116 research outputs found
Impact of data assimilation of glider observations in the Ionian Sea (Eastern Mediterranean)
Glider observations of temperature, salinity and vertically averaged velocity in the Ionian Sea
(Eastern Mediterranean Sea), made in the period October 2004 - December 2004, were assimilated
into an operational forecasting model together with other in-situ and satellite observations. The
study area has a high spatial and temporal variability of near-surface dynamics, characterized by
the entrance of the Atlantic Ionian Stream (AIS) into the Northern Ionian Sea. The impact of glider
observations on the estimation of the circulation is studied, and it is found that their assimilation
locally improves the prediction of temperature, salinity, velocity and surface elevation fields.
However, only the assimilation of temperature and salinity together with the vertically averaged
velocity improves the forecast of all observed parameters. It is also found that glider observations
rapidly impact the analyses even remotely, and the remote impacts on the analyses remain several
months after the presence of the glider. The study emphasizes the importance of assimilating as
much as possible all available information from gliders, especially in dynamically complex areas
Ionian Sea circulation as clarified by assimilation of glider observations
Glider observations of temperature and salinity in the Ionian Sea (Eastern Mediterranean
Sea), made in the period October 2004-December 2004, were assimilated into an operational
forecasting model together with other in-situ and satellite observations. The impact of glider
data on the estimation of the circulation is studied and it is found that the assimilation of
glider data significantly improve the vertical structure of temperature and salinity fields and
remove biases. The accurate representation of the dynamical structures due to the assimilation
of glider data allowed a detailed analysis of the dynamics of the Atlantic Ionian Stream (AIS).
During autumn and in the Sicily Strait, the AIS is strengthened by the positive but weak wind
stress curl near the southern Sicilian coast and by the temperature gradient between the warm
surface mixed layer and the cold upwelled waters near Sicily. In winter the change of position
of the wind stress curl zero line and the cooling of the surface mixed layer forces the AIS to
shift southward in the Ionian Sea. The AIS is shown for the first time to pinch off an eddy in
the Ionian Sea
The Massive Wolf-Rayet Binary SMC WR7
We present a study of optical spectra of the Wolf--Rayet star AzV 336a (= SMC
WR7) in the Small Magellanic Cloud. Our study is based on data obtained at
several Observatories between 1988 and 2001. We find SMC WR7 to be a double
lined WN+O6 spectroscopic binary with an orbital period of 19.56 days. The
radial velocities of the He absorption lines of the O6 component and the strong
He{\sc ii} emission at 4686\AA of the WN component describe antiphased
orbital motions. However, they show a small phase shift of 1 day. We
discuss possible explanations for this phase shift. The amplitude of the radial
velocity variations of He {\sc ii} emission is twice that of the absorption
lines. The binary components have fairly high minimum masses, 18
\modot and 34 \modot for the WN and O6 components, respectively.Comment: Accepted by MNRA
The massive Wolf-Rayet binary SMC WR7
We present a study of optical spectra of the Wolf-Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56 d. The radial velocities of the He absorption lines of the O6 component and the strong He II emission at λ4686 Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ∼ 1 d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He II emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼ 18 and 34 M⊙ for the WN and O6 components, respectively.Facultad de Ciencias Astronómicas y Geofísica
Integration of Argo trajectories in the Mediterranean Forecasting System and impact on the regional analysis of the western Mediterranean circulation
The impact of Argo float trajectory assimilation on the quality of ocean analyses is studied by means of an operational oceanographic model implemented in the Mediterranean Sea and a 3D-Var assimilation scheme. For the first time, both Argo trajectories and vertical profiles of temperature and salinity (TS) together with satellite altimeter data of sea level anomaly (SLA) are assimilated to produce analyses for short-term forecasts. The study period covers 3 months during winter 2005 when four Argo trajectories were present in the northwestern Mediterranean Sea. The scheme is first assessed computing the misfits between observations and model forecast and analysis. The misfit statistics appear improved for float trajectories, while they are not degraded for the other assimilated variables (TS profiles and SLA). This indicates that the trajectory integration is consistent with the other components of the assimilation system and provides new information on horizontal pressure gradients. Comparisons between analyses obtained with and without trajectory assimilation suggest that trajectory assimilation can have an impact on the description of boundary currents and their instabilities, as well as mesoscale activity at regional scales. Changes are depicted by intermediate water mass redistributions, mesoscale eddy relocations, and net transport modulations. These impacts are detailed and assessed considering historical and simultaneous in situ data sets. The results motivate the integration of Argo trajectories in the operational Mediterranean Forecasting System
Integration of ARGO trajectories in the Mediterranean Forecasting System and impact on the regional analysis of the Western Mediterranean circulation
The impact of ARGO trajectory assimilation on the quality of ocean analyses is studied by means of
an operational oceanographic model implemented in the Mediterranean Sea and a 3D-var
assimilation scheme. For the first time, both ARGO trajectories and vertical profiles together with
satellite data are assimilated to produce analyses for short term forecasts. The study period covers
three months during winter 2005 when four ARGO trajectories were present in the northwestern
Mediterranean Sea. It is shown that their integration is consistent with the other components of the
assimilation system, and it contributes to refine the model error structure with new information on
horizontal pressure gradients. So the analysis benefits of a more accurate description of the
boundary currents and their instabilities that drive the mesoscale activity of regional circulations.
As a consequence, the trajectory assimilation remotely and significantly influences the basin scale
circulation. Changes can be depicted by intermediate water mass redistributions, mesoscale eddy
relocations or net transports modulations. These impacts are detailed and assessed considering
historical and contemporary datasets. The obtained qualitative and quantitative agreements motivate
the integration of ARGO trajectories in the operational Mediterranean Forecasting System
Potential for an underwater glider component as part of the Global Ocean Observing System
The contributions of autonomous underwater gliders as an observing platform in the in-situ global ocean observing system (GOOS) are investigated. The assessment is done in two ways: First, the existing in-situ observing platforms contributing to GOOS (floats, surface drifters, moorings, research/commercial ships) are characterized in terms of their current capabilities in sampling key physical and bio-geochemical oceanic processes. Next the gliders’ capabilities are evaluated in the context of key applications. This includes an evaluation of 140 references presented in the peer-reviewed literature. It is found that GOOS has adequate coverage of sampling in the open ocean for several physical processes. There is a lack of data in the present GOOS in the transition regions between the open ocean and shelf seas. However, most of the documented scientific glider applications operate in this region, suggesting that a sustained glider component in the GOOS could fill that gap. Glider data are included for routine product generation (e.g. alerts, maps). Other noteworthy process-oriented applications where gliders are important survey tools include local sampling of the (sub)mesoscale, sampling in shallow coastal areas, measurements in hazardous environments, and operational monitoring. In most cases, the glider studies address investigations and monitoring of processes across multiple disciplines, making use of the ease to implement a wide range of sensors to gliders. The maturity of glider operations, the wide range of applications that map onto growing GOOS regional needs, and the maturity of glider data flow all justify the formal implementation of gliders into the GOOS. Remaining challenges include the execution of coordinated multinational missions in a sustained mode as well as considering capacity-building aspects in glider operations as well as glider data use
Integration of ARGO trajectories in the Mediterranean Forecasting System and impact on the regional analysis of the Western Mediterranean circulation
The impact of ARGO float trajectory assimilation on the quality of ocean analyses is studied by
means of an operational oceanographic model implemented in the Mediterranean Sea and a 3D-var
assimilation scheme. For the first time, both ARGO trajectories and vertical profiles of temperature
and salinity (TS) together with satellite altimeter data of sea level anomaly (SLA) are assimilated to
produce analyses for short term forecasts. The study period covers three months during winter 2005
when four ARGO trajectories were present in the northwestern Mediterranean Sea. The scheme is
first assessed computing the misfits between observations and model forecast and analysis. The
misfit statistics appear improved for float trajectories, while they are not degraded for the other
assimilated variables (TS profiles and SLA). This indicates that the trajectory integration is
consistent with the other components of the assimilation system, and provides new information on
horizontal pressure gradients. Comparisons between analyses obtained with and without trajectory
assimilation suggest that trajectory assimilation can impact on the description of boundary currents
and their instabilities, as well as mesoscale activity at regional scales. Changes are depicted by
intermediate water mass redistributions, mesoscale eddy relocations and net transport modulations.
These impacts are detailed and assessed considering historical and simultaneous in-situ datasets.
The results motivate the integration of ARGO trajectories in the operational Mediterranean
Forecasting System
The massive Wolf-Rayet binary SMC WR7
We present a study of optical spectra of the Wolf-Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double-lined WN+O6 spectroscopic binary with an orbital period of 19.56 d. The radial velocities of the He absorption lines of the O6 component and the strong He II emission at λ4686 Å of the WN component describe anti-phased orbital motions. However, they show a small phase shift of ∼ 1 d. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He II emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼ 18 and 34 M⊙ for the WN and O6 components, respectively.Facultad de Ciencias Astronómicas y Geofísica
- …