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1.
B. Meyssignac C. G. Piecuch C. J. Merchant M.-F. Racault H. Palanisamy C. MacIntosh S. Sathyendranath R. Brewin 《Surveys in Geophysics》2017,38(1):187-215
We analyse the regional variability in observed sea surface height (SSH), sea surface temperature (SST) and ocean colour (OC) from the ESA Climate Change Initiative datasets over the period 1993–2011. The analysis focuses on the signature of the ocean large-scale climate fluctuations driven by the atmospheric forcing and do not address the mesoscale variability. We use the ECCO version 4 ocean reanalysis to unravel the role of ocean transport and surface buoyancy fluxes in the observed SSH, SST and OC variability. We show that the SSH regional variability is dominated by the steric effect (except at high latitude) and is mainly shaped by ocean heat transport divergences with some contributions from the surface heat fluxes forcing that can be significant regionally (confirming earlier results). This is in contrast with the SST regional variability, which is the result of the compensation of surface heat fluxes by ocean heat transport in the mixed layer and arises from small departures around this background balance. Bringing together the results of SSH and SST analyses, we show that SSH and SST bear some common variability. This is because both SSH and SST variability show significant contributions from the surface heat fluxes forcing. It is evidenced by the high correlation between SST and buoyancy-forced SSH almost everywhere in the ocean except at high latitude. OC, which is determined by phytoplankton biomass, is governed by the availability of light and nutrients that essentially depend on climate fluctuations. For this reason, OC shows significant correlation with SST and SSH. We show that the correlation with SST displays the same pattern as the correlation with SSH with a negative correlation in the tropics and subtropics and a positive correlation at high latitude. We discuss the reasons for this pattern. 相似文献
2.
Using the data collected during the International Indian Ocean Expedition, maps showing the distribution of depth, acceleration
potential, salinity and oxyty were prepared for the northeast monsoon for the four potential thermosteric anomaly surfaces:
160, 120, 80 and 60 cl/t. Zonal components of current along 84°E were computed from the geopotential dynamic heights. From
such an analysis, it became clear that low-salinity water from the Pacific intrudes into the western Indian Ocean through
the Banda and Timor seas in the upper layers above 100 cl/t surface, while the North Indian Ocean Water penetrates towards
the Eastern Archipelago below 100 cl/t surface. The South Equatorial Countercurrent and the Tropical Countercurrent are well
depicted on the vertical section of zonal components as well as on the distribution of acceleration potential. 相似文献
3.
Polarizaton characteristics of completely diffuse light reflected from a wind roughened sea surface and its total reflectance are studied for various wind speeds on the assumption that distribution of wave slopes around their mean is Gaussian. The angular distribution of diffuse reflectance and polarization status of reflected light are also estimated with a view to exploring possibilities of using these parameters for remote sensing of sea state from a satellite, aircraft or an observation tower. The efficiency of Brewster’s angle technique in eliminating reflected light from the sea surface radiance for remote sensing of subsurface material is examined for non flat sea surface in the light of these results. the results show that the diffuse light reflected from the sea surface contains information on the sea state in the form of its status of polarization and can be used as an observational tool in remote sensing of sea state. The scope and limitations of the method proposed are discussed. 相似文献
4.
Shubha N. Pandit April Hayward Jan de Leeuw Jurek Kolasa 《Journal of Geographical Systems》2010,12(4):389-407
Species distribution models are used extensively in predicting the distribution of vegetation across a landscape. Accuracy
of the species distribution maps produced by these models deserves attention, since low accuracy maps may lead to erroneous
conservation decisions. While plot size is known to influence measures of species richness, its effect on our ability to predict
species distribution ranges has not been tested. Our aim is to test whether the accuracy of the distribution maps produced
depend on the size of the plot (quadrat) used to collect biological data in the field. In this study, the presences of four
plant species were recorded in five sizes of circular plots, with radii ranging from 8 to 100 m. Logistic regression-based
models were used to predict the distributions of the four plant species based on empirical evidence of their relationship
with eight environmental predictors: distance to river, slope, aspect, altitude, and four principle component axes derived
using reflectance values from Aster images. We found that plot size affected the probability of recording the four species,
with reductions in plot size generally increasing the frequency of recorded absences. Plot size also significantly affected
the likelihood of correctly predicting the distribution of species whenever plot size was below the minimum size required
to consistently record species’ presence. Furthermore, the optimal plot size for fitting species distribution models varied
among species. Finally, plot size had little impact on overall accuracy, but a strong, positive impact on Kappa accuracy (which
provides a stronger measure of model accuracy by accounting for the effects of chance agreements between predictions and observations).
Our results suggest that optimal plot size must be considered explicitly in the creation of species distribution models if
they are to be successfully adopted into conservation efforts. 相似文献
5.
We have reported for the first time total seven strong events of drifting ELF/VLF discrete emissions observed on 28th–29th April, 1990 in the pre-midnight sector at Varanasi (Geomag. lat. 14°55′N, long. 154°E, L = 1.07). The events exhibit a regular increasing as well as decreasing frequency drifts and are mainly discrete periodic emissions of riser, faller and hook types observed during a geomagnetic storm period, with minimum Dst-index ?98 nT and K p -index ≥ 5. The frequency drift in ELF/VLF emissions at low latitudes seems to be a rare phenomenon. The repetition period and the frequency drift rate have been evaluated for all the recorded events. The frequency drifts have been interpreted in terms of a combined effect of L-shell drift of interacting energetic electrons and the change in convection electric fields during the storm developments. The computed maximum spectral power density $ \left\langle {B_{f}^{2} } \right\rangle_{\max } $ of the wave varies between 1.8 × 10?21 and 4.08 × 10?22 Gauss2/Hz, whereas frequency drift rates are in agreement with the observed values. 相似文献
6.
We combined a surface irradiance model with a non-spectral photosynthesisirradiance model to estimate the daily, average rate
of mixed-layer primary production in the Arabian Sea for the 15th day of months at the end of the northeast monsoon, the southwest
monsoon, and the fall and spring inter-monsoons. Our model experiment uses climatologies of cloud cover, mixed-layer thickness,
and satellite ocean-color observations of phytoplankton biomass.
Modelled surface radiation is at an annual maximum in May beneath nearly cloud-free skies just prior to the summer solstice.
The model estimate of surface radiation diminishes through the southwest monsoon over most of the northern Arabian Sea to
an annual minimum in August due to intense cloudiness.
In agreement with previous ship-based measurements, the photosynthesis-irradiance model predicts that the mixed-layer primary
production in the Arabian Sea is extremely seasonal, and peaks annually during the southwest monsoon to the north-west of
the atmospheric Findlater Jet and along the coast of Somalia. Northern Arabian Sea maxima predicted for both the summer and
winter monsoons are separated by periods of low mixed-layer primary production, the fall and spring inter-monsoons. The annual
cycles of modelled mixed-layer primary production differ by region in the Arabian Sea due to varying monsoon influence and
circulation dynamics. 相似文献
7.
We treat the ocean carbon cycle as a coupled physical-biogeochemical process. The interactions between mixed-layer dynamics
and growth of phytoplankton in the layer are discussed, and the formal relationship between phytoplankton accumulation and
new production is examined. A coupled biological-physical model is presented for studying the classical spring bloom in the
N. Atlantic, and possible differences in the mechanisms that drive the seasonal phytoplankton blooms in the N. Atlantic and
the Arabian Sea are discussed. Finally, recommendations are made for observational programs to improve our understanding of
the biologically-mediated carbon cycle in the Arabian Sea. 相似文献
8.
An extensive study collected in situ data along the Yellow Sea(YS) and East China Sea(ECS) to assess the radiometric properties and the concentration of the water constituents derived from Moderate Resolution Imaging Spectroradiometer(MODIS). Thirteen high quality match-ups were obtained for evaluating the MODIS estimates of Rrs(λ), chlorophyll a(Chl a) and concentrations of suspended particulate sediment matter(SPM). For MODIS Rrs(λ), the mean absolute percentage difference(APD) was in the range of 20%–36%, and the highest uncertainty appeared at 412 nm, whereas the band ratio of Rrs(λ) at 488 nm compared with that at 547 nm was highly consistent, with an APD of 7%. A combination of near-infrared bands and shortwave infrared wavelengths atmosphere correction algorithm(NIR-SWIR algorithm) was applied to the MODIS data, and the estimation accuracy of Rrs were improved at most of the visible spectral bands except 645 nm, 667 nm and 678 nm. Two ocean-colour empirical algorithms for Chl a estimation were applied to the processed data, the results indicated that the accuracy of the derived Chl a values was obviously improved, the four-band algorithms outperformed the other algorithm for measured and simulated datasets, and the minimum APD was 35%. The SPM was also quantified. Two regional and two coastal SPM algorithms were modified according to the in situ data. By comparison, the modified Tassan model had a higher accuracy for the application along the YS and ECS with an APD of 21%. However, given the limited match-up dataset and the potential influence of the aerosol properties on atmosphere correction, further research is required to develop additional algorithms especially for the low Chl a coastal water. 相似文献
9.
M. R. Ramesh Kumar S. Sathyendranath N. K. Viswambharan L. V. Gangadhara Rao 《Journal of Earth System Science》1986,95(3):435-446
Using the satellite derived sea surface temperature (SST) data for 1979 (bad monsoon) and 1983 (good monsoon), the SST variability for two contrasting monsoon seasons is studied. The study indicates that large negative anomalies off the Somali and Arabian coasts are associated with good monsoon rainfall over India. The strong monsoonal cooling in these regions can be attributed to strong low level winds and intense upwelling. The reappearance of 27°C isotherm off Somali coast in May/June coincides with the onset of southwest monsoon over India. Further, the influence of zonal anomaly of SST off Somalia Coast (SCZASST) and Central Indian Ocean Zonal Anomaly of SST (CIOZASST) with monsoon rainfall over India is brought out. The former is negatively related to the monsoon rainfall over western and central parts of India, whilst CIOZASST is positively related. 相似文献
10.