nonlinearity of the extratropical response to tropical forcing abstract a primitive equations dry atmospheric model is used to investigate the atmospheric response to a tropical diabatic forcing pattern and explore how the atmospheric response changes as a function of the amplitude of the forcing the forcing anomaly represents a linear fit of the model forcing to a tropical sst pattern of an el nino la nina type the time averaged 500 hpa geopotential height anomaly responses of two long integrations with forcing anomalies of equal amplitudes but opposite signs show an asymmetric feature that is similar to observations and to previous modeling results related to el nino and la nina ensemble experiments with 61 different amplitudes of this forcing pattern are conducted an eof analysis of the ensemble mean of the 90 day averaged 500 hpa height for different amplitudes of forcings shows that the leading mode of the forced variability resembles the pacific north american pna pattern while the second mode is a wave train across the north atlantic to eurasia the r

the elat aqaba dead sea jordan subgraben system abstract the elat dead sea jordan rift zone is divided into distinct subgrabens these subgrabens are separated from one another by pivotal uplifted areas the subgrabens are usually asymmetric with the sense of asymmetry changing from west to east and vice versa along the length of the rift zone most faults are meridional n s trending or submeridional nne ssw trending transverse faulting is extremely rare thus opposing the key stone theory and also the fashionable rhomb chain model our levantine chain of subgrabens are but an infra pleistocene initial stage in the afro arabian rift system

impacts of mjo convection over the maritime continent on eastern china cold temperatures abstractthe present study shows that winter cold events over eastern china can be induced by madden julian oscillation mjo associated anomalous convection over the maritime continent we conduct

coherent fluctuations of extratropical geopotential height and tropical convection in intraseasonal time scales abstract coherent fluctuations between extratropical circulation and tropical conviction in the intraseasonal time scale are studied possible relationships between 500 mb height field and outgoing longwave radiation olr are examined using correlation complex eof and composite techniques results show that in the 20 70 day bands data there is a systematic evolution of extratropical wavetrains from eurasia across the pacific to north america and the north atlantic in the time scale of 5 to 10 days over the tropics the dominant mode of intraseasonal variation in convection is an east west dipole like feature which propagates from the western indian ocean eastward to the dateline with a quasi period of 40 50 days the space time evolution of these extratropical wavetrains is found to he coherent with the tropical dipolar convection and with the strongest convection over indonesia central pacific in approximate quadrature with the peak phase of the eurasia and pacific north america wavetrains while the

factors determining the extratropical response to equatorial diabatic heating anomalies abstract the steady linear response of a spherical baroclinic atmosphere to an equatorial diabatic heat source having a simple horizontal and vertical structure is examined this source is imposed upon representative zonally symmetric as well as zonally varying flows during the boreal winter two climatologies are considered one is a 6 year average of global observations analyzed at the european centre for medium range weather forecasts ecmwf the other is a 30 year average taken from a general circulation model gcm run at the geophysical fluid dynamics laboratory in princeton the extratropical response is found to be very sensitive to the basic state around which the governing primitive equations are linearized and in the case of the ecmwf climatology to the longitudinal position of the source with respect to the climatological waves there is also some sensitivity to the vertical level of maximum heating although again this is more evident in the case of the ecmwf basic state these results ar

tropical convection and precipitation regimes in the western united states abstract the authors have documented the relationship between tropical convection and precipitation regimes in the western united states circulation patterns associated with precipitation regimes are described and physical mechanisms are proposed contributions from intraseasonal and interannual bands are examined when enhanced convection is located in the western pacific dry conditions in the southwest sw and wet conditions in the pacific northwest pnw are observed fluctuations in both intraseasonal and interannual bands contribute to the rainfall variability enhanced convection in the western pacific is accompanied by suppressed convection in the central pacific the associated rossby wave vorticity source s anomalies keep the pacific jet west of 150 w a westward shift of the storm track to the north pacific also contributes to dry conditions in the sw and wetness in the pnw when enhanced tropical convection is located near 150 e substantial contributions to outgoing longwave radiation ano

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

the nonlinear transient atmospheric response to tropical forcing abstract ensemble integrations using a primitive equation dry atmospheric model were performed to investigate the atmospheric transient response to tropical thermal forcings that resemble el nino and la nina the response develops in the north pacific within 1 week after the integration the signal in the north atlantic and europe is established by the end of the second week significant asymmetry was found between the responses in el nino and la nina that is similar to the observations that is one feature is that the 550 hpa positive height response in the north pacific of the la nina run is located about 30 west of the negative response of the el nino run another feature is that the responses in the north atlantic and europe for the la nina and el nino cases have similar patterns with the same polarity the first feature is established within 2 weeks of the integration while the second feature develops starting from the end of the second week several factors contribute to this nonlinearity of the

unraveling the teleconnection mechanisms that induce wintertime temperature anomalies over the northern hemisphere continents in response to the mjo abstractsignificant extratropical surface air temperature variations arise as a result of teleconnections induced by the madden julian oscillation mjo the authors elucidate the detailed physical processes responsible for the development of temperature anomalies over northern hemisphere continents in response to mjo induced heating using an intraseasonal perturbation thermodynamic equation and a wave activity tracing technique a quantitative assessment demonstrates that surface air temperature variations are due to dynamical processes associated with a meridionally propagating rossby wave train over east asia a local hadley circulation causes adiabatic subsidence following mjo phase 3 to be a main driver for the warming meanwhile for north america and eastern europe horizontal temperature advection by northerlies or southerlies is the key process for warming or cooling a ray tracing analysis illustrates that rossby waves with zonal wavenumbers 2 and 3 influence the surface warming over north amer

the influence of the madden julian oscillation on canadian wintertime surface air temperature abstract using the homogenized canadian historical daily surface air temperature sat for 210 relatively evenly distributed stations across canada the lagged composites and probability of the above and below normal sat in canada for different phases of the madden julian oscillation mjo in the winter season are analyzed significant positive sat anomalies and high probability of above normal events in the central and eastern canada are found 5 15 days following mjo phase 3 which corresponds to an enhanced precipitation over the indian ocean and maritime continent and a reduced convective activity near the tropical central pacific on the other hand a positive sat anomaly appears over a large part of northern and northeastern canada about 5 15 days after the mjo is detected in phase 7 an analysis of the evolution of the 500 hpa geopotential height and sea level pressure anomalies indicates that the canadian sat anomaly is a result of a rossby wave train associated with the tropical convection anomal

persistent north pacific circulation anomalies and the tropical intraseasonal oscillation abstract a composite analysis of multiyear 1985 93 global reanalyses produced by the ncep ncar and the nasa dao is used to show that the development of persistent north pacific pnp circulation anomalies during nh winter is linked to tropical intraseasonal oscillations the development is initiated over the tropical west pacific by anomalous convection characterized by an east west dipole structure one to two weeks prior to the extratropical onset time in both reanalyses as tropical heating moves eastward toward the central pacific anomalous divergent outflow associated with the local hadley circulation generates an anomalous rossby wave sink source in the subtropics consistent with the retraction extension of the pacific jet prior to onset the signature of the forced anomalies is a pair of cyclonic anticyclonic circulation anomalies centered near the node of the tropical heating dipole wave trains extending from the region of anomalous convection into the extratropics set the stage for th

the interaction of the madden julian oscillation and the arctic oscillation abstract tropical and extratropical interactions on the intraseasonal time scale are studied in the context of the arctic oscillation ao and the madden julian oscillation mjo to simplify the discussion a high low mjo phase is defined as strong suppressed convective activity over the indian ocean in the northern hemisphere nh winter season a high low ao phase is found more likely coupled with a high low mjo phase based on the regressed patterns and composites of various dynamical fields and quantities possible mechanisms linking the ao and the mjo are examined the analysis indicates that the mjo influence on extratropical circulations seems more evident than the ao influence on tropical circulations the mjo interacts with the ao through meridional dispersion of rossby waves in the pacific sector the geopotential height anomaly center over the north pacific associated with the mjo can either reinforce or offset the ao pacific action center as a result the ao pattern can be greatly a

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

the global response to tropical heating in the madden julian oscillation during the northern winter a life cycle of the madden julian oscillation mjo was constructed based on 21 years of outgoing long wave radiation data regression maps of ncep ncar reanalysis data for the northern winter show statistically significant upper tropospheric equatorial wave patterns linked to the tropical convection anomalies and extratropical wave patterns over the north pacific north america the atlantic the southern ocean and south america to assess the cause of the circulation anomalies a global primitive equation model was initialized with the observed three dimensional 3d winter climatological mean flow and forced with a time dependent heat source derived from the observed mjo anomalies a model mjo cycle was constructed from the global response to the heating and both the tropical and extratropical circulation anomalies generally matched the observations well the equatorial wave patterns are established in a few days while it takes approximately two weeks for the extratropical patterns to appear the model response is robust and insensitive to realistic changes in damping and basic state the model tropical anomalies are consistent with a forced equatorial rossby kelvin wave response to the tropical mjo heating although it is shifted westward by approximately 20 longitude relative to observations this may be due to a lack of damping processes cumulus friction in the regions of convective heating once this shift is accounted for the extratropical response is consistent with theories of rossby wave forcing and dispersion on the climatological flow and the pattern correlation between the observed and modelled extratropical flow is up to 0 85 the observed tropical and extratropical wave patterns account for a significant fraction of the intraseasonal circulation variance and this reproducibility as a response to tropical mjo convection has implications for global medium range weather prediction copyright 2004 royal meteorological society

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

gas hydrate physical properties imaging by multi attribute analysis blake ridge bsr case history abstract we analysed the bottom simulating reflector bsr of the blake ridge by using the multi attribute analysis this technique allows prediction of petrophysical geological parameters along seismic lines velocity porosity density resistivity etc starting from log data seismic attributes can be thought of as all parameters derived from seismics by assuming that a seismic trace is the real component of a complex one the first attributes that can be calculated are the instantaneous amplitude the instantaneous phase and the instantaneous frequency all the other attributes that will be considered are derived from the previous ones the algorithm that allows the correlation between logs and seismics is the generalised multiple linear regression this equation is solved by a least squares approach called training phase which effectively consists of training the seismics to predict the reservoir parameter of interest at the tie locations the resulting function is then applied to the seismic profile generating a target log predicted section we obtained five sections vsp and p wave velocity density porosity and resistivity each of them representing the distribution of the corresponding property along the profile they permitted better characterisation of the nature of the bsr present in the blake ridge area the obtained velocity section was finally translated in terms of gas hydrate and free gas distribution by using theoretical approach

another look at influences of the madden julian oscillation on the wintertime east asian weather 1 as one of the major predictability sources on an intraseasonal time scale the madden julian oscillation mjo exerts a profound influence on the subseasonal forecast of the east asian ea surface air temperature sat and precipitation in this study we examine the direct link of the mjo with the ea sat and precipitation and its dynamical mechanism to represent the mjo we perform an empirical orthogonal function eof analysis on pentad outgoing longwave radiation olr over 20 s 20 n 60 e 150 w the eof1 mode is mostly characterized by a single convection center near the maritime continent 90 150 e whereas the eof2 mode has an east west dipole structure with enhanced convection over the eastern indian ocean and suppressed convective activities over the tropical western pacific at the same pentad of a positive eof1 phase large areas of cold anomalies with reduced precipitation emerge in the ea region north of 20 n and persist through two pentads later at the same pentad of a positive eof2 phase sat and precipitation exhibit a zonal dipole pattern with cold and dry anomalies covering the ea region west of 120 e and warm and wet anomalies to the east these dipole anomalies in sat and precipitation systematically move eastward in the next two pentads a linearized global primitive equation model is utilized to assess the cause of the intraseasonal variability in sat and precipitation over east asia associated with the tropical heating of the mjo the model responses to heating sources that mimic the eof1 and eof2 olr patterns match well the general features of the observed circulation anomalies under forcing of a positive phase of the eof1 pattern strengthened local hadley cell or monsoon circulations within 90 e 150 e are reproduced with anomalous northerly winds and dry anomalies prevailing in the lower troposphere over east asia the processes that influence east asia are mainly associated with intraseasonal changes in local hadley circulation and the northern hemisphere branch of the equatorially trapped rossby wave gyres forced by the mjo heating

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

el nino la nina and the nonlinearity of their teleconnections the paradigm of an atmospheric system varying linearly with respect to extreme phases of the el nino southern oscillation is questioned it is argued that the global response to tropical pacific sea surface temperature forcing will be inherently nonlinear a physical basis for this intrinsic nonlinearity is the thermodynamic control on deep convection climate statistics for warm and cold events of the tropical pacific are analyzed separately for the northern winter periods during 1950 96 composite analysis of 500 mb heights reveal planetary scale teleconnection patterns as noted in earlier studies a new result is the evidence for an appreciable 358 longitude phase shift between the warm and cold event circulation composites and the two wave trains appear to have different tropical origins a large nonlinear component in north american surface climate anomalies is also found which is consistent with such a phase shift in teleconnections in the tropics rainfall anomalies also show evidence of nonlinear behavior the maximum rain anomalies along the equator are located east of the date line during warm events but west of the date line during cold events the interpretation of this behavior is complicated however by the fact that composite warm event sst anomalies are not the exact inverse of their cold event counterparts idealized atmospheric general circulation model agcm experiments are performed in order to test the question of whether the observed nonlinearity is an intrinsic property of the atmospheric system the model is forced with a composite sst anomaly that undergoes a realistic seasonally varying enso life cycle as described by e rasmusson and t carpenter both positive and negative phases of the sst anomaly are used and a 40 member ensemble of warm and cold event model simulations is conducted a nonlinear climate response in the agcm is found that closely resembles the observed composites including a shift in the equatorial positions of the maxmium rain responses and a phase shift of teleconnection patterns in the upper troposphere barotropic model experiments indicate that the inherent nonlinearity in the tropical rain response may itself be responsible for the phase shift in the extratropical teleconnection patterns

intraseasonal variability in a dry atmospheric model abstract a long integration of a primitive equation dry atmospheric model with time independent forcing under boreal winter conditions is analyzed a variety of techniques such as time filtering space time spectral analysis and lag regressions are used to identify tropical waves it is evident that oscillations with intraseasonal time scales and a kelvin wave structure exist in the model tropical atmosphere coherent eastward propagations in the 250 hpa velocity potential and zonal wind are found with a speed of about 15 m s 1 the oscillation is stronger in the eastern hemisphere than in the western hemisphere interactions between the tropical and extratropical flows are found to be responsible for the simulated intraseasonal variability wave activity flux analysis reveals that a tropical influence occurs in the north pacific region where a northeastward wave activity flux is found associated with the tropical divergent flow in the western and central pacific in the north atlantic sector on the ot