On gradient currents in the Adriatic Sea
Abstract
To calculate the geopotential topographies for the region of the Adriatic Sea, the material collected by the NAJADE and CICLOPE Expeditions (1911-1914) was used, and to obtain the vertical distribution of current velocities in the section from Sicily to Peloponnesus, the data collected by the THOR (1910) and DANA (1930) Expeditions were applied.
The geopotential anomalies and current velocities were calculated from temperature and salinity data by applying the B j e r k n e s' Theorem and the H e l l a n d - H a n s e n formula respectively, and by taking - as reference depths - the isobaric depths of 50, 100 and 200 m for the Adriatic area, and the 500 and 1000 m ones for the Sicily to Peloponnesus profile.
The calculation of dynamic topographies for the Adriatic region covered six distinct situations: 16. VIII. - 6. IX. 1911., 16. II. - 11. III. 1912., 16. V. - 9. VI. 1913., 16. VIII. - 1. IX. 1913., 16. - 24. XI. 1913. and 16. II. - 9. III. 1914.
The presence of a cyclonic course of streamlines has been proved in the Adriatic.
Seasonal rhytmic changes have been found to occur in the system of Adriatic currents, i.e. swifter and more developed currents appear along the west coast in summer, and along the east coast in winter, while the spring and autumn circulations reach equal intensity along both the coasts. The currents are generally swifter in August-September and November (up to 30 cm/sec) than in February, when they are the weakest.
The course of the cyclonic streamlines in the Adriatic is connected with the character of gradient currents in that basin. Lighter water flows along both the coasts during the occurrence of a developed circulation, since a lighter water mass is formed during the spring - summer period in the northern Adriatic, and during the autumn - winter period in the southern Adriatic.
The author deals with the seasonal fluctuations of the positions of both the maximum and minimum of dynamic depths. The occurrence of a maximum in summer and a minimum in winter has been found in the northern part of the Adriatic. Great annual amplitudes in sea water temperature in the northern Adriatic and a considerable inflow of fresh water to that region in spring are held responsible for these changes. A connection has been found to exist between the appearance of the northern Adriatic maximum and the forming of the outgoing current, and between the appearance of the northern Adriatic minimum and the forming of the incoming current.
It has also been found that swifter incoming current coincides with a lower minimum in the northern part of the Adriatic, and that a swifter outgoing current concurs with a higher maximum. Since the current, entering the Adriatic in winter, flows from the Mediterranean which shows a higher degree of salinity, the author supposes that the salinity rise, occurring in the Adriatic basin in winter is caused by such a current, while the summer outgoing current produces the opposite result as the water mass of the north Adriatic origin has lower salinity in that period.
It has been established, that the annual variations in the circulation of Adriatic waters are in connection with the different stages of the hydrographic factors in that basin.
The conclusion has been drawn that the geopotential topographies show to a great deal a real picture of Adriatic currents.
A short survey of the distribution of currents in the Sicily - Peloponnesus profile as related to the circulation occurring in the Otranto Strait is also given.
