Kyung-Ae Park

Warm core ring velocities inferred from NSCAT

The NASA scatterometer, NSCAT, was designed to estimate from space the wind velocity relative to the ocean surface velocity. Assuming that the spatial scale of the meteorological forcing giving rise to the wind is large compared with the diameter of a warm core ring, it should be possible to obtain information about the currents in the ring from the demeaned scatterometer winds. To test this hypothesis, 14 NSCAT passes obtained within three days of clear AVHRR-derived sea surface temperature images showing a warm core ring were analyzed for evidence of circulation in the rings. The residual wind vectors for the 14 scatterometer passes were binned and averaged by radial distance from ring center. The mean azimuthal component of the speed compares well with ADCP data collected in one of the rings: a maximum of ≈ 0.89 m/s ≈ 50 km from ring center compared with 0.88 m/s and 1.0 m/s for the two ADCP transects, both also at 50 km from ring center.

RADARSAT-2 and Coastal Applications: Surface Wind, Waterline, and Intertidal Flat Roughness

RADARSAT-2 is a follow-up to RADARSAT-1 and is an all weather Earth observation satellite with fully polarimetric imaging capability. The synthetic aperture radars (SARs) onboard both RADARSATs are C-band imaging radars and they are well suited for Earths ecosystem monitoring and maritime surveillance, because of the near polar orbit and their unique all weather imaging capability, independent of solar illumination. In this paper, RADARSAT-2 is first introduced and several applications of various modes of SAR data to coastal zone problems are discussed, including the coastal surface wind, waterline mapping, and polarimetric SAR data inversion for topographic and geological parameters of tidal flats. Coastal zones, the important interface between the land and the ocean, where a large proportion of the worlds population inhabits, continuously change and evolve. The dynamic interaction of coastal winds, coupled with the coastal waves and currents, continuously erode rocks and land mass, and move and deposit various sediments on a continuous basis, along with the tides. Estimation of wind speeds and directions in coastal areas are empirically formulated and can further be improved with the available fully polarimetric data from RADARSAT-2. The water line mapping critically depends on the SAR frequency, or the wavelength of the SAR data used, and RADARSAT-2 SAR data using C-band should map waterlines more accurately than the longer wavelength L- or P-band SAR systems. The roughness parameters and partial information on the tidal flat compositions can be obtained from fully polarimetric SAR data. Some results obtained from NASA AIRSAR(2000) L-band data and RADARSAT-2(2008) C-band data do not fully agree with field measurements and further investigation is in progress. The inversion of polarimetric SAR data is a very complex problem and critically depends on the SAR signal frequency and model functions. RADARSAT-2 is an imaging radar, which is very flexible and powerful tool for potential coastal zone applications. Key RADARSAT-2 features and potential coastal zone application capabilities are also briefly reviewed.

Spatial and Temporal Scale Variations of Sea Surface Temperature in the East Sea Using NOAA/AVHRR Data

Sea surface temperature fields in the East Sea are composed of various spatial structures such as eddies, fronts, filaments, turbulent-like features and other mesoscale variations associated with the oceanic circulations of the East Sea. These complex SST structures have many spatial scales and evole with time. Semi-monthly averaged SST distributions based on extensive satellite observations of SSTs from 1990 through 1995 were constructed to examine the characteristics of their spatial and temporal scale variations by using statistical methods of multi-dimensional autocorrelation functions and spectral analysis. Two-dimensional autocorrelation functions in the central part of the East Sea revealed that most of the spatial SST structures are anisotropic in the shape of ellipsoids with minor axes of about 90–290 km and major axes of 100–400 km. Two dimensional spatial scale analysis demonstrated a consistent pattern of seasonal variation that the scales appear small in winter and spring, increase gradually to summer, and then decrease again until the spring of the next year. These structures also show great spatial inhomogeneity and rapid temporal change on time scales as short as a semi-month in some cases. The slopes in spectral energy density spectra of SSTs show characteristics quite similar to horizontal and geostrophic turbulence. Temporal spectra at each latitude are demonstrated by predominant peaks of one and two cycles per year in all regions of the East Sea, implying that SSTs present very strong annual and semi-annual variations.

Factors affecting the quality of life after ischemic stroke: young versus old patients.

Background Factors affecting the quality of life (QOL) may be different between young and old stroke patients. However, these issues have not yet been properly investigated. Methods We identified 170 young-onset stroke patients (onset between 15 and 45 years of age) who were admitted to the Asan Medical Center. Three hundred and forty follow-up period matched, old-onset stroke patients (onset >45 years of age) were chosen as a control group. A follow-up interview was performed 1~5 years after the onset of stroke in 96 young patients and 160 old patients. With the use of standardized questionnaire, we assessed physical disabilities, activity of daily living (Barthel Index Score, modified Rankin scale), the presence of depression (using DSM IV criteria and Beck Depression Inventory) and socio-economic/job status. The QOL was assessed using the Stroke Specific QOL developed by Williams et al. Results The QOL scores were significantly higher in young patients than in old ones. Univariate analysis showed that factors related to low QOL included unemployment, motor impairment, aphasia, dysarthria, dysaphagia and severe modified Rankin score in young patients while poor economic status, unemployment, supratentorial (vs. infratentorial) stroke, anterior (vs. posterior) circulation stroke, the presence of diabetes mellitus, motor impairment, aphasia, dysarthria, dysphagia, visual field defect, severe modified Rankin score, the presence of post-stroke seizures and depression were related to the low QOL in old patients. Cigarette smoking (in old patients) and alcohol drinking (in both young and old patients) were related to high QOL. Multiple regression analysis showed that modified Rankin score was the most important factor explaining low QOL in both groups, while other important factors included depression, visual field defect and anterior circulation stroke in old patients, and the motor dysfunction and dysarthria in young patients. Conclusions We conclude that aside from modified Rankin scale, factors affecting the quality of life are different between these two groups. Recognition of these differences may allow us to develop different strategies to improve the quality of life in stroke patients.

Comparison of Dietary Compliance and Dietary Knowledge Between Older and Younger Korean Hemodialysis Patients

OBJECTIVE The numbers of older hemodialysis patients (OHPs) are increasing very rapidly worldwide, but few studies have focused on the compliance of OHPs. This study compared the compliance with, and the knowledge of, dietary restriction regimens between OHPs and younger hemodialysis patients (YHPs). Mortality was also compared between these two groups. PATIENTS AND SETTING A total of 160 patients who were registered at the Asan Medical Center (Seoul, Korea) participated in the study, 64 of whom were classified as OHPs (age >or=65 years), and 96 as YHPs (age <65 years). MAIN OUTCOME MEASURES Data were collected between September 2003 and February 2004. General characteristics and dietary knowledge of potassium, phosphorus, and sodium and fluid restrictions were assessed by personal interview. Dietary compliance was determined by measuring serum levels of these nutrients and interdialytic weight gain. Subjective global assessments were used to evaluate nutritional status. Both OHPs and YHPs were followed until May 2007 for mortality analysis. The data were analyzed with descriptive statistics, Students t test, chi(2) test, and Spearman correlation using the SPSS statistical package (SPSS, Inc., Chicago, IL). RESULTS The OHPs had a lower appetite, lower physical activity, and lower educational level compared with the YHPs. Dietary compliance with phosphorus restriction and with sodium and fluid restriction was higher in the OHPs than in the YHPs (P < .01 and P < .05, respectively), whereas compliance with potassium restriction did not differ between groups. The knowledge scores concerning potassium (P < .05) and phosphorus (P < .01) restriction diets were lower in OHPs than in YHPs, whereas no differences were found for knowledge scores concerning sodium and fluid restriction diets. Mortality was higher in the OHPs than in the YHPs (P < .001). The OHPs with higher mortality had higher dietary compliance with sodium and fluid restriction (r = 0.248, P < .05), and lower nutritional status (r = -0.342, P < .05). CONCLUSIONS The OHPs were generally less knowledgeable and more compliant, and had a lower appetite and a higher mortality than the YHPs. Therefore, the current application of the same dietary education to both OHPs and YHPs may be problematic. Instead, developing age-specific strategies to increase dietary knowledge and nutritional intake is urgently needed to increase the survival rate of Korean hemodialysis patients.

Sea surface temperature retrievals optimized to the East Sea (Sea of Japan) using NOAA/AVHRR data

The accuracy of sea surface temperatures derived by NOAA/NESDIS (National Oceanic and Atmospheric Administration/National Environmental Satellite, Data, and Information Service) equations was tested by comparison with temperatures measured by thirty-four satellite-tracked ARGOS drifters deployed in the East Sea (Sea of Japan) from 1993 to 1997. Using an improved cloud-screening algorithm for the East Sea, we obtained 362 matchup points between the NOAA satellite data (NOAA-11, NOAA-12, and NOAA-14) and the drifter buoy temperatures. The split window technique of linear MCSST, non-linear CPSST and NLSST showed relatively small rms (root mean square) errors in the range of 0.9°C to 1.2°C compared with the other window methods. However, a predominant trend was found that satellite-derived SSTs are underestimated by as much as -2°C in dry atmospheric conditions during winter, and overestimated in very humid conditions in summer by approximately 2°C. The characteristic trend was removed using a regression method, and the rms errors of newly-derived equations for the split window MCSST and the non-linear SST optimized to the East Sea were improved to within 0.3°C ∼ 0.9°C. The locally-optimized SSTs may be more important than the SSTs based on the global database, particularly in the inaccessible regions off North Korea and sea ice regions that are important for the critical research issue of cold water formation in the East Sea.

Spatial scales of mesoscale eddies from GOCI Chlorophyll-a concentration images in the East/Japan Sea

The spatial scales of mesoscale eddies are of importance to understand physio-biogeochemical processes in the East/Japan Sea. Chlorophyll-a concentration images from the Geostationary Ocean Color Imager (GOCI) revealed numerous eddies during the phytoplankton bloom in spring. These eddies were manually digitized to obtain geolocation information at the peripheries from GOCI images and then least-square fitted to each ellipse. The elliptic elements were the geolocation position of the eddy center, the rotation angle from due east, the eccentricity, the lengths of the semi-major and semi-minor axes, and the mean radius of the ellipse. The spatial scales of eddies had a mean radii ranging from 10 km to 75 km and tended to be smaller in the northern region. The scales revealed a linear trend of about −7.26 km/°N as a function of the latitude. This tendency depended on the latitudinal variation of the internal Rossby radius of deformation, which originates from the substantial difference in the density structure of the water column. The scales from the sea surface temperature image were larger by 1.30 times compared to those from ocean color image. This implies that physical processes along the periphery of the eddy affect the nutrient dynamics.

Error Characteristics of Satellite-observed Sea Surface Temperatures in the Northeast Asian Sea

An extensive set of both in-situ and satellite data regarding oceanic sea surface temperatures in Northeast Asian seas, collected over a 10-year period, was collocated and surveyed to assess the accuracy of satellite-observed sea surface temperatures (SST) and investigate the characteristics of satellite measured SST errors. This was done by subtracting insitu SST measurements from multi-channel SST (MCSST) measurements. 845 pieces of collocated data revealed that MCSST measurements had a root-mean-square error of about 0.89 and a bias error of about 0.18. The SST errors revealed a large latitudinal dependency with a range of around 40, which was related to high spatial and temporal variability from smaller eddies, oceanic currents, and thermal fronts at higher latitudes. The MCSST measurements tended to be underestimated in winter and overestimated in summer when compared to in-situ measurements. This seasonal dependency was discovered from shipboard and moored buoy measurements, not satellite-tracked surface drifters, and revealed the existence of a strong vertical temperature gradient within a few meters of the upper ocean. This study emphasizes the need for an effort to consider and correct the significant skin-bulk SST difference which arises when calculating SST from satellite data.

Statistical analysis of upper ocean temperature response to typhoons from ARGO floats and satellite data

Even under extreme atmospheric and oceanic conditions such as tropical storms and typhoons, satellites and ARGO floats are continuously transferring their temperature observations to us at near real-time. These data enable us to monitor the typhoons and understand upper ocean response during typhoon events. Using both satellite data and ARGO float data, sea surface temperature (SST) response and mixed layer temperature (MLT) response are examined for the typhoons occurring from 2000 to 2003 in the North Pacific. There is a high correlation of temperature changes between MLT and SST, but shows dependence on latitude and initial mixed layer depth before arrival of typhoon. Statistically, majority of matchups for pre and post typhoon show the largest peak of MLT cooling of around 1.0C and deepening of ML of about 56m after typhoon passage. This study presents overall statistical characteristics of upper ocean response during typhoon events and discusses their causes.

SAR-derived wind fields at the coastal region in the East/Japan Sea and relation to coastal upwelling

The relationship between the modification of synthetic aperture radar (SAR) wind field and coastal upwelling was investigated using high-resolution wind fields from Advanced Land Observing Satellite (ALOS) Phased Array type L-band synthetic aperture radar (PALSAR) imagery and sea-surface temperature (SST) from National Oceanic and Atmospheric Administration/Advanced Very-High-Resolution Radiometer (NOAA/AVHRR) data. The retrieved SAR wind speeds seem to agree well with in situ buoy measurements with only a relatively small error of 0.7 m s−1. The SAR wind fields retrieved from the east coast of Korea in August 2007 revealed a spatial distinction between near and offshore regions. Low wind speeds of less than 3 m s−1 were associated with cold water regions with dominant coastal upwelling. Time series of in situ measurements of both wind speed and water temperature indicated that the upwelling was induced by the wind field. The low wind field from SAR was mainly induced by changes in atmospheric stability due to air–sea temperature differences. In addition, wind speed magnitude showed a positive correlation with the difference between SST and air temperature (R2 = 0.63). The dependence of viscosity of water on radar backscattering at the present upwelling region was negligible since SAR data showed a relatively large backscattering attenuation to an SST ratio of 1.2 dB °C−1. This study also addressed the important role of coastal upwelling on biological bloom under oligotrophic environments during summer.