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991.
In an earlier paper a particular discrete wavelet transform (DWT) was used to study the complex variation of beach profile changes. However, use of the DWT requires that the sequence of spatial and temporal resolution is fixed as a dyadic sequence, which means that the variability over longer intervals is not characterised well. Here we introduce the discrete wavelet packet transform (DWPT) that uses an adaptive scaling to partition the data variance, according to an entropy cost function. The advantages of this approach are demonstrated by its application to the study of temporal variability of a 22 year record of beach profile data from the Field Research Facility (FRF) at Duck, North Carolina, USA. Time series of beach elevations at three locations across a particular profile are investigated in detail. We conclude that the DWPT provides a superior analysis of non-stationary time series to that of the DWT, with improved resolution of the scale intervals of the variability. The beach elevation around the shoreline is shown to respond at both sub-annual and interannual scales, but variability at an annual scale is weak. Moving seaward into deeper water, the variance is partitioned into fewer and longer scales. It is confirmed that elevation changes around the inner bar at Duck exhibit a strong interannual variation consistent with Plant et al. (Plant, N.G., Holman, R.A. and Freilich, M.H., 1999. A simple model for interannual sandbar behaviour. Journal of Geophysical Research 104(C7), 15755–15776). Around 23% of the variance around the inner bar is explained at the temporal scale of 64–128 months, which is consistent with the bar behaviour of 6 years found by Ruessink et al. (Ruessink, B. G., Wijnberg, K. M., Holman, R. A., Kuriyama, Y. and Van Enckevort, I. M. J., 2003. Intersite comparison of interannual nearshore bar behaviour. Journal of Geophysical Research, 108 (C8): 1–12). A significant new finding is, however, that about 26% of the variance is attributable to temporal scales of 16–21.3 months. Reconstruction of the wavelet packet components for individual temporal scales is shown to provide a means for identifying the impact and scale of non-stationary events, such as storms, on the beach response. This provides further information that can be used to interpret the morphological changes in terms of the forcing processes and also serves to inform morphodynamic modelling. 相似文献
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995.
皱纹盘鲍微卫星研究进展 总被引:16,自引:2,他引:16
李琪 《中国海洋大学学报(自然科学版)》2004,34(3):365-370
微卫星标记(microsatellite markers)广泛分布于原核生物和真核生物基因组中,具有密度大、多态性丰富、遵循孟德尔分离定律共显性遗传、易于PCR扩增等特点,已成为近年来最引人注目的新型DNA标记。本文对皱纹盘鲍的微卫星标记的开发以及在种群遗传多样性评价、家系分析、人工苗种遗传变异监测研究方面的最新进展进行了综述,并阐述了微卫星标记在无效等位基因、大小承异同形性等方面存在的问题。 相似文献
996.
Indian summer monsoon variability during the holocene as recorded in sediments of the Arabian Sea: Timing and implications 总被引:1,自引:0,他引:1
Meloth Thamban Hodaka Kawahata Venigalla Purnachandra Rao 《Journal of Oceanography》2007,63(6):1009-1020
Indian monsoon precipitation fluctuated significantly during the Holocene and a reliable reconstruction of the timing of the
events and their implications is of great benefit to our understanding of the effect and response of low latitude climate
systems to the forcing factors. We have carried out high-resolution terrigenous proxy studies on a laminated sediment core
from the Oxygen Minimum Zone of the eastern Arabian Sea margin to reconstruct the summer monsoon-controlled precipitation
changes during the Holocene. The temporal variation in the terrigenous proxy indicators of this core, in combination with
other high-quality cores from the Arabian Sea, suggests several abrupt events in monsoon precipitation throughout the Holocene.
The early Holocene monsoon intensification occurred in two abrupt steps at 9500 and 9100 years BP and weakened gradually thereafter,
starting at 8500 years BP. A weakening in precipitation recorded at ∼7000 years BP, synchronous with similar conditions in
India. One of the most significant weak monsoon periods recorded in our studies lies between 6000 and 5500 years BP. Spectral
analysis of the precipitation records reveals statistically significant periodicities at 2200, 1350, 950, 750, 470, 320, 220,
156, 126, 113, 104 and 92 years. Most of these millennial-to-centennial cycles exist in various monsoon records as well as
the tree ring Δ14C data and/or other solar proxy records. We suggest that throughout the Holocene, externally, small changes in solar activity
controlled the Indian monsoon to a large extent, whereas internally, non-solar causes could have influenced the amplitude
of decadal-to-centennial oscillations. 相似文献
997.
Jane M. Caffrey Thomas P. Chapin Hans W. Jannasch John C. Haskins 《Estuarine, Coastal and Shelf Science》2007,71(3-4):368-380
Elkhorn Slough is a small estuary in Central California, where nutrient inputs are dominated by runoff from agricultural row crops, a golf course, and residential development. We examined the variability in nutrient concentrations from decadal to hourly time scales in Elkhorn Slough to compare forcing by physical and biological factors. Hourly data were collected using in situ nitrate analyzers and water quality data sondes, and two decades of monthly monitoring data were analyzed. Nutrient concentrations increased from the mid 1970s to 1990s as pastures and woodlands were converted to row crops and population increased in the watershed. Climatic variability was also a significant factor controlling interannual nutrient variability, with higher nutrient concentrations during wet than drought years. Elkhorn Slough has a Mediterranean climate with dry and rainy seasons. Dissolved inorganic nitrogen (DIN) concentrations were relatively low (10–70 μmol L−1) during the dry season and high (20–160 μmol L−1) during the rainy season. Dissolved inorganic phosphorus (DIP) concentrations showed the inverse pattern, with higher concentrations during the dry season. Pulsed runoff events were a consistent feature controlling nitrate concentrations during the rainy season. Peak nitrate concentrations lagged runoff events by 1 to 6 days. Tidal exchange with Monterey Bay was also an important process controlling nutrient concentrations, particularly near the mouth of the Slough. Biological processes had the greatest effect on nitrate concentrations during the dry season and were less important during the rainy season. While primary production was enhanced by nutrient pulses, chlorophyll a concentrations were not. We believe that the generally weak biological response compared to the strong physical forcing in Elkhorn Slough occurred because the short residence time and tidal mixing rapidly diluted nutrient pulses. 相似文献
998.
Yoshinobu Wakata Takashi Setou Ikuo Kaneko Hiroshi Uchida Shiro Imawaki 《Journal of Oceanography》2006,62(1):25-35
The interannual variability of the Kuroshio volume transport passing through the 137°E meridian south of Japan was simulated
with an ocean general circulation model (OGCM). The time series of the Kuroshio volume transport over the 1000 m depth in
the OGCM is well reproduced by the one-dimensional quasi-geostrophic (QG) vorticity equation with a windstress forcing. In
our analysis of the OGCM and QG results, we found that peaks and troughs of the time series of the Kuroshio volume transport
with 2–3 yr time-scale were induced by windstress curl, both local and immediately eastward, whereas longer time-scale variability
was also induced by windstress curl near the dateline. 相似文献
999.
Total sea surface temperature (SST) in a coupled GCM is diagnosed by separating the variability into signal variance and noise
variance. The signal and the noise is calculated from multi-decadal simulations from the COLA anomaly coupled GCM and the
interactive ensemble model by assuming both simulations have a similar signal variance. The interactive ensemble model is
a new coupling strategy that is designed to increase signal to noise ratio by using an ensemble of atmospheric realizations
coupled to a single ocean model. The procedure for separating the signal and the noise variability presented here does not
rely on any ad hoc temporal or spatial filter. Based on these simulations, we find that the signal versus the noise of SST
variability in the North Pacific is significantly different from that in the equatorial Pacific. The noise SST variability
explains the majority of the total variability in the North Pacific, whereas the signal dominates in the deep tropics. It
is also found that the spatial characteristics of the signal and the noise are also distinct in the North Pacific and equatorial
Pacific. 相似文献
1000.
Fogarty Michael J.; Myers Ransom A.; Bowen Keith G. 《ICES Journal of Marine Science》2001,58(5):952-961