Downwelling-related mesoscale motions at the entrance to the Gulf of Finland: observations and diagnosis

• Autorzy: Laanemets J. , Pavelson J. , Lips U. , Kononen K.
• Języki publikacji: EN

Abstrakty

EN

Hydrographic (towed CTD) and acoustic Doppler current profiler (ADCP) velocity surveys were conducted daily aboard the RV Aranda from July 15 to 26, 1996 at the entrance to the Gulf of Finland, Baltic Sea. Strong alongshore wind forcing that lasted two days caused an intensive downwelling event north of Hiiumaa Island with an approximate 20 m onshore descent of the thermocline. The associated eastward downwelling jet (~30 cm s^-1, width 8-12 km) developed into an anticyclonic eddy with a diameter of ~20 km. A strong jet (~35 cm s^-1, width 4-6 km) was observed in the periphery of the anticyclonic eddy, centered at the depth of reversal in baroclinicity. The geostrophic streamfunctions were derived from ADCP data and combined with the CTD density field to study the variations of isopycnal potential vorticity. The variation of relative vorticity from -0.95f to 1.2f and five-fold changes in the thickness of the selected isopycnal band caused up to fifty-fold variation of isopycnal potential vorticity over the survey area. The distribution of isopycnal potential vorticity as a conservative property correlated well with the isopycnal salinity distribution. The maximum upward and downward velocities, 35 and 26 m d^-1, correspondingly, were estimated through the divergence of the Q-vector using the ω-equation diagnostic technique.

Słowa kluczowe

EN

downwelling; jet; anticyclonic eddy; vorticity; vertical velocity; Gulf of Finland

• Wydawca: Institute of Oceanography University of Gdańsk
• Czasopismo: Oceanological and Hydrobiological Studies
• Rocznik: 2005
• Tom: Vol. 34, No.2
• Strony: 15--36
• Opis fizyczny: Bibliogr. 32, rys., wykr.

Twórcy

autor

Laanemets J.

• Marine Systems Institute, Tallinn University of Technology, Akadeemia tee 21, 12618 Tallinn, Estonia

autor

Pavelson J.

• Marine Systems Institute, Tallinn University of Technology, Akadeemia tee 21, 12618 Tallinn, Estonia

autor

Lips U.

• Estonian Maritime Academy, Mustakivi tee 25, 13912 Tallinn, Estonia

autor

Kononen K.

• Academy of Finland, Vilhonvuorenkatu 6, FIN-00120 Helsinki, Finland

Bibliografia

• [1]. Aitsam A., Elken J., 1982, Synoptic scale variability of hydrophysical fields in the Baltic Proper on the basis of CTD measurements, [in:] Hydrodynamics of Semi-enclosed Seas, Nihoul J. C. J. (ed.), Elsevier, Amsterdam, 433-467
• [2]. Aitsam A., Hansen H. P., Elken J., Kahru M., Laanemets J., Pajuste M., Pavelson Talpsepp L., 1984, Physical and chemical variability of the Baltic Sea: a joint experiment in the Gotland Basin, Cont. Shelf Res., 3, 291-310
• [3]. Alenius P., Myrberg K., Nekrasov A., 1998, The physical oceanography of the Gulf of Finland: a review, Boreal Environ. Res., 3, 97-125
• [4]. Allen J.T., Smeed D. A., 1996, Potential vorticity and vertical velocity at the Iceland-Fœrœs front, J. Phys. Oceanogr., 26, 2611-2634
• [5]. Castro C. G, Pérez F. F., Álvarez-Salgado X. A., Fraga F, 2000, Coupling between the thermohaline, chemical and biological fields during two contrasting upwelling events off the NW Iberian Peninsula, Cont. Shelf Res., 20,189-210
• [6]. Feliks Y., 1991, Downwelling along the northeastern coasts of the Eastern Mediterranean, J. Phys. Oceanogr., 21, 511-526
• [7]. Feliks Y., Ghil M., 1993, Downwelling-front instability and eddy formation in the Eastern Mediterranean, J. Phys. Oceanogr., 23, 61-78
• [8]. Fiekas V., Leach H., Mirbach K.-J., Woods J. D., 1994, Mesoscale instability and upwelling. Part I: Observations at the North Atlantic Intergyre Front, J. Phys. Oceanogr., 24, 1750-1758
• [9]. Greenan B. J. W., Petrie B. D., Harrison W. G., Oakey N. S., 2004, Are the spring and fall blooms on the Scotian Shelf related to short-term physical events?, Cont. Shelf Res.,24, 603-625
• [10]. Haapala J., 1994, Upwelling and its influence on nutrient concentration in the coastal area of the Hanko Peninsula, entrance of the Gulf of Finland, Estuar. Coast. Shelf Sei., 38, 507-521
• [11]. Hiller W., Käse R. H., 1983, Objective analysis of hydrographic data sets from mesoscale surveys, Berichte aus dem Institut für Meereskunde an der Christian-Albrechts-Universität Kiel, 116, 78 pp.
• [12]. Hoskins В. J., Draghici I., Davies H. C., 1978, A new look at the ω-equation, Q.J. R. Meteorol. Soc., 104, 31-38
• [13]. Joyce Т. M., 1989, On in situ “calibration” of shipboard ADCPs, J. Atmos. Oceanic Technol., 6, 169-172
• [14]. Kononen K., Huttunen M., Konoshina I., Laanemets J., Moisander P., Pavelson J., 1999, Spatial and temporal variability of a dinoflagellate-cyanobacterium community under a complex hydrodynamical influence: a case study at the entrance to the Gulf of Finland, Mar. Ecol. Progr. Ser., 186, 43-57
• [15]. Kononen K., Huttunen M., Hällfors S., Gentien P., Lunven M., Huttula Т., Laanemets J., Lilover М., Pavelson J., Stips A., 2003, Development of a deep chlorophyll maximum of Heterocapsa triquetra Ehrenb. at the entrance to the Gulf of Finland, Limnol. Oceanogr., 48, 594-607
• [16]. Kullenberg G., 1981, Physical oceanography, [in:] The Baltic Sea, Voipio, A. (ed.), Elsevier, Amsterdam, 135-181
• [17]. Leach H., 1987, The diagnosis of synoptic-scale vertical motion in the seasonal thermocline, Deep-Sea Res., 34, 2005-2017
• [18]. Myrberg K, Andrejev O., 2003, Main upwelling regions in the Baltic Sea – a statistical analysis based on three-dimensional modelling, Boreal Environ. Res., 8, 97-112
• [19]. Nelson D. M., McCarthy J. J., Joyce T. M., Ducklow H. W., 1989, Enhanced near-surface nutrient availability and new production resulting from the frictional decay of a Gulf Stream warm-core ring, Deep-Sea Res., 36, 705-714
• [20]. Onken R., 1990, The creation of reversed baroclinicity and subsurface jets in oceanic eddies, J. Phys. Oceanogr., 20, 786-791
• [21]. Onken R., 1992, Mesoscale upwelling and density finestructure in the seasonal thermocline - a dynamical model, J. Phys. Oceanogr., 22, 1257-1273
• [22]. Pavelson J., Laanemets J., Kononen K., Nömmann S., 1997, Quasi-permanent density front at the entrance to the Gulf of Finland: response to wind forcing, Cont. Shelf Res., 17, 253-265
• [23]. Pavelson J., Kononen K., Laanemets J., 1999, Chlorophyll distribution patchiness caused by hydrodynamical processes: a case study in the Baltic Sea, ICES J. Mar. Sei., 56 Suppl., 87-99
• [24]. Pingree R. D., Le Саnn В., 1992, Three anticyclonic Slope Water Oceanic eDDIES (SWODDIES) in the Southern Bay of Biscay in 1990, Deep-Sea Res., 39, 1147-1175
• [25]. Pinot J.-M., Tintoré J., Wang D.-P., 1996, A study of the omega equation for diagnosing vertical motion at ocean fronts, J. Mar. Res., 54, 239-259
• [26]. Pollard R. Т., Read J., 1989, A method for calibrating shipmounted acoustic Doppler profilers and the limitation of gyro compasses, J. Atmos. Oceanic Technol., 6, 859-865
• [27]. Pollard R. Т., Regier L., 1990, Large variations in potential vorticity at small spatial scales in the upper ocean, Nature, 348, 227-229
• [28]. Pollard R.T. , Regier L. A., 1992, Vorticity and vertical circulation at an ocean front, J. Phys. Oceanogr., 22, 609-625
• [29]. Shearman R. K., Barth J. A., Kosro P. M., 1999, Diagnosis of the three-dimensional circulation associated with mesoscale motion in the California Current, J. Phys. Oceanogr., 29, 651-670
• [30]. Strass V. H., 1994, Mesoscale instability and upwelling. Part 2: Testing the diagnostics of vertical motion with a three-dimentional ocean front model, J. Phys. Oceanogr., 24, 1759-1767
• [31]. Talpsepp L., Nöges Т., Raid Т., Kouts Т., 1994, Hydrophysical and hydrobiological processes in the Gulf of Finland in summer 1987: characterization and relationship, Cont. Shelf Res., 14, 749-763
• [32]. Viúdez Á., Tintoré J., Haney R. L., 1996, Circulation in the Alboran Sea as determined by quasi-synoptic hydrographic observations. Part I: Three-dimentional structure of the two anticyclonic gyres, J. Phys. Oceanogr., 26, 684-705