sity higher than 0.8 over the whole considered
period, the area to which the present analysis was
therefore limited. Monthly coverage was also
checked, and the three months considered resulted to be quite evenly represented.
In the adopted configuration. the system provides data averaged over 1 h periods. In order to
fllter out semi-diurnal and diurnal tides as well as
inertial oscillations, data were low-pass futered
with a Chebishev fllter with a 40 h cutoff and
averaged over weekly periods. Spatialltemporal
gaps were filled by means of linear interpolation
with neighbouring (in space and time) data.
Results and Concluding Remarks
In Fig. 2 we present weekly surface current maps
in the studied area relative to the months of
August, September and October 1997.
The surface circulation is dominated by a
southward coastal jet and by a single cyclonic
eddy farther offshore. This dynamical feature is
very frequent in our data set and it is often
detectable also in the hourly data; its typical
dimension is of the order of 2 times the Rossby
radius of deformation. which was estimated in
the same area and period at around 6.S km
(Budillon et al. 2000b).
The coastal current shows typical velocities
of the order of 10-20 cmls and extends its influence for 10-15 km from the coast. The cyclonic
circulation shows a symmetric field approximately located in the centre of the studied area.
We expect the topography to be important in setting the location and the persistence of the eddy
in this region. A major forcing setting up the
eddy field can obviously be related to the local
field of wind stress.
This quasi-permanent circulation pattern
does not occur in two situations detected at the
beginning of August and at the beginning of
September, when the coastal jet direction is
almost completely reversed and the investigated
area is dominated by an anticyclonic local circu1ation, most likely due to meteorological conditions.
The accuracy of the surface current measurements was assessed by a comparison with
data gathered by a current meter located at 5 m
depth and moored off Senigallia, i.e. in the western portion of the domain spanned by the radar
signal. The outcome of the comparison is shown
Surface Dynamics of a Coastal Area off Ancona
23
in Figs. 3 and 4: power spectra of the alongshore
current meter data and of the hourly radar ones
(collected at one selected location close to the
mooring site) are shown in Fig. 3a and b. respectively. Figure 3c and d display coherence and
phase between them; the coherence results quite
high both in the high frequency peaks associated with the tides, obviously, and in the low frequencies of the residual circulation. Figure 4
shows the time series, after low-pass mtering, of
the current records simultaneously measured by
the two systems. As can be seen, the agreement
between the two data sets is quite good, especially in the alongshore component. Velocities
measured by the currentmeter are systematically lower than the radar ones; this can explained
by the fact that radar data refer to the immediate
surface, whereas the currentmeter was moored
at 5 m depth, where we expect the dynamics to
be weaker.
The CODAR measurements in this area were
also compared with velocities drawn by surface
drifters launched off Senigallia in August 1997.
Even though comparing Eulerian and Lagrangian
data is never straightforward the agreement is
quite satisfactory, at least in qualitative terms (see
Mazzoldi et aI. 1999, for a description of the validation experiment and a thorough discussion of
the subtle points of the data analysis).
Acknowledgements. This work was carried out in the framework of the activities of Task 1 of PRISMA-2 Project, funded
by the Italian Ministry for Scientific Research. The authors
wish to thank M. Moretti and A. Ortona for helpful discussions.
References
ArtegianiA,Azzolini R,Moretti M, Vultaggio M (1980) A first survey on the Ancona coastal area currents. Ann 1st UnivNavale
49-50: 151-160
Artegiani A, Bregant D, Paschini E, Pinardi N, Raickh F, Russo A
(1997) The Adriatic Sea general circulation. II. Baroclinic
circulation structure. I Phys Oceanogr 27: 1515-1532
Barrick DE, Evans MW, Weber BL (1977) Ocean surface currents
mapped by radar. Science 198: 138-144
Bracalari M. Salusti E, Sparnocchia S,Zambianchi E (1989) On the
role of the froude number in geostrophic coastal currents
around Italy. Oceanol Acta 12:161-166
Budillon G, Paschini E, Russo A, Simioli A (2000a) Primi risultati
codar sulle correnti marine superficiali nell' area anconetana. Proc AIOL, Vol XIII(II): 23-32
Budillon G, GrotH M, Rivaro P, Sperle G, Thcci S (2000b) Physical
and geochemical transports along the Ancona coastal area
(PRISMA-2 Project). This volume
Crombie DD (1955) Doppler Spectrum of Sea Echo at 13.56 Mos.
Nature 175: 681-682
period, the area to which the present analysis was
therefore limited. Monthly coverage was also
checked, and the three months considered resulted to be quite evenly represented.
In the adopted configuration. the system provides data averaged over 1 h periods. In order to
fllter out semi-diurnal and diurnal tides as well as
inertial oscillations, data were low-pass futered
with a Chebishev fllter with a 40 h cutoff and
averaged over weekly periods. Spatialltemporal
gaps were filled by means of linear interpolation
with neighbouring (in space and time) data.
Results and Concluding Remarks
In Fig. 2 we present weekly surface current maps
in the studied area relative to the months of
August, September and October 1997.
The surface circulation is dominated by a
southward coastal jet and by a single cyclonic
eddy farther offshore. This dynamical feature is
very frequent in our data set and it is often
detectable also in the hourly data; its typical
dimension is of the order of 2 times the Rossby
radius of deformation. which was estimated in
the same area and period at around 6.S km
(Budillon et al. 2000b).
The coastal current shows typical velocities
of the order of 10-20 cmls and extends its influence for 10-15 km from the coast. The cyclonic
circulation shows a symmetric field approximately located in the centre of the studied area.
We expect the topography to be important in setting the location and the persistence of the eddy
in this region. A major forcing setting up the
eddy field can obviously be related to the local
field of wind stress.
This quasi-permanent circulation pattern
does not occur in two situations detected at the
beginning of August and at the beginning of
September, when the coastal jet direction is
almost completely reversed and the investigated
area is dominated by an anticyclonic local circu1ation, most likely due to meteorological conditions.
The accuracy of the surface current measurements was assessed by a comparison with
data gathered by a current meter located at 5 m
depth and moored off Senigallia, i.e. in the western portion of the domain spanned by the radar
signal. The outcome of the comparison is shown
Surface Dynamics of a Coastal Area off Ancona
23
in Figs. 3 and 4: power spectra of the alongshore
current meter data and of the hourly radar ones
(collected at one selected location close to the
mooring site) are shown in Fig. 3a and b. respectively. Figure 3c and d display coherence and
phase between them; the coherence results quite
high both in the high frequency peaks associated with the tides, obviously, and in the low frequencies of the residual circulation. Figure 4
shows the time series, after low-pass mtering, of
the current records simultaneously measured by
the two systems. As can be seen, the agreement
between the two data sets is quite good, especially in the alongshore component. Velocities
measured by the currentmeter are systematically lower than the radar ones; this can explained
by the fact that radar data refer to the immediate
surface, whereas the currentmeter was moored
at 5 m depth, where we expect the dynamics to
be weaker.
The CODAR measurements in this area were
also compared with velocities drawn by surface
drifters launched off Senigallia in August 1997.
Even though comparing Eulerian and Lagrangian
data is never straightforward the agreement is
quite satisfactory, at least in qualitative terms (see
Mazzoldi et aI. 1999, for a description of the validation experiment and a thorough discussion of
the subtle points of the data analysis).
Acknowledgements. This work was carried out in the framework of the activities of Task 1 of PRISMA-2 Project, funded
by the Italian Ministry for Scientific Research. The authors
wish to thank M. Moretti and A. Ortona for helpful discussions.
References
ArtegianiA,Azzolini R,Moretti M, Vultaggio M (1980) A first survey on the Ancona coastal area currents. Ann 1st UnivNavale
49-50: 151-160
Artegiani A, Bregant D, Paschini E, Pinardi N, Raickh F, Russo A
(1997) The Adriatic Sea general circulation. II. Baroclinic
circulation structure. I Phys Oceanogr 27: 1515-1532
Barrick DE, Evans MW, Weber BL (1977) Ocean surface currents
mapped by radar. Science 198: 138-144
Bracalari M. Salusti E, Sparnocchia S,Zambianchi E (1989) On the
role of the froude number in geostrophic coastal currents
around Italy. Oceanol Acta 12:161-166
Budillon G, Paschini E, Russo A, Simioli A (2000a) Primi risultati
codar sulle correnti marine superficiali nell' area anconetana. Proc AIOL, Vol XIII(II): 23-32
Budillon G, GrotH M, Rivaro P, Sperle G, Thcci S (2000b) Physical
and geochemical transports along the Ancona coastal area
(PRISMA-2 Project). This volume
Crombie DD (1955) Doppler Spectrum of Sea Echo at 13.56 Mos.
Nature 175: 681-682