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1.
Oceanographic climatology is widely used in different applications, such as climate studies, ocean model validation and planning of naval operations. Conventional climatological estimates are based on historic measurements, typically by averaging the measurements and thereby smoothing local phenomena. Such phenomena are often local in time and space, but crucial to some applications. Here, we propose a new method to estimate time-calibrated oceanographic profiles based on combined historic and real-time measurements. The real-time measurements may, for instance, be SAR pictures or autonomous underwater vehicles providing temperature values at a limited set of depths. The method employs empirical orthogonal functions and clustering on a training data set in order to divide the ocean into climatological regions. The real-time measurements are first used to determine what climatological region is most representative. Secondly, an improved estimate is determined using an optimisation approach that minimises the difference between the real-time measurements and the final estimate. 相似文献
2.
Analysis and modeling of the seasonal South China Sea temperature cycle using remote sensing 总被引：1，自引：0，他引：1
Daniel J. Twigt Erik D. De Goede Ernst J. O. Schrama Herman Gerritsen 《Ocean Dynamics》2007,57(4-5):467-484
The present paper describes the analysis and modeling of the South China Sea (SCS) temperature cycle on a seasonal scale.
It investigates the possibility to model this cycle in a consistent way while not taking into account tidal forcing and associated
tidal mixing and exchange. This is motivated by the possibility to significantly increase the model’s computational efficiency
when neglecting tides. The goal is to develop a flexible and efficient tool for seasonal scenario analysis and to generate
transport boundary forcing for local models. Given the significant spatial extent of the SCS basin and the focus on seasonal
time scales, synoptic remote sensing is an ideal tool in this analysis. Remote sensing is used to assess the seasonal temperature
cycle to identify the relevant driving forces and is a valuable source of input data for modeling. Model simulations are performed
using a three-dimensional baroclinic-reduced depth model, driven by monthly mean sea surface anomaly boundary forcing, monthly
mean lateral temperature, and salinity forcing obtained from the World Ocean Atlas 2001 climatology, six hourly meteorological
forcing from the European Center for Medium range Weather Forecasting ERA-40 dataset, and remotely sensed sea surface temperature
(SST) data. A sensitivity analysis of model forcing and coefficients is performed. The model results are quantitatively assessed
against climatological temperature profiles using a goodness-of-fit norm. In the deep regions, the model results are in good
agreement with this validation data. In the shallow regions, discrepancies are found. To improve the agreement there, we apply
a SST nudging method at the free water surface. This considerably improves the model’s vertical temperature representation
in the shallow regions. Based on the model validation against climatological in situ and SST data, we conclude that the seasonal
temperature cycle for the deep SCS basin can be represented to a good degree. For shallow regions, the absence of tidal mixing
and exchange has a clear impact on the model’s temperature representation. This effect on the large-scale temperature cycle
can be compensated to a good degree by SST nudging for diagnostic applications. 相似文献
3.
4.
This paper investigates the feasibility of an ocean data assimilation system to analyze the salinity variability associated with the barrier layer in the equatorial Pacific. In order to validate reproducibility of the temperature and salinity fields, we perform an assimilation run where some temperature and salinity observations by TRITON buoys and Argo floats are withheld. The assimilation run reproduces interannual variability of salinity in the equatorial Pacific exhibited in the data that are withheld. Statistics shows that salinity values and variations in the assimilation run are closer to the data than the climatology and in the model free run. We also confirm that zonal currents in the equatorial Pacific in the reanalysis, where all available temperature and salinity data are assimilated, are consistent with an observation-based mapping and the data of the Acoustic Doppler Current Profiler mounted on TAO buoys. Variability of the barrier layer and relevant salinity field in the reanalysis is consistent with former studies. A thick barrier layer area generally exists west of the equatorial salinity front and is displaced zonally with the migration of the front in the response to El Niño-Southern Oscillation, although the area moved to the east over the front in the 1997 El Niño. It is confirmed that the barrier layer thickness is closely correlated with the near-surface temperature in the equatorial Pacific. 相似文献
5.
Pascal Lazure Valérie Garnier Franck Dumas Christelle Herry Marina Chifflet 《Continental Shelf Research》2009,29(8):985-997
The hydrology of the Bay of Biscay was investigated using the regional ocean model MARS3D (Model for Application at Regional Scale). The simulated hydrology is compared to a set of various data encompassing monthly climatology, remote sensing SST, CTD casts, and coastal salinity measurements. Special focus was put on the validation over the continental shelf. This paper reports that despite some misfits, the climatological hydrology and its seasonal variability are correctly simulated. Various statistics computed over the period from 1999–2004 highlight different aspects of the hydrology. The biases and root mean square errors (RMSE) remain very weak at all depths when comparing salinity (<0.1 and <0.6 psu respectively). The predicted temperature shows a global overestimation of temperature (bias of around 0.8 °C) and the maximum errors are located near the thermocline (rmse of 1 °C at 20–40 m). The model is shown to properly reproduce the annual dynamics of sea surface temperature, as well as the dynamics of large river plumes observed by high frequency time series from coastal salinity gauges. The misfits highlighted by these various comparisons between model and observations are attributed to heat fluxes and mixing parameterisation. 相似文献
6.
Effects of rainfall intensity fluctuations on infiltration and runoff: rainfall simulation on dryland soils,Fowlers Gap,Australia 总被引：4，自引：0，他引：4
David Dunkerley 《水文研究》2012,26(15):2211-2224
Small plots and a dripper rainfall simulator were used to explore the significance of the intensity fluctuations (‘event profile’) within simulated rainfall events on infiltration and runoff from bare, crusted dryland soils. Rainfall was applied at mean rain rates of 10 mm/h. Fourteen simulated rainfall events each involved more than 5000 changes of intensity and included multipeak events with a 25‐mm/h peak of intensity early in the event or late in the event and an event that included a temporary cessation of rain. These are all event profiles commonly seen in natural rain but rarely addressed in rainfall simulation. A rectangular event profile of constant intensity, as commonly used in rainfall simulation experiments, was also adopted for comparative purposes. Results demonstrate that event profile exerts an important effect on infiltration and runoff for these soils and rainfall event profiles. ‘Uniform’ events of unvarying intensity yielded the lowest total runoff, the lowest peak runoff rate and the lowest runoff ratio (0.13). These parameters increased for ‘early peak’ profiles (runoff ratio 0.24) and reached maxima for ‘late peak’ profiles (runoff ratio 0.50). Differences in runoff ratio and peak runoff rate between the ‘uniform’ event profile and those of varying intensity were all statistically significant at p ≤ 0.01. Compared with ‘uniform’ runs, the varying intensity runs yielded larger runoff ratios and peak runoff rates, exceeding those of the ‘uniform’ events by 85%–570%. These results suggest that for small‐plot studies of infiltration and erosion, the continued use of constant rainfall intensity simulations may be sacrificing important information and misrepresenting the mechanisms involved in runoff generation. The implications of these findings for the ecohydrology of the research site, an area of contour‐aligned banded vegetation in which runoff and runon are of critical importance, are highlighted. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
7.
J.E. Ferguson G.M. Henderson M. Kucera R.E.M. Rickaby 《Earth and Planetary Science Letters》2008,265(1-2):153-166
The Mg/Ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures. Used in conjunction with δ18O of foraminiferal calcite it allows deconvolution of temperature and ice-volume signals to infer past ocean temperatures and salinities (assuming the relationship between seawater δ18O and salinity is known). Such work assumes that temperature is the only, or at least the dominant, environmental controller of foraminiferal Mg/Ca. The semi-enclosed Mediterranean Sea, where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 °C to 8 °C, provides a relevant setting to test this assumption outside the laboratory. In this study, planktonic foraminifera (O. universa, G. siphonifera, G. bulloides and G. ruber (white) and (pink)) were picked from 11 box core tops spanning the Mediterranean salinity gradient and analysed for their trace-element concentrations. Mg/Ca ratios are higher, for the associated calcification temperatures, than in other regions where calibrations have been conducted and correlate poorly with calcification temperature. Mg/Ca ratios are particularly high for samples from the Eastern Mediterranean where salinity is unusually high. Correlations of Mg/Ca with the calcification salinity are statistically significant with Mg/Ca changing by 15–59% per psu, suggesting that salinity may act as a control on Mg/Ca ratios in addition to the dominant temperature control. We show that contamination by non-carbonate material and diagenetic high-Mg carbonate overgrowths cannot account for the observed trend of increasing Mg/Ca with salinity. A relationship between Mg/Ca and salinity is also suggested by re-analysis of calibrations from open-ocean settings. These new Mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the Mg/Ca palaeothermometer should be considered even in open-ocean settings, particularly where large salinity changes occurred in the past. 相似文献
8.
With a detailed chemistry scheme for the middle atmosphere up to 70 km which has been added to the 3-D Karlsruhe simulation model of the middle atmosphere (KASIMA), the effects of coupling chemistry and dynamics through ozone are studied for the middle atmosphere. An uncoupled version using an ozone climatology for determining heating rates and a coupled version using on-line ozone are compared in a 10-month integration with meteorological analyses for the winter 1992/93 as the lower boundary condition. Both versions simulate the meteorological situation satisfactorily, but exhibit a too cold lower stratosphere. The on-line ozone differs from the climatological data between 20 and 40 km by exhibiting too high ozone values, whereas in the lower mesosphere the ozone values are too low. The coupled model version is stable and differs only above 40 km significantly from the uncoupled version. Direct heating effects are identified to cause most of the differences. The well-known negative correlation between temperature and ozone is reproduced in the model. As a result, the coupled version slightly approaches the climatological ozone field. Further feedback effects are studied by using the on-line ozone field as a basis for an artificial climatology. For non-disturbed ozone conditions realistic monthly and zonally averaged ozone data are sufficient to determine the heating rates for modelling the middle atmosphere. 相似文献
9.
10.
An event based, long-term, climatological analysis is presented that allows the creation of coastal ocean atmospheric forcing on the coastal ocean that preserves both frequency of occurrence and event time history. An algorithm is developed that identifies individual storm event (cold fronts, warm fronts, and tropical storms) from meteorological records. The algorithm has been applied to a location along the South Atlantic Bight, off South Carolina, an area prone to cyclogenesis occurrence and passages of atmospheric fronts. Comparison against daily weather maps confirms that the algorithm is efficient in identifying cold fronts and warm fronts, while the identification of tropical storms is less successful. The average state of the storm events and their variability are represented by the temporal evolution of atmospheric pressure, air temperature, wind velocity, and wave directional spectral energy. The use of uncorrected algorithm-detected events provides climatologies that show a little deviation from those derived using corrected events. The effectiveness of this analysis method is further verified by numerically simulating the wave conditions driven by the characteristic wind forcing and comparing the results with the wave climatology that corresponds to each storm type. A high level of consistency found in the comparison indicates that this analysis method can be used for accurately characterizing event-based oceanic processes and long-term storm-induced morphodynamic processes on wind-dominated coasts. 相似文献
11.
A 30-year (1971–2000) temperature and salinity climatology is presented for surface and near-bed regions of the NW European shelf seas, with a resolution of 1/6° longitude by 1/10° latitude. The data have been extracted from the International Council for the Exploration of the Sea (ICES) data centre and supplemented by additional records from the World Ocean Data Centre (WODC). From the original data, which are irregularly distributed in space and time, the mean monthly temperature and salinity are calculated, as well as the climatic mean annual cycle. The climatology presented here is an improvement upon all existing climatologies presented in the literature for the NW European shelf; covering a wider area on a finer scale and including the surface and near-bed distribution of both temperature and salinity. Comparison of our data with existing climatologies shows good agreement, with differences occurring where our climatology is an improvement. This climatology, which will prove to be valuable to many users in the marine community, will be regularly updated and made available to all users via the ICES data centre. 相似文献
12.
Clément de Boyer Montégut Fabien Durand Romain Bourdallé-Badie Bruno Blanke 《Ocean Dynamics》2014,64(6):809-822
The barrier layer (BL) — a salinity stratification embedded in the upper warm layer — is a common feature of the tropical oceans. In the northern Indian Ocean, it has the potential to significantly alter the air–sea interactions. In the present paper, we investigate the spatio-temporal structure of BL in the Arabian Sea during summer monsoon. This season is indeed a key component of the Asian climate. Based on a comprehensive dataset of Conductivity–Temperature–Depth (CTD) and Argo in situ hydrographic profiles, we find that a BL exists in the central Arabian Sea during summer. However, it is highly heterogeneous in space, and intermittent, with scales of about ～100 km or less and a couple of weeks. The BL patterns appear to be closely associated to the salinity front separating two water masses (Arabian Sea High Salinity Water in the Northern and Eastern part of the basin, fresher Bay of Bengal Water to the south and to the west). An ocean general circulation model is used to infer the formation mechanism of the BL. It appears that thick (more than 40 m) BL patterns are formed at the salinity front by subduction of the saltier water mass under the fresher one in an area of relatively uniform temperature. Those thick BL events, with variable position and timing, result in a broader envelope of thinner BL in climatological conditions. However, the individual patterns of BL are probably too much short-lived to significantly affect the monsoonal air–sea interactions. 相似文献
13.
地震剖面与海水物性之间的关系是地震海洋学亟待研究的关键问题之一.本文选取地中海涡旋、各大洋不同纬度和南海东北部不同月份的三组CTD资料,按海域、季节和深度对法向相对贡献进行计算和分析,并从地中海涡旋CTD资料中选取典型温盐界面进行非法向相对贡献的研究.结果表明声速和温度的平均法向相对贡献随着海域、季节和深度呈相似性变化,其变化范围主要由相邻海水团之间的物性差异决定,分别为78%~94%和74%~98%.声速和温度(密度和盐度)的非法向相对贡献随着入射角的增加而增大(减小).用于反演的叠前地震数据应尽量包含较宽入射角范围的道集,特别是对于相对贡献较小的密度和盐度,包含小入射角的地震道对提高反演结果的精度尤为重要.通过对比地中海涡旋的Turner角剖面和相对贡献结果,发现Turner角对相对贡献具有很好的指示作用,其密度和盐度相对贡献较大的区域对应于Turner角为-45°的双稳定区域与扩散对流区域的边界附近,在此区域的密度比为零或较小.南北极附近海域的密度比较小,从而导致高纬度站位出现声速和温度相对贡献偏小的现象.南海东北部冬季表层海水的温度和声速相对贡献偏大则可能是由于黑潮侵入导致海水层温度差异及密度比变大引起. 相似文献
14.
Evaluation of efficiency of different estimation methods for missing climatological data 总被引：2，自引：1，他引：1
Mahsa Hasanpour Kashani Yagob Dinpashoh 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(1):59-71
Reliable estimation of missing data is an important task for meteorologists, hydrologists and environment protection workers
all over the world. In recent years, artificial intelligence techniques have gained enormous interest of many researchers
in estimating of missing values. In the current study, we evaluated 11 artificial intelligence and classical techniques to
determine the most suitable model for estimating of climatological data in three different climate conditions of Iran. In
this case, 5 years (2001–2005) of observed data at target and neighborhood stations were used to estimate missing data of
monthly minimum temperature, maximum temperature, mean air temperature, relative humidity, wind speed and precipitation variables.
The comparison includes both visual and parametric approaches using such statistic as mean absolute errors, coefficient of
efficiency and skill score. In general, it was found that although the artificial intelligence techniques are more complex
and time-consuming models in identifying their best structures for optimum estimation, but they outperform the classical methods
in estimating missing data in three distinct climate conditions. Moreover, the in-filling done by artificial neural network
rivals that by genetic programming and sometimes becomes more satisfactory, especially for precipitation data. The results
also indicated that multiple regression analysis method is the suitable method among the classical methods. The results of
this research proved the high importance of choosing the best and most precise method in estimating different climatological
data in Iran and other arid and semi-arid regions. 相似文献
15.
Recently Thompson et al. (2006. A simple method for reducing seasonal bias and drift in eddy resolving ocean models. Ocean Modelling 13, 109–125.) proposed a new method for suppressing the bias and drift of ocean circulation models. The basic idea is to nudge the model toward gridded climatologies of observed temperature and salinity in prescribed frequency–wavenumber bands; outside of these bands the model's dynamics are not directly affected by the nudging and the model state can evolve prognostically. Given the restriction of the nudging to certain frequency–wavenumber bands, the method is termed spectral nudging. The frequency–wavenumber bands are chosen to capture the information in the climatology and thus are centered on the climatological frequencies of zero, one cycle per year and its harmonics, and also low wavenumbers (reflecting the smooth nature of gridded climatologies). The new method is applied in this study to a fully nonlinear, 3D baroclinic circulation model of the continental shelves and inland seas of Atlantic Canada and the northeast US. It is shown that the scheme can suppress drift and bias in a nine month integration (February–October, 2002) while still allowing realistic evolution of tides, surges and wind and tide-driven coastal upwelling. It is also shown that density stratification can affect significantly tidal elevations in some regions. The implications for ocean hindcasting and short-term forecasting are discussed. 相似文献
16.
Rathnayake Samurdhika Tenzer Robert Chen Wenjin Eshagh Mehdi Pitoňák Martin 《Surveys in Geophysics》2021,42(4):839-897
Surveys in Geophysics - Since marine seismic studies are relatively sparse and unevenly distributed, detailed tomographic images of the Moho geometry under large parts of the world’s oceans... 相似文献
17.
During the years 1993 to 1996 the MAST project “Northwest European Shelf Programme (NOWESP)p ]During the years 1993 to 1996 the MAST project “Northwest European Shelf Programme (NOWESP)” has compiled most available observations for nine key state variables, namely temperature, salinity, phosphate, nitrate, nitrite, ammonia, silicate, suspended particulate matter (SPM) and chlorophyll, for the Northwest European Shelf. One important aim of NOWESP was to derive mean spatial distributions for each month by merging the available data to construct climatological monthly mean distributions to picture the climatological annual cycle, disregarding possible trends, e.g. in the coastal areas. In these areas the horizontal distributions have a bias towards the last fifteen years of observation because of the trends and of the increasing number of observations, and the monthly mean data are representative of the decade 1984 to 1993. Maps of horizontal distributions of temperature and salinity and of the concentrations of the nutrients phosphate, nitrate, nitrite, ammonia and silicate, of SPM and of chlorophyll are presented here for the months February, May, August and November. The properties of a few averaging (interpolation) methods are discussed and the method chosen, i.e. exponentially distance weighted averaging, is compared to the other methods. More details and maps for every month are given in the corresponding technical report by Radach and Gekeler [1997]. 相似文献
18.
A Comprehensive Dynamic Threshold Algorithm for Daytime Sea Fog Retrieval over the Chinese Adjacent Seas 总被引：2，自引：0，他引：2
Sea fog influences human activities over oceans. It is somewhat difficult to separate sea fog from marine boundary stratus (low stratus and stratocumulus) by satellites due to their microphysical similarities and shared spectral features. For the purpose of improving sea fog detection over the Chinese adjacent seas where fog is common during the spring–summer seasons, the vertical structures of fog and stratus were analyzed using ground-based soundings, resulting in the observation of very explicit discrepancies between them, in terms of TAT ? SST (TAT, the temperature at tops of fog or stratus; SST, the sea surface temperature). Based on these discrepancies and on previous related studies, we suggest a comprehensive dynamic threshold algorithm. The method combines real-time brightness temperature from Moderate Resolution Imaging Spectroradiometer channel 31 (~11 μm) with climatological monthly mean SSTs to produce a threshold that is monthly-dependent. The retrieved results are generally consistent with the observations from meteorological stations near the coast, on islands and from ships, and the scores of validation by conventional methods are promising. The distribution patterns of the retrieved sea fog frequency in May and June from 2006 to 2010 are both compatible with that from ship-based observations and exhibit more details that are consistent with our understanding of sea fog characteristics. This study is helpful for marine weather service and the improvement of models for sea fog forecasting. 相似文献
19.
Abstract This paper describes a research project based in Cyprus to investigate a number of different methods for determining quantitative recharge to aquifers in semiarid areas. Large lysimeters and geochemical profile techniques have been used in the southeastern Mesaoria area of Cyprus where there has already been a quantitative water resources investigation and where a groundwater model is in preparation. Further joint geochemical and lysimeter studies are also being undertaken in the Akrotiri peninsula (average annual rainfall 430 mm). Excavation and piling techniques have been used to install the lysimeters which are up to 100 m2 in area by 4 m deep. The lysimeters have been made as large as possible to minimize edge effects whilst maintaining the soil and aquifer material within them in an ‘undisturbed’ state. A dry drilling method has been developed to obtain sand samples from the unsaturated zone together with a method for processing the core material to obtain data on moisture and solutes. Chloride profiles have been interpreted to provide estimates of the direct recharge component using a steady state, mass balance approach and initial results compare favourably with tritium estimates. The preliminary results for recharge obtained by the different techniques are compared with each other and with estimates obtained from conventional methods. Initial results from the lysimeters indicate a current annual recharge of 5 mm in southeastern Mesaoria (1978), whilst a mean annual recharge of 50 mm at Akrotiri has been obtained by the chloride profile method. 相似文献
20.
The ecohydrological imprint of deforestation in the semiarid Chaco: insights from the last forest remnants of a highly cultivated landscape 
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下载免费PDF全文 The semiarid Chaco plains present one of the highest rates of forest clearing and agricultural expansion of the world. In other semiarid plains, such massive vegetation replacements initiated a groundwater recharge and salt mobilization process that, after decades, raised regional water tables and salts to the surface, degrading agricultural and natural ecosystems. Indirect evidence suggests that this process (known as dryland salinity) began in the Chaco plains. Multiple approaches (deep soil profiles, geoelectric surveys and monitoring of groundwater salinity, level and isotopic composition) were combined to assess the dryland salinity status in one of the oldest and most active agricultural hotspots of the region, where isolated forest remnants occupy an extremely flat cultivated matrix. Full vadose moisture and chloride profiles from paired agriculture‐forest stands (17 profiles, six sites) revealed the following: a generalized onset of deep drainage with cultivation (32 to >87 mm year?1), full leaching of native chloride pools (13.7 ± 2.5 kg m?2) down to the water table after >40 years following clearing and differential groundwater table rises (0.7 to 2 m shallower water tables under agriculture than under neighbouring forests). Continuous level monitoring showed abrupt water table rises under annual crops (up to 2.6 m in 15 days) not seen under forests or pastures. Varying deep drainage rates and groundwater isotopic composition under agricultural plots suggest that these pulses are strongly modulated by crop choices and sequences. In contrast to other dryland salinity‐affected areas of the world, forest remnants in the study area (10–20% of the area) are not only surviving the observed hydrological shifts but also sustaining active salty groundwater transpirative discharge, as evidenced by continuous water table records. The overall impact of these forest remnants on lowering neighbouring water tables would be limited by the low hydraulic conductivity of the sediments. As highly cultivated areas of the Chaco evolve to new hydrological conditions of shallower saline water tables, innovative crop rotations that minimize recharge, enhance transpirative discharge and tolerate salinity will be needed. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献