Ekman motion in shallow open sea in the presence of time-harmonic variation of water depth

The time variation of the wind-induced flow in a homogeneous unbounded sea region has been analytically investigated. The time-dependent Ekman solution in a homogeneous, shallow open sea has been further extended by taking into account the time variation in water depth which might be caused by either tidal motion or change in the mixed layer thickness. The solution approach taken in this study is based on the Galerkin-eigenfunction method originally developed by Heaps [1972. On the numerical solution of three-dimensional hydrodynamical equations for tides and storm surges. Memoires de la Societe Royale des Sciences de Liege Serie 6(2), 143–180]. A series of calculations have been made with emphasis on the influence of the time variation in water depth upon the build-up of Ekman spirals in the presence of oscillatory variations in water depth. It has been found that two oscillations contribute to the wind drift current, the inertial oscillation and the depth-variation-induced oscillation; the inertial oscillation decays with time, but the depth-variation-induced oscillation remains undamped despite the presence of bottom friction. The presence of time-harmonic variation produces peculiar forms of hodograph with a curled or circular pattern according to the angular frequency of the water depth variation.     

Risk assessment for the Yucca Mountain high-level nuclear waste repository site: Estimation of volcanic disruption

In this article, we model the volcanism near the proposed nuclear waste repository at Yucca Mountain, Nevada, U.S.A. by estimating the instantaneous recurrence rate using a nonhomogeneous Poisson process with Weibull intensity and by using a homogeneous Poisson process to predict future eruptions. We then quantify the probability that any single eruption is disruptive in terms of a (prior) probability distribution, since not every eruption would result in disruption of the repository. Bayesian analysis is performed to evaluate the volcanic risk. Based on the Quaternary data, a 90% confidence interval for the instantaneous recurrence rate near the Yucca Mountain site is (1.85×10^–6/yr, 1.26×10^–5/yr). Also, using-these confidence bounds, the corresponding 90% confidence interval for the risk (probability of at least one disruptive eruption) for an isolation time of 10⁴ years is (1.0×10^–3, 6.7×10^–3), if it is assumed that the intensity remains constant during the projected time frame.     

凝结反馈对云层垂直发展影响的一个线性理论

根据小尺度垂直运动的线性分析,作者证明凝结反馈对云层的垂直发展有着很强的制约作用。这种制约作用在温度和湿度较大的情况下更为明显。作者引出了在凝结反馈作用下非定常运动中的频率公式和定常运动下的波速公式。这样,南方雨季中每次雨停时常常见到的云层迅速分层的现象得到了可能的理论解释。     

Estimation and improvement in the geolocation accuracy of rational polynomial coefficients with minimum GCPs using KOMPSAT-3A

ABSTRACT

In this paper, we propose a method to regenerate Rational Polynomial Coefficients (RPCs) using KOMPSAT-3A imagery and to reduce the geolocation error using minimum ground control points (GCPs). To estimate the new RPCs, the physical sensor model fitted to KOMPSAT-3A imagery was utilized and virtual GCPs over the study area were created. The size of the virtual grid used was 20x20x20. To remove the sensor-related errors in physical sensor model, three different image correction models (image coordinate translation model, shift and drift model, and affine transformation model) were additionally applied. We evaluated our proposed method in two areas within Korea, one in urban (Seoul) and one in rural (Goheung) areas. The results showed that there was a significant improvement after applying the suggested approach in the two areas. The image coordinate translation model is suggested in terms of GCP requirement and expected errors estimated from the error propagation analysis using Gauss–Markov Model (GMM).     

Outlying plasmasphere structure detected by whistlers

Whistlers recorded at Eights ($\text{L ? 4}$) and Byrd ($\text{f ? 7}$), Antarctica have been used to study large-scale structure in equatorial plasma density at geocentric distances $\text{?3–6}\text{R}{}_{\mathrm{E}}$. The observations were made during conditions of magnetic quieting following moderate disturbance. The structures were detected by a “scanning” process involving relative motion, at about one tenth of the Earth's angular velocity or greater, between the observed density features and the observing whistler station or stations. Three case studies are described, from 26 March 1965, 11 May 1965 and 29 August 1966. The cases support satellite results by showing outlying high density regions at $\text{?4–6}\text{R}{}_{\mathrm{E}}$ that are separated from the main plasmasphere by trough-like depressions ranging in width from $\text{?0.2}$ to 1 R_E. The structures evidently endured for periods of 12 hr or more. In the cases of deepest quieting their slow east-west motions with respect to the Earth are probably of dynamo origin. The cases observed during deep quieting (11 May 1965 and 29 August 1966) suggest the approximate rotation with the Earth of structure formed during previous moderate disturbance activity in the dusk sector. The third case, from 26 March 1965, may represent a structure formed near local midnight. The reported structures appear to be closely related to the bulge phenomenon. The present work supports other experimental and theoretical evidence that the dusk sector is one of major importance in the generation of outlying density structure. It is inferred that irregularities of the type reported here regularly develop near 4–5 R_E during moderate substorm activity. This research suggests that at least a major class of the density structures that develop near 4 R_E are tail-like in nature, joined to the main body of the plasmasphere. The apparent disagreement with Chappell's results from OGO 5, which are interpreted as showing regions of “detached” plasma beyond 5 R_E, may be related to the pronounced spatial structure of electric fields observed in high-latitude ionospheric regions that are conjugate to the magnetospheric regions in which the OGO-5 observations were made.     

Sea surface height and transport stream function of the South China Sea from a variable-grid global ocean circulation model

The study on the South China Sea (SCS) circulation has a history of more than 40 years. Nevertheless, the SCS circulation is not fully understood compared with the Bohai Sea, Yellow Sea and East China Sea (ECS). Many numerical studies on the SCS circulati…     

Biomonitoring of coastal pollution status using protozoan communities with a modified PFU method

Structural and functional parameters of protozoan communities were assessed as indicators of water quality in Korean coastal waters in the summer of 2000. A modified polyurethane foam unit (PFU) method, named the bottled PFU (BPFU) system, was used in order to carry out the bioassessment. Both parameters suggested that biomonitoring using the BPFU system was more effective than the conventional PFU method in offshore areas. The species number collected by the BPFU system generally decreased as pollution intensity increased at three main stations and was greater than that collected using the PFU method (paired t-test, t = 4.83, p < 0.0001). The Margalef diversity index coincided well with the water conditions. The diversity index values calculated from the BPFU system were also significantly higher than those from the PFU method (paired t-test, t = 5.37, p < 0.0001). Furthermore, the functional parameters, i.e. S(eq),G and T90%, correlated with the pollution status and could thus clearly discriminate the different classes of water quality.     

An overview of toxicant identification in sediments and dredged materials

The identification of toxicants affecting aquatic benthic systems is critical to sound assessment and management of our nation's waterways. Identification of toxicants can be useful in designing effective sediment remediation plans and reasonable options for sediment disposal. Knowledge of which contaminants affect benthic systems allows managers to link pollution to specific dischargers and prevent further release of toxicant(s). In addition, identification of major causes of toxicity in sediments may guide programs such as those developing environmental sediment guidelines and registering pesticides, while knowledge of the causes of toxicity which drive ecological changes such as shifts in benthic community structure would be useful in performing ecological risk assessments. To this end, the US Environmental Protection Agency has developed tools (toxicity identification and evaluation (TIE) methods) that allow investigators to characterize and identify chemicals causing acute toxicity in sediments and dredged materials. To date, most sediment TIEs have been performed on interstitial waters. Preliminary evidence from the use of interstitial water TIEs reveals certain patterns in causes of sediment toxicity. First, among all sediments tested, there is no one predominant cause of toxicity; metals, organics, and ammonia play approximately equal roles in causing toxicity. Second, within a single sediment there are multiple causes of toxicity detected; not just one chemical class is active. Third, the role of ammonia is very prominent in these interstitial waters. Finally, if sediments are divided into marine or freshwater, TIEs perforMed on interstitial waters from freshwater sediments indicate a variety of toxicants in fairly equal proportions, while TIEs performed on interstitial waters from marine sediments have identified only ammonia and organics as toxicants, with metals playing a minor role. Preliminary evidence from whole sediment TIEs indicates that organic compounds play a major role in the toxicity of marine sediments, with almost no evidence for either metal or ammonia toxicity. However, interpretation of these results may be skewed because only a small number of interstitial water (n = 13) and whole sediment (n = 5) TIEs have been completed. These trends may change as more data are collected.