MESOSCALE DYNAMICS IN THE MIDDLE ADRIATIC DEPRESSIONS (SPRING 1993) A. RUSSO, A. ARTEGIANI, E. PASCHINI C.N.R. - Istituto di Ricerche sulla PEsca Marittima (IRPEM) L.go Fiera della Pesca, 60125 Ancona, ITALY Web: http://adria.irpem.an.cnr.it C. J. LOZANO, A. R. ROBINSON Department of Earth and Planetary Sciences, Harvard University, Cambridge, USA N. PINARDI, M. ZAVATARELLI C.N.R. - I.S.A.O., Bologna, Italy

Mappa Adriatico

Schematic of the Adriatic Sea General Circulation (from Artegiani et al., 1997)

Position of the stations for the two experiments 9-11 May 1993 6-9 June 1993

Cumulative vertical profiles

OAG AMEX2-2

Bathy model

Zonal and meridional zero crossing of the correlation: 40 km Global OA parameters Zonal and meridional zero crossing of the correlation: 40 km Zonal decorrelation (decay) scale: 20 km Time decorrelation: 7 days PE model domain Grid: 39*39*20 levels 2 km horizontal resolution, 5 flat levels and 15 sigma levels 11 May 1993 7 June 1993 Base Base + ext. Forcing Assimilation Base B Base + ext. Forcing B Simulations table Assimil.+ext. Forcing

Base C4 13 day

BaseB Salinity and velocity 40m

frcB Salinity and velocity 40m

ECMWF wind in the AMEX domain. The average intensity in June 1993 (3.4 m/s) was about 20% greater than in May 1993 (2.8 m/s). Wind AMEX

Ass Salinity and velocity 40m

Ass+ frc Salinity and velocity 40m

Main remarks from the six examined simulations - Baroclinic component determines the coastal current, that represents one branch of the known ciclonic general circulation of the Meso-Adriatic Depressions; - Barotropic velocities dominate the Pits area in spring, with currents forming filaments about 10 km wide; the two “holes” are occupied by variable eddies, surrounded by an anticiclonic circulation; - Wind forcing did not affect the May 1993 simulation, while it was able to reverse the circulation in the Pits for the simulations initialized with the June data; this should be due to instability of June simulations, in fact wind stresses were similarly weak both in May and June, and the reversal did not appear between the two runs with data assimilation; - T, S and internal velocity data from the June cruise have been successfully assimilated through intermittent Optimal Interpolation; the two simulations with data assimilation were similar and much more stable than the previous ones. Next Improvements and Perspectives - Nesting in an Adriatic model to improve boundary conditions - Refinements of the atmospheric forcing (ECMWF reanalyzes, offshore platforms) - Real time regional forecast experiments - Ecosystem studies.

Base May Baro 4 days

Base June Baro 4 days

Frc June Baro 4 days

Position of the stations for the two experiments Position of the stations for the two experiments. The maps are rotated and converted to a cartesian reference system. 9-11 May 1993 75 CTD casts 6-9 June 1993 82 CTD casts

Bottom maps

Vertical profiles in the Western Pomo Pit in the 1993-96 period Depth (m) % sat. O2 Nitrate (µM) Silicate (µM) After a bottom water renewal, in the bottom layer density(not showed) and % of dissolved oxygen saturation decrease while temperature (not showed) and nutrient salts concentration increase

SW-NE cross-section (May 1993)

SW-NE cross-section (June 1993)

AMEX1 Sep. 1989 Profili verticali modi baroclini From Paschini et al., D.S.R.1993 AMEX1 Sep. 1989 Profili verticali modi baroclini

Profili verticali modi baroclini Squared Brunt-Vaisala frequency (N2) Baroclinic vertical modes First internal Rossby radius: AMEX Sept. 1989: 5.4 km AMEX2-A May 1993: 3.5 - 4.0 km AMEX2-B June 1993: 4.5 - 5.0 km Profili verticali modi baroclini

Profili verticali modi baroclini

Brunt-Vaisala

Base C4 10 day

Base C4 11 day

Base C4 12 day

Base C4 14 day

Base C4 15 day

Alongshore cross-section in the Western Pomo Pit (May 1993)

Temperature at Pescara section