Current observations from a looking down vertical V-ADCP: interaction with winds and tide? The case of Giglio Island (Tyrrhenian Sea, Italy)

ORIGINAL

RESEARCH

ARTICLE

Current

observations

from

a

looking

down

vertical

V-ADCP:

interaction

with

winds

and

tide?

The

case

of

Giglio

Island

(Tyrrhenian

Sea,

Italy)

Laura

Cutroneo

,

Gabriele

Ferretti

,

Davide

Sca

fidi

,

Gian

Domenico

Ardizzone

,

Greta

Vagge

,

Marco

Capello

*

a

DISTAV,UniversityofGenoa,Genoa,Italy b_{“Sapienza”,UniversityofRome,Rome,Italy}

Received22July2016;accepted23November2016 Availableonline14December2016

KEYWORDS Currents; Windinteractions; Sealevel; Normalised Cross-CorrelationFunction

Summary In thecontext oftheenvironmentalmonitoring oftheConcordiawreckremoval project,measurementsofcurrents,windsandsealevelheightweremadealongtheeasterncoast of theGiglio Island, Tyrrhenian Sea(Italy), during2012_—2013. The aimof thestudy wasto investigate theeffect of atmospheric forcing and periodicsea-level changeson thecoastal currents.NormalisedCross-CorrelationFunctionanalysisallowedustocorrelatethese observa-tions.A marked inter-seasonalvariability wasfound in bothcurrentand localwind velocity observationsbutasigni_ficantlevelofcorrelationbetweenthedatawasonlyfoundduringstrong windevents.Currentandwinddirectionsappearedtobeuncorrelatedandcurrentmeasurements showedapredominantNW—SEdirection,presumablylinkedtotheshapeandorientationofGiglio Islanditself.DuringstrongwindsfromtheSSE,currentflowwastowardstheNNWbutitsuddenly switchedfromtheNNWtotheSEattheendofwindevents.Theresultsshowthat,atGiglioIsland, currentsareprincipallydominatedbythegeneralcyclonicTyrrheniancirculation,and,secondly, bystrongwindevents.Thesealevelhadnoeffectsonthecurrentregime.

©2016InstituteofOceanologyofthePolishAcademyofSciences.Productionand hostingby Elsevier Sp. z o.o. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

PeerreviewundertheresponsibilityofInstituteofOceanologyofthePolishAcademyofSciences.

* Correspondingauthorat:DISTAV,UniversityofGenoa,26CorsoEuropa,I-16132Genoa,Italy.Tel.:+3901035338143;fax:+39010352169. E-mailaddress:capello@dipteris.unige.it(M.Capello).

Availableonlineatwww.sciencedirect.com

ScienceDirect

jo u rn al ho m e p age : w w w. jo ur na ls .e l se v i er.c o m / o ce an o lo g i a/

http://dx.doi.org/10.1016/j.oceano.2016.11.001

0078-3234/©2016InstituteofOceanologyofthePolishAcademyofSciences.ProductionandhostingbyElsevierSp.zo.o.Thisisanopen accessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).

1.

Introduction

Seaandoceancirculationisgenerallycharacterisedbythe interactionsoftidalcurrents,bathymetricconstraints,wind forcing,anddensitygradientsinducedbyriverinputandheat andmass(evaporationandrain)exchange.Inthiscomplex scenario,windhasbeenfoundtobethemainforcingfactor inducingcurrents,whiletidalandbaroclinicmotionsareof secondaryimportance(Bolañosetal.,2014).Thebarotropic componentofthecoastalcirculationismainlydrivenbylocal winds,butisalsohighlydependentonthetopographyofthe marinebasin,composedofsub-basinscalegyresthatcanbe seasonally variable and recurrent (Molcard et al., 2002; PieriniandSimioli,1998).

Theperiodicverticalmotionsproducedbytidescloseto thecoastinduce(horizontal)currentswithalternatingfloods andebbs.Inthesewatermovements,tidescanhavelocalor regionalandshort-rangeor long-range influences(Naranjo etal.,2014).Closetothecoast,sealeveldependsprimarily ontheperiodicchangeoflunarandsolarattraction (astro-nomicinfluences),butalsoonthelocalatmosphericpressure andwaveandwindchanges(atmosphericevents)thatinduce non-periodic signals of varying strength (amplitude) and duration(low-frequency)whichinfluencethedailyperiodic oscillations (Halverson,2014; Tsimplisetal., 2011). More-over,themagnitudeofthesealevelvariationissite depen-dent. In fact, in areas characterised by very small tidal ranges, such as the Mediterranean Sea, the atmospheric effectsmay have greater amplitude than the normaltide andcanpartiallyorcompletelyobscuretheastronomictide oscillations. These atmospheric effects vary,for example, withthedirection,strengthanddurationofthewindandare alsodependentonthemorphologyoftheareaandthedepth ofthebodyofwater(Halverson,2014).

In the contextof the environmental monitoring of the Concordia wreck removal project, measurements of cur-rents, winds and sea level were made during 2012—2013

alongtheeasterncoastoftheGiglioIslandintheTyrrhenian Sea(Italy)(Fig.1).Inordertostudythegeneraltrendofthe currents,andtheirdailyandseasonalvariationsinrelationto atmosphericforcing(winds)andperiodicsealevelchanges (tides),averticalAcousticDopplerCurrentProfiler(V-ADCP) wasdeployedunderabuoyfromthe29thAugust2012tothe 7thJuly2013.Theresultsofthecross-correlationanalysisof thecontinuousdatacollectedbytheV-ADCPandthe meteor-ological(windvelocityanddirection)andsealevel observa-tionsrecorded at thepermanentweather stationofGiglio Portoarereportedinthispaper.

2.

Study

area

2.1. Geologicalandclimaticcharacteristicsof GiglioIsland

Giglio Island (21.2km2) lies in the northern part of the Tyrrhenian Seainfrontof theArgentarioheadland, 14-km offtheTuscanycoast(Fig.1).Thesmalltownandtheharbour ofGiglioPortoareontheeasternsideoftheisland(Fig.1). Theislandis90%composedofamonzograniticpluton result-ingfromcrystallisationofmagmawithintheearth'scrustand raised to thesurface as aresult of atectonic extensional phasesubsequenttothecollisionbetweentheAdriaticand Corsica-Sardinia plates(Rossetti etal.,1999). The island's shapeisroughlyelliptical,8.5kmlongand4.5kmwide,with itsmajoraxisorientedNNW-SSE.Itscoastsarepredominantly highandrockywithnumeroussmallbaysandinlets.Thesea bottomofftheGiglioPortocoastischaracterisedbyasteep rockyslopethatslopesquicklytoa100-mdepthatadistance ofabout350mfromthecoast.Seabottom,beneath50-m depth,consistsofmorethan60%clay(FrezzaandCarboni, 2009).

Theisland'sclimateistypicallyMediterranean,withrare rainfallbetweenMayandOctober(almostcompletelyabsent

Figure1 Locationofthestudyarea(GiglioIsland,Italy).B1andC1arethebuoysunderwhichtheV-ADCPwasinstalledforthe continuousmonitoringofthecurrents;ConcordiawreckblackprofilehighlightsthepositionofthevesselnearthecoastoffGiglio Porto;theblackrhombusshowsthepositionoftheweatherstationoftheLaMMAConsortium(EnvironmentalModellingandMonitoring LaboratoryforSustainableDevelopment)oftheTuscanyRegion;theblackasteriskshowsthecollisionpointofthecruisevesselonthe rocks.

inthesummermonths),andmorefrequentrainfallbetween November andApril.The temperatureisrelativelymild in winter(minima>08C)andhighinsummer(maxima>308C). Theweatherconditionsoftheislandaremostlyinfluencedby windaction;inparticular,thewindsfromtheSE,S,SWand NEarelinkedwithrains,whilethewindsfromtheNW,Wand Narelinkedwithdryweather.TheNandNEwindstypically blowduringwinter(December,January,andFebruary)and canproducestorms,while,inautumnandspring,strongSE and S—SW winds generate rough seas, principally on the southern andeasterncoasts ofthe island.In summer, the dominantwind isfromtheSandoflowvelocity, generally associatedwithcalmseas(http://www.cmgizc.info).

2.2. Thecirculation andtidesintheTyrrhenian Sea

Thestudyareaisincludedinthegeneralcirculationofthe TyrrhenianSea.Thiscirculationischaracterisedbysurface andintermediatelayersrepresentedbyawell-definedfluxof AtlanticWater(AW;theTyrrhenianvein)enteringthebasin fromthesouthalongtheeasterncoastofSicilyandflowing counter-clockwise around the Tyrrhenian and northward alongtheItalianpeninsulareachingtheChannelofCorsica. Here, a part of the flow enters the Ligurian Sea, while anotherpartmovesinacyclonicgyreofftheBonifaceStrait (Astraldi and Gasparini, 1994; Millot and Taupier-Letage, 2005; Vetrano et al., 2010). When the Tyrrhenian vein of theAWreachesthechannelbetweenGiglioIslandandthe Italian coast, currents are forced in an SE—NW direction, disturbedbygyresandcounter-currentinducedbythe inter-actionwiththecoastalmorphology,frictionwiththeshallow bottom, and the influence of the freshwater inputs from torrentsandrivers.Thissituationwashighlightedinsatellite picturetakenonthe13thNovember2012afterheavyrains thathittheregion(Fig.2;sourceNASA).

The Tyrrheniancirculationsuffers from someimportant seasonalchanges,primarilyinthenorthernpartofthebasin. Here,thewatermasses aremostlyrecirculatedwithin the basininsummer,isolatingtheTyrrhenianandLigurianseas, withonlyasmallpartoftheflowpassingthroughtheCorsica Channel;inwinterandspring,thecommunicationbetween thetwobasinsisfull(AstraldiandGasparini,1994;Pieriniand Simioli,1998;Schroederetal.,2011).

Ingeneral,themaximumtidalrangeisrelativelylowin theTyrrhenianSea,equal0.45m(Ferrarinetal.,2013).Tidal

oscillations(Table1)aresemidiurnal,withtwohighsandtwo lowsduringtheday,whichoccurwithdifferentvaluesduring theyearproducingminorandmajortidesthatarestrongly correlatedwith themeansurfacepressurevariations; sea-sonal fluctuations have a progressive increase and sharp decrease, with the maximum signal in autumn (Mosetti andPurga, 1982;Polli,1955).Themeansealevelcurveis dominatedby astrong annual signalof 8cmin amplitude (Cazenaveetal.,2002).

Figure 2 Evidence of the current coastal gyres produced by coast morphology and fresh water input from rivers. Satellitepicturetakenonthe13thNovember2012afterheavy rains.Source:NASA.

Table1 Meantidalsemi-diurnalanddiurnalharmonicconstituents(M2,S2,K1,andO1)expressedinamplitude(incm)andphase (indegree,₈₎atthetidalgaugeoftheCivitavecchiaharbourduringtheperiod1951_—1952(Polli,1955).Solarannualcomponent (Sa),solarsemi-annualcomponent(Ssa),solarmonthlycomponent(MSm),andlunarmonthlycomponent(Mm)atthetidalgaugeof theCivitavecchiaharbourduringtheperiod1966—1968(MosettiandPurga,1982).

Polli(1955) M2(theprinciplelunar semi-diurnalharmonic) S2(theprinciple solarsemi-diurnal harmonic) K1(theprinciple luni-solardiurnal component) O1(theprinciple lunardiurnal component) Period1951—1952 10.9cm,2588 4.1cm,2808 2.8cm,2028 1.3cm,1158

MosettiandPurga(1982) Sa(solarannual component)

Ssa(solarsemi-annual component) MSm(solarmonthly component) Mm(lunarmonthly component) Period1966—1968 5.6cm,2168 3.4cm,1118 0.8cm,2768 0.3cm,2468

3.

Material

and

methods

ThesignalbuoysdelimitingthemarineyardoftheConcordia wreckremoval projectwerelocated 300—500moff Giglio Porto(Fig.1)atthe80—100misobaths.Thebuoys(Resinex Trading Srl) were manufactured with an external shell in roto-mouldedlinear polyethyleneandfilledwithelastomer polyurethanetoguaranteebuoyancy.

ATeledyneRDI 300-kHzdownward-lookingvertical four-beamV-ADCPwasinstalledunderbuoyC1onthe29thAugust 2012andmovedtobuoyB1onthe25thNovember2012,ata fixeddepthof6mtocontinuouslymonitorthecurrents.The 6-m depthwas chosen because of the shape of thebuoy, equippedwithapipeinitssubmergedpart.TheV-ADCPwas poweredby an internal battery packand installed on the buoycablewithastainlesssteelstructurethatavoidedbeam interaction with the cable itself. The instrument was equippedwithanarmouredsubmarinecablewithaterminal abovesealevelfromwhichdataweredownloaded.

TheV-ADCPcouldmeasurecurrentprofiles(velocityand direction)andtheintensityoftheecho(backscatter)alonga theoretical vertical line of about 120m (RD, Instruments 2007)fromthedepthofinstallation(6m)totheseabottom. Thesize ofV-ADCP binswas set at 4m andthemaximum numberofbinsat16,tocover70mofthewatercolumn,and, hence,the first measurement bin was centred at a 10-m depth.Theinstrumentmeasuredthevelocity[mms
1]and direction[8N]ofthecurrentwithasamplingof6min aver-aging30pingsforeachmeasurement(1pingevery12s).

The measurement period lasted from the 29th August 2012tillthe7thJuly2013,butitwasdividedintosub-periods of non-equal duration depending on yard operations and weatherconditions(Table2).Fromthe29thAugusttothe 25thNovember2012,theinstrumentwasfixedunderbuoyC1 (Fig.1),but,duetothefrequentremovalsandrepositioning ofthebuoyforthemanoeuvresoftugsandpontoonsengaged intheyardoperations,itwassuccessively(from25th Novem-ber2012)fixedunderbuoyB1(Fig.1)(Table2)situated800m totheNorth.

The softwareusedfortheV-ADCP configurationandthe datadownloadingwas WinSC(RDInstruments,Inc.), while the software used for data processing was WinADCP (RD Instruments,Inc.).

Followingtheoceanographicconvention,acurrent direc-tionwasdefinedasthedirectiontowardswhichthecurrents wereflowing.Themonthlymeanofthecurrentvelocitywas

calculatedatdifferentdepths(10,18,30,50,and70m)and released as histograms to show the velocity changes with depth during the study period. The data on the current velocityanddirectionweredividedaccordingtothe astro-nomicalseasonsandplottedinrosediagramstoinvestigate theseasonalbehaviourofthecurrentsandhighlightpossible prevailingdirections.

The meteorological parameters used inthis studywere measuredattheweatherstationinstalledonthebreakwater oftheGiglioPortoharbour(Fig.1)bytheLaMMA (Environ-mentalModellingandMonitoringLaboratoryforSustainable Development)ConsortiumoftheRegionofTuscanyandthe ItalianResearchCouncil.Theweatherstationprovided mea-surementsofsealevel[m],meanandmaximumwindvelocity [ms
1]andprevailingwindandgustdirection[8N].Thewind directionwasdefinedasthedirectionfromwhichthewinds werecoming.Thedatawereacquiredconsideringasampling of10min.

The weather data were used to support the marine weatherbulletinoftheGiglioIslandactivatedimmediately aftertheshipwreck.Theweatherstationwascomposedofa shaftencoder floating hydrometerina stillinganda 10-m heightfoldingpolewithwindvelocityanddirectionsensors (Siap+Micros,S.r.l.)poweredbyasolarpanel.Theweather station was0.5and1.2kmfrom buoysC1andB1, respec-tively.

Thecompletetemporalcoverageofthedatasetisshown inFig.3.

Aswasdoneforthecurrentdata,themonthlywindmeans werealsodetermined,andwindrosediagramsweredrawn withthedataofthehourlyprevailingwindandwindgust.

Table 2 Measurement periods ofcurrentsby V-ADCPand relatedposition(underC1orB1buoy)(periodtime:dd/mm/ yyyy).

Periodstart Periodend BuoyC1 29/08/2012 11/09/2012 04/10/2012 30/10/2012 23/11/2012 25/11/2012 BuoyB1 25/11/2012 11/12/2012 31/12/2012 16/04/2013 15/06/2013 27/06/2013 30/06/2013 07/07/2013

Figure3 Temporalcoverageofcurrentdata(underthebuoysC1andB1inblackandred,respectively),winddata(inblue),andsea leveldata(ingreen).(Forinterpretationofthereferencestocolorinthisfigurelegend,thereaderisreferredtothewebversionofthis article.)

Dailysealevelmeanswereextractedtohighlightthetrendof the sea level variations. Tidal harmonic analysis was per-formedonthehourlysealeveldataintheperiod29thAugust 2012—7th July 2013, using the Harmgen free software (version3.1.1,2006),consideringapackageof35 constitu-entsincludingthefourprimaryharmonicconstituentsofthe semi-diurnalanddiurnalfrequencies(S2,M2, K1,andO1). Becausetidalobservationsdidnotcoverafullyearperiod, wecouldnotcalculateorconsidertheannualandmonthly harmoniccomponents.

Acoreissuewhendealingwithtimeseriesisdetermining theirpairwisesimilarity,i.e.thedegreetowhichagiventime seriesresemblesanother.Therefore,inordertoevaluatethe presenceofpossiblecorrelationsbetweenthedatameasured bytheV-ADCP(velocityanddirectionofcurrent)andthose provided bytheweatherstation oftheLaMMAConsortium (sealevel,velocityanddirectionofwind),aprocedurebased on the use of the cross-correlation function (CCF) was applied.CCFisastandardmethodofestimatingthedegree towhichtwo-timeseriesaresimilar,andrepresentsauseful measureofstrengthanddirectionofthecorrelationbetween tworandomvariables(Wei,2006).Inthiswork,the Normal-isedCross-CorrelationFunction(N-CCF)wasconsidered:itis apopularandeasilyimplementedmetricthatwellfollows therapidchanges andtheamplitude oftwocompared sig-nals,andmakes itpossibleto evaluateboth thedegree of similaritybetweencouplesofcompareddatasetsorimages and the eventual time shift and delay between two-time series(Tsaietal.,2003;WhiteandPeterson,1994).N-CCF hasfoundapplicationsinabroadrangeoftheearthsciences suchasseismicity,meteorology,andhydrology(Campilloand Paul,2003;Capelloetal.,2016;McMillen,1987;Thouvenot etal.,2016).N-CCFisdefinedas:

N-CCF¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiC12ðtÞ C11ð0ÞC22ð0Þ p ; (1) where C12ðtÞ¼ Z þ1
1a1ðtÞa2ðtþtÞdt; (2)

wherea1(t)anda2(t)arethetwotimeseries.

Whendealing withdigitaldata,thediscrete (ordigital) cross-correlationfunctionisusedanditisdefinedas: Cxv¼

X1 m¼
1

xðmÞyðmþlÞ; (3)

wherex(m)andy(m)arethetwodiscrete-timesignals. Themaximumvalue oftheN-CCF(hereafter,the cross-correlationlevelorsimilaritylevel)measuresthesimilarity betweensignalsasafunctionofthelagofonerelativetothe other.ThemaximumcorrelationiswhenthemaximumN-CCF valueisequalto1,whereasanN-CCFvalueequalto0 indi-catesnocorrelationbetweensignals.

BeforethecomputationoftheN-CCF,thetimeseriesdata were processed applying the following procedure: (a) re-sampling to the common frequency of 0.0027778Hz (the sampling frequency ofthe V-ADCP data)through an inter-polationusing a4thdegree polynomial(Scherbaum etal., 1999);(b)extractionofacontinuoustimewindowcommonto boththewind andcurrentseries[theperiodfrom15:05of the31stDecember2012to14:00ofthe16thApril2013was

selected:inthistime-period, thecomplete (withoutgaps) time series of observations recorded by both V-ADCP and weatherstationofGiglioPortowereavailable];and(c)offset removal (e.g. removing from the time series the average valueofallpoints).

Thecross-correlationfunctionwascomputedinorderto assessthepossiblerelationshipbetween:(a)currentvelocity anddirectionmeasuredatdifferentdepths(10mand18m, 10m and30m,10m and50m, 10m and 70m); (b) wind velocityandcurrentvelocity measuredatdifferentdepths (10m,18m,30m,50m,and70m);(c)prevailingdirection ofwindanddirectionofcurrentmeasuredatdifferentdepths (10m,18m,30m,50m,and70m);and(d) sealevel and currentdirectionmeasuredat10-mdepth.

4.

Results

4.1. Currentvariabilityfrommoored measurements

Themonthlymean currentvelocities (Fig.4)show a pro-gressiveincreasefromAugust2012(81mms
1inthesurface layer at buoy C1) to the autumnal and winter months (251 and 165mms
1 of maxima measured in the surface layeratbuoyB1inNovemberandDecember2012, respec-tively), with a subsequent decrease in summer 2013 (84mms
1inthesurfacelayeratbuoyB1).Aprogressive decrease of current velocity was also visible analysing data from the surface layer(10-m depth) to the bottom layer(70-m depth)in the water column.Below the 50-m depth,themonthlymeancurrentvelocity attenuatesand themaximumvaluesdecreasetovaluesslightlyhigherthan 100mms
1(maximummonthlymeanvalueof136mms
1 wasobservedinNovemberatbuoyB1).

The maximum current velocity events (velocity> 500mms
1atthe10-mdepth;Fig. 5)wererecordedfrom the27th November to the 3rdDecember 2012 (showing a maximumof708mms
1),onthe6th—7th andon the18th March2013(showingamaximumof816mms
1).

Withregard to the current direction,some differences werefound among the values measured moving from the surfacelayertothebottominthefourseasons.Infact,inthe surfacelayer (10-mdepth;Fig. 6a),currentswere sharply oriented towards NNW and SSE, whereas moving to the bottomofthewatercolumnthiseffecttendedtodisappear andthecurrentdirectionbecamemorewidespread(Fig.6b). Analysing the data recorded at the different depths as a functionofthe seasons(Fig. 6aand b),it was possibleto highlightaseasonalbehaviourofcurrentdirection.In sum-merand spring,the prevailing current directions were SE with a smaller portion of NNW directions at the surface (Fig. 6a),whiletheSSEdirectionprevailswiththegreater depth (Fig. 6b). In autumn and winter, the currents are mainlyorientedtowards NNWin thewholewatercolumn, andat50and70-mdepths,thereisareversalofthedirection withaslightprevalenceofSSEnearthebottom(Fig.6b).

4.2. Variability insealevel

Thesealeveltrend showninFig. 7highlightstheirregular behaviourshownbythesealevelasafunctionoftime.The

sealeveldata, recordedatthe weather stationof Giglio Porto,rangedbetween
0.33mand0.49m.Twominimum values (
0.31 and
0.33m) were recorded on the 29th December2012andthe28thFebruary2013inthepresence ofastrongNandlightSW—SEwind,respectively,andafull moon(28thDecember2012and26thFebruary2013).While twopositivesealevelpeaksof0.41 and0.49m(seiches), observed on the 27th and 31st October, respectively, were produced by persistent bad weather conditions, characterised by low atmospheric pressure, a strong SSE

wind, rough seas and heavy precipitation, in conjunction with a full moon (30th October). Maximum sea level variations were recorded in autumn and winter, while minimum variations were observed during late spring and summer.

The main tidal harmonic constituents are reported in Table3:themainlunarsemi-diurnal(M2)prevailsoverthe otherconstituentswithanamplitudeof10.5cm,fourtimes strongerthantheamplitudeofthemajordiurnalconstituent (K1).

Figure4 Monthlymeancurrentintensities[mms
1]measuredat5differentdepthsinthewatercolumn(10,18,30,50,and70m)at buoyC1(grey)andB1(black).DataofMay2013arenotavailableaswellasdataofJuly2013at10-mdepth.

4.3. Seasonalvariabilityinwinds

WindvelocitymeasuredattheweatherstationofGiglioPorto ranged between 0 and 16.6ms
1 and showed a monthly mean of 3.2ms
1 in summer and of 4.9ms
1 in winter (Fig.8).Consideringonlythecaseofwindvelocitieshigher thanthemeanvalueofthe neargale velocities(15ms
1) accordingtotheBeaufortScale,onlyfiveeventsofsignificant windwererecordedinautumnandwinter.Thehighestwind velocitywasrecordedonthe11thNovember2012duringa robustanticyclonicfrontcharacterisedbySE-orientedwinds. Therosediagrams(Fig.9)reportingwindmeasurements showthatwindsoriginatemostlyfromtwodirections,SEand NNW; the strongest winds come from the SE. A SW wind direction is also visible mainly looking at the wind gusts diagram.

Itisalso possibletonotesomeseasonalvariationinthe winddirection;insummer,windscomemainlyfromtheNNW; in autumn, the predominant origin direction is the SE; in winter, the strongest winds come from the SE, whereas weakerwindscomefromtheNW;inspring,thetwo prevail-ingdirections(NNWandSE)are present,withaslight pre-valenceoftheSEdirection.

5.

Data

correlation

results

Fig.10showstheresultsoftheNormalisedCross-Correlation Function(N-CCF;Eq.(1))obtainedconsideringcurrent velo-cities measured at different depths (Fig. 10a) and those resultingfromcorrelatingwindvelocitiesandcurrent velo-citiesmeasuredatdifferentdepths(Fig.10b).

Thetimeseriesofcurrentvelocitiesmeasuredatdifferent depths(Fig. 10a)exhibitasimilaritylevel,whichtendsto decrease as the difference between measuring depth increases(y-axisofFig.10a);infact,thecross-correlation levelbetweenthecurrentvelocity valuesmeasuredatthe 10-mdepthandthosemeasuredatthe18-mdepthisequalto 0.82,whereasforthedatameasuredatthe10-mdepthand atthe70-mdepththesimilaritydecreasesto0.36.

Itshouldbenotedthatthetimeshift(x-axisofFig.10a)in currentvelocityvaluesmeasuredatdifferentdepthschanges too.Datameasuredatthe10-mdepthandthe18-mdepth arenotphase-shifted,whereasthetimeshiftbetweendata measuredatthe10-mdepthandthe70-mdepthisequalto about1hand30min(
1.5h).Similarresultsareobtainedby evaluating the similarity level between current directions measured at different depths (not showed in Fig. 10).

Betweendirections measuredat the10-mdepth andthose measuredatthe18-mdepthitispossibletoobserve0.52of similarity, while the similarity decreases to 0.16 when thedataofthe10-mdepthwerecomparedtothedataof the70-mdepth.

Thecorrelationbetweenthewindandcurrent(time ser-ies)wasextremelylow(Fig.10b).Itwaslowerthan0.20for thevelocitydata(Fig.10b)and0.10forthedirectiondata. Thisresultshowsthatthewinddoesnotseemtoberelatedto thecurrentvelocityorratherthewinddoesnotsignificantly influencethevelocityanddirectionofthecurrent.

Inordertobetterinvestigatethecorrelationbetweenthe windandcurrent,afurtheranalysiswasperformed estimat-ingtheN-CCF between windvelocity andcurrent velocity measuredatthe10-mdepthforthreeeventscharacterised by a wind velocity peak greater than 15ms
1 (the mean velocityoftheneargalewind; Figs.11—13).Inparticular, threesub-windowswithdurationofapproximatelyfivedays, aroundthe12thFebruary2013,the7thMarch2013,andthe 18th March 2013, were analysed. Considering only these events,thecorrelationbetweenthewindandcurrent velo-city significantly increased with respect to the previous analysis(performedconsideringtheentirerecordingperiod), showing similarity levels greater than 0.50 (panel c in Figs.11—13).Thetimeshiftbetweenthewindandcurrent velocitieswasverydifferentinthethreedifferentcases.In fact,inthefirstcase(Fig.11),thetimeshiftwasequalto4h ca,inthesecondcase(Fig.12)itwas21h,andinthethird caseitwas12hca(Fig.13).

Other important experimental evidence concerns the relationship between the wind and current direction observedduring these three events. In correspondence of maximum values of the wind and current velocity (high-lightedinFigs.11—13bythedashes),arelationshipbetween aSSEwind (e.g.“Scirocco” 1358—1808)anda Ncurrentis visible. It must be noted that the events of strong wind extrapolatedfromthestudyperiodare allanalogous,that is all come mainly from the SSE, and therefore, it is not possibletoanalyseothercasesofstrongwindswithdifferent directions.InFigs.11—13(panelsbande),itispossibleto noteaninversionofthecurrentdirectionattheendofthe wind actionand theconsequentlyvariation in thecurrent velocity:thecurrent directionswitchessuddenly fromthe NWtotheSEasifthesystemunbendsattheforcingend.

ThelastanalysishasbeenperformedcomputingtheN-CFF between the sea level data and the current direction measured at the 10-m depth. These two signals appear uncorrelated(similaritylevellowerthan0.10).

Figure5 Currentvelocitydistributionmeasuredat10-mdepthduringtheentiremeasureperiod.Thedottedlineshowsthecurrent velocityof500mms
1.

Figure6 (a)Seasonaldiagramsofcurrentvelocityanddirectiondistributionmeasuredat10,18and30-mdepthfromthe28th August2012tothe7thJuly2013.Currentdirection,followingoceanographicconvention,isthedirectiontowhichthecurrentsare going.(b)Seasonaldiagramsofcurrentvelocityanddirectiondistributionmeasuredat50and70-mdepthfromthe28thAugust2012to the7thJuly2013.Currentdirection,followingoceanographicconvention,isthedirectiontowhichthecurrentsaregoing.

Figure7 Hourly(inblack)anddailymean(inorange)sealevel[m]measurementsrecordedattheweatherstationofGiglioPorto betweenAugust2012andJuly2013.(Forinterpretationofthereferencestocolorinthis_figurelegend,thereaderisreferredtothe webversionofthisarticle.)

Figure8 Toppanel:windvelocitymeasuredatGiglioPortobetweenAugust2012andJuly2013;theblackdashlineshowsthemean valueoftheneargalewind(15ms
1).Bottompanel:monthlymean(black)andmaximum(grey)valuesofwindvelocity[ms
1]. Table3 Tidalsemi-diurnalanddiurnalharmonicconstituents(M2,S2,K1,andO1)ofGiglioPortoexpressedinamplitude(incm) andphase(indegree,8)andcalculatedbetween29/08/2012and07/07/2013.

Thisstudy(GiglioPorto,Italy) M2 S2 K1 O1

6.

Discussion

Theirregulartrendofthesealevelmeasuredattheweather stationof Giglio Porto highlightedthe combinedaction of meteorologicalforcing(autumn-winterwaves,atmospheric pressureandwinds)andtheastronomicaltidalcomponents (Earth-Moon-Sungravitationalrelationship).Tidalamplitude wasinaccordancewiththegeneralrangeoftheTyrrhenian Sea(Alberolaetal.,1995;Ferrarinetal.,2013).Themain

tidal harmonic constituents found atGiglio Porto retraced thevaluesfoundbybothPolli(1955)atCivitavecchiaharbour (Lazio,centralTyrrhenianSea)andAndrosovetal.(2002)at theScyllastation(northernStraitofMessina,Sicily,southern TyrrhenianSea)inbothamplitude andphase,althoughour datasetdidnotcoverafullyear.Onthecontrary,theGiglio Porto constituents were significantly different from those foundinotherseas(suchastheAdriaticSea;Janekovícand Kuzmíc,2005)ortheAtlanticOcean(Fanjuletal.,1997)due

Figure9 Rosediagrams showingthevelocityand thedirectionofprevailingwind(left panel)andthemaximumvelocityand directionofgusts(rightpanel).Thewinddirectionisheredefinedasthedirectionfromwhichthewindiscoming.Dataaremeasured every10minattheweatherstationofGiglioPortoduringthestudyperiod.

Figure10 NormalisedCross-Correlations(N-CCF)obtainedconsidering(a)currentvelocitymeasuredatdifferentdepth[current measuredat10and18m(red),10and30m(green),10and50m(blue),and10and70m(pink)],and(b)windvelocityandcurrent velocitymeasuredatdifferentdepth[10m(red),18m(green),30m(blue),50m(pink),and70m(cyan)]inthewholeperiod.Values areexpressedina0—1scale(y-axis),where1correspondstotheperfectcorrelationlevel,and0totheabsenceofcorrelation.They scaleofpanelbiszoomedto0.3tobettershowtheresults.(Forinterpretationofthereferencestocolorinthisfigurelegend,the readerisreferredtothewebversionofthisarticle.)

Figure11 Analysisoftherelationbetweenwindandcurrentduringtheperiod9th—15thFebruary2013.(a)Windvelocitydata,(b) currentvelocitydatameasuredat10m depth,(c)NormalisedCross-CorrelationFunction(N-CCF)obtainedconsideringwindand currentvelocityat10-mdepth,(d)winddirectiondata,and(e)currentdirectiondataat10-mdepth.

Figure12 Analysisoftherelationbetweenwindandcurrentduringtheperiod3rd—9thMarch2013.(a)Windvelocitydata,(b) currentvelocitydatameasuredat10m depth,(c)NormalisedCross-CorrelationFunction(N-CCF)obtainedconsideringwindand currentvelocityat10-mdepth,(d)winddirectiondata,and(e)currentdirectiondataat10-mdepth.

tothedifferentcharacteristicsanddynamicsthatinfluence thesewaterbasins.

Theresultsfoundintheareaunderstudyretracethewell knownsurfacecirculationcharacterisedbythepredominant movement of the water masses along a NW—SE direction (Schroeder et al., 2011), corresponding to the NNW—SSE orientation of the major axis of the Giglio Island andthe channelbetweentheislandandthemainland(westerncoast ofthe Italianpeninsula). This characteristicof the flowis evidenceoftheimportanceofthetopographyand morphol-ogy of the area (presence ofislands, canyons, headlands, etc.)on thecurrentregime(Gravilietal.,2001).The pre-dominance of NW currents in winter and autumn is also induced by the corresponding overall cyclonic Tyrrhenian circulation (Iermano et al., 2016), whereas the frequent inversions of current direction in summer and spring may berelatedtoepisodesofTyrrheniancurrentreversal(Gravili etal.,2001).

The inter-seasonaland dailyvariations in both velocity anddirectionofcurrentsconfirmtheshortperiodvariability oftheflowalreadyfoundintheTyrrhenianbasinonagreater scalebyPieriniandSimioli(1998),andsubjectedtostudyasa distinctivefeatureofoceanicbasins.

The study of theinteractions between external forcing processesandwatermasscirculationistypicallycarriedout with numerical model simulations (Dumas et al., 2012; Lovatoetal.,2010;Molcardetal.,2002;PieriniandSimioli, 1998) or the application, for example, of the Fourier or Wavelet transforms (Fontán et al., 2009; Lovato et al., 2010).TheuseoftheNCCFinourcaseallowedustohighlight someofthemaincharacteristicsofthecurrentstructureand

behaviourinrelationtoexternalforcing.Infact,the decreas-ingsimilaritylevelinvelocityanddirectionandthetimeshift inthecurrentswithincreasingdepthcanbeevidenceofboth Ekman'stheory(Bjerknes,1964)andthetimenecessaryfora boundary-forcingcurrenttomakealocalbarotropic adjust-ment(Gravilietal.,2001).

Ingeneral,asinthecaseofcurrents,theprevailingwind directionswereshowntoagreewiththeNNW-SSEorientation oftheisland'smajoraxisandalsothepositionoftheweather stationonthebreakwaterofGiglio Portothatisprotected fromwindsfromthewesternquadrantsbythepresenceof theisland.Thedirection(NNW-SSE)ofthedominantwindis seasonallyvariableovertheGiglioIslandshelf,inaccordance withthecirculation(withoppositedirections),ashappensin theentireTyrrhenianSea(PieriniandSimioli,1998). Never-theless,onalong-timescale,thewindsandcurrentsdonot seem to becorrelatedparameters in termofvelocity and direction,as foundinother cases onthe continentalshelf (e.g.south-easternAustralia;Woodetal.,2016).This con-dition is the oppositeof what was found, for example by Lentz (2007) and Liu and Weisberg (2012), on the Middle AtlanticBightandWestFloridacontinentalshelves, respec-tively,where thewindsare seasonallyconsistentand gen-erate steady seasonal responses in the circulation. Our resultswerealso incontrastwithwhatwasfoundbyChen et al. (1996) over the Texas-Louisiana shelf, where the correlationbetweenthealong-shorecurrentsandwindstress increasescloseto thecoast.Inadditionto thewind beha-viour,thesedifferencescanderivefromthemorphologyof theshelfandthecoastsandtheeffectoftheprevailing large-scale circulation (Fontán et al., 2009; Liu and Weisberg,

Figure13 Analysisoftherelationbetweenwindandcurrentduringtheperiod16th—22ndMarch2013.(a)Windvelocitydata,(b) currentvelocitydatameasuredat10mdepth, (c)NormalisedCross-CorrelationFunction(N-CCF)obtainedconsideringwindand currentvelocityat10-mdepth,(d)winddirectiondata,and(e)currentdirectiondataat10-mdepth.

2012; Woodetal.,2016), such as inour casethe general Tyrrheniancirculationaffects thecurrentmeasuredat the GiglioPortobuoy.

However,strongwindepisodes(velocity>15ms
1)over alimitedperiodofobservationseemtobeabletoinfluence thecurrentvelocitypatterncreatingacause-effect relation-shipthatprevailsintheactionoftheTyrrheniancirculation. As already found by Li etal. (2014) in the Gulf of Maine (U.S.A.),themeancoastalcurrentcentrednearthe100-m isobathcandeviatefairlyfrequentlyduetoeffectsofwind forcingandsmall-scalebaroclinicstructures.Theeffectofa strongwindoncurrentvelocitycouldbealsobefacilitatedby thehomogeneityofthewatercolumn;infact,allthethree casesstudiedtookplaceinwinter,whenthewatercolumn wasnotyetstratifiedbythespringandsummerwarmingof theatmosphere(Iermanoetal.,2016).

StartingfromtheelaborationreportedinFigs.11—13,it wasnotedthatwithoutexternalforcing(e.g.strongwind), nearthecoast,thecurrentdirectionreversesby1808(e.g. counter-current)withrespecttotheTyrrhenianflux,while ontheoccasionofastrongwindfromtheSE,alsonearthe coast,thecurrentdirectionalterstotheNorth.This condi-tionwas also noted by Gravili etal.(2001) inthe Gulf of Naples (south-eastern Tyrrhenian Sea), where a two-day intervalofNWflowwasfollowedbyarapidlineartransition toanoppositeflux.

Thesealevelandthecurrentdirectionarenotcorrelated, confirming the low influence of this phenomenon on the watermassesintheTyrrhenianbasin,at leastat theshort distancefrom thecoast thatthebuoy waslocated(Clarke andBattisti,1981).Boththeirregularsealeveltrendandthe prevalence of the semi-diurnal M2constant on the major diurnal constituents supports the argument that the tide doesnothavean evidentandquantifiable(withthe cross-correlationuse) effect on thecurrent. Therefore, thesea levelisinfluencedbyboththegeneralTyrrheniancirculation andtheinfluenceofthewind,phenomenaofhighintensity andlongduration.

7.

Conclusions

Thankstothemonitoringplancarriedoutduringtheremoval operation of the Costa Concordia wreck at Giglio Island (Italy),insituobservations(August2012—July2013), includ-ingcontinuouscurrentmeasurementsandwindandsealevel recordings,wereusedtostudythevariabilityofthese phe-nomenaneartheislandcoastsintheTyrrhenianbasin.

Theresultsshowedasignificantinter-seasonalvariability in both localwind and current velocity, and also in their directions despitethe factthat they are mainlyforced to moveinaNW—SEdirectionbythepresenceoftheisland.The currentsareprincipallydominatedbythegeneralTyrrhenian circulation,andonlypartiallyaffectedbythewind(onlyin strongwindcases),whilethesealevelhasnoeffectsonthe currentregimeduetoitslowintensity.

The N-CCF is a metric commonly used to evaluate the degree of similarity between two signals, and is usually appliedtoseismic,hydrologicalandmeteorologicalstudies in theEarthsciences, butit seems to beausefultoolfor oceanographicstudiesandanalysisofthephysicalprocesses drivingthelocalcirculationandtherelationshipwithforcing

factors.Infact,ourcontribution,withtheN-CCFappliedto theinfluenceoftheboundaryforcing(windandsealevel)on the currents, provided evidence that can highlight and explaincause-effectrelationships suchas, forexample,in the case of the high levels of correlation found between strongSEwindsandcurrentsortheabsenceofacorrelation betweencurrentsandsealevel.

Withinthiscontext,furtheranalysiswillbenecessaryto investigatethecorrelationlevelbetweencurrentsandother directionsofstrongwinds(e.g.NEandSW)measuredatthe GiglioIslandtoanalysethebehaviourofthecurrentstothese typesofstress.Furthermore,theapplicationofthismethod tootherstudycasesinotherlocationswithdifferent oceano-graphiccharacteristicswillallowustoconfirmtheusefulness oftheN-CCFinoceanographicstudies.

Acknowledgments

Thisresearchwas undertakenusing theweather data pro-videdbytheLaMMAConsortiumoftheRegionofTuscanyand theItalianResearchCouncil.Inparticular,theauthorswishto thankDrCarloBrandiniforhissupportinprovidinguswiththe wind and sea level data, andProf. Paul K. Nixon for the Englishrevisionofthepaper.Authorswishalsotothankthe anonymousReviewersthathavegreatlyimprovedthe manu-script.ThisstudywasfundedbyResearchFundingfrom Titan-Micoperigroup.Thispaperwasauthorisedforpublicationby CostaCrociereS.p.A.

References

Alberola, C., Rousseau, S., Millot, C., Astraldi, M., Font, J., Garcia-Lafuente, J., Gasparini, G.P., Send,U., Vangriesheim, A., 1995. Tidal currents in the western Mediterranean Sea. Oceanol.Acta18(2),273_—284.

Androsov,A.A.,Kagan, B.A.,Romanenkov, D.A., Voltzinger,N.E., 2002.Numericalmodellingofbarotropictidaldynamicsinthe straitofMessina.Adv.WaterResour.25(4),401—415,http://dx. doi.org/10.1016/S0309-1708(02)00007-6.

Astraldi,M.,Gasparini,G.P.,1994.Theseasonalcharacteristicsof thecirculationintheTyrrhenianSea.In:LaViollette,P.E.(Ed.), SeasonalInterannual VariabilityoftheWesternMediterranean Sea.Am.Geophys.Union,Washington,DC,115—134,http://dx. doi.org/10.1029/CE046p0115.

Bjerknes,J.,1964.Atlanticair—seainteraction.In:Landsberg,H.E., VanMieghem,J.(Eds.),AdvancesinGeophysics.AcademicPress, NewYork/London,1_—81.

Bolaños,R.,Tornfeldt Sørensen,J.V.,Benetazzo,A.,Carniel, S., Sclavo,M.,2014.Modellingoceancurrentsinthenorthern Adria-ticSea.Cont.ShelfRes.87,54_—72,http://dx.doi.org/10.1016/j. csr.2014.03.009.

Campillo,M.,Paul,A.,2003.Long-rangecorrelationsinthediffusion seismiccoda.Science299(5606),547_—549,http://dx.doi.org/ 10.1126/science.1078551.

Capello,M.,Cutroneo,L.,Ferretti,G.,Gallino,S.,Canepa,G.,2016. Changesinthephysicalcharacteristicsofthewatercolumnatthe mouthofatorrentduringanextremerainfallevent.J.Hydrol. 541 (Pt. A), 146—157, http://dx.doi.org/10.1016/j.jhy-drol.2015.12.009.

Cazenave,A.,Bonnefond,P.,Mercier,F.,Dominh,K.,Toumazou,V., 2002.SealevelvariationsintheMediterraneanSeaandBlackSea fromsatellitealtimetryandtidegauges.GlobalPlanet.Change 34 (1—2), 59—86, http://dx.doi.org/10.1016/S0921-8181(02) 00106-6.

Chen,C.,Reid,R.O.,NowlinJr.,W.D.,1996.Near-inertial oscilla-tionsovertheTexas—Louisianashelf.J.Geophys.Res.101(C2), 3509—3524.

Clarke,A.J.,Battisti,D.S.,1981.Theeffectofcontinentalshelveson tides.Deep-SeaRes.28A(7),665—682.

Dumas,F.,LeGendre,R.,Thomas,Y.,Andréfouët,S.,2012.Tidal flushingandwinddrivencirculationofAheatolllagoon(Tuamotu Archipelago, French Polynesia) from in situ observations and numericalmodelling. Mar. Pollut. Bull. 65 (10_—12), 425_—440,

http://dx.doi.org/10.1016/j.marpolbul.2012.05.041.

Fanjul,E.A.,Gomez,B.P.,Sanchez-Arevalo,I.R.,1997.A descrip-tionofthetidesintheEasternNorthAtlantic.Prog.Oceanogr. 40(1_—4),217_—244,http://dx.doi.org/10.1016/S0079-6611(98) 00003-2.

Ferrarin,C.,Roland,A.,Bajo,M.,Umgiesser,G.,Cucco,A.,Davolio, S., Buzzi, A.,Malguzzi, P., Drofa, O., 2013. Tide-surge-wave modellingandforecastingintheMediterraneanSeawithfocus ontheItaliancoast.OceanModel.61,38—48,http://dx.doi.org/ 10.1016/j.ocemod.2012.10.003.

Fontán,A.,González,M.,Wells,N.,Collins,M.,Mader,J.,Ferrer,L., Esnaola,G.,Uriarte,A.,2009.Tidalandwind-inducedcirculation withintheSoutheasternlimitoftheBayofBiscay:PasaiaBay. BasqueCoast.Cont.ShelfRes.29(8),998—1007,http://dx.doi. org/10.1016/j.csr.2008.12.013.

Frezza,V.,Carboni,M.G.,2009.Distributionofrecentforaminiferal assemblagesneartheOmbroneRivermouth(NorthernTyrrhenian Sea,Italy).Rev.Micropléontol.52(1),43_—66,http://dx.doi.org/ 10.1016/j.revmic.2007.08.007.

Gravili,D.,Napolitano,E.,Pierini,S.,2001.Barotropicaspectsof thedynamicsoftheGulfofNaples(TyrrhenianSea).Cont.Shelf Res.21 (5),455_—471, http://dx.doi.org/10.1016/S0278-4343 (00)00100-X.

Halverson,M.J.,2014.Atmosphericandtidalforcingoftheexchange betweenPrinceWilliamSoundandtheGulfofAlaska.Dyn.Atmos. Ocean. 65, 86—106, http://dx.doi.org/10.1016/j.dynatmoce. 2013.12.001.

Iermano,I.,Moore,A.M.,Zambianchi,E.,2016.Impactsof 4-dimen-sionalvariationaldataassimilationinacoastaloceanmodelof southern Tyrrhenian Sea.J. Mar. Syst. 154 (Pt.B), 157—171,

http://dx.doi.org/10.1016/j.jmarsys.2015.09.006.

Janekovíc,I.,Kuzmíc,M.,2005.NumericalsimulationoftheAdriatic Seaprincipaltidalconstituents.Ann.Geophys.23,3207_—3218.

Lentz,S.J.,2007. Seasonalvariationsin thecirculationover the MiddleAtlanticBightcontinental shelf.J.Phys.Oceanogr.38, 1486_—1500,http://dx.doi.org/10.1175/2007JPO3767.1. Li,Y.,He,R.,McGillicuddyJr.,D.J.,2014.Seasonalandinterannual

variabilityinGulfofMainehydrodynamics:2002_—2011.Deep-Sea Res. 103 (Pt. II), 210_—222, http://dx.doi.org/10.1016/j. dsr2.2013.03.001.

Liu,Y.,Weisberg,R.H.,2012.SeasonalvariabilityontheWestFlorida Shelf.Prog.Oceanogr.104,80—98,http://dx.doi.org/10.1016/j. pocean.2012.06.001.

Lovato,T.,Androsov,A.,Romanenkov,D.,Rubino,A.,2010.Thetidal andwindinducedhydrodynamicsofthecompositesystem Adria-tic Sea/Lagoon of Venice. Cont. Shelf Res. 30 (6), 692—706,

http://dx.doi.org/10.1016/j.csr.2010.01.005.

McMillen,R.T.,1987.Aneddycorrelationtechniquewithextended applicabilitytonon-simpleterrain.Bound.-LayMeteorol.43(3), 231_—245,http://dx.doi.org/10.1007/BF00128405.

Millot,C.,Taupier-Letage,I.,2005.CirculationintheMediterranean Sea.Handb.Environ.Chem.5(PtK),29—66,http://dx.doi.org/ 10.1007/b107143.

Molcard,A.,Pinardi,N.,Iskandarani,M.,Haivogel,D.B.,2002.Wind drivengeneralcirculationoftheMediterranean Seasimulated withaSpectralElementOceanModel.Dyn.Atmos.Ocean.35(2), 97_—130,http://dx.doi.org/10.1016/S0377-0265(01)00080-X. Mosetti,F.,Purga,N.,1982.Firstresultsonlong-andmidperiodtide

distributioninItalianseasandtheirexistenceinthegroundwater. IlNuovoCimento5C(2),143_—158.

Naranjo,C.,Garcia-Lafuente,J.,Sannino,G.,Sanchez-Garrido,J. C.,2014.Howmuchdotidesaffectthecirculationofthe Medi-terraneanSea?FromlocalprocessesintheStraitofGibraltarto basin-scaleeffects. Prog.Oceanogr.127,108—116,http://dx. doi.org/10.1016/j.pocean.2014.06.005.

Pierini,S.,Simioli,A.,1998.Awind-drivencirculationmodelofthe TyrrhenianSeaarea.J.Mar.Syst.18,161—178.

Polli,S.,1955.Variazionidellecostantiarmonichedellemareecol livellodelmare.Ann.Geofis.8(2),202—207.

Rossetti, F., Faccenna, C., Jolivet, L., Funiciello, R., Tecce, F., Brunet,C.,1999.Syn-versuspost-orogenicextension:thecase ofGiglioIsland(NorthernTyrrhenianSea,Italy).Tectonophysics 304 (1—2), 71—93, http://dx.doi.org/10.1016/S0040-1951(98) 00304-7.

Scherbaum,F.,Johnson,J.,Rietbrock,A.,1999.PITSA (Programma-bleInteractiveToolboxforSeismologicalAnalysis).PITSAUsers Manual,222pp.

Schroeder,K.,Haza,A.C.,Griffa,A.,Özgökmen,T.M.,Poulain,P.M., Gerin,R.,Peggion,G.,Rixen,M.,2011.Relativedispersioninthe Liguro-Provenc_¸albasin:fromsub-mesoscaletomesoscale. Deep-Sea Res. Pt. I 58 (3), 209_—228, http://dx.doi.org/10.1016/j. dsr.2010.11.004.

Thouvenot, F., Jenatton, L., Scafidi, D., Turino, C., Potin, B., Ferretti, G., 2016.Encore ubaye: earthquake swarms, fore-shocks, and aftershocks in the Southern French Alps. Bull. Seismol. Soc. Am. 106 (5), 2244—2257, http://dx.doi.org/ 10.1785/0120150249.

Tsai,D.M.,Lin,C.T.,Chen,J.F.,2003.Theevaluationofnormalized crosscorrelationsfordefectdetection.PatternRecogn.Lett.24 (15), 2525—2535, http://dx.doi.org/10.1016/S0167-8655(03) 00098-9.

Tsimplis, M., Spada, G.,Marcos, M., Flemming, N., 2011. Multi-decadalsealeveltrendsandlandmovementsinthe Mediterra-neanSeawithestimatesoffactorsperturbingtidegaugedataand cumulativeuncertainties.GlobalPlanet.Change76(1_—2),63_— 76,http://dx.doi.org/10.1016/j.gloplacha.2010.12.002. Vetrano,A.,Napolitano,E.,Iacono,R.,Schroeder,K.,Gasparini,G.

P., 2010. TyrrhenianSea circulationand watermass _fluxesin spring2004:observations andmodelresults.J.Geophys.Res. 115,C06023,http://dx.doi.org/10.1029/2009JC005680. Wei,W.W.S.,2006.TimeSeriesAnalysis,UnivariateandMultivariate

Methods, 2nded.Addison-Wesley,Boston,MA,614pp. White,R.J.,Peterson,B.M.,1994.Commentsoncross-correlation

methodologyinvariabilitystudiesofactivegalacticnuclei.Publ. Astron.Soc.Pac.106(702),879—889.

Wood,J.E.,Schaeffer,A.,Roughan,M.,Tate,P.M.,2016.Seasonal variability in the continental shelf waters off southeastern Australia: fact or fiction? Cont. Shelf Res. 112, 92—103,