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The Eastern Mediterranean Transient studied with Lagrangian diagnostics applied to a Mediterranean GCM forced by satellite SST and ECMWF wind stress for.

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Presentation on theme: "The Eastern Mediterranean Transient studied with Lagrangian diagnostics applied to a Mediterranean GCM forced by satellite SST and ECMWF wind stress for."— Presentation transcript:

1 The Eastern Mediterranean Transient studied with Lagrangian diagnostics applied to a Mediterranean GCM forced by satellite SST and ECMWF wind stress for the years Volfango Rupolo a, Salvatore Marullo a and Daniele Iudicone b a C.R. Casaccia ENEA Rome, Italy b, Istituto di Fisica dell'Atmosfera-CNR, Rome, Italy (subm. to JGR) After a long spin up phase (‘climatological’ field), the model is forced using daily ECMWF wind stress and relaxing temperature to daily satellite SST for the years from 1988 to (salinity continues to be restored to climatological values) The results are analysed computing: Water mass formation rate Transport in the straits (CretanArcs and Otranto Strait) and in the EM using Lagrangian diagnostics Upwelling (transport and location) of the ‘uplifted water’

2 Water mass formation analysis: From 1989 to 1991, the Adriatic produce less and less dense water while the Aegean continues its ‘normal’ activity In 1992 and especially 1993 all basins enhances activity but the densest water is produced in the Aegean Geographical distribution of formation of water denser than 29.10, units are in 10 2 m 3 sec -1 Km -2

3 Dashed line: density at the Bottom level in the Otranto strait Full line: density at the sill level in the Cretan See (WCA) No tracer drift. Interannual Variability is introduced after the 100 th year of the spin up. Otranto overflow becomes lighter during winter 1992 and1993 Density at the Antickithera sill depth and at the bottom of Otranto Straits ‘Standard run’ Yearly mean Years from 1988 to 1993 Monthly mean

4 Yearly mean salinity vertical profiles: the decrease of inflow of salty intermediate water in the Adriatic precedes the change in the stratification in the Ionian (fully development of the EMT occurring in 1992 and 1993) (‘+’=1989, ‘*’=1990, ‘  ’=1991, ‘Δ’=1992 and ‘  ’=1993 Full line without symbols= ‘climatologic year’)

5 Density vertical section at 35° N, yearly mean values ‘climatologic’ year 1993 The general mechanism of the transient is reproduced

6 Salinity vertical section at 37.5° N, yearly mean values ‘climatologic’ year 1993 Dashed area = S > PSU The general mechanism of the transient is reproduced

7 Left =1993, rigth=climatology In the climatology ADW is deeper and moves ciclonically in the Ionian. In 1993 the Aegean overflow is deeper and spreads in the Ionian developing energetic Coherent structures characterized by velocity O(10) cm/sec and L Km Particles initially sedded uniformly in the horizontal (300

8 1993: about particles are released at intermediate Depth. Colours indicate depth (blu 200 m, yellow 2700 m.) climatology

9 Lagangian Transport in the cretan Arcs. WEWE Sv m 3 Integrated transport of overflow Deeper than 600 m. From 1988 to 1993 about m 3 flow deeper than 600 m. From the Cretan Arcs (roughly the half of he estimate of Roether et al.; 1996 ) Considering only water flowing deeper than 1200 m in this period the Aegean is 4.5 times more active than Adriatic About the 80 % of this overflow occurs during 1992 and Strait of Otranto Antikithera Strait Kassos Strait O1 O2 A1A2 A£ A

10 Strait of Otranto Antikithera Strait Kassos Strait O1 O2 A1A2 A£ A Deep overflow (> 1500 m) over the Antikithera Strait during 1992 and 1993 End of February

11 To compute sub basins lagrangian transport estimate we consider Three –four years long – velocity field: 1)Four iterated years representative of the ‘climatologic’ – or pre EMT situation. (Clim4) 2) Years from 1988 to 1991 (F4, representative in our simulation of the pre conditioning phase) 3) 1993 followed by three years inwhich the model is forced with standard forcing (S4, useful to follow the propagation of a single event of deep Aegean overflow) Subbasins transport estimates

12 A3 SIC A1 O Green= ‘climatology’ (Clim4) Blu= preconditioning Phase (F4) Red = Fully developped EMT In the pink boxes are indicated the mean arrival times Intermediate Water: Only particles starting from A1 reaching ending sections in less than 4 years and between 200 and 600 m. are considered. Note the transport values in the preconditioning phase Recirculation A1  A3 persists in S4

13 O1 I37 A1 <0.01 <0.01 – 0.26 < 0.01 – < 0.01 – Green= ‘climatology’ (Clim4) Blu= preconditioning Phase (F4) Red = Fully developped EMT Deep Water: Only particles starting from A1and O1 and reaching ending section I37 deeper than 600 m. and 1500m in less than 4 years are considered. Mean arrival times and second row In the pink boxes are indicated the mean arrival times for particles reaching I37 deeper than 1500 m.

14 Vertical section of particles coming from the Adriatic (red) And the Aegean (black)) clim4 Clim4 F4S4

15 Kinetic energy in the deep (> 700 m) Ionian S4: years forced with climatological forcing The maximum is reached after 50 days from the inset of the deep Aegena flow The succesive e-folding time is 150 days

16 Upwelling through the nutricline: particles are released (homogeneously) at 160 m. of depth and they are integrated till they reach the depth of 30, 15 and 5 m. From 160 to 5: 0.02 Sv From 160 to 15: 0.04 Sv From 160 to 300: 0.07 Sv 1993:Fully developped EMT standard year From 160 to 5: 0.01 Sv From 160 to 15: 0.02 Sv From 160 to 300: 0.03 Sv

17 standard year From 160 to 5: From 160 to 15: From 160 to 30: 1993 From 160 to 5: From 160 to 15: From 160 to 30: Time behavior of flux through the ‘nutricline’ Red = flux at the starting section, black= flux at the ending section

18 Summary Relaxing model SST to satellite SST from 1988 to 1993, the general mechanism of the EMT is reproduced Lagrangian diagnostics make easier the analysis of the development of the EMT as it is represented by the model and allows quantitative estimates, in particular: i)In a preconditioning phase IW inflow in the Adriatic (Aegean) decreases (increases). Probably wind induced (Samuel et al, Demirov and Pinardi) ii)The EMT fully develops during 1992 and 1993, the overflow from the Aegean is concentrated during two events (O(months)). The total flow over the Cretan Arcs is m 3 (roughly the half of he estimate of Roether et al.; 1996 ) iii)Relaxation toward pre-EMT situatiuon (qualitative behavior and estimate of characteristic time) Moreover: Quantitative estimates of vertical transport before and after the EMT (up lifted water), Time statistics

19 Water mass formation rate F(  )= Adriatic Aegean [F(  )]=[Sv]

20 Transport section to section: Quantitative analysis Water path Tracers analysis Time statistics Particles are released from section 1 with some criterium (e.g. u>0, S

21 In a first phase (89-91) salinity decreases at intermediate depth both at Otranto Strait and in the Adriatic, indicating a less inflow of LIW (preconditioning). In this phase (not shown) density slowly increases in the Aegean below the sill of the Cretan Arc Only during 1992 and 1993 Ageean water replaces ADW. Note the wrong depth of ADW Salinity vertical profiles (‘+’=1989, ‘*’=1990, ‘  ’=1991, ‘Δ’=1992 and ‘  ’=1993 Full line without symbols= ‘climatic year’)

22 Climat ic year Flux (Sv) T S  0.31 (0.14) (0.06) ( ) (0.003 ) (0.009) (0.01 ) (0.01) Depth in the end section Clima tic year < z < 200 m Flux (Sv) T S  < z < 600 m Flux (Sv) T S  < z < 1200 m Flux (Sv) T S  < z < 1500 m Flux (Sv) T S  < 0.01 < < 0.01 < < z < 2000 m Flux (Sv) T S  < 0.01 < < 0.01 < < z < 3000 m Flux (Sv) T S  < 0.01 < 0.01 < 0.01 < 0.01 < Otranto Strait Antikithera Strait Fully developped EMT Preconditioning phase

23 O1 A1 L25 <0.01 <0.01 – 0.08 < 0.01 – <0.01 <0.01 – 0.01 < 0.01 – 0.05 < Green= ‘climatology’ (Clim4) Blu= preconditioning Phase (F4) Red = Fully developped EMT Deep Water: Only particles starting from A1and O1 and reaching ending section L25 deeper than 600 m. and 1500m in less than 4 years are considered. Mean arrival times and second row In the pink boxes are indicated the mean arrival times for particles reaching I37 deeper than 1500 m.

24 S4: years forced With climatological forcing Distribution of arrival times Of particles starting from the western Cretan Arc and reaching ending Sections I37 and L25

25 Upwelling from deep layers: particles are released (homogeneously) at 1250, 850 and 620 m. of depth and they are integrated till they reach the depth of 420m From 620 to 420: 1.30 Sv From 850 to 420: 0.54 Sv From 1250 to 420: 0.21 Sv standard year From 620 to 420: 0.33 Sv From 850 to 420: 0.11 Sv From 1250 to 420: 0.04 Sv 1993:Fully developped EMT

26 Black point: initial conditions in the lower surface Red points: final conditions in the upper surface

27 ‘Climatic year’ Adriatic (Reg. 1, in Fig 1) South Aegean (Reg. 2 in Fig1) Δρ (Aegean – Adriatic) Table. 1 Mean Hydrological values of the 20 days characterised by having the densest surface water in reg. 1 and reg. 2 of fig.1. Note that the surface water is denser in the Adriatic in the ‘climatic’ year (spin up of the model). The low density values in the Adriatic in the 1990 are due to an anomalous warming in the late winter. Model SST close to satellite SST Cold winters 1992 and 1993

28 Cross isopycnal surface flux F(  ) F(  ) ([F(  )]=[Sv]) is the contribution of air-sea fluxes to the mass flux across the isopycnal surface  = , normalised on the entire year. The water mass formation induced by air sea interactions in the density range  1 <  <  2, is given by the difference between the flux entering  1 an the flux leaving  2, i.e. it is equal to the difference F(  2 )-F(  1 ).. (  T is the time interval of integration, H(x,y,t) and Q(x,y,t) are the heat and freshwater surface fluxes, C p is the specific heat capacity of water, S(x,y,t) and  (x,y,t) are the surface salinity and density and  and  are the derivatives of density with respect to temperature and salinity.) A water mass body can cross a given isopycnal surface fixed in space or can simply change its density, as a result of air-sea interactions, but remain in place. In this latter case the cross isopycnal flux it is not across any physical surface

29 Surface cross isopycnal flux All basin AegeanAdriatic Levantine - Net decrease of ADW production during Net increase of DW production in all the basin (specially in the EM) during 1992 and 1993 (about 2 Sv). - In these years the Adriatic returns to its typical production rate but the Aegean Sea produce more and denser water

30 F( ,x,y), geographical distribution of the flow crossing the isopycnal During 1993 the shift from Adriatic and Levantine region to Aegean as predominant Source of DW is observed. Same color scale Only heat forcing (relaxation to satellite SST, H=C(T-T*) )

31 Vertical profiles of salinity difference between 1993 and the ‘climatic’ year The general mechanism of the EMT is reproduced, even with bias in salinity values and ADW depth

32 (‘+’=1989, ‘*’=1990, ‘  ’=1991, ‘Δ’=1992 and ‘  ’=1993 Full line without symbols= ‘climatic year’) Salinity vertical profiles In a first phase (89-91) salinity decreases at intermediate depth both at Otranto Strait and in the Adriatic, indicating a less inflow of LIW (preconditioning). In this phase (not shown) density slowly increases in the Aegean below the sill of the Cretan Arc Only during 1992 and 1993 Ageean water replaces ADW. Note the wrong depth of ADW

33 O1 O2 I37 A1 A3 A4 L25 SIC A Strait of Otranto Antikithera Strait Kassos Strait Aegean Sea Adriatic Sea Ionian Basin Levantine Basin Cretan Passage Strait of Sicily Fig. 1

34 O1 O2 A1 A3 A4 A2 Strait of Otranto Antikithera Strait Kassos Strait Aegean Sea Adriatic Sea Ionian Basin

35 Climatic year: about particles are released at intermediate Depth. Colours indicate depth (blu 200 m, yellow 1700 m.)

36 Tab.4 First row: Total, lost flux and meanders in the starting section A1. Following rows: Total mean flow connecting the western Cretan Arc to the Otranto Strait, Eastern Cretan Arc and Western Ionian (see Fig.1). No selecting criterion is applied at the ending section. Clim4F4S4 Total flux [Sv] Lost flux [Sv] ‘Meanders’ [Sv] A1  O1 Flux [Sv] A1  A3 Flux [Sv] A1  SIC Flux [Sv]

37 Clim4F4S4 I37  O1 600 < z < 1500 [Sv] z > 1500 [Sv] mean arrival time, z> 1500 [years] < I37  A1 600 < z < 1500 [Sv] z > 1500 [Sv] mean arrival time, z> 1500 [years] 0.14 < < L25  OI 600 < z < 1500 [Sv] z > 1500 [Sv] mean arrival time < < < L25  A1 600 < z < 1500 [Sv] z > 1500 [Sv] mean arrival time, z> 1500 [years] 0.01 < < Tab.6: Deep flow connections between Otranto Strait and Western Cretan Arc (O1 and A1) with a zonal section west of Crete in the Ionian basin (I37) and a meridional section east of the Cretan passage (L25, see Fig. 1). In particular are shown for each experiment the flow relative to particles reaching I37 an L25 with a depth z 600 < z < For particles that reach the ending section at a depthdeeper than 1500 m. we show both flux and mean arrival time. Mean characteristics are shown only if the flow connection is greater than 0.01 Sv.

38 Tab.7: Hydrological characteristics and mean depth of particles that starting from the Western Cretan Arc (A1) reach the zonal section west of Crete in the Ionian basin (I37) and the meridional section east of the Cretan passage (L25, see Fig. 1).

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