A numerical model of the Indian Ocean, driven by climatological monthly mean winds, realistically... more A numerical model of the Indian Ocean, driven by climatological monthly mean winds, realistically simulates the major features of the large scale upper ocean circulation observed in the southem hemisphere and equatorial regions. The principal feature in the tropical Indian Ocean is a basin-wide clockwise southem hemisphere (cyclonic) gyre comprised of the South Equatorial Current to the south, the the South Equatorial Countercurrent to the north, and the East African Coastal Current in the west. Rossby waves propagate westward in the shear zone between the South Equatorial Current and the South Equatorial Countercurrent, and are obstructed and partially reflected by the banks along the Seychelles-Maudflus Ridge (60øE). A region of high eddy activity northwest of Madagascar is an extension of the tropical gyre and is a tropical analog to the Gulf Stream recirculation region. Oscillations in meddional transport at the equator have westward phase speed and eastward group velocity and are the result of mixed Rossby-gravity (Yanai) waves forced by oscillations in the highly nonlinear wesrum boundary current region. Oscillations with 40-to 50-day periods are seen in most currents. These oscillations cannot be atmospherically forced, as the shortest period in the mean monthly wind forcing is 60 days. Mean transports in the wesrum basin agree with observations. Small (2 Sv) mean throughflow from the Pacific to the Indian Ocean at the eastem open boundary is due to wind-forced Indian Ocean dynamics alone and is within the range of observations of throughflow from the Pacific. computational expertise, and to Rita Kuj)per for document processing assistance. Thanks also to Jon Alquist, Sharon Nicholson, Klaus Wyrtki and John Kindle, as well as two anonymous reviewers, for their insightful comments and suggestions.
Ecological interactions between marine bacteria and phytoplankton play a pivotal role in governin... more Ecological interactions between marine bacteria and phytoplankton play a pivotal role in governing the ocean’s major biogeochemical cycles. Among these, members of the marine Roseobacter Group (MRG) can establish mutualistic relationships with phytoplankton that are, in part, maintained by exchanges of the organosulfur compound, dimethylsulfoniopropionate (DMSP). Yet most of what is known about these interactions has been derived from culture-based laboratory studies. To investigate temporal and spatial co-occurrence patterns between members of the MRG and DMSP-producing phytoplankton we analysed 16S and 18S rRNA gene amplicon sequence variants (ASVs) derived from 5 years of monthly samples from seven environmentally distinct Australian oceanographic time-series. The MRG and DMSP-producer communities often displayed contemporaneous seasonality, which was greater in subtropical and temperate environments compared to tropical environments. The relative abundance of both groups varied ...
Diatom communities significantly influence ocean primary productivity and carbon cycling, but the... more Diatom communities significantly influence ocean primary productivity and carbon cycling, but their spatial and temporal dynamics are highly heterogeneous and are governed by a complex diverse suite of abiotic and biotic factors. We examined the seasonal and biogeographical dynamics of diatom communities in Australian coastal waters using amplicon sequencing data (18S-16S rRNA gene) derived from a network of oceanographic time-series spanning the Australian continent. We demonstrate that diatom community composition in this region displays significant biogeography, with each site harbouring distinct community structures. Temperature and nutrients were identified as the key environmental contributors to differences in diatom communities at all sites, collectively explaining 21% of the variability observed in diatoms assemblages. However, specific groups of bacteria previously implicated in mutualistic ecological interactions with diatoms (Rhodobacteraceae, Flavobacteriaceae and Alter...
Atrioventricular septal defects (AVSD) are a severe congenital heart defect present in individual... more Atrioventricular septal defects (AVSD) are a severe congenital heart defect present in individuals with Down syndrome (DS) at a > 2000-fold increased prevalence compared to the general population. This study aimed to identify risk-associated genes and pathways and to examine a potential polygenic contribution to AVSD in DS. We analyzed a total cohort of 702 individuals with DS with or without AVSD, with genomic data from whole exome sequencing, whole genome sequencing, and/or array-based imputation. We utilized sequence kernel association testing and polygenic risk score (PRS) methods to examine rare and common variants. Our findings suggest that the Notch pathway, particularly NOTCH4, as well as genes involved in the ciliome including CEP290 may play a role in AVSD in DS. These pathways have also been implicated in DS-associated AVSD in prior studies. A polygenic component for AVSD in DS has not been examined previously. Using weights based on the largest genome-wide association...
Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral ga... more Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. Dwarf galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, The H I Nearby Galactic Survey (THINGS) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we show an application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity (CG) and Modified Newtonian Dynamics (MOND). In this work, we provide an analysis and discussion of the rotation curve predictions of each theory to the sample. Furthermore, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. This work highlights the similarities and differences of the predictions of the two theories in dwarf galaxies. The sample is not large or diverse enough to strongly favor a single theory, but we posit that both CG and MOND can provide an accurate description of the galactic dynamics in the LITTLE THINGS sample without the need for dark matter.
International Journal of Modern Physics: Conference Series, 2017
Gravitational theories outside standard general relativity have been drawing increased attention ... more Gravitational theories outside standard general relativity have been drawing increased attention over the past several years, mostly due to the lack of direct observational evidence of dark matter. With some recent very high level dark matter searches continuing, and the parameter space to search decreasing has lead to a new interest in rethinking gravity at the largest of scales. As an alternative gravitational theory, conformal gravity has enjoyed much of the success of Modified Newtonian Dynamics (MOND) in predicting phenomenology, but differs dramatically in its initial construction. In this work, we explore some recent advances in conformal gravity, which help to build the case for support of such an alternative theory. Here, we highlight conformal gravity’s success in fitting new rotation curves, its ability to explain velocity dispersions in clusters, the initial steps towards gravitational lensing and finally, some preliminary work on explaining universal centripetal acceler...
The life cycle of cyclonic eddies associated with the Loop Current (LC) evolution is studied usin... more The life cycle of cyclonic eddies associated with the Loop Current (LC) evolution is studied using the Navy Coastal Ocean Model, Topex/Poseidon altimetry, and AVHRR images. It is shown that the formation of the cyclones in the western side of the LC is related to its dynamics, with their time of generation in the last stage of the anticyclone shedding from the LC. It is shown that the longest period registered between eddy shedding, between February 1998 and August 1999, is associated with the presence of a large cyclone that remains north of the LC during several months. Using numerical simulations, it is shown that large cyclones develop sporadically in the region and that they block the northward penetration of the LC. The LC is shifted to the east and leaks mass, momentum, and energy through a jet and small anticyclones moving along the slope of the West Florida Shelf, east of the cyclone. The process causes an enlargement of the period between eddy shedding. .
The Journal of the Acoustical Society of America, 1994
The GAMOT group is developing two instruments that will economically map temperatures in the glob... more The GAMOT group is developing two instruments that will economically map temperatures in the global oceans at a resolution suitable for understanding natural variability in climate and separating that from a global warming trend. The status of these instruments, a surface suspended acoustic receiver and an autonomous source mooring, will be presented. According to state-of-the-art models of the ocean. changes in climate can be easily detected with acoustic thermometers. These types of models represent climatic variability quite well since they replicate variations in climate measured from satellite altimeters and infrared sensors. The fastest way to detect global warming is to subtract off natural variability and examine the residual for trends. [Work supported by the Advanced Research Projects Agency.]
The dynamics of the flow field surrounding New Zealand are investigated using a series of global ... more The dynamics of the flow field surrounding New Zealand are investigated using a series of global ocean models. The physical mechanisms governing the direction, magnitude, and location of the East Australian Current (EAC), the Tasman Front, the East Auckland Current (EAUC), and the East Cape Current (ECC) are studied using numerical simulations whose complexity is systematically increased. As new dynamics are added to each successive simulation, their direct and indirect effects on the flow field are examined. The simulations have horizontal resolutions of 1/8Њ, 1/16Њ, or 1/32Њ for each variable, and vertical resolutions ranging from 1.5-layer reduced gravity to 6-layer finite depth with realistic bottom topography. All simulations are forced by the Hellerman and Rosenstein monthly wind stress climatology. Analysis of these simulations shows that several factors play a critical role in governing the behavior of the examined currents. These factors include 1) mass balance of water pathways through the region, 2) gradients in the wind stress curl, 3) nonlinear flow instabilities, and 4) upper-ocean-topographic coupling due to mixed baroclinic and barotropic instabilities. Transport streamfunctions of a linear reduced gravity model reproduce the large-scale features well but produce an EAUC that flows counter to the observed direction. The residual of the mass balance of the transport through the Tasman Sea, the basinwide transport at 32ЊS, and the transport of the South Pacific subtropical gyre east of New Zealand determines the direction of the EAUC. The 6-layer nonlinear model allows isopycnal outcropping, which changes the transport through the Tasman Sea and produces an EAUC flowing in the observed direction. Gradients in the zonally integrated wind stress curl field determine the coastal separation points of the EAC, the EAUC, and the ECC, while a combination of nonlinear flow instabilities and upper-ocean-topographic coupling contribute to the formation of meanders in the Tasman Front. Increased resolution results in greater mixed baroclinicbarotropic instabilities and thus more upper-ocean-topographic coupling and surface variability, giving a more accurate simulation of topographically controlled mean meanders in the Tasman Front.
Meridional heat transport in the tropical Pacific is estimated using a linear numerical model wit... more Meridional heat transport in the tropical Pacific is estimated using a linear numerical model with realistic boundaries and forced by 18 years of observed wind, covering the period from January 1962 to December 1979. The long‐term mean heat transport estimated in this study is similar to the estimates based on heat balance and radiation considerations and on complex numerical models that account for thermodynamics as well. This points to the dominant role played by the adiabatic process, the only heat transport mechanism present in this study, in the heat balance for the equatorial Pacific. The combined Ekman and geostrophic heat transport can account for the net meridional heat transport, except near the equator, where continuity requirements dictate. The Ekman and geostrophic transport oppose each other, and their small difference in magnitude gives rise to the net meridional heat transport, resulting in transport away from the equator for the southern hemisphere and north of 6°N,...
The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is... more The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982–1983 El Niño. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982–1983 El Niño. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large‐scale atmosphere, while along the California coast and south to the equator, the dominant El Niño signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western ...
Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin w... more Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial stmcture function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originatinl in the equatorial Pacific. The spatial stmcture function is used to extract the interannual Rossby wave response from observed 300-m-depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike feanues observed in the projection mode are onIer 1(MX) km long with most periods ranging between 2 and 4 years. The wave numbeR and frequencies found are consistent with Rossby d~cs. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s-1, in agreement with the theoretical Rossby wave phase speed at 400N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2-4 years was identified by Pares-Sierra and O'Brien (1989) as poleward propaga~n~ Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a ~ty of their periods raDging between 2 and 4 yean, their forcing can be attributed to long-period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3-4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propaption. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300-m-depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300-m depth temperature anomalies.
Analysis of the results of a multilayer, adiabatic, numerical model of the upper Indian Ocean, dr... more Analysis of the results of a multilayer, adiabatic, numerical model of the upper Indian Ocean, driven by climatological monthly mean winds, shows that the simulated currents in the northeastern Indian Ocean are in general agreement with available observations and interpretations. The main features of the ocean currents include large anticyclonic flow in the Bay of Bengal surface waters during the northern hemisphere winter. This gyre decays into eddies in spring and then transitions into a weaker, cyclonic gyre by late summer. The western recirculation region of this flow is an intensified western boundary current which changes direction twice during the year. In the Andaman Sea, east of the Bay of Bengal, the oceanic flow changes direction twice during the year; it is cyclonic during the spring and early summer and anticyclonic the rest of the year. Flow in the equatorial region shows the North Equatorial Current (NEC) flowing west during winter. Further south is the eastward flowi...
The decadal variability of the convective activity in the Labrador Sea is investigated using 43 y... more The decadal variability of the convective activity in the Labrador Sea is investigated using 43 years of model output from a prognostic coupled ice‐ocean model that simulates both the Arctic and the North Atlantic Oceans. The fields of the surface density and the mixed‐layer depth indicate that the center of the convective activity is located in western Labrador Sea. The decadal variations of the convective depth are controlled to large extent by the oceanic preconditioning associated with changes in subsurface stratification. The intensity of the convective mixing varies from year to year, depending upon how strong the isopycnal doming is at the preconditioning stage at the center of the convective region. The variations of the subsurface stratification seem to be related to the subsurface temperature changes.
Outftow radiation conditions ba~ ~~tJy been used at Opal bouOOaries in oceaDOaraphyand meteorolog... more Outftow radiation conditions ba~ ~~tJy been used at Opal bouOOaries in oceaDOaraphyand meteorology. A new implcnxntation of Orlanski's !onnulation for problems UiriOI a radiation open boundary has been developed. Three dift"erent cases in wbkh R(8by and Kelvin waves are preIaIt are studied. ]n all these t~ the ~ open boundary condition sbows no ~ at the outflow 0(tbe Kdvin wa~ Howeva-, r eflection ~t the outflow of the RC»Sby wave is oblerved.
Objective-Hospital-level variations in structure and process may affect clinical outcomes in inte... more Objective-Hospital-level variations in structure and process may affect clinical outcomes in intensive care units (ICUs). We sought to characterize the organizational structure, processes of care, use of protocols and standardized outcomes in a large sample of U.S. ICUs. Design-We surveyed 69 ICUs about organization, size, volume, staffing, processes of care, use of protocols, and annual ICU mortality. Setting-ICUs participating in the United States Critical Illness and Injury Trials Group Critical Illness Outcomes Study (USCIITG-CIOS). Measurements and Main Results-We characterized structure and process variables across ICUs, investigated relationships between these variables and annual ICU mortality, and adjusted for illness severity using APACHE II. Ninety-four ICU directors were invited to participate in the study and 69 ICUs (73%) were enrolled, of which 25 (36%) were medical, 24 were surgical (35%) and 20 (29%) were of mixed type, and 64 (93%) were located in teaching hospitals with a median number of 5 trainees per ICU. Average annual ICU mortality was 10.8%, average APACHE II score was 19.3, 58% were closed units and 41% had a 24-hour in-house intensivist. In multivariable linear regression adjusted for APACHE II and multiple ICU structure and process factors, annual ICU mortality was lower in surgical ICUs than in medical ICUs (5.6% lower, 95% CI 2.4%-8.8%) or mixed ICUs (4.5% lower, 95% CI 0.4%-8.7%). We also found a lower annual ICU mortality among ICUs that had a daily plan of care review (5.8% lower, 95% CI 1.6%-10.0%) and a lower bed-to-nurse ratio (1.8% lower when the ratio decreased from 2:1 to 1.5:1; 95% CI 0.25%-3.4%). In contrast, 24-hour intensivist coverage (p=0.89) and closed ICU status (p=0.16) were not associated with a lower annual ICU mortality. Conclusions-In a sample of 69 ICUs, a daily plan of care review and a lower bed-to-nurse ratio were both associated with a lower annual ICU mortality. In contrast to 24-hour intensivist staffing, improvement in team communication is a low-cost, process-targeted intervention strategy that may improve clinical outcomes in ICU patients.
World Journal for Pediatric and Congenital Heart Surgery, 2020
The coronavirus disease 2019 (COVID-19) pandemic currently gripping the globe is impacting the en... more The coronavirus disease 2019 (COVID-19) pandemic currently gripping the globe is impacting the entire health care system with rapidly escalating morbidities and mortality. Although the infectious risk to the pediatric population appears low, the effects on children with congenital heart disease (CHD) remain poorly understood. The closure of congenital heart surgery programs worldwide to address the growing number of infected individuals could have an unintended impact on future health for COVID-19-negative patients with CHD. Pediatric and congenital heart surgeons, given their small numbers and close relationships, are uniquely positioned to collectively assess the impact of the pandemic on surgical practice and care of children with CHD. We present the results of an international survey sent to pediatric and congenital heart surgeons characterizing the early impact of COVID-19 on the care of patients with CHD.
A numerical model of the Indian Ocean, driven by climatological monthly mean winds, realistically... more A numerical model of the Indian Ocean, driven by climatological monthly mean winds, realistically simulates the major features of the large scale upper ocean circulation observed in the southem hemisphere and equatorial regions. The principal feature in the tropical Indian Ocean is a basin-wide clockwise southem hemisphere (cyclonic) gyre comprised of the South Equatorial Current to the south, the the South Equatorial Countercurrent to the north, and the East African Coastal Current in the west. Rossby waves propagate westward in the shear zone between the South Equatorial Current and the South Equatorial Countercurrent, and are obstructed and partially reflected by the banks along the Seychelles-Maudflus Ridge (60øE). A region of high eddy activity northwest of Madagascar is an extension of the tropical gyre and is a tropical analog to the Gulf Stream recirculation region. Oscillations in meddional transport at the equator have westward phase speed and eastward group velocity and are the result of mixed Rossby-gravity (Yanai) waves forced by oscillations in the highly nonlinear wesrum boundary current region. Oscillations with 40-to 50-day periods are seen in most currents. These oscillations cannot be atmospherically forced, as the shortest period in the mean monthly wind forcing is 60 days. Mean transports in the wesrum basin agree with observations. Small (2 Sv) mean throughflow from the Pacific to the Indian Ocean at the eastem open boundary is due to wind-forced Indian Ocean dynamics alone and is within the range of observations of throughflow from the Pacific. computational expertise, and to Rita Kuj)per for document processing assistance. Thanks also to Jon Alquist, Sharon Nicholson, Klaus Wyrtki and John Kindle, as well as two anonymous reviewers, for their insightful comments and suggestions.
Ecological interactions between marine bacteria and phytoplankton play a pivotal role in governin... more Ecological interactions between marine bacteria and phytoplankton play a pivotal role in governing the ocean’s major biogeochemical cycles. Among these, members of the marine Roseobacter Group (MRG) can establish mutualistic relationships with phytoplankton that are, in part, maintained by exchanges of the organosulfur compound, dimethylsulfoniopropionate (DMSP). Yet most of what is known about these interactions has been derived from culture-based laboratory studies. To investigate temporal and spatial co-occurrence patterns between members of the MRG and DMSP-producing phytoplankton we analysed 16S and 18S rRNA gene amplicon sequence variants (ASVs) derived from 5 years of monthly samples from seven environmentally distinct Australian oceanographic time-series. The MRG and DMSP-producer communities often displayed contemporaneous seasonality, which was greater in subtropical and temperate environments compared to tropical environments. The relative abundance of both groups varied ...
Diatom communities significantly influence ocean primary productivity and carbon cycling, but the... more Diatom communities significantly influence ocean primary productivity and carbon cycling, but their spatial and temporal dynamics are highly heterogeneous and are governed by a complex diverse suite of abiotic and biotic factors. We examined the seasonal and biogeographical dynamics of diatom communities in Australian coastal waters using amplicon sequencing data (18S-16S rRNA gene) derived from a network of oceanographic time-series spanning the Australian continent. We demonstrate that diatom community composition in this region displays significant biogeography, with each site harbouring distinct community structures. Temperature and nutrients were identified as the key environmental contributors to differences in diatom communities at all sites, collectively explaining 21% of the variability observed in diatoms assemblages. However, specific groups of bacteria previously implicated in mutualistic ecological interactions with diatoms (Rhodobacteraceae, Flavobacteriaceae and Alter...
Atrioventricular septal defects (AVSD) are a severe congenital heart defect present in individual... more Atrioventricular septal defects (AVSD) are a severe congenital heart defect present in individuals with Down syndrome (DS) at a > 2000-fold increased prevalence compared to the general population. This study aimed to identify risk-associated genes and pathways and to examine a potential polygenic contribution to AVSD in DS. We analyzed a total cohort of 702 individuals with DS with or without AVSD, with genomic data from whole exome sequencing, whole genome sequencing, and/or array-based imputation. We utilized sequence kernel association testing and polygenic risk score (PRS) methods to examine rare and common variants. Our findings suggest that the Notch pathway, particularly NOTCH4, as well as genes involved in the ciliome including CEP290 may play a role in AVSD in DS. These pathways have also been implicated in DS-associated AVSD in prior studies. A polygenic component for AVSD in DS has not been examined previously. Using weights based on the largest genome-wide association...
Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral ga... more Galactic rotation curves have proven to be the testing ground for dark matter bounds in spiral galaxies of all morphologies. Dwarf galaxies serve as an increasingly interesting case of rotation curve dynamics due to their typically rising rotation curve as opposed to the flattening curve of large spirals. Dwarf galaxies usually vary in galactic structure and mostly terminate at small radial distances. This, coupled with the fact that Cold Dark Matter theories struggle with the universality of galactic rotation curves, allow for exclusive features of alternative gravitational models to be analyzed. Recently, The H I Nearby Galactic Survey (THINGS) has been extended to include a sample of 25 dwarf galaxies now known as the LITTLE THINGS Survey. Here, we show an application of alternative gravitational models to the LITTLE THINGS survey, specifically focusing on conformal gravity (CG) and Modified Newtonian Dynamics (MOND). In this work, we provide an analysis and discussion of the rotation curve predictions of each theory to the sample. Furthermore, we show how these two alternative gravitational models account for the recently observed universal trends in centripetal accelerations in spiral galaxies. This work highlights the similarities and differences of the predictions of the two theories in dwarf galaxies. The sample is not large or diverse enough to strongly favor a single theory, but we posit that both CG and MOND can provide an accurate description of the galactic dynamics in the LITTLE THINGS sample without the need for dark matter.
International Journal of Modern Physics: Conference Series, 2017
Gravitational theories outside standard general relativity have been drawing increased attention ... more Gravitational theories outside standard general relativity have been drawing increased attention over the past several years, mostly due to the lack of direct observational evidence of dark matter. With some recent very high level dark matter searches continuing, and the parameter space to search decreasing has lead to a new interest in rethinking gravity at the largest of scales. As an alternative gravitational theory, conformal gravity has enjoyed much of the success of Modified Newtonian Dynamics (MOND) in predicting phenomenology, but differs dramatically in its initial construction. In this work, we explore some recent advances in conformal gravity, which help to build the case for support of such an alternative theory. Here, we highlight conformal gravity’s success in fitting new rotation curves, its ability to explain velocity dispersions in clusters, the initial steps towards gravitational lensing and finally, some preliminary work on explaining universal centripetal acceler...
The life cycle of cyclonic eddies associated with the Loop Current (LC) evolution is studied usin... more The life cycle of cyclonic eddies associated with the Loop Current (LC) evolution is studied using the Navy Coastal Ocean Model, Topex/Poseidon altimetry, and AVHRR images. It is shown that the formation of the cyclones in the western side of the LC is related to its dynamics, with their time of generation in the last stage of the anticyclone shedding from the LC. It is shown that the longest period registered between eddy shedding, between February 1998 and August 1999, is associated with the presence of a large cyclone that remains north of the LC during several months. Using numerical simulations, it is shown that large cyclones develop sporadically in the region and that they block the northward penetration of the LC. The LC is shifted to the east and leaks mass, momentum, and energy through a jet and small anticyclones moving along the slope of the West Florida Shelf, east of the cyclone. The process causes an enlargement of the period between eddy shedding. .
The Journal of the Acoustical Society of America, 1994
The GAMOT group is developing two instruments that will economically map temperatures in the glob... more The GAMOT group is developing two instruments that will economically map temperatures in the global oceans at a resolution suitable for understanding natural variability in climate and separating that from a global warming trend. The status of these instruments, a surface suspended acoustic receiver and an autonomous source mooring, will be presented. According to state-of-the-art models of the ocean. changes in climate can be easily detected with acoustic thermometers. These types of models represent climatic variability quite well since they replicate variations in climate measured from satellite altimeters and infrared sensors. The fastest way to detect global warming is to subtract off natural variability and examine the residual for trends. [Work supported by the Advanced Research Projects Agency.]
The dynamics of the flow field surrounding New Zealand are investigated using a series of global ... more The dynamics of the flow field surrounding New Zealand are investigated using a series of global ocean models. The physical mechanisms governing the direction, magnitude, and location of the East Australian Current (EAC), the Tasman Front, the East Auckland Current (EAUC), and the East Cape Current (ECC) are studied using numerical simulations whose complexity is systematically increased. As new dynamics are added to each successive simulation, their direct and indirect effects on the flow field are examined. The simulations have horizontal resolutions of 1/8Њ, 1/16Њ, or 1/32Њ for each variable, and vertical resolutions ranging from 1.5-layer reduced gravity to 6-layer finite depth with realistic bottom topography. All simulations are forced by the Hellerman and Rosenstein monthly wind stress climatology. Analysis of these simulations shows that several factors play a critical role in governing the behavior of the examined currents. These factors include 1) mass balance of water pathways through the region, 2) gradients in the wind stress curl, 3) nonlinear flow instabilities, and 4) upper-ocean-topographic coupling due to mixed baroclinic and barotropic instabilities. Transport streamfunctions of a linear reduced gravity model reproduce the large-scale features well but produce an EAUC that flows counter to the observed direction. The residual of the mass balance of the transport through the Tasman Sea, the basinwide transport at 32ЊS, and the transport of the South Pacific subtropical gyre east of New Zealand determines the direction of the EAUC. The 6-layer nonlinear model allows isopycnal outcropping, which changes the transport through the Tasman Sea and produces an EAUC flowing in the observed direction. Gradients in the zonally integrated wind stress curl field determine the coastal separation points of the EAC, the EAUC, and the ECC, while a combination of nonlinear flow instabilities and upper-ocean-topographic coupling contribute to the formation of meanders in the Tasman Front. Increased resolution results in greater mixed baroclinicbarotropic instabilities and thus more upper-ocean-topographic coupling and surface variability, giving a more accurate simulation of topographically controlled mean meanders in the Tasman Front.
Meridional heat transport in the tropical Pacific is estimated using a linear numerical model wit... more Meridional heat transport in the tropical Pacific is estimated using a linear numerical model with realistic boundaries and forced by 18 years of observed wind, covering the period from January 1962 to December 1979. The long‐term mean heat transport estimated in this study is similar to the estimates based on heat balance and radiation considerations and on complex numerical models that account for thermodynamics as well. This points to the dominant role played by the adiabatic process, the only heat transport mechanism present in this study, in the heat balance for the equatorial Pacific. The combined Ekman and geostrophic heat transport can account for the net meridional heat transport, except near the equator, where continuity requirements dictate. The Ekman and geostrophic transport oppose each other, and their small difference in magnitude gives rise to the net meridional heat transport, resulting in transport away from the equator for the southern hemisphere and north of 6°N,...
The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is... more The ocean's response to atmospheric forcing and to forcing along the coast by Kelvin waves is examined in light of nearshore seasonal variability and the major 1982–1983 El Niño. In addition to driving the northeast Pacific gyre and local currents, the wind modifies the depth to the main thermocline, changing the apparent westward phase speed of Rossby waves excited by passing Kelvin waves. The amplitude of the passing Kelvin wave determines whether the Rossby wave depresses or raises the thermocline while propagating westward. Along the northeast Pacific coast from Oregon to Washington, model results suggest that the wind raises the main thermocline during the 1982–1983 El Niño. Generally, the coastal response off Oregon and Washington appears to be strongly driven by the large‐scale atmosphere, while along the California coast and south to the equator, the dominant El Niño signal has an oceanic origin. That signal, with periods between 2 and 5 years, originates in the western ...
Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin w... more Complex empirical orthQIOnal function (CEOP) analysis is used to investigate the coastal Kelvin wave driven Rossby wave response in the northeast Pacific. Using CEOF analysis, a spatial stmcture function is obtained from model upper layer thickness data. The model is a nonlinear, reduced gravity model of the northeast Pacific forced by coastal Kelvin waves originatinl in the equatorial Pacific. The spatial stmcture function is used to extract the interannual Rossby wave response from observed 300-m-depth temperature anomalies. The observed Rossby wave signal is termed the projection mode. Rossby wavelike feanues observed in the projection mode are onIer 1(MX) km long with most periods ranging between 2 and 4 years. The wave numbeR and frequencies found are consistent with Rossby d~cs. The mean phase speed of the Rossby wavelike features within the projection mode is 1.3 cm s-1, in agreement with the theoretical Rossby wave phase speed at 400N. Large amplitude nearshore and decreasing amplitude away from shore suggests nearshore generation of these waves. An important source of sea level variability along the east coast of North America at periods of 2-4 years was identified by Pares-Sierra and O'Brien (1989) as poleward propaga~n~ Kelvin waves. Since the Rossby wavelike features observed in the projection mode have a ~ty of their periods raDging between 2 and 4 yean, their forcing can be attributed to long-period Kelvin waves. Spectral comparisons between the nearshore values in the projection mode and coastal sea level show greater than 90% coherence in the period band 3-4.4 years. The high coherence between coastal sea level variations and the projection mode shows that there is a strong correlation between the Rossby wavelike features within the projection mode and coastal Kelvin wave propaption. It is concluded that the Rossby waves within the projection mode are forced by coastal Kelvin wave propagation. The projection mode accounts for 47.5% of the variance in the 300-m-depth temperature anomalies. The implication of this result is that the physical mechanism of the numerical model, i.e., Rossby waves excited by coastal Kelvin wave propagation, accounts for 47.5% of the variance in the observed 300-m depth temperature anomalies.
Analysis of the results of a multilayer, adiabatic, numerical model of the upper Indian Ocean, dr... more Analysis of the results of a multilayer, adiabatic, numerical model of the upper Indian Ocean, driven by climatological monthly mean winds, shows that the simulated currents in the northeastern Indian Ocean are in general agreement with available observations and interpretations. The main features of the ocean currents include large anticyclonic flow in the Bay of Bengal surface waters during the northern hemisphere winter. This gyre decays into eddies in spring and then transitions into a weaker, cyclonic gyre by late summer. The western recirculation region of this flow is an intensified western boundary current which changes direction twice during the year. In the Andaman Sea, east of the Bay of Bengal, the oceanic flow changes direction twice during the year; it is cyclonic during the spring and early summer and anticyclonic the rest of the year. Flow in the equatorial region shows the North Equatorial Current (NEC) flowing west during winter. Further south is the eastward flowi...
The decadal variability of the convective activity in the Labrador Sea is investigated using 43 y... more The decadal variability of the convective activity in the Labrador Sea is investigated using 43 years of model output from a prognostic coupled ice‐ocean model that simulates both the Arctic and the North Atlantic Oceans. The fields of the surface density and the mixed‐layer depth indicate that the center of the convective activity is located in western Labrador Sea. The decadal variations of the convective depth are controlled to large extent by the oceanic preconditioning associated with changes in subsurface stratification. The intensity of the convective mixing varies from year to year, depending upon how strong the isopycnal doming is at the preconditioning stage at the center of the convective region. The variations of the subsurface stratification seem to be related to the subsurface temperature changes.
Outftow radiation conditions ba~ ~~tJy been used at Opal bouOOaries in oceaDOaraphyand meteorolog... more Outftow radiation conditions ba~ ~~tJy been used at Opal bouOOaries in oceaDOaraphyand meteorology. A new implcnxntation of Orlanski's !onnulation for problems UiriOI a radiation open boundary has been developed. Three dift"erent cases in wbkh R(8by and Kelvin waves are preIaIt are studied. ]n all these t~ the ~ open boundary condition sbows no ~ at the outflow 0(tbe Kdvin wa~ Howeva-, r eflection ~t the outflow of the RC»Sby wave is oblerved.
Objective-Hospital-level variations in structure and process may affect clinical outcomes in inte... more Objective-Hospital-level variations in structure and process may affect clinical outcomes in intensive care units (ICUs). We sought to characterize the organizational structure, processes of care, use of protocols and standardized outcomes in a large sample of U.S. ICUs. Design-We surveyed 69 ICUs about organization, size, volume, staffing, processes of care, use of protocols, and annual ICU mortality. Setting-ICUs participating in the United States Critical Illness and Injury Trials Group Critical Illness Outcomes Study (USCIITG-CIOS). Measurements and Main Results-We characterized structure and process variables across ICUs, investigated relationships between these variables and annual ICU mortality, and adjusted for illness severity using APACHE II. Ninety-four ICU directors were invited to participate in the study and 69 ICUs (73%) were enrolled, of which 25 (36%) were medical, 24 were surgical (35%) and 20 (29%) were of mixed type, and 64 (93%) were located in teaching hospitals with a median number of 5 trainees per ICU. Average annual ICU mortality was 10.8%, average APACHE II score was 19.3, 58% were closed units and 41% had a 24-hour in-house intensivist. In multivariable linear regression adjusted for APACHE II and multiple ICU structure and process factors, annual ICU mortality was lower in surgical ICUs than in medical ICUs (5.6% lower, 95% CI 2.4%-8.8%) or mixed ICUs (4.5% lower, 95% CI 0.4%-8.7%). We also found a lower annual ICU mortality among ICUs that had a daily plan of care review (5.8% lower, 95% CI 1.6%-10.0%) and a lower bed-to-nurse ratio (1.8% lower when the ratio decreased from 2:1 to 1.5:1; 95% CI 0.25%-3.4%). In contrast, 24-hour intensivist coverage (p=0.89) and closed ICU status (p=0.16) were not associated with a lower annual ICU mortality. Conclusions-In a sample of 69 ICUs, a daily plan of care review and a lower bed-to-nurse ratio were both associated with a lower annual ICU mortality. In contrast to 24-hour intensivist staffing, improvement in team communication is a low-cost, process-targeted intervention strategy that may improve clinical outcomes in ICU patients.
World Journal for Pediatric and Congenital Heart Surgery, 2020
The coronavirus disease 2019 (COVID-19) pandemic currently gripping the globe is impacting the en... more The coronavirus disease 2019 (COVID-19) pandemic currently gripping the globe is impacting the entire health care system with rapidly escalating morbidities and mortality. Although the infectious risk to the pediatric population appears low, the effects on children with congenital heart disease (CHD) remain poorly understood. The closure of congenital heart surgery programs worldwide to address the growing number of infected individuals could have an unintended impact on future health for COVID-19-negative patients with CHD. Pediatric and congenital heart surgeons, given their small numbers and close relationships, are uniquely positioned to collectively assess the impact of the pandemic on surgical practice and care of children with CHD. We present the results of an international survey sent to pediatric and congenital heart surgeons characterizing the early impact of COVID-19 on the care of patients with CHD.
Uploads
Papers by James O'Brien