排序方式： 共有8条查询结果，搜索用时 15 毫秒
1
1.
The Late Cretaceous deposits of the continental Tremp Formation in the Vallcebre Syncline (South-eastern Pyrenees) provide an extensive egg record of dinosaurs. The parataxonomical study and analysis of multiple eggshell samples, the precise stratigraphical control of several sections and the time calibration of the abundant egg levels enable the establishment of a robust oospecies succession. The successive occurrence of three megaloolithid oospecies (Megaloolithus siruguei-Megaloolithus mamillare-Megaloolithus sp.) in the Early and Late Maastrichtian is well correlated with the magnetic polarity time scale throughout the chron 31. The replacement of Megaloolithus siruguei with Megaloolithus mamillare occurs around the reversal of chrons 31r-31n. A comparison with oospecies successions from Arc basin localities (France) allows the age calibration for such oospecies replacement to be confirmed. This age refinement implies that some of the stated boundaries for the proposed oospecies assemblages may change and that an in-depth revision of the age and magnetic calibration of some south European egg localities is required. 相似文献
2.
A companion paper (Part I: Toma and Webster 2008), argued that the characteristics of the mean Intertropical Convergence Zone (ITCZ) arise from instabilities associated with
the strong cross-equatorial pressure gradient (CEPG) that exists in the eastern Pacific Ocean as a result of the latitudinal
sea-surface temperature (SST) gradient. Furthermore, it was argued that instabilities of the mean ITCZ resulted in the in
situ development of easterly waves. Thus, in Part I, it was hypothesized that the mean and transient state of eastern Pacific
convection was due to local processes and less so to the advection of waves from the North Atlantic Ocean. To test this hypothesis
and, at the same time, consider others such as a possible role of the equatorial and subtropical orography in generating local
instabilities, a series of controlled numerical experiments are designed using the WRF regional model. The domain of the model
was configured to include the western Atlantic Ocean, the Isthmus of Panama and the eastern Pacific Ocean to 155°W. Lateral
boundaries were set at 40°N and 40°S, thus containing the mountains of Central America, the Andes and the Sierra Madre of
Mexico. In a series of experiments, analysis products were used as boundary conditions that were successively updated four
times per day, set as 10-day running average fields or as running mean monthly fields. Finally, the model was run with topography
essentially eliminated over the land areas. Although there are differences between the details of the resultant fields, the
location of mean convection and the form of the transients remain the same. It is concluded, in support of the theoretical
and diagnostic studies of Part I that orographic forcing or waves generated in the North Atlantic Ocean are not the major
causes of the mean and transient nature of disturbances in the eastern Pacific. 相似文献
3.
Asian summer monsoon prediction in ECMWF System 4 and NCEP CFSv2 retrospective seasonal forecasts 总被引：3，自引：1，他引：2
The seasonal prediction skill of the Asian summer monsoon is assessed using retrospective predictions (1982–2009) from the ECMWF System 4 (SYS4) and NCEP CFS version 2 (CFSv2) seasonal prediction systems. In both SYS4 and CFSv2, a cold bias of sea-surface temperature (SST) is found over the equatorial Pacific, North Atlantic, Indian Oceans and over a broad region in the Southern Hemisphere relative to observations. In contrast, a warm bias is found over the northern part of North Pacific and North Atlantic. Excessive precipitation is found along the ITCZ, equatorial Atlantic, equatorial Indian Ocean and the maritime continent. The southwest monsoon flow and the Somali Jet are stronger in SYS4, while the south-easterly trade winds over the tropical Indian Ocean, the Somali Jet and the subtropical northwestern Pacific high are weaker in CFSv2 relative to the reanalysis. In both systems, the prediction of SST, precipitation and low-level zonal wind has greatest skill in the tropical belt, especially over the central and eastern Pacific where the influence of El Nino-Southern Oscillation (ENSO) is dominant. Both modeling systems capture the global monsoon and the large-scale monsoon wind variability well, while at the same time performing poorly in simulating monsoon precipitation. The Asian monsoon prediction skill increases with the ENSO amplitude, although the models simulate an overly strong impact of ENSO on the monsoon. Overall, the monsoon predictive skill is lower than the ENSO skill in both modeling systems but both systems show greater predictive skill compared to persistence. 相似文献
4.
Jae Seong Lee Dong-Jin Kang Elitsa Hineva Violeta Slabakova Valentina Todorova Jiyoung Park Jin-Hyung Cho 《Ocean Science Journal》2017,52(2):243-256
We measured the community-scale metabolism of seagrass meadows in Bulgaria (Byala [BY]) and Korea (Hoopo Bay [HP]) to understand their ecosystem function in coastal waters. A noninvasive in situ eddy covariance technique was applied to estimate net O2 flux in the seagrass meadows. From the high-quality and high-resolution time series O2 data acquired over > 24 h, the O2 flux driven by turbulence was extracted at 15-min intervals. The spectrum analysis of vertical flow velocity and O2 concentration clearly showed well-developed turbulence characteristics in the inertial subrange region. The hourly averaged net O2 fluxes per day ranged from -474 to 326 mmol O2 m-2 d-1 (-19 ± 41 mmol O2 m-2 d-1) at BY and from -74 to 482 mmol O2 m-2 d-1 (31 ± 17 mmol O2 m-2 d-1) at HP. The net O2 production rapidly responded to photosynthetically available radiation (PAR) and showed a good relationship between production and irradiance (P-I curve). The hysteresis pattern of P-I relationships during daytime also suggested increasing heterotrophic respiration in the afternoon. With the flow velocity between 3.30 and 6.70 cm s-1, the community metabolism during daytime and nighttime was significantly increased by 20 times and 5 times, respectively. The local hydrodynamic characteristics may be vital to determining the efficiency of community photosynthesis. The net ecosystem metabolism at BY was estimated to be -17 mmol O2 m-2 d-1, which was assessed as heterotrophy. However, that at HP was 36 mmol O2 m-2 d-1, which suggested an autotrophic state. 相似文献
5.
Castañeda Chávez Mdel R Pardio Sedas V Orrantia Borunda E Lango Reynoso F 《Marine pollution bulletin》2005,50(12):1641-1648
The influence of temperature and salinity on the occurrence of Vibrio cholerae, Escherichia coli and Salmonella spp. associated with water and oyster samples was investigated in two lagoons on the Atlantic Coast of Veracruz, Mexico over a 1-year period. The results indicated that seasonal salinity variability and warm temperatures, as well as nutrient influx, may influence the occurrence of V. cholera. non-O1 and O1. The conditions found in the Alvarado (31.12 °C, 6.27‰, pH = 8.74) and La Mancha lagoons (31.38 °C, 24.18‰, pH = 9.15) during the rainy season 2002 favored the occurrence of V. cholera O1 Inaba enterotoxin positive traced in oysters. Vibrio alginolyticus was detected in Alvarado lagoon water samples during the winter season. E. coli and Salmonella spp. were isolated from water samples from the La Mancha (90–96.7% and 86.7–96.7%) and Alvarado (88.6–97.1% and 88.6–100%) lagoons. Occurrence of bacteria may be due to effluents from urban, agricultural and industrial areas. 相似文献
6.
7.
We examine the mean and transient state of the intertropical convergence zone (ITCZ) by analyzing data and using simple theory.
We concentrate on the tropical eastern Pacific Ocean noting that there exists in this region a well-developed mean ITCZ. Furthermore,
it is a region where there has been considerable discussion in the literature of whether easterly waves develop in situ or
propagate westwards from the Atlantic Ocean. The region is typical of tropical regions where there is a strong cross-equatorial
pressure gradient (CEPG): mean convection well removed from the equator but located equatorward of the maximum sea-surface
temperature (SST) and minimum sea level pressure (MSLP). Further to the west, near the dateline where the CEPG is much smaller,
convection is weaker and collocated with SST and MSLP extrema. It is argued that in regions of significant CEPG that the near-equatorial
tropical system is inertially unstable and that the rectification of the instability for a given CEPG determines the location
and intensity of the climatological ITCZ. Using simple theoretical arguments, we develop an expression for the mean latitude
of the ITCZ as a function of the CEPG. We note on a day-by-day basis that the ITCZ is highly transient state with variability
occurring on 3–8 day time scales. Transients with amplitudes about half of the mean ITCZ, propagate northwards from the near-equatorial
southern hemisphere as anomalous meridional oscillations, eventually amplifying convection in the vicinity of the mean ITCZ.
It is argued that in these longitudes of strong CEPG the mean ITCZ is continually inertially unstable with advections of anticylonic
vorticity across the equator resulting in the creation of an oscillating divergence–convergence doublet. The low-level convergence
produces convection and the resultant vortex tube stretching generates cyclonic vorticity which counteracts the northward
advection of anticylonic vorticity. During a cycle, the mid-troposphere heating near 10oN oscillates between 6 and 12 K/day
at the inertial frequency of the latitude of the mean convection. As a result, there exists an anomalous and shallower, oscillating
meridional circulation with a magnitude about 50% of the mean ITCZ associated with the stable state following the generation
of anticylonic vorticity. Further, it is argued that the instabilities of the ITCZ are directly associated with in situ development
of easterly waves which occur with the inertial period of the latitude of the mean ITCZ. The dynamical sequences and the genesis
of easterly waves are absent in the regions further to the east where the CEPG is much weaker or absent altogether. In a companion
study (Part II), numerical experiments are conducted to test the hypothesis raised in the present study. 相似文献
8.
DALLA VECCHIA Fabio M. RIERA Violet OMS Josep Oriol DINARèS-TURELL Jaume GAETE Rodrigo GALOBART Angel 《《地质学报》英文版》2013,87(5):1198-1127
Pterosaur bones are for the first time reported from the Tremp Syncline(Spain) and the southern Pyrenees.They come from the Torrebilles-2 site(Isona,Lleida Province) in the upper Maastrichtian part of the Tremp Formation,which falls within the C29r magnetochron.Fragmentary long bones are referred to the Pterosauria based on their cortical thinness,micro-architecture,and histological features.They belong to very large to possibly giant individuals.The most complete specimen is possibly a partial right femur.The review of the Maastrichtian pterosaur record shows that only a few specimens can be referred to the C29r(which contains the K/Pg boundary).The identification of fragmentary remains could improve our knowledge about the abundance and distribution of these flying sauropsids just before the end-Cretaceous mass extinction. 相似文献
1