roles of synoptic to quasi biweekly disturbances in generating the summer 2003 heavy rainfall in east china abstractduring the mei yu season of the summer of 2003 the yangtze and huai river basin yhrb encountered anomalously heavy rainfall and the northern yhrb nyhrb suffered a severe flood because of five continuous extreme rainfall events a spectral analysis of daily rainfall data over yhrb reveals two dominant frequency modes one peak on day 14 and the other on day 4 i e the quasi biweekly and synoptic scale mode respectively results indicate that the two scales of disturbances contributed southwesterly and northeasterly anomalies respectively to the mei yu frontal convergence over the southern yhrb syhrb at the peak wet phase an analysis of bandpass filtered circulations shows that the lower and upper regions of the troposphere were fully coupled at the quasi biweekly scale and a lower level cyclonic anomaly over syhrb was phase locked with an anticyclonic anomaly over the philippines at the synoptic scale the strong northeasterly components of an anticyclonic anomaly with a deep cold

a spectrum analysis of synoptic scale disturbances in the itcz abstract spectral characteristics of convective signals in synoptic scale disturbances along the intertropical convergence zone itcz are examined using a 20 yr daily outgoing longwave radiation dataset a new analysis method which combines conventional wavenumber frequency spectrum analysis and wavelet analysis is developed to explore the longitudinal seasonal and interannual variations in these disturbances within the itcz whose seasonal migration varies in different parts of the tropics the analysis focuses on three longitudinal sectors where the itcz can be clearly identified the western central pacific the central eastern pacific and the atlantic west africa the most striking results are the evident zonal variability in the spectral properties of westward propagating synoptic scale disturbances the zonal variability exists not only in their dominant frequencies and zonal wavenumbers but also in their seasonal and interannual variations eastward propagating synoptic scale disturbances in

the structure and annual variation of antisymmetric fluctuations of tropical convection and their association with rossby gravity waves abstract the signature of 4 5 day period rossby gravity waves is searched for in the tropical convection field across the indian pacific oceans the convergence divergence field of these waves in the lower troposphere is anticipated to produce an antisymmetric fluctuation in tropical convection antisymmetric fluctuations of tropical convection are shown to exhibit a pronounced spectral peak at a 4 5 day period only during boreal fall and only within about 30 longitude of the date line the peak amplitude occurs around 7 5 latitude these fluctuations propagate westward at 15 20 m s 1 with zonal wavelength of about 7000 9000 km the fluctuations of convection are coherent and out of phase with the equatorial meridional wind which also exhibits a pronounced spectral peak at a 4 5 day period in the lower troposphere near the date line the antisymmetric zonal wind also is strongly coherent with the antisymmetric convective fluctuations in this region the horizontal distributions of the 4 5 day power an

sst anomalies of enso and the madden julian oscillation in the equatorial pacific this study explores whether anomalies of sea surface temperature sst in the equatorial pacific during warm events of el nino southern oscillation enso are related to the madden julian oscillation mjo an index is derived from surface wind data of a global model reanalysis to measure forcing of oceanic kelvin waves by wind stress associated with the mjo this kelvin wave forcing index of the mjo is used to relate interannual anomalies in seasonal activity of the mjo to interannual anomalies in equatorial sst for the 1980 99 time period evidence is found showing that during enso warm events stronger kelvin wave forcing in the western pacific precedes greater sst anomalies in the eastern pacific by 6 12 months no such evidence however can be found for the period of 1950 79 the result suggests that during enso warm events amplitudes of sst anomalies in the eastern pacific can be affected by the mjo at least for the 1980 99 period through its seasonal activity of kelvin wave forcing a possible mechanism for such an mjo enso relationship is described how enso prediction can be benefited from the precursory signals of the mjo is discussed

large scale characteristics of the atmospheric boundary layer in the eastern pacific cold tongue itcz region abstract observations from the eastern pacific investigation of climate 2001 epic2001 field campaign and a simple mixed layer model are used to study the large scale structure and dynamics of the atmospheric boundary layer abl in the eastern pacific vertical and latitudinal distributions of the meridional pressure gradient winds and other variables are examined and the momentum balance of the mixed layer is explored for a latitudinal range from 0 to 10 n along 95 w including the equatorial cold tongue sea surface temperature sst front and convective region at the latitude of the intertropical convergence zone itcz the surface meridional pressure gradient is partitioned into contributions from the abl largely controlled by the gradient in sst and from the troposphere above the boundary layer mainly controlled by elevated heating and atmospheric wave activity the mean meridional gradient in surface pressure is dominated 90 by the abl contribution however its temporal variability prim

cementation in oligo miocene non tropical shelf limestones otway basin australia abstract the oligocene to miocene heytesbury group of the otway basin southeastern australia is a non tropical carbonate shelf succession this subsurface stratigraphic succession consists of bioclastic grainstones to mudstones containing bryozoa benthonic and planktonic foraminifera echinoderms brachiopods and molluscs the basal bryozoa dominated clifton formation was deposited in relatively shallow waters the overlying gellibrand marl rich in planktonic foraminifera and bryozoa formed under deep waters the uppermost unit benthonic foraminifera dominated port campbell limestone was deposited in a moderately deep middle shelf environment cementation is limited and includes 1 scalenohedral calcite non luminescent to bright mn and fe poor in inter and intraparticle porosity 2 blocky equant calcite dull mn and fe rich in interparticle porosity 3 syntaxial calcite overgrowths on echinoderm particles non bright dull zoned 4 euhedral dolomite in the interparticle pore space of the port campbell limestone 5 bladed prismatic calcite ferroan in planktonic foraminifera 6 fibrous calcite non luminescent in intraparticle porosity and 7 glauconite and iron oxides only in intraparticle porosity all caco3 cements are low mg calcites the cements observed in the heytesbury group appear to have formed in three successive diagenetic environments 1 early shallow burial early fe and mn poor non luminescent syntaxial overgrowths and non luminescent scalenohedral calcite under oxidising conditions 2 late shallow burial bright more mn rich syntaxial overgrowth zone i e more than the initial non luminescent one and bright scalenohedral calcite under moderately reducing pore water conditions and 3 moderate burial ferroan dull blocky calcite and dull syntaxial overgrowth zone under reducing conditions pressure solution was the main cement producing mechanism although seawater and aragonite dissolution could account for the precipitation of the early non luminescent cements scarcity of early interparticle cements may have been caused by the calcite rich character of the original sediments the ferroan dully luminescent blocky equant calcite and syntaxial overgrowths typically interpreted to represent products of deep burial in ancient carbonate successions are observed in the shallow buried port campbell limestone

effects of zonal flows on equatorially trapped waves abstract linear shallow water equations are employed to study the effects of basic zonal flows on equatorially trapped waves analytical solutions are obtained for constant basic zonal flows it is shown that changes in the wave structures due to the non doppler effect of the basic zonal flow are considerable for the rossby wave moderate for the westward propagating mixed rossby gravity wave but negligible for the other equatorial waves the rossby wave and the westward propagating mixed rossby gravity wave possess greater eigenfrequencies and are less trapped in westerlies than in easterlies the dependence of the rossby wave structure upon the basic zonal flow is interpreted in terms of potential vorticity conservation in basic zonal flows with meridional shears the eigenfrequencies are found to be larger in equatorial easterlies than in equatorial westerlies for the westward propagating waves but smaller for the eastward propagating waves while the meridional structures of the eastward propagating

why the itcz is mostly north of the equator abstract although the distribution of sunshine is symmetrical about the equator the earth s climate is not climatic asymmetries are prominent in the eastern tropical pacific and atlantic oceans where the regions of maximum sea surface temperature convective cloud cover and rainfall are north of the equator this is the result of two sets of factors interactions between the ocean and atmosphere that are capable of converting symmetry into asymmetry and the geometries of the continents that determine in which longitudes the interactions are effective and in which hemisphere the warmest waters and the intertropical convergence zone are located the ocean atmosphere interactions are most effective where the thermocline is shallow because the winds can readily affect sea surface temperatures in such regions the thermocline happens to shoal in the eastern equatorial pacific and atlantic but not in the eastern indian ocean because easterly trade winds prevail over the tropical atlantic and pacific wher

synoptic scale disturbances near the equator abstract a spectral analysis of winds analyzed and initialized at the european centre for medium range weather forecasts reveals an abundance of power in the 850 mb meridional wind along the equator with periods near four days the power is mostly in the westward propagating component using high pass filtered data it is shown that the waves have westward phase and eastward group propagation relative to the mean wind the longest wavelengths are found over the pacific ocean while the shortest are found over the convectively variable regions of indonesia south america and africa mean phase speeds at 850 mb are positively correlated with the mean wind on the equator at 500 mb and below and negatively correlated with the mean wind above that level the effective advecting zonal wind of the disturbances seems to be the density weighted average of the lower troposphere the structure of the disturbances bears resemblance to the expected structure of an equatorially trapped mixed rossby gravity wave over t

cloud components of the intertropical convergence zone 1 this study explores the roles of different synoptic scale cloud systems in the making of the intertropical convergence zone itcz outgoing longwave radiation olr data are used to represent both the mean itcz and cloud systems an olr threshold of 205 w m 2 is used to distinguish daily mean deep convective clouds from nondeep clouds zonally moving synoptic scale cloud systems are identified through a cloud tracking method mean olr of the itcz is decomposed into five components westward and eastward moving synoptic scale deep convective clouds random nonpropagating deep convective clouds nondeep clouds and clear sky backgrounds hypothetical itczs each composed of one of the cloud components and the clear sky background are constructed and compared the largest synoptic scale cloud constituents of the itcz are nondeep clouds and deep clouds with no persistent tendency of zonal propagation each of the two comprises about 40 45 of total cloud signals in the itcz a weak itcz could exist solely because of westward propagating synoptic scale deep convective clouds in reality these westward propagating clouds contribute 25 40 of deep convective clouds and 10 20 of total clouds in the itcz contributions from eastward propagating synoptic scale clouds are much smaller 8 of the deep convective clouds and less than 5 of total clouds in the itcz an itcz without any zonally propagating synoptic scale deep convective clouds would be diffused in latitude the cloud compositions in the itcz and other tropical convective zones are compared their discrepancies indicate fundamental characteristics in large scale environments for the cloud components in different regions

annual and inter annual variability of the present climate in northern south america and southern mesoamerica abstract present climate of northwestern south america and the southern isthmus is detailed in terms of major hydro climatic controls supported by evidence from station records reanalysis data and satellite information in this tropical region precipitation is the principal hydro climatological variable to display great variability the primary objective is to view the controls that operate at intra seasonal to inter decadal time scales this is a topographical complex region whose climate influences range in provenance from the south atlantic to the canadian prairies and from the north atlantic to the eastern pacific the situation is further complicated by interactions and feedbacks in time and space between these influences which are interconnected over various scales the greatest single control on the annual cycle is the meridional migration of the inter tropical convergence zone and its pattern of associated trade winds consideration of these alone and their interaction with the cordilleras of the andes and central america produce a variety of unimodal and bimodal regimes regionally two low level jet streams the westerly choco jet 5 n and the easterly san andres jet 12 14 n and their seasonal variability have tremendous significance as do mesoscale convective storms and mid latitude cold fronts from both the northern nortes and southern friagems hemispheres there are many examples of hydro climatological feedbacks within the region of these the most notable is the interaction between evaporation over the amazon precipitation onto the eastern andes and streamflow from the headwaters of the amazon this is further compounded by the high percentages of recycled precipitation over large areas of the tropics and the potential impacts of anthropogenic modification of the land surface the el nino southern oscillation phenomenon enso is the greatest single cause of interannual variability within the region yet its effects are not universal in their timing sign or magnitude a set of regional physical connections to enso are established and their varying local manifestations are viewed in the context of the dominant precipitation generating mechanisms and feedbacks at that location in addition some potential impacts of longer run variations within the ocean atmosphere system of the atlantic are examined independently and in conjunction with enso this review of the climatic controls and feedbacks in the region provides a spatial and temporal framework within which the highly complex set of factors and their interactions may be interpreted from the past

diagenetic comparisons between non tropical cenozoic limestones of new zealand and tropical mississippian limestones from indiana usa is the non tropical model better than the tropical model abstract mississippian limestones exposed in indiana u s a were deposited in a shallow tropical ocean however many properties of these limestones are more like those of modern and cenozoic non tropical limestones such as those found in new zealand the dominant skeletal grains in the indiana limestones are calcitic echinoderms bryozoans and brachiopods the dominant skeletal grains in most cenozoic limestones of new zealand are calcitic bryozoans echinoderms bivalve molluscs and foraminifera in contrast modern and cenozoic tropical limestones contain an abundance of aragonitic green algae corals and molluscs early in diagenesis the metastable aragonite dissolves and reprecipitates as calcite causing early cementation of the sediments originally aragonitic fossils that have dissolved can be identified as molds that are commonly filled with secondary calcite because they contained little aragonite most of the indiana and new zealand limestones did not have an abundant source of early cement except for local cases in which grains were cemented in contact with carbonate supersaturated seawater grainstones were relatively deeply buried with little cement between the grains this resulted in mechanical and chemical compaction of skeletal grains producing a fitted fabric with greatly reduced pore space either open or filled with cement between the grains cement in these aragonite poor grainstones comes largely from pressure dissolution between grains and along stylolitic seams in the rock features that are common only after burial beyond a few hundred meters the final product of deeply buried up to 2000 m cenozoic new zealand grainstones is similar to the mississippian grainstones of indiana in the indiana limestones we have only the final product of this extensive burial diagenesis however the new zealand sediments and rocks reveal all steps of formation of the final deeply buried limestone the reason for the scarcity of originally aragonitic fossil grains in paleozoic rocks worldwide is unknown organisms with aragonitic skeletons such as some molluscan groups and calcareous green algae were present but seldom in much abundance the aragonitic scleractinian corals had not yet evolved previous researchers have noted that non skeletal precipitates such as ooids and cements have at times during the paleozoic been predominantly aragonite and at other times calcite they have attributed this difference to secular variation in seawater chemistry icehouse vs greenhouse seas abundance of aragonitic and calcitic skeletal grains does not follow this pattern

the relationship between anomalous presummer extreme rainfall over south china and synoptic disturbances a spectral analysis of daily rainfall data has been performed to investigate extreme rainfall events in south china during the presummer rainy seasons between 1998 2015 excluding 1999 2006 2011 and 2014 the results reveal a dominant frequency mode at the synoptic scale with pronounced positive rainfall anomalies by analyzing the synoptic scale bandpass filtered anomalous circulations 24 extreme rainfall episodes defined as those with a daily rainfall amount in the top 5 are categorized into cyclone 15 and trough 8 types with the remaining events as an anticyclone type according to the the primary anomalous weather system contributing to each extreme rainfall episode the 15 cyclone type episodes are further separated into 11 lower and 4 upper tropospheric migratory anomalies an analysis of their anomalous fields shows that both types could be traced back to the generation of cyclonic anomalies downstream of the tibetan plateau except for two episodes of lower tropospheric migratory anomalies originating over the south china sea however a lower tropospheric cyclonic anomaly appears during all phases in the former type but only in the wettest phase in the latter type with its peak disturbance occurring immediately beneath an upper level warm anomaly the production of extreme rainfall in the trough type episodes is closely related to a deep trough anomaly extending from an intense cyclonic anomaly over north china which in turn could be traced back to a mid latitude rossby wave train passing by the tibetan plateau the results have important implications for understanding the origin structure and evolution of synoptic disturbances associated with the pre summer extreme rainfall in south china

influence of surface processes over africa on the atlantic marine itcz and south american precipitation abstract previous studies show that the climatological precipitation over south america particularly the nordeste region is influenced by the presence of the african continent here the influence of african topography and surface wetness on the atlantic marine itcz ami and south american precipitation are investigated cross equatorial flow over the atlantic ocean introduced by north south asymmetry in surface conditions over africa shifts the ami in the direction of the flow african topography for example introduces an anomalous high over the southern atlantic ocean and a low to the north this results in a northward migration of the ami and dry conditions over the nordeste region the implications of this process on variability are then studied by analyzing the response of the ami to soil moisture anomalies over tropical africa northerly flow induced by equatorially asymmetric perturbations in soil moisture over northern tropical africa shifts the ami southward increasing the climatological pre

atlantic seasonal hurricane frequency part i el nino and 30 mb quasi biennial oscillation influences abstract this is the first of two papers on atlantic seasonal hurricane frequency in this paper seasonal hurricane frequency as related to e1 nino events during 1900 82 and to the equatorial quasi biennial oscillation qbo of stratospheric zonal wind from 1950 to 1982 is discussed it is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes hurricane days and tropical storms and moderate or strong 15 cases el nin off the south american west coast a similar negative anomaly in hurricane activity occurs when equatorial winds at 30 mb are from an easterly direction and or are becoming more easterly with time during the hurricane season this association of atlantic hurricane activity with el nino can also be made with the southern oscillation index by contrast seasonal hurricane frequency is slightly above normal in non el nino years and substantially above normal when equatorial stratospheric winds blow from a westerly direction and or are bec

observation of 3 6 day meridional wind oscillations over the tropical pacific 1973 1992 vertical structure and interannual variability abstract rawinsonde data from tropical pacific stations were examined for westward propagating 3 6 day meridional wind oscillations in the troposphere and lower stratosphere 1973 1992 four types were identified from cross spectrum and principal component analysis 1 the dominant oscillation near 250 mb had a period slightly greater than 5 days zonal wavenumber 4 6 and modified rossby gravity structure near the date line 2 in the western pacific lower troposphere there was broadband activity with short zonal scale coupled to upper tropospheric waves in nh summer 3 in the central pacific during nh autumn there was a well defined 4 day oscillation with maximum amplitude in the lower troposphere and baroclinic phase tilt above the vertical structure suggested coupling to deep tropical convection this interpretation was supported by correlation of meridional wind with antisymmetric outgoing longwave radiation 4 in the stratosphere rossby gravity waves had periods 4 days and zonal wavenu

a global view of equatorial waves and tropical cyclogenesis abstractthis study investigates the number of tropical cyclone formations that can be attributed to the enhanced convection from equatorial waves within each basin tropical depression td type disturbances i e easterly waves were the primary tropical cyclone precursors over the northern hemisphere basins particularly the eastern north pacific and the atlantic in the southern hemisphere however the number of storms attributed to td type disturbances and equatorial rossby waves were roughly equivalent equatorward of 20 n tropical cyclones formed without any equatorial wave precursor most often over the eastern north pacific and least often over the western north pacific the madden julian oscillation mjo was an important tropical cyclone precursor over the north indian south indian and western north pacific basins the mjo also affected tropical cyclogenesis by modulating the amplitudes of higher frequency waves each wave type reached the attribution threshold 1 5 times more often and tropi

an observational study of easterly waves over the eastern pacific in the northern summer using fgge data abstract fgge revel iii b data provided by the european centre for medium range weather forecasts and the outgoing longwave radiation data measured by satellites are used to investigate observationally relationships between deep cloud activity and large scale meteorological fields during the northern hemisphere summer may september of 1979 over the eastern pacific aside from the summer monsoon area over southern and eastern asia the eastern pacific is the area where strong deep convection frequently develops in the northern summer this is also one of the tropical ocean areas that have been least explored meteorologically a power spectral analysis using the maximum entropy method is made for the meridional wind component at 850 mb at various grid points in the analysis domain for each mouth from may through september the waves with a period of 4 6 days are not only stronger in july and august than those of other months but active in the regions of 100 130 w in the eastern pacific and 130 160 e i

easterly wave regimes and associated convection over west africa and tropical atlantic results from the ncep ncar and ecmwf reanalyses ncep ncar and ecmwf daily reanalyses are used to investigate the synoptic variability of easterly waves over west africa and tropical atlantic at 700 hpa in northern summer between 1979 1995 1979 1993 for ecmwf spectral analysis of the meridional wind component at 700 hpa highlighted two main periodicity bands between 3 and 5 days and 6 and 9 days the 3 5 day easterly wave regime has already been widely investigated but only on shorter datasets these waves grow both north and south of the african easterly jet aej the two main tracks noted over west africa at 5 n and 15 n converge over the atlantic on latitude 17 5 n these waves are more active in august september than in june july their average wavelength phase speed varies from about 3000 km 8 m s 1 north of the jet to 5000 km 12 m s 1 south of the jet rainfall convection and monsoon flux are significantly modulated by these waves convection in the inter tropical convergence zone itcz being enhanced in the trough and ahead of it with a wide meridional extension compared to the 3 5 day waves the 6 9 day regime is intermittent and the corresponding wind field pattern has both similar and contrasting characteristics the only main track is located north of the aej along 17 5 n both over west africa and the atlantic the mean wavelength is higher about 5000 km long and the average phase speed is about 7 m s 1 then the wind field perturbation is mostly evident at the aej latitude and north of it the perturbation structure is similar to that of 3 5 days in the north except that the more developed circulation centers moving more to the north lead to a large modulation of the jet zonal wind component south of the aej the wind field perturbation is weaker and quite different the zonal wind core of the jet appears to be an almost symmetric axis in the 6 9 day wind field pattern a clockwise circulation north of the aej being associated with a counter clockwise circulation south of the jet and vice versa these 6 9 day easterly waves also affect significantly rainfall convection and monsoon flux but in a different way inducing large zonal convective bands in the itcz mostly in the trough and behind it as opposed to the 3 5 day wave regime these rainfall anomalies are associated with anomalies of opposite sign over the guinea coast and the sahelian regions over the continent these waves are more active in june july and in august september over the ocean gate phase i gave an example of such an active 6 9 day wave pattern considered as a sequence of weak easterly wave activity this phase was also a sequence of high 6 9 day easterly wave activity we suggest that the 6 9 day regime results from an interaction between the 3 5 day easterly wave regime maintained by the barotropic baroclinic instability of the aej and the development of strong anticyclonic circulations north of the jet over west africa and both north and south of the jet over the atlantic significantly affecting the jet zonal wind component the permanent subtropical anticyclones azores libya st helena could help initiation and maintenance of such regime over west africa and tropical atlantic based on an a priori period band criterion our synoptic classification has enabled us to point out two statistical and meteorological easterly wave regimes over west africa and tropical atlantic ncep ncar and ecmwf reanalyses are in good agreement the main difference being a more developed easterly wave activity in the ncep ncar reanalyses especially for the 3 5 day regime over the atlantic

controls of facies and sediment composition on the diagenetic pathway of shallow water heterozoan carbonates the oligocene of the maltese islands relatively few studies have so far addressed diagenetic processes in heterozoan carbonates and the role that sediment composition and depositional facies exert over diagenetic pathways this paper presents a study of oligocene shallow water heterozoan carbonates from the maltese islands we investigate stratigraphic distribution abundance and timing of diagenetic features and their relationship to sediment composition and depositional facies the studied carbonate rocks comprise rud to packstones of the heterozoan association predominantly containing coralline red algae bryozoans echinoids and benthic foraminifers xrd analyses show that all high mg calcite has been transformed to low mg calcite and that no aragonite is preserved diagenetic processes include dissolution of aragonitic biota neomorphism of high mg calcitic biota to low mg calcite and cementation by fibrous bladed epitaxial and blocky cements stable isotopes on bulk rock integrated with petrographic data suggest that the study interval was not exposed to significant meteoric diagenesis we interpret early cementation to have taken place in the marine and marine burial environment the distribution and abundance of early diagenetic features determining the diagenetic pathway can be related to the primary sediment composition and depositional texture sorting and micrite content are important controls over the abundance of diagenetic features

frequency distribution of daily itcz patterns over the western central pacific abstract this study attempts to explore a comprehensive and compact approach for delineating the multiscale and multivariate characteristics of the itcz over the western central pacific based on daily satellite observations of precipitation ssts and surface winds essentially six distinct itcz spatial patterns namely the north south equator double full and weak are identified according to the daily percentage coverage of deep convection within different latitudinal bands on and off the equator over the western central pacific the evolving structure of the itcz over the western central pacific is investigated with a focus on the transient statistical characteristics the relationship between these daily itcz patterns and ssts and near surface winds is also examined the north 37 south 24 and weak 24 itczs represent the three major itcz daily patterns over the western central pacific and combined they account for almost 85 of the total number of days within a 10 yr period the other

synoptic scale dual structure of precipitable water along the eastern pacific itcz abstractusing 10 yr high resolution satellite and reanalysis data the synoptic scale dual structure of precipitable water pw in which the southern and northern bands straddled at the itcz produce zonally propagating meridional dipoles is observed over the eastern pacific ep during boreal summer and fall composites indicate that the pw dipole concurrent with the dipole like filtered divergence has a shift to the west of the anomalously cyclonic circulation the vertical structure of filtered meridional wind is characterized by a wavenumber 1 baroclinic mode and the vertical motion has two peaks situated at 850 and 300 hpa respectively to the east of the pw dipole the shallow convection is embedded within the deep convection forming a multilevel structure of meridional wind on the itcz equatorward side to the west of the pw dipole the deep convection tends to be suppressed because of the invasion of midlevel dry air advected by northerly flows the generation and propagation of the dual pw

soil water saturation dielectric determination dielectric measurements of moist soils are used to determine water saturations the degree of saturation of water is determined using a mixing law for the composite structure soil water and air which is verified experimentally for the lower water saturation range 60 a particularly simple form for the relationship between fractional water content and measured dielectric constant can be formulated in particular for sandy soils at 23 c the fractional water content is given by 0 128 c 0 204

paleoclimate support for a persistent dry island effect in the colombian andes during the last 4700 years we investigated middle and late holocene hydroclimate patterns in the colombian andes using indicators of watershed erosion lithic abundance precipitation intensity silt lake level variabi

capillary pressure and saturation relations for supercritical co2 and brine in sand high pressure pc sw controller meter measurements and capillary scaling predictions capillary pressure and saturation relations for supercritical co 2 and brine in sand high pressure p c s w controller meter measurements and capillary scaling predictions tetsu k tokunaga 1 jiamin wan 1 jong won jung 1 2 tae wook kim 1 3 yongman kim 1 and wenming dong 1 1 in geologic carbon sequestration reliable predictions of co 2 storage require understanding the capillary behavior of supercritical sc co 2 given the limited availability of measurements of the capillary pressure p c dependence on water saturation s w with scco 2 as the displacing fluid simulations of co 2 sequestration commonly rely on modifying more familiar air h 2 o and oil h 2 o p c s w relations adjusted to account for differences in interfacial tensions in order to test such capillary scaling based predictions we developed a high pressure p c s w controller meter allowing accurate p c and s w measurements drainage and imbibition processes were measured on quartz sand with scco 2 brine at pressures of 8 5 and 12 0 mpa 45 o c and air brine at 21 o c and 0 1 mpa drainage and rewetting at intermediate s w levels shifted to p c values that were from 30 to 90 lower than predicted based on interfacial tension changes augmenting interfacial tension based predictions with differences in independently measured contact angles from different sources led to more similar scaled p c s w relations but still did not converge onto universal drainage and imbibition curves equilibrium capillary trapping of the nonwetting phases was determined for p c 0 during rewetting the capillary trapped volumes for scco 2 were significantly greater than for air given that the experiments were all conducted on a system with well defined pore geometry homogeneous sand and that scco 2 brine interfacial tensions are fairly well constrained we conclude that the observed deviations from scaling predictions resulted from scco 2 induced decreased wettability wettability alteration by scco 2 makes predicting hydraulic behavior more challenging than for less reactive fluids and bachu 2008 benson and cole 2008 the depend ence of capillary pressure p c on water saturation s w under reservoir conditions is a basic constitutive relation needed to predict co 2 flow and capillary trapping during sequestration indeed with only knowledge of how rela tive permeability depends on s w neither fluid flow nor equilibrium saturation conditions are predictable at later stages of geologic carbon sequestration rewetting of reser voirs with native brine results in capillary trapping resid ual trapping of co 2 a main storage mechanism bachu et al 2007 ipcc 2005 the capillary trapping capacity of reservoir materials has complex dependence on porosity pore size distribution nonwetting phase displacement extent and the rewetting process iglauer et al 2011b tanino and blunt 2012 although capillary trapping of co 2 at its residual saturation depends on p c s w relations few investigations to date have directly measured these ba sic relations with co 2 h 2 o at reservoir pressures and tem peratures krevor et al 2011 pentland et al 2011 pini et al 2012 plug and bruining 2007 the study by plug and bruining 2007 appears to be the only one in which capillary trapped scco 2 saturation was determined while 1 introduction 2 geologic carbon sequestration may become an im portant technology for mitigating co 2 buildup in the atmosphere from fossil fuel combustion and for moderating climate change intergovernmental panel on climate change ipcc 2005 however predicting the perform ance of geologic co 2 sequestration requires reliable under standing of co 2 mobility and its saturation and pressure distribution within reservoirs bachu et al 2007 bennion earth sciences division lawrence berkeley national laboratory berkeley california usa now at civil and environmental engineering department louisiana state university baton rouge louisiana usa now at department of energy resources engineering stanford uni versity stanford california usa corresponding author t k tokunaga earth sciences division law rence berkeley national laboratory 1 cyclotron rd berkeley ca 94720 usa tktokunaga lbl gov

case studies of african wave disturbances in gridded analyses abstract african wave disturbances awds an important trigger of sahel summer rainfall are studied using ecmwf gridded datasets for july and august 1987 and 1988 power spectra of time series of 700 mb meridional winds near niamey taken from analyses at both 2 2 5 and 4 5 horizontal resolution are compared to spectra based on niamey station data in addition spatial distributions of meteorological fields at both resolutions are discussed for three case studies including the synoptic features of several awds additional examples are presented from gcm simulations at comparable horizontal resolutions while vertical motion and divergence centers were more extreme at 2 2 5 many of the deduced characteristics of an awd were similar at both resolutions the higher resolution analyses and simulation show a sharp transition across wave troughs between lower tropospheric convergence uplift on the west and divergence subsidence on the east for several awds for the two more southerly awds ana

regional changes in the annual mean hadley circulation in recent decades previous studies suggest that the zonally averaged hadley circulation zahc has experienced a robust poleward expansion and its trend in intensity displays inconsistency among different data sets this study examines changes in regional hc intensity and poleward edge using six reanalyses outgoing longwave radiation and precipitation data sets hcs in six regions including africa afhc the indian ocean iohc the western pacific wphc the eastern pacific ephc south america sahc and the atlantic athc are investigated intensity trends in the northern hemisphere nh wphc and athc and the southern hemisphere sh ephc and athc are in agreement with each other in the six reanalyses furthermore regional hcs in these domains appear to be intensifying although not all of the reanalyses show statistically significant trends for the poleward edge its trend in the nh afhc iohc ephc sahc and athc is significantly larger than zero and the northern hc poleward edge exhibits uniform poleward migrations in these five regions in the sh only the trend in the sahc poleward edge is significantly different from zero furthermore the trend in the sh sahc poleward edge is significantly larger than those in the sh afhc iohc and athc the results indicate that the poleward migration of the southern zahc poleward edge during recent decades that has been identified by previous studies may be attributed mainly to the poleward migration of the southern sahc poleward edge further analyses suggest that changes in regional hc poleward edges could have a significant impact on regional precipitation anomalies

recurrent neomorphic and cement microtextures from different diagenetic environments quaternary to late neogene carbonates great bahama bank abstract the cores clino and unda taken near the western margin of great bahama bank contain a diverse suite of quaternary to late neogene carbonates that have a variety of neomorphic and cement microtextures the microtextures of each of the different neomorphosed aragonitic grain types such as corals mollusks and plates of the calcareous green algae halimeda are very similar wherever the neomorphosed grains are present in the cores limestone samples that contain neomorphosed aragonitic fossils are cemented predominantly with blocky calcite despite the similar neomorphic and cement microtextures light stable isotope data reveal that these calcites precipitated in different diagenetic environments in different parts of the cores the neomorphic calcites and associated calcite cements in the upper parts of clino and unda precipitated in meteoric influenced pore waters as indicated by 18o values ranging from 1 9 to 3 7 whereas in the lower part of clino the calcites precipitated in marine pore waters as indicated by 18o values ranging from 0 1 to 2 4 essentially identical diagenetic microtextures were thus produced in different diagenetic environments revealing a significant limitation in the use of microtextural data to determine the diagenetic histories of carbonate rocks

time lapse seismic reservoir monitoring time lapse seismic reservoir monitoring has advanced rapidly over the past decade there are currently about 75 active projects worldwide and more than 100 cumulative projects in the past decade or so the present total annual expenditures on 4 d seismic projects are on the order of 50 100 million us this currently represents a much smaller market than 3 d seismic but the use of 4 d seismic has grown exponentially over the past decade and is expected to continue to do so

a multiscale model for the modulation and rectification of the itcz abstractthe authors introduce the modulation of the itcz equations m itcz which describes the multiscale dynamics of the itcz on diurnal to monthly time scales in which mesoscale convectively coupled rossby waves in the itcz are modulated by a large scale gravity wave that is also generated by convection westward propagating disturbances are observed to cause itcz breakup over the course of a few days and the m itcz meso planetary scale coupled waves provide a mechanism for this interaction thereby providing a framework to study the modulation and rectification of the hadley circulation over long zonal length scales in the itcz the authors consider examples of zonally symmetric heating profiles in the m itcz system and generate a hadley circulation consistent with the observed winds zonally localized heating creates a wind response throughout the tropics that is carried by a pair of zonally propagating gravity bores driving mean easterlies at the base and mean westerlies at the top of the troposph

westward propagating synoptic scale disturbances and the itcz abstract in an attempt to understand the dynamics of the intertropical convergence zone itcz this study explores the extent to which the itcz is causally related to zonally propagating synoptic scale disturbances the itcz measured by its mean convection is represented by mean outgoing longwave radiation olr synoptic scale disturbances measured by their deep convective signals are represented by the spectral power of the olr that is significantly above its red noise background time mean spatial distributions as well as annual and interannual variability of the itcz are compared with those of synoptic scale disturbances which are dominated by westward propagating signals in general they match each other well in their mean distributions and annual cycles but in detail discrepancies between the two fields exist some of them substantial the maximum disturbance activity tends to be located at the polar side of the itcz the seasonal cycles of the two share many similarities but the variatio

a climatology of waves in the equatorial region abstract propagating anomalies of moisture and moist deep convection in the tropics are organized into a variety of large scale modes these include but are not limited to the so called intraseasonal oscillations convectively coupled waves similar to those predicted by shallow water theory on the equatorial beta plane and tropical depression type disturbances along with the annual and diurnal cycles these modes act and interact to control much of the variance of tropical convection analyses of 10 yr of outgoing longwave radiation olr and precipitable water pw data are carried out to develop comparative climatologies of these wavelike modes the analysis relaxes the commonly used cross equatorial symmetry constraints which allows study of the portions of the wavelike processes that are asymmetric across the equator mean background states are found for olr and for pw as functions of day of the year examination of anomalies together with the background reveals much about how the waves are affec

the itcz in the central and eastern pacific on synoptic time scales the itcz in the central and eastern pacific on synoptic time scales is highly dynamic the active season extends roughly from may through october during the active season the itcz continuously breaks down and re forms and produces a series of tropical disturbances the life span of the itcz varies from several days to 3 weeks sixty five cases of itcz breakdown have been visually identified over five active seasons 1999 2003 in three independent datasets itcz breakdown can be triggered by two mechanisms 1 interaction with westward propagating disturbances wpds and 2 the vortex rollup vr mechanism results show that the frequency of occurrence of itcz breakdown from these two mechanisms is the same the vr mechanism may have been neglected because the produced disturbances are rather weak and they may dissipate quickly the itcz shows a strong tendency to re form within 1 2 days in the same location the itcz may break down via the vr mechanism without any other support and thus it may continuously generate numerous tropical disturbances throughout the season there are two main differences between the two mechanisms 1 the wpds induced itcz breakdown tends to create one or two vortices that may be of tropical depression strength the vr induced itcz breakdown generates several nearly equal sized weak disturbances 2 the wpds tend to disturb the itcz in the eastern pacific only disturbances generally move along the mexican coast after shedding off from the itcz and do not further disturb the itcz in the central pacific therefore the vr mechanism is observed more clearly and is the dominating mechanism for itcz breakdown in the central pacific

diversity of neomorphic fabrics in new zealand plio pleistocene cool water limestones insights into aragonite alteration pathways and controls abstract many ancient cool water carbonates include little or no evidence for aragonite being present in their primary sediment composition and consequently that they inherited a low diagenetic potential however despite differences in skeletal assemblages age and depositional settings plio pleistocene cool water limestones from eastern north island of new zealand are characterized by locally abundant aragonite remains typically c 20 range 60 either directly as variably altered skeletons or indirectly as biomolds oversized pores and detrital material resulting from collapse of dissolved shells specifically five types of aragonite preservation are evident a skeletons with original aragonite b skeletons with original aragonite but with leaching cavities c skeletons with aragonite relics encased in either dirty or pale brown neomorphic calcite spar d skeletons neomorphically altered to calcite preserving relic shell structures and e dissolved out skeletons leaving an empty or calcite cement filled cavity all these types of preservation including transitions between them can occur within the same sample these observations motivate a conceptual model for the timing and complex pathways of neomorphism in these plio pleistocene cool water limestones related to their diagenetic evolution from shallow marine to burial to uplift related meteoric environments in this the aragonite alteration pathways suggest that the different neomorphic fabrics formed at any stage during the diagenetic history of the host carbonates and are likely not unequivocal indicators of specific diagenetic environments instead differing alteration pathways can potentially produce similar fabrics the observations are consistent with the interpretation that shell microstructures controlling the nature of the intraskeletal neomorphic front and the degree of openness of the diagenetic system were of greater importance in determining the neomorphic fabrics and relic preservation of aragonite than was the general diagenetic environment be it marine meteoric or burial also important were external controls linked to the types of depositional settings that dictated the composition of carbonate factories the morpho tectonic evolution of the host basin and the influence of relative sea level fluctuations on sediment production accumulation and condensation these results illustrate that factors controlling ultimate preservation of carbonate biofacies are multifarious and complex moreover they suggest that the importance of aragonitic components could be underestimated for many ancient cool water carbonate deposits thereby compromising estimation of original skeletal assemblages depositional environments and sediment budgets

an introductory perspective on non tropical shelf carbonates abstract this brief account introduces the topic of non tropical shelf carbonate deposits both modern and ancient specific aspects of which are described and discussed in the 22 accompanying papers in this special issue of sedimentary geology non tropical shelves are loosely defined as lying poleward of the present limit of development of hermatypic coral reefs or beyond the mean annual surface water isotherm of about 20 c typically near 30 latitude most geoscientists have traditionally regarded shallow water carbonate formation as a low latitude phenomenon however wherever the rate and extent of terrigenous sediment dilution is small the potential exists for extensive deposits of skeletal carbonate to accumulate on shelves beyond the sub tropics the facies attributes of the modern non tropical carbonates are distinctive and contrast significantly with the structural lithological faunal floral mineralogical and diagenetic character of their tropical counterparts in the rock record non tropical limestones probably occur throughout the phanerozoic but generally remain to be identified and or interpreted as such they are presently described mainly from the ordovician permian and tertiary quaternary periods of major continental glaciations and accentuated latitudinal thermal gradients a uniformitarian approach to the recognition and interpretation of ancient shallow marine limestones requires acceptance of both tropical and non tropical carbonate facies models

the low level structure of african easterly waves in 1995 abstract the existence of african easterly waves aews north of the african easterly jet aej core with maximum amplitude at low levels has been confirmed and clarified using radiosonde data and the u k meteorological office global model analysis from the hurricane season of 1995 at bamako 12 5 n 8 0 w the aews were characterized mainly by maximum amplitudes at the level of the aej around 700 mb whereas at dakar 14 7 n 17 5 w the waves were characterized by maxima between 850 and 950 mb the low level waves to the north of the aej arise in association with baroclinic interactions between the negative meridional potential vorticity pv gradients in the jet core and the positive low level gradient of potential temperature enhanced by the presence of low static stability air north of the aej these waves follow the positive meridional gradients over northern africa in contrast to the jet level aews that follow the meridional pv gradients at the level of the aej cross correlation analysis

feasibility of geoelectrical monitoring and multiphase modeling for process understanding of gaseous co2 injection into a shallow aquifer potential pathways in the subsurface may allow upwardly migrating gaseous co2 from deep geological storage formations to be released into near surface aquifers consequently the availability of adequate methods for monitoring potential co2 releases in both deep geological formations and the shallow subsurface is a prerequisite for the deployment of carbon capture and storage technology geoelectrical surveys are carried out for monitoring a small scale and temporally limited co2 injection experiment in a pristine shallow aquifer system additionally the feasibility of multiphase modeling was tested in order to describe both complex non linear multiphase flow processes and the electrical behavior of partially saturated heterogeneous porous media the suitability of geoelectrical methods for monitoring injected co2 and geochemically altered groundwater was proven at the test site geoelectrical measurements reveal significant variations in electrical conductivity in the order of 15 30 however site specific conditions e g geological settings groundwater composition significantly influence variations in subsurface electrical conductivity and consequently the feasibility of geoelectrical monitoring the monitoring results provided initial information concerning gaseous co2 migration and accumulation processes geoelectrical monitoring in combination with multiphase modeling was identified as a useful tool for understanding gas phase migration and mass transfer processes that occur due to co2 intrusions in shallow aquifer systems

the role of inertial instability in determining the location and strength of near equatorial convection there are two major organized cloud configurations in the vicinity of the equator where there is a small cross equatorial surface pressure gradient convection is close to the equator and is generally tied to the location of the lowest sea level pressure slp and warmest sea surface temperature sst in agreement with arguments based upon simple thermodynamical considerations however when there is a substantial cross equatorial pressure gradient such as occurs in the monsoon regions organized convection appears off the equator in the summer hemisphere equatorward of the slp minimum and not necessarily collocated with the warmest ssts thus in this instance simple thermodynamical considerations alone cannot explain 2he location of the convection in this situation the zero absolute vorticity contour 0 also lies in the summer hemisphere therefore between the equator and the 0 contour is a region of locally anticyclonic absolute vorticity and an inertially unstable regime it is argued that the convection results from the low level divergence convergence doublet centred about the 0 contour which is the mitigating response to the inertial instability the associated latitude height secondary circulation should provide subsidence suppressed convection over the equator and rising motion enhanced convection to the north of the zero absolute vorticity contour signatures of the inertial instability predicted by theory are found in observations supporting the hypothesis wherever a strong cross equatorial pressure gradient exists the 0 contour bisects a maximum in the divergent wind field divergence is found equatorward of the zero contour and convergence on the poleward side latitude height cross sections show strong local meridional circulations with maximum rising motion on the poleward side of 0 as the regions where the rising motions occur are conditionally unstable there is deep convection and the vertical circulations extend throughout the troposphere it is noted that the intensity of the off equator convection is deeper and probably stronger than convection located at the equator this is probably because the convection associated with the inertial instability is more efficient necessary conditions for the location of near equatorial convection are listed arguments are presented whereby inertial instability is established as the cause rather than an effect of off equatorial convection these include an outline of the sequence of processes leading up to the convection the factors that limit the encroachment of the 0 contour into the summer hemisphere are discussed and an explanation for the existence of the low level westerly monsoon wind maximum is suggested the possible role played by the instability mechanism or the lack of it in coupled model simulations that produce seasonally migrating and or double itczs in the eastern pacific ocean is discussed finally it is proposed that the instability mechanism is important in the initiation of westward moving disturbances found in the eastern pacific and in determining active and break periods in the summer indian monsoon

maintenance of the intertropical convergence zones and the large scale tropical circulation on a water covered earth abstract how the surface boundary heating sea surface temperature and cumulus adjustment process affect the location structure energetics and dynamics of the intertropical convergence zones itczs is investigated a series of experiments is performed with a general circulation model where the lower boundary is specified to be water at a fixed sea surface temperature sst an aqua planet all experiments are run using equinoctal insolation with no longitudinal variation in sst two different convective parameterization schemes kuo and moist convective adjustment and several different zonally symmetric sst distributions are used in these experiments the location of the itcz is found to be sensitive to the convective parameterization scheme and the sst distribution the model with the moist convective adjustment scheme produces an itcz over the tropical sst maximum even under conditions where the sst gradient is weak by contrast the model with the kuo convective parameterization is not as sensit

barotropic aspects of itcz breakdown abstract in satellite images the itcz intertropical convergence zone is sometimes observed to undulate and break down into a series of tropical disturbances tropical cyclones may later develop within these disturbances and move into higher latitudes allowing the itcz to reform it has been proposed that itcz breakdown results from a convectively modified form of combined barotropic and baroclinic instability of the mean flow an unstable mean flow can be produced by itcz convection in just a couple of days in this sense the itcz produces favorable conditions for its own instability and breakdown in this study a nonlinear shallow water model on the sphere is used to simulate barotropic aspects of itcz breakdown in the shallow water model the itcz is simulated by a prescribed zonally elongated mass sink near the equator the mass sink produces a cyclonic potential vorticity pv anomaly that has a reversed meridional pv gradient on its poleward side according to the ripa theorem a flow that has a

dispersion characteristics and circulation associated with boreal summer westward traveling mixed rossby gravity wave like disturbances abstractan algorithm has been developed to track synoptic scale westward traveling mixed rossby gravity mrg wave like disturbances with a cross equatorial component applied to space time filtered meridional wind data this algorithm finds locations with gaussian shaped wind structures stated in the solutions of shallow water equations swes based on 850 hpa meridional wind from the global national centers for environmental prediction ncep climate forecast system reanalysis cfsr dataset local and instantaneous wave properties including the occurrence time wavenumber intrinsic frequency and magnitude were examined it was found that these low level mrg wave like disturbances can be classified into a longer wavelength group and a shorter wavelength group while most waves identified in the eastern pacific give longer wavelengths disturbances in the western pacific tend to have a wider range of wavenumbers composite analysis revealed that east of 140 e low level disturbances are characterize

development characteristics and dynamic structure of tropical intraseasonal convection anomalies abstract the development and dynamical structure of intraseasonal low frequency convection anomalies in the equatorial region are investigated using 10 years 1975 85 of outgoing longwave radiation olr and 7 years 1979 85 of 200 and 850 mb wind data the composite olr anomalies for 36 cases show a four stage development process initiation over equatorial africa rapid intensification when passing through the indian ocean mature evolution characterized by a weakening in the maritime continent and redevelopment over the western pacific and dissipation near the date line in moderate events or emanation from the equator toward north america and southeastern pacific in strong events a noticeable feature in vertical structure is that the 850 mb convergence leads convection and midtropospheric upward motion by about 30 degrees longitude in both developing and mature phases equatorial upper lower level easterly westerly anomalies and associated twin anomalous anticyclonic cyclonic circulation an

morlet wavelet analysis of tropical convection over space and time study of poleward propagations of intertropical convergence zone itcz a methodology to use continuous morlet wavelet transform over space and time has been developed by means of this method the power spectra in 4 dimensional space viz space the spatial scale time and the temporal scale can been estimated this is applied to study the spatial and temporal scales associated with the poleward propagations of the itcz intertropical convergence zone over the indian and west pacific longitudes the method has an added advantage that we can obtain the predominant spatial scales over a particular region the temporal scales associated with them and their time of occurrence we find that poleward propagations of itcz have a predominant spatial scale of about 30degrees however the predominant temporal scale varies from year to year other regions which do not have significant poleward propagations do not show these spatial and temporal characteristics

ground penetrating radar for high resolution mapping of soil and rock stratigraphy ground penetrating radar is a technique which offers a new way of viewing shallow soil and rock conditions the need to better understanding overburden conditions for activities such as geochemical sampling geotechnical investigations and placer exploration as well as the factors controlling groundwater flow has generated an increasing demand for techniques which can image the subsurface with higher resolution than previously possible the areas of application for ground penetrating radar are diverse the method has been used successfully to map ice thickness water depth in lakes bedrock depth soil stratigraphy and water table depth it is also used to delineate rock fabric detect voids and identify karst features the effective application of the radar for the high resolution definition of soil stratigraphy and fractures in bedrock is highlighted the basic principles and practices involved in acquiring high quality radar data in the field are illustrated by selected case histories one example demonstrates how radar has been used to map the bedrock and delineate soil horizons to a depth of more than 20 m two case histories show how radar has been used to map fractures and changes of rock type to 40 m range from inside a mine another case history demonstrates how radar has also been used to detect and map the extent of groundwater contamination the corroboration of the radar results by borehole investigations demonstrates the power and utility of the high resolution radar method as an aid for interpolation and extrapolation of the information obtained with conventional coring programmes with the advent of new instrumentation and field procedures the routine application of the radar method is becoming economically viable and the method will see expanded use in the future

observation of 3 6 day meridional wind oscillations over the tropical pacific 1973 1992 horizontal structure and propagation abstract twenty years of rawinsonde data 1973 1992 were examined in conjunction with european centre for medium range weather forecasts ecmwf analyses and outgoing longwave radiation olr in 1980 1989 to determine the horizontal structure propagation and convective coupling of 3 6 day meridional wind oscillations over the tropical pacific wave properties from ecmwf data determined by lag correlation with respect to rawinsonde or ecmwf principal components were consistent with what could be determined from the sparse rawinsonde network alone gridded analyses allowed a clearer distinction between equatorially trapped rossby gravity waves rgw and off equatorial tropical depression td disturbances so that the contrasting properties of these waves including their seasonal and interannual variation could be studied in better detail significant correlations with olr were found increasing in magnitude from eastern to western pacific the apparent group propagation of disturbances was equator

the influence of amazon rainfall on the atlantic itcz through convectively coupled kelvin waves abstract using outgoing longwave radiation olr and tropical rainfall measuring mission trmm daily rain rate data systematic changes in intensity and location of the atlantic intertropical convergence zone itcz were detected along the equator during boreal spring it is found that the changes in convection over the tropical atlantic may be induced by deep convection in equatorial south america lagged regression analyses demonstrate that the anomalies of convection developed over the land propagate eastward across the atlantic and then into africa the eastward propagating disturbances appear to be convectively coupled kelvin waves with a period of 6 7 5 days and a phase speed of around 15 m s 1 these waves modulate the intensity and location of the convection in the tropical atlantic and result in a zonal variation of the atlantic itcz on synoptic time scales the convectively coupled kelvin wave has substantial signals in both the lower and upper troposphere both a reanalysis dataset and the qui

potential vorticity easterly waves and eastern pacific tropical cyclogenesis abstract a significant sign reversal in the meridional potential vorticity gradient was found during the summer of 1991 on the 310 k isentropic surface near 700 mb over the caribbean sea the charney stern necessary condition for instability of the mean flow is met in this region it is speculated that the sign reversal permits either invigoration of african waves or actual generation of easterly waves in the caribbean during the same season a correlation existed between the strength of the negative potential vorticity gradient in the caribbean and subsequent cyclogenesis in the eastern pacific the meridional pv gradient convective heating measured by outgoing longwave radiation data and eastern pacific cyclogenesis all varied on the timescale of the madden julian oscillation mjo it is hypothesized that upstream wave growth in the dynamically unstable region provides the connection between the mjo or any other convective forcing and the associated enhanced downstream tropical cyclogenesis

development of synoptic scale disturbances over the summertime tropical northwest pacific abstract this study addresses the origin of the synoptic scale disturbances that occur in the tropical western north pacific ocean wp region in northern hemisphere summer these have been called easterly waves and tropical depression type td disturbances this analysis uses the national center for environmental prediction national center for atmospheric research reanalysis dataset by performing a regression analysis on several terms in the vorticity equation at 850 hpa it is shown that the td disturbances propagate approximately as barotropic rossby waves at 850 hpa given this ray tracing calculations and the wave activity diagnostic introduced by plumb are used to show that wave accumulation is a promising candidate for the initial development mechanism of the td disturbances the expected local growth rate from this mechanism is simply the convergence of the group velocity which reaches values corresponding to a growth timescale of 3 days this convergence is dominated by but somewhat lar

effects of early sea floor processes on the taphonomy of temperate shelf skeletal carbonate deposits abstract cool water shelf carbonates differ from tropical carbonates in their sources modes and rates of deposition geochemistry and diagenesis inorganic precipitation marine cementation and sediment accumulation rates are absent or slow in cool waters so that temperate carbonates remain longer at or near the sea bed early sea floor processes occurring between biogenic calcification and ultimate deposition thus take on an important role and there is the potential for considerable taphonomic loss of skeletal information into the fossilised record of cool water carbonate deposits the physical breakdown processes of dissociation breakage and abrasion are mediated mainly by hydraulic regime and are always destructive impact damage reduces the size of grains removes structure and therefore information and ultimately may transform skeletal material into anonymous particles abrasion is highly selective amongst and within taxa their skeletal form and structure strongly influencing resistance to mechanical breakdown dissolution and precipitation are the end members of a two way chemical equilibrium operating in sea water in cool waters inorganic precipitation is rare there is conflicting opinion about the importance of diagenetic dissolution of carbonate skeletons on the temperate sea floor but test maceration and early loss of aragonite in particular are reported dissolution may relate to undersaturated acidic pore waters generated locally by a combination of microbial metabolisation of organic matter strong bioturbation and oxidation of solid phase sulphides immediately beneath the sea floor in otherwise very slowly accumulating skeletal deposits laboratory experiments demonstrate that surface to volume ratio and skeletal mineralogy are both important in determining skeletal resistance to dissolution biological processes on the sea floor include encrustation and bioerosion encrustation a constructive process may be periodic or seasonal and can be reversed it produces both information and material bioerosion in contrast is destructive and permanent in temperate areas bioerosion may destroy even very large shells during their long residence at the sea floor on the order of hundreds to thousands of years overall processes on the temperate sea floor may combine to destroy more carbonate than they produce and the preservation potential of temperate shelf carbonate into the rock record may be significantly affected where preservation does occur in such a destructive regime the effects of early sea floor processes will be key determinants of the deposit resulting in a taphofacies characteristic of temperate shelf carbonate sediments

preferred latitudes of the intertropical convergence zone abstract the latitude preference of the intertropical convergence zone itcz is examined on the basis of observations theory and a modeling analysis observations show that convection is enhanced at latitudes of about 4 to 10 relative to the equator even in regions where the sea surface temperature sst is maximum on the equator both linear shallow water theory and a moist primitive equation model suggest a new explanation for the off equatorial latitude preference of the itcz that requires neither the existence of zonally propagating disturbances nor an off equatorial maximum in sst the shallow water theory indicates that a finite width zonally oriented midtropospheric heat source i e an itcz produces the greatest local low level convergence when placed a finite distance away from the equator this result suggests that an itcz is most likely to be supported via low level convergence of moist energy when located at these preferred latitudes away from the equator for a plausible range of

summer synoptic scale waves over west africa observed by trmm 1 a 5 year daily rainfall dataset 3b42 from trmm is used to investigate the activity and properties of westward propagating synoptic scale waves i e african easterly waves aew over tropical west africa evident wave signals appearing in wavenumber frequency space show their modulations on the surface rainfall pattern during the boreal summer interannual variability exists in both their intensity and spectral properties i e dominant frequency and wavenumber ranges these variabilities can be ascribed in part to year to year variations of their embedded large scale environment especially the mid tropospheric african easterly jet aej generally a stronger weaker aej indicates more less instability energy yielding a stronger weaker wave activity season both seasonal mean rainfall and aews were weak in 2001 but not in 1999 consequently there may exist a nonlinear relationship between the aej aews and mean rainfall to fully understand interannual variability of synoptic scale waves over tropical west africa including the variability in the waves preferred frequencies and wavenumbers it is necessary to examine possible intra seasonal variations in both wave activity and large scale fields in addition to their structure propagation and associated convection

the role of diffusion during carbonate diagenesis abstract the dissolution reprecipitation process which characterizes the early mineralogical stabilization of carbonate sediments takes place in a somewhat open chemical system studies of the trace element chemistries and isotopic compositions of carbonate grains before and after stabilization have documented the exchange of ions between the diagenetic site and the aquifer solution if the pores at reaction zone and in the immediate neighborhood of the diagenetic site are of insufficient diameter to allow effective solution flow the exchange of ions between the diagenetic site and the aquifer solution the large volume of water which flows through the macropores of the carbonate sediment takes place by aqueous diffusion this paper examines diffusion applied specifically to the conditions of carbonate diagenesis the diffusion equation modified to these circumstances serves as a guide to understanding the diffusion process at a given temperature three variables determine the efficacy of diffusion the diffusion coefficient the pore path and geometry and the concentration gradient the diffusion coefficient may be considered a measure of the inherent velocity at which a given ion travels under standard conditions the double positive cations common in carbonates ca2 sr2 ba2 zn2 mg2 etc and the carbonate anion all have similar diffusion coefficients thus this term of the equation exerts little influence during normal carbo ate diagenesis the pore path and geometry refer to the distance from aquifer to reaction zone and the diameter shape and directness of the pore passage this term is difficult to quantify in diagenetic systems but is constant for different ions at a single diagenetic site the longer and the more complex the path the less effective diffusion is there is a general facies dependence to this term grainstones have short paths from reaction zone to aquifer due to their permeability whereas mudstones and wackestones are characterized by long and torturous paths through the mud grains to the aquifer solution exchange of ions in the fast situation is more effective than in the second the concentration gradient the difference between the concentration of an ion in th reaction zone and in the proximal aquifer solution is the most variable parameter in diffusion the sign of the gradient which may be positive or negative indicates the direction of diffusion transport of the ions toward the region of lower concentration one cation may diffuse from the reaction zone while simultaneously a second cation diffuses toward the reaction zone this two way traffic has been documented in diagenetic calcite corals sr2 diffuses away from and mg2 diffuses toward the diagenetic site additionally one cation may diffuse effectively whereas a second diffuses ineffectively the latter species being characterized by a weaker concentration gradient thus a given diagenetic site may be chemically open for one cation and simultaneously somewhat closed for another application of diffusion principles to the aragonite calcite transformation during early diagenesis indicates the compositions of solutions and diagenetic calcites undergo temporal changes early on with few active diagenetic sites sr2 diffuses effectively from the reaction zone to the aquifer since there is a steep concentration gradient diagenetic calcites are relatively low in sr2 because of its effective removal from the diagenetic site as the number of active diagenetic sites increases so much sr2 may be delivered to the aquifer that sr2 builds up in the aquifer solution and the concentration gradient shallows diffusion from individual sites becomes less effective sr2 concentrates in the reaction zone and diagene ic calcites enriched in sr2 are produced as more and more aragonite is consumed a final phase is reached in which less total sr2 is delivered to the aquifer and the system returns to the conditions characteristic of the early phase