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Coastal upwelling by wind-driven forcing in the Caspian Sea: A numerical analysis

Fallah Fatemeh, Mansoury Dariush

Oceanologia

2022

No. 64 (2)

363--375

In this study, wind-driven coastal upwelling in the Caspian Sea was investigated using a developed three-dimensional hydrodynamic numerical model based on the Princeton Ocean Model (POM). The model was forced with wind fields and atmospheric fluxes from the ECMWF database and it considers freshwater inflows from the Volga, Kura and Ural Rivers. This model was implemented for 10 years (2008–2018). Findings indicated that the upwelling in the Caspian Sea was due to effects of wind and bottom topography, often occurring from May to September. In June and July, in the eastern part of the middle and sometimes southern basins, up to 3°C water temperature difference occurs between coastal and offshore areas. The vertical temperature gradient in the middle basin was larger than that in the southern basin. Upwelling in August in the eastern coasts of the middle basin within 25 km of coast from the depth of 15 m to the surface was shown, which was due to the effects of wind and bottom topography. In the middle basin, the highest vertical velocities caused by upwelling in June, July and August were 12, 13.82, and 10.36 m/day, respectively.

Laanemets J., Pavelson J., Lips U., Kononen K.

Oceanological and Hydrobiological Studies

2005

Vol. 34, No.2

15--36

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.