Im Sang Oh

Development of atmospheric correction algorithm for Geostationary Ocean Color Imager (GOCI)

This paper describes an atmospheric correction algorithm for Geostationary Ocean Color Imager (GOCI) and its early phase evaluation. This algorithm was implemented in GOCI Data Processing System (GDPS) version 1.1. The algorithm is based on the standard SeaWiFS method, which accounts for multiple scattering effects and partially updated in terms of turbid case-2 water correction, optimized aerosol models, and solar angle correction per slot. For turbid water correction, we used a regional empirical relationship between water reflectance at the red (660 nm) and near infrared bands (745 nm and 865 nm). The relationship was derived from turbid pixels in satellite images after atmospheric correction, and processed using aerosol properties derived for neighboring non-turbid waters. For validation of the GOCI atmospheric correction, we compared our results with in situ measurements of normalized water leaving radiance (nLw) spectra that were obtained during several cruises in 2011 around Korean peninsula. The match up showed an acceptable result with mean ratio of the GOCI to in situnLw(λ), 1.17, 1.24, 1.26, 1.15, 0.86 and 0.99 at 412 nm, 443 nm, 490 nm, 555 nm, 660 nm and 680 nm, respectively. It is speculated that part of the deviation arose from a lack of vicarious calibration and uncertainties in the above water nLw measurements.

Interannual and interdecadal variations of sea surface temperature in the East Asian Marginal Seas

Abstract Interannual and interdecadal variability of sea surface temperature (SST) in the East Asian Marginal Seas (EAMS) from 1951 to 1996 are investigated, and the teleconnection of the EAMS to the equatorial ocean is studied using empirical orthogonal function analysis and coherency analysis. The EAMS have significant coherency with the Nino 3.4 SST at 2- to 3-year periods with a phase lag of 5–9 months in the SST anomaly (SSTA). The EAMS also showed a higher coherency with a 6-year oscillation with a phase lag of 18–22 months. For the 6-year variability, the SSTA of the Nino 3.4 is highly coherent with the latent and sensible heat flux anomaly of the southern East Sea, indicating that the variability of the southern East Sea is related to that in the Nino 3.4 region through the ocean-atmosphere interactions. The southern East Sea also has a higher coherency with the East China Sea. Cooling in the southern East Sea and sudden warming in the northern East Sea were found to have occurred around 1965/1966 in the records of interdecadal variability. The decadal and interdecadal variabilities of the EAMS were found to be teleconnected to the western equatorial Pacific, whereas the interannual variability was highly correlated to the central equatorial Pacific, which is represented by Nino 3.4 SST.

Estimating horizontal diffusivity in the East Sea (Sea of Japan) and the northwest Pacific from satellite‐tracked drifter data

We use data of satellite-tracked, mixed-layer drifters collected for the World Ocean Circulation Experiment/Tropical Ocean-Global Atmosphere (WOCE/TOGA) Surface Velocity Program in the East Sea (Sea of Japan) and the northwest Pacific Ocean during 1991-1997 to obtain reliable estimates of geographically varying horizontal diffusivity, integral timescale and space scale. For the diffusivity we suggest calculation of both the minor principal component of the diffusivity tensor in a definition by Davis [1991] and the half growth rate of the minor principal component of the displacement variance tensor. Numerical simulation of particle motion is used to prove that the minor principal component estimates of diffusivity, in contrast to regular estimates, are insensitive to ensemble averaging over particles taken from a finite area in a shear mean flow. In the East Sea, typical values of the diffusivity, timescale, and space scale are (1.7-5.2) × 10 7 cm -2 s -1 , 0.7-1.7 days, and 10-25 km, respectively. In the northwest Pacific Ocean, typical estimates of the diffusivity, timescale, and space scale in mean are a factor 2-3 larger, namely, (2.3-15.1) X 10 7 cm -2 s -1 , 1.7-3.7 days, and 18-62 km, respectively. It was found that the space scale L and the first mode internal Rosshy radius Ri are related as L Ri, which suggests a parameterization of lateral diffusivity k∞ of the form k∞ = u Ri, where u is the rms current velocity fluctuation.

Monthly variation of pigment concentrations and seasonal winds in China's marginal seas

Chinas marginal seas extend from temperate, subtropical to tropical zones, which encounter different monsoons. This study investigates the monthly variation of phytoplankton pigment concentrations (PC) from 1978 to 1986, and analyzes seasonal winds with sea surface temperatures (SST) among the Bohai Sea, the Yellow Sea, the East China Sea and the northern South China Sea. Nimbus satellite Coastal Zone Color Scanner (CZCS)-derived PC images were averaged into monthly fields for the entire area; we then emphasize the period of one year from November 1979 to October 1980, when CZCS data availability was relatively good. Monthly variability of PC has been compared among three regions (the outlets of the Yellow River, the Yangtze River and the Pearl River). The results revealed well-defined seasonality of PC, wind and SST from north to south in Chinas marginal seas. In the northern area (Bohai Sea and Yellow Sea), variability in SST (0–28 °C) and PC (0.5–3.5 mg m−3) was high with two peaks of PC appeared in spring–summer and in fall–winter in each year. In the East China Sea, two peaks of PC (1.2 mg m−3 in March and 1.3 mg m−3 in November) were in evidence, where SST variations were ranged 7–28 °C in one year. However, in the southern area (northern South China Sea), variation in SST (15–29 °C) and PC (0.1–0.4 mg m−3) was relatively low; the monthly variation of PC was not so high compared with north area. OCTS derived ocean color data obtained from April 1997 conformed the spatial pattern of Chl-a and colored dissolved organic matter (CDOM), and showed high CDOM and total suspended material (TSS) in the coast waters in the north part of Chinas marginal seas. Seasonal variation of PC may be related to the reversed monsoon; and spatial variation of PC may be influenced by river discharge, upwelling and coastal currents. High PC areas match good fishing grounds in terms of season and location in the study waters.

Generation of cyclonic eddies in the Eastern Gotland Basin of the Baltic Sea following dense water inflows: numerical experiments

Abstract A sigma ( σ )-coordinate ocean model by Blumberg and Mellor (POM) is applied to study the formation processes of mesoscale cyclones observed in the Eastern Gotland Basin following the dense water inflows. The initial conditions simulate a situation when the Arkona and Bornholm basins and partially the Slupsk Furrow are already filled with the inflow water of the North Sea origin, while the Eastern Gotland and Gdansk basins still contain the old water of pre-inflow stratification. Model runs with constant and time-dependent winds, changing the buoyancy forcing, grid geometry and bottom topography display the following. Entering the Eastern Gotland Basin from the Slupsk Furrow, the bottom intrusion of saline inflow water splits in two: one goes northeast towards the Gotland Deep, and second moves southeast towards the Gulf of Gdansk. An intensive mesoscale cyclonic eddy carrying the inflow water is generated just east of the Slupsk Furrow with the inflow pulse. A number of smaller cyclones with boluses of the inflow water are formed in the permanent halocline along the saline intrusion pathway to the Gotland Deep. Following Spall and Price [J. Phys. Oceanogr. 28 (1998) 1598], the cyclones are suggested to form by the adjustment of the high potential vorticity inflow water column to a low potential vorticity environment.

Causes of the Unusual Coastal Flooding Generated by Typhoon Winnie on the West Coast of Korea

On 19 August 1997 Typhoon Winnie brought unusually strong and extensive coastal flooding from storm surges to the west coast of Korea, which was farenough from the typhoons center to lack significant local wind and pressure forcing.Sea levels at some tidal stations broke 36-year records and resulted in property damages of

Can Turbulence Suppress Double-Diffusively Driven Interleaving Completely?

18,000,000. This study investigated the causes of the unusual high sea levels by using an Astronomical-Meteorological Index (AMI) and a coupled ocean wave-circulation model developed by the present authors. The AMI analysis and the numerical simulation of the surge event showed that the major cause of the high sea levels was not the standard inverse barometric effect supplemented by water piling up along the coast by the wind field of the typhoon as is usual for a typical storm surge, but rather an enhanced tidal forcing from the perigean spring tide and water transported into the Yellow Sea by the currents generated by the typhoon. The numerical results also indicated that the transported water accounted for about 50% of the increased sea levels. Another cause for the coastal flooding was the resonance coupling of the Yellow Sea (with a natural normal mode period of 37.8 h) and the predominant period of the surge (36.5 h).

Vicarious calibration of the Geostationary Ocean Color Imager.

Abstract A linear stability problem is formulated to investigate the effect of turbulence on double-diffusively driven thermohaline interleaving in rotating media. Three cases are considered: (a) intrusions with an alongfront slope in rotating media, (b) intrusions with zero alongfront slope in nonrotating media, (c) intrusions with zero alongfront slope, where the Coriolis force is retained. The physical reason for case c is that the large-scale vertical geostrophic shear in baroclinic fronts will rotate any intrusion with nonzero alongfront slope as long as the alongfront slope vanishes. In all three cases, turbulence works to suppress interleaving so that the growth rate of the fastest growing intrusion decreases with the increase of turbulent diffusivity k*. However, in cases a and b the growing intrusions exist for any finite value of k*, while in case c there is a marginal (maximum) value of k* beyond which growing intrusions do not exist.

Study of spatial spectra of horizontal turbulence in the ocean using drifter data

Measurements of ocean color from Geostationary Ocean Color Imager (GOCI) with a moderate spatial resolution and a high temporal frequency demonstrate high value for a number of oceanographic applications. This study aims to propose and evaluate the calibration of GOCI as needed to achieve the level of radiometric accuracy desired for ocean color studies. Previous studies reported that the GOCI retrievals of normalized water-leaving radiances (nLw) are biased high for all visible bands due to the lack of vicarious calibration. The vicarious calibration approach described here relies on the assumed constant aerosol characteristics over the open-ocean sites to accurately estimate atmospheric radiances for the two near-infrared (NIR) bands. The vicarious calibration of visible bands is performed using in situ nLw measurements and the satellite-estimated atmospheric radiance using two NIR bands over the case-1 waters. Prior to this analysis, the in situ nLw spectra in the NIR are corrected by the spectrum optimization technique based on the NIR similarity spectrum assumption. The vicarious calibration gain factors derived for all GOCI bands (except 865nm) significantly improve agreement in retrieved remote-sensing reflectance (Rrs) relative to in situ measurements. These gain factors are independent of angular geometry and possible temporal variability. To further increase the confidence in the calibration gain factors, a large data set from shipboard measurements and AERONET-OC is used in the validation process. It is shown that the absolute percentage difference of the atmospheric correction results from the vicariously calibrated GOCI system is reduced by ~6.8%.

Seasonal characteristics of the near-surface circulation in the northern South China Sea obtained from satellite-tracked drifters

The statistics of a pair of Lagrangian particles offer, in principle, a possibility to estimate the structure functions of velocity, then the spatial autocorrelations, and finally the spatial spectra. On the basis of this strategy, the authors have developed an approach to estimate spatial spectra of mesoscale horizontal turbulence in the ocean using data of satellite-tracked drifters. The approach was applied to the data of 19 drifters deployed in the California Current System in 1993. It was found that the shape of both those spectra and this spectra calculated using drifterborne longitudinal and transverse correlations estimated by other authors are qualitatively in good accordance with theoretical predictions for 2D isotropic nondivergent turbulent flow. To relate obtained spectra to some physical parameters, kinematic stochastic models were developed that consisted of a population of randomly spaced, 2D axisymmetric eddies of a given shape. Numerical experiments with different eddy shapes showed that the model spectra obey a self-similarity; that is, at a given eddy shape they depend on the variance of stochastic process and a length scale of the eddy only. A model with the exponential eddy shape was found to fit drifterborne spectra better than other models. The best agreement between the drifterborne and model spectra was achieved when the radius of an exponentially shaped model eddy was taken equal to the internal Rossby radius.