Water mass transformation, Volume changes, transports in geographical coordinates

Previously• Diapycnal divergence in area integrated density flux

correlated with AMOC but only after taking account of a lag. – We assume, the lag is associated with time taken for newly formed water to be advected southwards.

• Or this could be due to a temporary local change in volume

• Southward transport of water > 27.6 kg m-3 might be estimated by transformation rate minus the rate of volume change (of water > 27.6 kg m-3 ).

a) Surface forced transformation rate (Sv)

b) Anomalous volume of water (x -1) that is > 27.6 kg m-3

c) Rate off volume change (Sv) (> 27.6)

d) Southward transport of water > 27.6 at 45N (blue) and sfc forcing minus volume change (red) (Sv)

• Location/ timing of Surface forcing anomalies often agrees with thickness anomaly.

• Building of the positive anomaly in the SPG can be seen –

• Moving cyclonically and then turning into a transport anomaly (also see next clip)

• On occasions (e.g 1972) there appears to be strong surface –water mass transformation –with not corresponding increase in volume or transport.

• This may be because surface forcing is occurring in regions where it does not directly effect southward transports at 45N (e.g. Nordic Seas)?

• May be there would be a stronger relationship between surface fluxes and southward dense water transport if we restricted the area for the analysis?

• In actual fact – when we restrict analysis area to south of Iceland, north of 53N there is not much sign of this

• Although, there is good agreement between southward transport of evolution of the (negative) dense water volume or the region (see over).

a) Surface forced transformation rate (Sv)

b) Anomalous volume of water (x -1) that is > 27.6 kg m-3

c) Rate off volume change (Sv) (> 27.6)

d) Southward transport of water > 27.6 at 45N (blue) and sfc forcing minus volume change (red) (Sv)