the enso asian monsoon interaction in a coupled ocean atmosphere gcm abstract in this study the authors evaluate the el nino southern oscillation enso asian monsoon interaction in a version of the hadley centre coupled ocean atmosphere general circulation model cgcm known as hadcm3 the main focus is on two evolving anomalous anticyclones one located over the south indian ocean sio and the other over the western north pacific wnp these two anomalous anticyclones are closely related to the developing and decaying phases of the enso and play a crucial role in linking the asian monsoon to enso it is found that the hadcm3 can well simulate the main features of the evolution of both anomalous anticyclones and the related sst dipoles in association with the different phases of the enso cycle by using the simulated results the authors examine the relationship between the wnp sio anomalous anticyclones and the enso cycle in particular the biennial component of the relationship it is found that a strong el nino event tends to be followed by a more rapid decay and i

western pacific interannual variability associated with the el nino southern oscillation observations of sea surface temperature sst sea level pressure slp surface wind and outgoing longwave radiation olr show that the el nino southern oscillation enso displays western pacific anomaly patterns in addition to eastern pacific anomaly patterns during the warm phase of enso warm sst and low slp anomalies in the equatorial eastern pacific and low olr anomalies in the equatorial central pacific are accompanied by cold sst and high slp anomalies in the off equatorial western pacific and high olr anomalies in the off equatorial far western pacific also while the zonal wind anomalies over the equatorial central pacific are westerly those over the equatorial far western pacific are easterly the nearly out of phase behavior between the eastern and western tropical pacific is also observed during the cold phase of enso but with anomalies of opposite sign these western pacific interannual anomaly patterns are robust features of enso independent of data sets it is argued that equatorial easterly westerly wind anomalies over the far western pacific during the warm cold phase of enso are initiated by off equatorial western pacific cold warm sst anomalies and that these winds are important for the evolution of enso an atmosphere model is employed to demonstrate that small off equatorial western pacific cold warm sst anomalies compared to those in the east are sufficient to produce equatorial easterly westerly wind anomalies as observed over the far western pacific the coupled ocean atmosphere model of zebiak and cane is then modified to investigate the evolution of the western pacific interannual anomaly patterns in a coupled ocean atmosphere system by including a meridional structure to the subsurface temperature parameterization in the western pacific the modified model produces both western and eastern pacific interannual anomaly patterns

analysis of the completeness magnitude and seismic network coverage of japan abstract a reliable estimate of completeness magnitude m c above which all earthquakes are considered to be detected by a seismic network is vital for seismicity related studies we show a comprehensive analysis of m c in japan we use the catalog maintained by the japan meteorological agency jma and also available information on seismic stations that report to jma for computing m c we adopt a commonly used method based on the gutenberg richter frequency magnitude law presently m c 1 0 might be typical in the mainland but to have a complete catalog one needs to use earthquakes with magnitudes of 1 9 or larger comparison with the southern california seismic network scsn suggests that the recent event detectability in the mainland generally shows similar completeness levels to that in the authoritative region of scsn we argue that the current m c of japan is due to the success of network modernization over time particularly we show that the spatiotemporal change of m c closely matches the addition of the hi net borehole stations to enhancing seismic station density it started in october 1997 in southwestern japan continuing to northeastern japan until 2002 as suggested from this matching we confirm that m c inversely correlates with station density further we find that irrespective of the network change after 1997 this correlation is unchanged in time demonstrating that the influence on m c from factors beyond station density does not vary in time contrary to alaska and california wiemer and wyss 2000 our results do not attribute such factors simply to anthropogenic noise because this is due to the borehole stations that reduce ambient noise we conclude that in japan the anthropogenic noise has an insignificant effect on m c

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

distinct modes of east asian winter monsoon documented by a southern red sea coral record the large scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope 18o record from the southern red sea covering most of the last century are investigated from the early 1930s to the early 1960s the winter coral 18o record reflecting temperature and salinity variations in southern red sea surface waters is associated with global or large scale sea surface temperature sst and 850 mb geopotential height z850 anomalies which project on the corresponding patterns associated with the el nino southern oscillation enso in contrast since the early 1960s the winter coral 18o record is related to a z850 pattern that reflects the enso independent part of the east asian winter monsoon eawm which includes the siberian high the east asian through and the east asian upper tropospheric jet our results indicate a weakening of the enso control on interannual temperature salinity variations in southern red sea surface waters in the early 1960s due to the warming of the indian ocean and suggest that information about the nonstationarity in the relationship between enso and two distinct modes of eawm can be documented in southern red sea coral 18o records

two regimes of the equatorial warm pool part i a simple tropical climate model abstract atmosphere ocean coupled processes responsible for generating and maintaining the equatorial warm pool were investigated using models of different complexities the primary focus was to answer the following question why is the observed warm pool concentrated around the maritime continent in this first of a two part series the solutions of a simple conceptual model that represents the tropical pacific and indian oceans interacting via the walker circulation are examined when the interbasin coupling is sufficiently strong surface wind convergence over the maritime continent associated with easterly trades over the pacific acts to generate the equatorial westerly over the indian ocean leading to a warm pool spontaneously emerging between the two ocean basins the conceptual model shows that tropical climate has two equilibria depending upon the ocean basin widths a single warm pool regime corresponding to the current climate and a split warm pool regime that accompanies warm pools created in

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

size distribution of parkfield s microearthquakes reflects changes in surface creep rate s u m m a r y the nucleation area of the series of m6 events in parkfield has been shown to be characterized by low b values throughout the seismic cycle since low b values represent high differential stresses the asperity structure seems to be always stably stressed and even unaffected by the latest main shock in 2004 however because fault loading rates and applied shear stress vary with time some degree of temporal variability of the b value within stable blocks is to be expected we discuss in this study adequate techniques and uncertainty treatment for a detailed analysis of the temporal evolution of b values we show that the derived signal for the parkfield asperity correlates with changes in surface creep suggesting a sensitive time resolution of the b value stress meter and confirming near critical loading conditions within the parkfield asperity

diverse influences of enso on the east asian western pacific winter climate tied to different enso properties in cmip5 models the influence of el nino southern oscillation enso on the east asian western pacific eawp climate in boreal winter is investigated in the phase 5 of the coupled model intercomparison project cmip5 model results and then compared to that in the phase 3 cmip3 results in particular the role played by the differences among models in enso properties including the amplitude and longitudinal extension of enso s sea surface temperature sst pattern is analyzed results show that an eastward shrinking of enso s sst pattern leads to quite weak circulation and climatic responses over the eawp regions in the models on the contrary a westward expansion of the sst pattern shifts the anomalous walker circulation too far west the resultant precipitation anomalies and lower tropospheric atmospheric rossby wave responses both extend unrealistically into the indian ocean and the hemispheric asymmetry of the rossby wave response is missing all these features lead to unrealistic climatic impacts of ensoover the eawp regions in contrasttothe abovetwocases areasonablelongitudinalextensionof enso s sst pattern corresponds to better enso teleconnections over the eawp regions nevertheless the atmospheric responses over the western pacific are still located farther west than observed implying a common bias of cmip5 models in this case a larger amplitude of enso variability to some extent helps to reduce model biases and facilitate better climatic responses to enso in the eawp regions compared with cmip3 models cmip5 models perform better in representing enso s impacts on the east asian winter climate

role of the enso indian ocean coupling on enso variability in a coupled gcm warming are only confined to the io and it has little impact on the tropical pacific during the boreal winter when the el nino is in its mature phase the anomalous warming extends eastward to cover the entire tropical io and the anomalous easterlies extend into the western pacific wp the anom alous easterlies in the wp generate oceanic upwelling kelvin waves which propagate eastward and accelerate the decay of the warm sst in the eastern pacific as a result the el nino is rapidly terminated and a la nina develops within one year from the el nino mature phase they concluded that the interaction between enso and the io may generate a biennial tendency for enso 4 the samples used for the composite analysis by kk06 are rather limited due to the relatively short length of the observational data in this study we intended to analyze a longer 200 yr data set obtained from the simulation of a sintex f scale interaction experiment frcgc cou pled gcm in order to verify the enso io feedback hypoth esis itturnsoutthatthefeedbackprocessbetweenensoand the io is quite plausible not only from observations but also from the state of the art coupled gcm

a moist linear baroclinic model coupled dynamical convective response to el nino a newly developed linear baroclinic model lbm and its application to the tropical enso teleconnection is described the model based on primitive equations linearized about the observed zonally varying basic state in northern winter involves linear schemes for the cumulus convection and surface sensible and latent heat fluxes referred to as the moist lbm this enables us to solve a steady state response of the coupled dynamical convective system to a given sst anomaly which is fairly different from the conventional dry lbm linear representation of the convection is acceptable for a realistic range of sst anomalies reproducing well the rossby wave train computed in the conventional lbm forced by a tropical heating the moist lbm is used to examine the formation mechanisms of an anomalous low level anticyclone near

characteristics of long recovery early vlf events observed by the north african awesome network 1 lightning strokes are capable of initiating disturbances in the lower ionosphere whose recoveries persist for many minutes these events are remotely sensed via monitoring subionospherically propagating very low frequency vlf transmitter signals which are perturbed as they pass through the region above the lightning stroke in this paper we describe the properties and characteristics of the early vlf signal perturbations which exhibit long recovery times using subionospheric vlf transmitter data from three identical receivers located at algiers algeria tunis tunisia and sebha libya the results indicate that the observation of long recovery events depends strongly on the modal structure of the signal electromagnetic field and the distance from the disturbed region and the receiver or transmitter locations comparison of simultaneously collected data at the three sites indicates that the role of the causative lightning stroke properties e g peak current and polarity or that of transient luminous events may be much less important the dominant parameter which determines the duration of the recovery time and amplitude appears to be the modal structure of the subionospheric vlf probe signal at the ionospheric disturbance where scattering occurs and the subsequent modal structure that propagates to the receiver location

interactive feedback between enso and the indian ocean abstract a feedback process of the indian ocean sst on enso is investigated by using observed data and atmospheric gcm it is suggested that warming in the indian ocean produces an easterly wind stress anomaly over indonesia and the western edge of the pacific during the mature phase of el nino the anomalous easterly wind in the western pacific during el nino helps a rapid termination of el nino and a fast transition to la nina by generating upwelling kelvin waves thus warming in the indian ocean which is a part of the el nino signal operates as a negative feedback mechanism to enso this indian ocean feedback appears to operate mostly for relatively strong el ninos and results in a la nina one year after the mature phase of the el nino this 1 yr period of phase transition implies a possible role of indian ocean enso coupling in the biennial tendency of the enso atmospheric gcm experiments show that indian ocean sst forcing is mostly responsible for the easterly wind anomalies in the western pacific

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

the climate of the mis 13 interglacial according to hadcm3 the climate of the marine isotopic stage 13 mis 13 is explored in the fully coupled atmosphere ocean general circulation model the hadley centre coupled model version 3 hadcm3 it is found that the strong insolation forcing at the time imposed a strengthened land ocean thermal contrast resulting in an intensified summer monsoon over asia the addition of land ice over north america and eurasia results in a stationary wave feature across the eurasian continent this leads to a high pressure anomaly over the sea of japan with increased advection of warm moist air onto the chinese landmasses this in turn reinforces the east asian summer monsoon easm highlighting the counterintuitive notion that depending on the background insolation and its size ice can indeed contribute to strengthening the easm the modeling results support the geological record indication of a strong easm 500 000 years ago furthermore arctic oscillation el nino southern oscillation and indian ocean dipole like teleconnection features are discussed in the mis 13 environment it is shown that the change in the tropical pacific sea surface temperature has the potential to impact the north atlantic climate through an atmospheric bridge

atmosphere ocean thermal coupling in the north atlantic a positive feedback in this article it is examined whether a positive atmosphere ocean feedback is found over the north atlantic through a series of general circulation model gcm experiments a 60 year integration of an atmospheric gcm agcm coupled with a 50 m deep motionless ocean was conducted the coupled run was compared with two uncoupled runs one with prescribed mid latitude climato logical sea surface temperatures ssts and the other with daily ssts derived from the coupled experiment the uncoupled atmosphere forces the slab ocean to obtain sst responses in these runs consistent with previous studies the coupled atmosphere ocean fields show interannual variances larger than those in the uncoupled runs due to reduction in the local thermal damping patterns of maximum atmosphere ocean covariability show the north atlantic oscillation nao and tripole sst anomalies both in the coupled and uncoupled fields indicating a dominant role of the atmosphere in generating the sst anomalies on the other hand analyses of the temporal variability in the three runs suggest an active role of sst anomalies in determining the polarity of the air sea coupled variability longer than the interannual time scale a combined analysis of forcing sst upper air height and the response sst anomalies in the uncoupled run identified that a patch of positive sst anomalies in the mid latitude band around 40 n effectively excite the positive phase of the nao which in turn reinforces the tripole sst anomalies this relationship was further confirmed by a nine member ensemble agcm experiment forced by the relevant sst anomalies since the forcing and response sst anomaly patterns bear some resemblance these results manifest positive feedback at work in the coupled atmosphere ocean patterns the processes responsible for this positive feedback were elaborated by a series of linear model experiments the local thermal adjustment of the atmosphere to the sst anomalies results in increased precipitation over the gulf stream region associated diabatic heating applied to a linear baroclinic model yields a positive height response to the east which highly influences the southern part of the nao this stationary response in turn induces a northward deflection in the storm track activity leading to an eddy vorticity feedback that tends to force the positive phase of the nao

impact of southeast indian ocean sea surface temperature anomalies on monsoon enso dipole variability in a coupled ocean atmosphere model recent studies show that southeast indian ocean seio ssts are a highly significant precursor of transitions of the whole monsoon el nino southern oscillation enso system during recent decades however the reasons for this specific interannual variability have not yet been identified unequivocally from the observations among these the possibility of seio sst driven variability in the monsoon enso system is investigated here by inserting positive negative seio temperature anomalies in the february s restart files of a state of the art coupled general circulation model gcm for 49 years of a control simulation for each year of the control simulation the model was then integrated for a 1 year period in fully coupled mode these experiments show that indian summer monsoon ism and tropical indian ocean dipole mode iodm events are significantly influenced by the seio temperature perturbations inserted in the mixed layer of the coupled gcm several months before a warm seio perturbation inserted in late boreal winter slowly propagates northward during the following seasons implies enhanced ism rainfall and finally triggers a negative iodm pattern during boreal fall in agreement with observations a reversed evolution is simulated for a cold seio perturbation it is shown that the life cycle of the simulated seio signal is driven by the positive wind evaporation sst coastal upwelling and wind thermocline sst feedbacks further diagnosis of the sensitivity experiments suggests that stronger ism and iodm variabilities are generated by excluding the el nino years of the control simulation or when the initial background state in the seio is warmer this finding confirms that iodm events may be triggered by multiple factors other than enso including subtropical seio sst anomalies however the enso mode does not react significantly to the seio temperature perturbation in the perturbed runs even though the simulated pacific pattern agrees with the observations during boreal fall these discrepancies with the observations may be linked to model biases in the pacific and to the too strong enso simulated by this coupled gcm these modeling evidences confirm that subtropical indian ocean sst anomalies generated by mascarene high pulses during austral summer are a significant precursor of both ism and iodm events occuring several months later

focal zone of a future tokai earthquake inferred from the seismicity pattern around the plate interface abstract a future large tokai earthquake has been considered to be the most urgent problem of impending disasters in the central part of the japanese islands since the first warning was announced in 1976 recent progress in observations has provided a great amount of data thus making a detailed investigation possible in this study based on the seismicity and the focal mechanism patterns of microearthquake data the mechanical situation that governs plate interactions around the tokai district was investigated it was found that the seismicity in the subducting philippine sea slab is composed of three characteristic groups of activities intense activity beneath lake hamana a linear cluster extending from lake hamana toward the northwest and a broad cluster expanding over the inland area in the west of suruga bay we propose that these activities occur inside the subducting oceanic crust and reflect the present stress state acting there the mechanism inducing these activities is assumed to come from two stress sources the lateral stretching of the slab and the partial locking between both plates this interpretation leads to the hypothesis that the broad cluster in the west of suruga bay represents a stress concentration due to locking the activity beneath lake hamana is proposed to represent shearing motion induced there and is interpreted to form the boundary between the rupture zones of the 1944 tonankai earthquake and a future large tokai earthquake these analyses resulted in identifying the wide inland area extending from the west coast of suruga bay to lake hamana to be a focal zone of a future tokai earthquake the zone proposed in this study indicates a significant deviation in its strike from the original model proposed by ishibashi in that the former parallels the nankai trough while the latter parallels the suruga trough

interactive feedback between enso and the indian ocean in an interactive ensemble coupled model an interactive feedback between enso and the indian ocean is investigated using a center for ocean land atmosphere studies cola interactive ensemble coupled model from a long term simulation of the coupled gcm it is shown that el nino events terminate relatively rapidly when the indian ocean sst is anomalously warm the anomalous indian ocean warming induces the anomalous easterlies over the western pacific by modulating the walker circulation in turn the anomalous easterlies generate oceanicupwelling kelvin waves over the western pacific which propagate eastward and accelerate the decay of the warm sst in the eastern pacific as a result el nino terminates relatively quickly and the phase transition from el nino to la nina progresses rapidly these interactive processes are consistent with those derived from the previous observational analyses

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

a proposed mechanism for the asymmetric duration of el nino and la nina el nino and la nina exhibit significant asymmetry not only in their spatial structure but also in their duration most el ninos terminate rapidly after maturing near the end of the calendar year whereas many la ninas persist into the following year and often reintensify in boreal winter through atmospheric general circulation model experiments it is shown that the nonlinear response of atmospheric deep convection to the polarity of equatorial pacific sea surface temperature anomalies causes an asymmetric evolution of surface wind anomalies over the far western pacific around the mature phase of el nino and la nina because of the eastward displacement of precipitation anomalies in the equatorial pacific during el nino compared to la nina surface winds in the western pacific are more affected by sst forcing outside the equatorial pacific which acts to terminate the pacific event

on the stress dependence of the earthquake b value laboratory experiments have shown that the b value in the size distribution of acoustic emission events decreases linearly with differential stress there have been a number of observations that indicate that this relation may also hold for earthquakes here using a simple frictional strength model for stresses in the continental lithosphere combined with earthquake b values measured as a function of depth in a wide variety of tectonic regions we verify and calibrate that relation finding b 1 23 0 06 0 0012 0 0003 1 3 where the stress difference 1 3 is in megapascal for subduction zones we find that b value correlates linearly with the slab pull force and with the net reduction of plate interface normal force both of which also indicate a negative linear relation between b value and differential stress

southern hemisphere extra tropical forcing a new paradigm for el nino southern oscillation the main goal of this paper is to shed additional light on the reciprocal dynamical linkages between mid latitude southern hemisphere climate and the el nino southern oscillation enso signal while our analysis confirms that enso is a dominant source of interannual variability in the southern hemisphere it is also suggested here that subtropical dipole variability in both the southern indian and atlantic oceans triggered by southern hemisphere mid latitude variability may also provide a controlling influence on enso in the equatorial pacific this subtropical forcing operates through various coupled air sea feedbacks involving the propagation of subtropical sea surface temperature sst anomalies into the deep tropics of the atlantic and indian oceans from boreal winter to boreal spring and a subsequent dynamical atmospheric response to these sst anomalies linking the three tropical basins at the beginning of the boreal spring this atmospheric response is characterized by a significant weakening of the equatorial atlantic and indian inter tropical convergence zone itcz this weakened itcz forces an equatorial cold kelvin wave response in the middle to upper troposphere that extends eastward from the heat sink regions into the western pacific by modulating the vertical temperature gradient and the stability of the atmosphere over the equatorial western pacific ocean this kelvin wave response promotes persistent zonal wind and convective anomalies over the western equatorial pacific which may trigger el nino onset at the end of the boreal winter these different processes explain why south atlantic and indian subtropical dipole time series indices are highly significant precursors of the nino34 sst index several months in advance before the el nino onset in the equatorial pacific this study illustrates that the atmospheric internal variability in the mid latitudes of the southern hemisphere may significantly influence enso variability however this surprising relationship is observed only during recent decades after the so called 1976 1977 climate regime shift suggesting a possible linkage with global warming or decadal fluctuations of the climate system

south asian summer monsoon and the eastern mediterranean climate the monsoon desert mechanism in cmip5 simulations abstractdry summers over the eastern mediterranean are characterized by strong descent anchored by long rossby waves which are forced by diabatic heating associated with summer monsoon rainfall over south asia the large scale teleconnection between rising and subsiding air masses is referred to as the monsoon desert mechanism this study evaluates the ability of the phase 5 of the coupled model intercomparison project cmip5 models in representing the physical processes involved in this mechanism an evaluation of statistics between summer climatologies of monsoon diabatic heating and that of vertical velocity over the eastern mediterranean suggests a linear relationship despite large spatial diversity in monsoon heating descent over the mediterranean is coherently located and realistic in intensity to measure the sensitivity of descent to the diversity in the horizontal and vertical distribution of monsoon heating a series of linear atmosphere model experiments are performed it is shown that col

observation of local and conjugate ionospheric perturbations from individual oceanic lightning flashes very low frequency vlf remote sensing observations of multifaceted local and conjugate ionospheric perturbations from geographically identified and well characterized oceanic lightning discharges are presented for the first time lightning induced electron precipitation lep events are shown to produce disturbances first in the conjugate hemisphere and subsequently in the hemisphere of the causative lightning discharge in agreement with theoretical predictions a rough threshold peak current of 100 ka is identified for lightning discharges to generate lep events for the geomagnetic conditions present during observations the occurrence of early vlf events and the subsequent duration of their recovery do not seem to fit any simple metric of lightning discharge peak current or proximity to great circle path knowledge of the full spectral density of the lightning electromagnetic pulse not just its peak current and the subionospheric mode structure are likely necessary to determine if a specific lightning discharge will generate an early vlf perturbation

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

combination mode dynamics of the anomalous northwest pacific anticyclone abstractnonlinear interactions between enso and the western pacific warm pool annual cycle generate an atmospheric combination mode c mode of wind variability the authors demonstrate that c mode dynamics are responsible for the development of an anomalous low level northwest pacific anticyclone nwp ac during el nino events the nwp ac is embedded in a large scale meridionally antisymmetric indo pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in asia in contrast to previous studies the authors find the role of air sea coupling in the indian ocean and northwestern pacific only of secondary importance for the nwp ac genesis moreover the nwp ac is clearly marked in the frequency domain with near annual combination tones which have been overlooked in previous indo pacific climate studies furthermore the authors hypothesize a positive feedback loop involving the anomalous low level nwp ac through el nino and c mode interactions the development o

pacific east asian teleconnection how does enso affect east asian climate observational evidence is presented to show a teleconnection between the central pacific and east asia during the extreme phases of enso cycles this pacific east asian teleconnection is confined to the lower troposphere the key system that bridges the warm cold events in the eastern pacific and the weak strong east asian winter monsoons is an anomalous lower tropospheric anticyclone cyclone located in the western north pacific the western north pacific wind anomalies develop rapidly in late fall of the year when a strong warm or cold event matures the anomalies persist until the following spring or early summer causing anomalously wet dry conditions along the east asian polar front stretching from southern china northeastward to the east of japan kuroshio extension using atmospheric general circulation and intermediate models the authors show that the anomalous philippine sea anticyclone results from a rossby wave response to suppressed convective heating which is induced by both the in situ ocean surface cooling and the subsidence forced remotely by the central pacific warming the development of the anticyclone is nearly concurrent with the enhancement of the local sea surface cooling both the anticyclone and the cooling region propagate slowly eastward the development and persistence of the teleconnection is primarily attributed to a positive thermodynamic feedback between the anticyclone and the sea surface cooling in the presence of mean northeasterly trades the rapid establishment of the philippine sea wind and sst anomalies implies the occurrence of extratropical tropical interactions through cold surge induced exchanges of surface buoyancy flux the central pacific warming plays an essential role in the development of the western pacific cooling and the wind anomalies by setting up a favorable environment for the anticyclone sst interaction and midlatitude tropical interaction in the western north pacific

tropical axisymmetric mode of variability in the atmospheric circulation dynamics as a neutral mode abstract there is an observational evidence that the variability in the global upper tropospheric flow fields on a monthly basis is dominated by a zonally uniform pattern symmetric about the equator this fluctuation is characterized by the zonal mean zonal wind anomaly having the same sign within the tropics and thus has been related to changes in the global atmospheric angular momentum in this paper the mechanism of this variability referred to as the tropical axisymmetric mode tam was investigated using the ncep ncar reanalysis an atmospheric general circulation model agcm and a linear baroclinic model an index of the tam defined by the leading principal component of the observed 300 hpa streamfunction anomalies shows quite significant correlation with the nino 3 sst anomalies consistent with a well known coherence between the angular momentum and el nino while this suggests that tam can be forced effectively by el nino events data analyses and an agcm experiment with climatological ss

interface locking along the subduction megathrust from b value mapping near nicoya peninsula costa rica 1 to understand controlling factors for seismogenesis and strain accumulation in subduction megathrusts we examine seismicity patterns across nicoya costa rica to determine the overall and spatial variability in the earthquake frequency magnitude distribution along the interface the mean reduction in earthquake activity with magnitude b value is higher 1 06 than global subduction zone averages 0 6 0 8 suggesting the interface here is weakly coupled strong spatial variations in b are anticorrelated 0 53 with geodetic estimates of interface locking of e norabuena et al 2004 high b prevails in two regions including the subducted fisher seamount chain a broad zone of reduced b is observed at and offshore the central nicoya coast extending towards an imaged locked patch these results suggest b value studies may be useful in identifying regions of increased interface locking in subduction zones which may indicate regions capable of large slip in future large earthquakes

a study on the variations of recent seismicity in and around the central anatolian region of turkey abstract variations of the recent seismicity in and around the central anatolian region of turkey were evaluated based on the seismic b value standard normal deviate z value genas modelling annual probabilities and return periods of the earthquakes the catalog includes 16 702 earthquakes between 1974 and 2019 with magnitudes from 1 0 to 6 3 time distribution of b value shows that there is a tendency to decrease after the year of 2002 and b value decreased from 1 58 0 03 to 1 25 0 05 at the beginning of 2019 annual probabilities for magnitude ranges of 3 0 4 0 have the values between 3 and 30 return periods for magnitude levels of 5 0 5 5 have the values from 5 to 20 years and a value of 80 years for magnitude level of 6 0 the genas results show the significant temporal variations in the number of earthquakes smaller and larger than specific magnitude intervals by supplying the beginning periods of increases and decreases in the earthquake activity rate remarkable reductions in region time distribution of b value at the beginning of 2019 were detected in the regions covering nigde fault and its vicinity along the south west northwest and southwest directions among the mut fault zone karsanti karaisali fault zone and karatas osmaniye fault zone in and around surgu fault and along its northwest direction between surgu fault and east anatolian fault zone significant seismic quiescence areas in z value distribution include the northwest ends of the tuzgolu fault zone and study area including akpinar fault the northeast of salanda fault between salanda fault and the central anatolian fault zone the northeast parts of the central anatolian fault zone the west of malatya fault between surgu fault and the east anatolian fault zone the southeast end of the tuzgolu fault zone karsanti karaisali fault zone and its vicinity the southwest of tuzgolu thus these anomaly areas observed in the central anatolian region and its vicinity at the beginning of 2019 may be one of the most likely zones for the next strong large earthquake occurrences

role of off equatorial sst in el nino teleconnection to east asia during el nino decaying spring observational evidences are presented to show significant differences in pacific east asian pea teleconnections during the el nino decaying period depending on the northern off equatorial sea surface temperature sst conditions on the basis of the northern off equatorial central pacific sst nocp index we separate el nino events into two groups distinctive differences are observed between the two groups not only in tropical features but also in mid latitude teleconnections in particular the nocp index is closely related to the strength of the local feedback between the sst anomalies and the anticyclonic flow over the western north pacific wnp during the ensuing spring of the el nino events because the wnp anticyclone tends to persist until boreal spring in the case of negative nocp diabatic cooling due to the reduced precipitation over the wnp induces anticyclonic flow over the kuroshio extension region via a rossby wave response which leads to warm and wet conditions over east asia however because the wnp anticyclone decays early in the case of positive nocp cyclonic circulation exists over the north pacific which leads to cold and dry conditions over east asia consequently the maintenance of the wnp anticyclone during the el nino decaying period may explain the discrepancy in the pea teleconnections in various types of el nino accordingly the nocp index could be a possible predictor for boreal spring climate conditions over east asia

establishment of the low level wind anomalies over the western north pacific during enso development abstract the anomalous low level anticyclone over the western north pacific presents a link between el nino and the western north pacific east asian climate during a la nina event however the low level wind anomalies over the western north pacific reverse sign the low level wind anomalies move eastward from south asia and are established over the western north pacific in the fall of the el nino la nina developing year the anomalous low level anticyclone associated with el nino is a response to suppressed convection this suppressed convection is mainly induced by a cooling tendency associated with the vertical average of the anomalous horizontal advection of moist static energy that is defined as the mechanism of the horizontal advection of moist static energy the el nino related sea surface temperature sst anomalies over the eastern pacific in particular create negative meridional gradients of temperature and moisture over the western north pacific when the winter monsoon starts to dominate

the coads sea level pressure signal a near global el nino composite and time series view 1946 1993 abstract using coads data for the period 1946 1993 the near global sea level pressure slp patterns associated with interannual variability and the climatological seasonal march are discussed a particular focus concerns the patterns associated with the two years before and after the south american sea surface temperatures rise el nino the ten el nino events in this record are composited and the robustness of the features of this composite is tested many features of the composite are quite robust they occur during most el nino events and are infrequent during non el nino periods the most robust feature is an area of negative slp anomaly slpa in the eastern equatorial pacific during year 0 of the composite this feature exceeds significance thresholds during every el nino year and never during non el nino years it correlates better with central pacific sst variability than does the soi a west central north pacific positive slpa occurring late in year 0 and lasting into the spring of year

pacific east asian teleconnection part ii how the philippine sea anomalous anticyclone is established during el nino development the anomalous philippine sea anticyclone psac conveys impacts of el nino to east asian climate during the mature and decay of an el nino from the winter to ensuing summer it is shown that the anomalous psac forms in fall about one season prior to the peak el nino its strength increases with the el nino intensity and its sign reverses during a la nina the psac formation concurs with abnormal deepening of the east asian trough and with increasing number of northward recurvature of tropical storms in the western pacific the psac establishment is abrupt coupling with a swing from a wet to dry phase of an intraseasonal oscillation iso and often concurrent with early retreat of the east asian summer monsoon the iso becomes inactive after psac establishment the development of the psac is attributed to combined effects of the remote el nino forcing tropical extratropical interaction and monsoon ocean interaction the developing el nino induces off equatorial as cending rossby wave responses and land surface cooling in northeast asia both deepen the east asian trough in fall and induces vigorous tropical extratropical exchange of air mass and heat which enhances the cold air outbreak and initiation of the psac through exciting descending rossby waves the el nino induced indonesian subsidence generates low level anticyclonic vorticity over south asia which is advected by mean monsoon westerly instigating the anomalous psac the iso interacting with the underlying ocean plays a critical role in the abrupt establishment of psac the wind evaporation entrainment feedback tends to amplify suppress iso before after winter northeasterly monsoon commences suggesting the roles of atmosphere ocean inter action and the seasonal march of background winds in changing the philippine sea iso intensity and maintaining psac

on the relationship between indian ocean sea surface temperature and the transition from el nino to la nina the relationship between indian ocean sea surface temperature and the transition of el nino events into either la nina or el nino southern oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the national center for environmental prediction climate forecast system the southern indian ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions these associations are described and a physical mechanism involving air sea interaction in the indian and western pacific oceans is proposed observations suggest that easterly surface wind anomalies in the western pacific ocean are associated with the emergence of la nina during boreal summer and fall here it is shown that these winds are significantly correlated to southern indian ocean sea surface temperature in the preceding spring that is characterized by a large scale zonal dipole of cool and warm anomalies in the southwestern and southeastern indian oceans respectively these associations are particularly pronounced for strong el nino conditions during the dissipation of which a pronounced wavetrain like atmospheric pattern accompanies sea surface temperature anomalies in the southern indian ocean together the circulation and sea surface temperature anomalies increase the meridional cross equatorial temperature gradient in the western indian ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the indo pacific warm pool collectively these anomalies favor subsequent la nina development on the basis of these observed associations a predictive model that demonstrates skill in anticipating the nature of el nino transitions involving the southern indian ocean asian monsoon and el nino southern oscillation is proposed in the national center for environmental prediction climate forecast system the relationships described above are simulated both consistently and realistically despite model weaknesses further bolstering a key role of southern indian ocean and predictive relationship comparison of fully coupled and sea surface temperature forced simulations suggests a key role for air sea interaction in the observed associations moreover it is demonstrated that coupled simulations of el nino southern oscillation may benefit substantially from improved representation of indian ocean variability and indo pacific interaction

an intensity index for the east asian winter monsoon the thermal contrast betweenthe asian continentand the adjacent oceans is the primary aspect of the east asian winter monsoon eawm that can be well represented in the sea level pressure slp field based on this consideration a new slp based index measuring the intensity of the eawm is proposed by explicitly taking into account both the east west and the north south pressure gradients around east asia the new index can delineate the eawm related circulation anomalies well including the deepened shallow midtropospheric east asian trough sharpened and accelerated widened and decelerated upper tropospheric east asian jet stream and enhanced weakened lower tropospheric northerly winds in strong weak eawm winters compared with previous indices the new index has a very good performance describing the winter mean surface air temperature variations over east asia especially for the extreme warm or cold winters the index is strongly correlated with several atmospheric teleconnections including the arctic oscillation theeurasianpattern andthenorthpacificoscillation westernpacificpattern implyingthepossible internal dynamics of the eawm variability meanwhile the indexis significantly linked to el ni oscillation enso and the sea surface temperature sst over the tropical indian ocean moreover the sst anomalies over the tropical indian ocean are more closely related to the index than enso as an independent predictor this adds further knowledge to the prediction potentials of the eawm apart from enso the predictability of the index is high in the hindcasts of the centre national de recherches m cnrm model from development of a european multimodel ensemble system for seasonal to interannual prediction demeter hence it would be a good choice to use this index for the monitoring prediction and research of the eawm

generation and termination of indian ocean dipole events in 2003 2006 and 2007 evolution of indian ocean dipole iod events in 2003 2006 and 2007 is investigated using observational and re analysis data products efforts are made to understand various processes involved in three phases of iod events activation maturation and termination three different triggers are found to activate the iod events in preceding months leading to the iod evolution the thermocline in southeastern indian ocean shoals by reflection of near equatorial upwelling rossby waves at the east african coast into anomalous upwelling equatorial kelvin waves strengthening weakening of northern southern portion of itcz in march april and may june of iod years leads to strengthening of alongshore winds along sumatra java coasts with the combined shallow thermocline and increased latent heat flux due to enhanced wind speeds the sst in the southeastern indian ocean cools in following months on intraseasonal time scales convection suppressing phase of madden julian oscillation mjo propagates from west to east in may june of iod year and easterlies associated with this phase of mjo causes further shoaling of thermocline in southeastern indian ocean through anomalous upwelling kelvin wave all these three mechanisms appear to be involved in initiating iod event in 2006 on the other hand except the strengthening weakening of itcz all other mechanisms are involved in activation of 2003 iod event activation of 2007 iod event was due to propagation of convection suppressing mjo in may june and strengthening of mean winds along sumatra java coast from march to june through changes in convection the iod events matured into full fledged events in the following months after activation by surface heat fluxes vertical and horizontal advection of cool waters supported by local along shore upwelling favorable winds and remote equatorial easterly wind anomalies through excitation of upwelling kelvin waves propagating mjo signals in the tropical indian ocean brings significant changes in evolution of iod events on mjo time scales termination of 2003 and 2007 iod events is achieved by strong convection enhancing mjos propagating from west to east in the tropical indian ocean which deepen the thermocline in the southeastern equatorial indian ocean iod event in 2006 was terminated by seasonal reversal of monsoon winds along sumatra java coasts which stops the local coastal upwelling

the influence of atmospheric convection on the interaction between the indian ocean and enso abstractin recent years it has been proposed that a negative positive indian ocean dipole iod in boreal autumn favors an el nino la nina at a lead time of 15 months observational analysis suggests that a negative iod might be accompanied by easterly anomalies over the western pacific such easterlies can enhance the western pacific warm water volume thus favoring el nino development from the following boreal spring onward however a gill model response to a negative iod forcing would lead to nearly zero winds over the western pacific the authors hypothesize that a negative iod or even a cool western indian ocean alone leads to low level air convergence and hence enhanced convectional heating over the maritime continent which in turn amplifies the wind convergence so as to cause easterly winds over the western pacific this hypothesis is tested by coupling an idealized indian ocean model and a convective feedback model over the maritime continent to the zebiak cane model it is found that for a

role of subtropical precipitation anomalies in maintaining the summertime meridional teleconnection over the western north pacific and east asia abstract the meridional teleconnection patterns over the western north pacific and east asia wnp ea during summer have a predominant role in affecting east asian climate on the interannual time scale a well known seesaw pattern of tropical subtropical precipitation is associated with the meridional teleconnection and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection in this study however the authors suggest that subtropical precipitation anomalies in turn can significantly affect large scale circulations and may be crucial for maintenance of the meridional teleconnection diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater the simulated results by a linear baroclinic model indicate that a subtropical heat source which is equivalent to the diagnosed positive subtropical precipitati

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

quasi periodic slow slip events in the afterslip area of the 1996 hyuga nada earthquakes japan 1 the time evolution of afterslip on a plate boundary experiencing interplate earthquakes is expected to show logarithmic decay the global positioning system network in japan has been monitoring transient deformation since the occurrence of two large interplate earthquakes with moment magnitudes of 6 8 and 6 7 in the hyuga nada area southwest japan in 1996 the spatial and temporal evolution of aseismic interplate slip based on crustal deformation data indicates that afterslip followed the two earthquakes and gradually declined to background rates by around 2004 with total moment magnitude of 7 3 however quasi periodic slow slip events suddenly began within the afterslip area in 2005 with approximately one year duration and two year recurrence interval the moment magnitudes of the three slow slip events since january 2005 range from 6 7 to 6 8 this differs greatly from the expected behavior of logarithmic decay over time both velocity strengthening and velocity weakening rate and state modes have been implicated as the cause of afterslip whose location is complementary to the main shock area of velocity weakening while a slow slip event occurs in the velocity weakening area with different frictional properties from those of an afterslip area in light of the seemingly different frictional properties the coexistence of afterslip and slow slip events in the same area would provide additional information about precisely how the plate interface is behaving the monitoring of these slow slip events should give the clues to understanding the coexistence of long term afterslip and slow slip events and the increasing risk of earthquakes in neighboring areas

spatial and temporal distributions of b values related to long term slow slip and low frequency earthquakes in the bungo channel and hyuga nada regions japan abstract long term slow slip events sses and low frequency earthquakes lfes repeatedly occur in the area encompassing the bungo channel and hyuga nada region in japan sses are slow earthquake events with a duration of months to years characterized by a type of slip that is considered transitional between the fast rupture of regular earthquakes and stable sliding along a plate interface and have characteristics sensitive to stress states near the plate interface in addition since lfes are also thought to occur at the plate interface it would be useful to infer the stress state in this region this study focuses on the stress dependent characteristics of the b values of regular earthquakes sses and lfes as well as the spatio temporal relationships between b values and these events in this area using the japan unified high resolution relocated catalog for earthquakes juice the b value which represents the relative proportion of large to small earthquakes is inversely related to differential stress or effective stress the b values are moderate to low b 0 6 1 1 in regions with a high incidence of long term sses this spatial b value anomaly is attributed to the partial release of accumulated stress in regions with a relatively high differential stress due to sse activity furthermore the b value distributions estimated in this study provide constraints on the mechanisms that generate lfes on the other hand the b values increase and decrease before and during periods of enhanced lfe activity in the bungo channel respectively the increase and following decrease in b values are thought to reflect episodes of low and high shear strength along the plate interface which were caused by the presence of abundant slab derived fluids under undrained conditions above the plate interface and decreased pore pressure related to fluid depletion via lfe generation respectively

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

enso and east asian winter monsoon relationship modulation associated with the anomalous northwest pacific anticyclone using observational datasets and numerical model experiments the mechanism on the slowly varying change in the relationship between the el nino southern oscillation enso and the east asian winter monsoon eawm is investigated the decadal window 11 15 and 21 year moving correlations show a significant change in the boreal wintertime enso eawm relationship between two sub periods of 1976 1992 and 1997 2013 such recent change in enso eawm relationship is mainly attributed to the changes in the intensity and zonal location of the anomalous lower tropospheric northwest pacific anticyclone nwp ac nwp ac commonly develops near the region of the philippine sea during the enso s peak phase and plays an important role of bridging the tropical convection and mid latitude teleconnection on one hand the intensity of the nwp ac is influenced by the interdecadal variation in a linkage between enso and the indian ocean sea surface temperature sst variability referring that a strong connection between the pacific and indian oceans results in the strengthening of nwp ac response to enso on the other hand the zonal displacement of the nwp ac is associated with the pacific decadal oscillation pdo and the atlantic multidecadal oscillation amo that is the tropical pacific mean state i e zonal sst gradient between climatologically warm western pacific and cold eastern pacific strengthened by either the negative pdo phase or the positive amo phase drives the anomalous enso induced convection to be shifted to the west with this westward shift the zonal center of the nwp ac also migrates westward over the philippine islands and exerts stronger connection between enso and eawm in contrast the relaxed zonal sst contrast associated with either the positive pdo phase or the negative amo phase tends to exhibit weaker enso eawm relationship via both of eastward shifted zonal centers of the anomalous enso induced convection and the nwp ac finally a series of the numerical experiments conducted by an atmospheric general circulation model supports the observational findings

a global search for triggered tremor following the 2011 mw 9 0 tohoku earthquake abstract the 2011 m w 9 0 tohoku japan earthquake triggered deep tectonic tremor and shallow microearthquakes in numerous places worldwide here we conduct a systematic survey of triggered tremor in regions where ambient or triggered tremor has been previously identified tremor was triggered in the following regions south central alaska the aleutian arc shikoku in southwest japan the north island of new zealand southern oregon the parkfield cholame section of the san andreas fault in central california the san jacinto fault in southern california taiwan and vancouver island we find no evidence of triggered tremor in the calaveras fault in northern california one of the most important factors in controlling the triggering potential is the amplitude of the surface waves data examined in this study suggest that the threshold amplitude for triggering tremor is 0 1 cm s which is equivalent to a dynamic stress threshold of 10 kilopascals the incidence angles of the teleseismic surface waves also affect the triggering potentials of love and rayleigh waves the results of this study confirm that both love and rayleigh waves contribute to triggering tremor in many regions in regions where both ambient and triggered tremor are known to occur tremor triggered by the tohoku event generally occurred at similar locations with previously identified ambient and or triggered tremor further supporting the notion that although the driving forces of triggered and ambient tremor differ they share similar mechanisms we find a positive relationship between the amplitudes of the triggering waves and those of the triggered tremor which is consistent with the prediction of the clock advance model online material table of measured parameters and other information related to triggering nontriggering information and figures of observed seismograms

interdecadal change in the relationship between enso and the intraseasonal oscillation in east asia abstract the northward propagating intraseasonal oscillation npiso during the boreal summer is closely linked to the onset retreat and intensity of the east asian summer monsoon easm in this study interdecadal variability in the relationships between the npiso and el nino southern oscillation enso was investigated using long term outgoing longwave radiation data obtained from the 40 yr ecmwf re analysis era 40 for a 44 yr period 1958 to 2001 it was found that before the late 1970s the preceding winter enso influenced the early summer i e may to june npiso activity whereas after the late 1970s a strong relationship appeared during the later summertime i e july to august the may june npiso before the late 1970s was modulated by springtime indian ocean sea surface temperature warming and central north pacific suppressed convection anomalies and was consequently related to the enso induced west pacific wp pattern which shows a north south dipole structure over the north pacific from

a diagnostic and modeling study of the monthly mean wintertime anomalies appearing in a 100 year gcm experiment abstract the nature of simulated atmospheric variability on monthly time scales has been investigated by analyzing the output from a 100 year integration of a spectral gcm with rhomboidal wavenumber 15 truncation in this experiment the seasonally varying climatological sea surface temperature was prescribed throughout the world oceans the principal modes of variability in the model experiment were identified by applying a rotated empirical orthogonal function eof analysis to the northern hemisphere monthly averaged 515 mb geopotential height for the winter season november through march the individual leading spatial modes are similar to the observed north south dipoles over the north atlantic and north pacific as well as wavelike patterns in the pacific north american and northern asian sectors quasigeostrophic geopotential tendencies forced by synoptic scale 2 5 6 day eddy vorticity and heat fluxes were computed for those months when the individual eof modes are particularly active the comp

seafloor geodetic constraints on interplate coupling of the nankai trough megathrust zone seafloor geodetic data from the nankai trough off southwestern japan show that most offshore sites in this earthquake prone region have high slip deficit rates revealing previously unknown locations that could be important for the mitigation of future earthquake and tsunami associated disasters yusuke yokota et al have used seafloor geodetic observations to visualize the seismogenic zone along the nankai trough off southwestern japan which is thought to be one of the most dangerous megathrust zones in the world they suggest that most offshore sites in this region have positive slip deficit rates revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis low slip deficit rates are observed in other regions consistent with distributions of shallow slow earthquakes and subducting seamounts interplate megathrust earthquakes have inflicted catastrophic damage on human society such an earthquake is predicted to occur in the near future along the nankai trough off southwestern japan an economically active and densely populated area in which megathrust earthquakes have already occurred1 2 3 4 5 megathrust earthquakes are the result of a plate subduction mechanism and occur at slip deficit regions also known as coupling regions 6 7 where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully many studies have attempted to capture distributions of slip deficit rates sdrs in order to predict earthquakes8 9 10 however these studies could not obtain a complete view of the earthquake source region because they had no seafloor geodetic data the hydrographic and oceanographic department of the japan coast guard jhod has been developing a precise and sustainable seafloor geodetic observation network11 in this subduction zone to obtain information related to offshore sdrs here we present seafloor geodetic observation data and an offshore interplate sdr distribution model our data suggest that most offshore regions in this subduction zone have positive sdrs specifically our observations indicate previously unknown regions of high sdr that will be important for tsunami disaster mitigation and regions of low sdr that are consistent with distributions of shallow slow earthquakes and subducting seamounts this is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the nankai trough subduction zone

second order moment of central california seismicity 1969 1982 the second order moment cross correlation function of earthquakes in the u s geological survey central california catalog between 1969 and 1982 was calculated with respect to a magnitude threshold m 4 0 over interevent distances up to 80 km and interevent times up to 320 days the statistical procedure results in a representation of the spatial temporal structure of the catalog associated with m 4 0 earthquakes and is capable of revealing patterns too weak to be detected in the space time distribution of seismicity for individual earthquake sequences a method is introduced for identifying aftershocks based on a physical two parameter model of the earthquake interaction process the results show that the aftershock process dominates the second order moment and may even obscure the statistical expression of a precursory process a concentration of foreshocks within 15 km and 3 days of m 4 0 main shocks exhibits an apparent migration toward the main shock loci with velocity 2 6 5 3 km d this concentration may be related to an observed tendency for m 4 0 events to cluster auto correlate over this interevent range with the identified aftershocks removed the residual catalog is poissonion in space and time when two m 4 0 earthquakes occur within 80 km and 40 days of each other aftershock productivity appears to be relatively enhanced in the earlier sequence this suggests that aftershock populations are not solely dependent on their main shocks and that unusually productive aftershock sequences may be predictors of future moderate earthquakes

winter precipitation variability over korean peninsula associated with enso in this study winter precipitation variability associated with the el nino southern oscillation enso over the korean peninsula was investigated using a 5 pentad running mean data because significant correlation pattern cannot be revealed using seasonal mean data it was found a considerably significant positive correlation between nino3 sea surface temperature and precipitation during early winter from mid november to early december when the correlation coefficient is close to 0 8 in early december the correlation is distinctively weakened during late winter it is demonstrated that such sudden intraseasonal change in relation to enso is associated with the presence of anticyclonic flow over the kuroshio extension region kuroshio anticyclone in early winter there is strong southerly wind over the korean peninsula which is induced by the philippine sea anticyclone and kuroshio anticyclone however in january although the philippine sea anticyclone develops further the kuroshio anticyclone suddenly disappears as a result the impact of enso is considerably weakened over the korean peninsula these results indicate that the kuroshio anticyclone during el nino peak phase plays a critical role by strongly affecting northeast asia climate including the korean peninsula in addition it is also found that there are distinctive interdecadal changes of the relationship between enso and precipitation over the korean peninsula in particular the strong correlation in early winter is clearer in the recent 30 years than that in the previous period of 1950 1979

relationship between enso and northward propagating intraseasonal oscillation in the east asian summer monsoon system 1 observational studies are presented on the relationship between el nino southern oscillation enso and the northward propagating intraseasonal oscillation npiso in the east asian summer monsoon easm system the summer npiso activity shows a significant correlation with the preceding winter extreme phase of enso cycles a higher correlation appears during late summer which is consistent with frequent heavy rainfall events at that time as revealed in some previous case studies the westward expansion of broad anticyclonic circulation over the western north pacific and the smaller cyclonic circulation around korea and japan are found to be associated with the npiso activity enso affects the late summer npiso activity through an atmospheric bridge and wave propagation the springtime indian ocean sea surface temperature warming induced by enso through the walker circulation leads to the downward motion and suppressed convection over the philippine sea and this generates the forced rossby wave train forming the above south to north low level circulation anomalies

japan unified high resolution relocated catalog for earthquakes juice crustal seismicity beneath the japanese islands abstract we have generated a high resolution catalog called the japan unified high resolution relocated catalog for earthquakes juice which can be used to evaluate the geometry and seismogenic depth of active faults in japan we relocated 1 1 million hypocenters from the nied hi net catalog for events which occurred between january 2001 and december 2012 to a depth of 40 km we apply a relative hypocenter determination method to the data in each grid square in which entire japan is divided into 1257 grid squares to parallelize the relocation procedure we used a double difference method incorporating cross correlating differential times as well as catalog differential times this allows us to resolve in detail a seismicity distribution for the entire japanese islands we estimated location uncertainty by a statistical resampling method using jackknife samples and show that the uncertainty can be within 0 37 km in the horizontal and 0 85 km in the vertical direction with a 90 confidence interval for areas with good station coverage our seismogenic depth estimate agrees with the lower limit of the hypocenter distribution for a recent earthquake on the kamishiro fault 2014 mj 6 7 which suggests that the new catalog should be useful for estimating the size of future earthquakes for inland active faults

interannual relationships between the tropical sea surface temperature and summertime subtropical anticyclone over the western north pacific 1 the interannual variability of the western north pacific subtropical high wnpsh in boreal summer is investigated with the use of the ncep ncar reanalysis data the most significant change of the 500 hpa geopotential height field appears at the western edge of the wnpsh with dominant 2 3 year and 3 5 year power spectrum peaks the 2 3 year oscillation of the wnpsh and associated circulation and sea surface temperature sst patterns possess a coherent eastward propagating feature with a warm sst anomaly ssta and anomalous ascending motion migrating from the tropical indian ocean in the preceding autumn to the maritime continent in the concurrent summer of a strong wnpsh a strong wnpsh is characterized by anomalous anticyclonic circulation and maximum subsidence in the western north pacific wnp the anomalous wnpsh circulation has an equivalent barotropic vertical structure and resides in the sinking branch of the local hadley circulation triggered by enhanced convection over the maritime continent a heat budget analysis reveals that the wnpsh is maintained by radiative cooling the 3 5 year oscillation of the wnpsh exhibits a quasi stationary feature with a warm ssta anomalous ascending motion located in the equatorial central eastern pacific and indian ocean and a cold ssta anomalous descending motion located in the western pacific the anomaly pattern persists from the preceding winter to the concurrent summer of a high wnpsh the greatest descent is located to the southeast of the anomalous anticyclone center where a baroclinic vertical structure is identified the zonal phase difference and the baroclinic vertical structure suggest that the anomalous anticyclone on this timescale is a rossby wave response to a negative latent heating associated with the persistent local cold ssta echam4 model experiments further confirm that the 2 3 year mode is driven by the ssta forcing over the maritime continent while the 3 5 year mode is driven by the local ssta in the wnp

different evolutions of the philippine sea anticyclone between the eastern and central pacific el nino possible effects of indian ocean sst abstractthe authors examine different evolution features of the low level anticyclone over the tropical northwestern pacific between eastern pacific ep el nino events and central pacific cp el nino events during ep el nino the low level anticyclone shows an eastward movement from the northern indian ocean to the east of the philippines during cp el nino however the anticyclone is mostly confined to the west of the philippines it is weaker exhibits a shorter lifetime and lacks eastward movement compared to the philippine sea anticyclone psac during ep el nino investigation into the possible impact of indian ocean io sea surface temperature sst on the evolution of the low level anticyclone during ep and cp el nino indicates that both sst and low level atmospheric circulation over the io are related more strongly with ep el nino than with cp el nino the io sst tends to exert a more prominent influence on psac during ep el nino than during cp el nino during the developing summer and autum

asymmetry in summertime atmospheric circulation anomalies over the northwest pacific during decaying phase of el nino and la nina the present study has revealed the asymmetric characteristics of summertime atmospheric circulation anomalies over the indo pacific for el nino and la nina as well as the possible mechanism during the summer when el nino has dissipated there are basin wide warming over the tropical indian ocean tio and cooling over the equatorial central and eastern pacific cep the northwest pacific nwp anticyclone is maintained by a combined effect of the tio warming and equatorial cep cooling the impact of tio warming is via the kelvin wave induced divergence mechanism and the effect of cep cooling is by stimulating a rossby wave response to its northwest correspondingly there are lower upper level convergence divergence over the tio and divergence convergence over the nwp the tropical atmospheric waves and large scale circulation anomalies could couple together and maintain the anticyclone however for la nina there are easterly wind anomalies over the equatorial western pacific and the anomalous nwp cyclone nwpc is weak and shifts northwestward which are largely different from el nino the equatorial cep cooling plays a dominant role in the maintenance of nwpc the negative rainfall anomalies induced by cep cooling force the anticyclonic wind anomalies over the wp as a rossby wave response which further cause the lower upper level convergence divergence over the mc and nwp the resultant convergence leads to the enhanced convection there inducing the nwpc as a rossby wave response besides the equatorial easterly wind anomalies trigger the upwelling oceanic kelvin wave and maintain the cep cooling as the bjerknes feedback

long range lightning geolocation using a vlf radio atmospheric waveform bank 1 lightning discharges generate broadband electromagnetic pulses with a peak component in the very low frequency vlf 3 30 khz range vlf waves propagate through the earth ionosphere waveguide with relatively low attenuation enabling the detection of these radio atmospherics at great distances from the lightning discharge a new technique of long range 6000 km global lightning geolocation via sferic detection is presented this new technique catalogs the dominant variation in expected received waveforms in a set of waveform banks which are then used to estimate the propagation distance and accurately determine the arrival time using three sensors in a trial network this new technique is used to demonstrate a median accuracy of 1 4 km depending on the time of day an overall cloud to ground cg stroke detection efficiency between 40 and 60 is estimated by correlating individual lightning stroke events to data from the national lightning detection network nldn additional events reported by the trial network are shown to have a tight spatial clustering to storm clusters identified by nldn suggesting that many of the unmatched events correspond to weak cloud to ground strokes m components or cloud pulses exploiting an empirical correlation between peak vlf field strength and peak current values reported by nldn we also provide unvalidated estimates of the peak current and lightning channel polarity the trial network does not distinguish between cloud and ground discharges so these peak current estimates only relate to an earth referenced channel current for the subset of reported events that are return strokes

combined effect of el nino southern oscillation and pacific decadal oscillation on the east asian winter monsoon using long term observational data and numerical model experiments the combined effect of the el nino southern oscillation enso and pacific decadal oscillation pdo on the variability of the east asian winter monsoon is examined in the observations it is found that when the enso and pdo are in phase combinations i e el nino positive pdo phase and la nina negative pdo phase a negative relationship between enso and east asian winter monsoon is significantly intensified in other words when el nino la nina occurs with positive negative pdo phase anomalous warm cold temperatures are dominant over the east asian winter continent on the other hand there are no significant temperature anomalies when the enso and pdo are out of phase combinations i e el nino negative pdo phase and la nina positive pdo phase further analyses indicate that the anticyclone over the western north pacific including the east asian marginal seas plays an essential role in modulating the intensity of the east asian winter monsoon under the changes of enso pdo phase relationship long lasting high pressure and warm sea surface temperature anomalies during the late fall winter and following spring over the western north pacific which appear as the el nino occurs with positive pdo phase can lead to a weakened east asian winter monsoon by transporting warm and wet conditions into the east asian continent through the southerly wind anomalies along the western flank of the anomalous high pressure and vice versa as the la nina occurs with negative pdo phase in contrast the anomalous high pressure over the western north pacific does not show a prominent change under the out of phase combinations of enso and pdo numerical model experiments confirm the observational results accompanying dominant warm temperature anomalies over east asia via strong anticyclonic circulation anomalies near the philippine sea as the el nino occurs with positive pdo phase whereas such warming is weakened as the el nino occurs with negative pdo phase this result supports the argument that the changes in the east asian winter monsoon intensity with enso are largely affected by the strength of the anticyclone over the western north pacific which significantly changes according to the enso pdo phase relationship

origins of biases in cmip5 models simulating northwest pacific summertime atmospheric circulation anomalies during the decaying phase of enso abstractpresent study documents the biases of summertime northwest pacific nwp atmospheric circulation anomalies during the decaying phase of enso and investigates their plausible reasons in 32 coupled model intercomparison project phase 5 models based on an inter model empirical orthogonal function eof analysis of el nino southern oscillation enso related 850hpa wind anomalies the dominant modes of biases are extracted the first eof mode explaining 21 3 of total inter model variance is characterized by a cyclone over the nwp indicating a weaker nwp anticyclone the cyclone appears to be a rossby wave response to unrealistic equatorial western pacific wp sea surface temperature sst anomalies related to excessive equatorial pacific cold tongue in the models on one hand the cold sst biases increase the mean zonal sst gradient which further intensifies warm zonal advection favoring the development and persistence of equatorial wp sst anomalies on the other hand they reduce the anomalou

perturbations of midlatitude subionospheric vlf signals associated with lower ionospheric disturbances during major geomagnetic storms 1 we examine the effects on the midlatitude ionospheric d region of the 7 april 2000 storm and the halloween storm of late october 2003 by means of the associated perturbations of several subionospheric vlf signals propagating in both the northern and southern hemispheres we use vlf nighttime data from the holographic array for ionospheric lightning research hail located in the united states l 2 3 as well as data from palmer station antarctica l 2 4 on 7 april 2000 a 5 db depression in vlf amplitudes is observed at multiple hail stations with a depression onset that occurs later for vlf signal paths at lower latitudes on both 7 april 2000 and 31 october 2003 fluctuations in the amplitude of the vlf signals are first observed in the premidnight sector and persist through the end of the data recording period dawn the frequency content of the fluctuations is predominantly in the 0 01 to 0 02 hz range but extends up to 0 03 hz increases in the energetic electron flux in the loss cone as measured by the noaa poes satellites are observed on both 7 april 2000 and 31 october 2003 we suggest that both the signal depressions and subsequent fluctuations are associated with variations in the precipitation flux of energetic electrons onto the upper atmosphere auroral activity patterns based on data from the noaa poes satellites show that the equatorward edge of the auroral oval expanded equatorward to lower l shells l 3 during both geomagnetic storms using the auoral activity patterns and multiple vlf lf signal paths we provide evidence that the fluctuations and the signal depression coincide with the equatorward edge of the auroral oval extending over the perturbed vlf lf great circle paths quantitative modeling of subionospheric vlf wave propagation incorporating energetic electron flux measurements and the associated altitude profiles of secondary ionization yields results consistent with the variations in the vlf signal amplitude observed

rapid termination of the 2006 el nino and its relation to the indian ocean 1 we investigated the rapid termination of the 2006 el nino using observed data and a coupled ocean atmosphere general circulation model cgcm observed data showed development of an anomalous south indian ocean sio anticyclone associated with the concurrent indian ocean dipole during september november 2006 at the end of 2006 the eastward retreat of the sio anticyclone in response to the indian ocean warming generated an easterly anomaly over the western pacific and the resultant oceanic upwelling kelvin wave terminated the el nino cgcm experiments indicated that the formation of the sio anticyclone was influenced remotely by the pacific ocean sst anomalies and that the easterly anomaly over the western pacific at the end of 2006 was reinforced by the indian ocean sst anomalies these results suggest that interactive feedback between the indian and pacific oceans helped the rapid termination of the 2006 event

the vlf fingerprint of elves step like and long recovery early vlf perturbations caused by powerful cg lightning em pulses 1 subionospheric vlf recordings are investigated in relation with intense cloud to ground cg lightning data lightning impacts the lower ionosphere via heating and ionization changes which produce vlf signal perturbations known as early vlf events typically early events recover in about 100 s but a small subclass does not recover for many minutes known as long recovery early events lore in this study we identify lore as a distinct category of early vlf events whose signature may occur either on its own or alongside the short lived typical early vlf event since lore onsets coincide with powerful lightning strokes of either polarity we infer that they are due to long lasting ionization changes in the uppermost d region ionosphere caused by electromagnetic pulses emitted by strong cg lightning peak currents of typically 250 ka which are also known to generate elves the lore perturbations are detected when the discharge is located within 250 km from the great circle path of a vlf transmitter receiver link the probability of occurrence increases with stroke intensity and approaches unity for discharges with peak currents 300 ka lores are nighttime phenomena that occur preferentially at least in the present regional data set during winter when strong cg discharges are more frequent and intense the evidence suggests lore as a distinct signature representing the vlf fingerprint of elves a fact which although was predicted by theory it escaped identification in the long going vlf research of lightning effects in the lower ionosphere