a record of holocene climate change in the guanzhong basin china based on optical dating of a loess palaeosol sequence optical dating was used to obtain a chronology for a loess palaeosol sequence in the guanzhong basin on the loess plateau in china the sedimentary sequence recorded two dry episodes 3 7 2 4 ka and 1 2 0 8 ka ago in the holocene as shown by the presence of two layers of loess within the holocene deposits these two arid events are consistent with records of global climate change in the holocene and also coincident with major historic events in china this finding suggests that loess paleosol sequences in china can record global climate changes and implies that rapid climate change affected the progress of human civilization in addition changes in the sedimentation rate through the section suggest that agricultural expansion may have accelerated the rate of dust accumulation

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

moment magnitude relations based on strong motion records in greece in this work the variation of the local magnitude mlsm derived from strong motion records at short distances is examined in terms of moment magnitude m w strong motion data from greek earthquakes are used to determine the strong motion local magnitude mlsm by performing an integration of the equation of mo tion of the wood anderson wa seismograph subjected to an input acceleration the most reliable strong motion data are utilized for earthquakes with seismic mo ments log m 0 22 0 dynecm and calculated local magnitudes mls m 3 7 the correlation between the seismic moments log m0 and the calculated local magni tudes mlsm using strong motion records is given by log m 0 1 5 mcsu 16 07 which is very similar to that proposed by hanks and kanamori 1979 moreover it is shown that mls m is equal to moment magnitude mw for a large mls m range 3 9 to 6 6 comparison of the strong motion local magnitude and the me magnitude estimated in greece ml n and surrounding area shows a systematic bias of 0 4 to 0 5 similar to the difference that has been found between m w and mlgr for the same area the contribution of the local site effects in the calculation of the local magni tude mlsm is also considered by taking into account two indices of soil classification namely rock and alluvium or the shear wave velocity vs30 of the first 30 m based on nehrp 1994 and ubc 1997 an increase of mls m by 0 16 is observed for alluvium sites alternative relations showing the mls m variation with v 3 are also presented finally examination of the wa amplitude attenuation log a0 with distance shows that the jennings and kanamori 1983 relation for a 100 km is appropriate for greece the same results confirm earlier suggestions that the 0 4 to 0 5 bias between mlgr and mw also mlsa4 should be attributed to a low static magnification 800 of the athens wa instrument on which all other m l relations in greece have been calibrated

a high resolution one layer model of breaking planetary waves in the stratosphere numerical integrations of a one layer hemispheric model of the winter stratosphere have been carried out at very high resolution of the order of a fraction of a degree of latitude the numerical experiments simulate planetary wave breaking and polar vortex erosion under conditions far closer to the real winter stratosphere than those assumed in earlier critical layer models the model has implications for stratospheric photochemistry and the antarctic ozone hole problem

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

a mid european decadal isotope climate record from 15 500 to 5000 years b p oxygen isotope ratios of precipitation delta18op inferred from deep lake ostracods from the ammersee southern germany provide a climate record with decadal resolution the record in detail shows many of the rapid climate shifts seen in central greenland ice cores between 15 000 and 5000 years before the present b p negative excursions in the estimated delta18op from both of these records likely reflect short weakenings of the thermohaline circulation caused by episodic discharges of continental freshwater into the north atlantic deviating millennial scale trends however indicate that climate gradients between europe and greenland changed systematically reflecting a gradual rearrangement of north atlantic circulation during deglaciation

cross equatorial response to middle latitude forcing in a zonally varying basic state abstract a nonlinear model based on the shallow water equations is used to study cross equatorial propagation of forced waves in the presence of a longitudinally varying time mean basic state zonal wind field it is found that global scale planetary waves are unable to propagate past a critical latitude where the mean zonal wind speed vanishes however if the longitudinally asymmetric basic state includes a duet in which the zonal winds are westerly waves of zonal scale less than the zonal scale of the westerly duct may propagate from one hemisphere to the other even though the zonally symmetric mean zonal wind remains easterly in the equatorial region the amplitude of the response in one hemisphere to forcing in the opposite hemisphere increases strongly with the magnitude of the westerlies in the equatorial duct the existence and annual variations of a westerly duct region in the upper troposphere in the eastern pacific appear to account for some features of the low frequency variability in the no

seismic source parameter relations for earthquakes in greece a data set of nineteen mainly shallow moderate to large earthquakes which occurred in the aegean and the surrounding area has been used to derive empirical relations for kinematic fault parameters thus the relations between seismic momentm 0 and magnitudem s andm b and betweenm 0 andm s and fault dimensionss andl have been determined from these relations and theoretical ones it was deduced that earthquakes in the aegean and the surrounding events chiefly interplate are characterized by low average stress drop values values of ranging from 1 to 30 bar are consistent with the data it was also found that in general terms most of the data obey the geometrical similarity conditionl 2w wherel is the fault length measured along the strike andw is its width measured along the dip for strike slip faults however the conditionl 4w seems to hold

the ustic isohumisol chernozem distributed over the chinese loess plateau modern soil or palaeosol abstract the ustic isohumisol chernozem widely distributed over the chinese loess plateau is classified as a modern soil by agricultural pedologists and as a palaeosol by geoscientists high resolution investigations into this soil including field observations element analysis optically simulated luminescence dating and measurements of magnetic susceptibility and particle size distribution were carried out over the plateau uplands the results show that the formation of physico chemical properties and development of the soil profiles has kept pace with the land surface growth because of incessant dust accumulation during the holocene the continuously intensified weathering of accumulated dust from 11 500 a b p had resulted in an increased chemical differentiation through time during the early holocene the development of the ustic isohumisol occurred over the uplands between 8500 and 3100 a b p when the chemical differentiation reached its maximum because of increased precipitation and ample soil moisture in response to the mid holocene climatic optimum the soil formation had sustained for ca 5400 years and ceased at 3100 a b p a major pedogenic regression occurred from 3100 a b p because of climatic aridity and intensified dust accumulation over the loess plateau the newly accumulated loess and topsoil has the ustic isohumisol buried at a depth of ca 50 80 cm in general the pedogenic regression has been intensified by incorporation of the reworked components by increased runoff and erosion redeposition large scale land reclamation extended to the uplands at ca 2170 a b p an agricultural landscape of dry farming has formed since ca 1500 a b p thereafter the present topsoil has accumulated and has been affected by the intensified cultivation and addition of barnyard manure in history the solubles are retained in the topsoil because of dry climate and scant soil moisture

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

source parameters of some large earthquakes in the eastern mediterranean region based on an itertive maximum entropy technique teleseismicp waves of some large earthquakes that occurred in the eastern mediterranean region have been analysed by using an iterative maximum entropy technique in order to obtain the independent spectral parameters the long period spectral level 0 and the corner frequencyf0 of the far field displacement spectra

a regional aridity phase and its possible cultural impact during the holocene megathermal in the guanzhong basin china evidence of climatic variations and the impact of past farming was identified in a holocene loess profile near xi an in the guanzhong basin china detailed studies of the profile indicate that crop cultivation began at 7000 yr bp in the neolithic and carried on to present in the area disturbance of the profile by cultivation has not masked evidence of changes in aeolian dust deposition and bio pedogenic processes caused by climatic variations increased dust deposition indicates that a remarkable aridity phase occurred from 6000 to 5000 yr bp during the holocene megathermal 8500 3000 yr bp the aridity and intensified aeolian dust deposition interrupted the formation of the brown soil developing under a warm humid subtropical climate during the megathermal the palaeosol s0 normally associated with the megathermal period is thus separated into two distinct soils namely s01 and s02 this variability in megathermal climate may have been widespread across northwestern china it is also possible that t

the tropical extratropical interaction between high frequency transients and the madden julian oscillation abstract the interaction between high frequency transient disturbances and convection and the madden julian oscillation mjo is investigated using ncep ncar reanalysis and satellite outgoing longwave radiation data for 15 northern winters during the phase of the mjo with enhanced convection over the east indian ocean and indonesia and suppressed convection over the south pacific convergence zone both the asian pacific jet and the region of upper tropospheric tropical easterlies over the warm pool are displaced westward these changes in the basic state lead to a weaker or leakier waveguide in the asian pacific jet with a westward displaced forbidden region of tropical easterlies such that high frequency transient waves propagate equatorward into the deep tropics over the central pacific near the date line as these waves induce convection in the region of ascent and reduced static stability ahead of the upper level cyclonic disturbances there is an enhancement of high frequency convective var

holocene environmental change inferred from the loess palaeosol sequences adjacent to the floodplain of the yellow river china abstract chinese loess deposits are generally considered to be the product of dust storms and dust falls from the central asia arid zones that were transported across china by the northwesterly continental monsoon in contrast the zhengzhou loess found southeast of the loess plateau adjacent to the floodplain of the yellow river records a different eolian regime and dust source the zhengzhou loess was investigated by field observations measurements of magnetic susceptibility particle size distribution loss on ignition caco3 and chemical contents both field observations and the laboratory results indicate that during the last glacial the zhengzhou loess was supplied by two different eolian regimes and dust sources one was from the fresh flood deposits of the yellow river driven by the northeast winds from the low lying floodplain and the other was from the dust storms and dust falls that traveled across the loess plateau driven by the northwesterly continental monsoon from the central asian arid lands the early holocene 11 500 8500 a bp was a transition during the change in eolian regime and dust source because of the weakened northwesterly monsoon along with the global climatic amelioration following the retreat of the northwesterly monsoon from the onset of the mid holocene climatic optimum at 8500 a bp dust supply from the drifting sand zone on the yellow river floodplain became dominant because of the intensified strength of the northeast winds from the bohai sea from 3100 a bp onwards climatic aridity and extensive human disturbance have resulted in intensive eolian processes causing the incursion of the drifting sand into the zhengzhou loess zone these results show that loess accumulation is more complex than traditionally assumed the origin of loess deposits elsewhere outside the loess plateau may be related to dust sources derived from alluvial sediments of major river systems

a soil chronosequence in the semi arid environment of patagonia argentina abstract soil development with time was investigated on beach ridges with ages ranging from about 1380 to 6240 14c years bp at the eastern coast of central patagonia the main pedogenic processes are accumulation of organic matter and carbonate leaching and accumulation within the upper part of the soils soil formation is strongly influenced by incorporation of eolian sediments into the interstitial spaces between the gravel of which the beach ridges are composed different amounts of eolian material in the soils lead to differentiation into leptosols containing 10 fine earth in the upper 75 cm and regosols containing 10 fine earth soil depth functions and chronofunctions of organic carbon calcium carbonate ph ca zr mg zr k zr na zr fe zr mn zr and si al obtained from x ray fluorescence analysis were evaluated to establish soil chronofunctions mean values of the horizon data of 0 10 cm below the desert pavement were used which were weighted according to the horizon thicknesses the depth function of ph shows a decrease towards the surface indicating leaching of bases from the upper centimeters chronofunctions of ph show that within 6000 radiocarbon years of soil development ph drops from 7 0 to 6 6 in the leptosols and from 8 1 to 7 5 in the regosols the higher ph of the regosols is due to input of additional bases from the eolian sediments chronofunctions of ca zr and k zr indicate progressive leaching of ca and k in the regosols showing close relationships to time r2 0 972 and 0 995 na leaching as indicated by decreasing na zr ratios shows a strong correlation to time only in the leptosols r2 0 999 both leptosols and regosols show close relationships to time for fe zr r2 0 817 and 0 824 mn zr r2 0 940 and 0 803 and si al 0 971 and 0 977 indicating enrichment of fe and mn and leaching of si leaching of mobile elements takes place on a higher level in the regosols than in the leptosols from the beginning of soil formation hence a significant part of the eolian sediments must have been incorporated into the beach ridges very soon after their formation

holocene colluviation and its implications for tracing human induced soil erosion and redeposition on the piedmont loess lands of the qinling mountains northern china abstract colluvial components incorporated in loess soil sequences have preserved evidence of soil erosion and redeposition in the middle reaches of the yellow river drainage basin holocene loess soil sequences on the gentle sloped lands were studied by measuring magnetic susceptibility particle size distribution caco3 and extraction and identification of the non dust materials the analytical results indicate that in the early holocene soil erosion and redeposition by overland flow occurred even on the loess lands with small ground gradient in response to climatic amelioration linked to global climatic change no obvious soil erosion and redeposition events were found to correspond with the climatic fluctuations recorded in the loess soil sequence during the holocene climatic optimum the primary neolithic farming did not cause apparent erosion and redeposition because the loess landscape was mantled by well developed ustic luvisols and probably by forest vegetation both provided adequate resistance to sheet erosion by overland flow enhanced soil erosion and redeposition are traceable back to ca 4000 a b p it is attributed to intensified land use of arable farming and human settlement from the early bronze age onward a major event of sheet erosion and redeposition by overland flow occurred in the loess landscape during 4000 3600 a b p in the xia dynasty soil degradation and reduced resistance caused by climatic aridity and intensified dust accumulation may have played a secondary role in promoting soil erosion since 3100 a b p these results provide new insights into the history of soil erosion in the semi arid and semi humid loess regions and into the evaluation of human induced accelerated soil erosion against the background of the holocene natural erosion forced by monsoonal climatic fluctuation

an early holocene erosion phase on the loess tablelands in the southern loess plateau of china abstract a holocene loess profile to the west of xi an china was studied multi disciplinarily to investigate the relationships between soil erosion and monsoonal climatic change the proxy data obtained from this aeolian loess and palaeosol sequence indicate large scale variations of climate in the southern loess plateau since the last glaciation a rainwash bed indicative of a wetter climate excessive runoff and erosion on the loess tablelands was identified relating to the early holocene before the onset of the climatic optimum this is synchronous with the early holocene physiographic erosional stage identified in the valleys in north china it means that severe erosion took place when the region was undergoing climatic amelioration during the early holocene the evidence presented in this paper shows that the erosion occurred as a regional response to a monsoonal climatic shift in the southern loess plateau during the last glaciation prior to the erosion phase the land surface on the tablelands had been largely stable except for the rapid accumulation of aeolian dust and the resultant increase in its elevation relatively slow dust accumulation and intensive bio pedogenesis responding to the holocene climatic optimum followed the erosion phase the loess tablelands were most vulnerable to erosion during the large scale monsoonal climatic shift from dry cold glacial to humid warm post glacial conditions in the southern loess plateau

impact of monsoonal climatic change on holocene overbank flooding along sushui river middle reach of the yellow river china abstract in the semiarid loess regions slackwater deposition of overbank flooding over the piedmont alluvial plains was episodic and alternated with dust accumulation and soil formation throughout the holocene the records of past hydrological events are therefore preserved within the architecture of loess and soils and are protected from subsequent erosion and destruction several holocene loess soil sequences with the deposits of overbank flooding over the semiarid piedmont alluvial plains in the southeast part of the middle reaches of the yellow river drainage basin were investigated by field observation osl and c14 dating measurement of magnetic susceptibility particle size distribution and chemical elements this enables the reconstruction of a complete catalog of holocene overbank flooding events at a watershed scale and an investigation of hydrological response to monsoonal climatic change as well during the holocene there are six episodes of overbank flooding recorded over the alluvial plain the first occurred at 11 500 11 000 a bp i e the onset of the holocene the second took place at 9500 8500 a bp immediately before the mid holocene climatic optimum after an extended geomorphic stability and soil formation the third overbank flooding episode came at about 3620 3520 a bp i e the late stage of the mid holocene climatic optimum and the floodwater inundated and devastated a bronze age town of the xia culture built on the alluvial plain and therefore the town was abandoned for a period of ca 100 years during the late holocene the alluvial plain experienced three episodes of overbank flooding at 2420 2170 1860 1700 and 680 100 a bp respectively the occurrence of these overbank flooding episodes corresponds to the anomalous change in monsoonal climate in the middle reaches of the yellow river drainage basin when rapid climate change or climatic decline occurs during at least the last four episodes both extreme floods and droughts occurred and climate departed from its normal condition which was defined as a balanced change between the northwestern continental monsoon and southeastern maritime monsoon over time great floods occurred as a result of extreme rainstorms in summers caused by rare intensive meridianal airflows involving northwestward moving tropical cyclone systems from the pacific these results could be applied to improve our understanding of high resolution climatic change and of hydrological response to climatic change in the semiarid zones

on the interpretation of eddy fluxes during a blocking episode abstract using twice daily synoptic charts objectively analyzed at the national meteorological centre horizontal eddy fluxes of temperature and quasi geostrophic potential vorticity are computed for the month of july 1976 when a blocking anticyclone was centered over western europe the local time averaged eddy variance equations are used to provide a dynamical basis for interpreting the spatial pattern of eddy fluxes and their relation to mean gradients it is shown that a rotational non divergent flux can be identified the cross gradient component of which balances the mean flow advection of eddy variance the remaining flux is the dynamically significant one which helps maintain the block and can be understood in terms of a response to sources and sinks of eddy variance

two paradigms of baroclinic wave life cycle behaviour two idealized baroclinic wave 6 life cycles examined here suggest a framework of opposite extremes a in which to view the behaviour of real synoptic scale disturbances in middle latitudes and b in which to interrelate the synoptic and wave theoretic viewpoints using the saturation propagation saturation sps picture of wave 6 life cycle behaviour the two life cycles dented by lc1 and lc2 are higher resolution versions of the simmons hoskins basic and anomalous cases showing strong and weak late decay of eddy kinetic energy eke they illustrate in varying degrees two extreme types of behaviour here disignated anticyclonic and cyclonic and epitomized by strongly contrasting upper air trough behaviour anticyclonic behaviour dominates the late stages of lc1 and is characterized by backward tilted thinning troughs being advected anticyclonically and equatorward as in the commoner cases of planetary scale mid stratospheric rossby wave breaking cyclonic behaviour dominates lc2 and is characterized by forward tilted broadening troughs wrapping themselves up cyclonically and poleward producing major cut off cyclones in high latitudes these morphologies are visualized by upper air maps of potential temperature on the nominal tropopause defined as a constant potential vorticity surface some atmospheric mid latitude disturbances examined here using the same visualization applied to operational analyses show the same two extreme types of trough behaviour together with intermediate cases the sps picture is re examined using eliassen palm and refractive index cross sections it is shown in particular by reference to a wave activity theorem of haynes that the late stages of lc2 can be looked upon as a remarkably clear and morphologically novel large amplitude counterpart of the nonlinear reflection scenario of rossby wave critical layer theory the late stages of lc1 by constrast look more akin to an nonlinear critical layer absorption scenario lc2 exhibits region of largely undular pv contours adjacent to a nonlinear of irreversiby deformen pv contous in the latter region pv rearrangement and hence absorption of rossby wave activity has largely ceased this accounts for the more persistent ekee in the lc2 case

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

coseismic crustal deformation from microseismicity in the patras area western greece summary the patras area lies in the western part of central greece it is an area characterized by high seismicity and complex neotectonics several devastating earthquakes have occurred in the region since 600 bc contemporary crustal deformation is examined in this area using microearthquake data recorded over a lengthy period during 1983 84 by the patras seismic network principally and to a lesser extent by the volos seismic network the microseismicity 1 8 3 9 ml defines a zone deepening to the ne which justifies a possible extension of the gulf of corinth major graben towards the trikhonis lake to the nw spectra of 108 well located microearthquakes are estimated using p waves obtained by selective windowing designed to include only the p phase seismic moments in the range 0 3 45 7 1012 nm are obtained accompanied by estimates of seismotectonic source parameters including source radii average stress drop and average coseismic slip poor correlation is found between seismic moment and magnitude and the likely reason is the complex nature of the neotectonic regime existing in the area two zones differing in crustal deformation characteristics are observed the corinth trikhonis zone reveals two sets of characteristic faults the first set is represented by microearthquakes showing distinctive and relatively higher seismic moments in conjunction with lower stress drops and seismic slips this set of faults shows greater source radius than the second set and therefore the faults are longer the second set is characterized by an almost constant source radius within the range of uncertainty and a wide range of seismic moments stress drops and seismic slips the rio zone is characterized by low seismic slip stress drop and fault radii with the exception of the locality south of the city of patras where relatively higher seismic slip stress drop and fault radius are observed

high resolution studies of the oldest cultivated soils in the southern loess plateau of china abstract the holocene loess soil sequence on the chinese loess plateau constitutes an excellent record of evolution of soil formation monsoonal climate eolian dust accumulation and influences of arable farming of over 8000 years a high resolution soil profile on the zhouyuan loess tableland to the west of xi an was studied using particle size analysis measurement of magnetic susceptibility total fe toc and caco3 the results provide new insights into the roles of eolian dust deposition and human impact of cultivation on soil development in this environmentally sensitive zone several loess layers are found interbedded with cinnamon soils in the profile this has been caused by changes in rainfall and intensity of dust deposition that is forced by changes in balance between the northwest continental monsoon and southeast maritime monsoon of east asia during the holocene the processes of soil formation were interrupted several times by intensified dust fall and climatic aridity in the last 11 500 years the initial clearance of forest for arable farming occurred at ca 7500 years bp on the loess tableland it was contemporaneous with the arrival of the wetter and warmer climate of the holocene megathermal 8500 3100 years bp thereafter arable farming has been maintained during both the time of soil formation and that of intensified dust accumulation though there could be temporary cessation or reduced intensity of cultivation in the drier intervals because of lack of rainfall and soil moisture increased intensity of dust accumulation has been ongoing since ca 3100 years bp in the loess plateau a loess deposit of 40 80 cm has overlaid the multiple or single welded cinnamon soils on the flat land over the plateau

spectral characteristics of the 1986 september 13 kalamata southern greece earthquake summary the seismic source parameters seismic moment m source dimension r fault length 1 average displacement u shear stress drop aa radiated energy es and apparent stress n a are calculated for the kalamata southern greece earthquake of 1986 september 13 these source parameters are obtained by using teleseismic p and sh wave spectra and making use of three independent spectral parameters the long period spectral level a the corner frequency f and the parameter e which controls the high frequency decay of the displacement spectrum the calculated far field spectra are based on the direct phases of pand s waves and they have been corrected for the instrumental response and for an average radiation pattern assuming normal faulting mechanism the striking feature of the obtained results is the low stress drop value of about 6 7 bar which is in deviation from the average value 30 bar for interplate earthquakes a seismic moment of 1 9 x and 2 2 x loz4 dyne cm a fault length of about 22 and 11 km and an average displacement of 15 and 9 cm are obtained on the basis of p and s waves respectively

out of phase evolution between summer and winter east asian monsoons during the holocene as recorded by chinese loess deposits we analyzed climate proxies from loessic soil sections of the southern chinese loess plateau the early holocene paleosol s0 is 3 2 m thick and contains six sub soil units co eval soils from the central loess plateau are thinner 1 m consequently higher resolution stratigraphic analyses can be made on our new sections and provide more insight into holocene temporal variation of the east asian monsoon both summer and winter monsoon evolution signals are recorded in the same sections enabling the study of phase relationships between the signals our analyses consist of i measurements of magnetic properties sensitive to the production of fine grained magnetic minerals which reflect precipitation intensity and summer monsoon strength and ii grain size analyses which reflect winter monsoon strength our results indicate that the holocene precipitation maximum occurred in the mid holocene 7 8 3 5 cal ka bp with an arid interval at 6 3 5 3 cal ka bp the winter monsoon intensity declined to a minimum during 5 0 3 4 cal ka bp these results suggest that the east asian summer and winter monsoons were out of phase during the holocene possibly due to their different sensitivities to ice and snow coverage at high latitudes and to sea surface temperature at low latitudes

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

interpretation of satellite imagery of a rapidly deepening cyclone model output and observational data are used to interpret in detail satellite images of a distinctive cloud system several hundred kilometres long which was observed before and during rapid cyclonic development that occurred over england conceptual models are forwarded which account for the structure of the major cloud areas and upper level moisture fields as observed by water vapour imagery immediately prior to and following the onset of vigorous cyclogenesis the cloud system corresponded to what r b weldon refers to as a baroclinic leaf cloud and was characterized by ana cold frontal ascent the baroclinic leaf lay within an area of enhanced ascent ahead of a major upper level trough a jet streak which originated upstream propagated rapidly around the base of the upper trough a tongue of dry air centred on the left flank of this jet streak lay immediately upstream of the leaf cloud and had a major influence on its subsequent development this intrusion of dry air was well represented by the meteorological office fine mesh model which showed it as a pronounced tongue of recently descended air with high potential vorticity which originated in the upper troposphere and lower stratosphere rapid cyclogenesis occurred as the dry intrusion overran low level air of high w within a warm conveyor belt at the southern tip of the leaf cloud interaction of the dry intrusion and baroclinic leaf cloud is shown to be particularly important in accounting for the detailed distribution of weather it also suggests a way of pinpointing the location and timing of vigorous cyclogenesis

relationship between the 13 may 1995 kozani grevena nw greece earthquake and the polyphyto artificial lake abstract on 13 may 1995 a strong earthquake of m s 6 6 struck the cities of kozani and grevena in northwestern greece this region is characterized by low seismicity in the same area three hydroelectric dams have been operating for the last 30 years one of them the polyphyto dam is located only 40 km from the epicenter of the 13 may earthquake in the present work all available seismological aspects of the main event such as focal properties and source parameters together with foreshock and aftershock characteristics of the earthquake sequence are considered in order to examine whether the water level changes behind the polyphyto dam induced the unusual seismic activity in this area thus a detailed examination of the seismic activity is made and this is compared to the seismotectonic regime of the region and the reservoir loading from 1976 to 1995 the results show that there is no obvious correlation between seasonal or sharp fluctuations in the water level and the seismicity of the region except once during 1989 moreover comparison with other previous cases of induced seismicity in greece and in other countries shows no similarities to the kozani grevena earthquake sequence it is concluded that the kozani grevena earthquake is therefore an event in the framework of the regional seismicity rather than an event triggered by the impounding of the polyphyto artificial lake

seismic moments of earthquakes at the western hellenic arc and their application to the seismic hazard of the area tselentis g a stavrakakis g m o ulos k latousakis j and drakopoulos j 1988 seismic moments of earthquakes at the western hellenic arc and their application to the seismic hazard of the area tectonophysics 148 73 82 seismic moments of 45 large earthquakes m 2 5 2 which occurred in the southwestern part of the hellenic arc trench system between 1950 and 1981 were used to express the frequency of occurrence of earthquakes in terms of the subduction rate and the largest seismic moment likely to occur in the region for this purpose a moment versus magnitude relationship for earthquakes characteristic of the region was derived and the subduction rate was estimated from seismic moment rates the hellenic arc trench system is a subduction zone of about 1000 km where the african lithosphere is subducting under the aegean lithospheric plate in a roughly sw ne direction this motion of the hellenic consuming boundary with respect to africa results from three different processes the northward motion of the african plate the aegean extensional spreading and the westward motion of turkey mckenzie 1970 1978

modulation of equatorial subseasonal convective episodes by tropical extratropical interaction in the indian and pacific ocean regions composite relationships among outgoing longwave radiation sea level pressure surface winds and upper tropospheric circulation are examined for northern winter during subseasonal episodes of eastward progression of convection from the indian ocean to the western pacific this evolution often culminates with westerly wind burst events and strong air sea interaction associated with regional scale convective blowups in the western equatorial pacific we first document some of these interactions in the composites for two timescales the submonthly 6 30 days and that of the madden julian oscillation mjo timescale 30 70 days we then analyze the december 1992 period during the tropical ocean global atmosphere coupled ocean atmosphere response experiment toga coare to illustrate how these composite relationships are manifested in a case study convection in the indian ocean for the composites is shown to be associated with a northern hemisphere wave train at 200 mbar arcing through the midlatitudes that can contribute to convective blowups farther east on the submonthly 6 30 days timescale in the intertropical convergence zone itcz in the eastern pacific the eastern asian trough that is part of this wave train is associated with pressure surges from the northern hemisphere and subsequent convection over southeast asia as the mjo convective envelope moves east to australasia midlatitude wave trains in either hemisphere include upper level troughs east of asia and australia and pressure surges from either hemisphere that contribute to pressure rises over the indonesian region and a subsequent shift of the convective envelope to the western pacific the vertical wind structure for the december 1992 case study is consistent with the composite surface and upper level winds and also shows strong vertical wind shear in the boundary layer a sharply defined westerly maximum near 700 mbar and an intensification of the upper level easterlies near 100 mbar very deep westerlies to 200 mbar are confined to shorter timescales the case study illustrates the various time and space scale interactions noted in the composites reciprocal interactions between the tropics and the midlatitudes on the submonthly and mjo timescales in both the composites and the case study involve pressure surges and wave interaction that influence subsequent convection as the convective envelope migrates eastward from the tropical indian to pacific ocean region

towards an orbital time scale for chinese loess deposits abstract in this study we analyzed the grain size of the baoji loess soil sequence at 10 cm intervals results show that grain size variations are very sensitive to loess soil alternations with loess units being much coarser than soils such a change in loess soil grains is interpreted as the result of the glacial interglacial cyclic variations in the intensity of the winter monsoon winds out of siberia the grain size record is thus employed as a proxy indicator of the winter monsoon circulation and tuned to the orbital records calculated recently by berger and loutre 1991 under the control of major magnetic reversals the tuning is independent of any correlation with 18o signals in the deep sea sediments the resulting grain size time scale is tightly constrained as suggested by the following facts 1 the filtered obliquity and precession components from the grain size data on the orbital time scale closely match the theoretical orbital records 2 ages of the major magnetic reversals estimated from the grain size time scale are in good agreement with the k ar dated ages 3 there is close coherence between the baoji grain size time series and the orbital variations at the orbital frequency bands over the entire 0 2 5 ma period and 4 the grain size record on the orbital time scale shows a close similarity to the orbitally tuned dsdp site 607 and odp site 677 18o records examination of time dependent characteristics of the grain size record suggests that there are two major shifts of dominant periodicities in the long term monsoonal cycles one occurring at about 0 8 ma bp and the other around 1 7 ma bp

geochronology and paleoenvironment of the taoshan site northeastern china and archaeological implications abstract the taoshan archaeological site located in northeastern china was found in 2011 and an area of 36 m 2 was excavated in 2013 and 2014 2908 stone artifacts 71 pottery fragments and five ornaments were excavated from three cultural layers similar sites with both stone artifact and pottery at least in heilongjiang province of china have not been reported the dating results showed that the optically stimulated luminescence technique is of great utility for such archaeological deposits and the three cultural layers were dated to 16 5 13 4 ka 13 4 8 7 ka and 8 7 5 6 ka respectively the climate proxies magnetic susceptibility total organic content and pollen indicate that the local climate was cold and dry for the period of 16 5 13 4 ka warm and wet for the period of 13 4 8 7 ka and warm and dry for the period of 8 7 5 6 ka respectively the types and amount of archaeological findings from each layer period reflect the human response to the past climate change implying that the human related processes identified at taoshan are associated with climatic and environmental changes the investigations of the site are very important for developing a better understanding of the colonization of this region by humans the transmission of technologies and the processes of economic and social change the local societies underwent the presence of microblades and pottery is the most significant for our reconstructing of the archaeology of the northernmost parts of northeast china

anthropogenic hillslope terraces and swidden agriculture in jiuzhaigou national park northern sichuan china abstract small irregular terraces on hillslopes or terracettes are common landscape features throughout west central china despite their prevalence there is limited understanding of the nature of these topographic features the processes that form them and the role humans played in their formation we used an interdisciplinary approach to investigate the geology ecology and cultural history of terracette development within jiuzhaigou national park sichuan province china terracettes occur on south facing 20 slopes at 2500 m elevation which appears to coincide with places people historically preferred to build villages ethnographic interviews suggest that traditional swidden agricultural cycles removed tree roots causing the loess sediments to lose cohesion slump and the terrace risers to retreat uphill over time this evidence is supported by landslide debris at terracette faces archaeological analysis of terracette sites reveal remains of rammed spread soil structures bones stone tools and ceramics dating from at least 2200 years before present within a distinct paleosol layer radiocarbon and optically stimulated luminescence dating of terracette sediments ranged in age from between 1500 and 2000 14 c yr bp and between 16 and 0 30 ka respectively these multiple lines of evidence indicate a long history of human habitation within jiuzhaigou national park and taken together suggest strong links between terracette formation and human landuse interactions

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

moment magnitude scaling in the aegean area abstract sixteen new determinations of scalar seismic moment from spectral modelling of rayleigh waves at 30 60 s period in the aegean area are presented when combined with earlier results obtained by a similar method the moment magnitude relationship from 50 events in the magnitude range 5 3 m s log m o 1 5 m s 9 198 0 317 for a constant stress drop dislocation model and m o in n m in contrast 15 published moments from body wave modelling at 20 s period and moment tensor inversion at periods greater than 45 s give log m o 1 5 m s 8 823 0 248 the surface wave results imply stress drops of 25 12 25 bar for the dislocation model and the body wave results imply systematically higher stress drops of 55 27 55 bar compared to 24 bar from field observation of the gulf of corinth sequence and 7 12 bar from inversion of body wave spectra and aftershock studies the latter are likely to be underestimates however the factor two scatter in the stress drops determined from the moment magnitude relation is much less than the factor four error in the estimated stress drop which might be introduced by model dependent systematics effects and these discrepancies may not be significant if the stress drop is free to vary then log m o 1 206 0 105 m s 10 970 0 632 surface waves log m o 1 160 0 181 m s 11 027 0 338 body waves this shows that the discrepancy between the two sets of results in negligible at m o 5 5 and thereafter increases slightly with earthquake size indicating that the underlying cause of the systematic difference in seismic moment for a given magnitude may be related to source size

late quaternary climate change loess sedimentation and soil profile development in the central great plains a pedosedimentary model research on soil genesis often assumes a top down model in which the soil profi le develops downward from a stable land surface this model is inapplicable to upland landscapes affected by frequent dust deposition where soils grow upward as they develop on the central great plains late quaternary loess sections proximal to immediate source areas contain the brady soil a prominent marker separating late pleistocene peoria loess from holocene bignell loess farther from immediate dust source areas the brady soil and bignell loess are not recognizable in the fi eld on loess tablelands in these distal regions surface soils typically contain a prominent clay rich b horizon below a thick silty a horizon assuming top down pedogenesis this could be interpreted as a postglacial soil profi le formed in peoria loess with the b horizon produced by weathering and clay illuviation we propose a strikingly different interpretation in which the upper b horizon at distal sites is the brady soil a horizon that has been transformed by burial organic matter loss and modern subsoil structure formation processes the overlying modern a horizon represents bignell loess properties of the brady soil at proximal sites a distinctive burrowed zone high clay content and tio 2 zro 2 and low volcanic glass content can be traced to the b horizon in distal soils a decrease in smectite abundance above the brady soil at proximal sites is identifi able at the top of the clay rich b horizon in distal soils the spatial variation of clay content in loess and soil horizons is best explained by eolian sedimentation patterns the higher clay content in the brady soil and distal b horizons defi nes a fi ne grained zone that represents a late phase of peoria loess accumulation evidence of chemical weathering is minimal and illuvial clay is rare to absent in the clay rich b horizons illuvial clay does often occur deep in the solum and is related to the depth below the top of the brady soil the depth of occurrence of illuvial clay is not related to modern climate parameters although depth to secondary carbonate appears to be in equilibrium with modern climate upland soils in the central great plains are composite soils their properties are the result of a pedosedimentary history linked to regional climate change that has infl uenced sedimentation and pedogenesis since the late pleistocene

climatology of intrusions into the tropical upper troposphere regions of upper tropospheric equatorial westerly winds observed over the pacific and atlantic oceans during northern fall to spring are important for extratropical tropical interactions this paper focuses on one feature of these westerly ducts that has received relatively little attention to date the occurrence of rossby wave breaking events that transport tongues of extratropical air deep into the tropics mix tropical and subtropical air and can affect deep convection a climatology of these intrusion events formed from 20 years of meteorological analyses shows a strong dependence on the basic state flow notably intrusion events are found to occur almost exclusively within westerly ducts with more events in the presence of stronger equatorial westerlies it is also found that there is strong interannual variability in the frequency of pacific events with fewer events during the warm phases of enso consistent with the changes in the basic flow since these intrusion events laterally mix trace constituents and have been linked to tropical convection their spatial and temporal variability may cause related variability in the distribution of trace constituents and tropical convection

pleistocene loess in the humid subtropical forest zone of east asia 1 loess deposits in asia have been used as indicators of palaeoclimate because they are usually found bordering deserts this paper reports extensive and thick deposits of loess in tropical southwest china between latitudes 18 and 23 30 n which is 1300 km south of known and extensively researched loess deposits in north china the present climate of the reported loess areas is hot and humid with mean annual rainfall of 1000 2000 mm and vegetation of subtropical evergreen broadleaf forest this compares with less than 400 mm rainfall and vegetation of semi desert steppe in areas of current loess accumulation on desert margins in north china the source area of the loess which is dated by optical luminescence to the late pleistocene from 90 222 ka is thought to be the exposed east asian shelf which was up to 140 m below present sea level during quaternary arid phases recent research on the nature of the shelf environment and the relatively large particle size of the loess suggests a local origin the reported loess is not interbedded with palaeosols and small amounts of soil cover the loess compared with well developed soils in loess in semiarid regions in north china this is explained by elimination of the supply source by sea level rise following each arid phase as continued dust supply appears necessary for soil to form this preliminary report of loess in southwest china conflicts with palynological evidence and suggests that recent reconstructions of pleistocene aridity in east asia may be conservative

phase speed spectra of transient eddy fluxes and critical layer absorption abstract tropospheric zonal mean eddy fluxes of heat and momentum and the divergence of the eliassen palm flux are decomposed into contributions from different zonal phase speeds data analyzed are ecmwf operational global analyses covering 1980 87 eastward moving medium scale waves zonal waves 4 7 dominate the spectra of lower tropospheric heat fluxes in both hemispheres and all seasons upper tropospheric wave flux spectra are similar to the low level spectra in midlatitudes but shift to slower zonal phase speeds as low latitudes are approached the cause of this shift is the selective absorption of faster moving components in midlatitudes as the waves propagate meridionally latitude phase speed distributions of eddy fluxes are constructed and compared to the zonal mean wind structure these results demonstrate that upper tropospheric eddies break and decelerate the zonal mean flow approximately 10 20 in latitude away from their critical line where phase speed equals zonal wind speed compari

episode of strengthened summer monsoon climate of younger dryas age on the loess plateau of central china abstract the baxie loess section just east of the tibetan plateau contains evidence showing that the asian monsoon climate experienced an abrupt reversal near the end of the last glacial age rapid deposition of dust under cool dry full glacial conditions gave way to an interval of soil development and reduced dust influx attributed to a strengthening of the warm moist summer monsoon a subsequent abrupt increase in dust deposition a response to a weakening of the summer monsoon was later followed by renewed soil formation as summer monsoon circulation again intensified during the early holocene by one interpretation the thin upper loess is a manifestation of the european younger dryas oscillation however in this case the available 14c ages require either that 1 onset of loess deposition lagged the beginning of the younger dryas event in europe by as much as 2000 calibrated 14c years or 2 all the 14c ages are too young possibly due to contamination alternatively the late glacial paleosol the top of which is synchronous with the abrupt end of the late glacial 18o anomaly in the dye 3 greenland ice core records the younger dryas event such an interpretation is consistent with general circulation model simulations of younger dryas climate that show strong seasonality and a strengthened summer monsoon and with marine cores from the western pacific ocean that contain evidence of pronounced cooling of surface waters during younger dryas time

the cold event 8200 years ago documented in oxygen isotope records of precipitation in europe and greenland stable oxygen isotope ratios of ostracod valves in late glacial and holocene sediments of core as 92 5 from deep lake ammersee southern germany reflect variations of mean oxygen isotope ratios in past atmospheric precipitation the record reconfirms the strong similarity of climate evolution in europe and greenland during the last deglaciation for the first time in europe we find a 200 year long negative 18o excursion which is contemporaneous with the strongest negative 18o excursion in the greenland ice around 8 2 ky before present the 8 2 ky isotopic event on both sides of the north atlantic ocean is interpreted as a cold period most probably induced by a perturbation of the north atlantic thermohaline circulation we discuss two possible triggering mechanisms 1 weak forcing as proposed by alley et al and 2 forcing by a strong and sudden freshwater pulse from the collapse of the hudson ice dome

reinterpreting climate proxy records from late quaternary chinese loess a detailed osl investigation abstract numerous authors have utilised physical properties of chinese loess and red clay deposits to develop apparently detailed and continuous past climate records from the miocene into the holocene many of these studies have further suggested that the principal climatic agent responsible for the aeolian emplacement and diagenesis of chinese loess the east asian monsoon has fluctuated rapidly on millennial to sub millennial timescales in concert with dramatic changes in the north atlantic dansgaard oeschger cycles and heinrich events and the western pacific el nino southern oscillation much of this evidence is based on reconstructions and age models that are tied to assumptions concerning the nature of loess sedimentation and diagenesis for example the belief that loess sedimentation can be viewed as essentially continuous some authors have however cast doubt on these assumptions and suggest that the application of radiometric techniques may be required to determine their validity recent studies utilising optically stimulated luminescence osl methods have reinforced these doubts and here osl dates obtained at 10 cm intervals from three sites along a transect across the chinese loess plateau have been used in combination with climate proxy evidence to test the existing assumptions that underpin many palaeoclimatic reconstructions from loess in this way the first time continuous and independently dated late quaternary climate reconstruction is developed from loess the data indicate that sedimentation is episodic and that once emplaced loess is prone to pedogenic disturbance diagenetic modification and in some cases erosion the relationships between proxies and sedimentation rates are also assessed and climatic interpretations based on different age models compared the implications of these findings for reconstructions of climate from loess are explored and comparisons are made between the developed palaeoclimate records and evidence from ice and ocean cores this exercise also highlights important information concerning the relative influence of forcing mechanisms behind east asian monsoon change over the late quaternary

holocene dust accumulation and the formation of polycyclic cinnamon soils luvisols in the chinese loess plateau chinese loess palaeosol sequences are well known for their records of monsoonal climatic variations however the modern processes of dust accumulation and soil formation remain poorly understood a high resolution investigation on modern soils including the measurement of magnetic susceptibility particle size distribution total fe total organic carbon caco3 content and optical stimulated luminescence osl dating was carried out on the zhouyuan loess tableland in the southern loess plateau the results indicate that modern cinnamon soils luvisols have developed on contemporarily accumulated aeolian dust during the holocene the aeolian loess accumulated during the younger dryas was identi ed in the top part of the malan loess that underlay the modern soil by osl dating and proxy climatic data it indicates that the malan loess accumulated during the last glaciation marine isotope stages 2 4 does not serve as the parent material for the modern soils pedogenesis of the soils started with the increased precipitation and soil moisture that have occurred on the loess tableland since the early holocene precipitation driven pedogenesis and organic activities are responsible for the leaching of caco3 decomposition of mineral dust and the production of clay and ferromagnetic minerals drier intervals have interrupted soil formation several times and therefore pro les with multiple soils have been developed at many sites on the loess tableland at places where soil erosion was relatively strong either a single soil or welded soils are preserved in the holocene pro les this does not necessarily mean however that modern soils over the plateau have been developed without interruption under a constantly warmer moister climate this is signi cant for understanding the surface processes and climatic variation during the formation of the numerous palaeosols over the loess plateau in the quaternary copyright 2003 john wiley sons ltd

effects of low frequency wave interactions on intraseasonal oscillations abstract intraseasonal oscillations isos control much of the large scale variability of convection in the tropics on time scales of about 15 100 days these disturbances are often thought to be dominated by eastward propagating modes especially during austral summer but disturbances that propagate westward are also important this work demonstrates by means of a multiple linear regression model and a brief case study that eastward and westward moving intraseasonal modes often cooperatively interact with one another to produce many of the characteristics of the observed southern hemisphere summer iso these interactions appear to be facilitated by topography and or by the convective anomalies that are cooperatively induced by the eastward and the westward moving components of the oscillations these interactions do not occur during every period of intraseasonal convective activity but they do commonly occur during periods of high amplitude convective anomalies this analysis shows that eastward and

east asian monsoon evolution during the eemian as recorded in the western chinese loess plateau abstract we present a high resolution environmental magnetic record of the east asian summer monsoon spanning paleosol s1 corresponding to marine oxygen isotope mis 5 from the jiuzhoutai jzt loess section in lanzhou on the northwestern edge of the chinese loess plateau we use a chronology based on a sediment grain size age model frequently used for chinese loess the eemian is dated to 127 37 121 31 ka bp and can be divided into three sub stages based on variations in summer monsoon intensity early eemian 127 37 125 67 ka bp with an intermediate summer monsoon intensity mid eemian 125 67 124 24 ka bp with weakest summer monsoon intensity and late eemian 124 24 121 31 ka bp with the strongest summer monsoon intensity contrasting the winter monsoon weakened at the beginning of mis5e reached its weakest intensity during the late eemian 121 ka bp and then commenced an irreversible strengthening trend furthermore the eemian exhibits a similar climatic trend to the holocene optimum since both are divided into two parts by an intervening arid interval and the most humid period occurs in the secondary pedogenic stage therefore we suggest that the climate evolution during eemian and later may provide useful information about climate forecast in the future

holocene wildfires related to climate and land use change over the weihe river basin china abstract charcoal particles preserved in the loess palaeosol profiles provide records of wildfires during the holocene total organic carbon magnetic susceptibility and charcoal analysis and osl dating were carried out in the holocene loess palaeosol profiles at two sites in the weihe river basin the analytical results show that natural wildfires occurred frequently during the last glaciation when climate was dominated by northwest continental monsoon and steppe vegetation expanded southerly to the weihe river basin wildfire occurrence decreased during climatic amelioration in the early holocene during the holocene climatic optimum between 8500 b p and 3100 b p natural wildfire occurrence was reduced greatly pedogenic alteration to the accumulated dust was intensified because of the humid warm climate brought on by southeast maritime monsoon localized fire events in connection with human activities of the neolithic occurred in several episodes over the region during the late holocene when climate become drier wildfire occurrence over the upland hills shows a pattern different from that in the guanzhong basin over the upland hills in the north charcoal concentrations show a decreasing trend in the recent loess and topsoil it indicates infrequent biomass burning during the last 3100 years this is attributable to nomadic occupation of the loess hills during the bronze age and the development of a land use pattern of livestock farming in most part of the history over the loess tableland in the guanzhong basin in the south abruptly increased charcoal concentrations in the recent loess and topsoil show very high level of biomass burning this is attributable to the increasingly intensified land reclamation for cereal cultivation from the bronze age this study provides new insights into wildfires over the semi arid and sub humid regions in connection with climate and land use change

modulation of the extratropical circulation by combined activity of the madden julian oscillation and equatorial rossby waves during boreal winter abstracttime indices of the madden julian oscillation mjo are often used to generate empirical forecasts of the global atmospheric circulation moist deep convection associated with the mjo initiates eastward propagating rossby waves that disperse into the midlatitudes the background circulation then guides extratropical waves back into the tropics of the eastern pacific ocean previous works have shown that equatorial rossby er waves occur following intrusion of extratropical rossby waves into the tropics westward propagating er waves and the mjo modulate the total convection this convection modulates the zonal wind which influences the location and existence of westerly wind ducts these wind ducts in turn guide extratropical waves into the tropics this paper demonstrates through a simple composite analysis that a simultaneous assessment of mjo and er waves yields more information about the extratropical circulation during boreal winter than can be obtained based on either type of disturbance

the modulation of the subtropical and extratropical atmosphere in the pacific basin in response to the madden julian oscillation abstract the 40 yr ecmwf re analysis era 40 data are combined with a number of novel climatologies to conduct a comprehensive examination of the response of the subtropical and extratropical atmosphere over the pacific basin to an evolving madden julian oscillation mjo event the adopted approach constitutes a symbiosis of a climatological analysis during the northern hemisphere winter from 1979 to 2002 and a case study analysis of a distinct mjo event that occurred in january february 1993 the former is designed to obtain the general characteristics observed during a composite mjo life cycle while the latter is used to provide insight into the instantaneous mechanisms responsible for the observed composite evolution a primary component of the study involves the diagnosis of anomalous wave breaking activity in response to mjo forcing in the form of tropical convection and or upper level divergence wave breaking events are separated by their characteristic life cycles lc1 anticyclonic and lc2 c

archaeology of the anthropocene in the yellow river region china 8000 2000 cal bp although archaeological analysis emphasizes the importance of climatic events as a driver of historical processes we use a variety of environmental and archaeological data to show that human modif

spatial and temporal reconstructions of changes in the asian palaeomonsoon a new mineral magnetic approach abstract a new quantitative approach is proposed for estimating palaeoprecipitation across the chinese loess plateau at present there is a strong rainfall gradient across the plateau from 300 mm yr in the near desert conditions in the northwest to over 750 mm yr in the southeast just 700 km distant we find that the concentration of ferrimagnetic iron oxide minerals in nine modern soil types represented by 37 individual soil profiles is strongly correlated with this contemporary rainfall gradient the ferrimagnetic concentration rises along this gradient from 0 01 in the northwest to over 0 2 in the southeast the nine modern soil types have been used in the construction of a rainfall vs magnetic susceptibility least squares regression climofunction past variations of loess soil iron oxide content are easily established through magnetic susceptibility measurements and so can be used to reconstruct the rainfall of former interglacial and glacial periods the physical and pedological basis of the rainfall vs susceptibility relationship is discussed and potential limitations of our rainfall reconstruction method are explored our palaeoclimate reconstructions indicate dramatic changes in rainfall due to variations in the structure of the asian monsoon the rainfall variations are about four times greater than has been suggested for this region by atmospheric general circulation modelling our data indicate increased rainfall throughout central china both in interglacial periods and in the early holocene the increases in monsoonal rain were particularly pronounced at our westernmost sites adjacent to the northeastern edge of the tibetan plateau in contrast for glacial periods a reduction in rainfall is found across the whole loess area with the greatest decreases in the southeast

baoji type pedostratigraphic section loess plateau north central china abstract the baoji section is judged to be the most complete pedostratigraphic section on the loess plateau of north central china it is located about 5 km north of the city of baoji and consists of 37 paleosols formed during more than the last 2 5 ma it is designated here as the type pedostratigraphic section with formally named geosols following the rules of the north american commission on stratigraphic nomenclature geochronological control is based largely on magnetostratigraphy with the brunhes matuyama and gauss epochs and jaramillo and olduvai events clearly recognized the baoji geosols can be correlated with equivalent pedostratigraphic units throughout the loess plateau by a combination of magnetostratigraphy and character position and the association of the pedostratigraphic units within the quaternary succession the variation of the geosols suggests climatic cycles of varying intensity and duration but generally warmer and moister conditions when compared with the loess units that suggest colder and drier periods

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

seismic source parameters from a new dial up seismological network in greece a regional dial up pt telemetric network of eight digital short period seismic stations has been in full operation since the beginning of 1995 in greece during the first year of full operation three destructive earthquake sequences struck different regions of central and northern greece the dial up network managed to successfully record more than 85 of these seismic events including foreshocks main shocks and aftershocks and 45 of these events were selected in order to determine their seismic source parameters by spectral analysis the results show that seismic moment correlates very well with earthquake magnitude fault radius and fault displacement the determined scaling relations are in general agreement with those obtained by other studies for greek earthquakes that used different methodologies since digital seismic instrumentation is now expanding in greece these first results from spectral analysis of digital short period data can be considered useful for future seismic hazard studies

the seismology of greece abstract a review and a bibliography are given of the seismological literature for the area of greece in the period from 1950 up to the present time the aim is to incorporate all aspects of seismology starting with instrumental installations passing on to earthquake catalogues statistics and effects and ending up with structural properties and seismotectonics the purpose is to provide a service to every geophysicist who has an interest in this tectonically complex area and particularly to the numerous researchers engaged in geophysical expeditions to greece

source processes of the 1981 gulf of corinth earthquake sequence from body wave analysis abstract teleseismic long period body waves from the 24 february 1981 gulf of corinth earthquake and its two principal aftershocks of 25 february 02h35m and 4 march 21h58m 1981 are studied to determine source characteristics focal mechanisms along with observed surface fault breaks suggest that the corinth earthquake sequence represents normal faulting due to the n s trending extension depths of the three shocks estimated by matching synthetic seismograms to observations are found to lie between 4 and 12 km the azimuthal variation of observed body wave duration indicates that the main shock is a multiple event and that the main rupture occurred about 3 to 4 sec after a relatively small foreshock and propagated toward the w nw seismic moments deduced from the body wave synthetics are 8 1 10 25 2 7 10 25 and 2 2 10 25 dyne cm for the main 25 february and 4 march shocks respectively average final displacements and stress drops are estimated to be 37 cm and 10 bars for the main shock for a circular fault of radius 15 km 22 cm and 8 bars for the 25 february shock and 18 cm and 7 bars for the 4 march shock for circular faults of radius 11 km the striking features of the earthquake sequence are the low stress drops of the main shock and its two principal aftershocks and the clear eastward migration of aftershock activities the unusually long source time function rise times 4 sec for the main shock 2 5 sec for both aftershocks and low stress drops suggest an overall slow energy release during the earthquake sequence

a study of the structure of mid latitude depressions in a numerical model using trajectory techniques i development of ideal baroclinic waves in dry and moist atmospheres trajectory tracing techniques are used to investigate the structure and air flow of developing baroclinic waves simulated by a numerical atmospheric forecast model three stages are described the structure of the linear stage is explained with reference to the normal mode theory of baroclinic instability in the mature stage flow separation zones form which are identified as warm and cold fronts at the occluded stage circulation of cold air round the centre of the depression leads to changes in the structure of the cold front when the initial state is nearly saturated the overall development is speeded up and at the mature stage the rate of deepening of the depression is doubled at the surface in the occluded stage formation of a warm air conveyor belt is observed comparisons are made with previously published integrations by specially constructed models in order to establish a basis for comparison of forecasts from real data which will appear in a future paper

a dynamic link between high intensity precipitation events in southwestern north america and europe at the last glacial maximum abstract both hydroclimate proxies and modeling studies alike present compelling evidence for abundant precipitation in southwestern north america and europe at the last glacial maximum lgm however model simulations exhibit an apparent disagreement between changes in precipitation and the orientation of the midlatitude jet streams relative to modern this is surprising as it is well known from modern observations that the jet streams and storm tracks closely follow one another in the time mean the present study shows that a substantial fraction between 35 and 50 of the precipitation along the western seaboards of the northern hemisphere continents at the lgm is due to short lived high intensity events rather than a permanent rearrangement of the circulation moreover these precipitation events are shown to be dynamically linked by a wavenumber 5 stationary wave packet that is trapped in a midlatitude waveguide when the wave energy is concentrated in the eastern north pacific an atmospheric river is excited that makes landfall along the north american west coast days later when the wave packet has reached europe the north atlantic jet stream assumes a zonally oriented state that brings abundant precipitation to the western mediterranean sector understanding the dynamics of this teleconnection pattern is not only key for interpreting proxy data signals in past climates but may also be important for improving predictions of storm track dynamics and water resources availability in the face of climate variability and change

magnetic properties of modern soils and quaternary loessic paleosols paleoclimatic implications the magnetic properties of paleosols developed in quaternary sequences of loess have been used for stratigraphic definition correlation with other terrestrial and deep sea sequences and paleoclimatic paleorainfall reconstruction in some loess paleosol sequences including those of the chinese loess plateau tajikistan and the czech republic maxima in magnetic susceptibility values correspond with the paleosol horizons and minima with the least weathered loess layers in other loess soil sequences including those of siberia alaska and argentina the relationship is completely opposite with susceptibility minima associated with the most developed paleosols to account for these opposite relationships the respective roles of 1 magnetic enhancement and 2 magnetic depletion and or dilution in determining soil magnetic properties are investigated for a range of modern soil types most magnetic enhancement is seen in the upper horizons of well drained cambisols absence or loss of magnetic iron oxides is apparent in acid podsol profiles and waterlogged soils for the cambisol profiles significant correlation is found between susceptibility and organic carbon cation exchange capacity and clay content the mineralogy morphology and grain size of soil magnetic carriers extracted from three modern enhanced soils and a paleosol from the chinese loess plateau are also identified by independent petrographic means microscopy and x ray diffraction of magnetic extracts magnetite and maghemite of ultrafine grain size from 0 4 to 0 001 i m are the major contributors to the magnetically enhanced soils weathering can concentrate detrital magnetic grains especially in the fine silt size fractions of soils the magnetic data from the modern soils indicate that interpretation of paleosol magnetic properties must be done on a site specific basis taking into account the possibilities of pedogenic enhancement pedogenic dilution or depletion and allochthonous inputs of magnetic minerals excessively arid wet or acid soils are unable to form significant amounts of pedogenic ferrimagnets well drained intermittently wet dry soils with reasonable buffering capacity and a substrate source of fe show most magnetic enhancement for those soils which favour magnetic enhancement processes correlation has been found between the maximum value of the pedogenic susceptibility and the annual rainfall the almost unique pedogenic system in the chinese loess plateau where variation in soil forming factors other than climate is reduced to a global minimum allows use of the paleo susceptibility values as proxy paleorainfall values to identify the mechanism of any link between magnetic properties for example susceptibility and climate change the mineralogy and grain size of soil magnetic carriers requires detailed investigation given the prospect of 1 quantitative paleorainfall records from continental loess records 2 predictions of present and future climate change and 3 the value of paleoclimate data for testing of numerical climate models such magnetic investigations can contribute significantly to our understanding of past and future environmental change

a case study of explosive cyclogenesis in the eastern pacific abstract an explosive cyclogenesis that occurred in the eastern pacific on 13 november 1981 is described and discussed on the basis of surface and upper air analyses and satellite imagery during one 12 h period the storm deepened by nearly 40 mb and subsequently attained a central pressure of 950 mb or less peak surface winds were in the 45 50 m s 1 range the limited area fine mesh lfm model 24 h forecast initialized at 0000 gmt on the thirteenth completely failed to predict the storm development the development took place within a strong baroclinic zone as a shallow frontal wave traveled from the relatively stable environment of a long wave ridge to the unstable environment of a long wave trough winds at jet stream level exceeded 90 m s 1 prior to the explosive deepening the lifted index in and ahead of the storm diminished and became negative prior to the rapid intensification measurements revealed that sensible and latent heat fluxes from the ocean contributed significantly to the reduced sta

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

wildfire history and climatic change in the semi arid loess tableland in the middle reaches of the yellow river of china during the holocene evidence from charcoal records high resolution macroscopic charcoal and sediment analysis was used to reconstruct fire history and environmental changes from three loess paleosol profiles on the semi arid loess tableland landsca

a source study of the thessaloniki northern greece 1978 earthquake sequence summary the thessaloniki northern greece earthquake sequence appears to have occurred along faults forming a graben structure this graben situated in the border region between the serbomacedonian massif and the vardar zone is bounded to the south west by clearly exposed north west striking north east dipping normal faults relative hypocentre determinations fault plane solutions surface faulting and the aftershock distribution suggest that some of these faults have been reactivated during the 1978 earthquakes the source parameters of the mainshock mb 6 1 ms 6 4 were determined by computing body wave synthetic seismograms in the time domain and comparing them with the observed this modelling constrained the orientation of faulting determined by the p wave fault plane solution it also constrained the source depth to 6 mp 2 km similar depths were calculated by a relative relocation method for the other three large events of the sequence the dislocation time function required for the far field had a total duration of 9 mp 1 5 s the body wave moment was 5 2 mp 1 8 times 1025 dyne cm for a fault length of 35 km and a fault width of 17 km both estimated from the aftershock distribution the static stress drop was found to be 4 bar an accelerograph record of the mainshock shows two distinct events 3 4 s apart these two events were unresolved by the long period data in the far field but the unusually long duration of the mainshock time function suggests an overall slow energy release which probably occurred as a sequence of events close in space and time seismic energy released in this fashion can account for waveform complexities observed at some stations

variations in loess and palaeosol properties as indicators of palaeoclimatic gradients across the loess plateau of north china abstract new data are presented on micromorphology magnetic susceptibility and particle size characteristics of three soil sediment units at four locations along a wnw ese transect across the loess plateau of north china differences and spatial trends are used to assess the sensitivity of such data as proxies of regional palaeoclimatic gradients the steepest climatic gradient suggested by the magnetic susceptibility for the s1 palaeosol is at the eastern humid end of the traverse micromorphology and particle size analysis show that the loess units in the east are richer in clay than the best developed palaeosols in the semi arid west and that particle size in the west appears to provide a more sensitive record of climatically driven changes than magnetic susceptibility the use of surface and near surface soils as a datum for inferring palaeoprecipitation values is reviewed in the light of recent evidence of substantial degradation of such soils micromorphological and particle size analysis of closely spaced samples from loess palaeosol sequences is a sensitive addition to magnetic susceptibility stratigraphy and correlation

coseismic crustal deformation on a fault zone defined by microseismicity in the pavliani area central greece summary pavliani is an area of high microseismicity in northern central greece there is no evidence in the historical record of large damaging earthquakes in this area since at least 600 bc we examine contemporary crustal deformation in this area using microearthquake data recorded during 1983 84 by the volos seismic network principally and to a lesser extent by the patras seismic network the microseismicity 1 4 6 ml defines an approximately vertical fault zone trending wsw ene of 55 km length and 25 km depth the fault plane solution for the 4 6 m earthquake shows a strike consistent with the trend of the microseismicity zone and an extension direction consistent with many large earthquakes in central greece associated with the extensional greater aegean spectra of the microearthquakes are estimated using p waves obtained by selective windowing designed to exclude other p phases from the coda seismic moments in the range 1 95 x 10 n m are obtained accompanied by estimates of seismotectonic source parameters including source radii average stress drop and average coseismic slip of prime utility is an excellent correlation found between seismic moment and magnitude and with coseismic slip this allows heterogeneity in the distribution of individual microearthquake source parameters to be mapped onto the vertical fault zone plane and the history of coseismic deformation for the whole seismicity observed during 1983 84 to be examined using cumulative slip and moment release rate peaks of high moment release rate occur in the east and centre of the fault zone that in the east is dominated by a few large moment release events that in the centre by a large number of small events both moment release rate peaks despite their different component seismicity are associated with high cumulative coseismic slip only the eastern peak is also associated with high stress drop it is also shallower and therefore any surficial interaction is less likely to be attenuated the surface projection of this peak is within 3 km of a mapped normal fault coincident with an alpine thrust front delineated by a major scarp of mesozoic limestone surface evidence of recent movement on this normal fault is only slight friable fault gouge is seen at a few localities displacement could not be determined because the limestone surfaces are deeply weathered and lack kinematic indicators however considering the whole fault zone as a cohesive entity and using a brune estimate of slip at the current moment release rate throughout the present extensional tectonic regime suggests a total vertical displacement of order 175 m similar to the elevation of the scarp

three dimensional seismic attenuation structure beneath the aegean region and its tectonic implication abstract the three dimensional attenuation structure beneath the aegean sea and the surrounding regions is determined by inversion of seismic intensity data a large number of seismic intensity data have been accumulated in a uniform scale in the aegean region where the seismic activity is much higher than that of the other mediterranean regions nearly 7000 seismic intensity data from 50 earthquakes that have occurred in these regions are used to determine seismic attenuation structure and source acceleration of the earthquakes the resultant structure reveals a remarkable contrast of attenuation in the top layer depth 0 40 km low q is dominant in the aegean sea while high q is dominant in the surrounding land areas except for the southwestern turkey the low q regions correspond to areas of neogene quaternary grabens where the high seismicity of shallow earthquakes appears in the upper mantle high q zones corresponding to the subducting african plate dominate along the hellenic arc the irregular shape of high q zones might reflect the split or disintegration of the african slab some low q spots corresponding to the distribution of volcanoes exist along the volcanic arc the low q spots might correspond to diapirs causing the subduction volcanism

a climatology of rossby wave breaking along the subtropical tropopause ten years 1986 95 of global analyses from the european centre for medium range weather forecasts are used to investigate the temporal and spatial distributions of rossby wave breaking rwb at 350 k along the tropopause herein defined by the 61 5 potential vorticity pv unit 10 26 km 2 s21 kg21 contours though many studies acknowledge rwb as an important contributor to the complex of mixing processes in the atmosphere there exists no prior climatological study of its distribution near the tropopause as in previous studies rwb is identified in the global analyses by southward directed pv gradients at 350 k rwb along the tropopause occurs preferentially during summer over the midoceans in relative proximity to the planetary scale high pressure systems in the subtropics isentropic trajectories at 350 k show that outflow from the tops of these subtropical highs directly participates in rwb over the adjacent downstream oceanic regions two regions are highlighted in this study the north pacific during boreal summer and the south atlantic during austral summer synoptic maps of breaking rossby waves in these regions are provided to reveal the acute tropopause folding in the meridional plane which characteristically accompanies rwb the rich interaction between the tropical flow and the extratropical westerly current exhibited by these cases suggests that the subtropical highs serve as important agents in the coupling between the tropical troposphere and the extratropical stratosphere as expected from theoretical considerations the locations where rwb occurs most frequently known as surf zones are shown to coexist with regionally weak time mean wind speeds and horizontal gradients of pv at 350 k

potential vorticity in the stratosphere derived using data from satellites maps of ertel s potential vorticity q are computed on an isentropic surface in the middle of the stratosphere they are derived using data from stratospheric sounding units on board noaa satellites the reliability of the maps is demonstrated mainly by conservation of q that is shown in successive analyses and by the close agreement obtained using independent data from two satellites the maps are used to follow the movement of material during the course of strong disturbances which occurred in december 1981 they clearly show the breaking of planetary waves in the stratosphere an inherently nonlinear process the effect of wave breaking on the structure of the westerly vortex is considered any mixing of q on isentropic surfaces during wave breaking is shown to be far from complete in the examples studied the behaviour of diagnostics based on zonal averaging such as the eliassen palm flux is accounted for by local changes in the distribution of q the implications of our findings for the study of stratospheric dynamics are discussed

suppression of baroclinic instability in horizontally sheared flows abstract baroclinic instability in the presence of a meridionally sheared barotropic component to the basic flow is studied using a two level model the inclusion of a linear shear results in merldionally confined normal modes with growth rates much reduced compared to the unsheared case similar results hold for more complicated situations such as a baroclinic jet with barotropic shear the results are applied to life cycle calculations in which it is shown that the nonlinear decay phase of a baroclinic disturbance sets up barotropic shears whichtend to suppress further baroclinic developments an example of the southern hemisphere winter mean flow is found to be strongly stabilized by virtue of a strong sheared barotropic part of the zonal flow