A linear projection for the timing of unprecedented climate in Korea     

Ho-Jeong Shin  Chan Joo Jang  Il-Ung Chung 《Asia-Pacific Journal of Atmospheric Sciences》2017,53(4):411-419

Recently we have had abnormal weather events worldwide that are attributed by climate scientists to the global warming induced by human activities. If the global warming continues in the future and such events occur more frequently and someday become normal, we will have an unprecedented climate. This study intends to answer when we will have an unprecedented warm climate, focusing more on the regional characteristics of the timing of unprecedented climate. Using an in-situ observational data from weather stations of annual-mean surface air temperature in Korea from 1973 to 2015, we estimate a timing of unprecedented climate with a linear regression method. Based on the in-situ data with statistically significant warming trends at 95% confidence level, an unprecedented climate in Korea is projected to occur first in Cheongju by 2043 and last in Haenam by 2168. This 125-year gap in the timing indicates that a regional difference in timing of unprecedented climate is considerably large in Korea. Despite the high sensitivity of linear estimation to the data period and resolution, our findings on the large regional difference in timing of unprecedented climate can give an insight into making policies for climate change mitigation and adaptation, not only for the central government but for provincial governments.  相似文献   

A western North Pacific tropical cyclone intensity prediction scheme          下载免费PDF全文

Peiyan Chen  Hui Yu  Johnny C. L. Chan 《Acta Meteorologica Sinica》2011,25(5):611-624

A western North Pacific tropical cyclone (TC) intensity prediction scheme (WIPS) is developed based on TC samples from 1996 to 2002 using the stepwise regression technique, with the western North Pacific divided into three sub-regions: the region near the coast of East China (ECR), the South China Sea region (SCR), and the far oceanic region (FOR). Only the TCs with maximum sustained surface wind speed greater than 17.2 m s⁻¹ are used in the scheme. Potential predictors include the climatology and persistence factors, synoptic environmental conditions, potential intensity of a TC and proximity of a TC to land. Variances explained by the selected predictors suggest that the potential intensity of a TC and the proximity of a TC to land are significant in almost all the forecast equations. Other important predictors include vertical wind shear in ECR, 500-hPa geopotential height anomaly at the TC center, zonal component of TC translation speed in SCR, intensity change of TC 12 or 24 h prior to initial time, and the longitude of TC center in FOR.  相似文献   

High-resolution subtropical summer precipitation derived from dynamical downscaling of the NCEP/DOE reanalysis: how much small-scale information is added by a regional model?     

Young-Kwon Lim  Lydia B. Stefanova  Steven C. Chan  Siegfried D. Schubert  James J. O��Brien 《Climate Dynamics》2011,37(5-6):1061-1080

This study assesses the regional-scale summer precipitation produced by the dynamical downscaling of analyzed large-scale fields. The main goal of this study is to investigate how much the regional model adds smaller scale precipitation information that the large-scale fields do not resolve. The modeling region for this study covers the southeastern United States (Florida, Georgia, Alabama, South Carolina, and North Carolina) where the summer climate is subtropical in nature, with a heavy influence of regional-scale convection. The coarse resolution (2.5° latitude/longitude) large-scale atmospheric variables from the National Center for Environmental Prediction (NCEP)/DOE reanalysis (R2) are downscaled using the NCEP/Environmental Climate Prediction Center regional spectral model (RSM) to produce precipitation at 20?km resolution for 16 summer seasons (1990?C2005). The RSM produces realistic details in the regional summer precipitation at 20?km resolution. Compared to R2, the RSM-produced monthly precipitation shows better agreement with observations. There is a reduced wet bias and a more realistic spatial pattern of the precipitation climatology compared with the interpolated R2 values. The root mean square errors of the monthly R2 precipitation are reduced over 93% (1,697) of all the grid points in the five states (1,821). The temporal correlation also improves over 92% (1,675) of all grid points such that the domain-averaged correlation increases from 0.38 (R2) to 0.55 (RSM). The RSM accurately reproduces the first two observed eigenmodes, compared with the R2 product for which the second mode is not properly reproduced. The spatial patterns for wet versus dry summer years are also successfully simulated in RSM. For shorter time scales, the RSM resolves heavy rainfall events and their frequency better than R2. Correlation and categorical classification (above/near/below average) for the monthly frequency of heavy precipitation days is also significantly improved by the RSM.  相似文献   

Numerical simulation of nonlinear dispersive waves propagating over a submerged bar by IB–VOF model     

Linwei Shen  Eng-Soon Chan 《Ocean Engineering》2011,38(2-3):319-328

It is a good test for a numerical model to simulate progressive waves propagating over a submerged bar with a relatively high ratio of slopes. In this paper, the combined IB–VOF model is used to predict nonlinear dispersive waves propagating over a submerged bar with both slopes of 1:2. The predicted free surface elevations are compared with the experimental data and numerical results presented by other researchers. The comparison shows that the IB–VOF model is able to provide satisfactory wave profiles in the shallow water with strong nonlinear effects and in the wave transmitted region with strong wave dispersion in particular. Moreover, the wave evolution behind the submerged bar is described in detail, including the spatial wave profile modulation, spectral analysis of the time-series waves, flow velocity and pressure fields, and kinetic energy distribution. The effect of fluid viscosity on the numerical simulations is also studied, and it is found that the effect on the wave evolution considered in this paper is not significant. Finally, the hydrodynamic force acting on the bar is calculated using the IB–VOF model.  相似文献   

U–Pb and Hf isotopic study of zircons from migmatised amphibolites in the Cathaysia Block: Implications for the early Paleozoic peak tectonothermal event in Southeastern China     

Long-Ming Li  Min Sun  Yuejun Wang  Guangfu Xing  Guochun Zhao  Shoufa Lin  Xiaoping Xia  Lungsang Chan  Feifei Zhang  Jean Wong 《Gondwana Research》2011,19(1):191-201

Amphibolites occur in a number of localities in the Cathaysia Block, some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings. Four migmatised amphibolites were collected from Jiangxi and Fujian Provinces. Cathodo-luminescence images of zircons extracted from the representative amphibolites show unzoned or sector-zoned structure. LA-ICP-MS analysis indicates that most zircons have high Th/U ratios and yield U–Pb zircon ages of 446 ± 5, 435 ± 2, 434 ± 4 and 423 ± 2 Ma, respectively. Lu–Hf isotopic analysis on these zircons gives Hf model ages ranging from 900 to 1200 Ma. Based on lithological observations and previously published geochronological data, we interpret that these U–Pb ages record an important tectonothermal event that led to the migmatization. This early Paleozoic (Caledonian) tectonothermal event in the Southeastern China has a great tectonic implication for the evolutionary history of the Cathaysia Block.  相似文献   

An empirical model of subcritical bedform migration     

Chan‐Yi Martin Lin  Jeremy G. Venditti 《Sedimentology》2013,60(7):1786-1799

The ability to predict bedform migration in rivers is critical for estimating bed material load, yet there is no relation for predicting bedform migration (downstream translation) that covers the full range of conditions under which subcritical bedforms develop. Here, the relation between bedform migration rates and transport stage is explored using a field and several flume data sets. Transport stage is defined as the non‐dimensional Shields stress divided by its value at the threshold for sediment entrainment. Statistically significant positive correlations between both ripple and dune migration rates and transport stage are found. Stratification of the data by the flow depth to grain‐size ratio improved the amount of variability in migration rates that was explained by transport stage to ca 70%. As transport stage increases for a given depth to grain‐size ratio, migration rates increase. For a given transport stage, the migration rate increases as the flow depth to grain‐size ratio gets smaller. In coarser sediment, bedforms move faster than in finer sediment at the same transport stage. Normalization of dune migration rates by the settling velocity of bed sediment partially collapses the data. Given the large amount of variability that arises from combining data sets from different sources, using different equipment, the partial collapse is remarkable and warrants further testing in the laboratory and field.  相似文献   

Shaping the relation between the mass of supermassive black holes and the velocity dispersion of galactic bulges     

M. H. Chan 《Astrophysics and Space Science》2013,345(1):195-198

I use the fact that the radiation emitted by the accretion disk of supermassive black hole can heat up the surrounding gas in the protogalaxy to achieve hydrostatic equilibrium during the galaxy formation. The correlation between the black hole mass M _BH and velocity dispersion σ thus naturally arises. The result generally agrees with empirical fittings from observational data, even with M _BH ≤10⁶ M _⊙. This model provides a clear picture on how the properties of the galactic supermassive black holes are connected with the kinetic properties of the galactic bulges.  相似文献   

Effect of prolonged hypoxia on food consumption, respiration, growth and reproduction in marine scavenging gastropod Nassarius festivus     

Cheung SG  Chan HY  Liu CC  Shin PK 《Marine pollution bulletin》2008,57(6-12):280-286

The effects of prolonged exposure to reduced oxygen levels (3.0 and 1.5 mg O(2)l(-1)) on marine scavenging gastropods Nassarius festivus were studied for 8 weeks. The percentages of individuals engaged in feeding and amount of food consumed were reduced as oxygen level decreased; absorption efficiency, however, did not vary significantly with oxygen level. Oxygen consumption rates and specific oxygen consumption rates were lower at reduced oxygen levels. Reproduction occurred at all oxygen levels with less egg capsules being produced at lower oxygen levels. Egg size and number of eggs per capsule, however, were not significantly affected by oxygen level. The increase in shell length was 12%, 6% and 5% at 6.0 mgO(2)l(-1) (normoxia), 3.0 mgO(2)l(-1) and 1.5 mgO(2)l(-1), respectively. At the end of the experiment, the amount of energy allocated to growth and reproduction decreased at reduced oxygen levels with values obtained at 3.0 mgO(2)l(-1) and 1.5 mgO(2)l(-1) being 48% and 70% lower than those at 6.0 mgO(2)l(-1). At all oxygen levels, most of the accumulated energy was allocated to shell growth and reproduction, and the amount allocated to somatic growth was relatively insignificant. The reduction in energy allocated to reproduction was greater than that to shell growth as the oxygen level was reduced, indicating a strategic energy allocation of marine scavengers under stressful conditions to enhance survival.  相似文献   

Seasonal changes in imposex and tissue burden of butyltin compounds in Thais clavigera populations along the coastal area of Mirs Bay, China     

Ka Ming Chan  Kenneth Mei Yee Leung  Kwai Chung Cheung  Ming Hung Wong  Jian-Wen Qiu   《Marine pollution bulletin》2008,57(6-12):645

We assessed the current status of tributyltin (TBT) contamination of Thais clavigera (Gastropoda) along the coastal area of Mirs Bay, China for the first time. The snail samples were collected from 10 different sites in the summer (June) and winter (December) of 2006, respectively. They were analyzed for imposex status, i.e. relative penis size index (RPSI) and vas deferens sequence index (VDSI), followed by quantification of butyltins in their tissues. Most of the collected females suffered from imposex, but the level of butyltin contamination varied with the distance from Yantian Port, which is currently the fourth busiest container port in the world. The tissue concentration of TBT varied with season. For a particular site, the winter samples in general contained much higher concentration of TBT than the summer samples. RPSI, VDSI and organotin concentrations were higher in T. clavigera collected from sites closer to the Port, such as the Seafood Street and Kat O. Both RPSI and VDSI were positively correlated with the tissue burden of tributyltin. VDSI exhibited little seasonal variability, whereas RPSI showed marked seasonal variability, with lower values in the summer samples. The current results will serve as an important reference for long-term monitoring of butyltin contamination in this area.  相似文献   

Lithium isotope systematics of lavas from the Cook–Austral Islands: Constraints on the origin of HIMU mantle     

Lui-Heung Chan  John C. Lassiter  Erik H. Hauri  Stanley R. Hart  Jerzy Blusztajn 《Earth and Planetary Science Letters》2009,277(3-4):433-442

Radiogenic isotope variations in lavas from the Cook–Austral volcanic chain have delineated three distinct mantle sources: a HIMU component, a depleted component (DM), and an enriched component (EM). To better constrain the mantle sources for South Pacific hot spot volcanism, we determined lithium isotopic compositions of lavas from Raivavae, Rapa, Mangaia and Tubuai of the volcanic chain. The study includes whole rock and mineral analyses. In general, δ⁷Li of most olivines resemble bulk rock composition whereas clinopyroxenes are variably lighter. This implies that clinopyroxene is more susceptible to diffusion-induced fractionation, in agreement with previous studies. Olivine δ⁷Li values span a narrower range than whole rock values, and do not extend to the very heavy compositions previously reported in HIMU bulk lavas. This discrepancy likely reflects alteration of bulk lavas, and suggests that Li-isotope analyses of bulk lavas should be interpreted with caution. Olivines from HIMU lavas have heavy δ⁷Li values (up to 6.2‰), and extend beyond the range reported for fresh MORB. Correlations between Li-isotopes and radiogenic isotopes suggest that the heavy δ⁷Li values in HIMU olivines are a source characteristic and not the result of post-magmatic alteration. Although the Li-isotope composition of recycled, dehydrated oceanic crust is currently under debate, our results suggest that HIMU lavas derive from a source containing recycled dehydrated oceanic crust, and that the “heavy” Li-isotope signature of altered oceanic crust is partially preserved during passage through the subduction factory.  相似文献