Influence of mean water depth and a subsurface sandbar on the onset and strength of wave breaking

Wave breaking in the open ocean and coastal zones remains an intriguing yet incompletely understood process, with a strong observed association with wave groups. Recent numerical study of the evolution of fully nonlinear, two-dimensional deep water wave groups identified a robust threshold of a diagnostic growth-rate parameter that separated nonlinear wave groups that evolved to breaking from those that evolved with recurrence. This paper investigates whether these deep water wave-breaking results apply more generally, particularly in finite-water-depth conditions. For unforced nonlinear wave groups in intermediate water depths over a flat bottom, it was found that the upper bound of the diagnostic growth-rate threshold parameter established for deep water wave groups is also applicable in intermediate water depths, given by k(0) h greater than or equal to 2, where k(0) is the mean carrier wavenumber and h is the mean depth. For breaking onset over an idealized circular arc sandbar located on an otherwise flat, intermediate-depth (k(0) h greater than or equal to 2) environment, the deep water breaking diagnostic growth rate was found to be applicable provided that the height of the sandbar is less than one-quarter of the ambient mean water depth. Thus, for this range of intermediate-depth conditions, these two classes of bottom topography modify only marginally the diagnostic growth rate found for deep water waves. However, when intermediate-depth wave groups ( k(0) h greater than or equal to 2) shoal over a sandbar whose height exceeds one-half of the ambient water depth, the waves can steepen significantly without breaking. In such cases, the breaking threshold level and the maximum of the diagnostic growth rate increase systematically with the height of the sandbar. Also, the dimensions and position of the sandbar influenced the evolution and breaking threshold of wave groups. For sufficiently high sandbars, the effects of bottom topography can induce additional nonlinearity into the wave field geometry and associated dynamics that modifies the otherwise robust deep water breaking-threshold results.

Mean sea surface heights of the South and East China Seas from ocean circulation model and geodetic leveling

The mean sea surface heights (sea surface topography) of the South China, East China, Yellow and Bohai Seas are derived from an ocean general circulation model and surface air pressure. The circulation model covers the global oceans, with fine grid (1/6degrees) covering the East Asian marginal seas and coarse grid (31) covering the rest part of the global oceans. The result shows that the China 1985 National Altitude Datum is 24.7 cm above the me-an sea surface height of the world oceans. The mean sea surface in the coastal ocean adjacent to China is higher in the south than in the north. Intercomparison of the model results with the geodetic leveling measurements at 28 coastal tidal stations shows a standard deviation of 4.8 cm and a fitting coefficient of 95.3%. After correction through linear regression, the standard deviation is reduced to 4.5 cm. This indicates that the accuracy of model results is sufficient for practical application. Based on the model results, the mean sea surface heights for the study area with a resolution of 1/6 degree are given. This result also links the mean sea levels at islands with those on the mainland coast and gives the mean sea surface heights at tidal stations in the Taiwan Island, the Dongsha Islands, the Yisha Islands and the Nansha Islands relative to the China 1985 National Altitude Datum.

Carbon isotopic studies of individual lipids in organisms from the Nansha sea area, China

Carbon isotopes of individual lipids in typical organisms from the Nansha sea area were measured by the GC-IRMS analytical technique. delta(13)C values of saturated fatty acids in different organisms examined are from -25.6parts per thousand to -29.7parts per thousand with the average values ranging from -26.4parts per thousand to -28.2parts per thousand and the variance range of 11.8parts per thousand, between different organisms is also observed. Unsaturated fatty acids have heavy carbon isotopic compositions and the mean differences of 2.9%.9-6.8parts per thousand compared to the same carbon number saturated fatty acids. delta(13)C values of n-alkanes range from -27.5%o to -29.7parts per thousand and their mean values, ranging from -28.6parts per thousand, to -28.9parts per thousand, are very close in different organisms. The mean difference in delta(13)C between the saturated fatty acids and n-alkanes is only 1.5parts per thousand, indicating that they have similar biosynthetic pathways. The carbon isotopic variations between the different carbon-number lipids are mostly within +/-2.0parts per thousand, reflecting that they experienced a biosynthetic process of the carbon chain elongation. At the same time, the carbon isotopic genetic relationships between the biological and sedimentary lipids are established by comparative studies of carbon isotopic compositions of individual lipids in organisms and sediments from the Nansha sea area, which provides scientific basis for carbon isotopic applied research of individual lipids.

Yellow perch strain evaluation I: Genetic variance of six broodstock populations

As a prelude to strain selection for domestication and future marker assisted selection, genetic variation revealed by microsatellite DNA was evaluated in yellow perch, Perca flavescens, from four wild North American populations collected in 2003-2004 (Maine, New York, North Carolina, and Pennsylvania,), and two captive populations (Michigan and Ohio). For the loci examined, levels of heterozygosity ranged from H-e=0.04 to 0.88, genetic differentiation was highly significant among all population pairs, and effective migration ranged from low (N(e)m=0.3) to high (N(e)m=4.5). Deviation from Hardy-Weinberg equilibrium was regularly observed indicating significant departures from random mating. Instantaneous measures of inbreeding within these populations ranged from near zero to moderate (median F=0.16) and overall inbreeding levels averaged F-IS=0.18. Estimates of genetic diversity, Phi(ST), and genetic distance were highest between Michigan and all other broodstock groups and lowest between New York and Ohio. Genetic differentiation among groups did not correlate with geographic distance. Overall, the patterns of variation exhibited by the captive (Michigan and Ohio) populations were similar to patterns exhibited by the other wild populations, indicating that spawning and management practices to date have not significantly reduced levels of genetic variation. (C) 2007 Elsevier B.V. All rights reserved.

Spatial and temporal relationships between precipitation and ANPP of four types of grasslands in northern China

Precipitation is considered to be the primary resource limiting terrestrial biological activity in water-limited regions. Its overriding effect on the production of grassland is complex. In this paper, field data of 48 sites (including temperate meadow steppe,temperate steppe, temperate desert steppe and alpine meadow) were gathered from 31 published papers and monographs to analyze the relationship between above-ground net primary productivity (ANPP) and precipitation by the method of regression analysis. The results indicated that there was a great difference between spatial pattern and temporal pattern by which precipitation influenced grassland ANPP. Mean annual precipitation (MAP) was the main factor determining spatial distribution of grassland ANPP (r~2 = 0.61,P ＜ 0.01); while temporally, no significant relationship was found between the variance of AN PP and inter-annual precipitation for the four types of grassland. However, after dividing annual precipitation into monthly value and taking time lag effect into account, the study found significant relationships between ANPP and precipitation. For the temperate meadow steppe, the key variable determining inter-annual change of ANPP was last August-May precipitation (r~2= 0.47, P = 0.01); for the temperate steppe, the key variable was July precipitation (r~2 = 0.36, P = 0.02); for the temperate desert steppe, the key variable was April-June precipitation (r~2 = 0.51, P ＜0.01); for the alpine meadow, the key variable was last September-May precipitation (r~2 = 0.29, P ＜ 0.05). In comparison with analogous research, the study demonstrated that the key factor determining inter-annual changes of grassland ANPP was the cumulative precipitation in certain periods of that year or the previous year.

Genetic variation in the endangered Anisodus tanguticus (Solanaceae), an alpine perennial endemic to the Qinghai-Tibetan Plateau

We used random amplified polymorphic DNA markers (RAPDs) to assess genetic variation between- and within-populations of Anisodus tanguticus (Solanaceae), an endangered perennial endemic to the Qinghai-Tibetan Plateau with important medicinal value. We recorded a total of 92 amplified bands, using 12 RAPD primers, 76 of which (P = 82.61%) were polymorphic, and calculated values of H-t and H-sp of 0.3015 and 0.4459, respectively, suggesting a remarkably high rate of genetic variation at the species level. The average within-population diversity also appeared to be high, with P, H-e and H-pop values of 55.11%, 0.1948 and 0.2918, respectively. Analyses of molecular variance (AMOVA) showed that among- and between-population genetic variation accounted for 67.02% and 32.98% of the total genetic variation, respectively. In addition, Nei's coefficient of differentiation (G(ST)) was found to be high (0.35), confirming the relatively high level of genetic differentiation among the populations. These differentiation coefficients are higher than mean corresponding coefficients for outbreeding species, but lower than reported coefficients for some rare species from this region. The genetic structure of A. tanguticus has probably been shaped by its breeding attributes, biogeographic history and human impact due to collection for medicinal purposes. The observed genetic variations suggest that as many populations as possible should be considered in any planned in situ or ex situ conservation programs for this species.

Stability of alpine meadow ecosystem on the Qinghai-Tibetan Plateau

The meadow ecosystem on the Qinghai-Tibetan Plateau is considered to be sensitive to climate change. An understanding of the alpine meadow ecosystem is therefore important for predicting the response of ecosystems to climate change. In this study, we use the coefficients of variation (Cv) and stability (E) obtained from the Haibei Alpine Meadow Ecosystem Research Station to characterize the ecosystem stability. The results suggest that the net primary production of the alpine meadow ecosystem was more stable (Cv = 13.18%) than annual precipitation (Cv = 16.55%) and annual mean air temperature (Cv= 28.82%). The net primary production was insensitive to either the precipitation (E = 0.0782) or air temperature (E = 0.1113). In summary, the alpine meadow ecosystem on the Qinghai-Tibetan Plateau is much stable. Comparison of alpine meadow ecosystem stability with other five natural grassland ecosystems in Israel and southern African indicates that the alpine meadow ecosystem on the Qinghai-Tibetan Plateau is the most stable ecosystem. The alpine meadow ecosystem with relatively simple structure has high stability, which indicates that community stability is not only correlated with biodiversity and community complicity but also with environmental stability. An average oscillation cycles of 3-4 years existed in annual precipitation, annual mean air temperature, net primary production and the population size of consumers at the Haibei natural ecosystem. The high stability of the alpine meadow ecosystem may be resulting also from the adaptation of the ecosystem to the alpine environment.

RAPD profiling in detecting genetic variation in endemic Coelonema (Brassicaceae) of Qinghai-Tibet Plateau of China

Random amplified polymorphic DNA ( RAPD) markers were used to measure genetic diversity of Coelonema draboides ( Brassicaceae), a genus endemic to the Qilian Mountains of the Qinghai-Tibet Plateau. We sampled 90 individuals in 30 populations of Coelonema draboides from Datong and Huzhu counties of Qinghai Province in P. R. China. A total of 186 amplified bands were scored from the 14 RAPD primers, with a mean of 13.3 amplified bands per primer, and 87% ( 161 bands) polymorphic bands (PPB) was found. Analysis of molecular variance (AMOVA) shows that a large proportion of genetic variation (84.2%) resides among individuals within populations, while only 15.8% resides among populations. The species shows higher genetic diversity between individuals than other endemic and endangered plants. The RAPDs provide a useful tool for assessing genetic diversity of rare, endemic species and for resolving relationships among populations. The results show that the genetic diversity of this species is high, possibly allowing it to adapt more easily to environmental variations. The main factor responsible for the high level of differentiation within populations and the low level of diversity among populations is probably the outcrossing and long-lived nature of this species. Some long-distance dispersal, even among far separated populations, is also a crucial determinant for the pattern of genetic variation in the species. This distributive pattern of genetic variation of C. draboides populations provides important baseline data for conservation and collection strategies for the species. It is suggested that only populations in different habitats should be studied and protected, not all populations, so as to retain as much genetic diversity as possible.

基于图像统计信息的去椒盐噪声算法

提出了一种基于图像统计信息的去椒盐噪声算法。该方法利用图像中心像素邻域的均值和方差来消除图像中椒盐噪声的影响。首先给出了这种算法的基本原理和实现,然后分别应用中值滤波算法、自适应中值滤波算法以及该算法对有椒盐噪声污染的图像进行滤波,并对实验结果进行比较和分析。实验结果表明,该方法不仅能够消除椒盐噪声,而且能够保持图像的特征信息。最后,对这种算法复杂度也进行了计算分析,并将其和中值滤波算法以及自适应中值滤波算法的复杂度进行了比较,证明该算法比中值滤波算法以及自适应中值滤波算法的复杂度低。

太阳辐射对热层和电离层变化性的影响

Solar ultraviolet (UV) radiation at wavelengths less than 400 nm is an important source of energy for aeronomic processes throughout the solar system. Solar UV photons are absorbed in planetary atmospheres, as well as throughout the heliosphere, via photodissociation of molecules, photoionization of molecules and atoms, and photoexcitation toexcitation including resonance scattering. In this paper, the solar irradiances data measured by TIMED SEE, as well as the solar proxies such as F10.7 and Mg II, thermosphere neutral density of CHAMP measurements and topside ionospheric plasmas densities from DMSP, are used to analyze solar irradiance effects on the variabilities of the thermosphere and the ionosphere. First, thermosphere densities near 410 km altitude are analyzed for solar irradiance variability effects during the period 2002-2004. Correlations between the densities and the solar irradiances for different spectral lines and wavelength ranges reveal significantly different characteristics. The density correlates remarkably well with all the selected solar irradiances except the lower chromospheric O I (130.4 nm) emission. Among the chosen solar proxies, the Mg II core-to-wing ratio index, EUV (30-120 nm) and F10.7 show the highest correlations with the density for short-term (< ~27 days) variations. For both long- (> ~27 days) and short-term variations, linear correlation coefficients exhibit a decreasing trend from low latitudes towards high latitudes. The density variability can be effectively modeled (capturing 71% of the variance) using multiple solar irradiance indices, including F10.7, SEUV (the EUV 30-120 nm index), and SFUV (the FUV 120-193 nm index), in which a lag time of 1 day was used for both F10.7 and SEUV, and 5 days for SFUV. In our regression formulation SEUV has the largest contribution to the density variation (40%), with the F10.7 having the next largest contribution (32%) and SFUV accounting for the rest (28%). Furthermore, a pronounced period of about 27.2 days (mean period of the Sun's rotation) is present in both density and solar irradiance data of 2003 and 2004, and a pronounced period of about 54.4 days (doubled period of the solar rotation) is also revealed in 2004. However, soft X-ray and FUV irradiances did not present a pronounced 54.4 day period in 2004, in spite of their high correlation with the densities. The Ap index also shows 54-day periodicities in 2004, and magnetic activity, together with solar irradiance, affects the 54-day variation in density significantly. In addition, NRLMSISE00, DTM-2000 and JB2006 model predictions are compared with density measurements from CHAMP to assess their accuracy, and the results show that these models underestimate the response of the thermosphere to variations induced by solar rotation. Next, the equatorial topside ionospheric plasmas densities Ni are analyzed for solar irradiance variability effects during the period 2002-2005. Linear correlations between Ni and the solar irradiances for different wavelength ranges reveal significantly different characteristics. XUV (0-35 nm) and EUV (115-130 nm) show higher correlation with Ni for the long-term variations, whereas EUV (35-115 nm) show higher correlation for the short-term variations. Moreover, partial correlation analysis shows that the long-term variations of Ni are affected by both XUV (0-35 nm) and EUV (35-115 nm), whereas XUV (0-35 nm) play a more important role; the short-term variations of Ni are mostly affected by EUV (35-115 nm). Furthermore, a pronounced period of about 27 days is present in both Ni and solar irradiance data of 2003 and 2004, and a pronounced period of about 54 days is also revealed in 2004. Finally, prompted by previous studies that have suggested solar EUV radiation as a means of driving the semiannual variation, we investigate the intra-annual variation in thermosphere neutral density near 400 km during 2002-2005. The intra-annual variation, commonly referred to as the ‘semiannual variation’, is characterized by significant latitude structure, hemispheric asymmetries, and inter-annual variability. The magnitude of the maximum yearly difference, from the yearly minimum to the yearly maximum, varies by as much as 60% from year to year, and the phases of the minima and maxima also change by 20-40 days from year to year. Each annual harmonic of the intra-annual variation, namely, annual, semiannual, ter-annual and quatra-annual, exhibits a decreasing trend from 2002 through 2005 that is correlated with the decline in solar activity. In addition, some variations in these harmonics are correlated with geomagnetic activity, as represented by the daily mean value of Kp. Recent empirical models of the thermosphere are found to be deficient in capturing most of the latitude dependencies discovered in our data. In addition, the solar flux and geomagnetic activity proxies that we have employed do not capture some latitude and inter-annual variations detected in our data. It is possible that these variations are partly due to other effects, such as seasonal-latitudinal variations in turbopause altitude (and hence O/N2 composition) and ionosphere coupling processes that remain to be discovered in the context of influencing the intra-annual variations depicted here. Our results provide a new dataset to challenge and validate thermosphere-ionosphere general circulation models that seek to delineate the thermosphere intra-annual variation and to understand the various competing mechanisms that may contribute to its existence and variability. We furthermore suggest that the term “intra-annual” variation be adopted to describe the variability in thermosphere and ionosphere parameters that is well-captured through a superposition of annual, semiannual, ter-annual, and quatra-annual harmonic terms, and that “semiannual’ be used strictly in reference to a pure 6-monthly sinusoidal variation. Moreover, we propose the term “intra-seasonal” to refer to those shorter-term variations that arise as residuals from the above Fourier representation.