ALBERT

Description: Long-time series of surface currents and meteorological parameters were analysed to estimate the variability of the upper layer circulation as a preliminary study of the Ligurian Air-Sea Interaction Experiment (LASIE07). Current meter data were collected by an upward-looking RDI Sentinel 300 kHz ADCP deployed in the Central Ligurian Sea (43°47.77' N; 9°02.85' E) near the meteo-oceanographic buoy ODAS ITALIA1 for over eight months. The ADCP sampled the upper 50 m of water column at 8 m vertical resolution and 1 h time interval; surface marine and atmospheric hourly data were provided by the buoy. Currents were mainly barotropic and directed NW, according to the general circulation of the area, had a mean velocity of about 18 cm s−1 and hourly mean peaks up to 80 m s−1. Most of the observed variability in the upper thermocline was determined by inertial currents and mesoscale activity due to the presence of the Ligurian Front. Local wind had a minor role in the near-surface circulation but induced internal waves propagating downward in the water column.

Description: Long-time series of surface currents and meteorological parameters were analysed to estimate the variability of the upper layer circulation and the response to the local winds. Current meter data were collected by an upward-looking RDI Sentinel 300 kHz ADCP deployed in the Central Ligurian Sea (43°47.77' N; 9°02.85' E) near the meteo-oceanographic buoy ODAS Italia 1 for more than eight months, from 13th of September 2003 to 24th of May 2004. The ADCP sampled the upper 50 m of water column at 8 m vertical resolution and 1 h time interval; surface marine and atmospheric hourly averaged data were provided by the buoy. Currents in the sampled layer were mainly barotropic, directed North-West in accordance with the general circulation of the area, and had a mean velocity of about 18 cm/s and hourly mean peaks up to 80 cm/s. Most of the observed variability in the upper thermocline was determined by inertial currents and mesoscale activity due to the presence of the Ligurian Front. Local wind had a minor role in the near-surface circulation but induced internal waves propagating downward in the water column.

Description: A network of three multi-sensor timeseries stations able to deliver real time physical and biochemical observations of the upper thermocline has been developed for the needs of the Mediterranean Forecasting System during the MFSTEP project. They follow the experience of the prototype M3A system that was developed during the MFSPP project and has been tested during a pilot pre-operational period of 22 months (2000–2001). The systems integrate sensors for physical (temperature, salinity, turbidity, current speed and direction) as well as optical and chemical observations (dissolved oxygen, chlorophyll-a, PAR, nitrate). The south Aegean system (E1-M3A) follows a modular design using independent mooring lines and collects biochemical data in the upper 100 m and physical data in the upper 500 m of the water column. The south Adriatic buoy system (E2-M3A) uses similar instrumentation but on a single mooring line and also tests a new method of pumping water samples from relatively deep layers, performing analysis in the protected "dry" environment of the buoy interior. The Ligurian Sea system (W1-M3A) is an ideal platform for air-sea interaction processes since it hosts a large number of meteorological sensors while its ocean instrumentation, with real time transmission capabilities, is confined in the upper 50 m layer. Despite their different architecture, the three systems have common sampling strategy, quality control and data management procedures. The network operates in the Mediterranean Sea since autumn 2004 collecting timeseries data for calibration and validation of the forecasting system as well for process studies of regional dynamics.

Description: A network of three multi-sensor timeseries stations able to deliver real time physical and biochemical observations of the upper thermocline has been developed for the needs of the Mediterranean Forecasting System during the MFSTEP project. They follow the experience of the prototype M3A system that was developed during the MFSPP project and has been tested during a pilot pre-operational period of 22 months (2000–2001). The systems integrate sensors for physical (temperature, salinity, turbidity, current speed and direction) as well as optical and chemical observations (dissolved oxygen, chlorophyll-a, PAR, nitrate). The south Aegean system (E1-M3A) follows a modular design using independent mooring lines and collects biochemical data in the upper 100 m and physical data in the upper 500 m of the water column. The south Adriatic buoy system (E2-M3A) uses similar instrumentation but on a single mooring line and also tests a new method of pumping water samples from relatively deep layers, performing analysis in the protected ''dry'' environment of the buoy interior. The Ligurian Sea system (W1-M3A) is an ideal platform for air-sea interaction processes since it hosts a large number of meteorological sensors while its ocean instrumentation, with real time transmission capabilities, is confined in the upper 50 m layer. Despite their different architecture, the three systems have common sampling strategy, quality control and data management procedures. The network operates in the Mediterranean Sea since autumn 2004 collecting timeseries data for calibration and validation of the forecasting system as well for process studies of regional dynamics.

Description: Three years of 300 kHz ADCP data collected in the central Ligurian Sea are analyzed to investigate the variability of the zooplankton biomass and the Diel Vertical Migrations (DVM) in the upper thermocline. After a pre-processing aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time-frequency analysis. The effect of changes in the environmental condition is also investigated. Highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern points to a "nocturnal" migration with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the historical ADCP time series available.

Description: Three years of 300 kHz acoustic doppler current profiler data collected in the central Ligurian Sea are analysed to investigate the variability of the zooplankton biomass and the diel vertical migration in the upper thermocline. After a pre-processing phase aimed at avoiding the slant range attenuation, hourly volume backscattering strength time series are obtained. Despite the lack of concurrent net samples collection, different migration patterns are identified and their temporal variability examined by means of time–frequency analysis. The effect of changes in the environmental condition is also investigated. The highest zooplankton biomasses are observed in April–May just after the peak of surface primary production in March–April. The main migration pattern found here points to a "nocturnal" migration, with zooplankton organisms occurring deeper in the water column during the day and shallower at night. Also, twilight migration is highlighted during this study. The largest migrations are recorded in November–December, corresponding to lowest backscattering strength values and they are likely attributable to larger and more active organisms (i.e. euphausiids and mesopelagic fish). The results suggest further applications of the available historical acoustic doppler current profiler time series.

Description: In the marine environment, complete datasets describing the surface layer and the vertical structure of the Marine Atmospheric Boundary Layer (MABL), through its entire depth, are less frequent than over land, due to the high cost of measuring campaigns. During the seven days of the Ligurian Air-Sea Interaction Experiment (LASIE), organized by the NATO Undersea Research Centre (NURC) in the Mediterranean Sea, extensive in situ and remote sensing measurements were collected from instruments placed on a spar buoy and a ship. Standard surface meteorological measurements were collected by meteorological sensors mounted on the buoy ODAS Italia1 located in the centre of the Gulf of Genoa. The evolution of the height (zi) of the MABL was monitored using radiosondes and a ceilometer on board of the N/O Urania. Here, we present the database and an uncommon case study of the evolution of the vertical structure of the MABL, observed by two independent measuring systems: the ceilometer and radiosondes. Following the changes of surface flow conditions, in a sequence of onshore – offshore – onshore wind direction shifting episodes, during the mid part of the campaign, the overall structure of the MABL changed. Warm and dry air from land advected over a colder sea, induced a stably stratified Internal Boundary Layer (IBL) and a consequent change in the structure of the vertical profiles of potential temperature and relative humidity.

Description: Meteorological and sea temperature data from the ODAS Italia 1 buoy (Ligurian Sea, Western Mediterranean) are used to study the anomalous warming of summer 2003 at sea. The event was related to the record heat wave that interested much of Europe from June to September of that year. The data show that the anomalous warming was prevalently confined to within a few meters below the sea surface. On the contrary, the temperatures in the underlying layers were lower than usual. The limited vertical propagation of heat is ascribed to the high temperature difference that arose between the surface and the deeper layers due to protracted calm weather conditions. The degree of penetration of heat deduced from the observations is consistent with that computed on the basis of an energetic argument, wherein the wind constitutes the sole supply of kinetic energy, while the heating is viewed as the source of potential energy that must be "subtracted" by mixing. The results support the hypothesis that the scanty energy from the wind is mainly responsible for the development of the temperature anomaly at the sea surface.

Description: Since numerical weather prediction (NWP) models are usually used to force ocean circulation models, it is important to investigate their skill in reproducing surface meteorological parameters in open sea conditions. Near-surface meteorological data (air temperature, relative humidity, barometric pressure, wind speed and direction) have been acquired from several sensors deployed on an offshore large spar buoy in the Ligurian Sea (Northern Mediterranean Sea) from February to December 2000. The buoy collected 7857 valid records out of 8040 during 335 days at sea. These observations have been compared with data from NWP models and specifically, the outputs of the ECMWF analysis in the two grid points closest to the buoy position. Hourly data acquired by the buoy have been undersampled to fit the data set of the model composed by values computed at the four synoptic hours. For each mentioned meteorological parameter an analysis has been performed by evaluating instantaneous synoptic differences, distributions, daily and annual variations and related statistics. The comparison shows that the model reproduces correctly the baric field while significant differences result for the other variables, which are more affected by local conditions. This suggests that the observed discrepancies may be due to the poor resolution of the model that probably is not sufficient to appropriately discriminate between land and ocean surfaces in a small basin such as the Ligurian Sea and to take into account local peculiarities. The use of time- and space-averaged model data reduces the differences with respect to the in situ observations, thus making the model data usable for analysis with minor requirements about time and space resolution. Although this comparison is strongly limited and we cannot exclude measurement errors, its results suggest a great caution in the use of the model data, especially at high frequency resolution. They may lead to incorrect estimates of atmospheric forcing into ocean circulation models, causing important errors in those areas, such as the Mediterranean Sea, where ocean circulation is strongly coupled with atmosphere and its high variability. Key words. Oceanography; general (marginal and semiclosed seas; marine meteorology; numerical modelling)