Eruption and emplacement of a laterally extensive, crystal-rich, and pumice-free ignimbrite (the Cretaceous Kusandong Tuff, Korea)     

Y.K. Sohn  M. Son  J.O. Jeong  Y.M. Jeon 《Sedimentary Geology》2009,220(3-4):190

The Cretaceous Kusandong Tuff, Korea, is a thin (1–5 m thick) but laterally extensive (~ 200 km) silicic ignimbrite emplaced in a fluviolacustrine basin adjacent to a continental volcanic arc. The tuff has been used as an excellent key bed because of its great lateral continuity and unique lithology, characterized by the virtual absence of juvenile clasts and an abundance of quartz and feldspar crystals (up to 55–73 vol.%). The tuff is mostly massive and ungraded and locally shows crude internal layering, basal inverse grading and near-top normal grading of crystals, either erosional or non-erosional lower surfaces, and flat-lying to imbricated grain fabrics. Fragile intraformational clasts of mudstone and tuff are also included. These features provide only ambiguous information on the properties of the responsible pyroclastic density currents: i.e. whether they were dense and laminar or dilute and turbulent. The overall lateral continuity and sheet-like geometry of the tuff suggests, however, that the transport system of the currents was highly expanded, dilute, and turbulent. A plug-flow or slab-flow model cannot explain the origin of crude internal layering, imbricated grain fabrics, and the high crystal content, which is most likely the result of vigorous sorting processes within a dilute and turbulent current. Features indicative of deposition from a dense and laminar transporting medium are locally present, suggesting that a dense and laminar depositional system could develop locally at the base of the dilute and turbulent transport system. The virtual absence of juvenile clasts in the tuff is interpreted to be due to rapid ascent, sudden decompression, and full fragmentation of silicic magma into fine glass shards and crystals. Scarcity of basement-derived accidental components together with the absence of pumiceous fallout deposits beneath the tuff is interpreted to be due to shallow-level fragmentation of magma followed by immediate generation of pyroclastic density currents from shallow-level blasts at the onset of eruption. The eruption occurred through multiple vent sites in a short period of time, producing a seemingly single but actually composite ignimbrite unit. Such an eruption was probably possible because of a regional tectonic event within the basin or in its vicinity. It is proposed that a composite ignimbrite with the characteristics of the Kusandong Tuff can be an exemplary product of syntectonic volcanism that can provide an insight into the interpretation of structural and stratigraphic evolution of a sedimentary basin.  相似文献   

Seasonal drivers and patterns of sediment temperatures in a New England salt marsh     

Julia A. Guimond  Barret L. Kurylyk  Robert A. Sohn 《水文研究》2024,38(2):e15100

Salt marshes are globally important ecosystems and thus their resilience to climate change holds societal importance. To date, studies addressing salt marsh responses to climate change have focused on sea-level rise and biogeochemical feedbacks with increasing inundation. Less is known about how salt marsh sediment temperatures, which impact physical, biological, and chemical ecosystem processes, will respond to climate change. In this study, we present multi-depth sediment temperature and porewater level data from low-, mid-, and high-marsh sites at a New England salt marsh for a 1-year period and investigate how salt marsh sediment temperatures respond to atmospheric and oceanic forcing. We use spectral analyses to identify the frequencies at which sediment temperatures vary and link the temperature variations to specific forcing mechanisms. We find that all sites across the marsh responded to air temperature with roughly equal amplitude whereas the responses to radiative heating and ocean tides varied spatially. The high-marsh site is more sensitive to radiative heating than the mid- and low-marsh sites. The low-marsh is affected by tidal processes and inundation whereas the high- and mid-marsh sites are not. In addition, we find that the bulk thermal diffusivity of the saturated sediments decreases with distance from the tidal channel. These factors contribute to considerable temporal and spatial variability in sediment temperatures with elevation, distance from the tidal channel, and time of year (season) being most important.  相似文献   

Color gradients in four king type globular clusters: NGC 2298, NGC 6402, NGC 6934, and NGC 7089     

Young-Jong Sohn  Yong-Ik Byun  Mun-Suk Chun 《Astrophysics and Space Science》1996,243(2):379-392

We present CCD surface photometry for four globular clusters: NGC 2298, NGC 6402, NGC 6934 and NGC 7089. Our photometry was aimed at the central 3 arcmin region in each cluster. We show that the surface brightness distributions of these clusters are well described by the isothermal King (1966) models. Our color analysis shows that NGC 7089 exhibits a remarkable color gradient in which the central region is bluer than the outer parts by the amplitude inB-V 0.1 mag/. Color gradients have also been detected in the central regions of NGC 6402 and NGC 6934, although the variation does not extend to outer part. No gradient has been detected in NGC 2298. Similar color gradients have been previsouly observed exclusively in highly concentrated systems classified as post core collapse clusters.  相似文献   

The urban density function and its application: cross-sectional approach     

Sohn HK 《The Indonesian journal of geography》1979,9(37):13-31

Using population census data for the years 1947-1971, the author analyzes the relationship between changes in urban density and population growth in three major coastal urban centers in Queensland, Australia. "Changes in density patterns over time are examined in terms of the empirical exponential density gradient models which emphasise the significance of the distance from the CBD (Central Business District), and a projection of residential population in the centres is made for the year 1990."  相似文献   

Long-runout pyroclastic surge on a Cretaceous alluvial plain, Republic of Korea     

Y. K. Sohn  J. O. Jeong  M. Son 《地学学报》2005,17(1):13-24

Pyroclastic surge is a dilute and turbulent flow of volcanic gas and tephra that is commonly generated during explosive volcanic eruptions and can threaten lives along its flow paths. Assessing its travel distance and delineating future volcanic hazards have therefore been major concerns of volcanologists. Historical eruptions show that most pyroclastic surges travel a few tens of kilometres or less from their sources. Aeolian or aquagene processes have therefore been evoked for the emplacement of supposed surge deposits much beyond this distance. Here we show that a Cretaceous tuff bed in Korea was emplaced by an exceptionally powerful pyroclastic surge that flowed as far as the most powerful pyroclastic flows that formed the low-aspect-ratio ignimbrites (LARI). This has significant implications for interpreting ancient volcanic eruptions and delineating volcanic hazards by pyroclastic surges, and casts intriguing questions on the eruption dynamics and physics of long-runout pyroclastic surges and their distinction from LARI-forming pyroclastic flows.  相似文献   

Physical explanation of the weakened brightness temperature difference signal over the yellow sea during a dust event: Case study for March 15–16, 2009     

Byung-Ju Sohn  Hyoung-Wook Chun  Hwan-Jin Song  Young-Chan Noh  Sang-Moo Lee  Sang-Sam Lee  Youngsin Chun 《Asia-Pacific Journal of Atmospheric Sciences》2013,49(1):41-48

This paper attempts to explain the cause of weakening or disappearing brightness temperature difference (BTD) signatures, in particular, over the Yellow Sea during the March 15–16, 2009 dust event. Using a simple correction approach that removes the effects of emissivity difference and water vapor effect difference, we confirmed that the weakening or disappearing BTD signatures noted over the Yellow Sea are largely due to the spectral emissivity contrast between land and ocean. The weakening or disappearing dust is hypothesized to be pronounced when the dust loading is weak because of the surface contribution to the top of atmosphere radiance, and that it is mainly due to the difference in spectral emissivity over the window band between land and ocean. It is further suggested that water vapor may be considered as a correction factor in spite of its smaller contribution.  相似文献   

Characteristics of sea surface temperature retrieved from MTSAT-1R and in-situ data     

Mee-Ja Kim  Mi-Lim Ou  Eun-Ha Sohn  Yoonjae Kim 《Asia-Pacific Journal of Atmospheric Sciences》2011,47(5):421-427

Multi-channel sea surface temperature (MCSST) data were retrieved from the Japanese geostationary satellite, MTSAT-1R, for East Asia in western North Pacific. The coefficients used to calculate the MCSST data were estimated by assuming a linear relationship between the brightness temperatures obtained from the satellite and the in-situ buoy SST. It is important to remove cloud contamination pixels to retrieve meaningful information from infrared data. Therefore, the cloud detection algorithm was improved by using a 10-day maximum or minimum composite map for infrared and visible channels. The RMSE of the MCSST in comparison with the two-year buoy SST was about 0.89oC. The error was the largest at mid-latitudes in summer. Additionally, the error between the two SSTs showed that diurnal variation had a positive bias during daytime and a negative bias during nighttime. Furthermore, in 2007, both SSTs showed seasonal and spatial diurnal variation. The magnitude of the daily variation in the MCSST was two times larger than that in the buoy SST, and this was attributed to diurnal heating with a weak surface wind speed.  相似文献   

Intercomparison of height assignment methods for opaque clouds over the tropics   总被引：1，自引：0，他引：1  

Eun-Han Kwon  Byung-Ju Sohn  Johannes Schmetz  Philip Watts 《Asia-Pacific Journal of Atmospheric Sciences》2010,46(1):11-19

Several methods of determining the height of opaque clouds over the tropics were compared using geostationary satellite measurements. The possible use of ozone channel measurements around the 9.7-μm ozone absorption band was examined in conjunction with the infrared window (IRW; 10.8 μm), H₂O (6.3 μm), and CO₂ (13.4 μm) channels, which are generally used for the assignment of cloud heights. Cloud top heights were retrieved from Meteosat-8 measurements with the aid of radiative transfer calculations using reanalysis data from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) as inputs. By using cloud top heights from collocated CloudSat observations as a reference, cloud top heights were determined from the one-channel radiance, two-channel brightness temperature difference (BTD), and two-channel radiance ratio methods, and the respective results were then compared for clouds with geometrical thicknesses of > 4 km. Overall, the retrievals from the CO₂-IRW ratio and O₃-CO₂ ratio methods are in substantial agreement with CloudSat observations, while the other methods either underestimate cloud top heights or demonstrate a lower ratio of successful height assignment. The O₃-CO₂ ratio method appears to be less practical than the CO₂-IRW ratio method because it requires two absorption channels. Our comparison also shows that the BTD between the ozone and IRW channels yields information that is similar to that of the IRW channel alone. It further shows that the O₃-IRW combination is not appropriate for the two-channel radiance ratio method. These results suggest that the inclusion of the ozone channel in BTD and ratio methods may not offer any significant improvement in convective cloud height retrieval over the tropics. In conclusion, the CO₂-IRW ratio method appears to provide the most accurate retrievals for opaque clouds.  相似文献   

Rational function model-based image matching for digital elevation models   总被引：1，自引：0，他引：1  

Hong-Gyoo  Sohn  Choung-Hwan  Park  Hoon  Chang 《The Photogrammetric Record》2005,20(112):366-383

This paper presents an image matching technique for IKONOS satellite imagery based on rational function models (RFMs). This algorithm adopts the object-space approach and reduces the search space to within the confined line-shaped area called the piecewise matching line (PML). Also, the detailed procedure of generating 3D surface information using the RFM coefficients (RFCs) is introduced to illustrate an end-user's point of view. The final digital elevation model (DEM) generated using the proposed scheme shows a mean error of 2·2 m and rmse of 3·8 m compared with that from a 1:5000 scale digital map.  相似文献   

Seasonally Varying Reference Atmospheres for East Asia     

Byung-Ju SOHN  Geun-Hyeok RYU 《大气科学进展》2007,24(2):181-190

  相似文献