Instability and energetics in a baroclinic ocean

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute and the Woods Hole Oceanographic Institution August 1975This thesis is made of two separate, but interrelated parts. In Part I the instability of a baroclinic Rossby wave in a two-layer ocean of inviscid fluid without topography, is investigated and its results are applied in the ocean. The velocity field of the basic state (the wave) is characterized by significant horizontal and vertical shears, non-zonal currents, and unsteadiness due to its westward propagation. This configuration is more relevant to the ocean than are the steady, zonal 'meteorological' flows, which dominate the literature of baroclinic instability. Truncated Fourier series are used in perturbation analyses. The wave is found to be unstable for a wide range of the wavelength; growing perturbations draw their energy from kinetic or potential energy of the wave depending upon whether the wavelength, 2πL, is much smaller or larger than 2πLρ, respectively, where Lρ is the internal radius of deformation. When the shears are comparable dynamically, L~Lρ , the balance between the two energy transfer processes is very sensitive to the ratios L/Lρ and U/C as well, where U is a typical current speed, and C a typical phase speed of the wave. For L = Lρ they are augmenting if U C. The beta-effect tends to stabilize the flow, but perturbations dominated by a zonal velocity can grow irrespective of the beta-effect. It is necessary that growing perturbations are comprised of both barotropic and baroclinic modes vertically. The scale of the fastest growing perturbation is significantly larger than L for barotropically controlled flows (L < Lρ ), reduces to the wave scale L for a mixed kind (L ~ Lρ ) and is fixed slightly larger than Lρ for baroclinically controlled flows (L > Lρ ). Increasing supply of potential energy causes the normalized growth rate, αL/U, to increase monotonically as L → Lρ from below. As L increases beyond Lρ, the growth rate αLρ /U shows a slight increase, but soon approaches an asymptotic value. In a geophysical eddy field like the ocean this model shows possible pumping of energy into the radius of deformation (~ 40 km rational scale, or 250 km wavelength) from both smaller and larger scales through nonlinear interactions, which occur without interference from the beta-effect. The e-folding time scale is about 24 days if U = 5 cm/sec and L = 90 km. Also it is strongly suggested that, given the observed distribution of energy versus length scale, eddy-eddy interactions are more vigorous than eddy-mean interaction, away from intènse currents like the Gulf Stream. The flux of energy toward the deformation scale, and the interaction of barotropic and baroclinic modes, occur also in fully turbulent 'computer' oceans, and these calculations provide a theoretical basis for source of these experimental cascades. In Part II an available potential energy (APE) is defined in terms appropriate to a limited area synoptic density map (e.g., the 'MODE-I' data) and then in terms appropriate to time-series of hydrographic station at a single geographic location (e. g., the 'Panulirus' data). Instantaneously the APE shows highly variable spatial structure, horizontally as well as vertically, but the vertical profile of the average APE from 19 stations resembles the profile of vertical gradient of the reference stratification. The eddy APE takes values very similar to those of the average kinetic energy density at 500 m, 1500 m and 3000 m depth in the MODE area. In and above the thermocline the APE has roughly the same level in the MODE area (centered at 28°N, 69° 40'W) as at the Panulirus station (32° 10'N, 64° 30'W), yet in the deep water there is significantly more APE at the Panulirus station. This may in part indicate an island effect near Bermuda.This research has been supported by the National Science Foundation grant IDO 73-09737, formerly GX-36342

On the eddy statistics in a ring-rich area: A hypothesis of bimodal structure

A hypothesis is introduced in constructing the statistics of an eddy field, which distinguishes Gulf Stream rings as a separate anomalous feature from the rnesoscale eddy field. Analysis of XBT sections between New York City and Bermuda with rings removed indicates that the therrnocline deepens toward the Gulf Stream from Bermuda and the r.rn.s. displacement of the 15°C isotherm is 50 m or less...

Aspiration and outflow of the intermediate water in the East/Japan Sea through the Tsugaru Strait

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 35 (2008): L07601, doi:10.1029/2007GL032981.Outflow of the intermediate water in the East/Japan Sea through the Tsugaru Strait is inferred from the fact that profiling floats deployed below the sill depth in the central East/Japan Sea moved out to the Northwest Pacific Ocean through the Strait. Careful analysis of the float trajectories reveals that profiling floats parked at 350m, 700m, and 800m could be uplifted from depths below the sill of the Tsugaru Strait and moved over the 140m deep sill with a probability close to 100%. Application of an analytical model for the Bernoulli suction shows that intermediate waters can be aspirated over the sill depth of the Tsugaru Strait in late winter.This study was partly supported by the project of ARGO for Data Assimilation project in the Meteorological Research Institute/KMA, the Korea EAST-1(East Asian Seas Time series East Sea) Program from the Ministry of Maritime Affairs and Fisheries, and Korea Research Foundation Grant (KRF-2005-070-C00142). The first author was partly supported by the Ministry of Education, Korea, through the BK21 project

Comparison between a reanalyzed product by 3-dimensional variational assimilation technique and observations in the Ulleung Basin of the East/Japan Sea

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Marine Systems 78 (2009): 249-264, doi:10.1016/j.jmarsys.2009.02.017.Reanalyzed products from a MOM3-based East Sea Regional Ocean Model with a 3- dimentional variational data assimilation module (DA-ESROM), have been compared with the observed hydrographic and current datasets in the Ulleung Basin (UB) of the East/Japan Sea (EJS). Satellite-borne sea surface temperature and sea surface height data, and in-situ temperature profiles have been assimilated into the DA-ESROM. The performance of the DA-ESROM appears to be efficient enough to be used in an operational ocean forecast system. Comparing with the results from Mitchell et al. (2005a), the DA-ESROM fairly well simulates the high variability of the Ulleung Warm Eddy and Dok Cold Eddy as well as the branching of the Tsushima Warm Current in the UB. The overall root-mean-square error between 100m temperature field reproduced by the DA-ESROM and the observed 100-dbar temperature field is 2.1°C, and the spatially averaged grid-to-grid correlation between the two temperature fields is high with a mean value of 0.79 for the intercomparison period. The DA-ESROM reproduces the development of strong southward North Korean Cold Current (NKCC) in summer consistent with the observational results, which is thought to be an improvement of the previous numerical models in the EJS. The reanalyzed products show that the NKCC is about 35 km wide, and flows southward along the Korean coast from spring to summer with maximum monthly mean volume transport of about 0.8 Sv in August-September.The major part of this works was conducted with financial support by Agency for Defense Development under the contract UD031003AD. The first and seventh authors were supported at the final stage of this work by KORDI’s research projects (PE9830Q and PG47100). The second author was supported by EAST-I Program of the Ministry of Maritime Affairs and Fisheries

Predicting rapid intensification of tropical cyclones in the western North Pacific: a machine learning and net energy gain rate approach

In this study, a machine learning (ML)-based Tropical Cyclones (TCs) Rapid Intensification (RI) prediction model has been developed by using the Net Energy Gain Rate Index (NGR). This index realistically captures the energy exchanges between the ocean and the atmosphere during the intensification of TCs. It does so by incorporating the thermal conditions of the upper ocean and using an accurate parameterization for sea surface roughness. To evaluate the effectiveness of NGR in enhancing prediction accuracy, five distinct ML algorithms were utilized: Decision Tree, Logistic Regression, Support Vector Machine, K-Nearest Neighbors, and Feed-forward Neural Network. Two sets of experiments were performed for each algorithm. The first set used only traditional predictors, while the second set incorporated NGR. The outcomes revealed that models trained with the inclusion of NGR exhibited superior performance compared to those that only used traditional predictors. Additionally, an ensemble model was developed by utilizing a hard-voting method, combining the predictions of all five individual algorithms. This ensemble approach showed a noteworthy improvement of approximately 10% in the skill score of RI prediction when NGR was included. The findings of this study emphasize the potential of NGR in refining TC intensity prediction and underline the effectiveness of ensemble ML models in RI event detection

Decadal variability of the upper ocean heat content in the East/Japan Sea and its possible relationship to northwestern Pacific variability

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C02017, doi:10.1029/2011JC007369.The upper ocean heat content variability in the East/Japan Sea was investigated using a 40 year temperature and salinity data set from 1968 to 2007. Decadal variability was identified as the dominant mode of variability in the upper ocean (0–300 m) aside from the seasonal cycle. The decadal variability is strong to the west of northern Honshu, west of the Tsugaru Strait, and west of southern Hokkaido. Temperature anomalies at 50–125 m exhibit a large contribution to the decadal variability, particularly in the eastern part of the East/Japan Sea. The vertical structure of regressed temperature anomalies and the spatial patterns of regressed 10°C isotherms in the East/Japan Sea suggest that the decadal variability is related to upper ocean circulation in the East/Japan Sea. The decadal variability also exhibits an increasing trend, which indicates that the regions showing large decadal variations experienced warming on decadal time scales. Further analysis shows that the decadal variability in the East/Japan Sea is not locally isolated but is related to variability in the northwestern Pacific.This work was supported by grants from the Ministry of Land, Transport, and Maritime Affairs, Korea (Ocean Climate Variability Program and EAST-I Project).2012-08-0

Surgical Treatments for Lumbar Disc Disease in Adolescent Patients; Chemonucleolysis / Microsurgical Discectomy / PLIF with Cages

The herniated lumbar disc (HLD) in adolescent patients is characterized by typical discogenic pain that originates from a soft herniated disc. It is frequently related to back trauma, and sometimes it is also combined with a degenerative process and a bony spur such as posterior Schmorl's node. Chemonucleolysis is an excellent minimally invasive treatment having these criteria: leg pain rather than back pain, severe limitation on the straight leg raising test (SLRT), and soft disc protrusion on computed tomography (CT). Microsurgical discectomy is useful in the cases of extruded or sequestered HLD and lateral recess stenosis due to bony spur because the nerve root is not decompressed with chymopapain. Spinal fusion, like as PLIF, should be considered in the cases of severe disc degeneration, instability, and stenosis due to posterior central bony spur. In our study, 185 adolescent patients, whose follow-up period was more than 1 year (the range was 1 - 4 years), underwent spinal surgery due to HLD from March, 1998 to December, 2002 at our institute. Among these cases, we performed chemonucleolysis in 65 cases, microsurgical discectomy in 94 cases, and posterior lumbar interbody fusion (PLIF) with cages in 33 cases including 7 reoperation cases. The clinical success rate was 91% for chemonucleolysis, 95% for microsurgical disectomy, and 89% for PLIF with cages, and there were no nonunion cases for the PLIF patients with cages. In adolescent HLD, chemonucleolysis was the 1st choice of treatment because the soft adolescent HLD was effectively treated with chemonucleolysis, especially when the patient satisfied the chemonucleolysis indications

Manifestation of the Pacific Decadal Oscillation in the Kuroshio

Author Posting. © American Geophysical Union, 2009. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 36 (2009): L16602, doi:10.1029/2009GL039216.Pacific Decadal Oscillation (PDO) index is strongly correlated with vertically integrated transport carried by the Kuroshio through the East China Sea (ECS). Transport was determined from satellite altimetry calibrated with in situ data and its correlation with PDO index (0.76) is highest at zero lag. Total PDO-correlated transport variation carried by the ECS-Kuroshio and Ryukyu Current is about 4 Sv. In addition, PDO index is strongly negatively correlated, at zero lag, with NCEP wind-stress-curl over the central North Pacific at ECS latitudes. Sverdrup transport, calculated from wind-stress-curl anomalies, is consistent with the observed transport variations. Finally, PDO index and ECS-Kuroshio transport are each negatively correlated with Kuroshio Position Index in the Tokara Strait; this can be explained by a model in which Kuroshio path is steered by topography when transport is low and is inertially controlled when transport is high.MA, MW and JP were supported by ONR grant N000140210271. XZ was supported by the National Natural Science Foundation of China under grant 40776021 and the National Basic Research Programs of China under grant 2006CB400603. KK and KC were supported by the Korea EAST-I Program

Types and Prevalence of Coexisting Spine Lesions on Whole Spine Sagittal MR Images in Surgical Degenerative Spinal Diseases

∙The authors have no financial conflicts of interest. Purpose: We investigated types and prevalence of coexisting lesions found on whole spine sagittal T2-weighted images (WSST2I) acquired from magnetic resonance imaging (MRI) and evaluated their clinical significance in surgical degenerative spinal diseases. Materials and Methods: Coexisting spinal lesions were investigated using WSST2I from 306 consecutive patients with surgical degenerative spinal diseases. Severity of coexisting lesions was classified into four grades (0-3). Lesions of grade 2 and 3 were defined as “meaningful coexisting spine lesions ” (MCSL). Degenerative spinal diseases were classified into three pathologies: simple disc herniation, degenerative spinal stenosis, and ligament ossification disease. The relationships between MCSL, gender, age, and primary spine lesions were analyzed. Results: MCSL were found in 95 patients: a prevalence of 31.1%. Five out of 95 MCSL were surgically managed. The most common types of MCSL were disc herniation with 13.1 % prevalence, followed b