interannual variability of summer biochemical enhancement in relation to mesoscale eddies at the shelf break in the vicinity of the pribilof islands bering sea abstract this study examined variability of the eddy field and primary production over the bering sea s eastern shelf break area during summer using a satellite multi sensor data set the eddy field and on shelf nutrient flux below 50 m water depth were also investigated using a numerical model the satellite altimeter data analysis and numerical experiments indicated that the eddy field was induced by perturbations of the bering slope current system and or instabilities in the bering sea basin via flow through the aleutian passes the distribution of high primary production roughly coincided with the high variability area of the eddy field numerical experiments showed a 70 increase in net on shelf flux and 54 increase in net on shelf transport by the generation propagation of eddies along the shelf break at pribilof canyon towed ctd fluorometer measurements during the summer of 2003 revealed a stable water column and high fluorescence 10 g l 1 in the area between the 200 and 1000 m isobaths at a time when there was a low level of on shelf flux regardless of the eddy field conversely the eddy induced on shelf flux and stable water column can enhance primary production from spring to summer at the shelf break moreover the eddy induced on shelf nutrient flux probably contributes to the primary productivity at the western shelf of the pribilof islands where the bering sea ecosystem is very dynamic this eddy related shelf break process can be applied to not only the bering sea shelf break but also all shelf break areas in which propagating eddies are found

interannual westward propagating baroclinic long wave activity on line p in the eastern midlatitude north pacific abstract for the period 1959 81 quasi zonal hydrographic sections have been made between the southern coast of vancouver island 49 n 126 w and ocean station p 50 n 145 w approximately every two months along this section called line p hydrographic std stations were repeated at nearly the same locations approximately 2 of longitude apart and at closer intervals near the coast as such 13 stations in all were made nearly every two months over the 23 year period thus the line p dataset has particular value in verifying the existence of interannual baroclinic long waves near 50 n in previous studies white kang and magaard and white and saur had found evidence of annual and interannual baroclinic long wave activity in the eastern midlatitude north pacific over the range 20 40 n but earlier attempts could not discover these westward traveling waves along line p in this study both spectral analysis and complex empirical orthogonal function analysis are used to do just that concentrating u

observational evidence for predictions of tropical cyclone propagation relative to environmental steering abstract theories of vortex motion due to the variations of the coriolis parameter and environmental vorticity are compared to observations of tropical cyclone motion relative to computed steering flows using previously published composite data the composite results are manipulated to obtain a vector quantity for the difference between tropical cyclone motion and steering and this vector difference is termed propagation the properties of these propagation vectors within various composite data stratifications provide tentative support for nonlinear numerical results such as i the general magnitude and direction of the induced propagation ii the dependence of such propagation on the outer wind strength of the tropical cyclone and iii the dependence of such propagation on the direction of the environmental vorticity gradient ambiguities in the composite data are discussed with respect to linear and nonlinear theories of tropical cyclone propagation and several new composite data stratific

the application of icp ms methods to tephrochronological problems pearce nicholas westgate j a perkins w t preece s j 2004 the application of icp ms methods to tephrochronological problems applied gechemistry 19 3 pp 289 322 rae2008

impact of intraseasonal oscillations on the activity of tropical cyclones in summer over the south china sea part i local tropical cyclones abstractthe south china sea scs is affected by two intraseasonal components in summer the madden julian oscillation mjo and the quasi biweekly oscillation qbwo in the present study the impacts of the mjo and qbwo on tropical cyclones tcs locally formed in the scs local tcs in summer are investigated the results show that both the mjo and qbwo can affect the genesis frequency location and motion of the local tcs more tcs form in the convectively active phases of the mjo and qbwo in the northern scs with the northward propagation of the mjo and qbwo convective signals the major tc genesis location also shifts northward since the western pacific subtropical high shifts eastward westward when convection associated with the mjo and qbwo in the northern scs is enhanced suppressed the steering flow in the major tc genesis region is favorable for the eastward westward movement of tcs results from the composite analysis of the steering flow indicate that both the mjo and qbwo play an im

mean sea surface and variability of the gulf of mexico using geosat altimetry data geosat exact repeat mission erm altimetric measurements of the sea surface height in the gulf of mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along geosat ground tracks in the gulf for the time period from november 8 1986 to november 25 1988 the alongtrack mean sea surface is determined using a regional crossover adjustment procedure in which the tilt and bias of mean arcs are estimated using a least squares technique to minimize the height differences at crossovers points a mean surface generated using the geosat erm alongtrack mean is calculated and contrasted with a previously derived mean surface determined using geos 3 and seasat crossover differences this provides a first look at the variability in the mean between the time periods of 1987 1988 and 1975 1978 in addition the alongtrack mesoscale variability time series has been produced from the geosat erm data set by using a robust orbit error removal algorithm to determine the variability of the sea surface height with respect to the alongtrack mean a surface generated using the rms of this alongtrack time series shows good qualitative and quantitative agreement with previous in situ observations in the region this study demonstrates the potential of satellite altimetry for oceanographic studies of the gulf of mexico

the shedding of an anticyclonic eddy from the alaskan stream as observed by the geosat altimeter the evolution of a meander into an anticyclonic eddy which separates from the alaskan stream in the vicinity of the central aleutian islands is observed in two years of sea surface height anomalies computed from geosat exact repeat mission altimeter data the trajectory of the center of mass is estimated using a modified perpendicular bisector method eddy separation is inferred to occur where the trajectory makes a distinct turn to the southwest the observed region of meander growth and eddy separation agrees with that predicted by theory the evolution of meander eddy height and radius is estimated from least squares fits of the data to an axially symmetric gaussian profile the heights and radii are used to calculate the strength vorticity and energetics of the meander eddy ekman dynamics are assumed to govern the eddy decay spin down times based on vorticity are much longer than those based on energetics this is consistent with an eddy s ability to maintain its integrity as it decays representative height diameter and velocity scales of the eddy are characteristic of rings spawned by other current systems assuming a ring structure for this eddy the estimated ring volume represents a 21 transport anomaly referenced to the mean annual transport into the bering sea

pattern classification of typhoon tracks using the fuzzyc means clustering method abstract a fuzzy c means clustering method fcm is applied to cluster tropical cyclone tc tracks fcm is suitable for the data where cluster boundaries are ambiguous such as a group of tc tracks this study introduces the feasibility of a straightforward metric to incorporate the entire shapes of all tracks into the fcm that is the interpolation of all tracks into equal number of segments four validity measures e g partition coefficient partition index separation index and dunn index are used objectively to determine the optimum number of clusters this results in seven clusters from 855 tcs over the western north pacific wnp from june through october during 1965 2006 the seven clusters are characterized by 1 tcs striking the korean peninsula and japan with north oriented tracks 2 tcs affecting japan with long trajectories 3 tcs hitting taiwan and eastern china with west oriented tracks 4 tcs passing the east of japan with early recurving tracks 5 tcs traveling the easternmost re

tropical indian ocean influence on northwest pacific tropical cyclones in summer following strong el nino abstract in the summer following a strong el nino tropical cyclone tc number decreases over the northwest nw pacific despite little change in local sea surface temperature the authors analysis suggests el nino induced tropical indian ocean tio warming as the cause the tio warming forces a warm tropospheric kelvin wave that propagates into the western pacific inducing surface divergence off the equator the tropospheric kelvin wave suppresses convection and induces an anomalous anticyclone over the nw pacific both anomalies unfavorable for tcs the westerly vertical shear associated with the warm kelvin wave reduces the magnitude of vertical shear in the south china sea and strengthens it in the nw pacific an east west variation that causes tc activity to increase and decrease in respective regions these results help improve seasonal tc prediction

indian ocean capacitor effect on indo western pacific climate during the summer following el nino significant climate anomalies persist through the summer june august after el nino dissipates in spring over the equatorial pacific they include the tropical indian ocean tio sea surface temperature sst warming increased tropical tropospheric temperature an anomalous anticyclone over the subtropical northwest pacific and increased mei yu baiu rainfall over east asia the cause of these lingering el nino effects during summer is investigated using observations and an atmospheric general circulation model gcm the results herein indicate that the tio warming acts like a capacitor anchoring atmospheric anomalies over the indo western pacific oceans it causes tropospheric temperature to increase by a moist adiabatic adjustment in deep convection emanating a baroclinic kelvin wave into the pacific in the northwest pacific this equatorial kelvin wave induces northeasterly surface wind anomalies and the resultant divergence in the subtropics triggers suppressed convection and the anomalous anticyclone the gcm results support this kelvin wave induced ekman divergence mechanism in response to a prescribed sst increase over the tio the model simulates the kelvin wave with low pressure on the equator as well as suppressed convection and the anomalous anticyclone over the subtropical northwest pacific an additional experiment further indicates that the north indian ocean warming is most important for the kelvin wave and northwest pacific anticyclone a result corroborated by observations these results have important implications for the predictability of indo western pacific summer climate the spatial distribution and magnitude of the tio warming rather than simply whether there is an el nino in the preceding winter affect summer climate anomalies over the indo western pacific and east asia

out of phase relationship between tropical cyclones generated locally in the south china sea and non locally from the northwest pacific ocean tropical cyclones tcs in the south china sea scs are either generated locally or formed non locally in the northwest pacific ocean nwp and entered into the scs here it is found that local tcs vary out of phase with non local tcs in summer that is if fewer more tcs enter into the scs from the nwp more fewer tcs are generated over the scs further analyses show that variability of the western pacific subtropical high wpsh is responsible for the out of phase relationship as the wpsh shifts eastward westward fewer more non local tcs formed in the nwp can enter into the scs because tcs are recurved northward moved westward due to the eastward westward movement of the wpsh positive negative low level vorticity anomalies weak strong vertical wind shear between the upper and lower troposphere and anomalous upward downward motion in the middle troposphere are induced in the northern scs the changes in the relative vorticity vertical wind shear and vertical velocity are favorable unfavorable for the local tc genesis in the scs these variations of non local and local tcs result in an out of phase relationship between tcs formed locally in the scs and non locally in the nwp

modulation of north pacific tropical cyclone activity by three phases of enso abstract tropical pacific ocean warming has been separated into two modes based on the spatial distribution of the maximum sea surface temperature sst anomaly an east pacific warming epw and a central pacific warming cpw when combined with east pacific cooling epc these three regimes are shown to have different impacts on tropical cyclone tc activity over the north pacific by differential modulation of both local thermodynamic factors and large scale circulation patterns in epw years the genesis and the track density of tcs tend to be enhanced over the southeastern part and suppressed in the northwestern part of the western pacific by strong westerly wind shear the extension of the monsoon trough and the weak wind shear over the central pacific increases the likelihood of tc activity to the east of the climatological mean tc genesis location in cpw years the tc activity is shifted to the west and is extended through the northwestern part of the western pacific the westward shifting of c

effects of mesoscale eddies on the flow of the alaskan stream 1 using a high resolution pan arctic ice ocean model forced with realistic atmospheric data we examine the mean transport and temporal and spatial variability within the alaskan stream model results are analyzed and compared with observations including satellite altimetry and ctd measurements the mean net transport of the alaskan stream is found to be between 34 and 44 sv intensifying downstream mesoscale eddies are found to periodically move along the path of the alaskan stream and alter the mean position of the typically westward flowing current however the strength of the current is not reduced as an anticyclonic eddy passes a point along the path instead there appears to be an offshore or southward shift in the current velocity core stationary measurement instruments may not be able to detect this shift in position over the slope if their southernmost location does not coincide with the current shift due to an eddy this may result in recording of a weakened or sometimes reversed flow finally we examine and demonstrate that modeled eddies within the alaskan stream have dominant effect on northward transport and variability through the eastern and central aleutian island passes

identification of a kulshan caldera correlative tephra in the palouse loess of washington state northwest usa abstract the kulshan caldera formed at 1 15 ma on the present day site of mt baker washington state northwest usa and erupted a compositionally zoned dacite rhyolite magma and a correlative eruptive the lake tapps tephra this tephra has previously been described but only from the puget lowland of nw washington here an occurrence of a kulshan caldera correlative tephra is described from the quaternary palouse loess at the washtucna site wa 3 site wa 3 is located in east central washington 340 km southeast of the kulshan caldera and 300 km east southeast of the lake tapps occurrence in the puget lowland major and trace element chemistry and location of the deposit at washtucna within reversed polarity sediments indicates that it is not correlative with the mesa falls rockland bishop ash lava creek b or huckleberry ridge tephras instead the washtucna deposit is related to the lake tapps tephra by fractional crystallisation but is chemically distinct a consequence of its eruption from a compositionally zoned magma chamber the correlation of the washtucna occurrence to the kulshan caldera forming eruption indicates that it had an eruptive volume exceeding 100 km3 and that its tephra could provide a valuable early pleistocene chronostratigraphic marker in the pacific northwest

potential impact of the pacific decadal oscillation and sea surface temperature in the tropical indian ocean western pacific on the variability of typhoon landfall on the china coast the landfall activity of typhoons tys along the coast of china during july august september jas shows significant interdecadal variation during 1965 2010 we identify three sub periods of ty landfall activity in jas along the china coast in this period with more ty landfall during 1965 1978 period i and 1998 2010 period iii and less during 1982 1995 period ii we find that the interdecadal variation might be related to the combined effects of pacific decadal oscillation pdo phase changes and sea surface temperature sst variation in the tropical indian ocean and western pacific io wp during the negative pdo phase in periods i and iii a cyclonic anomaly is located in the western north pacific wnp inducing easterly flow in its northern part which favors ty landfall along the eastern china coast warm sst anomalies over the tropical io wp during period iii induce an anomalous anticyclonic circulation in the wnp through both the gill pattern response to the warm sst in the tropical io and the anomalous meridional circulation induced by the warm sst in the tropical wnp as a result the northern south china sea and wnp 10 20 n are dominated by southeasterly flow which favors tys making landfall on both the southern and eastern china coast with both landfalling favorable conditions satisfied there are significantly more tys making landfall along the china coast during period iii than during period i which shows cool sst anomalies in the tropical io wp

a numerical study of the circulation of the bering sea basin and exchange with the north pacific ocean abstract a limited area primitive equation three layer hydrodynamic model with realistic coastlines and bathymetry and resolution is used to investigate the circulation of the bering sea basin and the adjacent north pacific ocean the westward flowing alaskan stream to the south of the aleutian island chain is specified as a boundary condition at inflow and outflow ports with a constant throughput of 15 sv sv 1 106 m3 s 1 atmospheric forcing is based an the hellerman and rosenstein monthly climatological wind field the model is spun up over 50 years and the statistics of the final decade are described the general features of the model circulation as discussed below are consistent with available hydrographic and buoy drift observations the model alaskan stream separates from the aleutian island chain near 175 beyond this point there is strong interannual variability associated with meandering and occasional eddy shedding along the northern arm of the western subarctic gyre there is a gen

diagnosis of the mjo modulation of tropical cyclogenesis using an empirical index the modulation of tropical cyclone activity by the madden julian oscillation mjo is explored using an empirical genesis potential gp index composite anomalies of the genesis index associated with the different mjo phases are consistent with the composite anomalies in tc genesis frequency that occur in the same phases indicating that the index captures the changes in the environment that are at least in part responsible for the genesis frequency changes of the four environmental variables that enter the genesis potential index the midlevel relative humidity makes the largest contribution to the mjo composite gp anomalies the second largest contribution comes from the low level absolute vorticity and only very minor contributions come from the vertical wind shear and potential intensity when basin integrated mjo composite anomalies of the gp index are regressed against basin integrated composite anomalies of tc genesis frequency the results differ quantitatively from those obtained from the analogous calculation performed on the annual climatologies in the two quantities the gp index captures the mjo modulation of tc genesis to a lesser degree than the climatological annual cycle of genesis to which it was originally tuned this may be due to weaknesses of the reanalysis or indicative of the importance of precursor disturbances not well captured in the gp index computed from weekly data to the intraseasonal tc genesis frequency fluctuations

systematic variation of summertime tropical cyclone activity in the western north pacific in relation to the madden julian oscillation abstract the variability of observed tropical cyclone tc activity i e genesis track and landfall in the western north pacific wnp is examined in relation to the various categories of the madden julian oscillation mjo during summer june september for the period 1979 2004 the mjo categories are defined based on the empirical orthogonal function analysis of outgoing longwave radiation data the number of tcs increases when the mjo related convection center is located in the wnp the axis of a preferable genesis region systematically shifts like a seesaw in response to changes in the large scale environments associated with both the eastward and northward propagation of the mjo and the intraseasonal variability of the wnp subtropical high furthermore the authors show that the density of tc tracks in each mjo category depends on the systematic shift in the main genesis regions at first order also the shift is affected by the prevailing large scale steering flows in each mjo category when th

tropical cyclone movement and surrounding flow relationships abstract this paper presents results of a comprehensive study of the relationship between the movement of tropical cyclones and the large scale circulation which surrounds them cyclones have been stratified by direction and speed of movement latitude intensity change and size as determined by the radius of the outermost closed surface isobar in three ocean basins the northwest pacific the west atlantic and the australian south pacific region twenty one different stratifications are available in the northwest pacific 13 in the west atlantic and 6 in the australian south pacific area cyclone movement and surrounding flow relationships were studied at different pressure levels and a variety of radii pressure weighted layer averages were also analyzed in search of such relationships results show an important relationship between surrounding large scale flow and tropical cyclone movement for all stratifications the winds in the mid troposphere 500 700 mb at 5 7 latitude radius from the cyclone

revised age of the rockland tephra northern california implications for climate and stratigraphic reconstructionsin the western united states lanphere et al 1999 1 presented new data for the age of the rockland pumice tuff breccia of wilson 1961 2 using the incremental heating 40ar 39ar technique their age 610 ka is 200 ka older than zircon fission track ages obtained on this tuff by meyer et al 1980 3 1991 4

multiscale phenomena in the tropical atmosphere over the western pacific abstract multiscale variabilities in the atmosphere over the tropical western pacific during the 1979 northern hemisphere winter are studied with an aim at identifying possible interactions between phenomena of different spatial and temporal scales based on the convection index information derived from satellite measurements two intra seasonal oscillations isos are identified within the equatorial belt between 0 and 10 s in the analyzed period the two isos accompanied by both rotational and divergent circulations propagate eastward from the indian ocean to the western pacific over the warm pool in the western pacific the isos develop into quasi stationary systems with an enhanced rotational circulation characterized by a strong westerly jet in the lower troposphere the isos appear to interact with a number of regional and synoptic scale phenomena in the maritime continent and western pacific region for example the onset of the monsoon coincides with the arrival of the first iso at northern a

volcanic ash beds recorders of upper cenozoic silicic pyroclastic volcanism in the western united states stratigraphic relationships and tephrochronologic information for volcanic ash beds 4 0 0 1 m y of the western interior allow the recognition of at least 68 different ash falls the average reoccurrence rate based on the succession of the isotopically dated ash beds is near one eruption every 57 000 years the ash beds were grouped into two chemical types rhyolitic and dacitic the main property that distinguishes dacitic from rhyolitic ashes is the larger ca and mg and smaller k content in dacitic ashes dacitic volcanic ashes were defined to have more than 0 55 wt ca rhyolitic ashes were subdivided further into two types w and g type based on the presence of biotite in the w type and its absence in g type w type rhyolitic ashes are chalky white have less than 0 55 wt fe have colorless glass shards of pumiceous habit g type rhyolitic ashes are light to medium gray have from 0 55 to 2 0 wt fe in the glass shards lack biotite have colorless platy bubble wall and bubble junction glass shards dacitic ashes are light gray to grayish brown have more than 0 55 wt fe and ca and have a complex mixture of colorless to light brown shards including pumiceous fibrous chunky and bubble wall and bubble junction types w type rhyolitic ashes possibly formed from magmas that were cooler 695 to 830 c and thus more viscous than the hotter 870 to 1000 c magma progenitors of g type ashes based on fe ti oxide mineral compositions primary microphenocrysts in the ash beds comprise assemblages of the following quartz sanidine plagioclase biotite amphibole clinopyroxene orthopyroxene fayalite zircon apatite allanite chevkinite sphene magnetite and ilmentite fayalite and chevkinite only have been found in g type biotite and sphene only have been found in w type rhyolitic ashes are highly evolved and contain 74 79 wt sio2 dacitic ashes vary from 67 77 wt sio2 al ranges from 10 5 to 14 5 wt al2o3 mg ranges from 0 06 to 1 0 wt mgo and fe as fe3o4 ranges from 0 50 to 4 1 wt dacitic ash beds have the most 0 80 3 8 wt as fe3o4 and rhyolitic ashes have the least 0 50 1 9 wt as fe3o4 ca varies from an unusually low amount 0 25 wt cao in a few rhyolitic ashes to as much as 2 2 in some dacitic ashes rhyolitic glasses show larger eu deficiencies compared to dacitic glasses on rare earth element diagrams w type rhyolitic glasses have moderately large la to sm ratios and have la contents from about 30 to 100 times chondrite values g type rhyolitic glasses also have moderately large la to sm ratios and contain somewhat more la than do the w type rhyolitic ashes generally from 100 to 300 times chondrites amounts

a simple atmospheric model of the local and teleconnection responses to tropical heating anomalies abstract a minimal complexity model of both the local and remote stationary responses of the atmosphere to tropical heating anomalies is described and demonstrated two levels are recast as baroclinic and barotropic components with thermal advection in the tropics neglected the model is linearized about some idealized and realistic background wind fields and forced with a localized heating for illustration in the tropics the baroclinic responses are familiar from the matsuno gill model these excite barotropic responses by advective interactions with vertical background wind shear the barotropic signals are in turn transmitted to high latitudes only in the presence of barotropic background westerly winds for an el nino like equatorial heating the barotropic response has anticyclones to the north and south of the heating reinforcing opposing the anticyclonic cyclonic baroclinic gyres in the upper lower troposphere with realistic background flows the model reproduces the hemispheric asymmetry

four dimensional transform fault processes progressive evolution of step overs and bends many bends or step overs along strike slip faults may evolve by propagation of the strike slip fault on one side of the structure and progressive shut off of the strike slip fault on the other side in such a process new transverse structures form and the bend or step over region migrates with respect to materials that were once affected by it this process is the progressive asymmetric development of a strike slip duplex consequences of this type of step over evolution include 1 the amount of structural relief in the restraining step over or bend region is less than expected 2 pull apart basin deposits are left outside of the active basin and 3 local tectonic inversion occurs that is not linked to regional plate boundary kinematic changes this type of evolution of step overs and bends may be common along the dextral san andreas fault system of california we present evidence at different scales for the evolution of bends and step overs along this fault system examples of pull apart basin deposits related to migrating releasing right bends or step overs are the pliopleistocene merced formation tens of km along strike the pleistocene olema creek formation several km along strike along the san andreas fault in the san francisco bay area and an inverted colluvial graben exposed in a paleoseismic trench across the miller creek fault meters to tens of meters along strike in the eastern san francisco bay area examples of migrating restraining bends or step overs include the transfer of slip from the calaveras to hayward fault and the greenville to the concord fault ten km or more along strike the offshore san gregorio fold and thrust belt 40 km along strike and the progressive transfer of slip from the eastern faults of the san andreas system to the migrating mendocino triple junction over 150 km along strike similar 4d evolution may characterize the evolution of other regions in the world including the dead sea pull apart the gulf of paria pull apart basin of northern venezuela and the hanmer and dagg basins of new zealand d 2004 elsevier b v all rights reserved

effect of enso and the mjo on western north pacific tropical cyclones prior work has suggested that rossby wave accumulation in the lower troposphere may be an important mechanism for the development of synoptic scale disturbances in the western north pacific in northern summer this work examines the intraseasonal and interannual variability of wave accumulation by computing the barotropic wave activity flux divergence at 850 hpa for different phases of the madden julian oscillation mjo and el nino southern oscillation enso indirectly and without ruling out other influences the results suggest a physical mechanism behind previously identified relationships between tropical cyclogenesis statistics and these two modes of variability mjo and enso

primary and successive events in the madden julian oscillation conventional analyses of the mjo tend to produce a repeating cycle such that any particular feature cannot be unambiguously attributed to the current or previous event we take advantage of the sporadic nature of the mjo and classify each observed madden julian mj event as either primary with no immediately preceding mj event or successive which does immediately follow a preceding event 40 of mj events are primary events precursor features of the primary events can be unambiguously attributed to that event a suppressed convective anomaly grows and decays in situ over the indian ocean prior to the start of most primary mj events an associated mid tropospheric temperature anomaly destabilises the atmosphere leading to the generation of the active mj event hence primary mj events appear to be thermodynamically triggered by a previous dry period although stochastic forcing may also be important other theories predict that boundary layer convergence humidity propagation of dynamical structures around the equator sea surface temperatures and lateral forcing by extratropical transients may all be important in triggering an event although precursor signals from these mechanisms are diagnosed from reanalysis and satellite observational data in the successive mj events they are all absent in the primary mj events hence it appears that these apparent precursor signals are part of the mjo once it is established but do not play a role in the spontaneous generation of the mjo the most frequent starting location of the primary events is the indian ocean but over half of them start elsewhere from the maritime continent to the western pacific copyright 2008 royal meteorological society

tropical cyclone motion and evolution in vertical shear abstract the motion and the evolution of tropical cyclone like vortices in an environmental flow with vertical shear are investigated using a baroclinic primitive equation model the study focuses on the fundamental dynamics of a baroclinic vortex in vertical shear the influence of vortex structure and the role of diabatic heating the results show that the initial response of the vortex to the vertical shear is to tilt downshear as soon as the tilt develops the upper level anticyclonic and lower level cyclonic circulations begin to interact with each other as a result of these interactions the tilted axis of the vortex reaches a stable state after an initial adjustment which varies with the structure of the vortex its environmental flow shear and the cumulus convective heating the motion of an adiabatic vortex in vertical shear is controlled by both the steering of the environmental flow and vertical coupling mechanisms most of the vortices move with the environmental flow at about 650 hpa or

seasonal modulation of tropical intraseasonal oscillations on tropical cyclone geneses in the western north pacific the seasonal modulationof tropicalintraseasonal oscillation tiso on tropicalcyclone tc geneses over the western north pacific ocean wnp is investigated in three periods of the wnp tc season may june mj july september jas and october december ond the modulation of the tiso tc geneses over the wnp is strong in mj while it appears weaker in jas and ond in mj tiso propagates northward via two routes the west route through the south china sea and the east route through the wnp monsoon trough region which are two clustering locations of tc geneses tiso can synchronously influence most tc geneses overthese two regions in jas however the modulation is out of phase betweenthe monsoontrough region and the east asian summer monsoon region as well as the wnp subtropical high region as a result of further northward propagation of tiso and scattered tc geneses the tiso tc genesis modulation in each individual region is comparable to that in mj although the modulation over the entire wnp in jas appears weaker in ond tiso has a stronger influence on tc geneses west than east of 1508e because tiso decays and its convection center located at the equator is out of the tc genesis region when propagating eastward into east of 1508e midlevel relative humidity is the primary contribution to the modulations of tiso on the genesis environment while vorticity could contribute to the modulation over the subtropics in jas

two types of el nino events cold tongue el nino and warm pool el nino abstract in this study two types of el nino events are classified based on spatial patterns of the sea surface temperature sst anomaly one is the cold tongue ct el nino which can be regarded as the conventional el nino and the other the warm pool wp el nino the ct el nino is characterized by relatively large sst anomalies in the nino 3 region 5 s 5 n 150 90 w while the wp el nino is associated with sst anomalies mostly confined to the nino 4 region 5 s 5 n 160 e 150 w in addition spatial patterns of many atmospheric and oceanic variables are also distinctively different for the two types of el nino events furthermore the difference in the transition mechanism between the two types of el nino is clearly identified that is the discharge process of the equatorial heat content associated with the wp el nino is not efficient owing to the spatial structure of sst anomaly as a result it cannot trigger a cold event it is also demonstrated that zonal advective feedback i e zonal adve

cluster analysis of typhoon tracks part i general properties a new probabilistic clustering technique based on a regression mixture model is used to describe tropical cyclone trajectories in the western north pacific each component of the mixture model consists of a quadratic regression curve of cyclone position against time the best track 1950 2002 dataset is described by seven distinct clusters these clusters are then analyzed in terms of genesis location trajectory landfall intensity and seasonality both genesis location and trajectory play important roles in defining the clusters several distinct types of straight moving as well as recurving trajectories are identified thus enriching this main distinction found in previous studies intensity and seasonality of cyclones though not used by the clustering algorithm are both highly stratified from cluster to cluster three straight moving trajectory types have very small withincluster spread while the recurving types are more diffuse tropical cyclone landfalls over east and southeast asia are found to be strongly cluster dependent both in terms of frequency and region of impact the relationships of each cluster type with the large scale circulation sea surface temperatures and the phase of the el nino southern oscillation are studied in a companion paper

fission track age 400 000 yr of the rockland tephra based on inclusion of zirco grains lacking fossil fission tracks abstract a zircon fission track age of about 400 000 yr b p has been determined for the rockland tephra a widespread pyroclastic layer in northern california and western nevada new ages of zircon separates from both proximal and distal exposures of this layer range from 370 000 to 460 000 yr ages of the best material provide a narrower range from 370 000 yr for unwelded ash flow tuff to 420 000 yr for distal air fall ash that appears to be uncontaminated by clastic detritus or xenocrysts detrital or xenocrystic grains in the ash flow tuff may have been annealed during emplacement and cooling of the tuff detrital and xenocrystic zircons are identified on the basis of their physical characteristics and distinctly older ages independent stratigraphic and magnetostratigraphic data constrain the age of the rockland tephra between 300 000 and 600 000 yr a range that is compatible with the fission track age zircon grains containing no spontaneous fossil tracks are regarded as part of the normal population of comagmatic grains because maximum ages calculated for these grains form a population that mimics the distribution of ages of individual zircon grains that contain fossil tracks modal ages of both groups fall between 250 000 and 500 000 yr induced fission tracks from grains that lack fossil tracks are included in the age calculations resulting in significantly younger and more coherent dates than would result if these tracks had been omitted especially those of the finer grained distal samples

isothermal plateau fission track age and revised distribution of the widespread mid pleistocene rockland tephra in west central united states a tephra bed in southeastern idaho is correlated to rockland tephra a widespread silicic air fall unit previously identified in northern california and western nevada correlation of proximal rockland tephra and its distal correlative is based on glass chemistry determined by electron microprobe and neutron activation analysis an age estimate of proximal rockland tephra is precisely determined by application of the isothermal plateau fission track itpft technique to its hydrated glass shards a weighted mean age of 0 47 0 04 ma compares well with age estimates based on co existing mineral phases using the external detector fission track and additive dose thermoluminescence techniques the presence of rockland tephra 800 km east of its presumed eruptive source will improve the development of detailed chronologies and correlation of pleistocene sedimentary sequences located in coalescent intermontane basins of west central united states

the shedding of mesoscale anticyclonic eddies from the alaskan stream and westward transport of warm water abstract the south flowing waters of the kamchatka and oyashio currents and west flowing waters of the alaskan stream are key components of the western sub arctic pacific circulation we use ctd data argo buoys woce surface drifters and satellite derived sea level observations to investigate the structure and interannual changes in this system that arise from interactions among anticyclonic eddies and the mean flow variability in the temperature of the upstream oyashio and kamchatka currents is evident by warming in mesothermal layer in 1994 2005 compared to 1990 1991 a major fraction of the water in these currents is derived directly from the alaskan stream the stream also sheds large anticyclonic aleutian eddies averaging approximately 300 km in diameter with a volume transport significant in comparison with that of the kamchatka current itself these eddies enclose pools of relatively warm and saline water whose temperature is typically 4 c warmer and salinity is 0 4 greater than that of cold core kamchatka eddies in the same density range aleutian eddies drift at approximately 1 2 km d 1 and retain their distinctive warm and salty characteristics for at least 2 years selected westward pathways during 1990 2004 are identified if the shorter northern route is followed aleutian eddies remain close to the stream and persist sufficiently long to carry warm and saline water directly to the kamchatka current this was observed during 1994 1997 with substantial warming of the waters in the kamchatka current and upstream oyashio if the eddies take a more southern route they detach from the stream but can still contribute significant quantities of warm and saline water to the upstream oyashio as in 2004 2005 however the eddies following this southern route may dissipate before reaching the western boundary current region

possible linkage between the monsoon trough variability and the tropical cyclone activity over the western north pacific abstractthe present study investigates the influence of the monsoon trough mt on the interannual variability of tropical cyclone tc activity over the western north pacific during july november for the period 1979 2007 it is shown that the tc activity is closely related to the mt location during the years when the mt extends eastward retreats westward more less tcs form within the southeastern quadrant of the western north pacific such a relationship can be explained by the changes in large scale environmental factors associated with the movement of the mt an eastward extension of the mt coincides with warmed ocean surface enhanced convection increased relative humidity in the lower and midtroposphere reduced vertical shear of zonal wind intensified upper level divergence and low level anomalous cyclonic vorticity over the southeast quadrant of the western north pacific these conditions associated with the eastern extension of the mt are favorable for tc genesis while those associated w

geostrophic control of fluctuating barotropic flow through straits abstract a simple model in which the cross strait sea surface slope is geostrophically balanced and the along strait slope is balanced by acceleration and friction is shown to be supported by the results of buchwald and miles for fluctuating flow through a gap between two semi infinite oceans for a narrow gap compared with the rossby radius and the scale of the motion in the far field the transport through it is exactly the same as that predicted by the model provided that the gap is regarded as having an elective length as determined in this paper the importance of the models is that they demonstrate that at low frequency the flow may be geostrophically controlled and the transport limited to a value much less than that which would arise in a nonrotating system the neglect of nonlinear advective terms in the models is justified by a comparison or the bernoulli set down in the strait with the driving head and the mean water depth the formula for the flux through a strait may be applied in stu

tropical cyclone activity in the northwest pacific in relation to the el nino southern oscillation phenomenon abstract the interannual variations in tropical cyclone activity in the northwest pacific nwpac and their relationships with the el nino southern oscillation enso phenomenon were studied using the method of spectral analyses time series of a southern oscillation index soi defined as the sea level pressure difference between easter island and darwin and tropical cyclone activity in the entire nwpac ocean basin as well as in different regions of the nwpac were analyzed two spectral peaks are apparent in all these time series one corresponds to the generally accepted southern oscillation with a period of 3 to 3 5 years and another at the quasi biennial oscillation qbo frequency cross spectral analyses between the soi and tropical cyclone activity show significant coherence in these two spectral peaks the dominant peak is at the southern oscillation frequency with the soi leading typhoon activity by almost a year at the qbo frequency the two series are almost in phase cyclone activity in t

tropical cyclone track direction climatology and its intraseasonal variability in the australian region aspects of tropical cyclone tc activity such as the influence of the el nino southern oscillation and the variability of tc genesis location have been examined in numerous previous studies however relatively few studies have examined aspects such as the influence of intraseasonal variability on tc track direction here we focus on a number of knowledge gaps relating to observed tc track directionality and intraseasonal variability in the australian region climatological examinations are presented for tc track directional variability throughout the australian region in contrast to previous studies that have focused on the mean direction of tc movement in this region tc tracks are examined here based on the full spectrum of track directions for a given location or region variability in initial tc track directions is investigated including an examination of the influence of the madden julian oscillation mjo it is demonstrated that there is a considerable degree of seasonal and intraseasonal variation in tc motion in this region these variations result from variations in genesis location throughout the tc season as well as zonal wind anomalies associated with the influence of the mjo on the steering flow winds anomalous westerly steering flow occurs during mjo phase 4 5 and anomalous easterly flow during phase 8 1 in the western basin with resulting changes in the proportion of tc tracks in each direction during these phases of the mjo the results presented here are intended to provide improved seasonal tc activity guidance and enhanced resilience to tc impacts 2016 american geophysical union all rights reserved

pleistocene incision rates in the western united states calibrated using lava creek b tephra the lava creek b ash bed erupted from the yellowstone caldera ca 0 64 ma provides a datum for measuring long term fluvial incision west of the mississippi river the ash is widely preserved due to its substantial volume broad initial dispersal and the aggrading environment into which the ash fell drainages incised soon after lava creek b deposition isolating the ash from fluvial erosion and preserving it in fill terraces calculated rates of incision since ca 0 60 ma range from 2 to 30 cm k y 1 rates are high in most areas near the rocky mountains and downstream along rivers draining mountainous terrain and are lowest east of the high plains and along the snake river incision rates along many rivers decrease downstream rates of downcutting increased in the late pleistocene along several major rivers indicating that climate change altered sediment budgets regional and temporal data suggest that fluvial incision records increased middle and late pleistocene runoff from the southern rocky mountains rather than epeirogenic uplift but regional rock uplift cannot be excluded as a significant factor

use of principal component analysis for identification of rockland and trego hot springs tephras in the hat creek graben northeastern california usa abstract discontinuous tephra layers were discovered at burney spring mountain northern california stratigraphic relationships suggest that they are two distinct tephras binary plots and standard similarity coefficients of electron probe microanalysis data have been supplemented with principal component analysis to correlate the two tephra layers to known regional tephras using principal component analysis we are furthermore able to bound our uncertainty in the correlation of the two tephra layers after removal of outliers within the 95 prediction interval we can say that one tephra layer is likely the rockland tephra aged 565 610 ka and the second layer is likely from mt mazama the trego hot springs tephra aged 29 ka in the case of the rockland tephra the new findings suggest that dispersal to the north was highly restricted for trego hot springs ash the new findings extend the distribution to the southwest with a rapid thinning in that direction coupled with considerations of regular tephra dispersal patterns the results suggest that the primary dispersal direction for both tephras was to the south and that occurrences in other directions are unlikely or otherwise anomalous

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

cluster analysis of typhoon tracks part ii large scale circulation and enso abstract a new probabilistic clustering method based on a regression mixture model is used to describe tropical cyclone tc propagation in the western north pacific wnp seven clusters were obtained and described in part i of this two part study in part ii the present paper the large scale patterns of atmospheric circulation and sea surface temperature associated with each of the clusters are investigated as well as associations with the phase of the el nino southern oscillation enso composite wind field maps over the wnp provide a physically consistent picture of each tc type and of its seasonality anomalous vorticity and outgoing longwave radiation indicate changes in the monsoon trough associated with different types of tc genesis and trajectory the steering winds at 500 hpa are more zonal in the straight moving clusters with larger meridional components in the recurving ones higher values of vertical wind shear in the midlatitudes also accompany the straight moving tracks compared to

modulation of tropical cyclone tracks over the western north pacific by intra seasonal indo western pacific convection oscillation during the boreal extended summer this study investigates the effect of the intra seasonal indo western pacific convection oscillation ipco on tropical cyclone tc tracks over the western north pacific wnp during the boreal extended summer may october the number of west and northwest moving tc tracks is found to sharply increase over the wnp in the positive intra seasonal ipco phase recurving tracks have greater weight in the negative intra seasonal ipco phase possible physical mechanisms are further examined in terms of steering flow energy conversion and energy propagation when the intra seasonal ipco phase is positive the first order moment term of perturbation potential energy ppe1 converts into perturbation kinetic energy pke at lower latitudes the pressure trough spreads farther to the east meanwhile rossby waves emanating from the convective centers of the intra seasonal ipco over the wnp wavewnp and eeio waveeeio travel into the trough region thereby deepening the trough these features enhance the westward and northwestward steering flow between 20 n and about 30 n sharply increasing the number of straight west and northwest moving tc tracks over the wnp when the intra seasonal ipco is in a negative phase conversion from ppe1 to pke at lower latitudes is suppressed and the trough weakens more ppe1 converts to pke in the climatological western pacific subtropical high wpsh region and the wpsh is intensified moreover waveeeio intensifies the north south ridge of the wpsh over the southern indian peninsula meanwhile part wavewnp propagate northeastward these features favor northeastward motion of tcs over the wnp

el nino modoki and its possible teleconnection 1 using observed data sets mainly for the period 1979 2005 we find that anomalous warming events different from conventional el nino events occur in the central equatorial pacific this unique warming in the central equatorial pacific associated with a horseshoe pattern is flanked by a colder sea surface temperature anomaly ssta on both sides along the equator empirical orthogonal function eof analysis of monthly tropical pacific ssta shows that these events are represented by the second mode that explains 12 of the variance since a majority of such events are not part of el nino evolution the phenomenon is named as el nino modoki pseudo el nino modoki is a classical japanese word which means a similar but different thing the el nino modoki involves ocean atmosphere coupled processes which include a unique tripolar sea level pressure pattern during the evolution analogous to the southern oscillation in the case of el nino hence the total entity is named as el nino southern oscillation enso modoki the enso modoki events significantly influence the temperature and precipitation over many parts of the globe depending on the season the impacts over regions such as the far east including japan new zealand western coast of united states etc are opposite to those of the conventional enso the difference maps between the two periods of 1979 2004 and 1958 1978 for various oceanic atmospheric variables suggest that the recent weakening of equatorial easterlies related to weakened zonal sea surface temperature gradient led to more flattening of the thermocline this appears to be a cause of more frequent and persistent occurrence of the enso modoki event during recent decades

eddy induced cross slope exchange maintaining summer high productivity of the bering sea shelf break 1 eddy related cross slope exchange along the bering sea shelf break was investigated using a hydrographic observations data set and a numerical model results of observations in summer of 2001 showed a shelf break front that formed at a shelf break near an anticyclonic eddy high nitrate nitrite concentrations in the subsurface layer and high chlorophyll a chl a concentrations 6 mg m 3 in the surface layer a hydrographic observation in summer of 2002 exhibited relatively high chl a concentrations at the surface around the anticyclonic eddy tracer experiments revealed two types of cross slope exchange under isopycnals nutrient rich water in the basin is transported to the shelf and there is about a 64 53 increase in integrated nitrate nitrite on shelf flux 50 m depth bottom when mesoscale eddies are formed and propagated along the shelf break at the surface high chl a waters in the shelf are advected to the deep basin area by eddy transport and propagation these indicate that 1 mesoscale eddies supply nutrients and sustain primary productivity at the shelf break and 2 eddies expand the high chl a area to the basin then to the highly productive area so that the green belt is maintained

iso modulation on the submonthly wave pattern and recurving tropical cyclones in the tropical western north pacific abstract this study demonstrates the multiscale nature from synoptic to intraseasonal time scales of the atmospheric flow in the tropical western north pacific the multiscale features include intraseasonal oscillations iso northwestward propagating submonthly wave patterns and recurving tropical cyclones tcs in the iso westerly phase the wave pattern was better organized and the tcs were clustered near the cyclonic circulation of the wave pattern during the genesis development and propagation on the other hand the wave pattern and tcs were weak and poorly organized in the iso easterly phase the distinct characteristics between the westerly and easterly phases could be attributed to the iso modulation on the monsoon trough and the subtropical anticyclonic ridge the iso in the westerly phase provided a favorable background e g enhanced monsoon trough and moisture confluent zone for the wave tc pattern development while the iso in the easterly phase provided a less favorable environment

asymmetric distribution of convection associated with tropical cyclones making landfall along the south china coast this study examines the convection distribution associated with 18 tcs that made landfall along the south china coast during 1995 and 2005 cloud top temperatures from high resolution satellite imageries of the geosynchronous meteorological satellite 5 are used as proxy of strong convection it is found that convection tends to be enhanced on the western side of the tc as it makes landfall in 10 of the cases in agreement with the conclusion of some previous studies four cases have stronger convection on the eastern side this deviation from the general rule appears to be related to the tcs being more slow moving or their interaction of the tc with another land surface prior to its making landfall along the south china coast for the remaining cases in which no significant asymmetries in convection can be identified the vertical wind shear appears to enhance convection on the east side

summer upwelling in the south china sea and its role in regional climate variations seasonal and interannual variations of summer upwelling off the south vietnam coast and the offshore spread of cold water are investigated using a suite of new satellite measurements in summer as the southwesterly winds impinge on annam cordillera a north south running mountain range on the east coast of indochina a strong wind jet occurs at its southern tip offshore east of saigon resulting in strong wind curls that are important for ocean upwelling off the coast in july and august an anticyclonic ocean eddy develops to the southeast advecting the cold coastal water offshore into the open south china sea scs the center of this cold filament is located consistently north of the wind speed maximum indicating that open ocean upwelling helps to cool the ocean surface corroborating evidence for the cold filament is found in ocean color observations that reveal a collocated tongue of high chlorophyll concentration the development of this cold filament disrupts the summer warming of the scs and causes a pronounced semiannual cycle in sst moreover the cold filament is an important player in interannual variability in the summer scs in 1998 the cold filament and mid summer cooling never took place giving rise to a strong basin wide surface warming interannual sst variance has a local maximum over the climatological cold filament and is much greater than the variance over the adjacent indian and western pacific oceans a cold filament index is constructed which displays significant lagged correlation with sst in the eastern equatorial pacific and indian oceans indicative of a teleconnection from el nino

classifying el nino modoki i and ii by different impacts on rainfall in southern china and typhoon tracks based on their opposite influences on rainfall in southern china during boreal fall this paper classifies el nino modoki into two groups el nino modoki i and ii which show different origins and patterns of sst anomalies the warm sst anomalies originate in the equatorial central pacific and subtropical northeastern pacific for el nino modoki i and ii respectively thus el nino modoki i shows a symmetric sst anomaly distribution about the equator with the maximum warming in the equatorial central pacific whereas el nino modokiii displays an asymmetric distribution with the warmsstanomaliesextending fromthe northeastern pacifictotheequatorialcentralpacific additionally thewarmsstanomaliesintheequatorialcentralpacific extend farther westward for el nino modoki ii than for el nino modoki i similar to the canonical el nino el nino modoki i is associated with an anomalous anticyclone in the philippine sea that induces south westerly wind anomalies along the south coast of china and carries the moisture for increasing rainfall in southern china for el nino modoki ii an anomalous cyclone resides east of the philippines associated with northerly wind anomalies and a decrease in rainfall in southern china the canonical el nino and el nino modoki i are associated with a westward extension of the western north pacific subtropical high wnpsh whereas el nino modoki ii shifts the wnpsh eastward differing from canonical el nino and el nino modoki i el nino modoki ii corresponds to northwesterly anomalies of the typhoon steeringflow which are unfavorable for typhoons to make landfall in china

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

anticyclonic eddies in the alaskan stream abstract anticyclonic eddies propagating southwestward in the alaskan stream as were investigated through analysis of altimetry data from satellite observations during 1992 2006 and hydrographic data from profiling float observations during 2001 06 fifteen long lived eddies were identified and categorized based on their area of first appearance three eddies were present at the beginning of the satellite observations another three formed in the eastern gulf of alaska off sitka alaska and four were first detected at the head of the gulf of alaska near yakutat alaska the other five eddies formed along the as between 157 and 169 w and were named as eddies while the eddies that formed in the gulf of alaska mainly decayed before exiting the gulf of alaska the as eddies mostly crossed the 180 meridian and reached the western subarctic gyre four of five as eddies formed under negative or weakly positive wind stress curls which possibly caused as separation from the coast comparison of eddy propag

have steering flows in the western north pacific and the south china sea changed over the last 50 years 1 long term trends in steering flows over the western north pacific wnp and the south china sea scs are examined during the peak typhoon season a nonparametric and robust trend detection method is employed both the ncep and era reanalysis data sets suggest a statistically significant decreasing trend in steering flows in the subtropical region of the western wnp between 120 e or near taiwan and 145 e and the northern scs during 1958 2001 over this period the decrease in the wnp is quite large with a magnitude of 1 1 m s 1 given that the background mean steering flow is only 3 26 m s 1 this decrease corresponds approximately to one third of the mean flow when the data are extended from 1958 to 2009 the long term decrease in steering flows in the aforementioned subtropical region are still significant although more modest at a rate of 0 7 m s 1 time series of translational speeds averaged over the same subtropical region also exhibit a slow down of storms motion over the last 52 years this is consistent with the weakening of easterly steering flows analyzed from independent data sets results of this study imply a longer life span for tropical cyclones and a greater tendency for storms along prevailing typhoon tracks to recurve

impact of the quasi biweekly oscillation on the super typhoon tracks in winter over the western north pacific this study investigates the tracks of category 4 and 5 typhoons tys in the western north pacific wnp in november december during 1979 2016 and their relationships with the intraseasonal oscillation iso including the 30 60 day and 12 25 day variations it is shown that the impact of iso on the ty tracks found in previous studies is mainly contributed by the quasi biweekly oscillation qbwo the impact on the ty tracks is through influence on the steering flows over the wnp accordingly tys are separated into two types moving westward tyw and northeastward tye qbwo in the wnp is associated with an active convection originated from the equatorial wnp which propagates northwestward and reaches the scs and middle high latitudes tyw mostly occurs in the decline stage of the qbwo life cycle while tye appears in the mature stage of qbwo for tyw qbwo hardly changes the background large scale circulation which features an anticyclonic circulation covering the entire wnp and scs thus tyw moves westward however tye appears in the mature phase of qbwo the strong convection induces an intense cyclonic circulation in western part of the wnp thus changes the steering flow the steering flow features an anticyclonic circulation over the mid eastern wnp which is favorable for tye to divert the direction and move northeastward

the middle pleistocene merced 2 and 3 sequences from ocean beach san francisco the merced formation comprises a 2 km thick shallow marine and non marine succession that was deposited in a small transtensional basin along the san andreas fault during the late pliocene to middle pleistocene the sediments dip between 10 and 80 to the northeast and are locally disrupted by small faults during tilting the beds have been rotated into subparallelism with the san andreas fault zone splays of which bound the outcrop belt of merced sediments to both the southwest and northeast the merced formation contains more than 20 transgressive regressive sedimentary rhythms cyclothems or sequences that are generally between 40 and 120 m thick and which were deposited mostly during interglacial time under the influence of rising highstand and early falling sea levels sequences merced 2 units m1 n of soc econ paleontol mineral field guidebook 3 1984 1 and merced 3 units o p though in fault contact comprise typical plio pleistocene shallow water cyclothems the merced 2 sequence is 22 m thick and comprises a sandy and shelly transgressive systems tract including a basal type a shellbed an in situ type b mid cycle shellbed and a highstand systems tract of massive siltstone the merced 3 sequence is 47 m thick and comprises a basal compound shellbed a thin highstand systems tract siltstone and a sand rich regressive systems tract the rst comprises distal shoreface sands with an abundant in situ molluscan fauna and upper shoreface and back beach trough cross bedded sands and pebbly sands the top of the merced 3 cycle comprises a beach sand capped by a palaeosol and lignite the beetle bed which together mark the subaerial exposure of the site during the ensuing glacial sea level lowstand analysis of 10be across the merced 3 sequence shows major peaks indicative of sedimentation starvation in the basal transgressive systems tract shellbed and in the capping lignite of the beetle bed smaller 10be peaks are associated with a shellbed that is inferred to represent winnowing at the foot of the shoreface and with a minor exposure surface that delimits a small paracycle in the top of the sequence otherwise 10be abundances decline regularly across the merced 3 sequence consistent with an increasing sedimentation rate as shoreface progradation and regression progressed the character of cycles merced 2 and merced 3 respectively resembles the seafield and rangitikei sequence motifs described from similar plio pleistocene sediments in new zealand the cycles are of mid pleistocene age and were probably deposited during interglacial oxygen isotope stages 21 and 19 respectively

asymmetric modulation of western north pacific cyclogenesis by the madden julian oscillation under enso conditions abstractthe present study investigates the modulation by the madden julian oscillation mjo and the impact of the el nino southern oscillation enso on tropical cyclone tc genesis in the western north pacific wnp during the period 1975 2010 results reveal a stronger modulation of cyclogenesis by the mjo during el nino years while the modulations in neutral and la nina years are comparable to each other the asymmetric background modification by enso is found to greatly affect the extent of mjo modulation under different enso conditions first mjo activity is intensified and extends farther eastward during el nino years instead of being confined west of 150 e as in neutral and la nina periods thus the influence of mjo is stronger and more zonally widespread in el nino years causing significant differences in cyclogenesis parameters in most parts of the wnp in el nino years cyclogenesis is further enhanced in the active phase due to synchronization of mjo signals with favorable background enso

clouds associated with the madden julian oscillation a new perspective from cloudsat abstractthe evolution of total cloud cover and cloud types is composited across the madden julian oscillation mjo using cloudsat data for june 2006 may 2010 two approaches are used to define mjo phases 1 the local phase is determined at each longitude and time from filtered outgoing longwave radiation and 2 the global phase is defined using a popular real time multivariate mjo rmm index which assigns the tropics to an mjo phase each day in terms of local phase cloudsat results show a familiar evolution of cloud type predominance in the growing stages shallow clouds coexist with deep intense but narrow convective systems widespread cloud coverage and rainfall appear during the active phases becoming more anvil dominated with time and finally suppressed conditions return results are compared to the convectively coupled kelvin wave which has a similar life cycle to the mjo convection in the mjo tends to be modulated more by moisture variations compared to the kelvin wave in terms of globa

interdecadal variability of western north pacific tropical cyclone tracks abstract this study examines the interdecadal variability of the tropical cyclone tc tracks over the western north pacific wnp during the 1960 2005 period an empirical orthogonal function analysis of the 10 yr gaussian filtered annual frequency of tc occurrence shows three leading modes of tc occurrence patterns the first mode is related to the variation of tc activity in the areas near japan and its east the second mode is characterized by a northeast southwest dipole of tc occurrence anomalies along the southeast coast of china and an east west dipole near japan and its east the third mode is similar to the second mode except for the absence of the east west dipole these patterns are shown to be related to the decadal changes in the prevailing tc tracks two characteristic flow patterns related to the first and third modes of tc occurrence pattern are identified the first pattern is characterized by a north south dipole of 500 hpa geopotential anomalies over the wnp such a pattern may affect

the influence of an alaskan stream eddy on flow through amchitka pass flow into the bering sea through amchitka pass in the central aleutian islands is shown to respond to the presence of a large meander eddy in the alaskan stream south of the pass maximum flow into the aleutian basin of the bering sea occurs when the eddy center lies nearest to the axis of amchitka pass a conceptual model of low frequency circulation variability within the bering sea based upon results of empirical orthogonal function analyses of sea surface height anomalies measured by the geosat radar altimeter is presented

impact of intraseasonal oscillation on the tropical cyclone track in the south china sea this study investigates the impact of the intraseasonal oscillation iso on tropical cyclone tc tracks in the south china sea scs during 1970 2010 about one third of tcs in the scs move eastward while the other two thirds move westward in the tc genesis peak seasons of june october jjaso the westward moving tcs are controlled by the background tc steering flow of easterly and the eastward moving tcs by the tc steering flow induced by the iso the outgoing longwave radiation and wind fields show that the eastward moving tcs were mostly along the main axis of strong tc steering flow anomaly of westerly associated with the iso while the westward moving tcs were only weakly associated with the iso an experiment performed with a simple two level model further confirmed the result the interannual variation of tc tracks in the scs is also discussed it is found that the steering flow anomalies in the scs mostly favor eastward moving tcs in central pacific cp el nino and eastern pacific ep el nino years however the eastward flow anomalies are too weak to have strong influence on the majority of the tcs during la nina years tcs in the scs tend to move westward possibly related to the westward steering flow anomalies

age of the rockland tephra western usa abstract the age of the rockland tephra which includes an ash flow tuff south and west of lassen peak in northern california and a widespread ash fall deposit that produced a distinct stratigraphic marker in western north america is constrained to 565 000 to 610 000 yr by 40ar 39ar and u pb dating 40ar 39ar ages on plagioclase from pumice in the rockland have a weighted mean age of 609 000 7000 yr isotopic ages of spots on individual zircon crystals analyzed by the shrimp rg ion microprobe range from 500 000 to 800 000 yr a subpopulation representing crystal rims yielded a weighted mean age of 573 000 19 000 yr overall stratigraphic constraints on the age are provided by two volcanic units including the underlying tephra of the lava creek tuff erupted within yellowstone national park that has an age of 639 000 2000 yr the basaltic andesite of hootman ranch stratigraphically overlies the rockland in the lassen peak area and has 40ar 39ar ages of 565 000 29 000 and 565 000 12 000 yr for plagioclase and groundmass respectively identification of rockland tephra in odp core 1018 offshore of central california is an important stratigraphic age that also constrains the eruption age to between 580 000 and 600 000 yr

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties

revised ages for tuffs of the yellowstone plateau volcanic field assignment of the huckleberry ridge tuff to a new geomagnetic polarity event 40 ar 39 ar ages were determined on the three major ash flow tuffs of the yellowstone plateau volcanic field in the region of yellowstone national park in order to improve the precision of previously determined ages total fusion and incremental heating ages of sanidine yielded the following mean ages huckleberry ridge tuff 2 059 0 004 ma mesa falls tuff 1 285 0 004 ma and lava creek tuff 0 639 0 002 ma the huckleberry ridge tuff has a transitional magnetic direction and has previously been related to the reunion normal polarity subchron dating of the reunion event has been reviewed and its ages have been normalized to a common value for mineral standards the age of the huckleberry ridge tuff is significantly younger than lava flows of the reunion event on re union island supporting other evidence for a normal polarity event younger than the reunion event