oalib

OALib Journal期刊

ISSN: 2333-9721

费用：99美元

投稿

时间不限

( 2673 )

( 2672 )

( 2208 )

( 2027 )

自定义范围…

匹配条件： “C.-C. Hung” ，找到相关结果约264397条。
列表显示的所有文章，均可免费获取
第1页/共264397条
每页显示 条
The effect of typhoon on particulate organic carbon flux in the southern East China Sea
C.-C. Hung,G.-C. Gong,W.-C. Chou,C.-C. Chung
Biogeosciences Discussions , 2010, DOI: 10.5194/bgd-7-3521-2010
Abstract: Severe tropical storms play an important role in triggering phytoplankton blooms, but the extent to which such storms influence carbon flux from the euphotic zone is unclear. In 2008, typhoon Fengwong provided a unique opportunity to study the in situ biological responses including phytoplankton blooms and particulate organic carbon fluxes associated with a severe storm in the southern East China Sea (SECS). After passage of the typhoon, the sea surface temperature (SST) in the SECS was markedly cooler (~25 to 26 °C) than before typhoon passage (~28 to 29 °C). The POC flux 5 days after passage of the typhoon was 265 ± 14 mg-C m 2 d 1, which was ~1.7-fold that (140–180 mg-C m 2 d 1) recorded during a period (June–August, 2007) when no typhoons occurred. A somewhat smaller but nevertheless significant increase in POC flux (224–265 mg-C m 2 d 1) was detected following typhoon Sinlaku which occurred approximately 1 month after typhoon Fengwong, indicating that typhoon events can increase biogenic carbon flux efficiency in the SECS. Remarkably, phytoplankton uptake accounted for only about 5% of the nitrate injected into the euphotic zone by typhoon Fengwong and it is likely that phytoplankton population growth was presumably constrained by a combination of light limitation and grazing pressure. Modeled estimates of new/export production were remarkably consistent with the average of new and export production following typhoon Fengwong. The same model suggested that during non-typhoon conditions approximately half of the export of organic carbon occurs via convective mixing of dissolved organic carbon, a conclusion consistent with earlier work at comparable latitudes in the open ocean.
Carbonate mineral saturation states in the East China Sea: present conditions and future scenario
W.-C. Chou,G.-C. Gong,C.-C. Hung,Y.-H. Wu
Biogeosciences Discussions , 2013, DOI: 10.5194/bgd-10-5555-2013
Abstract: To assess the impact of rising atmospheric CO2 and eutrophication on the carbonate chemistry of the East China Sea shelf waters, saturation states (Ω) for two important biologically-relevant carbonate minerals, calcite (Ωc) and aragonite (Ωa) were calculated throughout the water column from dissolved inorganic carbon (DIC) and total alkalinity (TA) data collected in spring and summer of 2009. Results show that the highest Ωc (~9.0) and Ωa (~ 5.8) values were found in surface water of the Changjiang plume area in summer, whereas the lowest values (Ωc=~2.7 and Ωa=~1.7) were concurrently observed in the bottom water of the same area. This divergent behavior of saturation states in surface and bottom waters was driven by intensive biological production and strong stratification of the water column. The high rate of phytoplankton production, stimulated by the enormous nutrient discharge from the Changjiang, acts to decrease the ratio of DIC to TA, and thereby increases Ω values. In contrast, remineralization of organic matter in the bottom water acts to increase the DIC to TA ratio, and thus decreases Ω values. The projected result shows that continued increases of atmospheric CO2 under the IS92a emission scenario will decrease Ω values by 40–50% by the end of this century, but both the surface and bottom waters will remain supersaturated with respect to calcite and aragonite. Nevertheless, superimposed on such Ω decrease is increasing eutrophication, which would mitigate or enhance the Ω decline caused by anthropogenic CO2 uptake in surface and bottom waters, respectively. Our simulation reveals that under the combined impact of eutrophication and augmentation of atmospheric CO2, the bottom water of the Changjiang plume area will become undersaturated with respect to aragonite (Ωa=~0.8) by the end of this century, which would threaten the health of the benthic ecosystem.
Behavior and fluxes of particulate organic carbon in the East China Sea
C.-C. Hung,C.-W. Tseng,G.-C. Gong,K.-S. Chen
Biogeosciences Discussions , 2013, DOI: 10.5194/bgd-10-4271-2013
Abstract: To better understand carbon cycling in marginal seas, particulate organic carbon (POC) concentrations, POC fluxes and primary production (PP) were measured in the East China Sea (ECS) in summer 2007. Higher concentrations of POC were observed in the inner shelf and lower POC values were found in the outer shelf. Similar to POC concentrations, elevated uncorrected POC fluxes (720–7300 mg C m 2 d 1) were found in the inner shelf and lower POC fluxes (80–150 mg C m 2 d 1) were in the outer shelf, respectively. PP values (~340–3380 mg C m 2 d 1) had analogous distribution patterns to POC fluxes, while some of PP values were significantly lower than POC fluxes, suggesting that contributions of resuspended particles to POC fluxes need to be appropriately corrected. A vertical mixing model was used to correct effects of bottom sediment resuspension and the corrected POC fluxes ranging from 41 ± 20 to 956 ± 443 mg C m 2 d 1, which were indeed lower than PP values. The results suggest that 49–93% of the POC flux in the ECS might be from the contribution of resuspension of bottom sediments rather than from the actual biogenic carbon sinking flux. While the vertical mixing model is not a perfect model to solve sediment resuspension because it ignores biological degradation of sinking particles, Changjinag plume (or terrestrial) inputs and lateral transport, it makes significant progress in both correcting resuspension problem and in assessing a reasonable quantitative estimate in a marginal sea.
Solar cycle effect on geomagnetic storms caused by interplanetary magnetic clouds
C.-C. Wu,R. P. Lepping
Annales Geophysicae (ANGEO) , 2006,
Abstract: We investigated geomagnetic activity which was induced by interplanetary magnetic clouds during the past four solar cycles, 1965–1998. We have found that the intensity of such geomagnetic storms is more severe in solar maximum than in solar minimum. In addition, we affirm that the average solar wind speed of magnetic clouds is faster in solar maximum than in solar minimum. In this study, we find that solar activity level plays a major role on the intensity of geomagnetic storms. In particular, some new statistical results are found and listed as follows. (1) The intensity of a geomagnetic storm in a solar active period is stronger than in a solar quiet period. (2) The magnitude of negative Bzmin is larger in a solar active period than in a quiet period. (3) Solar wind speed in an active period is faster than in a quiet period. (4) VBsmax in an active period is much larger than in a quiet period. (5) Solar wind parameters, Bzmin, Vmax and VBsmax are correlated well with geomagnetic storm intensity, Dstmin during a solar active period. (6) Solar wind parameters, Bzmin, and VBsmax are not correlated well (very poorly for Vmax) with geomagnetic storm intensity during a solar quiet period. (7) The speed of the solar wind plays a key role in the correlation of solar wind parameters vs. the intensity of a geomagnetic storm. (8) More severe storms with Dstmin≤ 100 nT caused by MCs occurred in the solar active period than in the solar quiet period.
Selection effects in identifying magnetic clouds and the importance of the closest approach parameter
R. P. Lepping,C.-C. Wu
Annales Geophysicae (ANGEO) , 2010,
Abstract: This study is motivated by the unusually low number of magnetic clouds (MCs) that are strictly identified within interplanetary coronal mass ejections (ICMEs), as observed at 1 AU; this is usually estimated to be around 30% or lower. But a looser definition of MCs may significantly increase this percentage. Another motivation is the unexpected shape of the occurrence distribution of the observers' "closest approach distances" (measured from a MC's axis, and called CA) which drops off somewhat rapidly as |CA| (in % of MC radius) approaches 100%, based on earlier studies. We suggest, for various geometrical and physical reasons, that the |CA|-distribution should be somewhere between a uniform one and the one actually observed, and therefore the 30% estimate should be higher. So we ask, When there is a failure to identify a MC within an ICME, is it occasionally due to a large |CA| passage, making MC identification more difficult, i.e., is it due to an event selection effect? In attempting to answer this question we examine WIND data to obtain an accurate distribution of the number of MCs vs. |CA| distance, whether the event is ICME-related or not, where initially a large number of cases (N=98) are considered. This gives a frequence distribution that is far from uniform, confirming earlier studies. This along with the fact that there are many ICME identification-parameters that do not depend on |CA| suggest that, indeed an MC event selection effect may explain at least part of the low ratio of (No. MCs)/(No. ICMEs). We also show that there is an acceptable geometrical and physical consistency in the relationships for both average "normalized" magnetic field intensity change and field direction change vs. |CA| within a MC, suggesting that our estimates of |CA|, BO (magnetic field intensity on the axis), and choice of a proper "cloud coordinate" system (all needed in the analysis) are acceptably accurate. Therefore, the MC fitting model (Lepping et al., 1990) is adequate, on average, for our analysis. However, this selection effect is not likely to completely answer our original question, on the unexpected ratio of MCs to ICMEs, so we must look for other factors, such as peculiarities of CME birth conditions. As a by-product of this analysis, we determine that the first order structural effects within a MC due to its interaction with the solar wind, plus the MC's usual expansion at 1 AU (i.e., the non-force free components of the MC's field) are, on average, weakly dependent on radial distance from the MC's axis; that is, in the outer reaches of a typical MC the non-force free effects show up, but even there they are rather weak. Finally, we show that it is not likely that a MC's size distribution statistically controls the occurrence distribution of the estimated |CA|s.
Quiet-condition variations in the scale height at F2-layer peak at Jicamarca during solar minimum and maximum
C.-C. Lee,B. W. Reinisch
Annales Geophysicae (ANGEO) , 2008,
Abstract: This study is the first attempt to examine the quiet-condition variations in scale height (Hm) near the F2-layer peak in the equatorial ionosphere. The data periods of Hm derived from the Jicamarca ionograms are January-December 1996 and April 1999–March 2000. The results show that the greatest and smallest Hm values are generally at 11:00–12:00 LT and 04:00–05:00 LT, respectively. Additionally, the sunrise peak occurs at 06:00 LT only during solar minimum. The post-sunset peaks in the equinoctial and summer months are more obvious during solar maximum. The Hm difference between solar minimum and maximum are significant from afternoon to midnight. On the other hand, the Hm values during 07:00–10:00 LT for solar minimum are close to those for solar maximum. Furthermore, the correlation of Hm with the critical frequency (foF2) of F2-layer is generally low. In contrast, the correlation between Hm and the peak height (hmF2) of F2-layer is high. For Hm and the thickness parameter (B0) of F2-layer, the correlation between these two parameters is almost perfect.
Nonextensive analysis of crustal seismicity in Taiwan
L. Telesca,C.-C. Chen
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2010, DOI: 10.5194/nhess-10-1293-2010
Abstract: Using the Taiwan Central Weather Bureau earthquake catalogue, the crustal seismicity of Taiwan was analyzed by means of a nonextensive approach. The time span of the analyzed catalogue is from 1 January 1990 to 30 November 2007, and only earthquakes with magnitude M≥2.0 were considered. Our findings reveal that the nonextensive statistics furnishes a very good prediction of the cumulative magnitude distribution of crustal seismicity in Taiwan, even if the aftershocks are removed, indicating that the approach is robust for clustered as well as declustered seismicity.
Simulated radiative forcing from contrails and contrail cirrus
C.-C. Chen,A. Gettelman
Atmospheric Chemistry and Physics Discussions , 2013, DOI: 10.5194/acpd-13-10939-2013
Abstract: A comprehensive general circulation model including ice supersaturation is used to estimate the climate impact of aviation induced contrails. The model uses a realistic aviation emissions inventory for 2006 to initiate contrails, and allows them to evolve consistently with the model hydrologic cycle. The radiative forcing from linear contrails is very sensitive to the diurnal cycle of flights. For linear contrails, including the diurnal cycle of flights reduces the estimated global radiative forcing by 55%, and for contrails cirrus estimates, the global radiative forcing is reduced by 25%. Estimated global radiative forcing from linear contrails is 0.0029±0.00125 W m 2. The instantaneous radiative forcing for contrails is found to exhibit a strong diurnal cycle. The integrated effect of contrail cirrus is much less sensitive to the diurnal cycle of flights. The estimated global radiative forcing from contrail cirrus is 0.012±0.01 W m 2. Over regions with the highest air traffic, the regional effect can be as large as 1 W m 2.
Multimedia Encryption with Joint Randomized Entropy Coding and Rotation in Partitioned Bitstream
Dahua Xie,C.-C. Jay Kuo
EURASIP Journal on Information Security , 2007, DOI: 10.1155/2007/35262
Abstract: This work investigates the problem of efficient multimedia data encryption. A novel methodology is proposed to achieve encryption by controlling certain operations in the data compression process using a secret key. The new encryption approach consists of two cascaded modules. The first one is called randomized entropy coding (REC) while the second one is called rotation in partitioned bitstream (RPB). By leveraging the structure of the entropy coder, the joint REC/RPB encryption scheme incurs extremely low computational and implementation costs. Security analysis shows that the proposed scheme can withstand the ciphertext-only attack as well as the known/chosen plaintext attack. The efficiency and security of the proposed encryption scheme makes it an ideal choice in secure media applications where a large amount of multimedia data has to be encrypted/decrypted in real time.
Characteristics of long-term regional seismicity before the 2008 Wen-Chuan, China, earthquake using pattern informatics and genetic algorithms
H.-C. Li,C.-C. Chen
Natural Hazards and Earth System Sciences (NHESS) & Discussions (NHESSD) , 2011, DOI: 10.5194/nhess-11-1003-2011
Abstract: To understand the generation of the 2008 Wen-chuan, China earthquake, we developed a strategy to objectively identify possible seismic precursors. Based on the pattern informatics (PI) method, the pattern of seismic anomaly was identified by the aid of genetic algorithms (GA) to be highly similar to the spatial distribution of the Wen-chuan earthquake sequence. We found that smaller earthquakes (M < 4.4) showed a linear relationship of Gutenberg-Richter (G-R) distribution. However, the frequency of the intermediate earthquakes (M ≥ 4.4) showed an uplift. This uplift supports the seismic activation hypothesis developed by Rundle et al. (2000b) and is similar to the case of the 1999 Chi-chi, Taiwan earthquake sequence reported by Chen (2003).
第1页/共264397条
每页显示 条


Home
Copyright © 2008-2020 Open Access Library. All rights reserved.