Sim u la tion of Ice berg Drift as a Com po nent of Ice Mon i toring in the West Arc tic

Transcription

1 ISSN , Russian Meteorology and Hydrology, 201, Vol. 0, No. 12, pp Allerton Press, Inc., 201. Original Russian Text M.Yu. Kulakov, D.M. Demchev, 201, published in Meteorologiya i Gidrologiya, 201, No. 12, pp. 7. Sim u la tion of Ice berg Drift as a Com po nent of Ice Mon i toring in the West Arc tic M. Yu. Kulakov and D. M. Demchev Arc tic and Ant arc tic Re search In sti tute, ul. Beringa 38, St. Pe ters burg, Rus sia, mod@aari.ru Received October 1, 201 Ab stract Dis cussed is the hy dro dy namic model of ice berg drift. Pres ented are the ex am ples of its use in op er a tional prac tice for pre dict ing ice berg drift in the Kara Sea and for en hanc ing ice mon i tor ing in the Barents Sea. DOI: /S Keywords: Arctic seas, simulation, iceberg drift, forecast, ice monitoring INTRODUCTION Icebergs are observed in the most part of the areas of West Arctic seas, they present great hazard for ships and marine industrial objects [10]. In recent years, in view of the active development of oil and gas fields on the shelf of the Barents and Kara seas the problem of iceberg hazard prevention has become especially urgent. Ice hazards are referred to the category of controllable ones because there is a possibility of affecting heavy ice and icebergs using icebreakers and other instruments using the system of ice condition control or ice management. Ice monitoring includes observations, estimation, and forecast of expected changes in ice conditions, and it is a key component of ice condition control. Nu mer i cal hy dro dy namic mod el ing can con sid er ably as sist the or ga ni za tion of ice mon i tor ing sys tem in the West Arc tic. Hy dro dy namic mod els form the base for pre dict ing the move ment and trans for ma tion of ice bergs, and help to clas sify ice berg sources ac cord ing to the de gree of their haz ard for the re gion un der study. The ob jec tive of the pres ent pa per is to dem on strate the po ten tial of the de vel oped hy dro dy namic model of ice berg drift for the op er a tional sup port of ma rine ac tiv i ties on the shelf and for research works on the op ti mi za tion of ice mon i tor ing sys tem in the West Arc tic. THE MODEL The equa tion of the bal ance of forces af fect ing an iceberg that drifts in the sur face wa ter layer, can be writ ten in the fol low ing form: m dw i Fa Fw Fif Fp FC (1) dt where W i is the ve loc ity of the ice berg drift; m is the ice berg mass; F a is wind force; F w is cur rent force; F if is the drift ing ice force; F p is the pres sure gra di ent force; F C is the Coriolis force; t is time. Let us write the wind force af fect ing the ice berg ac cord ing to the clas sic qua dratic de pend ence on wind speed: Fa a S ac a Wa ( Wa ) (2) where W a is wind speed; a is air den sity; S a is the above-water area of the ice berg which is per pen dic u lar to wind di rec tion; C a is the empirical coefficient. Let us ex press the cur rent force af fect ing the ice berg by the qua dratic de pend ence on the dif fer ence be - tween the ve loc ity of the cur rent and ve loc ity of the ice berg drift: 807

2 808 KULAKOV, DEMCHEV F S C W W ( W W ) (3) w w w w w i w i where W w is the average velocity of the current in the layer from the surface to the base of the iceberg; w is water density; S w is the underwater area of the iceberg which is perpendicular to the direction of the mean current; C w is the empirical coefficient. Let us ex press the ice drift force af fect ing the ice berg by the qua dratic de pend ence on the dif fer ence be - tween the ve loc ity of ice drift and ve loc ity of ice berg drift: Fif i S if C if Wif Wi ( Wif Wi ) () where W if is the velocity of ice drift; i is ice density; S if is the area of the iceberg being in contact with the drifting ice and perpendicular to the direction of its drift; C if is the empirical coefficient. The pres sure gra di ent force is de fined by the pro jec tion of grav ity force to the hor i zon tal sur face: F gm () p where g is acceleration of gravity; is the exceeding of the sea level over the undisturbed surface. Let us write the Coriolis force in the clas sic form: F mk W (6) C where is the Earth an gu lar ve loc ity; k is the unit vec tor di rected straight up. The for mu lated prob lem (1) (6) al lows the de ter mi na tion of ve loc ity and then of tra jec tory of ice berg drift at the known ef fects us ing the nu mer i cal math e mat i cal mod el ing. How ever, if there are sev eral avail able ways of wind speed de ter mi na tion, such pa ram e ters as the cur rent ve loc ity, ice drift ve loc ity, and the denivellation of the sea level sur face can be ob tained only by com put ing them in the ice ocean cou pled model. The AARI-IOCM model was used as such model []. It com bines three mod els: the three-di men - sional baroclinic model of wa ter cir cu la tion, the ice cover drift model, and the ther mo dy namic model of sea ice. The AARI-IOCM model is adapted to the Arc tic Ocean area and ad join ing area of the At lan tic Ocean and has a spa tial res o lu tion of 13.8 km. The size of the grid do main is 0 39 points. Ver ti cal res o lu tion is vari able and com pu ta tion is car ried out at 33 lev els. To de scribe the bot tom to pog ra phy and coast line con fig u ra tion, the GEBCO ar chive was used. Av er age long-term monthly mean val ues of wa ter dis charge on 17 main rivers flow ing into the Arc tic Ocean were used as bound ary con di tions. The val ues of tem per a - ture and sa lin ity of wa ter from World Ocean At las (WOA0) were taken as ini tial con di tions for sum mer and win ter. The data on the sea-level air pres sure and air tem per a ture at the height of 2 m from the NCEP/NCAR reanalysis for di ag nos tic com pu ta tions or the prog nos tic data of the Eu ro pean Cen ter for Me - dium-range Weather Fore casts with the res o lu tion of were used as the ex ter nal forc ing. It was dem on strated in the pre vi ous pa pers [ 6] that the AARI-IOCM model sim u lates rather well ice con di tions and wa ter cir cu la tion in the Arc tic Ocean and The Method and Tech nol ogy of Com pu ta tion and Short-term Fore cast of Sea Level and Cur rents in the Arc tic Ocean and Its Seas Based on Three-dimensional Hy dro dy namic Model of Cou pled Ice Ocean Cir cu la tion was rec om mended by the Roshydromet Cen tral Meth od olog i cal Com mit tee in 2012 for use in op er a tional prac tice of Arc tic and Ant arc tic Re search In sti tute (AARI). The model was verified using the data of ARGOS radio beacons installed on icebergs during the Kara-Winter-2013 expedition. The analysis of the results of computations demonstrated that the model well simulated iceberg drift parameters (Fig. 1). OP ER A TIONAL SUP PORT OF EX PLO RA TION DRILLING IN THE KARA SEA Based on the above model, the tech nol ogy of ice berg drift fore cast ing was created [8]. It enables predicting drift of icebergs for the time pe riod up to five days in the au to matic mode. The model was sub stan - tially mod i fied. To re duce the grid spac ing of the AARI-IOCM model, the fol low ing tele scop ing pro ce dure was ap plied: the usual large grid spac ing (in our case, 13.8 km) is used for the whole Arc tic Ocean area, and the grid spac ing be ing smaller by sev eral times is used for the wa ter area for which the fore cast ing is car ried out. The model grid spac ing for the Kara Sea is.6 km. To pro vide the better sim u la tion of at mo spheric forc ing, the WRF at mo spheric re gional model was in - cluded into the model set. At pres ent, the Po lar WRF model ver sion [11] is adapted to the area cov er ing the south west ern part of the Kara Sea and the Pechora Sea; the hor i zon tal res o lu tion is km. Post-processing i

3 SIM U LA TION OF ICE BERG DRIFT AS A COM PO NENT 809 Fig. 1. The com par i son of real (the heavy line) and sim u lated (the thin line) tra jec to ries of the drift of (a d) four ice bergs in scripts were worked out us ing the Py thon lan guage; they form lin ear shape files be ing the fi nal prod ucts of the tech no log i cal chain. These files en able the user to view op er a tion ally the re sults of com pu ta tions and to con trol the qual ity of com pu ta tions. The technology of numerical hydrodynamic forecasting of iceberg drift was successfully tested during the operational support of exploration works on the Kara Sea shelf. In August October 201 well exploration drilling was carried out at Universitetskaya-1 geologic structure in the Vostochno-Prinovozemel skii-1 licensed area in the Kara Sea. The drilling was carried out by West Alpha semisubmersible drilling rig (SDR) which had no ice class that caused the heightened requirements for its ice and hydrometeorological support. The specialists of AARI carried out the full set of works on the environmental monitoring and provision of the sea operation leaders and SDR captain with hydrometeorological data. The main objectives of ice monitoring were the detection of hazardous ice formations (ice fields, floebergs, and icebergs) and the prediction of their drift and potential collision with SDR. The possibility of the transport of icebergs and their pieces from the outlet glaciers of the Novaya Zemlya archipelago to the area of Universitetskaya-1 structure was also taken into account [7]. The ice drift forecast with the lead time of 2 72 hours was produced almost every day and was transmitted in the shape file format to the Shore Operational Center (SOC) located in Moscow. In SOC all information was analyzed and transmitted to SDR and auxiliary vessels. An example of iceberg drift forecast for the user is presented in Fig. 2. The ac cu racy and ef fi ciency of ice and hydro meteoro logi cal fore casts met all cri te ria of reg u la tory doc - u ments in force. In 201 the hydro meteoro logi cal and ice sup port of ex plo ra tion drill ing in the Kara Sea en - sured the safety and ef fi ciency of works that fa vored the dis cov ery of the new oil field Pobeda. RE CON STRUC TION OF ICE BERG DRIFT TO THE AREA OF SHTOKMAN GAS FIELD IN 2003 Drifting ice bergs are the most dan ger ous for the pro duc tion com plexes in the Shtokman gas field (SGF) in the Barents Sea. Ac cord ing to the ob ser va tional data for and , 220 ice bergs and ice berg pieces [1] were reg is tered in the area ad join ing SGF in 1967, 1968, 1971, 197, 1981, 1986, 1987, 1989, 1991, and 2003.

4 810 KULAKOV, DEMCHEV Fig. 2. An example of iceberg drift forecast on September 9, 201 presented in the framework of ice and hydrometeorological support of the drilling in the Kara Sea. (1) The iceberg location; (2) the iceberg drift forecast for 7 days. The sources of ice bergs ob served in the Barents Sea area are the Arc tic ar chi pel a gos Svalbard, Franz Josef Land, Novaya Zemlya (Severnyi Is land), some Arc tic is lands (Ushakov and Vic to ria), and even the Severnaya Zemlya ar chi pel ago [3, 1]. The es sen tial com po nent of ice mon i tor ing is the timely de tec tion of ice bergs be ing po ten tially haz ard ous for the pro duc ing plat form. This prob lem can be suc cess fully solved if only all ice berg sources are clas si fied fol low ing the de gree of their haz ard. Sev eral at tempts were made to use the math e mat i cal mod el ing for as sess ing ice berg dan ger. For ex am - ple, pa per [12] pres ents the re sults of model com pu ta tions of ice berg drift from the south ern coast of the Franz Josef Land to the area of SGF. The au thors com puted the tra jec to ries of 3000 ice bergs which started in July, Au gust, and Sep tem ber in Ac cord ing to the ob tained re sults, no ice bergs reached the area of SGF. The most part of ice bergs drifted to the west to the Svalbard ar chi pel ago, many ice bergs moved to the Cen tral Arc tic Ba sin, and only a few ice bergs drifted to the east to the north ern edge of the Novaya Zemlya. The data of ice berg ob ser va tions car ried out in the frame work of the Shtokman-Winter-2003 ex pe di - tion [9] when 10 ice bergs and their pieces drifted di rectly through the area of SGF, proved the op po site. Ac cord ing to some in di rect signs, the ice bergs de tected in the area of SGF were the pieces of gla ciers from the Franz Josef Land ar chi pel ago. Paper [1] describes how modeling was used for corroborating the hypothesis that the icebergs detected in 2003 in the area of SGF came from the Franz Josef Land archipelago. For this purpose the series of computations using the hydrodynamic model was carried out [13] with the included unit of iceberg movement [2]. The initial point of iceberg transport was the area in the vicinity of Wilczek Land island (the Franz Josef Land archipelago; N, E) whose glacier is supposedly a producer of large ice formations being of the greatest danger for technical facilities in the open part of the Barents Sea. Proceeding from the prerequisite on the initial time of the transport dated to the end of summer, September 1, 2002 was taken as a starting point. The total duration of computations is 8 months (September 1, 2002 May 30, 2003). The model experiment was conducted for 10 icebergs with the mass from to t. Model com pu ta tions dem on strated that large ice bergs (with the mass of more than t) formed of the Franz Josef Land ar chi pel ago gla ciers in Sep tem ber 2002 drifted mainly in the south west ern and south - ern di rec tions and there were all pre req ui sites for their pen e tra tion to the area of SGF. It should be noted that all these ice bergs in the given area were reg is tered dur ing the AARI ex pe di tion works in May The inverse problem was solved in the present paper using the AARI-IOCM model. For this purpose time was counted out in the reverse order and the increments of iceberg drift coordinates computed from the model were not added to but were subtracted from the previous coordinates. The computations for the period of May 2003 May 2002 were carried out for 12 icebergs (see the table) whose morphometric sizes were determined in the framework of the Shtokman-Winter-2013 expedition. For the sake of analysis convenience and for the sake of clearness, the results of computations of reverse iceberg drift were grouped according to the mass (Fig. 3): below , (100 00) 10 3, (00 700) 10 3 t, and above t.

5 SIM U LA TION OF ICE BERG DRIFT AS A COM PO NENT 811 Morphometric pa ram e ters of ice bergs in ves ti gated on May 13 1, 2003 in the area of SGF Iceberg num ber Co or di nates, degree Iceberg parameters N E length, m width, m height, m mass, 10 3 t draught, m Note: The date of in ves ti ga tion is May 13 for ice bergs Nos. 2, 3, and 11 and May 1 for the rest of the ice bergs. Fig ure 3 pres ents the com puted tra jec to ries of the re verse ice berg drift in from the area of SGF pre sented in the form of the se ries of points that register an ice berg po si tion ev ery 6 hours. Ac cord ing to the ob tained re sults, all ice bergs de tected and mea sured dur ing the Shtokman-Winter-2013 ex pe di tion drifted to the area of SGF from the Franz Josef Land. It should be noted that in spite of the va ri ety of morphometric fea tures and ice berg masses, the most part of tra jec to ries of ice berg drift (9 of 12) ended near the south east ern coast of the Franz Josef Land ar chi pel ago. This cor rob o rates the sup po si tion of the au thors of [1] that the gla cier on Wilczek Land is the most likely source of ice bergs which can reach the area of SGF. The com puted time of ice berg drift from the coast of the Franz Josef Land to the area of SGF equals five months for the small est ice berg No. 1 and from 7 to 10 months for the rest of the ice bergs. Hence, the most fa vor able pe riod for icebergs to reach the area of SGF is July Oc to ber. This does not con tra dict the ice con - di tions ob served around the Franz Josef Land in In early July the south ern coast was free not only of drift ice but also of fast ice. Thus, the model experiments demonstrated that the glaciers of the Franz Josef Land archipelago are the most probable sources of icebergs being hazardous for the producing platform in SGF. The time the icebergs need to reach the area of SGF is from 7 to 10 months but more rapid movement is also possible. All these should be taken into account when developing the iceberg drift monitoring system in the Barents Sea area. CONCLUSIONS The nu mer i cal hy dro dy namic model of ice berg drift was worked out which can be used for solv ing a num ber of prob lems in the sys tem of ice con di tion mon i tor ing in the west ern Arc tic zone of the Rus sian Federation. The model of short-term forecasts (2 72 hours) was operatively used for the hydrometeorological support of exploration drilling at Universitetskaya-1 geologic structure in the Vostochno-Prinovozemel skii-1 licensed area in the Kara Sea in 201. The model use demonstrated the efficiency of the technology developed. The gained experience will be applied in creating the automatic monitoring system. Using the re sults of nu mer i cal hy dro dy namic mod el ing, the es sen tial reg u lar i ties of ice berg move ment in the Barents Sea were de rived which can be use ful for op ti miz ing the ice mon i tor ing sys tem in the West Arc tic. ACKNOWLEDGMENTS The re search was sup ported by the Min is try of Ed u ca tion and Sci ence of the Rus sian Fed er a tion in the frame work of ap plied sci en tific re search and ex per i men tal de vel op ments (ASRED) on Cre ation of New

6 812 KULAKOV, DEMCHEV Fig. 3. Com puted tra jec to ries of re verse ice berg drift in from the area of SGF (the rect an gu lar) for the fol low ing ice berg cat e go ries: the mass is (a) less than 60, (b) 100 to 00, (c) 00 to t, and (d) above t. Methods and In stru ments of Mon i toring of Hydro meteoro logi cal and Geo phys i cal Con di tions on the Svalbard Ar chi pel ago and in the West Arc tic Zone of the Rus sian Fed er a tion (Agree ment on the Pro vi sion of Sub sidy on No , ASRED unique iden ti fier RFMEFI6101X0006). REF ER ENCES 1. I. V. Buzin, A. F. Glazovskii, Yu. P. Gudoshnikov, et al., Icebergs and Glaciers of the Barents Sea: Recent Researches, Part 2: Iceberg Drift from In Situ Observations and Modeling Results and Assessment of Risks of an Iceberg Collision with Hydrotechnical Equipment, Problemy Arktiki i Antarktiki, No. 1 (2008) [in Russian]. 2. N. E. Dmitriev and I. V. Polyakov, Three-dimensional Hydrodynamic Model of Iceberg Drift in the Barents Sea, in Proceedings of International Conference Development of the Russian Arctic Offshore (RAO-9) (St. Petersburg State Technical Univ., 199) [in Russian]. 3. V. S. Koryakin, The Arc tic Gla ciers (Nauka, Mos cow, 1988) [in Rus sian].. M. Yu. Kulakov and A. P. Makshtas, The Role of Ice Drift in Formation of the Ice Cover of the Arctic Ocean in the Beginning of the 21st Century, Problemy Arktiki i Antarktiki, No. 2 (2013) [in Rus sian].. M. Yu. Kulakov, A. P. Makshtas, and S. V. Shutilin, AARI-IOCM the Coupled Model of Water and Ice Circulation of the Arctic Ocean, Problemy Arktiki i Antarktiki, No. 2 (2012) [in Rus sian]. 6. M. Yu. Kulakov, A. P. Makshtas, and S. V. Shutilin, Model Estimates of Sensibility of the Arctic Ocean Ice Cover to Forcing Changes, Problemy Arktiki i Antarktiki, No. 3 (2012) [in Rus sian].

7 SIM U LA TION OF ICE BERG DRIFT AS A COM PO NENT E. U. Mironov and V. G. Smirnov, Mon i toring of Ice Cover and Ice bergs for Pro viding Hydro meteoro logi cal Safety of Ex plo ra tion Drilling in the Kara Sea, in Proceedings of 12th In ter na tional Con fer ence RAO/CIS Off - shore, Sep tem ber 1 18, 201, 8. E. U. Mironov, V. G. Smirnov, I. A. Bychkova, et al., New Technologies for Iceberg Detection and the Iceberg Drift Forecast in the Western Part of the Arctic, Problemy Arktiki i Antarktiki, No. 2 (201) [in Rus sian]. 9. A. K. Naumov, G. K. Zubakin, Yu. P. Gudoshnikov, et al., Ice and Ice bergs in the Area of Shtokman Gas Field, in Proceedings of International Con fer ence De vel op ment of the Rus sian Arc tic Off shore (RAO-03), St. Pe ters - burg, Sep tem ber 16 19, 2003 [in Rus sian]. 10. Haz ard ous Ice Events for Nav i ga tion in the Arc tic, Ed. by E. U. Mironov (Arc tic and Ant arc tic Res. Inst., St. Pe - ters burg, 2010) [in Rus sian]. 11. D. H. Bromwich, K. M. Hines, and L.-S. Bai, De vel op ments and Testing of Po lar Weather Re search and Fore - casting Model: 2. Arc tic Ocean, J. Geophys. Res., 11 (2009). 12. K. Johannesse, S. Loset, and P. Strass, Sim u la tion of Ice berg Drift, in Pro ceed ings of 1th In ter na tional Con - fer ence on Port and Ocean En gi neering un der Arc tic Con di tions POAC 99 (Espoo, Fin land, 1999). 13. I. V. Polyakov, I. Yu. Kulakov, S. A. Kolesov, et al., Cou pled Sea Ice Ocean Model of the Arc tic Ocean, J. Off - shore Me chanics and Arc tic Engin., 120 (1998). 1. K. S. Sandfor, Tab u lar Ice bergs be tween Spitsbergen and Franz-Josef Land, Geograph. J., 121 (19). 1. G. K. Zubakin, Yu. P. Gudoshnikov, A. K. Naumov, et al., Re sults of In ves ti ga tions of Ice bergs, Gla ciers and Their Fron tal Zones in the North east ern Part of the Barents Sea, in Pro ceed ings of 19th In ter na tional Con fer ence on Port and Ocean En gi neering un der Arc tic Con di tions (POAC-2007), Dalian, June 27 30, 2007.