Integration of a relocatable ocean model in the Mediterranean Forecasting System

International audienceThe MFS (Mediterranean Forecasting System) project and its follower MFSTEP (Mediterranean ocean Forecasting System?Towards Environmental Prediction) are being covering the Mediterranean Sea with operational Ocean General Circulation Models (OGCMs) at horizontal resolution varying from about 12 km till 2005 to 6.5 km in 2006 (reaching 3 km with some regional models and 1.5 km for few shelf models). Heat, water and momentum fluxes through the air-sea interface are derived from the European Center for Medium-range Weather Forecast (ECMWF) output at 0.5° horizontal resolution. Such horizontal resolutions could be not able to provide the needed forecast accuracy in some cases (localized emergencies at sea, e.g. oil spill; need for high resolution current forecasts, e.g. offshore works). A solution to this problem is represented by relocatable models able to be rapidly deployed and to produce forecasts starting from the MFS products. The Harvard Ocean Prediction System (HOPS) has been chosen as base of the relocatable model and it has been interfaced with the MFSTEP OGCM and one regional model. The relocatable model has demonstrated capability to produce forecasts within 2-3 days in many cases, and more rapid implementation may be obtained

47-fs Kerr-lens mode-locked Cr:ZnSe laser with high spectral purity

We report on a room-temperature Kerr-lens mode-locked Cr:ZnSe femtosecond laser operating at around 2.4 µm emission wavelength. Self-starting nearly transform-limited pulse trains with a minimum duration of 47 fs, corresponding to six optical cycles, and average output power of 0.25 W are obtained with repetition frequencies in the range from 140 to 300 MHz. The femtosecond pulse train is characterized by high-spectral purity and low time jitter

The optical frequency comb fibre spectrometer

Optical frequency comb sources provide thousands of precise and accurate optical lines in a single device enabling the broadband and high-speed detection required in many applications. A main challenge is to parallelize the detection over the widest possible band while bringing the resolution to the single comb-line level. Here we propose a solution based on the combination of a frequency comb source and a fibre spectrometer, exploiting all-fibre technology. Our system allows for simultaneous measurement of 500 isolated comb lines over a span of 0.12 THz in a single acquisition; arbitrarily larger span are demonstrated (3,500 comb lines over 0.85 THz) by doing sequential acquisitions. The potential for precision measurements is proved by spectroscopy of acetylene at 1.53 μm. Being based on all-fibre technology, our system is inherently low-cost, lightweight and may lead to the development of a new class of broadband high-resolution spectrometers

Frequency-noise measurements of optical frequency combs by multiple fringe-side discriminator

open5noThe frequency noise of an optical frequency comb is routinely measured through the hetherodyne beat of one comb tooth against a stable continuous-wave laser. After frequency-to-voltage conversion, the beatnote is sent to a spectrum analyzer to retrive the power spectral density of the frequency noise. Because narrow-linewidth continuous-wave lasers are available only at certain wavelengths, heterodyning the comb tooth can be challenging. We present a new technique for direct characterization of the frequency noise of an optical frequency comb, requiring no supplementary reference lasers and easily applicable in all spectral regions from the terahertz to the ultraviolet. The technique is based on the combination of a low finesse Fabry-Perot resonator and the so-called "fringe-side locking" method, usually adopted to characterize the spectral purity of single-frequency lasers, here generalized to optical frequency combs. The effectiveness of this technique is demonstrated with an Er-fiber comb source across the wavelength range from 1 to 2 μm.Coluccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, GianlucaColuccelli, Nicola; Cassinerio, Marco; Gambetta, Alessio; Laporta, Paolo; Galzerano, Gianluc

250-MHz synchronously pumped optical parametric oscillator at 2.25-2.6 {\mu}m and 4.1-4.9 {\mu}m

A compact and versatile femtosecond mid-IR source is presented, based on an optical parametric oscillator (OPO) synchronously pumped by a commercial 250-MHz Er:fiber laser. The mid-IR spectrum can be tuned in the range 2.25-2.6 \mu m (signal) and 4.1-4.9 \mu m (idler), with average power from 20 to 60 mW. At 2.5 \mu m a minimum pulse duration of 110 fs and a power of 40 mW have been obtained. Active stabilization of the OPO cavity length has been achieved in the whole tuning range

Fiber-format dual-comb coherent Raman spectrometer

We demonstrate a fiber-format system for dual-comb coherent anti-Stokes Raman scattering spectroscopy. The system is based on two ytterbium fiber (Yb) femtosecond lasers at repetition frequencies of 94 MHz, a Yb amplifier, and a photonic crystal fiber for spectral broadening and generation of pulses with a central wavelength of 1040 nm and durations in the sub-20-fs regime. We observed Raman spectra of acetonitrile and ethyl acetate with spectral coverage from 100 to 1300  cm-1, resolution of 8  cm-1, and a signal-to-noise ratio of around 100, when averaging over 10 acquisitions. The design is suitable for implementing portable dual-comb coherent Raman spectrometers

Operativni sustav za prognoziranje hipoksije u sjevernom Jadranu

The northern Adriatic Sea (NA), the northernmost region of the Mediterranean Sea, is affected by strong anthropogenic pressure (e.g., tourism, fisheries, maritime traffic, discharge from agriculture and industry), superimposed to a large river runoff. The consequent pressure exerted on the NA ecosystem either triggers or worsens massive mucilage insurgence, harmful algal blooms, eutrophication and even anoxic/hypoxic events. This work focuses on the anoxic/hypoxic events. During the summer-autumn period, the NA is often exposed to these events, which can be categorised as either coastal (relatively frequent south of the Po River delta during the summer) and offshore (rare, affecting wider areas). In order to improve our knowledge about these processes and to meet the needs of local governments and decision makers, an operational system for monitoring and forecasting anoxic and hypoxic events has been set up in the framework of the EU LIFE "EMMA" project. The system is composed of a meteo-oceanographic buoy; a numerical prediction system based on the Regional Ocean Modelling System (ROMS), including a Fasham-type module for biogeochemical fluxes; and periodic oceanographic surveys. Every day since June 2007, the system provides 3-hourly forecasts of marine currents, thermohaline and biogeochemical fields for the incoming three days. The system has demonstrated its ability to produce accurate temperature forecasts and relatively good salinity and dissolved oxygen forecasts. The Root Mean Square Error of the dissolved oxygen forecast was largely due to the mean bias. The system is currently being improved to include a better representation of benthic layer biogeochemical processes and several adjustments of the model. While developing model improvements, dissolved oxygen forecasts were improved with the removal of the 10-day mean bias.Sjeverni Jadran (NA), najsjeverniji dio Sredozemnog mora, pod utjecajem je jakog antropogenog djelovanja (poput turizma, ribarenja, morskog prometa, istjecanje onečišćujućih tvari u poljoprivredi i industriji) te dodatno, velikog dotoka rijeka. Posljedično, djelovanje na NA ekosustav potiče ili pojačava uzdizanje sluzavih nakupina, štetno cvjetanje algi, eutrofikaciju pa čak i događaje anoksije/hipoksije. Ovaj se rad fokusira na anoksiju/hipoksiju. Tijekom ljetno-jesenskog razdoblja, NA je često izložen ovim doga|ajima, koji se mogu kategorizirati kao obalni (relativno učestali južno od delte rijeke Po ljeti) ili udaljeni od obale (rijetki, zahvaćajući šira područja). Kako bi poboljšali poznavanje tih procesa te zbog potreba lokalne uprave, uspostavljen je operativni sustav za praćenje i prognoziranje anoksije i hipoksije u okviru EU LIFE "EMMA" projekta. Sustav se sastoji od meteorološko-oceanografske plutače; sustava za numeričku prognozu, koji se temelji na regionalnom oceanografskom modelu (ROMS), uključujući modul Fasham-tipa za biogeokemijske tokove; i periodičnim oceanografskim istraživanjima. Svakog dana, počev od lipnja 2007, sustav omogućava 3-satne prognoze morskih struja te termohalina i biogeokemijska polja za sljedeća tri dana. Sustav se pokazao sposobnim za davanje točnih prognoza temperature i relativno dobrih prognoza saliniteta i otopljenog kisika. Korijen srednje kvadratne pogreške prognoziranog otopljenog kisika postojao je uglavnom zbog srednje pristranosti (biasa). Sustav je trenutno poboljšan tako da uključuje bolji prikaz biogeokemijskih procesa u području sloja bentosa i nekoliko prilagodba modela. Tijekom poboljšavanja modela, uklanjanjem 10-dnevne srednje pristranosti (biasa) poboljšane su prognoze otopljenog kisika

Passive mode locking of a Tm,Ho:KY(WO4)(2) laser around 2 μm

We report the first demonstration, to our knowledge, of passive mode locking in a Tm3+, Ho3+-codoped KYWO42 laser operating in the 2000-2060 nm spectral region. An InGaAsSb-based quantum well semiconductor saturable absorber mirror is used for the initiation and stabilization of the ultrashort pulse generation. Pulses as short as 3.3 ps were generated at 2057 nm with average output powers up to 315 mW at a pulse repetition frequency of 132 MHz for 1.15 W of absorbed pump power at 802 nm from a Ti:sapphire laser