排序方式： 共有93条查询结果，搜索用时 849 毫秒
41.
《Marine pollution bulletin》2012,64(5-12):523-527
Concentrations of trace metals (Zn, Cr, Cu, V, Cd and Pb), total organic carbon (TOC), black carbon (BC) and their granulometry were examined in 25 surface sediment samples from the northern Bering Sea, Chukchi Sea and adjacent areas. Trace metal concentrations in the sediments varied from 21.06–168.21 mg kg−1 for Zn, 8.91–46.94 mg kg−1 for Cr, 2.69–49.39 mg kg−1 for Cu, 32.46–185.54 mg kg−1 for V, 0.09–0.92 mg kg−1 for Cd, and 0.95–15.25 mg kg−1 for Pb. The geoaccumulation index (Igeo) indicated that trace metal contamination (Zn and Cd) existed in some stations of the study area. The distribution of grain size plays an important role in influencing the distribution of trace metals (Zn, Cr, Cu, V, and Pb) in sediments from the Chukchi Sea and adjacent areas. 相似文献
42.
Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies 总被引：2，自引：1，他引：1
Jason C. Furtado Emanuele Di Lorenzo Bruce T. Anderson Niklas Schneider 《Climate Dynamics》2012,39(12):2833-2846
The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Ni?o events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7–10?years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7?years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Ni?o-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Ni?o, the Aleutian Low, and the Pacific Decadal Oscillation). 相似文献
43.
《Geochimica et cosmochimica acta》1999,63(11-12):1853-1863
The oxidation states of Ni, Co, Mn, Cr, V and Si in magnesiowüstite have been determined in metal-oxide distribution experiments using a multi anvil apparatus at 9 and 18 GPa and 2200°C as a function of oxygen fugacity. Despite limitations to control oxygen fugacity by applying conventional buffering methods in high pressure experiments, a wide range of redox-conditions (3 log bar units) has been imposed to the metal-oxide partitioning experiments by varying the Si/O ratio of the starting material. The oxygen fugacity was calculated according to the Fe-FeO equilibrium between the run products. The ability to impose different oxygen fugacities by varying the starting material is confirmed by the large variation of element partitioning coefficients obtained at constant pressure and temperature. The calculated valences at both pressures investigated are divalent for Co, Mn, V and 4+ for Si. The results for Cr (∼2.5+) and Ni (∼1.5+) indicate non-ideal mixing of Ni and Cr in at least one of the product phases. Because the application of 1 bar activity coefficients for Ni and Cr in metal alloys does not change these valences, non-ideal mixing in magnesiowüstite or significantly larger non-ideal mixing properties of Ni and Cr in metal alloys at high pressure are likely to be responsible for the apparent valences. Omitting such non-ideal mixing properties when extrapolating high-pressure element partitioning data may be significant. The elements Cr, V and Mn become siderophile (DMmet/ox > 1) at 9–18 GPa and 2200°C at oxygen fugacities below IW-2.7 to IW-3.7. Considering, in addition, the influence of temperature, the depletion of Cr, Mn and V in the Earth’s mantle may be due, at least partly, to siderophile behavior at high pressure and temperature. 相似文献
44.
We explored the variability of the Egyptian shelf zone circulation connected to atmospheric forcing by means of a numerical simulation of the general circulation. A high resolution model grid was used at 1/60° horizontal resolution and 25 sigma layers. The simulation was carried out using the most recent version of the Princeton Ocean Model (POM). The initialised model was run the whole year of 2006 using the analysis forcing data for the same year obtained from ECMWF and MFS (Mediterranean Forecasting System, Pinardi et al., 2003). The model skills were evaluated by means of the root mean square error (RMSE) and correlations. The Egyptian Shelf Model (EGYSHM) simulation suggests the presence of an Egyptian Shelf Slope Current (ESSC), which is flowing eastward at different depths in the domain. We found that the maximum velocity of the ESSC [0.25 m/s] is located near the continental slope during the summer time, while in winter the velocity of ESSC is weaker [0.12 m/s] in the same location. The ESSC appears to be directly affected by Mersa-Matruh gyre system. EGYSHM reproduced the main region circulation patterns, especially after adding the Nile River outflow. We found that wind stress is crucial to force the circulation of the Egyptian shelf zone. EGYSHM SST was significantly correlated to satellite SST in all months at a 95% confidence limit, with a maximum of 0.9743 which was obtained in May 2006. The RMSE between EGYSHM and Argo floats salinity data was about 0.09. We compared our results with satellite altimetry to verify the positions and shapes of mesoscale features. 相似文献
45.
Zhao Kai Zhao Haikun Raga Graciela B. Yoshida Ryuji Wang Weiqiang Klotzbach Philip J. 《Climate Dynamics》2021,56(1-2):515-535
Climate Dynamics - This study examines extended boreal summer (May–October) tropical cyclogenesis events (TCGEs) associated with large-scale flow patterns (LFPs) over the western North... 相似文献
46.
Latent Heat Flux (LHF) and Sensible Heat Flux (SHF) are the two important parameters in air-sea interactions and hence have significant implications for any coupled ocean-atmospheric model. These two fluxes are conventionally computed from met-ocean parameters using bulk aerodynamic formulations; or the Coupled Ocean Atmosphere Response Experiment (COARE) bulk flux algorithms. Here COARE 3.5 algorithm is used to estimate the heat flux from two Ocean Moored Buoy Network for northern Indian Ocean (OMNI) buoy met-ocean observations in Arabian Sea (AS) and the Bay of Bengal (BoB). The AS and BoB are two ocean basins which are situated in same latitudinal range, but experience drastically differing in their met-ocean conditions, especially during the monsoon seasons. In this study, we have computed and compared the LHF and SHF at two different buoy locations in the AS and BoB and analysed their variability during three different seasons from November 2012 to September 2013. Additionally, 20 years (1998–2017) of Objectively Analysed (OA) Flux data sets collocated with the OMNI buoy locations were also utilised to the analyse the long period seasonal variabilities. The flux terms show strong seasonal variability with several peaks during the monsoon seasons in both the ocean basins. LHF varies directly with wind speed (WS) and inversely with relative humidity (RH). The correlation of LHF with WS is greater than 0.7 and RH is nearly -0.6 with few exceptions during pre-monsoon season in the AS and southwest monsoon in the BoB. However, SHF is less correlated with WS (∼0.3 to 0.5). The difference of sea surface temperature and air temperature (denoted as SST-AT) plays a significant role in determining SHF with a correlation greater than 0.6 in both the basins. 相似文献
47.
Indian Ocean Dipole (IOD) and Equatorial Indian Ocean oscillation (EQUINOO) are important climatic system oscillation events in the Indian Ocean region that affects the Indian summer monsoon rainfall (ISMR). The prime focus of this study is to deliberate the influence of these events on ISMR and an attempt has been made to predict these events for future time scales using a Long short term memory (LSTM) deep learning model. LSTM is a special kind of recurrent neural network (RNN) which specializes in learning long-term dependencies and extracting important features. The features learnt by the model is then ranked using correlational analysis (linear and nonlinear). This approach helps in selecting decisive and imperative set of relevant predictors, which can be employed to predict IOD and EQUINOO. Nonlinear correlational identified predictors are found to forecast with greater precision as to their linear counterparts. The model-calibrated correlation coefficient for IOD and for EQUNIOO was 0.90 and 0.88 respectively at a lead of 5 months. Our proposed model was observed to work at par with the other existing models in terms of various statistical evaluation measures. 相似文献
48.
《Deep Sea Research Part II: Topical Studies in Oceanography》2009,56(17):1274-1289
The role of mesozooplankton as consumers and transformers of primary and secondary production in the Beaufort and Chukchi Seas was examined during four cruises in spring and summer of both 2002 and 2004 as part of the western Arctic Shelf–Basin Interactions (SBI) program. Forty-seven grazing experiments using dominant mesozooplankton species and life stages were conducted at locations across the shelf, slope, and basin of the Chukchi and Beaufort Seas to measure feeding rates on both chlorophyll and microzooplankton and to determine mesozooplankton prey preferences.Mesozooplankton biomass was at all times dominated by life stages of four copepod taxa: Calanus glacialis, Calanus hyperboreus, Metridia longa, and Pseudocalanus spp. Significant interannual, seasonal, regional, between species and within species differences in grazing rates were observed. Overall, the dominant zooplankton exhibited typical feeding behavior in response to chlorophyll concentration that could be modeled using species and life-stage specific Ivlev functions. Microzooplankton were preferred prey at almost all times, with the strength of the preference positively related to the proportion of microzooplankton prey availability. Average mesozooplankton grazing impacts on both chlorophyll standing stock (0.6±0.5% d−1 in spring, 5.1±6.3% d−1 in summer) and primary production (12.8±11.8% d−1 in spring, 27.6±24.5% d−1 in summer) were quite low and varied between shelf, slope, and basin. Coincident microzooplankton grazing experiments [Sherr, E.B., Sherr, B.F., Hartz, A.J., 2009. Microzooplankton grazing impact in the Western Arctic Ocean. Deep-Sea Research II] were conducted at most stations. Together, microzooplankton–mesozooplankton grazing consumed only 44% of the total water-column primary production, leaving more than half directly available for local export to the benthos or for offshore transport into the adjacent basin. 相似文献
49.
The Asian summer monsoon: an intercomparison of CMIP5 vs. CMIP3 simulations of the late 20th century 总被引：4，自引：0，他引：4
K. R. Sperber H. Annamalai I.-S. Kang A. Kitoh A. Moise A. Turner B. Wang T. Zhou 《Climate Dynamics》2013,41(9-10):2711-2744
The boreal summer Asian monsoon has been evaluated in 25 Coupled Model Intercomparison Project-5 (CMIP5) and 22 CMIP3 GCM simulations of the late twentieth Century. Diagnostics and skill metrics have been calculated to assess the time-mean, climatological annual cycle, interannual variability, and intraseasonal variability. Progress has been made in modeling these aspects of the monsoon, though there is no single model that best represents all of these aspects of the monsoon. The CMIP5 multi-model mean (MMM) is more skillful than the CMIP3 MMM for all diagnostics in terms of the skill of simulating pattern correlations with respect to observations. Additionally, for rainfall/convection the MMM outperforms the individual models for the time mean, the interannual variability of the East Asian monsoon, and intraseasonal variability. The pattern correlation of the time (pentad) of monsoon peak and withdrawal is better simulated than that of monsoon onset. The onset of the monsoon over India is typically too late in the models. The extension of the monsoon over eastern China, Korea, and Japan is underestimated, while it is overestimated over the subtropical western/central Pacific Ocean. The anti-correlation between anomalies of all-India rainfall and Niño3.4 sea surface temperature is overly strong in CMIP3 and typically too weak in CMIP5. For both the ENSO-monsoon teleconnection and the East Asian zonal wind-rainfall teleconnection, the MMM interannual rainfall anomalies are weak compared to observations. Though simulation of intraseasonal variability remains problematic, several models show improved skill at representing the northward propagation of convection and the development of the tilted band of convection that extends from India to the equatorial west Pacific. The MMM also well represents the space–time evolution of intraseasonal outgoing longwave radiation anomalies. Caution is necessary when using GPCP and CMAP rainfall to validate (1) the time-mean rainfall, as there are systematic differences over ocean and land between these two data sets, and (2) the timing of monsoon withdrawal over India, where the smooth southward progression seen in India Meteorological Department data is better realized in CMAP data compared to GPCP data. 相似文献
50.
By analyzing NCEP-NCAR reanalysis daily data for 1979–2016, the modulation by Madden-Julian Oscillation (MJO) of the wintertime surface air temperature (SAT) over high latitude is examined. The real-time multivariate MJO (RMM) index, which divides the MJO into eight phases, is used. It is found that a significantly negative SAT anomaly over the northern high latitude region of (180°–60 °W, 60°–90 °N) lags the MJO convection for 1∼2 weeks in phase 3, in which the enhanced convective activity exists over the Indian Ocean. While a significantly positive SAT anomaly appears over the same region following the MJO phase 7, as the tropical heating shows an opposite sign. Analysis of the anomalous circulation indicates that the observed SAT signal is probably a result of the northeastward propagating Rossby wave train triggered by MJO-related tropical forcing through Rossby wave energy dispersion. By using an anomalous atmospheric general circulation model (AGCM), the significant effect of tropical forcing on organizing the extratropical circulation anomaly is confirmed. Analysis of a temperature tendency equation further reveals that the intraseasonal SAT anomaly is primarily attributed to the advection of the mean temperature by the wind anomaly associated with the anomalous circulation of the MJO-related variability. 相似文献