observations of rossby waves linked to convection over the eastern tropical pacific rossby wave activity propagating into the eastern tropical pacific from the midlatitudes during northern winter is examined in some detail these waves are associated with the intrusion of high potential vorticity air into low latitudes and they modulate cloudiness stability and vertical motion in the vicinity of the itcz in the upper troposphere and lower stratosphere the horizontal phase and group propagation of the wave activity are qualitatively like those of a nondivergent barotropic rossby wave as the waves move equatorward they become more shallow and propagate upward into the stratosphere the horizontal and vertical propagation is consistent with the tilts of the waves the large scale three dimensional background flow and with the signatures of momentum and heat fluxes associated with the wave activity in the lower troposphere paired cyclonic anomalies on either side of the equator accompany the upper level wave activity to the west of the itcz cloudiness signal these waves amplify following the peak in the itcz cloudiness and propagate westward along the equator this suggests that the upper level wave activity and possibly the associated convective heating can trigger the excitation of the equatorially trapped rossby modes the transient wave activity appears to be a crucial component of the momentum balance of the eastern tropical pacific circulation there is substantial interannual variability in the wave activity consistent with observed changes in the large scale basic state associated with the southern oscillation

upstream subtropical signals preceding the asian summer monsoon circulation in this study the authors address several issues with respect to the antecedent signals of the large scale asian summer monsoon that were earlier identified by webster and yang in particular they revisit the changes in the subtropical upper tropospheric westerlies preceding the monsoon depict the detailed structure of the monsoon s antecedent signals and investigate the physical processes from the signals to the monsoon they also explore the teleconnection of these signals to various large scale climate phenomena and emphasize the importance of the upstream location of the signals relative to the tibetan plateau and the monsoon before a strong weak asian summer monsoon the 200 mb westerlies over subtropical asia are weak strong during the previous winter and spring a significant feature of these signals is represented by the variability of the middle east jet stream whose changes are linked to the arctic oscillation north atlantic oscillation el

two types of strong northeast asian summer monsoon the characteristics of a strong northeast asian summer monsoon neasm with and without a and b type respectively a basinwide warming in the indian ocean during the preceding winter are examined for the period of 1979 2006 in the case of the a type strong el nino like sea surface temperature sst decays very rapidly from the preceding winter december february to the following summer june august which may be due to a feedback process of the warm indian ocean in addition the a type strong neasm is more associated with a weak western north pacific summer monsoon than the b type strong neasm on the other hand for the b type an el nino like sst during the preceding winter is a persistent influence into the following summer a striking difference can be found in the atmospheric teleconnection pattern from the tropics to the midlatitudes over the indo pacific region that is the pacific japan like pattern versus a pronounced rossby wave train pattern this may result from the difference in location of the maximum center of rainfall anomalies over the tropical northwestern pacific between the two types of strong neasm the authors argue that indian ocean basin warming plays a role in modifying the convective system over the subtropical western pacific resulting in changes in atmospheric teleconnections between the two types of strong neasm the weak neasm in which the anomalous rainfall pattern resembles that of the a type strong neasm except for the sign is also discussed

thermal contrast between the middle latitude asian continent and adjacent ocean and its connection to the east asian summer precipitation abstract to analyze the middle to lower troposphere atmospheric thermal contrast between the middle latitude over the asian continent and over its eastern adjacent ocean near japan an empirical orthogonal function eof analysis of the 40 yr ecmwf re analysis era 40 data of the june august jja 500 hpa geopotential height over the asia pacific area 10 80 n 60 180 e during 1958 2000 was done it shows that the dominating pattern of the thermal contrast may well be represented by a seesaw of 500 hpa geopotential height anomalies between a land area 40 55 n 75 90 e and an oceanic area 35 42 5 n 140 150 e an index showing the difference between the two areas is defined as the middle latitude land sea thermal contrast index lsi the lsi has significant interannual and interdecadal variability its interannual variation is mainly attributed to the atmospheric thermal condition over the ocean which has a remarkably regional unique feature while the interdecadal variability is greatly a

on the interannual variability of the bonin high associated with the east asian summer monsoon rain in order to assess how the bonin high affects interannual variability of the east asian summer monsoon easm around the korean peninsula the pulsation of the bonin high and its association with teleconnection patterns was examined the major factor for the interannual intensity of the easm is the center position of the bonin high rather than its center pressure up to 12 harmonics over time can be used to reconstruct the bonin high demonstrating its intraseasonal variation the interannual variability of the bonin high correlates with the tibet high this correlation is dominant for the easm onset time though not its retreat the primary teleconnection pattern reliant up on the interannual variability of the bonin high is the western pacific oscillation wpo in april in relation to long term variability the correlation between the wpo and the bonin high appears to contribute to the retreat stage of the easm which has itself increased since the mid 1970s furthermore the wpo in may and the tibet correlation has marked the onset rather than the retreat of the easm since the 1970s this highly correlated pattern since the mid 1970s may be the result of el nino

connections between potential vorticity intrusions and convection in the eastern tropical pacific abstract the connections between intrusions of stratospheric air into the upper troposphere and deep convection in the tropical eastern pacific are examined using a combination of data analysis potential vorticity pv inversion and numerical simulations analysis of ncep ncar reanalyses and satellite measurements of outgoing longwave radiation during intrusion events shows increased cloudiness lower static stability upward motion and a buildup of convective available potential energy cape at the leading edge of the intruding tongue of high pv potential inversion inversion calculations show that the upper level pv makes the dominant contribution to the changes in the quantities that characterize convection this supports the hypothesis that upper level pv anomalies initiate and support convection by destabilizing the lower troposphere and causing upward motion ahead on the pv tongue the dominant role of the upper level pv is confirmed by simulations using the fifth generation pennsylvania state u

an air mass with high potential vorticity preceding the formation of the marcus convergence zone 1 we examined the convective activity and dynamical field over the subtropical north pacific by focusing on the relationship between upper cold lows ucls and the formation of the marcus convergence zone mcz in mid july we detected a ucl near marcus island that was associated with the formation of the mcz the convective activity associated with the mcz followed the ucl implying that the ucl contributed to the mcz formation analysis of the temporal evolution of the dynamic field revealed that the ucl appeared in a large scale high potential vorticity pv air mass migrating from the east we had already identified the high pv region near the mid pacific trough in late july it stretched westward and reached marcus island in mid july suggesting that the ucl in the high pv air mass over the north pacific contributed to the formation of the mcz

dynamical processes related to the appearance of the okhotsk high during early midsummer abstract the authors identified an upper level pressure anomaly pattern corresponding to the interannual variability of the okhotsk high in midsummer late july and early august as a predominant anomaly pattern in the northern hemisphere by using objectively analyzed data according to the results of empirical orthogonal function eof analyses and composite analyses a positive pressure anomaly appeared near the tropopause over eastern siberia in years with strong okhotsk highs examination of the heat budget in the lower troposphere revealed that a negative surface temperature anomaly observed in northern japan was brought by the advection of the climatological temperature gradient from the anomalous wind associated with the upper level anticyclonic anomaly it was also demonstrated that the anomaly field over siberia does not accompany predominant vorticity forcing or rossby wave propagation from the west with a specific phase however positive kinetic energy conversion from the climatological basic

northwestward propagation of the intraseasonal oscillation in the western north pacific during the boreal summer structure and mechanism abstract the convection of the intraseasonal timescale in the western north pacific during the boreal summer tends to propagate northwestward in the philippine sea to near 20 n and then continues propagating westward the formation of enhanced convection in the western north pacific is a result of the merging of a convective system moving eastward along the equator and a westward propagating low level convergence anomaly which is located to the east of a vortex in the subtropics a positive feedback between the anomalous circulation and convection leads to a rapid enhancement of the system the strengthened southwesterly associated with the vortex enhances evaporation over the oceans e g the eastern indian ocean the bay of bengal and the south china sea and transports moisture northeastward the moisture converges at the northwestern corner of the convection and results in a potentially unstable atmosphere the result is the northwestward propagation of the coupled circulation convection system in

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

a new method of seismic site classification using hvsr curves a case study of the 12 november 2017 mw 7 3 ezgeleh earthquake in iran abstract on the 12th of november 2017 a strong earthquake with a moment magnitude of 7 3 struck the west of iran causing massive damage in sarpolezahab and surrounding areas in this study the horizontal to vertical spectral ratio hvsr or h v technique of strong ground motion recorded at 60 stations is used for identifying of site response and subsequent site classification very clear amplification is observed at stiff and soft soil sites empirical equations from the literature relating frequency of hvsr peak to average shear wave velocity in the upper 30m vs30 commonly used as a proxy for site classification were found to be unreliable making site classification difficult to overcome this problem a soft computing method based on the generalized regression neural networks grnn algorithm is used this algorithm relies on hvsr curves at the recording stations and uses pattern recognition against a set of pre defined curves for different site types in this approach site characterization is based on the overall features of the hvsr curves rather than just the peak frequency the stations are classified into four different site classes and the results are consistent with local geotechnical information where available rather than relying on vs30 which has been found deficient in many studies and is known to have difficulty in reliably estimating when geotechnical data is lacking site classification proposed in this study uses the overall characteristics of hvsr curves of response spectra of recorded strong motion data this method is proposed as a more reliable and direct method for site characterization in seismically hazardous regions

degree of magnetic anisotropy as a strain intensity gauge in ferromagnetic granites anisotropy of magnetic susceptibility data for a ferromagnetic granite godhra granite nw india are presented and it is shown that the degree of magnetic anisotropy p is not controlled by the mean susceptibility k m analyses carried out across a high strain zone lying between granite and adjacent gneiss show that p values are highest in samples that lie close to the contact and decrease away from it based on these results it is concluded that if p is not controlled by k m then the former can be used to gauge strain intensity variations in ferromagnetic granites

multi stage onset of the summer monsoon over the western north pacific the climatological summer monsoon onset displays a distinct step wise northeastward movement over the south china sea and the western north pacific wnp 110 160 e 10 20 n monsoon rain commences over the south china sea philippines region in mid may extends abruptly to the southwestern philippine sea in early to mid june and finally penetrates to the northeastern part of the domain around mid july in association three abrupt changes are identified in the atmospheric circulation specifically the wnp subtropical high displays a sudden eastward retreat or quick northward displacement and the monsoon trough pushes abruptly eastward or northeastward at the onset of the three stages the step wise movement of the onset results from the slow northeastward seasonal evolution of large scale circulation and the phase locked intraseasonal oscillation iso the seasonal evolution establishes a large scale background for the development of convection and the iso triggers deep convection the iso over the wnp has a dominant period of about 20 30 days this determines up the time interval between the consecutive stages of the monsoon onset from the atmospheric perspective the seasonal sea surface temperature sst change in the wnp plays a critical role in the northeastward advance of the onset the seasonal northeastward march of the warmest sst tongue sst exceeding 29 5 c favors the northeastward movement of the monsoon trough and the high convective instability region the seasonal sst change in turn is affected by the monsoon through cloud radiation and wind evaporation feedbacks

the information content of high frequency seismograms and the near surface geologic structure of hard rock recording sites due to hardware developments in the last decade the high frequency end of the frequency band of seismic waves analyzed for source mechanisms has been extended into the audio frequency range 20 hz in principle the short wavelengths corresponding to these frequencies can provide information about the details of seismic sources but in fact much of the signal is the site response of the nearsurface several examples of waveform data recorded at hard rock sites which are generally assumed to have a flat transfer function are presented to demonstrate the severe signal distortions includingfmax produced by near surface structures analysis of the geology of a number of sites indicates that the overall attenuation of high frequency 1 hz seismic waves is controlled by the whole path q between source and receiver but the presence of distinctfmax site resonance peaks is controlled by the nature of the surface layer and the underlying near surface structure models of vertical decoupling of the surface and nearsurface and horizontal decoupling of adjacent sites on hard rock outcrops are proposed and their behaviour is compared to the observations of hard rock site response the upper bound to the frequency band of the seismic waves that contain significant source information which can be deconvolved from a site response or an array response is discussed in terms offmax and the correlation of waveform distortion with the outcrop scale geologic structure of hard rock sites it is concluded that although the velocity structures of hard rock sites unlike those of alluvium sites allow some audio frequency seismic energy to propagate to the surface the resulting signals are a highly distorted limited subset of the source spectra

upper tropospheric forcing on late july monsoon transition in east asia and the western north pacific abstractby investigating the large scale circulation in the upper troposphere it is demonstrated that the rapid late july summer monsoon transition in the east asia and western north pacific ea wnp is associated with a weakened westerly at the exit of the east asian jet stream eajs even in a normally stable atmosphere under the influence of the north pacific np high in late july convection rapidly develops over the midoceanic region of the western np 15 25 n 150 170 e prior to the rapid transition the eajs weakens and shifts northward which induces a series of changes in downstream regions the northeastern stretch of the asian high weakens upper tropospheric divergence in the region southwest of the mid np trough increases and convection is enhanced at the monsoon transition upper level high potential vorticity intrudes southward and westward convection expand from the mid np westward to cover the entire subtropical western np the lower tropospheric monsoon trough deepens surface

summer monsoon onset in the subtropical western north pacific 1 monsoon onset in july over the subtropical western north pacific swnp 15 25 n 130 150 e is investigated by focusing on the westward movement of cloudy region east of the swnp which is associated with high vorticity in the upper troposphere at least in seven of the 22 years between 1985 and 2006 the arrival of clouds at the swnp from the east coincides with a significant change in the upper tropospheric circulation and a rapid northeastward extension of strong convections from the tropical western north pacific which essentially is monsoon onset before the monsoon onset the sea surface temperature sst increases but winds remain divergent over the swnp right after the monsoon onset winds turn convergent and convections enhance leading to a rapid decrease of surface heating and sst it is suggested that westward moving upper level disturbances might trigger onset of monsoon in july when low level atmospheric conditions favor development of deep convections

evolution and dynamics of summertime blocking over the far east and the associated surface okhotsk high time evolution and dynamics of an upper level blocking ridge over the far east and the associated surface high over the sea of okhotsk that give rise to abnormal summertime coolness over eastern japan are investigated through a composite analysis applied to distinct surface high events the formation mechanism and vertical structure of the blocking differ fundamentally between may and july attributable to seasonal changes in the jet structure storm track activity over the far east and the land sea thermal contrast within the okhotsk region in may forcing from migratory eddies is strong enough for precursory anticyclonic anomalies retrograding slowly over the north pacific to develop into a blocking ridge the ridge remains equivalent barotropic under the weak land sea thermal contrast in the okhotsk region in contrast the eddy forcing is no longer the primary factor for the blocking formation in july in the presence of the weakened and split westerlies rather the propagation of a stationary rossby wave packet that has emanated from precursory anticyclonic anomalies over northern europe stagnates over the far east and the subsequent local breaking of the packet leads to the blocking formation in a particular case in july 1993 a wave packet involved in blocking formation could be traced back as far upstream as the east coast of north america over the two previous weeks acting on the strong thermal contrast in july between the cool sea surface and a warm land mass to the west the anomalous surface easterlies induced by the blocking ridge can build up a cold surface anticyclone through cold advection rendering the blocking anomalies distinctly baroclinic copyright 2004 royal meteorological society

quaternary negative tectonic inversion along the sibillini mts thrust zone the arquata del tronto case history central italy geological and geophysical investigations have been carried out in the surroundings of the villages of pretare and piedilama in the central apennines this area located at the footwall of the prominent nne ssw oriented sibillini thrust front was struck by the august 24th 2016 mw 6 earthquake the results of the geological field survey combined with geological and geophysical subsurface investigations are here illustrated by a detailed geological map and by two significant cross sections the studied area is crossed by the fosso di morricone valley that entrenched within the messinian pelitic arenaceous succession of the laga formation hosts a late pleistocene palaeo landslide the study evidences the occurrence of a n 10 oriented west dipping normal fault here named pretare piedilama fault that controlled the left side of the fosso di morricone valley producing a vertical displacement of the palaeo landslide deposits of about 50 m the geological geomorphological and geophysical data indicate that the fault was active during the late pleistocene and part of the holocene thus constraining a minimum vertical displacement rate of 0 4 mm a in the last 125 ka the geometry of the deformed laga formation cut by the fault suggests to relate it to the late quaternary negative tectonic inversion of a previous thrust plane located in the footwall of the sibillini thrust front the pretare piedilama fault would represent the easternmost tectonic expression of this main potentially active structure future researches could be addressed to detail the age and the actual motion rate of the structure and to define its seismic hazard assessment

layer wise attribution of vertical motion and the influence of potential vorticity anomalies on synoptic development a methodology is presented for attributing vertical motion to potential vorticity pv in a explicit manner using the quasi geostrophic omega equation the methodology is then used to determine the contribution individual pv anomalies make to the synoptic development it is shown how the total vertical motion may be decomposed into self generating and interaction terms the former correspond to vertical motion that arises from one pv region alone whilst each of the interaction terms represent vertical motion due to the interaction of two different regions of pv the method is applied to a number of cyclones studied in the fronts and atlantic storm tracks experiment in order to determine the dynamical role of individual pv regions in cyclogenesis for purposes of comparison cyclones were chosen to be representative of the types a b and c of an extended petterssen smebye scheme devised by deveson browning and hewson in terms of our new pv method the type a and b cyclones exhibit only subtle differences with the upper level layer of pv playing a larger role in the case of the type b cyclone a much larger difference is apparent between the type a and b cyclones on the one hand and the type c cyclone on the other in the type c cyclone the upper level pv self generating term plays an important role whereas in the type a and b cases the influence of the upper level pv is largely restricted to the interaction terms in all of the cases the vertical motion attributable to the interaction between the low level pv and boundary thermal gradient was found to be large hence from the viewpoint of instantaneous attribution we conclude that the low level pv is always important copyright 2003 royal meteorological society

are microtremors useful in site response evaluation we have reviewed the applicability of microtremor measurements to evaluate site response of soft soils to this end we evaluated three different techniques commonly used to estimate site effects from microtremor measurements interpretation of fourier amplitude spectra computation of spectral ratios relative to a firm reference station and finally computation of spectral ratios of horizontal components relative to the vertical component of ground motion nakamura s technique these techniques are applied to microtremor records obtained in three cities in mexico mexico city oaxaca and acapulco these cities differ in their local geological conditions and in their seismotectonic environment in order to evaluate the results obtained from microtremor measurements we compare them with standard spectral ratios of the intense s wave part of weak or strong motion records obtained at the same sites our results showed that microtremor measurements can be used to estimate the dominant period of a site with very acceptable reliability in the range 0 3 to 5 hz the best results were obtained with nakamura s technique which also gives a rough estimate of amplification of seismic waves when the local geology is relatively simple simple numerical simulations indicate that the underlying assumptions of nakamura s technique are consistent with the propagation of rayleigh waves these simple numerical simulations also explain why different researchers have been able to successfully characterize 1d site effects using microtremor records regardless of whether they consider microtremors to consist of surface or body waves our results strongly suggest that the technique by nakamura effectively compensates for source effects in microtremor measurements which eliminates a major limitation to their application in earthquake engineering

seasonal evolution of the upper tropospheric westerly jet core over east asia the location change of the westerly jet core at upper troposphere in june and july is investigated by using the ncep ncar reanalysis data the results show that the location of the westerly jet core changes rapidly from 140 e to 90 e during 35th 39th pentads which corresponds to the plum rain period over east asia the location change of the jet core is actually the relative intensity change of the different westerly jet centers the meridional temperature contrast in the troposphere is associated with the rapid location change of the jet core the diabatic heating changes are the primary factor determining the seasonal evolution of the westerly jet core over east asia

site effects close to structural lineaments in eastern sicily italy abstract this paper analyses site effects that are applied to compute the h v spectral ratio close to structural lineaments aseismic creep and seismic creep have been examined the lineaments are located in different types of volcanic soil the aim of the work is to verify the possibility of fault guided seismic waves within the structures which behave as a waveguide for trapped waves the measurements of ambient noise were carried out along profiles crossing the structures and the standard nakamura technique was applied to calculate the spectral h v ratio it was observed that horizontal components of ground motion were found to be significantly amplified within the shear zone