bacterial magnetite produced in water column dominates lake sediment mineral magnetism lake ely usa summary environmental magnetic studies of annually laminated sediments from lake ely northeastern pennsylvania usa indicate that bacterial magnetite is the dominant magnetic mineral in the lake sediment in previous studies of lake ely sediment the dark organic rich layers in the annual laminae were interpreted to have high intensity saturation isothermal remanent magnetizations sirms while the light coloured silt rich layers have low intensity sirms to test the hypothesis that the magnetic grains in the sediments were an authigenic product of magnetotactic bacteria rather than detrital magnetic grains eroded from the watershed we analysed samples from the water column the lake sediment and a sediment trap installed near the lake bottom direct microscopic observation of the water column samples showed the presence of magnetotactic bacteria in and below the oxic anoxic transition zone oatz to characterize the magnetic minerals rock magnetic parameters were measured for material from the water column the sediment trap and the dark and light coloured lake sediments low temperature magnetic measurements tested for the presence of magnetosomes in separated dark and light coloured layer samples numeric unmixing of the low temperature results showed that biogenic magnetites were present in the lake sediment and contributed more significantly to the sirm in the dark organic rich layers than in the light coloured inorganic silt rich layers observations under the transmission electron microscope tem of magnetic extracts also show the abundance of magnetosomes in the lake sediment the presence of live magnetotactic bacteria in the water column and the predominance of bacterial magnetites in filtered particulate matter sediment traps and recent lake sediment all suggest that bacterial magnetites are the main magnetic minerals in lake ely sediment this finding suggests that changes in environmental factors that control the productivity of magnetic bacteria in the lake likely contribute to the variability of magnetic mineral concentrations observed in the lake sediments

convective momentum transport by rainbands within a madden julian oscillation in a global nonhydrostatic model with explicit deep convective processes part i methodology and general results abstractthe convective momentum transport cmt properties of 13 215 rainbands within a madden julian oscillation mjo event simulated by a global nonhydrostatic model are examined cmt vectors which represent horizontal accelerations to the mean winds due to momentum flux convergences of deviation winds are derived for each rainband the cmt vectors are composited according to their locations relative to the mjo center while a similar number of rainbands are detected in the eastern and western halves of the mjo convective envelope cmt vectors with large zonal components are most plentiful between 0 and 20 to the west of the mjo center the zonal components of the cmt vectors exhibit a coherent directionality and have a well organized three layer structure positive near the surface negative in the low to midtroposphere and positive in the upper troposphere in the low to midtroposphere where the longitudinal difference in the mean zonal wind across the mjo is 10 m s 1 on average the net acceler

momentum transport by a line of cumulonimbus abstract the vertical transport of horizontal momentum normal to a line of cumulonimbus observed during gate on 14 september 1974 is against the vertical momentum gradient contrary to the predictions of mixing length theory data from repeated aircraft passes normal to the line s axis at heights from 0 15 to 5 5 km are used to document the flux and determine its source the flux is concentrated in roughly a 25 km wide active zone just behind the leading edge of the line in kilometer scale convective updrafts accelerated upward by buoyancy and toward the rear of the line by mesoscale pressure forces the fall in mesoscale pressure from the leading edge to the rear of the active zone is mainly hydrostatic resulting from relatively high virtual temperatures and the 60 degree tilt of the leading edge from the vertical with the clouds at the surface well ahead of those aloft evaluation of the terms in the momentum flux generation equation confirms that the above process reflected by the velocity buoyan

anhysteretic remanent magnetization of fine magnetic particles 1 various magnetic parameters are in common use for estimating the grain size of magnetic particles among these the ratio of the intensity of anhysteretic remanent magnetization arm to that of isothermal remanent magnetization as well as their alternating field af demagnetization curves are used as an indicator of the domain state of the particles several models have been proposed to describe physically the acquisition of arm in a biased af field jaep 1969 first developed a semiquantitative theory based entirely on the thermal fluctuation analysis developed by neel 1949 1954 1955 significant discrepancies were found between his model and experimental results on magnetite a new general theory of arm based on the work of jaep is presented here with particular regard to the influence of various parameters like grain size coercivity and mineralogy on arm intensity an analytical expression for arm intensity in the special case of very fine particles was derived from this theory and a good agreement with experimental results and data from the literature was found a new estimation of the atomic reorganization time was obtained from arm measurements on a sample of the yucca mountain tuff which has well known mineralogy and grain size distribution the results are in agreement with the value proposed by mcnab et al 1968 for magnetite some authors considered magnetic interactions as the key to understand the arm in fine particles and this is certainly true for strongly interacting samples in this case arm would be useless for the characterization of magnetic grains however many sediments have a very low concentration of well distributed magnetic grains for these samples the explanation of an arm in terms of intrinsic properties of the grains as qualitatively proposed by other authors is more suitable

parameterization of the vertical transport of momentum by cumulus clouds part i theory abstract a scheme is developed to parameterize the vertical transport of momentum by cumulus clouds in which the effect of a cloud induced pressure field is included in addition a new form for momentum exchange between clouds and their environment is used the scheme incorporates a simple cloud model which includes both updraft and downdraft and specifies the cloud dynamic fields to enable us to determine the mean pressure gradient force across the clouds it is shown that in a typical environment with vertical wind shear the pressure gradient force is along the direction of the wind shear the equation governing cloud mean momentum together with the diagnostic equation for cloud induced pressure field is solved by iteration to evaluate quantitatively the horizontal pressure gradient force across the cloud and determine the cloud mean momentum application of the parameterization scheme to gate convective events will be presented in part ii of this paper

the detection of magnetotactic bacteria and magnetofossils by means of magnetic anisotropy an important characteristic of magnetotactic bacteria mtb is the anisotropy of one dimensionally aligned magnetite particles this paper introduces the use of ferromagnetic resonance spectroscopy fmr at two different frequencies to compare the anisotropic properties of magnetite chains of cultured intact mtb with those of lake sediments of holocene age in order to detect magnetofossils and to characterize their preservation in a geological system magnetite chains of intact mtb exhibit a predominantly uniaxial anisotropy in the lake sediments where diagenetic processes disintegrate the chains and diminish their uniaxiality magnetite chains or chain fragments and dissociated bulk magnetite particles differ in their anisotropy properties the two groups of assembly can be distinguished by empirical spectral separation of the fmr signal this straightforward use of the characteristics of magnetic anisotropy provides a way to detect magnetofossils experimentally thus allowing a better insight into microbial ecology during earth s history

a numerical study of the stratiform region of a fast moving squall line part ii relationship between mass pressure and momentum fields abstract in a companion paper a two dimensional simulation of a fast moving tropical squall line was successfully compared to observations performed during the copt81 experiment over west africa the full ice phase parameterization is shown to be crucial in the simulation of trailing anvil precipitation different diagnostic tools are applied to the simulated fields to further our understanding of the scale interactions within a squall line type mesoscale convective system the pressure organization is characterized by two marked features important for explaining the inner circulation first a front to rear midlevel pressure gradient and second the surface pressure mesohigh extending from the gust front to the rear of the most active part of the trailing stratiform region based on the hydrostatic approximation an original method of decomposition of the pressure field is proposed whereby dynamical and buoyant contributions depend only on the horizontal and vertical respectively the mean pressure i

symmetry and asymmetry of the asian and australian summer monsoons the rainfalls associated with the asian summer monsoon have significant correlation with succeeding aus tralian summer monsoon rainfalls this is partly due to the typical life cycle of the el nino southern oscillation enso phase locked with the annual cycle within an asian monsoon year may april this feature is referred to as the symmetric behavior of the asian australian monsoon system however preceding australian summer monsoon rainfalls have no significant impact on succeeding asian summer monsoon rainfalls thus there is a one way asymmetric relationship between the two monsoons and a communication gapexists in boreal spring prior to the onset of the asian summer monsoon the annual cycles of precipitation associated with the intertropical convergence zone itcz and the sea surface temperature sst anomaly in the indonesia sector 908 1208e that links the two monsoon regions are compared the continuous propagation of the itcz from the asian to the australian summer monsoon regions in northern hemisphere nh fall provides a one way link between them however the sst anomaly shows a sudden change of sign in november suggesting that the anomaly is mainly a response to the itcz movement rather than its cause from january to may the itcz is confined at the latitudes south of 58n due to the subsidence in oceanic regions adjacent to the southern coast of asia this subsidence prevents the itcz from propagating northward until the abrupt onset of the asian summer monsoon with the reversal of meridional temperature gradient the discontinuity of the itcz movement and the seasonal heating over the asian continent result in the communication gap in nh spring

rock magnetic criteria for the detection of biogenic magnetite abstract we report results on the magnetic properties of magnetites produced by magnetotactic and dissimilatory iron reducing bacteria magnetotactic bacterial mtb strains ms1 mv1 and mv2 and dissimilatory iron reducing bacterium strain gs 15 grown in pure cultures were used in this study our results suggest that a combination of room temperature coercivity analysis and low temperature remanence measurements provides a characteristic magnetic signature for intact chains of single domain sd particles of magnetite from mtbs the most useful magnetic property measurements include 1 acquisition and demagnetization of isothermal remanent magnetization irm using static pulse and alternating fields 2 acquisition of anhysteretic remanent magnetization arm and 3 thermal dependence of low temperature 20 k saturation irm after cooling in zero field zfc or in a 2 5 t field fc from 300 k however potentially the most diagnostic magnetic parameter for magnetosome chain identification in bulk sediment samples is related to the difference between low temperature zero field and field cooled sirms on warming through the verwey transition t 100 k intact chains of unoxidized magnetite magnetosomes have ratios of fc zfc greater than 2 where the parameter is a measure of the amount of remanence lost by warming through the verwey transition disruption of the chain structure or conversion of the magnetosomes to maghemite reduces the fc zfc ratio to around 1 similar to values observed for some inorganic magnetite maghemite greigite and gs 15 particles numerical simulations of fc zfc ratios for simple binary mixtures of magnetosome chains and inorganic magnetic fractions suggest that the fc zfc parameter can be a sensitive indicator of biogenic magnetite in the form of intact chains of magnetite magnetosomes and can be a useful magnetic technique for identifying them in whole sediment samples the strength of our approach lies in the comparative ease and rapidity with which magnetic measurements can be made compared to techniques such as electron microscopy

impact of a modified convective scheme on the madden julian oscillation and el nino southern oscillation in a coupled climate model 1 the connection between the intraseasonal madden julian oscillation mjo and interannual el nino southern oscillation enso has been proposed and investigated for the last two decades however many fully coupled atmosphere ocean general circulation models gcms are still unable to simulate many important characteristics of these two phenomena partly due to the great uncertainty in the representation of subgrid scale cloud systems we report herein the simulation of an el nino in a fully coupled gcm with a modified convection scheme which captures many of the observed features of the 1997 1998 el nino event the representation of convection in the coupled model plays a major role in modeling both interannual enso and intraseasonal mjo variability in closer accord with observations and in reproducing the evolution of 1997 1998 el nino type events

experimental observation of magnetosome chain collapse in magnetotactic bacteria sedimentological paleomagnetic and evolutionary implications magnetotactic bacteria precipitate intracellular crystals of single domain magnetite fe3o4 and or greigite fe3s4 which have often been implicated in carrying the natural remanent magnetization nrm of freshwater and marine sediments in vivo the magnetic crystals are usually aligned in chains such that their moments add together generating net cellular moments high enough to rotate the cells passively to align with the geomagnetic field a magnetostatic biophysical analysis demonstrates that this arrangement is out of dynamic equilibrium and would collapse spontaneously without a support mechanism past rock magnetic analyses of shallow water marine carbonates suggest that partial collapse does occur during diagenesis and dolomitization to calibrate this effect we induced magnetosome chain collapse in magnetospirillum magnetotacticum strain ms 1 by progressive sonification and treatment with detergents and monitored the changes with rock magnetic analysis and tem although it has been speculated that the cell wall and associated membrane structures act to prevent magnetosome chain collapse our data indicate that magnetosome linearity persists long after cells are disrupted this is consistent with prior observations that in some magnetotcocci the magnetosome chains pass through the cell interior precluding continuous contact with the cell wall and implying additional support structures exist in some species using tem tomographic reconstructions prepared with a magnetic technique that prevents chain collapse we examined the three dimensional ultrastructure of magnetosomes without the problem of post mortem magnetosome motion this method revealed the presence of an intracellular organic sheath beyond that of actin like filaments reported recently that follows the chain of magnetosomes which we postulate evolved to hold the crystals in place and enhances their ability to preserve nrm in sediments as the genomes of two magnetotactic bacteria contain several apparent homologues of known eukaryotic cytoskeletal proteins natural selection for magnetotaxis may have played a role in the evolution of precursors to the eukaryotic cytoskeleton the presence of this sheath is also consistent with the observation of electron translucent material associated with putative magnetofossil chains in alh84001

convective momentum transport in a simple multicloud model for organized convection abstractconvective momentum transport cmt is the process of vertical transport of horizontal momentum by convection onto the environmental flow the significance of cmt from mesoscale to synoptic and planetary scale organized cumulus convection has been established by various theoretical and observational studies a new strategy mimicking the effect of unresolved mesoscale circulation based on the weak temperature gradient wtg approximation with a gaussian profile to redistribute the heating due to parameterized cumulus convection at the subgrid scale is adopted here to construct a cmt parameterization for general circulation models gcms two main regimes of cmt are considered an upscale squall line regime and a downscale non squall line regime an exponential probability distribution is used to select which of these two effects is active conditional on the state of the large scale shear the shear itself is used as a measure of the persistence of mesoscale organized circulation due to the presen

rock magnetic artifacts on long term relative paleointensity variations in sediments 1 long term changes of geomagnetic field intensity including possible dependence on lengths of polarity intervals provide fundamentally important information for understanding the geodynamo a positive correlation between paleointensity and polarity interval length was previously suggested from an oligocene ca 23 34 ma relative paleointensity record at deep sea drilling program site 522 in the atlantic ocean which is the only continuous paleointensity data set published so far for this age interval we have conducted a paleomagnetic study of eocene to oligocene sediments at three sites in the eastern equatorial pacific ocean our objectives include revisiting the issue of the paleointensity polarity length correlation magnetic properties of the sediments meet the frequently used criteria for reliable relative paleointensity estimation although short wavelength normalized remanence intensity fluctuations associated with polarity boundaries and possible geomagnetic excursions agree among the three sites long term changes are inconsistent apparent positive correlation between normalized intensity and polarity length was observed but the normalized intensity has an obvious anti correlation with the ratio of anhysteretic remanent magnetization arm to isothermal remanent magnetization irm which is mainly controlled by the relative abundance of biogenic and terrigenous magnetic minerals furthermore the normalized intensity correlates with sedimentation rate these facts indicate a lithological contamination on the normalized intensity records the dependence on arm irm and sedimentation rate is also evident at site 522 it is inferred that variations in sedimentation rate and the relative abundance of biogenic magnetite on depositional remanent magnetization acquisition efficiency may not be well compensated by the normalization it is therefore premature to conclude that stronger geomagnetic fields were recorded during longer polarity intervals from currently available normalized intensity records

detection of noninteracting single domain particles using first order reversal curve diagrams we present a highly sensitive and accurate method for quantitative detection and characterization of noninteracting or weakly interacting uniaxial single domain particles unisd in rocks and sediments the method is based on high resolution measurements of first order reversal curves forcs unisd particles have a unique forc signature that can be used to isolate their contribution among other magnetic components this signature has a narrow ridge along the hc axis of the forc diagram called the central ridge which is proportional to the switching field distribution of the particles therefore the central ridge is directly comparable with other magnetic measurements such as remanent magnetization curves with the advantage of being fully selective to sd particles rather than other magnetic components this selectivity is unmatched by other magnetic unmixing methods and offers useful applications ranging from characterization of sd particles for paleointensity studies to detecting magnetofossils and ultrafine authigenically precipitated minerals in sediments

notes and correspondence convective eddy momentum tendencies in long cloud resolving model simulations abstract domain average momentum budgets are examined in several multiday cloud resolving model simulations of deep tropical convection in realistic shears the convective eddy momentum tendency f neglected in many global circulation models looks broadly similar in two and three dimensional simulations it has a large component in quadrature with the mean wind profile tending to cause momentum profile features to descend this component opposes and exceeds in magnitude the corresponding large scale vertical advective tendency which would tend to make features ascend in convecting regions the portion of f in phase with the mean wind is isolated by vertically integrating f u yielding a kinetic energy tendency that is overwhelmingly negative the variation of this energy damping with shear flow kinetic energy and convection intensity measured by rain rate gives a cumulus friction coefficient around 40 to 80 per centimeter of rain in 3d runs large scatter reflects the effects of varying co

ferromagnetic resonance and magnetic characteristics of intact magnetosome chains in magnetospirillum gryphiswaldense abstract the magnetic characteristics of intact magnetosome chains in magnetospirillum gryphiswaldense bacteria were investigated by means of static and dynamic magnetic analyses and ferromagnetic resonance spectroscopy the nano sized magnetosomes are generally in a stable single domain state but magnetosomes smaller than 30 nm characteristic of superparamagnetic magnetite particles were also found alternating current ac susceptibility indicates that all magnetosomes are blocked below 150 k at room temperature the anisotropy of m gryphiswaldense is dominated by the shape of the magnetosome chains low temperature ferromagnetic resonance fmr spectroscopy indicates that this dominant shape anisotropy can affect the detection of the verwey transition at 100 k the static and dynamic magnetic analyses show that the verwey transition is smeared and that our magnetotactic bacteria fail the moskowitz test this failure is explained by the biomineralization of non stoichiometric magnetosomes this interpretation is based on the increase in high field susceptibility and the distinct peak in the out of phase component of the ac susceptibility below 50 k these results are attributed to freezing of spins associated with defect structures in the core and at the surface of nano sized magnetosomes the results obtained from m gryphiswaldense demonstrate that intrinsic properties of nano sized magnetosomes are significantly influenced by non stoichiometry and by the anisotropy excited from their arrangement in the bacteria

magnetotactic bacteria and their magnetofossils in sediments abstract living magnetotactic bacteria from freshwater environments show under natural and laboratory conditions a great variety of morphological appearances their magnetosomes vary in number shape and size one species of bacteria yields up to 1000 magnetosomes per cell individual particles reach a size of up to 200 nm as a rule they form elongated chains in bacteria which are held under laboratory conditions loop shaped arrangements and nearly unordered clusters are also found during the laboratory experiments different species of bacteria periodically dominated freshwater samples always exhibited a great variety of different magnetosomes on the other hand samples from marine environment clearly showed the preponderance of one type of particle these observations may reflect specific properties of the physico chemical milieu in which the bacteria grew at the end of our experiments north and south seeking bacteria co existed in roughly equal quantities quaternary unconsolidated sediments from the ammersee bavaria and the antarctic quaternary to tertiary deep sea sediments from the atlantic and pacific and jurassic limestones from the sonnwendgebirge tyrol austria were analyzed for fossil magnetosomes we found that fossil magnetosomes were morphologically similar to those from living bacteria but seemed to be corroded in some cases the observed differences in quantity size and shape of magnetosomes from various sediments may be influenced by variations in bacterial viability and particle stability at different sites but are not determined by geographical latitude

comparison between a three dimensional simulation and doppler radar data of a tropical squall line transports of mass momentum heat and moisture abstract results from a detailed three dimensional cloud model are extensively compared with doppler radar data in the case of a fast moving tropical squall line observed during the copt81 experiment the comparisons use a two dimensional statistical analysis in which we consider each four dimensional field as the sum of a two dimensional averaged vertical field and a four dimensional residual field representative of along line and temporal fluctuations these fluctuations are analyzed by computing the time average of spatial variances and the temporal variance of spatial averages the results indicate good agreement in both quality and quantity particularly for the vertical velocity and line normal wind the consequences of this agreement are two fold first a physical and comprehensive model of the convective part of a tropical squall line emerges that is coherent with both observations and simulations this conceptual model emphasizes the importance of along line fluctuations second it is possib

fossil bacterial magnetite in deep sea sediments from the south atlantic ocean the magnetostratigraphy of deep sea sediment cores has proven to be a powerful and high resolution method of dating and comparing sedimentary records in contrast to this widespread application relatively few attempts have been made to analyse and identify the mineralogy grain size and origin of the carrier of the remanent magnetization1 2 it is widely assumed that dominant ferrimagnetic minerals in deep sea sediments are of lithogenic origin that is that they derive from oceanic or continental detritus volcanic ashfalls micrometeorites hydrothermal precipitation or chemical mineralization processes a very different view was taken by kirschvink and lowenstam3 who suggested that fossil remnants of magnetite mineralizing organisms in particular magnetotactic bacteria might play an important part in the magnetization of sediments deposited in certain detritus poor aquatic systems we have used rock magnetic diagnostic methods to characterize the magnetic phases in deep sea sediments from the south atlantic these phases were then extracted and studied with the electron microscope our results indicate that fossil bacterial magnetite is the main carrier of the natural remanent magnetization in sediments ranging in age from quarternary to eocene different types of bacterial magnetosomes were detected most of them occurring in chains of identical particles and nearly all of them falling into the theoretically determined4 size range of single domain magnetitite

biochemical vs detrital mechanism of remanence acquisition in marine carbonates a lesson from the k t boundary interval abstract an apparently complete carbonate rich cretaceous tertiary boundary interval in odp section 119 738c 20r 5 from the southern kerguelen plateau provides a unique insight into processes of magnetization acquisition in marine carbonates the boundary interval is characterized by a 1 m thick clay rich zone distinct depositional lamina are preserved within the basal 15 cm of this zone the upper part is bioturbated previous studies have demonstrated that the bulk of the detrital fraction in the laminated and bioturbated carbonates has the same local source and hence the two intervals likely had similar initial detrital assemblages magnetic properties of these rocks however differ significantly the laminated sediments have a higher content of non silicate bound iron yet approximately an order of magnitude lower intensity of the natural remanent magnetization compared to the bioturbated rocks our detailed rock magnetic study indicates that in the bioturbated interval the dominant iron bearing phase is single domain magnetite likely of biogenic origin in the laminated interval apart from a small ferromagnetic fraction with multi domain like behavior non silicate bound iron is mainly sequestered in paramagnetic phases likely poorly crystalline oxyhydroxides it appears that a shut down of biological productivity after the k t event allowed preservation of the initial detrital early authigenic iron phases that are dominated by reactive iron oxyhydroxides with recovery of the normal biological activity as evidenced by resumption of bioturbation the oxyhydroxides had been replaced with biogenic magnetite thus produced biochemical magnetization led to a several fold increase in the remanence our results suggest that in areas where bioavailable iron constitutes a significant part of the detrital input such as in pelagic marine environments distant from clastic sources the biochemical remanent magnetization may be the dominant process of magnetization acquisition

ferromagnetic resonance and low temperature magnetic tests for biogenic magnetite magnetite is both a common inorganic rock forming mineral and a biogenic product formed by a diversity of organisms magnetotactic bacteria produce intracellular magnetites of high purity and crystallinity magnetosomes arranged in linear chains of crystals magnetosomes and their fossils magnetofossils have been identified using transmission electron microscopy tem in sediments dating back to 510 570 ma and possibly in 4 ga carbonates in martian meteorite alh84001 we present the results from two rock magnetic analyses the low temperature moskowitz test and ferromagnetic resonance fmr applied to dozens of samples of magnetite and other materials the magnetites in these samples are of diverse composition size shape and origin biologically induced extracellular biologically controlled magnetosomes and chiton teeth magnetofossil synthetic and natural inorganic we confirm that the moskowitz test is a distinctive indicator for magnetotactic bacteria and provide the first direct experimental evidence that this is accomplished via sensitivity to the magnetosome chain structure we also demonstrate that the fmr spectra of four different strains of magnetotactic bacteria and a magnetofossil bearing carbonate have a form distinct from all other samples measured in this study we suggest that this signature also results from the magnetosomes unique arrangement in chains because fmr can rapidly identify samples with large fractions of intact isolated magnetosome chains it could be a powerful tool for identifying magnetofossils in sediments

a strong angular dependence of magnetic properties of magnetosome chains implications for rock magnetism and paleomagnetism 1 single domain magnetite particles produced by magnetotactic bacteria magnetosomes and aligned in chains are of great interest in the biosciences and geosciences here we investigated angular variation of magnetic properties of aligned magnetospirillum magneticum amb 1 cells each of which contains one single fragmental chain of magnetosomes with measurements at increasing angles from the chain direction we observed that i the hysteresis loop gradually changes from nearly rectangular to a ramp like shape e g bc and remanence decrease ii the acquisition and demagnetization curves of irm shift toward higher fields e g bcr increases and iii the forc diagram shifts toward higher coercivity fields e g bc forc increases for low temperature results compared to unoriented samples the samples containing aligned chains have a much lower remanence loss of field cooled fc and zero field cooled zfc remanence upon warming through the verwey transition higher ratio fc zfc for the measurement parallel to the chain direction and lower ratio larger fc and zfc values for the perpendicular measurement micromagnetic simulations confirm the experimental observations and reveal that the magnetization reversal of magnetosome chain appears to be noncoherent at low angles and coherent at high angles the simulations also demonstrate that the angular dependence of magnetic properties is related to the dispersion degree of individual chains indicating that effects of anisotropy need to be accounted for when using rock magnetism to identify magnetosomes or magnetofossils once they have been preserved in aligned chains additionally this study experimentally demonstrates an empirical correspondence of the parameter bc forc to bcr rather than bc at least for magnetite chains with strong shape anisotropy this suggests forc analysis is a good discriminant of magnetofossils in sediments and rocks

physical mechanisms for the maintenance of gcm simulated madden julian oscillation over the indian ocean and pacific abstractthe kinetic energy budget is conducted to analyze the physical processes responsible for the improved madden julian oscillation mjo simulated by the iowa state university general circulation models isugcms the modified deep convection scheme that includes the revised convection closure convection trigger condition and convective momentum transport cmt enhances the equatorial 10 s 10 n mjo related perturbation kinetic energy pke in the upper troposphere and leads to a more robust and coherent eastward propagating mjo signal in the mjo source region the indian ocean 45 120 e the upper tropospheric mjo pke is maintained by the vertical convergence of wave energy flux and the barotropic conversion through the horizontal shear of mean flow in the convectively active region the western pacific 120 e 180 the upper tropospheric mjo pke is supported by the convergence of horizontal and vertical wave energy fluxes over the central eastern pacific 180 120 w where convection is s

effects of vertical wind shear on the cumulus transport of momentum observations and parameterization abstract dynamical effects of organized cumulus convection on its environment with vertical wind shear are studied analyses of the wind field and momentum budget residual for mesoscale convective systems observed during sesame and pre storm reveal systematic differences in the vertical transport of horizontal momentum between mesoscale convective complex mcc and squall line cases in the mcc a distinct minimum in wind speed appears over the area of intense convection and the momentum budget residual acts to decelerate the environmental wind and to reduce the upper level vertical shear therefore the inferred vertical transport of momentum in the mcc is downgradient in the upper layer on the other hand in the squall line there is no wind speed minimum and the upper level vertical shear of the line normall component of the environmental wind increases as convection develops thus the vertical transport of momentum normal to the squall line is upgradient in the upper layer although the transport of

numerical archetypal parameterization for mesoscale convective systems abstractvertical shear commonly organizes atmospheric convection into coherent multiscale structures the associated countergradient vertical transport of horizontal momentum by organized convection can enhance the wind shear and transport kinetic energy upscale however organized convection and its upscale effects are not represented by traditional mass flux based parameterizations the present paper sets the archetypal dynamical models originally formulated by the second author into a parameterization context by utilizing a nonhydrostatic anelastic model with segmentally constant approximation nam sca using a two dimensional framework as a starting point nam sca spontaneously generates propagating tropical squall lines in a sheared environment high numerical efficiency is achieved through a novel compression methodology the numerically generated archetypes produce vertical profiles of convective momentum transport that are consistent with the analytic archetype

cloud resolving modeling of cloud systems during phase iii of gate part ii effects of resolution and the third spatial dimension abstract two and three dimensional simulations of cloud systems for the period of 1 7 september 1974 in phase iii of the global atmospheric research programme garp atlantic tropical experiment gate are performed using the approach discussed in part i of this paper the aim is to reproduce cloud systems over the gate b scale sounding array comparison is presented between three experiments driven by the same large scale conditions i a fully three dimensional experiment ii a two dimensional experiment that is an east west section of the three dimensional case and iii a high resolution version of the two dimensional experiment differences between two and three dimensional frameworks and those related to spatial resolution are analyzed the three dimensional experiment produced a qualitatively realistic organization of convection nonsquall clusters a squall line and scattered convection and transitions between regimes were simulated the two dimensional experiments produced convective organ

the late holocene history of gormire lake ne england and its catchment a multiproxy reconstruction of past human impact sedimentary evidence spanning the last 3500 years from cores taken from the centre of gormire lake cleveland northeast england points to two periods of deforestation and catchment erosion the first mainly late iron age romano british phase began c 200 bc and ended c ad 600 the second began c ad 1200 the time of early monastic activity and continued into the nineteenth century the chronology for the core rests on 137cs 210pb and 14c measurements and on the history of lead accumulation in the sediments the majority of the ams 14c dates are shown to be too old to varying degrees depending on the source of the organic matter in the sediments the record of vegetation change is derived from pollen analysis evidence for changes in sediment composition and source and for catchment erosion comes from magnetic measurements element analyses using xrf and organic biogeochemical analyses there is a high degree of coherence between all these lines of evidence interpretation of the magnetic record

magnetic properties of marine magnetotactic bacteria in a seasonally stratified coastal pond salt pond ma usa summary magnetic properties of suspended material in the water columns of freshwater and marine environments provide snapshots of magnetic biomineralization that have yet to be affected by the eventual time integration and early diagenetic effects that occur after sediment deposition here we report on the magnetism geochemistry and geobiology of uncultured magnetite and greigite producing magnetotactic bacteria mb and magnetically responsive protists mrp in salt pond falmouth ma usa a small coastal marine basin 5 m deep that becomes chemically stratified during the summer months at this time strong inverse o2 and h2s concentration gradients form in the water column and a well defined oxic anoxic interface oai is established at a water depth of about 3 5 m at least four morphological types of mb both magnetite and greigite producers and several species of magnetically responsive protists are found associated with the oai and the lower sulphidic hypolimnion magnetic properties of filtered water were determined through the water column across the oai and were consistent with the occurrence of magnetite and greigite producing mb at different depths sharp peaks in anhysteretic remanent magnetization arm and saturation isothermal remanent magnetization sirm and single domain sd values of arm sirm occur within the oai corresponding to high concentrations of mb and mrp with magnetically derived cell densities of 10 4 10 6 ml 1 low temperature 1 per cent is present within magnetite magnetosomes produced either

a new geochemical classification of sedimentary environments because of the relative constancy of ph in most subaqueous sediments and the general lack of measurability of eh these parameters are not practically useful for classifying sedimentary environments in their place a new classification is offered which derived from studies of modern sediments is based on the presence or absence of dissolved oxygen and dissolved sulfide in the sediments at the time of authigenic mineral formation sedimentary environments are first of all divided into oxic and anoxic depending upon the presence or absence of measurable dissolved oxygen anoxic environments in turn are divided into sulfidic and non sulfidic depending upon the presence of measurable dissolved sulfide anoxic nonsulfidic environments are further divided into postoxic or resulting from oxygen removal without sulfate reduction weakly reducing and methanic or resulting from complete sulfate reduction with consequent methane formation strongly reducing the environments are shown to succeed one another during early diagenesis in the order oxic post oxic sulfidic methanic iron and manganese minerals characteristic and stable in each environment are listed and discussed so that they may be used to distinguish the environments when studying the ancient geological record

bacterial magnetite and the magnetic properties of sediments in a swedish lake a comparison of the magnetic properties of lake sediments and catchment materials from pajep njakajaure north sweden demonstrates that high concentrations of single domain sd magnetite in the upper 70 cm of gyttja in the deepest part of the basin are not of detrital origin tem and light microscope examination revealed the existence of bacterial cells and magnetosomes in the upper sediments which are responsible for the presence of the sd magnetite most of the fossil magnetosomes appear to have been dissolved through reductive processes at lower depths although some are preserved in the lower sediments and carry a post depositional remanent magnetization pdrm the results highlight the complex effects of post depositional processes on mineral magnetic assemblages and natural remanent magnetization aquisition and demonstrate how mineral magnetic measurements may be used to identify magnetic grain size changes brought about by sediment diagenesis

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

low temperature magnetic properties of pelagic sediments ocean drilling program site 805c tracers of maghemitization and magnetic mineral reduction magnetic properties of pelagic sediments from the western equatorial pacific ocean drilling program odp site 805c have been measured at low temperatures to investigate changes in magnetic mineralogy and the distribution of bacterial magnetite with depth a saturation isothermal remanent magnetization mrs was given to the samples by applying a strong magnetic field 2 5 t at 20 k after cooling both in the absence zero field cooling zfc and presence of a 2 5 t magnetic field field cooling fc the thermal demagnetization of both mrszfc and mrsfc was measured from 20 to 300 k no pronounced verwey transition was observed in the data from samples shallower than the iron redox boundary below the boundary the verwey transition is visible for all samples studied we interpret this behavior as reflecting low temperature oxidation maghemitization of primary magnetite and the subsequent dissolution of maghemite coatings below the iron redox boundary the low temperature oxidation may occur both at the water sediment interface and deeper in the suboxic zone of sediments as a result of bacteria mediated processes including the reduction of nitrate compounds mrszfc and mrsfc thermal demagnetization curves of all samples diverge for the entire temperature range measured the divergence may be caused by the low temperature stabilization of spontaneous magnetization vectors along with exchange interaction in the magnetite maghemite system together maghemitization and magnetic reduction diagenesis appear to play a dominant role in controlling the low temperature properties of the sediment studied as a result low temperature magnetic studies may provide more information on differences in reduction diagenesis than on the distribution of bacterial magnetite in natural sediments the changes in effective oxidation state below the iron redox boundary detected by low temperature methods may be useful in the study of some paleoenvironmental processes

the effect of horizontal pressure gradients on the momentum transport in tropical convective lines part i the results of the convective parameterization abstract measuremenits of the momentum transport in tropical convective lines suggest that horizontal momentum can be generated by the pressure low located near the center of the convective part of the line a simple convective parameterization is used to evaluate this effect the parameterization is a version of the fritsch and chappell scheme modified in order to evaluate the influence of the horizontal pressure gradients on momentum transport the results suggest that in modeling of convective particularly slow moving lines with 20 km resolution subgrid horizontal pressure gradients should be taken into account sensitivity studies show that the magnitude of the calculated momentum flux strongly depends on the average vertical velocity and the vertical velocity in clouds

paleomagnetic evidence for fossil biogenic magnetite in western crete abstract previous paleomagnetic research has shown that the concentration of fine grained magnetite preserved in miocene marine clays of western crete drops during two successive geomagnetic transitions although the mechanism responsible for this effect was not known magnetite precipitation by magnetotactic bacteria offers a straightforward explanation for this decrease reduced field strengths during a reversal will strain the competitive advantage of having intracellular magnetite and will force bacteria to precipitate correspondingly more magnetite if they are to maintain the same alignment in the geomagnetic field their ability to do this is limited by several magnetophysical constraints which should act to reduce the numbers of magnetite precipitating cells particularly in fields of less than about 12 of the present level this would lead to a decrease in the supply of bacterial magnitude to the sediments recovery of intact magnetotactic bacterial fossils may lead to a new method for estimating paleointensities from sedimentary rocks

bacterial magnetite in swedish varved lake sediments a potential bio marker of environmental change abstract detailed mineral magnetic measurements were carried out on three varved lake sediment sequences in sweden which extend to ca 7000 bc the comparison of the magnetic properties of the organic rich varved lake sediments with their respective catchment materials indicates that the magnetic properties of the sediments are dominated by relatively high concentrations of single domain magnetite magnetosomes produced by magnetotactic bacteria the dimictic nature of the lakes which help form and preserve the varves due to the weakly oxic or suboxic environment also appear to be suitable for a high degree of magnetosome preservation the concentration of the magnetosomes in two of the sequences as determined by mass specific magnetic measurements exhibits a positive linear relationship with the total organic carbon content and suggests that magnetic remanence measurements reflect lake productivity via processes of organic matter accumulation and decomposition further research should focus on the potential to use the fossil magnetosomes as proxy climate environmental change indicators and as recorders of geomagnetic field variations and behaviour

magnetic detection and characterization of biogenic magnetic minerals a comparison of ferromagnetic resonance and first order reversal curve diagrams australian research council grant number dp120103952 australia new zealand iodp consortium anzic grant number le0882854

biogenic magnetite in stromatolites i occurrence in modern sedimentary environments abstract in this paper we report the occurrence of biogenic ultra fine grained single domain magnetite in both marine and non marine modern stromatolitic environments magnetotactic bacteria were found associated with the microbial communities involved in the deposition of laminated sediments at laguna figueroa baja california mexico and carbonate stromatolitic nodules at sugarloaf key fl u s a these bacteria and the ultra fine grained magnetite they produce have a profound effect on the magnetic properties of the sediments the presence of this single domain magnetite was detected using rock magnetic methods while the morphology was identified by transmission electron microscopy examination by rock magnetic methods of microbial mats and laminated sediments from solar lake sinai guerrero negro baja california mexico and shark bay australia as well as stromatolites from shark bay and clifton lake australia bacalar lake and cuatro cienegas mexico and walker lake u s a indicate these localities contain single domain magnetite biogenic magnetites of presumed bacterial origin have been extracted from shark bay mats walker lake stromatolites and bahama carbonates these findings suggest that bacterial magnetites can be recognized as the tiniest trace fossil and may be found preserved in fossil stromatolites and laminated sediments

palaeogeographic evolution of the pieniny klippen basin using stratigraphic and palaeomagnetic data from the veliky kamenets section carpathians ukraine abstract a 40 m thick carbonate succession of the bajocian to berriasian age from the veliky kamenets quarry novoselica area pieniny klippen belt ukraine resembles both the czorsztyn and niedzica successions of the pieniny klippen belt traditionally considered ridge slope related deposits a total of 176 individually oriented cores collected from the bottom to the top of the sequence with sampling density dependent on inferred sedimentation rates show multicomponent remanent magnetization with magnetite as a main magnetic carrier thermal demagnetization revealed two main components of natural remanent magnetization nrm a low blocking temperature component s of normal polarity is considered of posttectonic probably thermoviscous origin due to overheating by neogene volcanics a stable high blocking temperature nrm component p shows dual polarity distribution and is considered primary it was possible to recognize 23 polarity zones that have been correlated with a biostratigraphic scale since two significant sedimentary gaps occur at 422 and 860 cm the main hiatus ms from the base the latter comprising the middle callovian early oxfordian time span 6 8 ma an obtained pattern of magnetic reversals presented in this study cannot be considered complete a palaeolatitude of 41 5 is calculated for the mid jurassic part below ms similar to that expected for the european craton at the kamenets locality the mid oxfordian limestone directly overlying the ms has palaeolatitudes around 28 6 this implies a relatively fast opening of the oceanic domain to the north from the kamenets block this conclusion combined with similarity of the kamenets sequence to ridge related sediments of the pieniny klippen belt makes it possible to speculate on the existence of the kamenets ridge a new term a structure of uncertain although possible structural links to the czorsztyn ridge palaeomagnetic declinations suggest 100 counterclockwise rotation of the whole section before the neogene

stochastic models for convective momentum transport the improved parameterization of unresolved features of tropical convection is a central challenge in current computer models for long range ensemble forecasting of weather and short term climate change observations theory and detailed smaller scale numerical simulations suggest that convective momentum transport cmt from the unresolved scales to the resolved scales is one of the major deficiencies in contemporary computer models here a combination of mathematical and physical reasoning is utilized to build simple stochastic models that capture the significant intermittent upscale transports of cmt on the large scales due to organized unresolved convection from squall lines properties of the stochastic model for cmt are developed below in a test column model environment for the large scale variables the effects of cmt from the stochastic model on a large scale convectively coupled wave in an idealized setting are presented below as a nontrivial test problem here the upscale transports from stochastic effects are significant and even generate a large scale mean flow which can interact with the convectively coupled wave

a study of the response of deep tropical clouds to mesoscale processes three dimensional numerical experiments abstract a three dimensional numerical cloud ensemble model has been developed to investigate the collective feedback effects of cloud systems on the large scale environment an observed large scale lifting is imposed continuously in the model small amplitude random perturbations in the form of temperature fluctuations are also continuously fed into the model at low levels to simulate random thermals over the tropical ocean the model allows several clouds of various sizes to develop simultaneously inside the domain an integration of the model is made for six hours of simulated time in order to allow large numbers of convective clouds to develop following each simulation the collective feedbacks of cloud systems on the large scale temperature moisture and horizontal momentum fields are computed horizontal and time averages of various relevant variables are also computed to elucidate the statistical properties of the clouds the model was applied to a case of a well defined itcz rainband over the eas

the detection of bacterial magnetite in recent sediments of lake chiemsee southern germany the sediments of lake chiemsee located in the alpine foreland in southern germany host a variety of magnetotactic bacteria mtb which contain intracellular crystals of magnetite arranged in linear chains to detect bacterial magnetite in the carbonate dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments we conducted detailed rock magnetic measurements as well as complimentary non magnetic analyses electron microscopy powder x ray diffraction and sediment pore water analysis our results demonstrate that biogenic single domain magnetite characterized by bullet and truncated hexagonal prismatic shapes is the dominant ferrimagnetic component in the topmost few centimetres of the sediment the changes of magnetic properties with depth are due to the occurrence of live mtb and the downward increasing dissolution of biogenic magnetite moreover the ratios of remanence loss on warming through the verwey transition after field cooling and zero field cooling of saturation isothermal remanence dfc dzfc were determined as 1 47 and 1 25 for freeze dried and air dried sediment samples containing mtb respectively these low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and or that the bacterial magnetosomes might have undergone partial

searching for single domain magnetite in the pseudo single domain sedimentary haystack implications of biogenic magnetite preservation for sediment magnetism and relative paleointensity determinations 1 magnetic hysteresis measurements of sediments have resulted in widespread reporting of pseudo single domain like magnetic properties in contrast the ideal single domain sd properties that would be expected to be responsible for high quality paleomagnetic records are rare determining whether sd particles are rare or common in sediments requires application of techniques that enable discrimination among different magnetic components in a sediment we apply a range of such techniques and find that sd particles are much more common than has been reported in the literature and that magnetite magnetofossils the inorganic remains of magnetotactic bacteria are widely preserved at depth in a range of sediment types including biogenic pelagic carbonates lacustrine and marine clays and possibly even in glaci marine sediments thus instead of being rarely preserved in the geological record we find that magnetofossils are widespread this observation has important implications for our understanding of how sediments become magnetized and highlights the need to develop a more robust basis for understanding how biogenic magnetite contributes to the magnetization of sediments magnetofossils also have grain sizes that are substantially smaller than the 1 15 m size range for which there is reasonable empirical support for relative paleointensity studies the different magnetic response of coexisting fine biogenic and coarser lithogenic particles is likely to complicate relative paleointensity studies this issue needs much closer attention despite the fact that sediments have been subjected to paleomagnetic investigation for over 60 years much remains to be understood about how they become magnetized

a numerical study of the vertical transport of momentum in a tropical rainband abstract the vertical transport of horizontal momentum in a convective tropical rainband is studied using a two dimensional cloud ensemble model twelve simulations are made under the same large scale conditions the vertical transports of v momentum parallel to the rainband are essentially the same in all of the simulations even though the structure of the clouds is different in each of the runs the magnitude of the v memomentum transport by clouds is fairly large it takes only half of a day to smooth out the tropical low level easterly jet parallel to the rainband if no other processes am operating the vertical transports of u momentum perpendicular to the rainband are quite different in all of the simulations this difference can be explained by the dissimilarities in the distributions of horizontal momentum associated with various cloud configurations the simulated vertical transports of horizontal momentum are compared with those computed with the schneider and lindzen scheme the results su

convective momentum transport and perturbation pressure field from a cloud resolving model simulation this study uses a 2d cloud resolving model to investigate the vertical transport of horizontal momentum and to understand the role of a convection generated perturbation pressure field in the momentum transport by convective systems during part of the tropical ocean and global atmosphere coupled ocean atmosphere response experiment toga coare intensive observation period it shows that convective updrafts transport a significant amount of momentum vertically this transport is downgradient in the easterly wind regime but upgradient during a westerly wind burst the differences in convective momentum transport between easterly and westerly wind regimes are examined the perturbation pressure gradient accounts for an important part of the apparent momentum source in general it is opposite in sign to the product of cloud mass flux and the vertical wind shear with smaller magnitude examination of the dynamic forcing to the pressure field demonstrates that the linear forcing representing the interaction between the convective updrafts and the large scale wind shear is the dominant term while the nonlinear forcing is of secondary importance thus parameterization schemes taking into account the linear interaction between the convective updrafts and the large scale wind shear can capture the essential features of the perturbation pressure field the parameterization scheme for momentum transport by zhang and cho is evaluated using the model simulation data the parameterized pressure gradient force using the scheme is in excellent agreement with the simulated one the parameterized apparent momentum source is also in good agreement with the model simulation other parameterization methods for the pressure gradient are also discussed

depth distribution of magnetofossils in near surface sediments from the blake bahama outer ridge western north atlantic ocean determined by low temperature magnetism 1 fe oxide and fe sulfide trace minerals in sediments and sedimentary rocks provide proxy records of biogeochemical processes record past variations in the geomagnetic field and can serve as proxies for climatic variations an important class of these fe oxides is produced by bacteria magnetic particles produced by magnetotactic bacteria have been proposed as a primary recorder of the geomagnetic field in many terrestrial marine sediments and have also been suggested to represent fossil evidence of life on the planet mars to better understand their distribution and preservation in the sediment column and their relationship to other biochemical processes we present rock magnetic data that document the occurrence and abundance of fossil biogenic magnetite magnetofossils in marine sediments from the blake bahama outer ridge magnetic hysteresis and low temperature magnetism both indicate that the occurrence of magnetofossils is closely linked to the depth of the modern fe redox boundary within the sediment column and that a fraction of the magnetic minerals in the sediment column above the fe redox boundary are in the form of intact and relatively unaltered chains of nanophase magnetite crystals below the fe redox boundary the abundance of these magnetofossils is markedly decreased the important conclusions of this work are to demonstrate that nondestructive rock magnetic methods can be used to successfully document the occurrence and relative abundance of magnetofossils in geologic materials

palaeomagnetism and magnetomineralogy of a holocene lake sediment from vagsoy western norway abstract stable remanent directions encountered in three oriented lake sediment cores covering 6 m of gyttja deposits reveal declination swings with amplitudes of the order of 50 anomalously low inclinations scattered around the horizontal in the upper 2 m of core is attributed to compressional disturbances of the alignment of magnetic grains during the coring procedure four 14c dates obtained 1250 1940 4600 and 6330 y b p have enabled a correlation with features c g of the british geomagnetic master curve for the older part of the curve features h and i the correlation is questionable magneto mineralogical parameters and qualitative chemical analysis of individual grains by secondary x ray emission analysis reveal the presence of pure magnetite grains scanning electron micrographs show a dominant proportion of concoidal slightly elongated grains 10 80 m a few almost perfect octahedral magnetite crystals can be related to outcrops of augen gneisses in the vicinity confirming a detrital origin of these grains

detection of live magnetotactic bacteria in south atlantic deep sea sediments abstract since they were first descrbed in 1975 1 magnetotactic bacteria have been observed in a wide variety of environments including soils 2 rivers freshwater lakes and coastal marine sediments 3 4 and in one case at a water depth of about 600 m in a hemipelagic sediment 5 here we report the first systematic findings of magnetotactic bacteria in pelagic and hemipelagic sediments of the eastern south atlantic different morphologies were identified cocci spirilla vibrionic and rod shaped forms at water depths to about 3000 m on the african continental margin between the equator and 30 s and on the walvis ridge in a pelagic environment about 1400 km off the coast no actively swimming magnetotactic bacteria could be detected in deeper waters magnetotactic bacteria were observed only in the upper 10 cm of the sediments with the highest concentrations always found in a well defined narrow subsurface layer the depth of this layer is dependent on the input and turnover rates of organic matter in the sediment measurements of oxygen and nitrate concentrations 6 7 provide an assignment of depth distributions of magnetotactic bacteria to the stratification of terminal electron acceptors in the sediment the data show clearly that the majority of marine magnetotactic bacteria live in the anaerobic zone in contrast to former assumptions that they may inhabit microaerobic layers 8 11

seasonal migration of itcz precipitation across the equator why can t gcms simulate it 1 the secondary meridional circulation induced by convective momentum transport cmt within the ascending branch of the hadley circulation is a missing dynamical mechanism that can cause common failure of general circulation models gcms in simulating seasonal migration of the intertropical convergence zone itcz precipitation maximum across the equator this failure is manifested by the model bias that the precipitation peak remains north of the equator during november march the cmt induced secondary circulation characterized by strong downward motion along the equatorial belt and upward motion south and north of the belt tends to modify the meridional distribution of precipitation with the strongest impacts during boreal winter and spring a 20 year gcm simulation with the cmt parameterization successfully reproduces the observed seasonal migration of the itcz precipitation across the equator with the peaks near 8 n during boreal summer and near 8 s during boreal winter

combined use of magnetometry and spectroscopy for identifying magnetofossils in sediments identification of the mineral remains of magnetotactic bacteria mtb known as magnetofossils is of particular interest because their occurrence can be used for environmental and climatic reconstructions single domain magnetite particles which are biomineralized in the cell body of mtb have characteristic properties that can be used to detect their fossil remains acquisition of anhysteretic and isothermal remanent magnetization arm and irm first order reversal curve forc diagrams and ferromagnetic resonance fmr spectra were used to detect the magnetic mineral inventory in holocene lake sediments a comparative analysis in terms of the discriminatory power of these methods is presented the forc diagrams contain two distinct features a sharp horizontal ridge centered on the horizontal axis bc and a feature with symmetric spread along the vertical bb axis the coercivity spectra derived from the central ridge coincides with that derived from arm and irm acquisition curves and is compatible with the presence of noninteracting linear chains of single domain magnetite the second feature on forc diagrams is indicative of interacting particles in clusters in the fmr spectra from bulk sediment two populations are separated empirically based on the forc information an asymmetric signal is taken to describe the population which contains single domain particles in clusters empirical spectral separation of this contribution results in fmr spectra that are similar to those of intact mtb which strongly suggests that a fraction of linear magnetosome chains is present combination of fmr and forc results demonstrates the strong potential of these methods for identifying magnetofossils based on alignment and interaction patterns of magnetic particles

parametrization of momentum transport by convection ii tests in single column and general circulation models diagnostics derived from cloud resolving model simulations in part i of this study relating to the vertical transport of horizontal momentum by convection are used to develop a parametrization of convective momentum transports for deep convection based upon the mass flux convection scheme discussed by gregory and rowntree the importance of cloud pressure gradients to the flow within the cloud is emphasised and a simple method of representing their effect is suggested the scheme is able to reproduce the fluxes derived from the cloud resolving model studies where cloud organization by the flow is unimportant inclusion of the parametrization in a version of the meteorological office unified model demonstrates that convective momentum transports play a large role in the momentum balance of the atmosphere generally simulation of the mean atmospheric circulation by the unified model is improved by the inclusion of such transports

ferromagnetic resonance characterization of greigite fe3s4 monoclinic pyrrhotite fe7s8 and non interacting titanomagnetite fe3 xtixo4 ferromagnetic resonance fmr spectroscopy has become an increasingly useful tool for studying the magnetic properties of natural samples magnetite fe3o4 is the only magnetic mineral that has been well characterized using fmr this limits the wider use of fmr in rock magnetism and paleomagnetism in this study we applied fmr analysis to a range of magnetic minerals including greigite fe3s4 monoclinic pyrrhotite fe7s8 magnetically non interacting titanomagnetite fe3 xtixo4 and synthetic magnetite chains to constrain interpretation of fmr analysis of natural samples and to explore applications of fmr spectroscopy we measured the fmr signatures of a wide range of well characterized samples at the x and q bands fmr spectra were also simulated numerically to compare with experimental results the effects of magnetic anisotropy mineralogy domain state and magnetostatic interactions on the fmr spectra are discussed for all studied minerals our experimental and theoretical analyses of magnetically non interacting tuff samples and magnetically interacting chains enable quantitative assessment of contributions of magnetostatic interactions and magnetic anisotropy to the fmr spectra our results also indicate that intact magnetosomes are a unique system with distinct fmr signatures while fmr analysis is useful for characterizing magnetic properties of natural samples care is needed when making interpretations because of overlaps in a range of fmr signatures of different magnetic minerals with different magnetic properties our analyses will help to constrain such interpretations in rock magnetic studies

low temperature remanence in stable single domain magnetite 1 a numerical model is developed in order to simulate the loss of low temperature remanence while warming through the verwey transition we concentrate on the amount of remanence lost fc and zfc during field cooled and zero field cooled low temperature demagnetization curves for stable single domain ssd particles of 1 inorganic magnetite and 2 biogenic magnetite in the form of magnetosome chains the model predicts that delta ratios fc zfc for inorganic ssd magnetite increase from 1 to 1 6 with increasing aspect ratio and that magnetosome chains have elevated delta ratios of at least 2 0 disaggregated magnetosomes are predicted to behave similarly to inorganic acicular ssd magnetite the numerical results agree with experimental results

the identification and biogeochemical interpretation of fossil magnetotactic bacteria magnetotactic bacteria which most commonly live within the oxic anoxic transition zone oatz of aquatic environments produce intracellular crystals of magnetic minerals specifically magnetite or greigite the crystals cause the bacteria to orient themselves passively with respect to the geomagnetic field and thereby facilitate the bacteria s search for optimal conditions within the sharp chemical gradients of the oatz the bacteria may also gain energy from the redox cycling of their crystals because magnetotactic bacteria benefit from their magnetic moments natural selection has promoted the development of traits that increase the efficiency with which the intracellular crystals impart magnetic moments to cells these traits also allow crystals produced by magnetotactic bacteria called magnetofossils when preserved in sediments to be distinguished from abiogenic particles and particles produced as extracellular byproducts of bacterial metabolism magnetofossils are recognizable based on their narrow size and shape distributions distinctive morphologies with blunt crystal edges chain arrangement chemical purity and crystallographic perfection this article presents a scheme for rating magnetofossil robustness based on these traits the magnetofossil record extends robustly to the cretaceous and with lesser certainty to the late archean because magnetotactic bacteria predominantly live in the oatz the abundance and character of their fossils can reflect environmental changes that alter the chemical stratification of sediments and the water column the magnetofossil record therefore provides an underutilized archive of paleoenvironmental information several studies have demonstrated a relationship between magnetofossil abundance and glacial interglacial cycles likely mediated by changes in pore water oxygen levels more speculatively a better developed magnetofossil record might provide constraints on the long term evolution of marine redox stratification more work in modern and ancient settings is necessary to explicate the mechanisms linking the abundance and character of magnetofossils to ancient biogeochemistry

cloud resolving modeling of tropical cloud systems during phase iii of gate part i two dimensional experiments abstract a formal framework is established for the way in which cloud resolving numerical models are used to investigate the role of precipitating cloud systems in climate and weather forecasting models emphasis is on models with periodic lateral boundary conditions that eliminate unrealistic numerically generated circulations caused by open boundary conditions in long term simulations defined in this formalism is the concept of large scale forcing and the cloud environment interactions that are consistent with the periodic boundary conditions two dimensional numerical simulations of the evolution of cloud systems during 1 7 september 1974 in phase iii of the global atmospheric research program atlantic tropical experiment gate are conducted based on the above formalism a simple technique is used to force an anelastic cloud resolving model with evolving large scale horizontal wind field and large scale forcing for the temperature and moisture obtained from the gate data the 7 day period selected i

an explicit representation of vertical momentum transport in a multiscale modeling framework through its 2 d cloud resolving model component in this study an explicit representation of vertical momentum transport by convective cloud systems including mesoscale convective systems mcss is proposed and tested in a multiscale modeling framework mmf the embedded cloud resolving model crm provides vertical momentum transport in one horizontal direction the vertical momentum transport in the other direction is assumed to be proportional to the vertical mass flux diagnosed from the crm in addition to the effects of entrainment and detrainment in order to represent both upgradient and downgradient vertical momentum transports the orientation of the embedded crm must change with time instead of being stationary typically in mmfs the orientation is determined by the stratification of the lower troposphere and environmental wind shear introducing the variation of the orientations of the embedded crm is responsible for reducing the stationary anomalous precipitation and many improvements improvements are strengthened when the crm simulated vertical momentum transport is allowed to modify the large scale circulation simulated by the host general circulation model these include an improved spatial distribution amplitude and intraseasonal variability of the surface precipitation in the tropics more realistic zonal mean diabatic heating and drying patterns more reasonable zonal mean large scale circulations and the east asian summer monsoon circulation and an improved annual mean implied meridional ocean transport in the southern hemisphere further tests of this convective momentum transport parameterization scheme will be performed with a higher resolution mmf to further understand its roles in the intraseasonal oscillation and tropical waves monsoon circulation and zonal mean large scale circulations

magnetofossils the magnetization of sediments and the evolution of magnetite biomineralization magnetite fe 3o 4 is one of the most stable carriers of natural remanent magnetization nrm in sedimentary rocks and paleomagnetic studies of magnetite bearing sediments such as deep sea cores and pelagic limestones have provided a detailed calibration between the biostratigraphic and magnetic polarity time scales despite this important role there is as yet a very poor understanding of how ultrafine grained 0 1 m magnetite is formed transported and preserved in marine environments a major conceptual advance in our understanding of these processes is the recent discovery that biogenic magnetite formed by magnetotactic bacteria and or other magnetite precipitating organisms is responsible for much of the stable magnetic remanence in many marine sediments and sedimentary rocks since these magnetite particles are of biogenic origin they are termed properly magnetofossils kirschvink chang 1984

changes in lake stratification and oxygen distribution inferred from two contrasting records of magnetotactic bacteria and diatoms 1 magnetotactic bacteria mtb and diatoms produce hard parts on seasonal timescales that continuously becomes embedded in various soft sediment archives consequently they can and are frequently used to reconstruct past environmental conditions in oceans fjords and freshwater basins in this study we observe how these two cosmopolitan creatures can be used to track vertical shifts in the distribution of oxygen in a small mountain lake situated in western norway several short and long sediment cores have been retrieved from the lake allowing for a detailed reconstruction that spans the last 2500 years during periods of enhanced runoff from the catchment the oxic anoxic transition zone oatz is lowered down to the lake sediment interface due to increased convection we posit that this condition reduces the concentration of microaerophilic magnetite producing mtb an interpretation partly supported by rock magnetic analyzes preservation of diatom frustules is however improved whenever this oxygen rich scenario prevails similarly when runoff is low and the oatz is lifted above the lake sediment interface mtb concentration seems to increase whereas dissolution of diatoms is more common this consistent antiphase relationship between mtb concentration and diatom preservation occurring on a multidecadal timescale during lowest reconstructed lake water ph in the lake s history suggest a coupled response to subtle changes in external environmental variables that affect catchment and lake hydrology

magnetic properties of pelagic marine carbonates abstract pelagic carbonates are deposited far from continents usually at water depths of 3000 6000 m at rates below 10 cm kyr and are a globally important sediment type recent advances with recognition of widespread preservation of biogenic magnetite the inorganic remains of magnetotactic bacteria have fundamentally changed our understanding of the magnetic properties of pelagic carbonates we review evidence for the magnetic minerals typically preserved in pelagic carbonates the effects of magnetic mineral diagenesis on paleomagnetic and environmental magnetic records of pelagic carbonates and what magnetic properties can tell us about the open ocean environments in which pelagic carbonates are deposited we also discuss briefly late diagenetic remagnetisations recorded by some carbonates despite recent advances in our knowledge of these phenomena much remains undiscovered we are only at early stages of understanding how biogenic magnetite gives rise to paleomagnetic signals in sediments and whether it carries a poorly understood biogeochemical remanent magnetisation recently developed techniques have potential for testing how different magnetotactic bacterial species which produce different magnetite morphologies respond to changing nutrient and oxygenation conditions future work needs to test whether it is possible to develop proxies for ancient nutrient conditions from well calibrated modern magnetotactic bacterial occurrences a tantalizing link between giant magnetofossils and paleogene hyperthermal events needs to be tested much remains to be learned about the relationship between climate and the organisms that biomineralised these large and novel magnetite morphologies rather than being a well worn subject that has been studied for over 60 years the magnetic properties of pelagic carbonates hold many secrets that await discovery

organized convection parameterization for the itcz abstractmesoscale convective systems mcss are of fundamental importance in the dynamics of the atmospheric circulation and the climate system they are often observed to develop over significant terrain in ambient shear flows in midlatitudes and embedded within the madden julian oscillation mjo and convectively coupled equatorial wave ccew envelopes as well as in the intertropical convergence zone itcz yet general circulation models gcms fail to resolve these systems and their underlying convective parameterizations are not directed to represent organized circulations shear parallel mcss which are common in the itcz have a three dimensional structure and as such present a serious modeling challenge here a previously developed multicloud model mcm is modified to parameterize mcss one of the main modifications is the parameterization of stratiform condensation to capture extended stratiform outflows which characterize mcss resulting from strong upper level jets linear analysis show

effects of convective processes on gcm simulations of the madden julian oscillation abstract weak temporal variability in tropical climates such as the madden julian oscillation mjo is one of major deficiencies in general circulation models gcms the uncertainties in the representation of convection and cloud processes are responsible for these deficiencies with the improvement made to the convection scheme the iowa state university isu gcm which is based on a version of the ncar community climate model is able to simulate many features of mjo as revealed by observations in this study four 10 yr 1979 88 isu gcm simulations with observed sea surface temperatures are analyzed and compared to examine the effects of the revised convection closure convection trigger condition and convective momentum transport cmt on the mjo simulations the modifications made in the convection scheme improve the simulations of amplitude spatial distribution eastward propagation and horizontal and vertical structures especially for the coherent feature of eastward propagating convection a

parametrization of momentum transport by convection i theory and cloud modelling results summary the theory of the mass flux approach to parametrization of convective momentum transport is presented a cloud resolving model is used to simulate momentum transport by ensembles of deep convective clouds in two very different regimes a mid latitude cold air outbreak and tropical convection forced by convergence idealized unidirectional wind profiles are used to simplify interpretation of the results diagnostics relevant to the parametrization problem are presented and it is shown that for both regimes the approximations inherent in the parametrization equations are reasonable the pressure gradients inside clouds play an important role in determining horizontal velocities in the clouds for the cold air outbreak with linear shear the results suggest that these pressure gradients are proportional to the shear and to the up downdraught mass fluxes sensitivity studies suggest that the results are not very sensitive to resolution or parametrization of subgrid scale processes giving some confidence that the results are reasonably accurate for the tropical case with a low level jet the pressure gradients change sign with the wind shear in part i1 of this paper these results will be used to develop and validate a mass flux parametrization of convective momentum transport which is tested in single column and global versions of the meteorological office unified model

coupling of convective momentum transport with convective heating in global climate simulations abstract the effects of convective momentum transport cmt on global climate simulations are examined in this study comparison between two sets of 20 yr 1979 98 integration using the ncar community climate model version 3 ccm3 illustrates that the inclusion of cmt in the convection scheme systematically modifies the climate mean state over the equatorial region the convective momentum tendencies slow down the equatorward flow at higher latitudes near the surface and weaken the equatorial convergence and convection this reduces the convective heating and drying around the equator and produces an improved meridional distribution within the upward branch of the hadley circulation the major heating peak during the boreal winter is moved to south of the equator at about 10 s which is closer to the heat budget residuals of the ecmwf reanalysis data the responses of meridional wind to the reduced heating result in the secondary meridional circulation within the intertropical convergence zone

biogenic magnetite in stromatolites ii occurrence in ancient sedimentary environments abstract in this paper we report the discovery of fossil bacterial single domain magnetite particles in ancient stromatolites the biogenicity of the crystals was determined by the following criteria 1 distinctive morphology and habit 2 composition and 3 environment of deposition stromatolites ranging in age from the middle archean to pleistocene composed of both carbonate and chert were analyzed for the presence of single domain magnetite using rock magnetic methods the granulometry and composition of the ultra fine grained magnetite crystals extracted were determined by transmission electron microscopy and electron diffraction the oldest magnetofossils were extracted from stromatolitic chert of the gunflint iron formation which is approximately 2000 ma old the implications of these findings and the potential uses of fossil bacterial magnetite in studies of the evolution of biomineralization and prokaryotic metabolic processes paleomagnetism and as an indicator of ancient oxygen levels are discussed bacterial magnetite represents the oldest evidence of biomineralization yet discovered in the fossil record

bacterial magnetite in lake sediments late glacial to holocene climate and sedimentary changes in northern norway magnetic properties of sediments retrieved from a small lake in northern norway spanning the last f14500 cal years have been analyzed in detail the high resolution core with its ability to detect sub centurial variability records the rapid retreat of the fennoscandian ice sheet fis in northern lyngen and subsequently the establishment of a stable allerod to younger dryas watershed from early holocene and to the present magnetotactic bacteria mb producing stable single domain ssb magnetite become the dominating magnetic carrier the small low relief catchment area with its quartzite bedrock scattered till and vegetated surface generates a negligible contribution of detrital magnetic minerals this allows for the opportunity to follow the presence and changes of the magnetosomes during the last 10000 years a strong positive statistical relationship r 2 0 83 between the anhysteretic remanent magnetisation susceptibility varm and loss on ignition loi suggests an environmental control over the bacteria magnitude quart int 88 2002 13 that most likely is related to summer climate a comparison between the magnetic mineralogy as evident from the s ratio jirm100mt jsirm3t and the reconstructed summer temperatures from a nearby lake shows a close covariation between cooler summers and harder s ratios for a series of climatic events intervariability of loi data and other proxies such as august sea surface temperatures sst from the nordic sea suggests land ocean connections during converging phases of cooler climate where the most prominent in phase periods are approximately 1 6500 5000 2 3500 2400 and 3 1700 1000 cal years bp the most significant change in the holocene magnetic signal is initiated at f3700 cal years bp which we refer to here as the holocene turnover d 2004 elsevier b v all rights reserved

chemical signature of magnetotactic bacteria there are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite on earth magne totactic bacteria perform biomineralization of intracellular magne tite nanoparticles under a controlled pathway these bacteria are ubiquitous in modern natural environments however their identification in ancient geological material remains challenging together with physical and mineralogical properties the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification but this had never been explored quantitatively and systematically for many trace elements here we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium magnetospirillum magneticum strain amb 1 we show that in biomagnetite most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion furthermore we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record magnetotactic bacteria magnetite biomineralization trace element incorporation

the role of momentum transport in the motion of a quasi idealized mesoscale convective system abstract momentum transport is examined in a simulated midlatitude mesoscale convective system mcs to investigate its contribution to mcs motion momentum budgets are computed using model output to quantify the role of specific processes in determining the low level wind field in the system s surface based cold pool results show that toward the leading convective line of the mcs and near the leading edge of the cold pool the momentum field is most strongly determined by the vertical advection of the storm induced perturbation wind across the middle rear of the system the wind field is largely a product of the pressure gradient acceleration and to a lesser extent the vertical advection of the background environmental i e base state wind the relative magnitudes of the vertical advection terms in an eulerian momentum budget suggest that for gust front driven systems downward momentum transport by the mcs is a significant driver of mcs motion and potentially severe surface winds results furthe

magnetic anisotropy magnetostatic interactions and identification of magnetofossils 1 single domain magnetite particles produced by magnetotactic bacteria mtb and aligned in chains called magnetosomes are potentially important recorders of paleomagnetic paleoenvironmental and paleolife signals rock magnetic properties related to the anisotropy of magnetosome chains have been widely used to identify fossilized magnetosomes magnetofossils preserved in geological materials however ambiguities exist when linking magnetic properties to the chain structure because of the complexity of chain integrity and magnetostatic interactions among magnetofossils that results from chain collapse during post depositional diagenesis in this paper magnetic properties of three sets of samples containing extracted magnetosomes of the culturedmagnetospirillum magneticumstrain amb 1 were analyzed to determine how chain integrity and particle concentration influence magnetic properties intact mtb and well dispersed magnetosome chains are characterized by strong magnetic anisotropy and weak magnetostatic interactions but progressive chain breakup and particle clumping significantly increase the degree of magnetostatic interaction this results in a change of the magnetic signature toward properties typical of interacting single domain particles i e a decrease of the ratio of anhysteretic remanent magnetization to the saturation isothermal remanent magnetization decreasing in the crossing point of the wohlfarth cisowski test and in the delta ratio between losses of field and zero field cooled remanent magnetization across the verwey transition as well as vertical broadening of the first order reversal curve distribution we propose a new diagram that summarizes the verwey transition properties with diagnostic limits for intact and collapsed chains of magnetosomes this diagram can be used in conjunction with other parameters to identify unoxidized magnetofossils in sediments and rocks

quantifying the concentration of ferrimagnetic particles in sediments using rock magnetic methods 1 we have developed a quantification method that uses mainly room temperature rock magnetic measurements to calculate concentrations of ferrimagnetic particles in sediments our method uses saturation magnetization ms as a total ferrimagnetic concentration proxy the saturation remanence ratio mrs ms as a magnetic grain size proxy the anhysteretic remanence ratio a mrs to estimate inter particle magnetostatic interactions and the normalized susceptibility of the ferrimagnetic fraction f ms to calculate the proportion of ultrafine superparamagnetic particles this approach eliminates the effect of dilution of the magnetic properties by weakly magnetic matter and allows the calculation of direct concentrations or fluxes for dated sedimentary profiles of constituent ferrimagnetic components we test our method on a short sediment core from an urban minnesota lake for which we calculate ferrimagnetic fluxes of four magnetic components and compare their pre and post european settlement values our quantification technique can be applied for reconstructing past environmental changes in a range of sedimentary environments and is particularly useful for large sets of samples where detailed magnetic unmixing methods are unfeasible due to time or instrument constraints

characterization of momentum transport associated with organized moist convection and gravity waves abstract tropical convection is inherently multiscalar involving complex fields of clouds and various regimes of convective organization ranging from small disorganized cumulus up to large organized convective clusters in addition to being a crucial component of the atmospheric water cycle and the global heat budget tropical convection induces vertical fluxes of horizontal momentum there are two main contributions to the momentum transport the first resides entirely in the troposphere and is due to ascent descent and organized circulations associated with precipitating convective systems the second resides in the troposphere stratosphere and farther aloft and is caused by vertically propagating gravity waves both the convective momentum transport and the gravity wave momentum flux must be parameterized in general circulation models yet in existing parameterizations these two processes are treated independently this paper examines the relationship between the convective momentum transport and

iron sulfides from magnetotactic bacteria structure composition and phase transitions using transmission electron microscopy we studied the structures and compositions of fe sulfides within cells of magnetotactic bacteria that were collected from natural habitats ferrimagnetic greigite fe3s4 occurred in all types of sulfide producing magnetotactic bacteria examined mackinawite tetragonal fes and tentatively sphalerite type cubic fes were also identified in contrast to earlier reports we did not find pyrite fes 2 or pyrrhotite fe12xs mackinawite converted to greigite over time within the bacteria that were deposited on electron microscope grids and stored in air orientation relationships between the two minerals indicate that the cubic close packed s substructure remains unchanged during the transformation only the fe atoms rearrange neither mackinawite nor cubic fes are magnetic and yet they are aligned in chains such that when converted to magnetic greigite the probable easy axis of magnetization 100 is parallel to the chain direction the resulting chains of greigite are ultimately responsible for the magnetic dipole moment of the cell both greigite and mackinawite magnetosomes can contain cu depending on the sampling locality because bacterial mackinawite and cubic fes are unstable over time only greigite crystals are potentially useful as geological biomarkers

on the mass flux representation of vertical transport in moist convection abstractthis study investigates to what extent the convective fluxes formulated within the mass flux framework can represent the total vertical transport of heat and moisture in the cloud layer and whether the same approach can be extended to represent the vertical momentum transport using large eddy simulations less of six well documented cloud cases including both deep and shallow convection two methods are used to decompose the les resolved vertical fluxes decompositions based on the coherent convective features using the mass flux top hat profile and by two dimensional fast fourier transform 2d fft in terms of wavenumbers the analyses show that the convective fluxes computed using the mass flux formula can account for most of the total fluxes of conservative thermodynamic variables in the cloud layer of both deep and shallow convection for an appropriately defined convective updraft fraction a result consistent with the mass flux dynamic view of moist convection and previous studies however