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Inga Golbeck Xin Li Frank Janssen Thorger Brüning Jacob W. Nielsen Vibeke Huess Johan Söderkvist Bjarne Büchmann Simo-Matti Siiriä Olga Vähä-Piikkiö Bruce Hackett Nils M. Kristensen Harald Engedahl Ed Blockley Alistair Sellar Priidik Lagemaa Jose Ozer Sebastien Legrand Patrik Ljungemyr Lars Axell 《Ocean Dynamics》2015,65(12):1603-1631
2.
Remotely sensed observations of sea-level anomaly and sea-surface temperature have been assimilated into an implementation
of the Miami Isopycnic Coordinate Ocean Model (MICOM) for the Indian Ocean using the Ensemble Kalman Filter (EnKF). The system
has been applied in a hindcast validation experiment to examine the properties of the assimilation scheme when used with a
full ocean general circulation model and real observations. This work is considered as a first step towards an operational
ocean monitoring and forecasting system for the Indian Ocean. The assimilation of real data has demonstrated that the sequential
EnKF can efficiently control the model evolution in time. The use of data assimilation requires a significant amount of additional
processing and computational resources. However, we have tried to justify the cost of using a sophisticated assimilation scheme
by demonstrating strong regional and temporal dependencies of the covariance statistics, which include highly anisotropic
and flow-dependent correlation functions. In particular, we observed a marked difference between error statistics in the equatorial
region and at off-equatorial latitudes. We have also demonstrated how the assimilation of SLA and SST improves the model fields
with respect to real observations. Independent in situ temperature profiles have been used to examine the impact of assimilating
the remotely sensed observations. These intercomparisons have shown that the model temperature and salinity fields better
resemble in situ observations in the assimilation experiment than in a model free-run case. On the other hand, it is also
expected that assimilation of in situ profiles is needed to properly control the deep ocean circulation.
Received: 8 January 2002 / Accepted: 8 April 2002 相似文献
3.
Maria Gästgifvars Sylvin Müller-Navarra Lennart Funkquist Vibeke Huess 《Ocean Dynamics》2008,58(2):139-153
This paper is devoted to the validation of water level forecasts in the Gulf of Finland. Daily forecasts produced by four
setups of operational, three-dimensional Baltic Sea oceanographic models are analyzed using statistical means and are compared
with water level observations at three Finnish stations located on the northern coast of the Gulf of Finland. The overall
conclusion is that the operational systems were skillful in forecasting water level variations during the study period from
November 1, 2003, to January 31, 2005. The factors causing differences between the water level forecasts of different models
are discussed as well. An important task of operational sea level forecasting services is to provide accurate and early information
about extreme water levels, both positive and negative surges. During the study period, two major winter storms occurred which
caused coastal flooding in the region. According to our analysis, the operational models forecast the rise of water levels
during these events rather successfully. Nowadays, operational forecasts can provide early warnings of extreme water levels
at least 1 day in advance, which may be regarded as a minimum requirement for an operational forecasting system. The paper
concludes that the models generally performed very well, with over 93% of the hourly water level forecasts found to be within
the range of ±15 cm of the observed water levels, and with the timing of the water level peaks accurately predicted. Further
discussion and studies dealing with the assessment of the skills of both operational meteorological and oceanographic forecasts,
especially in connection with rare surge events, will be necessary. Skill assessment of operational oceanographic models would
be relatively easy if acceptable error limits or a quality system was developed for the Baltic Sea operational models. 相似文献
4.
Mesoscale modeling study of the oceanographic conditions off the southwest coast of India 总被引:1,自引:0,他引:1
Vibeke E. Haugen Ola M. Johannessen Geir Evensen 《Journal of Earth System Science》2002,111(3):321-337
A high resolution model, using the Miami Isopycnic Coordinate Ocean Model (MICOM), has been implemented for the first time
to study the seasonal circulation and coastal upwelling off the southwest Indian coast during 1974. This model is part of
a model and data assimilation system capable of describing the ocean circulation and variability in the Indian Ocean and its
predictability in response to the monsoon system.
Along the southwest coast of India the dominant coastal current is the reversing West Indian Coastal Current which is well
simulated and described, in addition to the weaker undercurrent of the opposite direction. Upwelling of cold water, 4‡C lower
than offshore temperatures appear in April. The upwelling intensifies with the southwest monsoon and is simulated in accordance
within situ observations. Upwelling appears to be strongest off Cochin and Quilon, and the upwelling of cold water is seen together with
a decrease in salinity in the model simulation. 相似文献
5.
Vibeke Bruvoll Yngve Kristoffersen Bernard J. Coakley John R. Hopper 《Marine Geophysical Researches》2010,31(3):149-171
The first high resolution multichannel seismic data from the Mendeleev and Alpha Ridges in the Arctic Ocean have been used
to investigate the depositional history, and compare acoustic stratigraphies of the three main sub-marine ridges (Mendeleev,
Alpha and Lomonosov) in the polar ocean. Acoustic basement on the Mendeleev Ridge is covered by a ~0.6–0.8 s thick sediment
drape over highs and up to 1.8 s within grabens. A pronounced angular discordance at 0.18–0.23 s below the seafloor along
the middle to upper slopes divides the succession into an upper, undisturbed, uniformly thick, hemipelagic drape (Unit M1)
and a partially truncated lower unit (Unit M2) characterized by strong reflection bands. Unit M2 is thicker in intra-ridge
grabens and includes three sub-units with abundant debris flows in the uppermost subunit (M2a). The discordance between Units
M1 and M2 most likely relates to instability along the middle to upper slopes and mass wasting, triggered by tectonic activity.
The scars were further smoothed by bottom current erosion. We observe comparable acoustic stratigraphy and discordant relationships
on the investigated northwestern part of Alpha Ridge. Similarly, on the central Lomonosov Ridge, Paleocene and younger sediments
sampled by scientific drilling include an uppermost ~0.2 s thick drape overlying, highly reflective deposits with an angular
unconformity confined to the upper slope on both sides of the ridge. Sediment instability on the three main ridges was most
likely generated by a brief phase of tectonic activity (~14.5–22 Ma), coinciding with enhanced bottom circulation. These events
are coeval with the initial opening of the Fram Strait. The age of the oldest sediments above acoustic basement on the Mendeleev-
and west-central Alpha Ridges is estimated to be 70–75 Ma. 相似文献
6.
Geochemical processes and solute transport at the seawater/freshwater interface of a sandy aquifer 总被引:2,自引:0,他引:2
Martin Søgaard Andersen Vibeke Nyvang Rasmus Jakobsen Dieke Postma 《Geochimica et cosmochimica acta》2005,69(16):3979-3994
Geochemical processes occurring at a seawater/freshwater interface were studied in a shallow coastal siliclastic aquifer containing minor amounts of calcite. Data were collected from 106 piezometers in a 120-m transect from the coastline and landward. In the first 40 m from the coastline, a wedge of saltwater is intruding below the freshwater aquifer. The aquifer is strongly reduced with mineralization of organic matter by methanogenesis in the freshwater aquifer, and sulfate reduction dominating in the most seaward part of the saline aquifer. The spatial separation of cations in the aquifer indicated a slow freshening process where Ca2+ from freshwater displaced the marine cations Na+ and Mg2+ from the exchanger complex. The resulting loss of Ca2+ from solution decreases the saturation state for calcite and possibly causes calcite dissolution. A storm-flooding event was recorded where pulses of dense seawater sank through the fresh aquifer. As a result, the terminal electron accepting process switched from methanogenesis to sulfate reduction. The pulses of sinking seawater also triggered cation exchange reactions where Ca2+ was expelled from the exchanger by seawater Na+ and Mg2+. The released Ca2+ is being flushed from the aquifer by groundwater flow, and this export of Ca2+ will, in the long term, cause decalcification of the sediment. The water composition in the aquifer is in a transient state as the result of various processes that operate on different timescales. Oxidation of organic matter occurs continuously but at a rate decreasing on a geological time scale. The freshening of the aquifer operates on the timescale of a few years. The episodic flooding and sinking of seawater through the aquifer proceeds in the course of days to weeks, but occurs irregularly with years in between. 相似文献
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