Oil spill forecasting in the Mediterranean Sea

Transcription

1 Ol spll forecastng n te Medterranean Sea M. De Domncs *1, N. Pnard 2, N. Fabbron 2, G. Coppn 1, G. Zodats 3 and. Lardner 3 1 Isttuto Nazonale d Geofsca e Vulcanologa, Bologna, Italy 2 Corso d Scenze Ambental, Unersty of Bologna, aenna, Italy 3 Oceanograpc Centre, Unersty of Cyprus, Cyprus * Correspondng autor, emal: dedomncs@bo.ng.t Abstract In ts work senstty experments to te coupled MFS currents) and MEDSLIK ol spll) nput parameters wll be sown and results wll be compared wt obseratons. In tese experments te drft angle, te drft factor, te currents dept, te type of ol, orzontal dffusty and te orzontal and temporal current resoluton were canged. Keywords: ol spll, operatonal oceanograpy, Medterranean Sea 1. Introducton For many years now te Medterranean ocean Forecastng System MFS, Pnard et al, 2003) current forecasts ae been coupled to te MEDSLIK fate and dspersal ol spll model Lardner et al., 2006). Snce 2006 seeral accdents occurred n te Medterranean from te Lebanese coasts to te Gbraltar Strat tat sowed te mportance of connectng GMES core serce products yder, 2007) to downstream serces suc as ol spll forecastng n real tme. Te flow feld arablty n te Medterranean s as g as n oter world ocean regons and tere s a need to ae real tme currents togeter wt clmatologes to augment te accuracy of te fate and dspersal of ol splls. In ts paper, senstty experments to ol spll model parameters wll be sown for dfferent coupled model forecasts tat wll be compared wt obseratons from buoy trajectores to real accdents. 2. Descrpton of te ol dsperson model: MEDSLIK MEDSLIK s a user-frendly software package desgned to predct te fate and transport of an ol spll. It uses a lagrangan representaton of te ol slck,.e., te ol slck s represented by a large number of partcles. MEDSLIK requres as nput data te type of ol and ts caracterstcs, te wnd feld, te sea surface temperature and te teedmensonal sea currents. MEDSLIK s ntegrated wt MFS currents and t s capable of reproducng te ol dsperson takng nto account te weaterng of te ol. MEDSLIK smulates te transport of te surface slck goerned by bot water currents and by drect wnd forcng. Te adecte elocty of eac ol parcel can be a sum of te mean and turbulent fluctuaton components of te drft elocty. Te turbulent fluctuatons are parameterzed as orzontal turbulent dffuson based on te random walk ypotess. 1

2 Te mean adecton of te slck s caused by te combned effects of surface currents and wnd drag. MEDSLIK, lke most ol spll models, uses a drft factor approac, wc s consdered to be a most practcal approac for adjustng te mean adecton of ol slcks comng from rater low resoluton crculaton models. Wt ts metod te mean drft elocty of te surface ol s consdered to be a wegted sum of te wnd elocty and te surface euleran elocty feld. Let X, Y, Z) be te poston of te -t parcel at te begnnng of a partcular step. Ten at te end of te tme step of lengt τ te parcel s dsplaced to te pont X X Y Y + Z Z + Z + { u X, Y, Z ) + α Wx cos β + Wy sn β )} { X, Y, Z ) + α W sn β + W cos β )} were X, Y, Z ) u and X, Y, Z ) x and y drectons at a fxed reference water leel, y τ + X τ + Y are te water elocty components n te x Z, W x and 1) W y te components of wnd elocty, α and β are te drft factor and te drft angle respectely and te dffuse dsplacements are gen by X Y Z 1] 6Kτ 1] 6Kτ 1] 6K τ were K and K are te orzontal and ertcal dffustes respectely, cosen as fxed alues and rand0,1) s a unform random number between 0 and 1. It can easly be seen tat te root mean square alues of te dffuse dsplacements are r. ms. X, Y, Z ) { 2K 2K 2K } It can be sown tat a cloud of suc partcles undergong random walks wt tese r.m.s. dsplacements satsfes te conecton-dffuson equaton wt K and K te orzontal and ertcal dffuson coeffcents. Te successe postons of te parcel of ol descrbed by 1) and 2) s called te trajectory model of MEDSLIK. In addton to conecte and dffuse dsplacements, te ol spll parcels cange due to arous pyscal and cemcal processes tat transform te ol. Te lgter fractons of te ol dsappear troug eaporaton and te remanng fractons begn to be absorbed n water, or emulsfy. Eac partcle of ol, wle mong wt te flow as descrbed before, canges ts ol propertes, suc as ts densty and scosty. Fnally, some of te ol s dren below te surface by wae acton tat s parameterzed n a smple way n MEDSLIK. It may also appen tat te orzontal dsplacement takes a partcular parcel of ol onto te coast. 2) 2

3 3. esults 3.1 Study case: te Lebanon Accdent On te 13 and 15 of July 2006 te ol tanks at Je power staton, located 30 km sout of Berut and drectly on te coast, were t by bombs. Te amount of ol spll was reported as beng between and tons and te type of ol was beleed to be a eay fuel ol of about API 20. Dfferent smulatons ae been carred wt te MFS current felds and te ECMWF wnd forcng. Te poston of te spll was N and E actually te spll was on te coast, but we must coose te MFS grd pont nearest to te coast), te spll olume was tons and te duraton of spll was supposed equal to 96 rs. Fgure 1 sows te comparson between te results of te smulatons carred out wt dfferent wnd correcton factors, wnd angles, current reference depts and orzontal dffusty. Fgure 2 sow te temporal eoluton of te percentage of ol eaporated and te percentage of ol on te surface for tree dfferent type of ol. From satellte mages of te accdent we know tat te case of Fg. B and C are realstc Scarra et al., 2006). A) B) C) Fgure 1: Comparson between smulaton performed wt te followng parameters: A) wnd correcton factor: 0, wnd angle: 0, current reference dept: 30 m and orzontal dffusty: 2 m 2 s -1 ; B) wnd correcton factor: 0.03, wnd angle: 0, current reference dept: 30 m and orzontal dffusty: 2 m 2 s -1 ; C) wnd correcton factor: 0, wnd angle: 0, current reference dept: 30 m and orzontal dffusty: 0.1 m 2 s -1. A) B) Fgure 2: Temporal eoluton of a) te percentage of ol eaporated and of b) te percentage of ol on surface n smulaton wt dfferent type of ol, wt te followng caracterstcs : 1) API20, Densty of ol ton/m 3 ): 0.934, Vscosty: 136.9; 2) API27, Densty of ol ton/m 3 ): 0.893, Vscosty: 33.7; 3) API34, Densty of ol ton/m 3 ): 0.855, Vscosty: 8.3 3

4 3.2 Study case: te Mersea drfters and MEA07 drfters Te trajectory model wtn MEDSLIK as been used to smulate drfters trajectores. In te smulatons te currents were taken from MFS analyses and wnds are from ECMWF analyses. A subset of te user defned model parameters as been studed. In tese experments te drft angle, te drft factor and te current reference depts were canged. Te frst study case s te Mersea Project Ol Spll Demonstratons n te Western Medterranean. Seen drfters 75660, 75661, 75662, 75663, 75664, and 60213) were deployed on October 10, 2007 sout of Nce. Te drfters are ol montorng buoys to emulate a surface ol spll. Te second study case s te Marne apd Enronmental Assessment MEA07) experment. Durng ts experment fe drfters 74871, 74872, 74873,74874 and 74875) were deployed on May 14, 2007 n te Lguran sea. Fgure 3 sows te Medslk trajectores wt te dfferent model parameters. We can see tat n te Mersea case te model s capable to reproduce te trajectory n at least few of te parameter cases wle n te MEA07 case te model s not capable to reproduce te correct drecton. Wen ger resoluton modelng s used for te euleran elocty feld, te trajectory n te Lguran Sea s reconstructed not sown). A) B) Fgure 3: Oerlay of te obsered drfter trajectory bold wte-lgt blue lne) and te Medslk trajectores: 1) Wnd Correcton: 0, Wnd Angle: 0, Current dept: 30 m; 2) Wnd Correcton: 0.15, Wnd Angle: 0, Current dept: 30 m; 3) Wnd Correcton: 0.03, Wnd Angle: 13, Current dept: 30 m; 4) Wnd Correcton: 0.03, Wnd Angle: 25, Current dept: 30 m; 5) Wnd Correcton: 0.03, Wnd Angle: 0, Current dept: 30 m; 6) Wnd Correcton: 0, Wnd Angle: 0, Current dept: 0 m; 7) Wnd Correcton: 0.03, Wnd Angle: 0, Current dept: 30 m. Te smulaton n te panel A) s from 12/05/2007 to 22/05/2007, n te panel B) s from 14/05/2007 to 24/05/2007. Te model parameter senstty experments are capable to capture te correct trajectory of te drftng buoy, at least for te Mersea experment, and ge enoug spread n te fnal trajectores. Tus an ensemble of suc senstty experments could be a startng pont for te determnaton of te model trajectory forecast uncertanty. On te oter ands, wen te euleran elocty feld s naccurate enoug, as te MEA07 case, te cange of coupled model parameters does not capture completely te uncertanty of te predctons. Tus tere s a need to add a more detaled 4

5 representaton of te currents, at ger resoluton and ts wll be part of te future deelopments. 4. Fnal remarks In conclusons we ae sown tat te coupled MFS-MEDSLIK ol spll forecastng system can ae skll n reproducng bot real accdents and drfter trajectores n te Medterranean Sea. Te senstty experments carred out n ts paper sow tat canges n te ol spll model parameters could offer some nsgt n te uncertanty of te ol spll predctons by te MFS and MEDSLIK coupled systems. In te future we wll re-cast te determnstc forecast n terms of suc ensemble of dfferent model projectons gng tus te probablty of te azard for ol splls. eferences Lardner., G. Zodats, D. Hayes and N. Pnard, 2006). Applcaton of te MEDSLIK ol spll model to te Lebanese spll of July European Group of Experts on satellte montorng of sea based ol polluton. European Communtes ISSN Lardner., 2006) MEDSLIK Verson User Manual Pnard N., I. Allen, E. Demro, P. De Mey, G. Korres, A. Lascaratos, P.-Y. Le Traon, C. Mallard, G. Manzella, and C. Tzaos, 2003). Te Medterranean ocean forecastng system: frst pase of mplementaton ). Annales Geopyscae, 21: 3 20 c yder, P. 2007). Sustanable Marne Enronmental Informaton Serces to Meet Collecte European Needs, EuroGOOS Publcaton no. 26, EuroGOOS Offce, Scarra., G. Coppn, N. Pnard, Santoler., P. Ncolos, V. Lyubartse, 2006). Te Italan decson support system for ol spll detecton and forecastng n te wole Medterranean Sea: applcaton to te Lebanese ol spll accdent of July European Group of Experts on satellte montorng of sea based ol polluton. European Communtes ISSN