The influence of digitisation and timing errors on the estimation of tidal components at Split (Adriatic Sea)

International audienceThe paper comprises the calculations of amplitudes and phases of tidal harmonic constituents, performed on hourly sea level data recorded at the Split tide gauge in the period 1957-2001. Interannual changes in all constituents have been detected, stronger in phases than in amplitudes. For example, the estimated change in M2 amplitude and phase is 22% (1.31 cm) and 24.9° between the 1962?1978 and 1957?1961 periods, respectively. Some of the differences are generated artificially throughout the measurements (clock errors, positioning and stretching of a chart) and within the digitising procedure, rather than by natural processes and changes (e.g. changes in mean sea level). This is the reason why the M2 and K1 amplitudes were recomputed with 3?4 mm larger values using newer software, thereby decreasing their standard deviation by 60?70% in the 1986?1995 period. Artificial errors may be reduced by the upgrading of digitising software; however, most of the errors still remain in the series. These errors may have repercussions when trying to explain some unusual findings: the energy of de-tided sea level series at the M2 tidal period (12.4 h) has been assumed previously to be a result of nonlinear coupling, but it may be caused, at least partly, by timing errors in the time series

Forced and free response of the Adriatic Sea level

The aim of this paper is to improve the knowledge of the variations of the sea level in the Adriatic Sea in the domains of forced and free oscillations. For this purpose, one-year long-time series of data collected at nine tide gauge stations placed on the eastern shoreline have been collected and processed by spectral analysis. The harmonic constituents have been calculated too. Semidiurnal and diurnal tides have got larger variations of amplitude on the islands than on the coast. The response of the sea level in the domain of synoptic and planetary formations is quite synchronous in the whole Adriatic for periods longer than 3.5 days, with a gap around 9.5 days. These formations excite the sea level first in the North Adriatic, and then, secondly in the Middle and South Adriatic. The seiches occurred at already known periods of 22-23, 10.8 and 7.5-8 hours, and at a new one of about 4 hours. 4 hour seiche occurs in the region inside the Middle Adriatic islands, and it is predominantly influenced by the Sirocco wind forcing

Coastal high-frequency radars in the Mediterranean - Part 1: Status of operations and a framework for future development

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world. With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementation of this integrated HFR regional network

Spatial and temporal variability of sea ambient noise as an anthropogenic pressure index: the case of the Cres-Losinj archipelago, Croatia

This study monitors the spatial and temporal variability of sea ambient noise (SAN) in the Cres-Losinj archipelago from 2007 to 2009 (north-eastern Adriatic Sea, Croatia). The archipelago is an important marine habitat for many protected species, including the bottlenose dolphin (Tursiops truncatus) that is considered as vulnerable to disturbance from intense local vessel traffic. Systematic monthly sampling of SAN was carried out at ten predefined acoustic stations. Data on the presence, type and distance of vessels from these stations was also collected during sampling and vessels were allocated into four main classes. A sample of noise produced by a representative vessel of each vessel class was collected and the noise levels were extracted on the 1/3 octave band standard centre frequencies. All the recordings were analysed in terms of instantaneous sound pressure level (L-LSP, L-weighted, 63 Hz-20 kHz, root mean square fast). The equivalent continuous sound pressure levels (L-Leq) for vessel and SAN were calculated averaging the LLSP of vessel and SAN samples. Results indicate an increase of SAN levels particularly in the range of low frequencies (63 Hz-1 kHz) during the tourist season. A positive relationship was found between the spatial and temporal distribution of SAN and seasonal changes in anthropogenic pressure, in terms of vessel traffic. Potential implications for local marine life, with particular reference to bottlenose dolphins, are discussed