south atlantic circulation from global 1/12 º resolution simulations
DESCRIPTION
South Atlantic circulation from global 1/12 º resolution simulations Z. Garraffo 1 , S. Garzoli 2 , S. Dong 3 , M. Baringer 2 , A. Srinivasan 1 U. Miami (CCS); AOML/NOAA; CIMAS With NOAA/AOML funding. WORK IN PROGRESS Study of the Global 1/12 º HYCOM products for the South Atlantic. - PowerPoint PPT PresentationTRANSCRIPT
South Atlantic circulation from global 1/12º resolution simulations
Z. Garraffo1, S. Garzoli2, S. Dong3, M. Baringer2, A. Srinivasan1
U. Miami (CCS); AOML/NOAA; CIMAS
With NOAA/AOML funding
WORK IN PROGRESSStudy of the Global 1/12º HYCOM products
for the South Atlantic.
Objectives:
• Analyze different models and compare with observations• Determine the main characteristics of the modeled South
Atlantic flows, in particular in relation to the Atlantic Meridional Overturning Circulation
SIMULATIONS:HYCOM global 1/12º produced at NRL: • Climatological simulation (expt 09.4) with updated
forcing (ECMWF with satellite corrected winds, with 6-hourly anomalies), updated source and layer structure.
• 2004-2006 simulation, NOGAPS winds. • Hindcast 2004-2006 (with data assimilation) (simulations produced by Metzger, Smedstad, Wallcraf;
Chassignet and Hurlburt PIs) • Regional model for extra diagnostics
AX22
AOML High density XBT lines:
•Temperature from AOML high density XBT lines,
•Salinity, based on historical T/S relationship (derived from CTD and Argo floats)
Upper ~800m
lay σ2* Depth (m)
lay σ2* Depth (m)
lay σ2* Depth (m)
1-19 ≤ 36.52
<1200 1-19 ≤ 36.52 <1200 1-17 ≤36.20 <1000
20-28 36.62-37.06
<4000 20-27 36.62-37.06
<4000 18-27 36.38-37.06
<4000
29-32 ≥ 37.09 >4000 28-32 ≥ 37.10 >4000 28-32 ≥37.10 >4000
climatological interannual hindcast
Climatological model AMOC (yr 15)
15Sv
1Sv
Hindcast AMOC (yr 2005)
12Sv
2Sv
Nested model, as global model, with purpose of saving extra diagnostic quantities. Boundary conditions from global model.
daily archives (full), and every time step flux (dashed)
(with A. Wallcraft’s advise)
(regional model shows lower Drake transport than global model, 130 Sv vs 150 Sv)
Our region of higher insterest
S. Atlantic volume transport: upper, deep, bottom
upper
bottom
deep
35S 20N
10 Sv
-10 Sv
From Dong, Garzoli, Baringer
Adjusted with total interannual model transport
AX22•Temperature from AOML high density XBT lines, •salinity, based on historical T/S relationship (derived from CTD and Argo floats)
Baroclinic, unadjusted
XBT HYCOM
(151 Sv full 4yr mean)
(150 Sv full 4yr mean)
(Observational transports from Dong, Garzoli, Baringer)
Volume transport (SV) Temperature transport (Pw)
ObservationsClimatol. HYCOM expt 09.4 (yr 11-15)Interannual HYCOM expt 05.8Hindcast
Drake passage: Seasonal cycle of volume and heat transport
flows
Adapted from Stramma & England 1999
South Atlantic circulation: Upper, intermediate, deep
NADW (>2000m)
AAIW (500-1200m)SACW (100-500m)
Deep western boundary current eddies after 8ºS topography(as in Dengler, Schott, Eden, Brant, Nature 2004)
instantaneous mean
> 2000m
11S velocity section
-19.3
-3.7
4.1
22.8
Deep south: -35.5SvDeep north: 18.9SvNet deep: -16.6Sv
Upper 23.8Sv
Deep south: -19.3SvDeep north: 4.1SvNet deep: -15.2Sv
Upper 22.8 Sv
6 year mean expt 09.4 5 section avg Schott et al, JPO 2005
Climatological Interannual
Hindcast
Upper flow: Lay 10,100m
SSEC
SAtlCAgC
MCACC
15SSTG
TG
Climatological Interannual
Hindcast
Intermediate flow: lay 18,~1000m
18S
14Sv 11Sv
11Sv
Climatological
Hindcast
interannual
Transport: Upper branch (integrated in layers)
Color plots: longitudinal dependence of meridional transport integrated from the west (from 70W). Box: region of closed sections. Brazil Current intensifies to the south in Climatolog. and Interannual expts
Exchange with lower layers
Climatological Interannual
Hindcast
Deep flow, lay 28, ~2000-3000m
Climatological
Hindcast
interannual
Transport: Deep branch
Color plots: longitudinal dependence of meridional transport integrated from west.
Exchange with upper layers
Climatological
Hindcast
interannual
Transport: Bottom branch
1Sv
1.5 Sv
0.5Sv
ConclusionsSimulations reproduce the known aspects of the South Atlantic circulation, for the upper and deep flow: main currents and locations, mean pathways. Temperature transport time series at Drake passage is in good agreement between model and observations.
Future workFurther identification of mean pathways and quantification of the current transports in all the simulations.Comparison with Argo floats reconstructions.Estimation of water mass transformations from HYCOM.
Lay 28
Lay 18
Salinity section showing AAIW minimum
Climatology (PH3) Jan section
Climatological year 11-15 Interannual 2004-2006 Hindcast 2004-2006
80ºS 30ºN
Upper volume transport difference accum flux – daily archives
28.5S difference
28.5S