pass a fold test the paleolatitude indicated by this component 19 2 10 3 is similar to those determined for various portions of wrangellia consistent with the geologic interpretation that the alexander terrane was with the wrangellia terrane in late triassic time we found two overprint directions in the hound island volcanics component b was acquired 23 m y ago due to intrusion of gabbroic dikes and sills this interpretation is indicated by the similarity of upper hemisphere directions in the hound island volcanics to those in the gabbro component c found in both the hound island volcanics and the permian pybus formation is oriented northeast and down fails a regional fold test and was acquired after regional deformation around 90 to 100 ma this overprint direction yields a paleolatitude similar to but slightly higher than slightly older rocks from the coast plutonic complex suggesting that the alexander terrane was displaced 17 in early late cretaceous time the occurrence of these two separate overprinting events provides a satisfying explanation of the earlier puzzling results from the hound island volcanics hillhouse and gromme 1980 finally great circle analysis of the paleomagnetic data from the pybus formation suggests the alexander terrane may have been in the northern hemisphere in permian time

a possible new mechanism for northward propagation of boreal summer intraseasonal oscillations based on trmm and merra reanalysis boreal summer intraseasonal oscillations bsisos manifest in the active and break spells and act as the primary building block of the indian summer monsoon although recent research has evolved a basic framework for understanding the scale selection and northward propagation of the bsiso the role of different hydrometeors in modulating these processes remains poorly explored in this study trmm 2a12 retrievals and modern era retrospective analysis for research and applications reanalysis data are examined to establish relationship between cloud hydrometeors and other atmospheric dynamical parameters with the northward propagation of the bsisos the study reveals that the cloud liquid water leads the deep convection during the northward propagation of bsisos in the lower troposphere while the cloud ice slightly lags the convection this distribution indicates the occurrence of a possible mechanism of the lower level moistening through the large scale moisture advection in lower atmosphere and boundary layer pbl convergence followed by triggering of the deep convection the analyses of moisture advection and the dynamical fields with respect to the convection center show that low level moistening is a manifestation of the barotropic vorticity and pbl convergence of moisture anomaly north of the convection center a new internal dynamical thermodynamical mechanism is unraveled to understand the reason behind the middle tropospheric heating maximum and its role on the northward propagation it is shown that the enhanced moisture perturbation in lower levels together with the heat transport by the sub grid scale eddies within the pbl induces lower level instability required to precondition the lower atmosphere for triggering the deep convection vigorous upward motion inside the deep convection uplifts the liquid hydrometeors to upper levels and the formation of precipitable ice leads to the heating maxima in the middle troposphere to check the robustness of the proposed hypothesis similar analysis is performed for the weak northward propagating bsiso cases

seasonal variations of tropical intraseasonal oscillations a 20 25 day oscillation in the western pacific abstract spectral analysis within a movable time window is used to investigate the frequency and intensity of tropical oscillations with intraseasonal time scales surface and rawinsonde time series from several locations in the western pacific and indian oceans are used evidence is provided that the madden julian oscillation mjo in the indian ocean region shows a seasonal variation in its preferred period from 50 days during northern hemisphere winter to about 35 days during summer though this evidence is weak and stretches the limits of our ability to define a precise period for the oscillation in the western tropical pacific during the september december season a pronounced spectral peak with a central frequency between 20 and 25 days is observed this spectral peak appears to reveal an oscillation that is distinct from the mjo but may also result from coupling between the large scale motion and latent heat release on much smaller scales a relationship between the oscillation and the occurrence

fossil wood in coal forming environments of the late paleocene early eocene chickaloon formation the early cenozoic chickaloon formation is the main coal bearing sequence in south central alaska coal and associated plant macrofossils are well exposed in the eska premier and jonesville coal groups in the wishbone hill district there is a striking variation in the degree and mode of preservation of fossil trees in a vertical sequence through these coal groups we examined the wood taxonomy mineralogy and geochemistry to elucidate potential cause s for these differences the wood anatomy indicates that the wood is all assignable to the cupressaceae taxodiaceae s str and assignable to the form genus taxodioxylon hartig emend gothan however we found no significant variation in the taxonomy of the wood between stratigraphic layers the wood generally becomes better preserved in the jonesville coal group wood from the stratigraphically lower premier coal group exhibits greater plastic deformation and contains less well preserved wood anatomical features the wood from the overlying jonesville coal group retains most of its original morphology but has suffered from brittle fracture the geochemistry and mineralogy of the wood follow a pattern that corresponds to the degree of preservation the less well preserved wood tends to have a higher concentration of iron carbonate minerals e g siderite and ankerite whereas the better preserved wood contains more calcium carbonate or silica all evidence points to rapid permineralization of the original wood although the least well preserved wood shows evidence of greater organic matter decomposition than the better preserved wood the wood taxonomy and mode of preservation of wood from the upper part of the chickaloon formation is similar to wood from coeval fossil forests that developed at higher polar paleolatitudes

application of paleomagnetism to accretionary tectonics and structural geology the use of paleomagnetism to determine translations and rotations of geologic terranes has contributed to a better understanding of deformation within accretionary complexes shear zones and rifts in this report to the i u g g we review the progress resulting from paleomagnetic studies during the last four years in the cordillera of north america the appalachian orogen and the circum pacific region

the cenozoic denali fault system and the cretaceous accretionary development of southern alaska the juxtaposition of disparate geologic terranes in southern alaska has been previously interpreted to be mainly the result of several hundred kilometers of right lateral offset along the denali fault system in cenozoic time recent geologic investigations in the healy quadrangle strongly suggest that cenozoic horizontal displacements of such magnitude along the denali fault system do not exist in the healy quadrangle isograds and metamorphic facies boundaries of an early late cretaceous metamorphic belt trend across the cenozoic mckinley strand of the denali system without significant horizontal offsets the present geologic makeup of most of southern alaska is primarily the result of the talkeetna superterrane consisting of the previously assembled peninsular terrane and wrangellia colliding with and subsequently being thrust upon the yukon tanana and nixon fork terranes of the ancient north american continent in about middle cretaceous time the leading edge of the talkeetna superterrane faces a wide complexly deformed zone that contains numerous northwestward thrust miniterranes tectonically intermixed with jurassic and cretaceous flysch the flysch is interpreted to have been deposited mostly in the narrowing and subsequently collapsed oceanic basin between the converging continental blocks the postcollisional denali fault system developed in cenozoic time across the already accreted continental margin in eastern alaska along an older cretaceous suture

development of convection along the spcz within a madden julian oscillation a subtropical rossby wave propagation mechanism is proposed to account for the poleward and eastward progression of intraseasonal convective anomalies along the south pacific convergence zone spcz that is observed in a significant proportion of madden julian oscillations mjos large scale convection associated with an mjo is assumed to be already established over the indonesian region the latent heating associated with this convection forces an equatorial rossby wave response with an upper tropospheric anticyclone centred over or slightly to the west of the convection large potential vorticity pv gradients associated with the subtropical jet and the tropopause lie just poleward of the anticyclone and large magnitude pv air is advected equatorwards on the eastern side of the anticyclone this high pv air or upper tropospheric trough is far enough off the equator that it has associated strong horizontal temperature gradients and it induces deep ascent on its eastern side at a latitude of about 15 30 if this deep ascent is over a region susceptible to deep convection such as the spcz then convection may be forced or triggered hence convection develops along the spcz as a forced response to convection over indonesia the response mechanism is essentially one of subtropical rossby wave propagation this hypothesis is based on a case study of a particularly strong mjo in early 1988 and is tested by idealized modelling studies the mechanism may also be relevant to the existence of the mean spcz as a forced response to mean indonesian convection

quasi periodic oscillations in a symmetric general circulation model abstract long lime integrations with a symmetric version of the clas climate model with hydrology have shown that the hadley circulation has well defined strong and weak episodes this oscillation of the hadley circulation seems to occur in two dominant range of periodicities one with periods between 10 and 15 days and another with periods between 20 and 40 days this quasi periodic behavior of the hadley circulation is seen only when the moist convective heating is determined by dynamics if the latent beating in the atmosphere is prescribed and kept artificially fixed this oscillation of the hadley circulation disappears thus this oscillation of the hadley circulation appears as a result of interactions between moist convective and dynamical processes a wave phenomenon is seen in the lower atmosphere that propagates toward the position of maximum radiative beating this wave perturbation has a length scale of about 15 20 degrees latitude in the north south direction this phenomenon has large ampli

early cretaceous paleolatitude of the yukon koyukuk province alaska we report results from a paleomagnetic study of the yukon koyukuk province a key region for reconstructing the cretaceous paleogeography of northern alaska and northeastern asia the province lies between the displaced continental fragment of arctic alaska and the accreted terranes of southern alaska although lower cretaceous volcanogenic rocks of the yukon koyukuk province preserve primary remanent magnetizations the primary component is masked by a pervasive overprint the over printing magnetization which has dual polarity was acquired after a late cretaceous orogeny left the region highly deformed by fitting planes to tilt corrected thermal demagnetization data and solving for the best intersection of the corresponding remagnetization circles we separated the primary component presumably a vestige of the original thermoremanent magnetization from the overprinting component of the natural remanence the primary magnetization corresponds to a mean paleopole of early cretaceous age at 60 2 n 159 e the mean paleolatitude is 69 n with the 95 confidence ellipse ranging from 60 to 75 n this analysis was successful because the tilt corrections of the sampled strata had sufficient variation to ensure a strong intersection of the remagnetization circles we infer that lower cretaceous rocks of the brooks range and the yukon koyukuk province were once separated by a wide ocean basin that was closed by subduction probably during the cretaceous the northern limb of the angayucham terrane which lies between the brooks range and the yukon koyukuk province may contain remnants of the now closed ocean basin

seasonality of the structure and propagation characteristics of the mjo the seasonality of the madden julian oscillation mjo is documented in observational data and a nonlinear shallow water model is used to help interpret some of the contrasts in mjo structure between the boreal winter season november march ndjfm and the asian summer monsoon period june september jjas at upper tropospheric levels the flanking rossby waves remain centered around 28 degrees n s year round but they tend to be stronger in the winter hemisphere where the climatological mean jet stream is stronger rendering the subtropical circulation more sensitive to forcing by a near equatorial heat source amplitudes of the mjo related deep convection and lower tropospheric zonal wind are stronger in the summer hemisphere where the column integrated water vapor is larger during ndjfm the equatorial asymmetry is subtle as in the annual mean moisture convergence into swallowtail shaped regions of enhanced deep convection is an integral part of the equatorial rossby wave signature and the eastward propagation is due to moistening of the air to the east of the enhanced convection by poleward moisture advection during the asian summer monsoon in jjas the convection assumes the form of northward propagating west northwest east southeast oriented rainbands embedded within cyclonic shear lines these features are maintained by frictional convergence of moisture and their northward propagation is mainly due to the presence of features in the climatological mean fields that is the west east moisture gradient over india and the arabian sea and the southwesterly low level monsoon flow over the northwest pacific

tectonic implications of paleomagnetic poles from lower tertiary volcanic rocks south central alaska we have determined the paleolatitude of lower tertiary volcanic rocks in southern alaska to measure possible poleward translation of the wrangellia and the peninsular terranes after 50 m y ago previous paleomagnetic studies have shown that in triassic and jurassic time these terranes were located near the equator and have moved at least 3000 km poleward relative to the north american craton our sample localities are in the northern talkeetna mountains in mildly deformed andesite and dacite flows 50 4 51 3 53 9 and 56 3 m y by k ar that overlap lower cretaceous flysch lower permian volcanic rocks of wrangellia and upper triassic pillow basalt of the susitna terrane results from 26 cooling units 23 of reversed polarity and 3 of normal polarity give a mean paleomagnetic pole at 69 5 n 179 6 e 95 12 2 stratigraphic sections from opposite limbs of a syncline yield directional paths that pass the fold test satisfying a necessary condition for primary origin of the magnetization the corresponding mean paleolatitude 76 n of the northern talkeetna mountains is 8 10 higher than the latitude predicted from the eocene reference pole for north america therefore northward drift of the talkeetna superterrane which is the amalgamation of the wrangellia and peninsular terranes during and after middle jurassic time was probably complete by 50 m y ago our results are consistent with paleomagnetic poles from uppermost cretaceous and paleocene volcanic sequences in denali national park the lake clark region northern bristol bay region and near mcgrath these poles generally lie south of the cratonic poles suggesting that the region between the kaltag bruin bay and castle mountain faults has rotated counterclockwise relative to north america since the early eocene

structural evolution of the early tertiary cantwell basin south central alaska the cantwell basin is a paleogene intermontane basin located in south central alaska the cantwell formation which fills the basin is as much as 4000 m thick and consists of a lower sedimentary sequence of fluvial and alluvial fan origin and an upper sequence of calc alkaline volcanic rocks the east trending cantwell basin developed as a southward thickening asymmetrical graben between the hines creek and denali faults substantial dip slip displacement and local dextral strike slip displacement on the hines creek fault during basin subsidence was followed by dip slip displacement in late cenozoic time strike slip movement along the denali fault to the south exerted primary control on basin subsidence and subsequent structural inversion during the paleocene kula plate motion was nearly perpendicular to the axis of the cantwell basin however kula plate motion was oblique to southeastern alaska and produced regional dextral slip on the denali fault system the cantwell basin appears to have developed as a pull apart basin in which northwest striking syndepositional normal faults linked the denali fault with the western part of the hines creek fault in early eocene time an increased rate of plate convergence resulted in substantial displacement on the denali fault concurrent counterclockwise rotation of southern alaska produced a regional constraining bend in the denali fault and resulted in strong compressional deformation of the cantwell basin

a preliminary neogene paleomagnetic data set from leyte and its relation to motion on the philippine fault abstract leyte island is bisected by the left lateral philippine fault paleomagnetic samples were collected from nineteen lava flows in leyte and nearby islands to the north the data collected from these sites were combined with previously reported results from northeastern mindanao the paleomagnetic data from neogene rocks within or very near the philippine fault zone on leyte mindanao biliran maripipi and genuruan islands fall into two populations seventeen late neogene sites fourteen normal polarity and three reversed polarity yield a mean direction d 358 9 i 20 1 95 6 6 k 30 1 and a paleomagnetic pole 88 9 n 12 5 e a95 4 8 k 56 1 eight early neogene sites three normal polarity and five reversed polarity give a mean direction d 23 2 i 13 9 95 9 3 k 36 2 and a paleomagnetic pole 66 5 n 220 5 e a95 7 1 k 62 0 the late neogene pole is indistinguishable from plio pleistocene poles from the philippines taiwan and vietnam and the late miocene pole of the central philippines suggesting there have been no significant rotations or translations of this region with respect to other southeast asian regions during the past 5 m y the early neogene paleomagnetic pole is statistically indistinguishable from the middle to early miocene pole of the central philippines the early neogene pole is statistically distinguishable from early miocene pole of marinduque island philippines as well as the late miocene pole of the central philippines and the plio pleistocene pole of the entire philippines this preliminary paleomagnetic data set suggests that leyte and adjacent islands to the north have been a portion of the same tectonic block as northeastern mindanao cebu and western panay since early neogene there are also no paleomagnetically detectable fault related rotations associated with the philippine fault given the resolution of this data set no consensus exists as to the amount of offset or the age of inception of the philippine fault the 110 km offset between ophiolitic basement in northeast leyte and that in southwest leyte suggests this amount of left lateral displacement has occurred along the philippine fault since the middle tertiary in contrast to data from continental regions no shear related rotations are found associated with the philippine fault this observation suggests that the hot immature transitional island arc continental crust of the philippine region deforms differently in response to shear than well developed continental crust

major dextral transcurrent displacements along the northern rocky mountain trench and related lineaments in north central british columbia the northern rocky mountain trench and a number of other prominent lineaments along and east of the eastern margin of the intermontane belt mark faults along which dextral transcurrent movements have been dominant offsets of shelf to off shelf facies boundaries in lower paleozoic rocks indicate a cumulative displacement of at least 750 km and probably 900 km within the system of faults related to those in the northern rocky mountain and the tintina trenches farther west another system of faults appears to offset plutons and stratigraphic assemblages along the eastern margin of the intermontane belt by as much as 300 km these faults including the kutcho and the pinchi connect in part with the teslin suture zone in yukon territory and probably with the fraser river straight creek fault zone in southern british columbia although dextral transcurrent faulting may have taken place between the middle jurassic and early cenozoic the most convincing evidence points to middle cretaceous and particularly to early cenozoic eocene displacements the eocene movements were temporally related to plutonism volcanism lamprophyre dike emplacement high heat flow sedimentation in grabens and rapid uplift of northwesterly trending elongate ranges climactic episodes of granite emplacement particularly in and near the northern omineca crystalline belt at 100 m y 70 m y and 50 m y ago may have been facilitated by changes from dominantly compressional to dominantly transcurrent and related tensional strain

northward translation of baja british columbia along the late cretaceous to paleocene margin of western north america paleomagnetic data suggest that a large part of british columbia and southern alaska was at the latitude of baja california mexico in early late cretaceous time this allochthonous block baja bc includes the insular talkeetna in alaska and intermontane composite terranes the miniterranes between them and possibly part of the omineca metamorphic belt assuming that baja bc was adjacent to north america by middle cretaceous an analysis using plate kinematics of the pacific basin produces a model of northward movement of baja bc which is compatible with the known geology of the reconstructed margin of western north america baja bc moved north 2400 km as part of the kuia plate along a transform margin with north america from 85 to 66 ma this time interval is marked by the cessation of igneous activity in the sierra nevada development of wrench faults and basins along coastal california and initiation of laramide style tectonics to the east within baja bc diminished igneous activity to the west was coeval with possible wrench tectonic basins along its eastern margin by the end of the cretaceous baja bc was positioned from oregon to northern british columbia between 66 and 56 ma baja bc became attached to north america in a dextral transpressive stage during which the kula north america plate boundary expanded to encompass the whole block with a series of northwest trending strike slip faults a fold and thrust belt in the east and large scale uplifts and the formation of an incipient volcanic arc on the west southern alaska was the site of convergence during the whole of the period of northward translation of baja bc a late cretaceous subduction zone in alaska evolved into a major compressional belt as the basin and miniterranes on the northern margin of baja bc collided with interior alaska the collision culminated in the paleocene with formation of the mckinley granites and coeval dextral slip on the denali fault system

paleomagnetism of eocene volcanic rocks talkeetna mountains alaska previous paleomagnetic studies of eocene rocks deposited in the talkeetna mountains on the northern edge of the combined peninsular wrangellia and alexander terranes the southern alaska superterrane sas yield a paleolatitude of 76 n while late cretaceous rocks on the southern edge of the sas record a 32 n paleolatitude at face value these drastically different paleolatitudes imply that wrangellia moved 44 to the north in only 20 m y requiring a northward component of velocity of about 24 cm yr alternatively the discrepancy might be explained by postulating an unrecognized tectonic boundary separating the two localities allowing different emplacement ages we have tested the unrecognized tectonic boundary hypothesis allowing post eocene emplacement of the sas by sampling eocene volcanic rocks deposited near the southern edge of the sas in the talkeetna mountains our data set comprises measurements from 97 oriented cores collected from 26 lava flows and two tuffs distributed over a distance of 50 km a primary remanence is indicated by positive fold tests and penecontemporaneous intrusion tests age control is provided by nine new k ar whole rock age determinations ranging from 38 8 to 53 6 ma the mean paleomagnetic pole calculated for this study is not significantly different from the pole derived from the eocene flows to the north and gives a paleolatitude of 78 thus ruling out the hypothesis of an unrecognized suture accommodating major post eocene displacement this result has prompted a reevaluation of the data which suggest rapid movement including the precision of the age control the adequacy of averaging of secular variation and the possibility of sedimentary inclination error the bulk of the evidence suggests northward displacement from lower latitudes however the error limits are such that the dramatic velocities previously postulated are not required

kinematics of basin development during the transition from terrane accretion to strike slip tectonics late cretaceous early tertiary cantwell formation south central alaska the cantwell basin was formed during late cretaceous time in the suture zone between the wrangellia composite terrane and the former continental margin of southern alaska the late cretaceous 80 70 ma lower cantwell formation represents the initial fill of this basin and includes 4000 m of sedimentary rock between maastrichtian and late paleocene time 70 60 ma rocks of the lower cantwell formation were deformed by nearly eastwest trending folds and north vergent thrust faults this deformation can be linked to the northward accretion and suturing of the wrangellia composite terrane to southern alaska during late paleocene to early eocene time 60 55 5 ma at least 2750 m of volcanic rocks of the upper cantwell formation were deposited above the folded lower cantwell formation new 40ar 39ar ages for the upper cantwell formation range from 59 8 0 2 to 55 5 0 2 ma and reveal that the unconformity between the lower and upper cantwell formations represents a 10 20 million year hiatus following volcanism the cantwell formation was crosscut by northeast trending folds northwest trending normal faults north trending left lateral slip faults northeast trending reverse faults and east trending right lateral slip faults these structures are consistent with northwest southeast compression in a zone of right lateral simple shear along a fault with the same trend east northeast as that of the present mckinley strand of the denali fault system cantwell basin kinematics are compatible with an escape tectonics model for south central alaska whereby the cantwell basin was formed folded and partially uplifted during northward terrane accretion and suturing and was deformed again during the westward transfer of terranes along right lateral strike slip fault systems

northward displacement and accretion of wrangellia new paleomagnetic evidence from alaska wrangellia is a vast terrane that accreted along the pacific margin of north america from oregon to central alaska previous paleomagnetic studies of the triassic volcanic rocks of wrangellia in south central alaska and british columbia have given paleolatitudes of 10 17 which are anomalously low in comparison to results from similar aged rocks of nuclear north america the discrepancy in paleolatitude implies substantial northward drift of the terrane relative to the craton we have extended paleomagnetic sampling to the northern boundary of the terrane in the mount hayes and healy quadrangles of the central alaska range this collection of 46 triassic lava flows yields a mean paleolatitude of 13 9 95 3 8 the polarity of the data and hence the hemisphere of origin are not resolved with certainty in contrast triassic paleomagnetic poles from the stable part of north america predict a paleolatitude of 42 1 n 95 4 6 for the region the northernmost fragment of wrangellia probably reached mainland alaska in the middle cretaceous when upper jurassic and lower cretaceous flysch within the intervening basin underwent severe deformation tertiary transcurrent faulting has modified the positions of wrangellian fragments in alaska but such displacements are probably minor as indicated by paleomagnetic data from early tertiary volcanic rocks that overlap the terrane

intraseasonal periodicities in indian rainfall abstract spectral analysis of a 70 year 1901 70 record of daily precipitation from 3700 stations in the country of india is carried out to search for periodicities on subseasonal time scales during the summer monsoon two statistically significant spectral peaks are found a 40 50 day spectral peak corresponding to the madden julian oscillation is found over most of the portion of india south of 23 n the phase of the oscillation is such that the precipitation maximum appears first over the relatively dry southeastern portion of the peninsula ten to 12 days later the precipitation peaks simultaneously all along the coast west of the western ghats and along a line running across india between 20 and 25 n the precipitation maximum then spreads slowly northward and loses significance cross spectral analysis shows strong coherence between the precipitation patterns and wind oscillations the zonal wind oscillations at 850 and 200 mb am about 180 degrees out of phase equatorward of about 20 n but in pha

paleoenvironment and paleoecology of a late paleocene high latitude terrestrial succession arkose ridge formation at box canyon southern talkeetna mountains alaska abstract paleogene sedimentary rocks of the arkose ridge formation talkeetna mountains alaska preserve a record of a fluvial lacustrine depositional environment and its forested ecosystem in an active basin among the convergent margin tectonic processes that shaped southern alaska an 800 m measured succession at box canyon indicates braid plain deposition with predominantly gravelly deposits low in the exposure to sandy and muddy facies associations below an overlying lava flow sequence u pb geochronology on zircons from a tuff and a sandstone within the measured section as well as an ar ar date from the overlying lava constrain the age of the sedimentary succession to between 59 ma and 48 ma fossil plant remains occur throughout the arkose ridge formation as poorly preserved coalified woody debris and fragmentary leaf impressions at box canyon however a thin lacustrine depositional lens of rhythmically laminated mudrocks yielded fish fossils and a well preserved floral assemblage including foliage and reproductive organs representing conifers sphenopsids monocots and dicots leaf physiognomic methods to estimate paleoclimate were applied to the dicot leaf collection and indicate warm temperate paleotemperatures 11 15 4 c mat and elevated paleoprecipitation 120 cm yr map estimates as compared to modern conditions results that are parallel with previously published estimates from the partly coeval chickaloon formation deposited in more distal depositional environments in the same basin the low abundance of leaf herbivory in the box canyon dicot assemblage 9 of leaves damaged is also similar to the results from assemblages in the meander plain depositional systems of the chickaloon this new suite of data informs models of the tectonostratigraphic evolution of southern alaska and the developing understanding of terrestrial paleoecology and paleoclimate at high latitudes during the late paleocene early eocene greenhouse climate phase

coupled model simulations of boreal summer intraseasonal 30 50 day variability part 1 systematic errors and caution on use of metrics boreal summer intraseasonal 30 50 day variability bsisv over the asian monsoon region is more complex than its boreal winter counterpart the madden julian oscillation mjo since it also exhibits northward and northwestward propagating convective components near india and over the west pacific here we analyze the bsisv in the cmip3 and two cmip2 coupled ocean atmosphere models though most models exhibit eastward propagation of convective anomalies over the indian ocean difficulty remains in simulating the life cycle of the bsisv as few represent its eastward extension into the western central pacific as such few models produce statistically significant anomalies that comprise the northwest to southeast tilted convection which results from the forced rossby waves that are excited by the near equatorial convective anomalies our results indicate that it is a necessary but not sufficient condition that the locations the time mean monsoon heat sources and the easterly wind shear be simulated correctly in order for the life cycle of the bsisv to be represented realistically extreme caution is needed when using metrics such as the pattern correlation for assessing the fidelity of model performance as models with the most physically realistic bsisv do not necessarily exhibit the highest pattern correlations with observations furthermore diagnostic latitude time plots to evaluate the northward propagation of convection from the equator to india and the bay of bengal also need to be used with caution here incorrectly representing extratropical tropical interactions can give rise to apparent northward propagation when none exists in association with the eastward propagating equatorial convection despite these cautions the use of multiple cross checking diagnostics enables the fidelity of the simulation of the bsisv to be meaningfully assessed

eastward propagating mjo during boreal summer and indian monsoon droughts improved understanding of underlying mechanism responsible for indian summer monsoon ism droughts is important due to their profound socio economic impact over the region while some droughts are associated with external forcing such as the el nino and southern oscillation enso many ism droughts are not related to any known external forcing here we unravel a fundamental dynamic process responsible for droughts arising not only from external forcing but also those associated with internal dynamics we show that most ism droughts are associated with at least one very long break vlb breaks with duration of more than 10 days and that the processes responsible for vlbs may also be the mechanism responsible for ism droughts our analysis also reveals that all extended monsoon breaks whether co occurred with el nino or not are associated with an eastward propagating madden julian oscillation mjo in the equatorial indian ocean and western pacific extending to the dateline and westward propagating rossby waves between 10 and 25 n the divergent rossby wave associated with the dry phase of equatorial convection propagates westward towards indian land couple with the northward propagating dry phase and leads to the sustenance of breaks thus the propensity of eastward propagating mjo during boreal summer is largely the cause of monsoon droughts while short breaks are not accompanied by westerly wind events wwe over equatorial western pacific favorable for initiating air sea interaction all vlbs are accompanied by sustained wwe the wwes associated with all vlb during 1975 2005 initiate air sea interaction on intraseasonal time scale extend the warm pool eastward allowing the convectively coupled mjo to propagate further eastward and thereby sustaining the divergent circulation over india and the monsoon break the ocean atmosphere coupling on interannual time scale such as el nino can also produce vlb but not necessary

cloud regime evolution in the indian monsoon intraseasonal oscillation connection to large scale dynamical conditions and the atmospheric water budget we examine the intraseasonal oscillation iso of the indian summer monsoon to establish the connections of cloud regimes to large scale dynamical states defined by dynamical convergence and moisture advection over the indian subcontinent the developing phase toward iso peaks rainfall maximum is associated with positive anomalies of moisture advection leading in 4 6 days to positive anomalies of dynamical convergence triggering abrupt transitions from shallow cumulus to deep convections in 1 2 days the decaying phase toward iso troughs rainfall minima is associated with negative anomalies of moisture advection and decreasing dynamical convergence accompanying opposite transitions in cloud regimes due to northward propagation of anomalies processes over the indian ocean are similar but lead those over the subcontinent by 10 days during the transitions cirrus clouds always accompany but lag deep convective clouds by 10 days over the equatorial indian ocean cirrus clouds are modulated by equatorial waves

paleomagnetism and geochronology of 23 ma gabbroic intrusions in the keku strait alaska and implications for the alexander terrane samples of tertiary gabbro from 24 sites in the keku strait alaska help constrain the displacement history of the alexander terrane step heating experiments on a plagioclase separate from these previously undated intrusions indicate a discordant 40ar 39ar age of 23 1 1 7 ma the characteristic magnetization resides in magnetite is easily isolated by thermal and alternating field demagnetization and has both normal and reversed polarities the mean paleomagnetic pole with no structural correction is latitude 87 1 n longitude 141 6 e a95 10 1 with n 20 sites this pole indicates insignificant tectonic displacement 0 5 8 2 southward and rotation 0 6 15 2 counterclockwise we therefore conclude that any northward displacement or vertical axis rotation of the alexander terrane and or tilting in the vicinity of the keku strait must have occurred before 23 ma

structures and mechanisms of the northward propagating boreal summer intraseasonal oscillation abstract the spatial and temporal structures of the northward propagating boreal summer intraseasonal oscillation bsiso are revealed based on the analysis of both the echam4 model simulation and the ncep ncar reanalysis the bsiso structure and evolution characteristics simulated by the model bear many similarities to those derived from the ncep ncar reanalysis the most notable features are the remarkable meridional asymmetries relative to the bsiso convection in the vorticity and specific humidity fields a positive vorticity perturbation with an equivalent barotropic structure appears a few latitude degrees north of the convection center the maximum specific humidity also shows a clear northward shift in the lower troposphere two internal atmospheric dynamics mechanisms are proposed to understand the cause of the northward propagation of the bsiso the first is the vertical shear mechanism the key process associated with this mechanism is the generation of barotropic vorticity due to the couplin

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

paleomagnetism of the paleocene ghost rocks formation prince william terrane alaska the mean paleomagnetic inclination of paleocene volcanics from two regions on kodiak island in the ghost rocks formation suggests that the prince william terrane originated at mid latitudes about 25 south of its expected alaskan latitude in paleocene time the remanent magnetization of these rocks passes both the fold and reversal tests and is well constrained in age the mean declinations of the two regions however differ by approximately 120 suggesting they have rotated with respect to each other perhaps during emplacement we suggest that despite the lack of evidence for a major tertiary suture zone between the prince william terrane and central alaska the prince william and perhaps adjacent terranes may have lain substantially south of their present position in the early tertiary

emplacement of the resurrection peninsula ophiolite in the southern alaska forearc during a ridge trench encounter the 57 1 ma resurrection peninsula ophiolite of southern alaska s chugach terrane formed in a near trench environment as the kula farallon ridge was being subducted beneath north america the magmatic sequence includes pillow lavas sheeted dikes gabbros trondhjemites and a poorly exposed ultramafic section the lavas show mid ocean ridge basalt and arc like geochemical signatures interpreted to reflect compositionally diverse melts derived from near fractional melting of a variably depleted mantle source mixed with variable amounts of assimilated continentally derived flysch a sedimentary sequence overlying the ophiolite here named the humpy cove formation of the orca group preserves a continuous 3 6 plusmn 1 4 ma record of turbidite sediments that were deposited on the ophiolite as it was transported to north america and emplaced in the chugach accretionary prism a transition from thinly bedded turbidites at the base of the section to thickly bedded turbidites is interpreted as a distal to proximal facies change recording the migration of the ophiolite toward the continent chemical trends vertically through the sedimentary sequence show an increasing biogenic component diluting terrigenous matter 950 m above ophiolitic basalt signaling a change to more favorable biologic conditions or increased preservation of biogenic matter with proximity to the continent hydrothermal metals are not resolvable in sediments interbedded with pillow lavas or in sediments above the ophiolite suggesting that they were diluted by turbidite sedimentation the top of the section is truncated by the fox island shear zone a 1 km thick greenschist facies west over east thrust related to the emplacement of the ophiolite into the accretionary wedge the fox island shear zone is intruded by a 53 4 0 9 ma granite showing that the ophiolite formed was transported to the north american continent overthrust by a major accretionary prism related thrust and intruded by granite all within 3 6 1 4 ma using these estimates for the timing of formation and emplacement of the ophiolite with palinspastic reconstructions and plate motion vector triangles we suggest that the resurrection peninsula ophiolite was transported up to 500 km 461 79 km relative to north america from the place of its formation at the kula farallon ridge prior to its emplacement into the north american margin since the best estimates of the amount of translation of the chugach terrane come from paleomagnetism of the resurrection peninsula ophiolite current estimates of margin parallel strike slip need to be reduced considerably

the mckinley sequence of granitic rocks a key element in the accretionary history of southern alaska the mckinley sequence of granitic rocks consists of several discrete plutons in the central alaska range most of these plutons crop out south of the denali fault system dfs in the talkeetna quadrangle plutons of the mckinley sequence largely intrude deformed upper meszoic flysch between the dfs and the northern edges of wrangellia and the peninsular terrane which jointly make up the talkeetna superterrane the average k ar age of biotite from nine granites of the mckinley sequence is 57 3 ma rb sr data for whole rock samples indicate that the mckinley sequence cannot be older than 60 ma a selected suite of 20 samples of granite and granodiorite range in sio2 from 65 9 to 77 6 all 20 samples are corundum normative and 18 are moderately peraluminous initial 87sr 86sr ratios range from 0 7054 to 0 7085 the 18o values range from 11 2 to 14 6 these high and variable sr isotopic ratios peraluminous nature rare earth element patterns and high 18o values suggest that granitic rocks of the mckinley sequence crystallized from hybrid magmas produced by assimilation of sedimentary rocks by a mantle derived melt mesozoic flysch is the likely source of the crustal component of the hybrid magmas geologic evidence suggests that the talkeetna superterrane collided with stable alaska after early cretaceous time the flysch basin lying south of stable alaska was closed by northward movement of the talkeetna superterrane maximum age for basin closure and terrane accretion is middle cretaceous cenomanian paleomagnetic evidence indicates that all terranes north of the dfs have been part of stable alaska since the paleocene and that northward movement of wrangellia was completed by 50 ma granitic rocks of the mckinley sequence may be products of terrane accretion the granitic rocks crystallized from hybrid magmas produced during terrane collision and deformation of the flysch basin isotopic ages of the mckinley sequence establish the time of final accretion of the talkeetna superterrane as paleocene

paleolatitudes versus time for southern alaska paleomagnetic determinations of the inclination of the ancient geomagnetic field for localities in the alaska peninsula wrangellia chugach and kuskokwim tectonostratigraphic terranes of alaska show systematic northward motion from late cretaceous time until the present prior to this the ambiguity of polarity of the ancient geomagnetic field allow several interpretations however the preferred interpretation involves southerly motion of the terranes from triassic to early jurrassic time and steady northward motion from then up to the present the latitudinal rate is about 6 cm yr

tectonic implications of out of sequence faults in an accretionary prism prince william sound alaska the chugach and prince william terranes constitute a mesozoic through tertiary accretionary complex bordering the gulf of alaska faults of the contact fault system juxtapose the two terranes across the previously mapped trace of the contact fault in western prince william sound we studied three belts of alternately higher and lower deformation intensity and metamorphism out of sequence reverse faults separate these belts until recently researchers assumed that the prince william terrane was accreted to the chugach terrane along the contact fault however our work supports an emerging view that the chugach and prince william terranes represent older and younger parts of a continuously evolved accretionary prism best considered a single terrane we found that we cannot distinguish the chugach from the prince william terrane on the basis of lithology deformation or metamorphism therefore we cannot precisely identify the local strand of the contact fault system furthermore the major faults in the study area are relatively late stage features related not to initial accretion but rather to internal deformation of the prism west northwest shortening characterizes the deformation along the contact fault system in western prince william sound whereas dextral slip faulting characterizes the deformation along the contact fault system in eastern prince william sound we ascribe this difference to development of the alaska orocline coeval with changes in plate motions during eocene time which resulted in convergence in western prince william sound remaining relatively orthogonal while convergence in eastern prince william sound became increasingly oblique

the 30 50 day variation of convective activity over the western pacific ocean with emphasis on the northwestern region abstract coherent 30 50 day oscillations between regions north and south of 20 n were observed using the latitude time y t diagram of a convective index ic along 140 e over the entire 1979 summer may september the oscillation in the northern region exhibits a relatively regular north south movement of deep convective clouds while the oscillation in the southern region shows enhancement or suppression fluctuations of broad and intensive deep convective clouds with a period of 30 50 days the southward northward movement of the midlatitude oscillation coincides with the suppression enhancement of the tropical deep convective clouds the midlatitude deep convective clouds are usually maintained by the divergent circulation and are associated with fronts the empirical orthogonal function eof analysis of velocity potential at 200 mb shows that the north south 30 50 day oscillation of deep convective clouds over the northwestern pacific is a response of the regional weather system to the eastwar

frictional moisture convergence in a composite life cycle of the madden julian oscillation abstract a composite life cycle of the madden julian oscillation mjo is constructed using an index based on the first two eofs of the bandpass filtered 20 80 days 850 mb zonal wind averaged from 5 n to 5 s every 2 5 around the equator precipitation 1000 mb convergence 850 mb wind and 200 mb wind are composited for the period 1979 95 water vapor integrated from the surface to 300 mb is composited for the period 1988 92 frictional moisture convergence at the equator is shown to play an important role in the life cycle of the madden julian oscillation mjo regions of boundary layer convergence foster growth of positive water vapor anomalies to the east of convection this convergence coincides with 850 mb easterly wind anomalies as is consistent with kelvin wave dynamics drying of the atmosphere occurs rapidly after the passage of convection with the onset of 850 mb westerly perturbations possible mechanisms for this drying include boundary layer divergence and subsidence or horizontal advect

evolution of the queen charlotte basin further paleomagnetic evidence of tertiary extension and tilting abstract the queen charlotte islands form the northwestern margin of the queen charlotte basin the basin which was formed by extension contains numerous mid tertiary lavas plutons and dykes referred to as the masset igneous complex and eocene to present marine and non marine sedimentary rocks throughout its history the basin has been bounded on the west by a north northwest oriented transform plate boundary the queen charlotte fault initially motion along this fault was transtensional phase 1 then more purely transform phase 2 and finally transpressive phase 3 most of the masset igneous complex appears to have been formed under transtension phase 1 middle eocene through early miocene previous paleomagnetic studies of the complex 129 sites mainly from the southern queen charlotte islands and new results herein 102 sites mainly from the northern islands illustrate magnetizations with inclinations generally steeper than those expected from coeval rocks of continental north america indicating north south extension segmentation and tilting of fault bound slivers along the western margin of the basin we argue that this north south extension occurred in phase 2 during the middle and or late miocene long after the main east west extension of phase 1 results from the northwest corner of the queen charlotte islands although commonly anomalous are not oversteepened and may delineate a structural domain separate from the rest of the archipelago as a by product this study provides two reference paleopoles for north america one for the late eocene early oligocene from ramsay island lavas 78 1 n 119 9 e a 95 7 0 and one of lesser reliability for the early miocene from the lavas of dinan bay 83 3 n 137 8 e a 95 9 8 a second by product is that the magnetic polarities and radiometric ages are consistent with the cande and kent global geomagnetic polarity time scale

the boreal summer intraseasonal oscillation relationship between northward and eastward movement of convection the summertime intraseasonal oscillation iso is an important component of the south asian monsoon lagged regressions of intraseasonally filtered 25 80 days outgoing longwave radiation olr reveal that centers of convection move both northward and eastward from the central equatorial indian ocean subsequent to the initiation of an iso eastward movement of convection is also seen at indian subcontinent latitudes 10 8 208n based on the regression results the summertime iso convection signal appears as a band tilting northwestward with latitude and stretching from the equator to about 208n viewed along any meridian convection appears to propagate northward while equatorial convection propagates to the east to examine the robustness of the connection between eastward and northward movement individual isos are categorized and composited relative to the strength of the large scale eastward component of convection in the central equatorial indian ocean it is found that the majority of isos that exhibit northward movement onto the indian subcontinent 42 out of 54 isos or 78 also exhibit eastward movement into the western pacific ocean it is also found that when convection in the central indian ocean is not followed within 10 20 days by convection in the western pacific ocean 12 out of 54 isos or 22 the independent northward movement of convection in the indian ocean region is somewhat stunted the link between the eastward and northward movement of convection is consistent with an interpretation of the summertime iso in terms of propagating equatorial modes the northward moving portion of convection is forced by surface frictional convergence into the low pressure center of the rossby cell that is excited by equatorial iso convection a similar convergence pattern is seen for the northern winter iso but it does not generate poleward movement due to relatively cool ssts underlying the surface convergence

dynamics of breaks in the indian summer monsoon abstract in this paper the authors present results of diagnostic analysis of observations and complementary experiments with a simple numerical model that enable them to synthesize the morphology and dynamics of breaks in the indian summer monsoon ism almost one week ahead of the onset of a break spell over india a monotonically decreasing trend in convective activity is found to occur over the bay of bengal in response to a steady eastward spreading of dry convectively stable anomalies from the equatorial indian ocean a major intensification of the convectively stable anomalies over the bay of bengal is seen about 2 3 days prior to commencement of a monsoon break both observations and modeling experiments reveal that rapid northwest propagating rossby waves are triggered in response to such a large strengthening of the convectively stable anomalies it is shown that an abrupt movement of anomalous rossby waves from the bay of bengal into northwest and central india marks the initiation of a break

quasi biweekly oscillations of the south asian monsoon and its co evolution in the upper and lower troposphere the upper tropospheric quasi biweekly oscillation uqbw of the south asian monsoon is studied using the potential vorticity field on the 370 k isentrope the uqbw is shown to be a common occurrence in the upper troposphere during the monsoon and its typical evolution is described we suggest that the uqbw is a phenomenon of both the middle and tropical latitudes owing its existence to the presence of the planetary scale upper tropospheric monsoon anticyclone the uqbw is first identified as rossby waves originating in the northern flank of the monsoon anticyclone these rossby waves break when reaching the pacific ocean and their associated cyclonic pv anomalies move southward to the east of asia and then westward across the indian ocean and africa advected by the monsoon anticyclone a strong correlation or co evolution between the uqbw and quasi biweekly oscillations in the lower troposphere qbw is also found in particular analysis of vertically integrated horizontal moisture transport 850 hpa geopotential and outgoing long wave radiation show that the uqbw is usually observed at the same time as and co evolves with the lower tropospheric qbw over south asia we discuss the nature of the uqbw and its possible physical link with the qbw

intraseasonal variability in south america during the cold season intraseasonal is variability in south america is analyzed during the cold season using 10 90 day bandpass filtered olr anomalies folr is variability explains a large percentage of variance with maximum values over paraguay northeastern argentina and southern brazil the leading pattern of folr as isolated from an eof analysis cold season is pattern csis is characterized by a monopole centered over southeastern south america sesa with a northwest southeast orientation csis induces a large modulation on daily precipitation anomalies especially on both wet spells and daily precipitation extremes which are favored during positive wet csis phases large scale olr anomalies over the tropical indian and west pacific oceans associated with csis exhibit eastward propagation along tropical latitudes in addition circulation anomalies in the southern hemisphere reveal the presence of an anticyclonic anomaly over antarctica with opposite sign anomalies in middle latitudes 10 days before csis is maximum as well as evidence of rossby wave like patterns positive precipitation anomalies in sesa are favored during wet csis phases by the intensification of a cyclonic anomaly located further south which is discernible over the southeastern pacific for at least 14 days before csis peaks the cyclonic anomaly evolution is accompanied by the intensification of an upstream anticyclonic anomaly which remains quasi stationary near the antarctica peninsula before the csis peak we speculate that the stationary behavior of the anticyclonic center is favored by a hemispheric circulation anomaly pattern resembling that associated with a negative southern annular mode phase and a wavenumber 3 4 pattern at middle latitudes

three dimensional convection planforms with internal heat generation thermal convection planforms in an infinite prandtl number isoviscous fluid layer with basal and internal heating are determined using three dimensional finite difference calculations with basal heating only at rayleigh number ra sub t 1 5 times 10 sup 5 the planform consists of a weakly time dependent spoke pattern with connected networks of equally buoyant up and downwellings with volumetric heat sources the planform is strongly time variable it consists of negatively buoyant flow concentrated in thermal trenches discrete arcuate sheets and spots cylindrical columns separated by diffuse nonbuoyant upwellings rapid planform changes occur primarily by trench propagation as observed experimentally by weinstein and olson this issue the analogy between thermal trenches in internally heated convection and convergent plate boundaries on earth suggests that the global pattern of subduction may evolve by propagation of wadati benioff zones along the strike of the slab

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

mechanisms of monsoon low frequency variability surface hydrological effects abstract observations indicate that monsoon systems are characterized by orderly large scale and low frequency variations with a time scale of two weeks and sometimes longer regions of ascending motion are observed to form to the north of the equator and propagate slowly northward across southeast asia the propagation appears to be associated with the active break sequence of the summer monsoon which acts as a modulator on the activity of the synoptic scale disturbances a zonally symmetric non linear two layer model containing an interactive ocean and a continent poleward of 18 n is used to investigate the mechanisms which produce the observed low frequency variability only when a full hydrology cycle is considered does the model product variations which resemble the observed structures mechanisms are traced to include the interaction of the components of the total heating function the sensible heat input in the boundary layer although considerably smaller than the other heating components de

the 30 50 day mode at 850 mb during monex abstract the analyzed wind field at 850 mb during the summer monsoon experiment monex is subjected to a time series analysis to confirm the existence of a peak in the time range of 30 50 days having established that this study presents a mapping of the motion field for this time scale in this short paper we illustrate the steady meridional propagation of a train of troughs and ridges that seem to form near the equator and dissipate near the himalayas the meridional scale of this mode is around 300 km and its meridional speed of propagation is 0 75 latitude per day the amplitude of the wind for this mode is around 3 6 m s 1 the salient contributions here are the mapping and the demonstration of a very regular behavior of this mode its existence is here noted from a period well before the onset of monsoon i e from early may to late july three major storms during monex were noted to form within the trough line of this system and the period of major cessation of rains over the indian subconti

character distribution and tectonic significance of accretionary terranes in the central alaska range the central part of the alaska range near mount mckinley is composed of nine separate tectonostratigraphic terranes that were accreted in southern alaska during late mesozoic time these terranes now form long linear fault bounded belts that are subparallel to the denali fault on the north but oblique to the fault on the south the postaccretion right lateral offset along the denali fault system is about 200 km from north to south the major terranes are 1 yukon tanana terrane metasedimentary and metavolcanic rocks mostly undated but including rocks of known late paleozoic age polymetamorphosed with terminal events in late mesozoic 2 pingston terrane isoclinally folded upper triassic deep water silty limestone quartzite and carbonaceous slate folded with upper paleozoic phyllite chert tuff and minor limestone 3 mckinley terrane upper paleozoic flysch chert and minor limestone intruded by large gabbro sills and dikes and overlain by thick piles of triassic porphyritic pillow lava the top of the section is thick sequence of upper mesozoic conglomerate flysch chert and phyllite 4 dillinger terrane very thick sequence of strongly folded lower paleozoic micaceous sandstone turbidites graptolitic shale and deep water limestone locally overlain unconformably by jurassic fossiliferous sandstone or triassic pillow basalt 5 windy terrane heterogeneous assemblage of serpentinite basalt tuff and chert ophiolite with paleozoic and mesozoic flysch and blocks of mid paleozoic fossiliferous limestone 6 mystic terrane predominantly upper paleozoic flysch and conglomerate but also includes lower paleozoic graptolitic shale pillow basalt and shallow water limestone and upper paleozoic fossiliferous limestone sandstone chert and undated pillow basalt 7 chulitna terrane upper devonian ophiolite overlain by upper paleozoic chert volcanic conglomerate limestone and flysch capped by lower triassic limestone and upper triassic red beds basalt and interbedded basalt and limestone later mesozoic rocks are sandstone chert and argillite 8 westfork terrane jurassic chert sandstone conglomerate and triassic and jurassic crystal tuff 9 broad pass terrane upper paleozoic chert tuff and argillite with blocks of devonian and older limestone locally associated with serpentinite these diverse terranes of mixed oceanic and continental affinities are now juxtaposed to form a complex sequence of folded and faulted rootless nappes major suture zones between them are occupied by intensely deformed upper mesozoic flysch all of the terranes differ markedly from wrangellia the southermost coherent accreted terrane in alaska paleomagnetic measurements from triassic rocks prove that wrangellia originated near the equator probably in the southern heimsphere paleolatitudes for terranes in the central alaska range are not yet determined but other lines of evidence biogeographic and lithologic suggest large scale northern transport for some terranes

denali fault system of southern alaska an interior strike slip structure responding to dextral and sinistral shear coupling the denali fault system dfs extends for 1200 km from southeast to south central alaska the dfs has been generally regarded as a right lateral strike slip fault along which post late mesozoic offsets of up to 400 km have been suggested the offset history of the dfs is relatively unconstrained particularly at its western end for this study we calculated relative motion vectors at discrete points along the length of the dfs based on the well understood kinematic interaction between the north american pacific and kula plates and the following assumptions 1 the arcuate geometry of the dfs has existed essentially unchanged since the late cretaceous 2 the yukon tanana terrane and other terranes north of the dfs were fixed in situ prior to the accretion of the southern alaskan terranes and 3 tangential and normal relative motion vector components calculated for points along the dfs using the plate model of kelley 1993 describe the plate kinematics of the dfs since the late cretaceous the consequent kinematic model for the dfs predicts that left lateral stresses have acted upon the western end of the dfs for much of its history and conflicting senses of shear exist between the eastern and western ends of the system the offset history of the western end of the denali fault system should be significantly different than the history of the central and eastern sections consequently individual crustal blocks in southeast and southwest alaska may have undergone respectively clockwise and counterclockwise rotations the sense of rotation predicted by our model is in agreement with rotations determined by paleomagnetic studies and provides an alternative model to the alaskan orocline hypotheses

limits to northward drift of the paleocene cantwell formation central alaska volcanic rocks of the paleocene cantwell formation in central alaska apparently originated at a paleolatitude of 83 n 95 9 7 as indicated by paleomagnetic results when compared with the paleocene pole for the north american craton the 95 confidence limits of the results suggest that terranes north of the denali fault have moved no more than 550 km northward relative to the north american craton since paleocene time

paleomagnetism of the resurrection peninsula alaska implications for the tectonics of southern alaska and the kula farallon ridge the rocks of the resurrection peninsula compose an ophiolite 57 1 ma within the vast accretionary prism of the chugach prince william terrane paleomagnetic data from pillow basalt and sheeted dikes of the ophiolite yield a mean paleolatitude of 54 7 which implies 13 9 of poleward displacement the characteristic component of the remanence resides in a ti poor titanomagnetite with a blocking temperature close td 580 c a positive fold test and the petrology of the magnetic minerals lead us to conclude that the characteristic remanent magnetization chrm in the sheeted dikes originated as a primary thermoremanent magnetization trm we hypothesize that the chrm of the pillow basalt originated as a chemical remanent magnetization crm acquired soon after formation of the rocks during hydrothermal metamorphism structural data indicate polyphase deformation with folding about vertical and horizontal axes the paleomagnetic data pass a fold test only when we incorporate this interpretation in our structural correction geologic relationships lead us to interpret the resurrection peninsula ophiolite as a fragment of the extinct kula farallon ridge that accreted to the chugach prince william terrane soon after formation the paleomagnetic paleolatitude indicates that the ridge intersected the north american continental margin in the vicinity of northern washington in late paleocene time the paleostrike of the sheeted dikes n26 e 12 shows that the ridge trended nne according to current plate tectonic models if the chugach prince william terrane moved north with the full coastwise displacement of the kula plate the resurrection peninsula ophiolite would have arrived at its present position at 45 ma this age is perhaps slightly later than that of the terranes that lay immediately inboard peninsular and wrangellia terranes indicating some relative displacement between those terranes and the chugach prince william terrane such displacement in turn agrees with studies which imply a coast plutonicmetamorphic complex provenance for the chugach prince william terrane

the south to north progression of rainfall anomalies across india during the summer monsoon season the low frequency spatio temporal intraseasonal evolution of monsoon rainfall over india is studied by considering the pentad rainfall averages taken over 2 5 wide and 5 0 long blocks lying across the central longitudinal and latitudinal transacts the time latitude cross sections show south to north progressions of rainfall anomalies with a recurrence period of about 40 days the progressions show considerable inter annual and intra seasonal variation in frequency amplitude and rate of progression the extended empirical orthogonal function analysis shows that the first two most important functions correspond to this northward progression of rain anomalies recurring after an interval of about 40 days the rate of progression of anomalies is about 0 5 lat day the time longitude cross sections show the movement of rainfall anomalies towards both directions east and the west with slight preference towards the east the importance of these signals in rainfall forecasting is foreseen

propagating and standing components of the intraseasonal oscillation in tropical convection abstract two questions related to the intraseasonal variability of tropical convection and circulation remain controversial 1 to what degree is the convective component of the madden julian oscillation mjo a standing oscillation 2 is the eastward propagating circulation anomaly of the mjo coherent with a standing oscillation in convection in an attempt to settle these issues the authors undertake a series of statistical analyses of gridded outgoing longwave radiation and winds to quantify the magnitudes of the propagating and standing components of convection and their coherence with the propagating component of the circulation they demonstrate that no dominant standing oscillation in convection can be identified instead intraseasonal variability of convection is dominated by an eastward propagating mode which the authors interpret as the convective signal of the mjo this propagating component accounts for almost all of the convective variance that is coherent with the eastward propagating di

intraseasonal behavior of clouds temperature and motion in the tropics abstract the spectral character of tropical convection is investigated in an 11 yr record of outgoing longwave radiation from the advanced very high resolution radiometer to identify interaction with the tropical circulation along the equator in the eastern hemisphere the space time spectrum of convection possesses a broad peak at wave numbers 1 3 and eastward periods of 35 95 days significantly broader than the dynamical signal of the madden julian oscillation mjo this quasi discrete convective signal is associated with a large scale anomaly that propagates across and modulates time mean or climatological convection over the equatorial indian ocean and western pacific outside that region the convective signal is small even though under amplified conditions coherence can be found east of the date line and in the subtropics having a zonal scale of approximately wavenumber 2 anomalous convection propagates eastward at some 5 m s 1 and suppresses as well as reinforces climatological convection

paleomagnetic data from alaska reliability interpretation and terrane trajectories virtually the entire body of paleomagnetic data collected from southern alaska depicts a clear decrease in paleolatitude with increasing age strongly suggesting that southern alaska represents a displaced terrane in this paper paleomagnetic studies from southern alaska have been classified with respect to a quality index that is based on four criteria these criteria are the presence of both polarities of magnetic remanence stepwise thermal or alternating field demagnetization of specimens principal component analysis of demagnetization data and a successful fold test of the 51 studies compiled only four from southern alaska and one from western canada are demonstrated to satisfy all criteria and fall therefore in the category of group 3 highly reliable two studies from southern alaska satisfy three of the four criteria lacking both polarities of characteristic remanence and are judged to be of group 2 reliable two of these paleomagnetic studies constrain the accretion time of the southern alaska terrane to the relatively stationary region of central alaska north of the denali fault four paleomagnetic studies from the southern alaska terrane show a distinct paleolatitude anomaly when compared with their expected paleolatitudes from the north american apparent polar wander path using the model of engebretson et al 1984 a series of models are presented to best fit these highly reliable and reliable paleomagnetic studies the model preferred in this article assumes an accretion time with north america of 50 ma and documents pre 50 ma displacement of the southern alaska terrane on the kula plate if the ghost rocks paleomagnetic magnetizations plumley et al 1983 are assumed to be of earliest tertiary age this model fits all of the low paleolatitudes observed in southern alaska models incorporating coastwise translation of the southern alaska terrane along the western boundary of the north america plate and a 50 ma suturing age of this terrane to north america do not satisfy the paleomagnetic constraints four of the reliable studies can be modeled assuming strike slip motion of the southern alaska terrane along the western boundary of the north america plate if a 40 ma suturing age is assumed in this model however the paleomagnetic data must be presumed to represent the highest permissible paleolatitude and the ghost rocks formation paleolatitudes are problematically lower than is possible to model with coastwise translation

a model for the boreal summer intraseasonal oscillation abstract the tropical intraseasonal oscillation iso exhibits pronounced seasonality the boreal summer iso is more complex than its winter counterpart due to the coexistence of equatorial eastward off equatorial westward and northward propagating low frequency modes and their interactions based on observational evidence and results obtained from numerical experiments a mechanism is proposed for the boreal summer iso in which the northern hemisphere summer monsoon nhsm circulation and moist static energy distribution play essential roles with a climatological july mean basic state the life cycle of model low frequency waves consists of four processes an equatorial eastward propagation of a coupled kelvin rossby wave packet an emanation of moist rossby waves in the western pacific a westward propagation and amplification of the rossby waves in south asian monsoon regions and a reinitiation of the equatorial disturbances over the central indian ocean the life cycle spans about one month and p

origin of low frequency intraseasonal oscillations in the tropical atmosphere iii monsoon dynamics abstract this is the third in a series of papers to study the origin of intraseasonal oscillations in this paper we address the issue of the interaction of the monsoon large scale circulation and intraseasonal oscillations we show that as a result of the interaction of the large scale monsoon flow with the near equatorial intraseasonal oscillation unstable baroclinic disturbances are generated over the monsoon region these disturbances have spatial scales of approximately 3000 4000 km and periods of 5 6 days with the vertical wave axis tilting eastward with height the rapid development of these cyclonic disturbances along 15 20 n and the concomitant weakening of the equatorial disturbances are accompanied by the rapid northward shift of the rising branch of the local hadley circulation they may also be identified with the observed sudden jump of the mei yu rainband over east asia and the inverse relationship between the monsoon itcz and the equatorial itcz over india and east asia from a linear s