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11.
Xavier Fettweis Georges Mabille Michel Erpicum Samuel Nicolay Michiel Van den Broeke 《Climate Dynamics》2011,36(1-2):139-159
In order to assess the impact of the mid-tropospheric circulation over the Greenland ice sheet (GrIS) on surface melt, as simulated by the regional climate model MAR, an automatic Circulation type classification (CTC) based on 500?hPa geopotential height from reanalyses is developed. General circulation correlates significantly with the surface melt anomalies for the summers in the period 1958?C2009. The record surface melt events observed during the summers of 2007?C2009 are linked to the exceptional persistence of atmospheric circulations favouring warm air advection. The CTC emphasizes that summer 500?hPa circulation patterns have changed since the beginning of the 2000s; this process is partly responsible for the recent warming observed over the GrIS. 相似文献
12.
Michael Fettweis Frederic Francken Dries Van den Eynde Toon Verwaest Job Janssens Vera Van Lancker 《Continental Shelf Research》2010
Multi-sensor tripod measurements in the high-turbidity area of the Belgian nearshore zone (southern North Sea) allowed investigating storm effects on near bed suspended particulate matter (SPM) concentrations. The data have shown that during or after a storm the SPM concentration increases significantly and that high concentrated mud suspensions (HCMS) are formed. Under these conditions, about 3 times more mass of SPM was observed in the water column, as compared to calm weather conditions. The following different sources of fine-grained sediments, influencing the SPM concentration signal, have been investigated: wind direction and the advection of water masses; the previous history and occurrence of fluffy layers; freshly deposited mud near the disposal grounds of dredged material, navigation channels and adjacent areas; and the erosion of medium-consolidated mud of Holocene age. 相似文献
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Hydro-meteorological influences and multimodal suspended particle size distributions in the Belgian nearshore area (southern North Sea) 总被引：5，自引：2，他引：3
Michael Fettweis Matthias Baeye Byung Joon Lee Peihung Chen Jason C. S. Yu 《Geo-Marine Letters》2012,32(2):123-137
Suspended particulate matter (SPM) concentration and particle size distribution (PSD) were assessed in a coastal turbidity
maximum area (southern North Sea) during a composite period of 37 days in January–April 2008. PSDs were measured with a LISST
100X and classified using entropy analysis in terms of subtidal alongshore flow. The PSDs during tide-dominated conditions
showed distinct multimodal behaviour due to flocculation, revealing that the building blocks of flocs consist of primary particles
(<3 μm) and flocculi (15 μm). Flocculi comprise clusters of clay minerals, whereas primary particles have various compositions
(calcite, clays). The PSDs during storms with a NE-directed alongshore subtidal current (NE storms) are typically unimodal
and characterised by mainly granular material (silt, sand) resuspended from the seabed. During storms with a SW-directed alongshore
subtidal current (SW storms), by contrast, mainly flocculated material can be identified in the PSDs. The findings emphasise
the importance of wind-induced advection, alongshore subtidal flow and highly concentrated mud suspensions (HCMSs) as regulating
mechanisms of SPM concentration, as well as other SPM characteristics (cohesiveness or composition of mixed sediment particles)
and size distribution in a high-turbidity area. The direction of subtidal alongshore flow during SW storm events results in
an increase in cohesive SPM concentration, HCMS formation, and the armouring of sand; by contrast, there is a decrease in
cohesive SPM concentration, no HCMS formation, and an increase in sand and silt in suspension during NE storms. 相似文献
15.
Samuel Nicolay Georges Mabille Xavier Fettweis Michel Erpicum 《Climate Dynamics》2009,33(7-8):1117-1129
A wavelet-based methodology is applied to relevant climatic indices and air temperature records and allow to detect the existence of unexpected cycles. The scale spectrum shows the presence of two cycles of about 30 and 43 months, respectively, in the air–temperature time series, in addition to the well-known cycles of 1 day and 1 year. The two cycles do not affect the globe uniformly: some regions seem to be more influenced by the period of 30 months (e.g. Europe), while other areas are affected by the period of 43 months (e.g. North-West of the USA). Similar cycles are found in the indices and the regions influenced by these indices: the NAO index and the Western Europe display a cycle of 30 months, while the cycle of 43 months can be found in the ENSO index and in regions where it is known to have an impact. 相似文献
16.
Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensing (moderate resolution imaging spectroradiometer, MODIS) samplings in the Belgian nearshore area (southern North Sea) are combined in order to evaluate their heterogeneity and the sampling techniques. In situ SPM concentration measurements are from a vessel (tidal cycle) and from a tripod. During the tidal cycle measurements, vertical profiles of SPM concentration have been collected; these profiles have been used as a link between satellite surface and near-bed tripod SPM concentrations. In situ time series at fixed locations using a tripod are excellent witnesses of SPM concentrations under all weather conditions and may catch SPM concentration variability with a much finer scale. The heterogeneity has been statistically assessed by comparing the SPM concentration frequency distributions. Tidal cycle, tripod and MODIS datasets have different distributions and represent a different subpopulation of the whole SPM concentrations population. The differences between the datasets are related to meteorological conditions during the measurements; to near-bed SPM concentration dynamics, which are partially uncoupled from processes higher up in the water column; to the sampling methods or schemes and to measurement uncertainties. In order to explain the differences between the datasets, the tripod data have been subsampled using wave height conditions and satellite and tidal cycle sampling schemes. It was found that satellites and low-frequent tidal cycle measurements are biased towards good weather condition or spring–summer seasons (satellite). The data show that the mean surface SPM concentration derived from satellite data is slightly lower than from in situ tidal cycle measurements, whereas it is significantly lower than the mean SPM concentration interpolated to the water surface from the tripod measurements. This is explained by the errors arising from the interpolation along the vertical profiles, but also by the fact that satellite-measured signal saturates in the visible band used to retrieve SPM concentration in very turbid waters. 相似文献
17.
High-resolution modelling of the Antarctic surface mass balance, application for the twentieth, twenty first and twenty second centuries 总被引：1，自引：1，他引：0
Cécile Agosta Vincent Favier Gerhard Krinner Hubert Gallée Xavier Fettweis Christophe Genthon 《Climate Dynamics》2013,41(11-12):3247-3260
About 75 % of the Antarctic surface mass gain occurs over areas below 2,000 m asl, which cover 40 % of the grounded ice-sheet. As the topography is complex in many of these regions, surface mass balance modelling is highly dependent on horizontal resolution, and studying the impact of Antarctica on the future rise in sea level requires physical approaches. We have developed a computationally efficient, physical downscaling model for high-resolution (15 km) long-term surface mass balance (SMB) projections. Here, we present results of this model, called SMHiL (surface mass balance high-resolution downscaling), which was forced with the LMDZ4 atmospheric general circulation model to assess Antarctic SMB variability in the twenty first and the twenty second centuries under two different scenarios. The higher resolution of SMHiL better reproduces the geographical patterns of SMB and increase significantly the averaged SMB over the grounded ice-sheet for the end of the twentieth century. A comparison with more than 3200 quality-controlled field data shows that LMDZ4 and SMHiL reproduce the observed values equally well. Nevertheless, field data below 2,000 m asl are too scarce to efficiently show the added value of SMHiL and measuring the SMB in these undocumented areas should be a future scientific priority. Our results suggest that running LMDZ4 at a finer resolution (15 km) may give a future increase in SMB in Antarctica that is about 30 % higher than by using its standard resolution (60 km) due to the higher increase in precipitation in coastal areas at 15 km. However, a part (～15 %) of these discrepancies could be an artefact from SMHiL since it neglects the foehn effect and likely overestimates the precipitation increase. Future changes in the Antarctic SMB at low elevations will result from the competition between higher snow accumulation and runoff. For this reason, developing downscaling models is crucial to represent processes in sufficient detail and correctly model the SMB in coastal areas. 相似文献
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Sediment mobility in response to tidal and wind-driven flows along the Belgian inner shelf,southern North Sea 总被引：3，自引：2，他引：1
Matthias Baeye Michael Fettweis George Voulgaris Vera Van Lancker 《Ocean Dynamics》2011,61(5):611-622
The effect of hydro-meteorological forcings (tidal and wind-induced flows) on the transport of suspended particulate matter
(SPM), on the formation of high-concentrated mud suspensions and on the occurrence of sand–mud suspensions has been studied
using long-term multi-parametric observations. Data have been collected in a coastal turbidity maximum area (southern North
Sea) where a mixture of sandy and muddy sediments prevails. Data have been classified according to variations in subtidal
alongshore currents, with the direction of subtidal flow depending on wind direction. This influences the position of the
turbidity maximum; as such also the origin of SPM. Winds blowing from the NE will increase SPM concentration, whilst SW winds
will induce a decrease. The latter is related to advection of less turbid English Channel water, inducing a shift of the turbidity
maximum towards the NE and the Westerschelde estuary. Under these conditions, marine mud will be imported and buffered in
the estuary. Under persistent NE winds, high-concentrated mud suspensions are formed and remain present during several tidal
cycles. Data show that SPM consists of a mixture of flocs and locally eroded sand grains during high currents. This has implications
towards used instrumentation: SPM concentration estimates from optical backscatter sensors will only be reliable when SPM
consists of cohesive sediments only; with mixtures of cohesive and non-cohesive sediments, a combination of both optical and
acoustic sensors are needed to get an accurate estimate of the total SPM concentration. 相似文献
20.
Fettweis M Baeye M Francken F Lauwaert B Van den Eynde D Van Lancker V Martens C Michielsen T 《Marine pollution bulletin》2011,62(2):258-269
The impact of continuous disposal of fine-grained sediments from maintenance dredging works on the suspended particulate matter concentration in a shallow nearshore turbidity maximum was investigated during dredging experiment (port of Zeebrugge, southern North Sea). Before, during and after the experiment monitoring of SPM concentration using OBS and ADV altimetry was carried out at a location 5 km west of the disposal site. A statistical analysis, based on the concept of populations and sub-sampling, was applied to evaluate the effect. The data revealed that the SPM concentration near the bed was on average more than two times higher during the dredging experiment. The disposed material was mainly transported in the benthic layer and resulted in a long-term increase of SPM concentration and formation of fluid mud layers. The study shows that SPM concentration can be used as an indicator of environmental changes if representative time series are available. 相似文献