numerical simulations of radiative cooling beneath the anvils of supercell thunderstorms abstract numerical simulations of supercell thunderstorms that include parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps to investigate the effects of anvil shadows on the near storm environment if the simulated storm is nearly stationary the maximum low level air temperature deficits within the shadows are about 2 k which is roughly half the cooling found in some previous observations it is shown that the extinction of downwelling shortwave radiation by the anvil cloud creates a differential in the flux of downwelling shortwave radiation between the sun and the shade that is at least an order of magnitude greater than the differential of any other term in either the surface radiation or the surface energy budgets the loss of strong solar heating of the model surface within the shaded regions leads to a reduction of surface temperatures and stabilization of the model surface layer beneath the anvil the reduction in vertical mixing

the variability of conditions of carbonate allocation on the example of a small flow through łeczna wlodawa lake eastern poland a synthetic index lsi langelier saturation index was calculated to analyze conditions of carbonates allocation the higher lsi value positive or negative the better conditions to deposition or chemical denudation respectively physical chemical research was carried out in the lake catchment system of lake syczynskie located in the border zone of polish lowland and lublin upland the data were collected during the three water years 2007 2009 a hydro chemical state of products of caco3 dissociation in waters was close to the equilibrium for most of the year values of the lsi ranged from 0 08 to 1 44 in the water of the catchment under study the highest lsi values were observed in the lake water the lowest lsi values occurred in waters of the inlet originated from a cretaceous spring allocation conditions were established along inlet lake outlet transect a decrease of carbonates translocation along the transect was typical for the lake syczynskie and it occurred in all seasons a clear seasonality of the carbonate equilibrium state was observed in the lake catchment system under study results showed that inlet of groundwater determined transport of products of calcium and magnesium carbonate dissociation in the catchment lake syczynskie the most stable chemical conditions were observed in winter which resulted from an intense groundwater inflow the least stable conditions occurred in spring in which season conditions of carbonates allocations were modified by precipitation and or surface runoff

solid phase phosphorus pools in highly organic carbonate sediments of northeastern florida bay currently few studies have investigated sediment phosphorus p pools or identified the chemical processes important in the p cycle of fine grained carbonate sediments particularly in coastal estuaries with high organic matter to determine the role of fine grain calcium carbonate and high organic matter on sedimentary p we investigated the solid phase p pools in seagrass sediments of north eastern ne florida bay at the bay mangrove ecotone sediments were fractionated by sequential extractions into seven chemically defined groups exchangeable inorganic and organic p reducible inorganic and organic p fe bound acid extractable inorganic and organic p ca bound and residual organic p calcium bound p accounted for approximately 56 of total p and 96 of inorganic p our total calcium bound p was in the range 34 151 gpg 1 reported for coarse grained low organic sediments while the organic p associated with this fraction was slightly 10 higher than those reported for other carbonate systems the second dominant p fraction was residual organic p 30 71 gpg 1 accounting for 42 of tp this high residual pool suggests the importance of fringing mangrove and seagrass detritus in long term p storage in contrast to temperate estuaries the iron bound p fraction in ne florida bay sediments was low 70 gg 1 at the surface and undetectable 1 gg 1 below 10 cm based on our findings we hypothesize that carbonate chemisorption reactions along with potential reactive organic surfaces and the sequestering of p into recalcitrant organic pools maintain low exchangeable and pore water p concentrations across the ne florida bay estuary and account for the reported autotrophic p limitation 2001 academic press

the cause of internal outflow surges in a high resolution simulation of the 8 may 2003 oklahoma city tornadic supercell abstracta high resolution simulation of the 8 may 2003 oklahoma tornadic supercell is analyzed to determine the origin of internal outflow surges within the low level cold pool the analyzed simulation has 50 m horizontal grid spacing and is quadruply nested within larger lower resolution domains that were initialized via three dimensional variational data assimilation 3dvar of radar and other observations the high resolution simulation produces two tornadoes that track in close proximity to the observed tornado on 8 may 2003 the authors previous study determined that an internal outflow surge instigated tornadogenesis for the first tornado in this simulation but the cause of this internal outflow surge was unclear in this study the vertical momentum equation is analyzed along backward trajectories that are initialized within the tornado triggering internal outflow surge the analysis reveals that the internal outflow surge is forced by the dynamic part of the vertical pressure gradient further ex

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

a theory for strong long lived squall lines abstract we study herein the mechanics of long lived line oriented precipitating cumulus convection squall lines using two and three dimensional numerical models of moist convection these models used in juxtaposition enable us to address the important theoretical issue of whether a squall line is a system of special long lived cells or whether it is a long lived system of ordinary short lived cells our review of the observational literature indicates that the latter is the most consistent paradigm for the vast majority of cases but on occasion a squall line may be composed of essentially steady supercell thunderstorms the numerical experiments presented herein show that either type of squall line may develop from an initial line like disturbance depending on the magnitude and orientation of the environmental shear with respect to the line with shallow shear oriented perpendicular to the line a long lived line evolves containing individually short lived cells our analysis of this type o

simulated supercells in nontornadic and tornadic vortex2 environments abstractthe composite near storm environments of nontornadic and tornadic supercells sampled during the second verification of the origins of rotation in tornadoes experiment vortex2 both appear to be generally favorable for supercells and tornadoes it has not been clear whether small differences between the two environments e g more streamwise horizontal vorticity in the lowest few hundred meters above the ground in the tornadic composite are actually determinative of storms tornadic potential from the vortex2 composite environments simulations of a nontornadic and a tornadic supercell are used to investigate storm scale differences that ultimately favor tornadogenesis or tornadogenesis failure both environments produce strong supercells with robust midlevel mesocyclones and hook echoes though the tornadic supercell has a more intense low level updraft and develops a tornado like vortex exceeding the ef3 wind speed threshold in contrast the nontornadic supercell only produces shallow vortic

supercell low level mesocyclones in simulations with a sheared convective boundary layer abstractsimulations of supercell thunderstorms in a sheared convective boundary layer cbl characterized by quasi two dimensional rolls are compared with simulations having horizontally homogeneous environments the effects of boundary layer convection on the general characteristics and the low level mesocyclones of the simulated supercells are investigated for rolls oriented either perpendicular or parallel to storm motion as well as with and without the effects of cloud shading bulk measures of storm strength are not greatly affected by the presence of rolls in the near storm environment though boundary layer convection diminishes with time under the anvil shadow of the supercells when cloud shading is allowed simulations without cloud shading suggest that rolls affect the morphology and evolution of supercell low level mesocyclones initially cbl vertical vorticity perturbations are enhanced along the supercell outflow boundary resulting in nonnegligible near ground vertical vorticity regardles

fluorine mobility during early diagenesis of carbonate sediment an indicator of mineral transformations abstract the abundant occurrence of calcium carbonate minerals in marine sediment their well documented dissolution or precipitation during diagenesis and their high f content suggest that carbonate mineral diagenesis may be an important influence on f behavior in marine sediment to test this hypothesis we have examined the geochemistry of f in shallow carbonate mud bank sediment of florida bay usa the f content of biogenic calcium carbonate in florida bay varies with mineralogy positively correlates with the mg content of calcite and occurs in similar abundance to sr high mg calcite f sr 2 4 mol mol aragonite 0 53 0 79 mol mol low mg calcite 0 22 mol mol models of porewater distributions direct solute flux measurements and reaction rate estimates over the upper 0 16 cm of sediment from bob allen key bank predict net fluxes out of the sediment of 170 mol f m2 d 230 mol sr m2 d and 5 6 mmol ca m2 d the net solute flux ratio of f sr 0 71 mol mol is consistent with dissolution of aragonite or high mg calcite but f ca and sr ca ratios 28 mmol mol and 40 mmol mol respectively are 3 10 that of biogenic carbonate sources selective dissolution of a high f and sr content phase or more likely based on dissolution experiments concurrent dissolution and reprecipitation of phases with different f and sr contents account for this discrepancy the loss of f sr and ca to fluorapatite precipitation as predicted from a stoichiometric model of phosphate release can be added to the transport reaction model predicted net fluxes a resulting more complete mass balance model incorporating both carbonate mineral reactions and fluorapatite formation yields total release estimates of f sr and ca of 770 mol 332 mol and 53 mmol m2 d respectively calcium carbonate minerals apparently undergo transformation whereby 34 mmol high mg calcite m2 d and 19 mmol aragonite m2 d dissolve and 46 mmol low mg calcite m2 d precipitates ignoring other cations besides ca if no fluorapatite formation occurs the required fluxes are that 23 mmol aragonite m2 d dissolves and 3 4 mmol high mg calcite m2 d and 14 mmol low mg calcite m2 d precipitate net loss of caco3 from the deposit by dissolution is 6 7 mmol m2 d 3 of the accumulation flux the magnitude of these fluxes could cause significant mineralogical and chemical changes on rapid time scales in nearshore carbonate sediment fluorine is probably mobile in other carbonate deposits undergoing diagenetic alteration on short and longer time scales and is a powerful additional constraint on the rates and nature of carbonate mineral diagenesis

enriched stable carbon isotopes in the pore waters of carbonate sediments dominated by seagrasses evidence for coupled carbonate dissolution and reprecipitation studies of the 13c of pore water dissolved inorganic carbon 13c dic were carried out in shallow water carbonate sediments of the great bahamas bank gbb to further examine sediment seagrass relationships and to more quantitatively describe the couplings between organic matter remineralization and sediment carbonate diagenesis at all sites studied 13c dic provided evidence for the dissolution of sediment carbonate mediated by metabolic co2 i e co2 produced during sediment organic matter remineralization these observations are also consistent with pore water profiles of alkalinity total dic and ca2 at these sites in bare oolitic sands isotope mass balance further indicates that the sediment organic matter undergoing remineralization is a mixture of water column detritus and seagrass material in sediments with intermediate seagrass densities seagrass derived material appears to be the predominant source of organic matter undergoing remineralization however in sediments with high seagrass densities the pore water 13c dic data cannot be simply explained by dissolution of sediment carbonate mediated by metabolic co2 regardless of the organic matter type rather these results suggest that dissolution of metastable carbonate phases occurs in conjunction with reprecipitation of more stable carbonate phases simple closed system calculations support this suggestion and are broadly consistent with results from more eutrophic florida bay sediments where evidence of this type of carbonate dissolution reprecipitation has also been observed in conjunction with our previous work in the bahamas these observations provide further evidence for the important role that seagrasses play in mediating early diagenetic processes in tropical shallow water carbonate sediments at the same time when these results are compared with results from other terrigenous coastal sediments as well as supralysoclinal carbonate rich deep sea sediments they suggest that carbonate dissolution reprecipitation may be more important than previously thought in general in the early diagenesis of marine sediments

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

rates of carbonate dissolution in permeable sediments estimated from pore water profiles the role of sea grasses in this study we estimate sediment carbonate dissolution rates for sandy sea grass sediments on the bahamas bank using an inverse pore water advection diffusion reaction model constrained by field observations this model accounts for sea grass o2 input to these sediments and also parameterizes pore water advection through these permeable sediments as a nonlocal exchange process the resulting rates of carbonate dissolution are positively correlated with sea grass density and are comparable with previous rate estimates for florida bay sediments in contrast the advective uptake of o2 by these sediments decreased with increasing sea grass density this suggests that the competing interplay between bottom water flow near seabed pressure gradients and the presence of a sea grass canopy is important in controlling this type of sediment oxygen uptake when the carbonate dissolution rates estimated here are examined in the context of carbonate budgets for shallow water carbonate platforms systems they suggest that carbonate dissolution may be a significant loss term in these budgets sea grass mediated carbonate dissolution may also exert a negative feedback on rising atmospheric co2 although the magnitude of this effect remains to be quantified

climatic variability and deep ocean circulation evidence from the north atlantic abstract rhythmic fluctuations of the faunal composition of deep sea benthic foraminifers during the past 24 000 years occurred at periodicites of about 2500 1500 1000 and 650 years these faunal fluctuations apparently are recordings of global climate fluctuations which have left similar records in climate sensitive biotic and abiotic indicators the reddenings of the power spectra occur in a manner very similar to those produced by the models of hasselmann and lemke with slopes of approximately 2 on a log log plot which could imply that the observed climatic variance is stochastic in origin the presence of significant spectral peaks suggests that the propagation of variance from high to low frequencies is held up or accelerated at frequencies characteristics of turnover times of the oceanic deep water circulation the most sensitive triggering point to influence the deep thermohaline circulation lies in the northern north atlantic where the rate of bottom water formation and its physical and chemical characteristics are easily modulated by local atmospheric and oceanographic conditions any change in the deep water characteristics propagate through the ocean basins with delays determined by the speed and length of deep water flow feedback to the north atlantic is provided by the direct return flow of some of these water masses as surface currents and by the influence that changes in the rate and character of upwelling deep waters may have upon shaping surface climate variations of the rates and temperatures of north atlantic downwelling and north pacific upwelling influences the overall energy balance the steering effect of north pacific sea surface temperature anomalies upon the jet stream as noted by namias provides an atmospheric teleconnection from the north pacific to north america and the north atlantic which controls the regional energy distribution and in turn the modulation of north atlantic downwelling

tornadogenesis in a simulated mesovortex within a mesoscale convective system abstractthe advanced regional prediction system arps is used to simulate a tornadic mesovortex with the aim of understanding the associated tornadogenesis processes the mesovortex was one of two tornadic mesovortices spawned by a mesoscale convective system mcs that traversed southwestern and central oklahoma on 8 9 may 2007 the simulation used 100 m horizontal grid spacing and is nested within two outer grids with 400 m and 2 km grid spacing respectively both outer grids assimilate radar upper air and surface observations via 5 min three dimensional variational data assimilation 3dvar cycles the 100 m grid is initialized from a 40 min forecast on the 400 m grid results from the 100 m simulation provide a detailed picture of the development of a mesovortex that produces a submesovortex scale tornado like vortex tlv closer examination of the genesis of the tlv suggests that a strong low level updraft is critical in converging and amplifying vertical vorticity associated with the mesovortex

tornadogenesis in a high resolution simulation of the 8 may 2003 oklahoma city supercell abstracta 50 m grid spacing advanced regional prediction system arps simulation of the 8 may 2003 oklahoma city tornadic supercell is examined a 40 min forecast run on the 50 m grid produces two f3 intensity tornadoes that track within 10 km of the location of the observed long track f4 intensity tornado the development of both simulated tornadoes is analyzed to determine the processes responsible for tornadogenesis trajectory based analyses of vorticity components and their time evolution reveal that tilting of low level frictionally generated horizontal vorticity plays a dominant role in the development of vertical vorticity near the ground this result represents the first time that such a mechanism has been shown to be important for generating near surface vertical vorticity leading to tornadogenesis a sensitivity simulation run with surface drag turned off was found to be considerably different from the simulation with drag included a tornado still developed in the no drag simulation but it was

coupling between sulfur recycling and syndepositional carbonate dissolution evidence from oxygen and sulfur isotope composition of pore water sulfate south florida platform u s a sulfur cycling in fe poor organic rich shelf carbonates known to have rapid rates of so4 2 reduction remains poorly studied despite the volumetric significance of shelf deposits in modern and ancient carbon budgets we investigated sulfur cycling in modern carbonates of the florida platform from end member depositional environments muddy sands from the atlantic reef tract and finer grained mudbank and island flank deposits from florida bay relations between pore water chemistry so4 2 co2 ca 2 cl and oxygen and sulfur stable isotope compositions of so4 2 require direct coupling between sulfur redox cycling and syndepositional carbonate dissolution oxygen isotope compositions of pore water sulfate were remarkably shifted away from the established value for marine so4 2 9 5 despite near normal so4 2 cl ratios chemical evolution was least in reef tract pore waters and greatest in florida bay relative to overlying seawater mudbank sediments exhibited sulfate depletion with 18oso4 and 34sso4 values both increasing by about 7 more bioturbated island flank sediments colonized by thalassia grass had a 5 increase in 18oso4 variable 34sso4 values 17 7 to 23 3 and exceptionally high ca 2 cl ratios the large excess of ca 2 up to 1 7 mm requires a much larger acid source than the amounts derived from utilization of dissolved o2 0 3 mm and small degrees of net so4 2 reduction 0 5 mm reduced a conceptual model was constructed using chemical and isotopic data on natural pore waters and on sulfate isotope fractionation factors obtained from sediment incubation experiments the model outputs show that pore water compositions can be explained by a redox cycle where microbial so4 2 reduction is followed by very efficient h2s oxidation thus maintaining virtually invariant so4 2 cl ratios the enhanced o2 transport may be driven by associated marine grass rhizome systems and microbial communities established in bioturbated sediments the net result of the cycle is that the rate of sulfide oxidation which is largely balanced by the rate of microbial sulfate reduction is stoichiometrically related to the rate of carbonate dissolution this is consistent with previously reported rates of carbonate dissolution 400 mol cm2 yr and average rates of sulfate reduction 200 mol cm2 yr from the florida platform and a 2 1 stoichiometry

the role of organic acid exudates in liberating phosphorus from seagrass vegetated carbonate sediments sediment bound phosphorus p is a potential nutrient source for p limited seagrasses inhabiting carbonate sediments we explored the role of organic acid oa exudation by seagrasses in liberating mineral p from carbonate sediments organic acids can act to increase available p by dissolving carbonate sediment competing with p for binding sites and complexing dissolution end products and also by fueling microbial processes that change pore water ph we used dialysis tubing placed around individual roots in situ to quantify dissolved species immediately adjacent to roots root zone and compared these to bulk pore water concentrations in vegetated and nonvegetated sediments total oa concentrations were highest in the root zone 29 8 6 1 8 mmol l21 compared to bulk measures of 15 5 6 1 9 and 7 5 6 0 6 mmol l21 in vegetated and nonvegetated sediments respectively phosphate concentrations were also highest in the root zone and were linearly related to oa concentrations r2 5 0 63 organic acid concentrations increased along a seagrass productivity gradient and ratios of oa concentrations to productivity showed a significant response to a gradient in p limitation of seagrasses organic acid concentrations found in and around roots compared to those found in bulk sediment measures indicate that seagrasses are a significant source of oa sampling at small spatial scales mm immediately adjacent to the roots is critical because bulk sediment pore water measures did not capture the observed fluctuations caused by the rapid reaction and consumption of oa in the sediment root zone processes can liberate considerable quantities of p and oa exudates likely contribute significantly to the success of t testudinum in p limited environments

what is the intrinsic predictability of tornadic supercell thunderstorms abstracta 25 member ensemble of relatively high resolution 75 m horizontal grid spacing numerical simulations of tornadic supercell storms is used to obtain insight on their intrinsic predictabil

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

forms and availability of sediment phosphorus in carbonate sand of bermuda seagrass beds primary production by seagrasscs in tropical and subtropical carbonate sediments often appears to be phosphorus p limited and several studies have sought to identify the possible sources of p for long term growth here we quantify concentrations of particulate and dissolved p and fluoride f in carbonate sediments sediment water p exchange and leaf tissue p concentrations in three seagrass beds in bermuda we also present data on the sequential extraction of p and f from the sediments at each site total sediment p tp in the upper 20 cm ranged from 650 to 1 250 mmol p m 2 and was some 500 fold larger than the pool of p dissolved in pore waters loosely adsorbed inorganic p comprised 2 of tpsed while a surface bound inorganic p pool extracted by dithionite buffer constituted 15 20 most of the remaining p and nearly all of the ca and f present in the sediment was recovered when the remaing sediment was dissolved in an acetic acid buffer solution this pool includes calcium fluoroapatite cfa which is considered the primary diagenetic sink for p in carbonate sands dissolved inorganic p and fwere both elevated in the rhizosphere pore waters from the three seagrass beds in combination with our analysis of sediments by sequential extraction this result indicates that the carbonate matrix of the sediment is being dissolved in the rhizosphere with a resulting release of p to the pore water and hence to the seagrass roots we suggest that this is important in the p economy of these subtropical seagrass thalussia testudinum beds and note that the carbonate bound p pool is large enough to sustain seagrass p requirements for decades nonetheless primary production in such seagrass systems can remain p limited if the rate of p release from sediment dissolution is too slow to support maximum seagrass growth rates analysis of seagrass leaf tissues revealed that p availability was highest at the site with the highest anthropogenic influences this site was also characterized by the highest sediment p release indicating that high p availability may also be partly due to higher release of p as sediments are dissolved phosphorus was released from the sediment mainly as dissolved organic p causing a net efflux of dissolved p at all sites in april and at two sites in august

phosphorus release with carbonate dissolution coupled to sulfide oxidation in florida bay seagrass sediments we hypothesized that caco3 dissolution coupled to sulfide oxidation is an important mechanism by which solid phase inorganic p ip becomes available to seagrass in tropical carbonate sediments to examine this supposition we measured field sulfate reduction rates and simulated the acidity 10 50 mmol h2so4 cm23 sediment generated by subsequent sulfide oxidation from high western and low eastern total p tp sediments in florida bay dissolution experiments were conducted using sediment slurries at field ph pore water ph 6 5 7 5 while caco3 dissolution maximum 1 3 of sediment dry weight was evidenced at all sites by leaching of ca2 into slurries at three of the four sites po 3 4 was primarily recovered in the sediment exchangeable pools and at a lower p ca ratio than observed in source sediments in contrast no po 3 4 was recovered from an eastern bay site with the lowest tp and finest grained sediments suggesting that po 3 4 was either tightly adsorbed or incorporated into the carbonate matrix post acidification the potential for tight po 3 4 resorption by sediment from the low tp site was also supported by the rapid rate of isotopic exchange of 33po 3 4 into the sediment matrix these adsorptive and incorporation processes may explain the low po 3 4 in pore waters in the eastern vs western regions of florida bay even upon dissolution of carbonates carbonate dissolution coupled to sulfide oxidation could potentially provide 1 8 and 23 5 mmol ip m22 d21 at eastern and western bay sites respectively meeting 5 of eastern and 29 of western bay seagrass thalassia testudinum p requirements

impact of sea grass density on carbonate dissolution in bahamian sediments carbonate dissolution has been widely observed in shallow water tropical sediments however sediment budgets have generally not been closed with respect to the amount of acid required to produce the observed carbonate dissolution recently it has been suggested that enhanced oxygen transport into sediments through the roots and rhizomes of sea grasses might play a role in resolving this mass balance problem we conducted studies of sea grass carbonate sediment interactions around lee stocking island exuma islands bahamas to further examine this problem our studies showed that alkalinity total dissolved inorganic carbon sco2 and ca 21 increased with depth in the pore waters while ph and calculated carbonate ion concentration decreased with depth these observations are consistent with the occurrence of carbonate dissolution in these sediments the magnitude of pore water alkalinity sco2 and ca 21 changes was also related to sea grass density with the largest gradients seen in the sediments of dense sea grass beds calculations suggested that less than 50 of the o2 needed to drive aerobic respiration and ultimately carbonate dissolution via co2 production could be supplied by transport processes such as diffusion bioturbation and physical pore water advection furthermore the o 2 needed to balance the carbonate dissolution budget could be provided by the transport of 15 of the photosynthetically derived o2 to the sediments through sea grass roots and rhizomes without enhancing the removal of carbonate dissolution end products thus sea grasses play an important role in controlling the rates of carbonate dissolution in shallow water tropical marine sediments

properties of a simulated convective boundary layer in an idealized supercell thunderstorm environment abstractnearly all previous numerical simulations of supercell thunderstorms have neglected surface fluxes of heat moisture and momentum this choice precludes horizontal inhomogeneities associated with dry boundary layer convection in the near storm environment as part of a broader study on how mature supercell thunderstorms are affected by a convective boundary layer cbl with quasi two dimensional features i e boundary layer rolls this paper documents the methods used to develop a realistic cbl in an idealized environment supportive of supercells the evolution and characteristics of the modeled cbl including the horizontal variability of thermodynamic and kinematic quantities known to affect supercell evolution are presented the simulated rolls result in periodic bands of perturbations in temperature moisture convective available potential energy cape vertical wind shear and storm relative helicity srh vertical vorticity is shown to arise within the boundary layer through the tilt

climatic fluctuations due to deep ocean circulation a simple climate model that includes the effect of deep ocean turnover as a pure time delay exhibits an oscillatory behavior the deep ocean signal contains frequencies characteristic of both the forcing function and the deep ocean delay

potential availability of sedimentary phosphorus to sediment resuspension in florida bay the central bay the spatial pattern of tsp is consistent with distribution of both seagrass and phytoplankton that are limited by available phosphorus in florida bay among the five pools the authigenic carbonate fluorapatite biogenic apatite and caco3 bound phosphorus account for the largest fraction 45 of tsp of which inorganic phosphorus is the dominant form and organic phosphorus accounts for about 30 in the western and north central regions and less than 10 in other areas of florida bay the second largest pools are the refractory organic phosphorus 24 of tsp and reductant soluble inorganic phosphorus 19 of tsp readily exchangeable phosphorus accounts for 8 of tsp of which organic phosphorus is 60 detrital apatite phosphorus of igneous or metamorphic origin represents the smallest fraction only 5 of tsp spatial distribution of phosphorus and iron in sediments indicates that external sources of these two essential plant nutrients to florida bay are spatially separated with phosphorus introduced by west coast waters across the western margin of florida bay and iron from freshwater flow into the eastern region index terms 1030 geochemistry geochemical cycles 0330 1050 geochemistry marine geochemistry 4835 4850 4805 oceanography biological and chemical biogeochemical cycles 1615 4845 oceanography biological and chemical nutrients and nutrient cycling keywords florida bay phosphorus sediment

dynamical influences of anvil shading on simulated supercell thunderstorms abstractnumerical simulations of supercell thunderstorms including parameterized radiative transfer and surface fluxes are performed using the advanced regional prediction system arps model to investigate how low level air temperature deficits within anvil shadows affect the simulated storms the maximum temperature deficits within the modeled cloud shadows are 1 5 2 0 k which is only about half that previously observed within the shadows the loss of strong solar heating cools and stabilizes the near surface layer which suppresses vertical mixing and modifies the near surface vertical wind shear in a case of a stationary storm the enhanced easterly shear present beneath the anvil leads to a thinning of the outflow layer and corresponding acceleration of the rear flank gust front far ahead of the overlying updraft weakening the low level mesocyclone it is further shown that the direct absorption and emission of radiation by clouds does not significantly affect the simulated supercells varying th

a theory for strong long lived squall lines revisited based on the analysis of idealized two and three dimensional cloud model simulations rotunno et al hereafter rkw and weisman et al hereafter wkr put forth a theory that squall line strength and longevity was most sensitive to the strength of the component of low level 0 3 km agl ambient vertical wind shear perpendicular to squall line orientation an optimal state was proposed by rkw based on the relative strength of the circulation associated with the storm generated cold pool and the circulation associated with the ambient shear whereby the deepest leading edge lifting and most effective convective retriggering occurred when these circulations were in near balance since this work subsequent studies have brought into question the basic validity of the proposed optimal state based on concerns as to the appropriate distribution of shear relative to the cold pool for optimal lifting as well as the relevance of such concepts to fully complex squall lines especially considering the potential role of deeper layer shears in promoting system strength and longevity in the following the basic interpretations of the rkw theory are reconfirmed and clarified through both the analysis of a simplified two dimensional vorticity streamfunction model that allows for a more direct interpretation of the role of the shear in controlling the circulation around the cold pool and through an analysis of an extensive set of 3d squall line simulations run at higher resolution and covering a larger range of environmental shear conditions than presented by wkr

observations of near surface vertical wind profiles and vertical momentum fluxes from vortex se 2017 comparisons to monin obukhov similarity theory abstractobservations of near surface vertical wind profiles and vertical momentum fluxes obtained from a doppler lidar and instrumented towers deployed during vortex se in the spring of 2017 are an

the role of surface drag in mesocyclone intensification leading to tornadogenesis within an idealized supercell simulation abstractthe idealized supercell simulations from our previous study are further analyzed to clarify the physical mechanisms leading to differences in mesocyclone intensification between an experiment with surface friction applied to the full wind fwfric and an experiment with friction applied to the environmental wind only envfric the low level mesocyclone intensifies rapidly during the 3 minutes preceding tornadogenesis in fwfric while the intensification during the same period is much weaker in envfric which fails to produce a tornado to quantify the mechanisms responsible for this discrepancy in mesocyclone evolution material circuits enclosing the low level mesocyclone are initialized and traced back in time and circulation budgets for these circuits are analyzed the results show that in fwfric surface drag directly generates a substantial proportion of the final circulation around the mesocyclone especially below 1 km agl in envfric circulation budgets indicate the mesocyclone circulat

the genesis of mesovortices within a real data simulation of a bow echo system abstractthe genesis of two mesovortices mvs within a real data convection resolving simulation of the 8 may 2009 central u s bow echo system is studied both mvs form near the bow apex but differ distinctively in intensity lifetime and damage potential the stronger and longer lived mesovortex mva stays near the bow apex where the system scale rear inflow jet rij is present the descending rij produces strong downdrafts and surface convergence which in turn induce strong vertical stretching and intensification of mva into an intense mesovortex in contrast the weaker and shorter lived mesovortex mvb gradually moves away from the bow apex accompanied by localized convective scale downdrafts lagrangian circulation and vorticity budget analyses reveal that the vertical vorticity of mvs in general originate from the tilting of near surface horizontal vorticity which is mainly created via surface friction the circulation of the material circuit that ends up to be a horizontal circuit at the fo

les of laminar flow in the pbl a potential problem for convective storm simulations abstractin idealized simulations of convective storms which are almost always run as large eddy simulations les the planetary boundary layers pbls are typically laminar i e they lack turbulent eddies when compared with turbulent simulations theory or simulations with pbl schemes the typically laminar les used in the severe storms community produce unrealistic near surface vertical wind profiles containing excessive vertical wind shear when the lower boundary condition is nonfree slip such simulations are potentially problematic given the recent interest within the severe storms community in the influence of friction on vorticity generation within tornadic storms simulations run as les that include surface friction but lack well resolved turbulent eddies thus probably overestimate friction s effects on storms

the development of severe vortices within simulated high shear low cape convection abstractenvironments characterized by large values of vertical wind shear and modest convective available potential energy cape are colloquially referred to as high shear low cape hslc environ

the influence of environmental low level shear and cold pools on tornadogenesis insights from idealized simulations abstractidealized dry simulations are used to investigate the roles of environmental vertical wind shear and baroclinic vorticity generation in the development of near surface vortices in supercell like pseudostorms a cyclonically rotating updraft is produced by a stationary cylindrical heat source imposed within a horizontally homogeneous environment containing streamwise vorticity once a nearly steady state is achieved a heat sink which emulates the effects of latent cooling associated with precipitation is activated on the northeastern flank of the updraft at low levels cool outflow emanating from the heat sink spreads beneath the updraft and leads to the development of near surface vertical vorticity via the baroclinic mechanism as has been diagnosed or inferred in actual supercells that have been simulated and observed an intense cyclonic vortex forms in the simulations in which the environmental low level wind shear is strong and the heat sink is of intermediate strength relative to the

application of a perturbation recycling method in the large eddy simulation of a mesoscale convective internal boundary layer an arrangement of boundary conditions is described and demonstrated that facilitates the large eddy simulation les of inhomogeneous boundary layers such as internal boundary layers in addition to the domain where the internal boundary layer develops the method requires a section of domain over the upwind surface that is of the order of 10 boundary layer thicknesses and thus similar in size to that needed for the les of the upwind boundary layer in addition to periodic lateral closed upstream and open downstream boundary conditions a simple and efficient perturbation recycling technique which follows from one of lund wu and squires is used to generate a steady supply of fully developed turbulence from the inflow boundary the arrangement is used to simulate a convective internal boundary layer during a cold air outbreak over water results show the method consistently produces a solution that is homogeneous over the upwind surface and inhomogeneous over the downwind surface and that the statistics are stationary after spinup the sensitivity to the placement of the outflow boundary is tested and examples of instantaneous and mean fields generated by the simulations are shown

a method to control the environmental wind profile in idealized simulations of deep convection with surface friction abstractin idealized horizontally homogeneous cloud model simulations of convective storms the action of surface friction can substantially modify the near ground environmental wind profile over

the sensitivity of simulated supercell structure and intensity to variations in the shapes of environmental buoyancy and shear profiles abstract convective storm simulations are conducted using varying thermal and wind profile shapes subject to the constraints of strict conservation of convective available potential energy cape and hodograph trace small and large cape regimes and straight and curved hodographs are studied each with a matrix of systematically varying thermal and wind profile shapes having identical levels of free convection and bulk richardson numbers favorable to supercell development differences in storm intensity and morphology resulting from changes in the profile shapes can be profound especially in the small cape regime where for the moderate shears studied here storms are generally weak except when the buoyancy is concentrated at low levels in stronger cape regimes less dramatic relative enhancements of storm updraft intensity are found when both the buoyancy and shear are concentrated at low levels peak midlevel vertical vorticity correlates roughly with peak updraft speed in the small cape regime but

tropopause evolution in a rapidly intensifying tropical cyclone a static stability budget analysis in an idealized axisymmetric framework abstractupper level static stability n2 variations can influence the evolution of the transverse circulation and potential vorticity in intensifying tropical cyclones tcs this paper examines t

numerical study of the 6 may 2012 tsukuba supercell tornado vorticity sources responsible for tornadogenesis abstractremarkable progress has been achieved in understanding the vorticity source responsible for tornadogenesis nevertheless the answer to this question remains elusive particularly after int