Effects of prescribed initial cloud droplet spectra on convective cloud and precipitation developments under different thermodynamic conditions: A modeling and observational study   总被引：1，自引：1，他引：0  

Hee-Jung Yang  Seong Soo Yum   《Atmospheric Research》2007,86(3-4):207-224

A two-dimensional cloud model with bin microphysics was used to investigate the effects of cloud condensation nuclei (CCN) concentrations and thermodynamic conditions on convective cloud and precipitation developments. Two different initial cloud droplet spectra were prescribed based on the total CCN concentrations of maritime (300 cm^− 3) and continental (1000 cm^− 3) air masses, and the model was run on eight thermodynamic conditions obtained from observational soundings. Six-hourly sounding data and 1-hourly precipitation data from two nearby weather stations in Korea were analyzed for the year 2002 to provide some observational support for the model results.For one small Convective Available Potential Energy (CAPE) ( 300 J kg^− 1) sounding, the maritime and continental differences were incomparably large. The crucial difference was the production of ice phase hydrometeors in the maritime cloud and only water drops in the continental cloud. Ice phase hydrometeors and intrinsically large cloud drops of the maritime cloud eventually lead to significant precipitation. Meanwhile negligible precipitation developed from the continental cloud. For the three other small CAPE soundings, generally weak convective clouds developed but the maritime and continental clouds were of the same phases (both warm or both cold) and their differences were relatively small.Model runs with the four large CAPE ( 3000 J kg^− 1) soundings demonstrated that the depth between the freezing level (FL) and the lifting condensation level (LCL) was crucial to determine whether a cloud becomes a cold cloud or not, which in turn was found to be a crucial factor to enhance cloud invigoration with the additional supply of freezing latent heat. For two large CAPE soundings, FL–LCL was so deep that penetration of FL was prohibitive, and precipitation was only mild in the maritime clouds and negligible in the continental clouds. Two other soundings of similarly large CAPE had small FL–LCL, and both the maritime and continental clouds became cold clouds. Precipitation was strong for both but much more so in the maritime clouds, while the maximum updraft velocity and the cloud top were slightly higher in continental clouds. Although limited to small CAPE cases, more precipitation for smaller FL–LCL for a selected group of precipitation and thermodynamic sounding data from Korea was in support of these model results in its tendency.These results clearly demonstrated that the CCN effects on cloud and precipitation developments critically depended on the given thermodynamic conditions and not just the CAPE but the entire structure of the thermodynamic profiles had to be taken into account.  相似文献   

Partitioning of dioxins (PCDDs/Fs) in ambient air at urban residential locations     

Md. M. Rahman  Z.-H. Shon  C.-J. Ma  R. J. C. Brown  S. K. Pandey  C. G. Park  I. S. Bae  J. R. Sohn  H.-O. Yoon  K.-H. Kim 《International Journal of Environmental Science and Technology》2014,11(7):1897-1910

In this work, 17-polychlorinated dibenzo-p-dioxin/furan (PCDD/Fs) isomers were measured in ambient air at four urban sites in Seoul, Korea (from February to June 2009). The concentrations of their summed values (ΣPCDD/Fs) across all four sites ranged from 1,947 (271 WHO₀₅ TEQ) (Jong Ro) to 2,600 (349 WHO₀₅ TEQ) fg/m³ (Yang Jae) with a mean of 2,125 (± 317) fg/m³ (292 WHO₀₅ TEQ fg/m³). The sum values for the two isomer groups of ΣPCDD and ΣPCDF were 527 (30 WHO₀₅ TEQ) and 1,598 (263 WHO₀₅ TEQ) fg/m³, respectively. The concentration profile of individual species was dominated by the 2,3,4,7,8-PeCDF isomer, which contributed approximately 36 % of the ΣPCDD/Fs value. The observed temporal trends in PCDD/F concentrations were characterized by relative enhancement in the winter and spring. The relative contribution of different sources, when assessed by principal component analysis, is explained by the dominance of vehicular emissions along with coal (or gas) burning as the key source of ambient PCDD/Fs in the residential areas studied.  相似文献   

Bathymetry enhancement by altimetry-derived gravity anomalies in the East Sea (Sea of Japan)   总被引：1，自引：0，他引：1  

Kwang Bae Kim  Yu-Shen Hsiao  Jeong Woo Kim  Bang Yong Lee  Yi Kyun Kwon  Chang Hwan Kim 《Marine Geophysical Researches》2010,31(4):285-298

The gravity-geologic method (GGM) was used to enhance the bathymetry of the East Sea (Sea of Japan) with satellite altimetry-derived free-air gravity anomalies and shipborne depth measurements. By comparison with the bathymetry model of Smith and Sandwell’s (SAS) approach (1994), GGM was found to have an advantage with short wavelength (≤12 km) components, while SAS better predicts longer wavelength (≥25 km) components, despite its dependency on density contrast. To mitigate this limitation, a tuning density contrast of 10.25 g/cm³ between seawater and the seafloor was primarily estimated by the downward continuation method and then validated by the check points method with GGM. Similarly, SAS is limited by the “A” value in low-pass part of the Wiener filter, which defines the effective range of the wavelength components on bathymetry. As a final result, we present an enhanced GGM bathymetry model by integrating all available data.  相似文献   

A steepness index unit volume flood hydrograph approach for sub‐daily flow disaggregation     

Kim‐Seong Tan  Francis H. S. Chiew  Rodger B. Grayson 《水文研究》2007,21(20):2807-2816

The estimation of sub‐daily flows from daily flood flows is important for many hydrological and hydraulic applications. Flows during flood events often vary significantly within sub‐daily time‐scales, and failure to capture the sub‐daily flood characteristic can result in an underestimation of the instantaneous flood peaks, with possible risk of design failure. It is more common to find a longer record of daily flow series (observed or modelled using daily rainfall series) than sub‐daily flow data. This paper describes a novel approach, known as the steepness index unit volume flood hydrograph approach, for disaggregating daily flood flows into sub‐daily flows that takes advantage of the strong relationship between the standardized instantaneous flood peak and the standardized daily flood hydrograph rising‐limb steepness index. The strength of this relationship, which is considerably stronger than the relationship between the standardized flood peak and the event flood volume, is shown using data from six rivers flowing into the Gippsland Lakes in southeast Australia. The results indicate that the steepness index unit volume flood hydrograph approach can be used to disaggregate modelled daily flood flows satisfactorily, but its reliability is dependent on a model's ability to simulate the standardized daily flood hydrograph rising‐limb steepness index and the event flood volume. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Adaptive Surface Interference Suppression for Matched-Mode Source Localization     

Kim  K. Seong  W. Lee  K. 《Oceanic Engineering, IEEE Journal of》2010,35(1):120-130

Localizing a quiet submerged target in the presence of loud interfering surface ships is an important problem for matched-field processing (MFP) in shallow water. Typically, a data-driven interference suppression scheme is employed which requires neither prior information of the interferer's location nor filter design optimization and iterative estimation. However, the target and the interferers are usually in motion resulting in spreading or mixing of signal energies in their subspaces, thus making it difficult to determine the interference subspace dimension. In this paper, we exploit the difference in modal amplitudes for surface and submerged sources by eigenanalysis of the modal cross-spectral density matrix (CSDM). Simulation and experimental data results show that the interference subspace can be estimated adaptively and the beam output for the target is enhanced.   相似文献   

A simplified pseudo-fluid model derived from biot theory through low grazing angle approximation     

Keunhwa Lee Woojae Seong 《Oceanic Engineering, IEEE Journal of》2005,30(4):651-659

We propose an approximation technique with which the porous Biot model can be converted into a pseudo-fluid medium model, i.e., a medium represented by its sound speed and density. This technique begins from an analytic derivation of the reflection coefficient on a planar interface of fluid and porous ocean sediment. Invoking the low grazing angle approximation, useful for solving long range propagation problems, the pseudo-fluid medium is obtained. Alternate pseudo-fluid medium can be obtained through the weak frame approximation (Williams, J. Acoust. Soc. Am. 110, 2276-2281, 2001). In this paper, we discuss the accuracy and limitations of the low grazing angle approximation by numerically comparing the reflection coefficient to the full Biot model cases as functions of various Biot parameters, frequency, and water sound speed. The usefulness of the present low grazing angle approximated pseudo-fluid medium in ocean wave propagation modeling is demonstrated by comparing the transmission loss results with that of the full Biot model.  相似文献   

Time-domain geoacoustic inversion of high-frequency chirp signal from a simple towed system     

Cheolsoo Park Woojae Seong Gerstoft  P. Siderius  M. 《Oceanic Engineering, IEEE Journal of》2003,28(3):468-478

An inversion method using a towed system consisting of a source and two receivers is presented. High-frequency chirp signals that have been emitted from the source are received after multiple penetrations and reflections from the shallow water sub-bottom structure and are processed for geoacoustical parameter estimation. The data are processed such that a good resolution and robustness is achieved via matched filtering, which requires information about the source signal. The inversion is formulated as an optimization problem, which maximizes the cost function defined as a normalized correlation between the measured and modeled signals directly in the time domain. The very fast simulated reannealing optimization method is applied to the global search problem. The modeled time signal is obtained using a ray approach. An experiment was carried out in the Mediterranean Sea using a towed source and receiver system. The inversion method is applied to the experimental data and results are found to be consistent with previous frequency-domain analyses using measurements from a towed horizontal array of receivers and measurements on a vertical array.  相似文献   

Galaxy activity in merging binary galaxy clusters     

Ho Seong Hwang †  Myung Gyoon Lee 《Monthly notices of the Royal Astronomical Society》2009,397(4):2111-2122

We present the results of a study of galaxy activity in two merging binary clusters (A168 and A1750) using the Sloan Digital Sky Survey (SDSS) data supplemented with the data in the literature. We have investigated the merger histories of A168 and A1750 by combining the results from a two-body dynamical model and X-ray data. In A168, two subclusters appear to have passed each other and to be coming together from the recent maximum separation. In A1750, two major subclusters appear to have started interaction and to be coming together for the first time. We find an enhanced concentration of the galaxies showing star formation (SF) or active galactic nuclei (AGN) activity in the region between two subclusters in A168, which were possibly triggered by the cluster merger. In A1750, we do not find any galaxies with SF/AGN activity in the region between two subclusters, indicating that two major subclusters are in the early stage of merging.  相似文献   

Modifications of resonant column and torsional shear device for the large strain     

Yoon-Shin Bae  James A. Bay 《Computers and Geotechnics》2009

Conventional RC/TS (resonant column and torsional shear) devices use a specimen with an aspect ratio (height-to-diameter) of 2:1 and this generates a maximum shear strain in the sample of about 1.5% at the maximum rotation of the driving system. The objective of this study is to modify the RC/TS device to generate higher strain amplitude. The modifications include a new base pedestal to overcome the limitations in the travel of the drive system and modification of the coil wiring to increase torque. The effects of the new coil wire on torque in the electromagnetic drive system were evaluated and the application of the modified device was illustrated using sand soil.  相似文献   

A Review on Marine N2 Fixation: Mechanism,Evolution of Methodologies,Rates, and Future Concerns     

Bhavya  P. S.  Min  Jun-Oh  Kim  Min-Seob  Jang  Hyo Keun  Kim  Kwanwoo  Kang  Jae Joong  Lee  Jae Hyung  Lee  Dabin  Jo  Naeun  Kim  Myung Joon  Kim  Yejin  Lee  Junbeom  Lee  Chang Hwa  Bae  Hyeonji  Yoo  Hyeju  Park  Sanghoon  Yun  Mi Sun  Lee  Sang Heon 《Ocean Science Journal》2019,54(4):515-528

Ocean Science Journal - Investigations on marine N2 fixation have gained momentum since 1960s with eventual establishments of relevant methodologies to identify species involved and quantify the...  相似文献